Al₁Fe₄₉Mn₃₀Co₁₀Cr₁₀, Al₁Fe_48.5Mn₃₀Co₁₀Cr₁₀C_0.5 and Al₁Fe_48.475Mn₃₀Co₁₀Cr₁₀C_0.5B_0.025 high entropy alloys were prepared by vacuum arc melting method, and then hot rolling, homogenization, cold rolling and annealing at 700 ℃ for 30 min for the three alloys were carried out. The effects of C and B interstitial atoms on the microstructure and mechanical properties of the tested high entropy alloys were studied by using XRD, EBSD and universal testing machine. The results show that the addition of C and B interstitial atoms makes the grain size of the alloys smaller after hot rolling and homogenization, and the degree of recrystallization reduces after annealing at 700 ℃, the dislocation density and the content of small angle grain boundaries increase, which reduces the formation ability of annealing twins. The addition of B element strengthens the grain boundary, increases the cohesion of the grain boundary, reduces the probability of intergranular fracture during deformation, and improves the plasticity, so that the Al₁Fe_48.475Mn₃₀Co₁₀Cr₁₀C_0.5B_0.025 alloy exhibits excellent product of strength and elongation of 42.11 GPa·%.

Refractory high entropy alloys, as complex-composition alloys with simple crystalline structures, consist of a mixture of early transition metals with high melting points. The refractory high-entropy alloy systems are classified based on the compositional characteristics, and the composition, phase constituents, microstructure and multiple properties (mechanical and functional) are reviewed in detail. Most of the refractory high entropy alloys are BCC/B2-based alloys and possess excellent mechanical properties, good irradiation resistance, prominent oxidation resistance, damping capability, energetic performance and so on, showing great potential for application as structural-functional integrated materials, and are expected to be applied in the fields of nuclear reactor, aerospace, energy and chemical industry and machinery and electronics. Particularly, some refractory high entropy alloys show great value for high-temperature applications due to the high melting point, excellent high-temperature microstructural stability and high-temperature mechanical properties. Finally, the main problems and challenges faced by refractory high entropy alloys are introduced, and the prospects for their development and application are prospected.

Effect of laser power on microstructure and corrosion resistance of the laser clad CrCoFeNiMoSi_1.2B_1.1 high entropy alloy (HEA) coating was studied. The results show that the coating exhibits single FCC structure under different laser powers. The microstructure in cross section of the coating can be divided into substrate, heat affected zone, fusion zone and HEA zone. The fusion zone is a mixed crystal structure composed of dense columnar crystals and equiaxed crystals when the laser power is 2600 W, while it is a fine equiaxed crystal when the laser power is 2200 W and 3000 W. The HEA coating is dendritic structure and Mo is enriched in dendrites. When the laser power is 2600 W, the FCC phase of the coating has better crystallinity and smaller grain boundaries/lattice defects, lower self-corrosion current density (2.40 μA/cm²), more positive self-corrosion potential (-0.2760 V), and larger impedance modulus (34 713.63 Ω·cm²) and the charge transfer resistance (3.22×10⁴ Ω·cm²), exhibiting superior electrochemical corrosion performance. This can be attributed to the combined effect of the higher crystallinity, fewer grain boundary/lattice defects, denser structure and passivation film, and a single FCC solid solution phase of the coating.

FeCrNiMo high-entropy alloy powder was prepared via mechanical alloying, and the effects of ball milling control agent content, milling time and annealing on the preparation and microstructure of the FeCrNiMo high-entropy alloy powder were investigated. The results show that the addition of an appropriate mass fraction of anhydrous ethanol during the ball milling process improves the powder productivity after mechanical alloying of the high-entropy alloy powder. With the extension of ball milling time, the diffraction peak position shifts, and the peak broadens due to the occurrence of cold welding in the high-entropy alloy powder. After ball milling for 50 h, the peak shape nearly remains unchanged, the distribution of high-entropy alloy powder particles becomes more uniform, and a good refinement effect is achieved. After annealing at 400 ℃, 500 ℃, and 600 ℃ for 1 h, the phase composition of the FeCrNiMo high-entropy alloy powder remains unchanged and still consists of FCC and BCC phases. With the annealing temperature further increases, Co₇Mo₆ and Mo_1.24Ni_0.76 phases precipitate in the high-entropy alloy powder, and the powder particles agglomerate and increase in size.

Fe₃₅Mn₃₅Ni₁₀Cr₁₀Al₁₀ high entropy alloy was prepared by vacuum arc-melting method, followed by solution treatment at 1200 ℃ for 2 h and aging at 600 ℃ for 4 h. XRD, SEM, TEM and Vickers hardness tester were used to detect the microstructure and hardness of the high entropy alloy. The results show that the microstructure of the as-cast Fe₃₅Mn₃₅Ni₁₀Cr₁₀Al₁₀ high entropy alloy exhibits dendrite. The dendrite regions are FCC phase, while the interdendrite regions are BCC phase, in which a large number of B2 nanoparticles are uniformly exist. After solution treatment at 1200 ℃ for 2 h, the microstructure of the high entropy alloy transforms from dendrite to equiaxed grains where the intragranular orderd B2 phase is, and only a small amount of FCC phase exists at the grain boundaries. After sequential aging at 600 ℃ for 4 h, the B2 phase transform into FCC phase, resulting in the decrease of the volume fraction of B2 phase. Besides, the elliptic nanoparticles with α-Mn structure are precipitated in the B2 region. The appearance of B2 phase and the elliptic nanoparticles with α-Mn structure increase the hardness of the Fe₃₅Mn₃₅Ni₁₀Cr₁₀Al₁₀ high entropy alloy in solution treated and aged states, respectively, which are 419 and 517 HV0.5, 51% and 86% higher than that of the as-cast Fe₃₅Mn₃₅Ni₁₀Cr₁₀Al₁₀ high entropy alloy, respectively.

Taking ZG25CrNiMo low alloy wear-resisting steel as the research object, two groups of the tested steels without Ce and with 0.021%Ce were prepared. Firstly, the influence of quenching temperature on hardness was studied to determine the best heat treatment process. Then the effect of rare earth Ce on inclusions, microstructure, impact property and wear resistance of the tested steel was studied and the mechanism was analyzed. The results show that the best heat treatment scheme of the ZG25CrNiMo low alloy wear-resistant steel is 980 ℃×1 h normalizing+675 ℃×1 h tempering+970 ℃×1 h water quenching+205 ℃×1 h tempering. Compared with the steel without Ce, the inclusions in the steel adding 0.021%Ce are modified from large and irregular Al₂O₃ and MnS inclusions to small and spherical Ce₂O₂S rare earth inclusions. After heat treatment, the hardness of the tested steel increases from 512 HV0.1 to 538 HV0.1. The group of martensitic lath per unit area increases, and the width of the lath decreases from 0.50 μm to 0.36 μm. The impact absorbed energy of the tested steel increases from 20.7 J to 32.0 J at －40 ℃ and from 31.3 J to 44.7 J at 25 ℃, and the impact property increases significantly. After 120 min impact wear, the wear mass loss decreases from 660 mg to 550 mg. After wear, the ploughing depth on the surface becomes shallow, the proportion of peeling pits is significantly reduced, and the wear resistance is increased by 20%. The improvement of inclusions and refinement of microstructure in the low alloy wear-resistant steel ZG25CrNiMo by rare earth Ce is the main reason for the improvement of impact property and wear resistance of the tested steel.

Effect of Nb and V microalloying on microstructure and mechanical properties of Q355B steel after normalizing, quenching, and tempering were studied. The results show that Nb and V microalloying introduces undissolved spherical MC carbides at austenite grain boundaries, which inhibits boundary movement at high temperature, leading to significant grain refinement of the 900 ℃ normalized and 900 ℃ quenched steel. Additionally, Nb and V microalloying enhances the martensitic fraction of the quenched steel, thereby improving hardenability. After quenching at 900 ℃ and tempering at 450-530 ℃, the strength of the tested steel increases first and then decreases with the tempering temperature increases, while the elongation remains consistently above 25%, and the strength is the highest when the tempering temperature is 480 ℃. Combined with the microstructure and mechanical properties analysis results, 480 ℃ is determined as the optimal tempering temperature. At this temperature, Fe₃C carbides are uniformly dispersed within the martensitic matrix, significantly enhancing the precipitation strengthening effect. Furthermore, Nb and V microalloying further optimizes the microstructure of the Q355B steel, promoting the precipitation of rod-like MC-type carbides. After tempering at 480 ℃, the yield strengths of the Q355B steel and the Nb-V-Q355B tested steel reach 469 MPa and 582 MPa, respectively, with elongations of 26.5% and 25.0%. These results indicate that Nb and V microalloying, while ensuring good ductility, leads to a 113 MPa increase in yield strength.

In-situ observation of austenite grain growth of two automotive gear carburized steels 20CrMnTi with different compositions was studied by using high temperature laser confocal microscope. The austenite grain growth, inhomogeneity factor and second phase particle distribution were discussed to reveal the microstructure evolution during normalizing and pseudo-carburizing. The results show that the austenite grain size of the Nb-Ti-Mo steel is always smaller than that of the Ti-Mo steel during normalizing and pseudo-carburizing, and the austenite inhomogeneity factor of the Nb-Ti-Mo steel is also always smaller than that of the Ti-Mo steel, which is related to the better aging resistance of (Nb, Ti, Mo)(C, N) particles. In addition, the austenite inhomogeneity factor increases gradually with the extension of normalizing time and pseudo-carburizing time, and the inhomogeneity factor during the pseudo-carburizing is slightly larger than that during the normalizing. Moreover, in the pseudo-carburizing stage, the occurrence of the sharp increase in austenite grain size inhomogeneity factor of the Nb-Ti-Mo steel is later than that of Ti-Mo steel. Austenite grain size is more sensitive to temperature than time, and the temperature fluctuation is easy to cause obvious grain growth.

High-Mo die casting die steel 4Cr5Mo2V is the domestically made steel similar to the advanced imported die casting die steel Dievar. Based on the previous research of this type of steel, the influence of chemical composition on the microstructure and properties of this type of die casting die steel, the best heat treatment process selection, and the evolution mechanism of carbide precipitation during annealing, quenching and tempering were summarized. At the same time, it was suggested that further research should be carried out on the mechanism of carbide interaction and microalloying mechanism.

Effect of 0.5%Mo addition on the microstructure, phase transformation behavior, and mechanical properties of NM400 grade wear resistant steel was investigated through optical microscope (OM), electron backscatter diffraction (EBSD), and JMatPro software analysis. The results demonstrate that the Mo addition significantly enhances the hardenability of the tested steel, enabling the formation of lath martensite at lower cooling rates, and with the increase of precipitation of M₂C carbides, the refinement of hierarchical microstructure is significant, thereby improving grain refinement strengthening and solution strengthening effects. Compared with the steel without Mo addition, the 0.5%Mo steel exhibits enhanced yield strength and tensile strength reaching 996.6 MPa and 1350.0 MPa, respectively, while maintaining good plasticity, though accompanied by a slight reduction in total elongation.

Effect of Ag and Sc combined microalloying on microstructure and high-temperature properties of Al-Cu-Li alloys was studied through mechanical property testing at 250 ℃ and 300 ℃ and microstructure analysis. The results show that the Al-Cu-Li alloy with Ag and Sc combined microalloying has high high-temperature mechanical properties at 250 ℃, and its tensile strength, yield strength and elongation are 340 MPa, 297 MPa and 11.1%, respectively. Microalloying with Sc instead of Ag makes Al-Cu-Li alloy have excellent mechanical properties at 300 ℃, and its tensile strength, yield strength and elongation are 325 MPa, 292 MPa and 9.3%, respectively. The main reason for improving the high-temperature strength of the Al-Cu-Li alloy at 250 ℃ is the large amount of the high temperature stable strengthening T₁ precipitates at the grain boundary and inside the grain. The Ag and Sc combined microalloying can refine the grain of the Al-Cu-Li alloy, and the as-cast microstructure of the Al-Cu-Li alloy can be further refined when microalloying with more Sc instead of Ag. The refined grain is more conducive to recrystallization, the high temperature holding promotes the coarsening of the recrystallized grain, and the recrystallized grain is deformed again by the secondary medium temperature hot rolling, so that the alloy has better high temperature strength and plasticity matching at 300 ℃.

Effects of different C and N contents on intergranular corrosion property of NS1402 alloy was investigated. The results show that no precipitate is produced in the microstructure of the NS1402 alloy after sensitization at 675 ℃ and 750 ℃. When the sensitization temperature is 675 ℃, reducing the C content has little effect on the intergranular corrosion rate of the alloy with the N content of less than 0.01%. When raising the sensitization temperature to 750 ℃, the intergranular corrosion of the alloy with both the C and N contents above 0.01% shows relatively serious corrosion characteristics as the average corrosion rate is 0.03 mm/month and the corrosion depth is to 24 μm. However, the intergranular corrosion of the alloy with both the C and N contents below 0.01% exhibits excellent intergranular corrosion resistance under the sensitization temperature of 750 ℃, and the average corrosion rate is only 0.01 mm/month.

Equilibrium phase diagram and element content changes in precipitated phases of a novel high-strength austenitic stainless steel were calculated based on Thermo-Calc thermodynamic software. At the same time, the types of precipitated phase in the solution treated steel were determined by SEM and TEM, and the precipitation temperature and amount of the precipitated phase were calculated when the contents of C, Nb, V, N, Ni, Mo, Cr and Mn elements in the steel changed. The results show that after solution treatment, the precipitated phases in the steel are mainly large-sized rod-shaped precipitated phases and fine spherical precipitated phases, both of which are Z phases. The Z phase is primarily affected by C, Nb, V and N elements. As the content of C and V increases, the precipitation temperature of the Z phase decreases. As the content of Nb and V increases, the amount of Z phase precipitation increases. Conversely, as the content of N increases, the amount of Z phase precipitation decreases. The Ni, Mo, Cr, and Mn elements have a relatively minor impact on the precipitation of the Z phase. Considering the solution strengthening and precipitation strengthening effects of elements in the material, as well as their impact on grain boundary corrosion, within the composition range, C, Nb and N elements are the key focuses for optimizing the composition of the steel.

Influence of cooling rate on the microstructure, hardness, and phase transformation behavior of low-alloy ferritic low-temperature steel was investigated by means of Gleeble-3800 thermal simulator, OM and Vickers hardness tester through thermal expansion method and metallographic-hardness method, and the continuous cooling transformation curve of the low-temperature steel was drawn. The results show that when the cooling rate is 0.1-1 ℃/s, the microstructure of the low-temperature steel is ferrite, pearlite and bainite, and the content of bainite increases continuously with the increase of cooling rate, and the hardness of the low-temperature steel increases from 166 HV0.5 to 217 HV0.5. When the cooling rate is 3-15 ℃/s, the increase of undercooling inhibits the transformation of proeutectoid ferrite, the content of ferrite decreases, and the microstructure of the low-temperature steel is ferrite and bainite, and the microstructure is fine and uniform. The hardness of the low-temperature steel increases continuously and reaches 224-243 HV0.5. When the cooling rate is 20-40 ℃/s, the larger undercooling causes the undercooled austenite to transform into martensite. At this time, the microstructure of the low-temperature steel is ferrite, bainite and a small amount of martensite, and the microhardness continues to increase, reaching the maximum value of 290 HV0.5 at cooling rate of 40 ℃/s. Considering the plasticity, toughness and hardness comprehensively, the optimal controlled cooling range of the novel low-alloy ferritic low-temperature steel is 3-15 ℃/s.

Precipitation behavior of V(C, N) in V-microalloyed steels was studied by calculation using FactSage thermodynamic software, and experiments on the tested steels with and without addition of 0.05%V by scanning electron microscope and microhardness tester. The calculation results indicate that the precipitation amount of V(C, N) phase increases gradually with the increase of V content, while when the V content exceeds 0.02%, the initial precipitation temperature of V(C, N) phase does not increase significantly. After quenching at 950 ℃ and tempering at 550 ℃, the measured precipitation amount of V(C, N) phase in the tested 0.05%V microalloyed steel is the largest, and the hardness reaches the maximum. With the decrease of simulated coiling temperature, the hardness of 0.05%V steel increases firstly, then decreases and finally increases, the hard phase martensite structure increases, but the precipitation amount of V(C, N) phase increases firstly and then decreases, and reaches the maximum at 400 ℃, indicating that the hardness of the tested steel is influenced by both the microstructure characteristics and precipitated phases.

Microstructure and mechanical properties of GH4706 alloy after long-term aging at 700 ℃ were analyzed by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and tensile test. The reason for abnormal grain growth of the GH4706 alloy during long-term aging was investigated. The results show that after aging at 700 ℃ for 5000 h, γ ′phase in the GH4706 alloy changes from disk to long strip, and the needle η phase at the grain boundary distributes like Widmanstatten structure. The precipitation free zone on both sides widens and weakens the grain boundary, and affects the mechanical properties of the GH4706 alloy. With the increase of aging time, the number of large angle grain boundaries decreases gradually, the number of twins decreases, and the grains coarsen and grow by merging common twins. In the long-term aging process, the mechanical properties of the alloy show a continuous decreasing trend with the extension of aging time.

A 2017 aluminum alloy with high fault energy face centered cubic structure was selected as the research object. Based on the grain size, recrystallization degree and the {111}/{111} near-singular boundary ratio after annealing twin optimization process in grain boundary engineering, a three-factor and three-level orthogonal test was subject to study the effects of aging state (80, 110, 140 HV), rolling deformation (15%, 45%, 75%) and annealing temperature (440, 460, 480 ℃) on the microstructure of the alloy. The grain boundary data of the specimens were measured by the combination of electron back scattering diffraction (EBSD) and five-parameter analysis, and the orthogonal test results were analyzed through range and variance analysis. Based on the range analysis of orthogonal experiments, the main and secondary factors affecting the grain size, recrystallization degree, and the proportion degree of {111}/{111} near-singular boundaries were pointed out successively. Finally, the corrosion performance differences of the three orthogonal test schemes with the ratio of {111}/{111} near-singular boundaries as the main measurement factor were compared by intergranular corrosion test, electrochemical test and overlapping pole map trace analysis. The results show that {111}/{111} near-singular boundaries has good corrosion resistance, which can interrupt the general grain boundary connectivity and inhibit grain boundary corrosion. Therefore, the optimal scheme with a higher proportion of {111}/{111} near-singular boundaries has the best corrosion resistance.

To investigate the influence of long-term aging treatment on the microstructure and hardness of DZ411 alloy, microstructural observation and hardness measurement of the DZ411 alloy following long-term aging at various temperatures were conducted using field emission scanning electron microscope and Vickers hardness testing device to quantitatively analyze the morphology, dimensions, and quantity of γ′ phases, and to investigate the relationship between the quantitative parameters of γ′ phases and the corresponding changes in hardness. The results indicate that the heat-treated alloy exhibits a microstructure featuring the coexistence of γ/γ′ phases, with the γ′ phase being cubic and evenly dispersed, alongside a sunflower-like eutectic structure containing a proportion of blocky carbides. Following the long-term aging treatment, the size of the γ′ phase increases gradually, cubicity decreases, particle density reduces, area fraction remains relatively constant, and the rate of quantitative parameters change accelerates with higher temperatures. The growth of the γ′ phase is governed by alloying element diffusion, adhering to the LSW mechanism for growth kinetics, while precipitation strengthening of the alloy is weakened, resulting in decreased hardness values.

Microstructure evolution and strengthening and toughening mechanisms of 2024 aluminum alloy thin-walled tube subjected to indirect isothermal extrusion and after annealing treatment were studied by means of SEM and TEM characterization techniques. The results show that during the extrusion process, plastic deformation induces the precipitation of fine S(Al₂CuMg) phase along the extrusion direction, while the homogenized state T(Al₂₀Cu₂Mn₃) dispersed phase is retained, which plays a dual role of suppressing recrystallization and dispersion strengthening, and produces high-density dislocations and forms a subgrain structure. As a result, the tensile strength of the extruded alloy increases to 304.73 MPa, and the elongation after fracture reaches 12.3%. After the annealing treatment, the partial coarsening of the S phase weakens the precipitation strengthening effect. However, the dislocation entanglement network promotes the refinement of sub-grains and enhances the grain boundary pinning effect, further improving the plasticity (the elongation after fracture reaches 15.7%). At the same time, the orientation of the S phase weakens and tends to be equiaxed, reducing the anisotropy and resulting in a decrease in the strength of the alloy.

A medium carbon silicon-rich alloy steel was pre-treated by water cooling and furnace cooling respectively from 1100 ℃, reheated to 930 ℃ and then austempered at 260 ℃ (below Ms) and 320 ℃ (above Ms) respectively, by which the effects of austenite grain refinement and isothermal quenching temperature on the microstructure and mechanical properties of the medium carbon carbide-free bainitic steel were studied by means of scanning electron microscope, X-ray diffractometer, tensile and impact tests. The results show that the grain size of the water quenching pre-treated tested steel after re-austenitizing is about 55 μm, which is much smaller than that of the furnace cooling pre-treated tested steel (about 155 μm). Due to refinement of the prior austenite grains, compared with the furnace cooled tested steel, the bainite lath of the water cooled tested steel is refined after isothermal quenching, and the size of blocky M/A islands becomes smaller but the number increases. For both the water cooled and furnace cooled tested steels, below-Ms isothermal quenching can significantly refine the M/A islands size, and thus obtaining a higher strength-elongation product and impact properties.

Microstructure of 304 stainless steel was nanostructured by using cryogenic rolling combined with reverse phase transformation annealing, and the synergistic effect of precipitates and grain size factors on the intergranular corrosion performance of the 304 stainless steel was studied by means of electron back-scattered diffraction, electron probe micro analyzer and transmission electron microscopy. The results show that the initial grain size of the cryogenic rolling tested steel after annealing at 700 ℃ for 20, 60 and 120 min is 0.34, 0.67 and 1.12 μm, respectively. There are a large amount of Cr-rich carbide precipitates in the three annealed specimens, which are M₂₃C₆ precipitates. The three annealed specimens are sensitized at 650 ℃ for 2 h, and then immersed in a slightly boiling H₂SO₄-CuSO₄ solution for 16 h. The nano/ultrafine grained 304 stainless steel annealed at 700 ℃ for 20 min exhibits similar intergranular corrosion resistance compared to the micron grained steel prepared at the same temperature. The reason of which is that the precipitation of Cr-rich carbides formed in the initial structure greatly weakens the positive effect of grain refinement on the intergranular corrosion resistance of the material.

By using laser powder bed fusion (LPBF) process, 316L austenitic stainless steel was prepared with high energy density and inter-layer stay printing strategy, and then the solution treatment at 1300 ℃ was carried out. The microstructure, mechanical properties and corrosion resistance of the stainless steel were studied. The results show that the near-equiaxed grains with populated annealing twins was obtained in the 316L steel by LPBF, and the fraction of Σ3ⁿ(n=1, 2, 3) grain boundaries reaches 47.3%, indicating that dynamic recrystallization (DRX) occurs during the LPBF thermal cycles. Compared to the specimen treated by post solution treatment, the LPBF specimen has high strength and excellent corrosion resistance. It suggested that the fine and uniform equiaxed grain microstructure and the high fraction of special grain boundaries after dynamic recrystallization are responsible for the simultaneous improvement of strength and corrosion resistance of the LPBF specimen.

A solution treated Fe-Ni based austenitic alloy was aged at 740 ℃ for different time, and the metastable pitting resistance of the alloy was characterized by potentiodynamic polarization test and potentiostatic polarization test. Then the causes of pitting were analyzed by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The results show that the alloy solution treated at 980 ℃ for 1 h then air cooling has the best metastable pitting resistance. In the alloy specimens aged at 740 ℃ for different time (4, 8, 16, 32 h), the pitting of specimen aged for 4 h occurs around the Al-rich precipitates, while that for 8, 16 and 32 h is on the Ti-rich precipitates. Both precipitates are deficient in Ni. As the aging time increases, the size of the precipitates increases, the Ni-poor region correspondingly increases, and metastable pitting occurs in the Ni-poor region.

Taking 4 kinds of hot stamping steels with different strength grades as the object, the hot stamping quenching tests with different forming temperatures were carried out by using a Π-shaped molds in laboratory, and the influence of forming temperature on the microstructure, properties and dimensional accuracy of the hot stamping parts were studied. The results show that as the forming temperature decreases, the martensite content in the 600 MPa hot stamping parts decreases, and the martensite morphology transforms from blocky to granular, resulting in a gradual decrease in tensile strength. For the 1000 MPa and 1500 MPa hot stamping parts, ferrite appears in the microstructure when the forming temperature decreases to 700 ℃ and 650 ℃, respectively, and the mechanical properties undergo a significant reduction at 600 ℃. However, the microstructure of the 2000 MPa hot stamping parts maintains a fully martensitic under different forming temperatures, and the mechanical properties do not exhibit significant degradation. Comparing the springback data of the hot stamping parts with different strength grades at forming temperature of 700 ℃, it is found that the dimensional accuracy order of the parts is 1500 MPa>2000 MPa>600 MPa>1000 MPa. The variation pattern of phase transformation dilatometric amount is largely consistent with the springback pattern of the hot stamping parts.

For 17Cr16Ni2 stainless steel bolts used in train brake lever systems, both high tensile properties and excellent impact property are required during service, and tempering process plays a key role in regulating and improving the mechanical properties of the 17Cr16Ni2 stainless steel. Different tempering treatment processes were designed, and the tensile properties and impact absorbed energy of the tempered specimens were evaluated through tensile and impact tests, while microstructure and impact fracture morphologies were characterized. The results demonstrate that two-stage tempering process significantly enhances the impact property of the 17Cr16Ni2 stainless steel bolts while maintaining its tensile properties. The optimal heat treatment for the 17Cr16Ni2 stainless steel bolts identified as: 1000 ℃×180 min quenching, 635-650 ℃ first tempering and 600-620 ℃ second tempering. After this process, the bolt exhibits a tensile strength of 910.0-957.0 MPa, a yield strength of 746.5-829.0 MPa, and a room-temperature impact absorbed energy of up to 50 J, far exceeding the design specifications.

Hot-rolled and cold-rolled C-Si-Mn sheets with the same composition and thickness were subjected to intercritical austenitization, followed by direct water quenching and quenching and partitioning (Q&P) treatment, respectively. The microstructure and mechanical properties of direct water quenched and Q&P treated sheets were investigated by means of SEM, EBSD, TEM, tensile testing machines. The results show that the microstructure of the directly water quenched sheets mainly consists of ferrite and martensite. The microstructure the cold-rolled sheets after direct water quenching is mainly blocky and the hot-rolled sheets is mainly lath-like. After Q&P treatment, the retained austenite content of the sheets significantly increases, and the main morphology of retained austenite in the cold-rolled Q&P steel and hot-rolled Q&P steel are blocky and lathy, respectively. The volume fraction and carbon content of retained austenite in the hot-rolled sheet after Q&P treatment are higher and smaller in size compared to the cold-rolled sheet. The sheets after Q&P treatment exhibit lower strength but significantly higher ductility and product of strength and elongation (PSE) compared to the direct water quenched sheets, and the hot-rolled Q&P sheet shows better ductility and PSE than the cold-rolled Q&P sheet. The excellent plasticity of the hot-rolled sheet after Q&P treatment is mainly attributed to the higher content and the higher mechanical stability of retained austenite, which significantly extends the TRIP effect region. Therefore, compared with the direct water quenching, the Q&P treatment can significantly improve the elongation and PSE of the steel, and using hot-rolled sheet with initial microstructure of martensite+ferrite for Q&P treatment can obtain better PSE than the cold-rolled sheet with initial microstructure of pearlite+ferrite.

For 12.9 grade high strength bolts used in high-speed trains, the heat treatment process of SCM435 steel for the bolts and its mechanical properties, delayed-fracture resistance, and high-cycle fatigue property were studied. The results show that the optimal quenching and tempering process for the SCM435 steel is quenching at 880 ℃ for 30 min followed by tempering at 500 ℃ for 60 min. The properties of the specimens treated by the process meet the strength and plasticity requirements of 12.9 grade bolts. Under the optimal heat treatment process, the delayed-fracture strength ratio (DFSR) of the bolt steel specimens is 0.69. Through the tension-tension fatigue test, the stress level is grade 3, and the tension-tension fatigue strength is (756 ± 441) MPa.

Effects of annealing temperature and time on the microstructure, hardness and interfacial bonding strength of copper-clad aluminum composite flat strips formed by continuous casting and rolling were studied. The results show that when annealed at 150 ℃ and 200 ℃ for 60 min, the copper cladding occurs only recovery, and the hardness is about 120 HV0.025. Recrystallization begins at 250 ℃, and complete recrystallization occurs at 350 ℃, and the hardness drops to 61 HV0.025. When annealed at 150-250 ℃ for 60 min, the aluminum core only occurs recovery, and the hardness is about 45 HV0.025. Recrystallization begins at 300 ℃, complete recrystallization occurs at 350 ℃, and the hardness drops to 23 HV0.025. With the annealing temperature increases from 150 ℃ to 300 ℃, the thickness of Cu-Al interfacial layers increases from 0 to 1.0 μm, and the interfacial bonding strength decreases from 75.0 MPa to 66.0 MPa. When the annealing temperature rises to 350 ℃, the thickness of interface layers increases rapidly. The thickness of interface layers at 400 ℃ is 7.6 μm, and the interface bonding strength is 45.7 MPa. When annealing at 300 ℃, with the annealing time extends from 10 min to 90 min, the recrystallization degree of the copper cladding increases gradually, and the hardness decreases from 120.3 HV0.025 to 63.8 HV0.025. After the annealing time reaches 90 min, the microstructure is partially recrystallized. The microstructure and hardness have little change when annealing time is further extended. With the annealing time extends from 10 min to 120 min, the recrystallization degree of aluminum core is slightly increased, and the hardness is reduced from 41.3 HV0.025 to 33.8 HV0.025. The thickness of the Cu-Al interfacial layers increases from 0.2 μm to 1.3 μm, and the interfacial bond strength decreases from 80.0 MPa to 62.3 MPa.

In order to clarify the reliability of laser energy density as a basis for selective laser melting (SLM) process optimization, the effect of volume energy density (process combinations of different laser powers, scanning speeds and scanning spacing) on the microstructure and properties of SLM-formed alloy by means of an orthogonal experimental design was investigated. The AlSi12 alloy was fabricated by SLM forming technology, and the densities, melt pool boundary, microstructure and mechanical properties of the alloy were characterized and investigated by optical microscope, scanning electron microscope and room temperature tensile tests. The results show that under the same volume energy density, with the increase of the laser power, the melt pool deepens, the proportion of equiaxed grains in the heat-affected zone at the edge of the melt pool decreases, and the microstructure of the fine grain zone gradually coarsens; while with the increase of the scanning speed, the melt pool broadens, the proportion of equiaxed dendrites in the fine grain zone increases, the microstructure of the coarse grain zone refines, and the fine Si particles in the heat-affected zone gradually increase. The volume energy density cannot be used as the only influencing factor for the judgement of quality of the shaped parts. The laser power has the greatest influence on densification, tensile strength and yield strength, while the scanning speed has the greatest influence on elongation. The mechanical properties of the specimens are optimal at the laser power of 300 W, scanning speed of 1200 mm/s and scanning spacing of 60 μm, with the tensile strength of 447.1 MPa, yield strength of 433.7 MPa and elongation of 7.6%.

Heat treatment between 780-1200 ℃ for RAFM steel extruded tube with size of ø57 mm×6 mm obtained by double vacuum melting combined with multi-pass hot forging and re-hot extrusion was carried out, and the microstructure and mechanical properties of the extruded tube at different heat treatment temperatures were studied. The results show that after heat treatment between 780-1200 ℃, the microstructure evolution of the RAFM steel extruded tube with increasing temperature is as follows: tempered lath martensite (780-900 ℃), martensite matrix+ferrite+fine dispersed carbides (950-1000 ℃) and lath martensite (1050-1200 ℃). The tensile strength, yield strength and hardness of the RAFM steel extruded tube at room temperature decreases first and then increases with the increase of heat treatment temperature, while the elongation increases first and then decreases. After heat treatment at 850 ℃, the RAFM steel extruded tube obtains relatively excellent room temperature elongation and relatively low strength, which is convenient for subsequent production and processing.

Dissolution behavior of residual phases at grain boundaries during the solution process of 2A12 alloy was studied by using techniques such as differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the overburning temperature of the 2A12 alloy is 509.6 ℃, and the main phases in the rolled state alloy are non-equilibrium solidification eutectic phases of Al, Cu, and Mg. During the solution treatment process, the non-equilibrium eutectic phase in the alloy gradually melts and spheroidizes, and the segregated elements dissolve into the matrix. As the solution treatment temperature increases, the hardness of the specimen increases. This is because more non-equilibrium eutectic phases in the specimen dissolve into the matrix, increasing the solubility of the matrix and increasing the number of solute atoms dissolved into the solvent lattice, resulting in an increase in hardness.

An ultra-thin grain-oriented silicon steel was subjected to different cold rolling processes and recrystallization annealing at 820 ℃, and the effect of cold rolling process on the magnetic properties and texture of the tested steel was studied. The results show that under different cold rolling processes, {111}<112> texture is formed and a large amount of shear bands is contained in the cold-rolled steels. In order to obtain excellent magnetic properties, different cold rolling processes need to be matched with different annealing processes. When the first pass reduction rate is 43%-52% and annealing time is 25 min, or the first pass reduction rate is 29%-37% and annealing time is 20 min, the microstructure with 70%-75% η-fibre texture and average grain size of 35 μm can be obtained, which leads that the magnetic properties of the ultra-thin grain-oriented silicon steel reach the optimal state, with the magnetic induction intensity B₈₀₀ ≥ 1.80 T and the iron loss P_1.5/400 ≤ 12.5 W/kg. The smaller reduction rate of first pass cold rolling, the shorter annealing time and the better uniformity of the microstructure. In industrial production, the reduction rate of first pass cold rolling could be properly reduced.

Using the Gleeble-3800 thermal simulation experimental machine, different over-aging temperature tests of 1.2 mm thick 1.2 GPa high-strength steel bearing C-Si-Mn-Cr-Mo-B were conducted on the cold-rolled hardening raw materials and the research of influencing law about different over-aging temperatures on mechanical properties and microstructure was focused on. The results show that, in the range of 260-340 ℃, as the over-aging temperature increases, the tensile strength monotonically decreases, while the yield strength and yield ratio monotonically increase, and the change in elongation after fracture is not obvious. Meanwhile, as the rapid cooling temperature increases with the aging temperature, the degree of undercooling during the cooling process decreases, resulting in the gradually decreases of martensite content, and even white granular second phase precipitates inside the grain and the convex features of martensite gradually weaken, and the large angle grain boundaries gradually increase. The amount of (Fe, Mn)_xC_y precipitates inside the ferrite grains gradually decreases. Under the trial production process with an annealing temperature of 800 ℃ and an over-aging temperature of 280 ℃, the mechanical properties of the finished product meet the national standard requirements. It is successfully applied to the roll forming of the front bumper crossbeam.

Effects of tempering temperature, time and inclusion on microstructure and mechanical properties of 150 KSI 30CrNi2MoV steel for deep wells were studied by means of optical microscope, scanning electron microscope, ASPEX scanning analyzer, tensile test and impact test. The results show that after quenching at 860 ℃ and tempering at 590-610 ℃ for 60 min, the yield strength of the 30CrNi2MoV steel decreases from 1152 MPa to 1058 MPa with the increase of tempering temperature, the tensile strength decreases from 1239 MPa to 1135 MPa, the elongation increases from 17% to 19%, the percentage reduction of area increases from 56% to 61%, and the normal temperature minimum impact absorbed energy increases from 80 J to 99 J. When tempered at 600 ℃ for 60-240 min, the precipitates inside the grains increase with the increase of tempering time. When tempered at 600 ℃ for 60 min, with the inclusion index decreases from 12.8 to 1.1, the mean impact absorbed energy of the tested steel increases from 57 J to 95 J.

On-line continuous annealing of two kinds of cold-rolled low carbon steel (0.076%C and 0.140%C, respectively) was carried out by using a continuous hot-dip galvanizing/continuous annealing dual-purpose unit, and the effect of aging starting temperature after rapid cooling on microstructure and properties of the steels was studied. The results show that when the aging starting temperature after rapid cooling decreases in the range of 400-480 ℃, the strength of the two steels increases slightly and the elongation changes a little. In addition, the aging starting temperature change has a little effect on the ferrite, but can change the morphology of the second phase. When the aging starting temperature is 480 ℃, the preformed precipitation of cementite maintains the original lamellar morphology. When the aging begins from 450 ℃ and 400 ℃, the cementite is mostly spherical or granular, distributed in the grain and at the grain boundary, the size of the cementite in the grain is small, generally at the nanoscale, and the precipitation size of a small amount of cementite at the grain boundary is relatively large.

High-carbon low-alloy wear-resistant cast steel was heated at 860-940 ℃ for 2 h with intermittent controlled air cooling and then followed by stress-relieving tempering at 550 ℃ for 2 h. The microstructure, hardness, and impact properties of the tested steel after heat treatment were observed and measured. The results show that with the increase of heating temperature, the hardness value of the tested steel shows a trend of first increasing and then decreasing, with a narrow range of 32.9-38.7 HRC. The impact absorbed energy shows an overall decreasing trend, and the fracture morphology transitions from ductile dimples and quasi cleavage to quasi cleavage. Within the heating temperature range of 860-940 ℃, the microstructure is composed of pearlite and carbides. However, as the heating temperature increases, the lamellar spacing of pearlite microstructure widens from 0.123 μm to 0.169 μm.

Cold-rolled Ti-6.5Al-2Zr-1Mo-1V(TA15) titanium alloy sheet was conventionally annealed at different temperatures ranging from 750 ℃ to 980 ℃ and dual-stage annealed, respectively, and the effect of different annealing treatments on the microstructure and hardness of the alloy was investigated. The results indicate that when the cold-rolled TA15 titanium alloy sheet is conventionally annealed at a temperature lower than the phase transformation point, an equiaxed primary α(α_P) phase can be obtained. After conventional annealing at a temperature close to the phase transformation point (965 ℃), a bimodal structure composed of α_P and lamellar α(α_S) phases is obtained. When the conventional annealing temperature is higher than the phase transformation point, the α_P phase disappears, and the microstructure consists of coarse Widmansttten α_W phase. After primary annealing near the phase transformation point and secondary annealing in the two-phase region, the cold-rolled TA15 titanium alloy sheet can obtain a tri-modal structure composed of α_P, α_W and α_S phases. Under conventional annealing, with the increase of annealing temperature, the hardness of the cold-rolled TA15 titanium alloy sheet first decreases and then increases. After the dual-annealing of 965 ℃×30 min, WQ+920 ℃×100 min, AC, due to the coarsening of α_S phase, the hardness is lower than that after the conventional annealing.

Effect of quenching and tempering processes on microstructure and mechanical properties of the working layer of vertically centrifugally composite casting backup roll, via heat treatment tests of specimens from working layer of the backup roll, was studied, and microstructure observations and mechanical property tests were carried out. The results show that the microstructure of the working layer of the backup roll after final quenching and tempering treatment is composed of tempered martensite, bainite, retained austenite and carbide particles with a dispersed distribution, and the carbide particles are fine and uniformly distributed. Through comparative is analysis, it is found that the optimal quenching and tempering temperatures of the centrifugally composite backup roll are 1000 ℃ and 500 ℃, respectively. The hardness of the working layer reaches 63.9 HRC, the tensile strength reaches 549 MPa. The tensile fracture shows a quasi-cleavage morphology and there are typical lamellar structures. The impact fracture shows typical intergranular cracking characteristics, the cleavage plane of the fracture is refined, and the carbide particles are fine and uniformly distributed.

A nitrided layer was prepared on TA7 titanium alloy by plasma nitriding technology. The microstructure, hardness, tribological properties and wear mechanism of the nitrided layer were investigated by means of friction and wear testing, X-ray diffraction (XRD), hardness tester, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that after plasma nitriding at 800 ℃ for 10 h, the thickness of the nitrided layer is about 5 μm, which is composed of TiN and Ti₂N. The surface hardness of the nitrided specimen can reach 1183.6 HV0.05, which is about 2.6 times higher than that of the unnitrided specimen. The wear resistance of TA7 titanium alloy is improved after nitriding, as the wear rate of the nitrided specimen is reduced by more than 99.3% compared with that of the unnitrided specimen. The evolution of wear of nitrided layer is from the abrasive wear into the slightly adhesive and oxidative wear. The main phase composition of the subsurface of the nitrided layer is Ti₂N. Friction-induced periodic structure is the main wear mechanism of the nitrided layer.

Through adding a certain amount of rare earth SmCl₃ to the aluminium infiltrant and using low temperature powder-embedded aluminizing method, the P92 steel was aluminized at different temperatures and time. The morphology of the aluminized layer was observed by using OM and SEM, the element distribution in cross-section and phase structure of the aluminized layer were analyzed by means of EDS and XRD, respectively, and the microhardness of the aluminized layer was measured by microhardness tester. The results show that after aluminizing at 550 ℃ for 6, 8, 10 h, respectively, no aluminizing layer is found on the surface of the P92 steel. After aluminizing at 750 ℃ for 10 h, the aluminized layer has defects like being loose and porous, whereas the quality of the aluminized layer is better at 650 ℃, with no shrinking pore cracks or other defects. After aluminizing at 650 ℃ for 6, 8, 10 h, respectively, the average thicknesses of the aluminizing layers are 27, 30, 31 μm, respectively. The hardness of the aluminized layer is approximately 260 HV0.025 higher than the average hardness of the P92 steel substrate. After aluminizing at 650 ℃, the surface phase of the P92 steel is AlFe₃ and AlCrFe₂, and after aluminizing at 750 ℃, it is AlFe.

Microstructure and friction and wear properties of carburized layer of a Cr-Co-Mo carburizing bearing steel after quenching at 1060 ℃, cryogenic treating twice at -73 ℃ and tempering twice at 540 ℃ were investigated by means of metallurgical microscope, scanning electron microscope, hardness test and Thermo-Calc software calculation. The results show that after low pressure pulse carburization at 980 ℃ for 50 h, the carbides in carburized layer of the tested steel are mainly M₂₃C₆, and a small number of M₇C₃ and M₆C carbides. The carburization significantly increases the hardness of the steel, resulting in a increment of 230 HV, and the carburized depth is about 1.55 mm. The friction coefficient of the uncarburized steel is larger, and the wear volume is about 5 times of that of the carburized steel. After carburizing, only slight wear occurs at the carburized layer, the wear resistance is significantly improved, and the main wear mechanisms are still adhesive wear and abrasive wear.

The 2Cr13 stainless steel was treated by active screen plasma source nitriding. The effect of the distance between the 2Cr13 stainless steel specimens and the metal screen on the phase structure and properties of the nitrided layer was studied, and it was compared with the traditional direct current plasma nitriding. The results show that a uniform and compact nitrided layer is formed on the surface of the 2Cr13 stainless steel when using both two kinds of nitriding processes. The thickness of the compound layer of the active screen plasma source nitrided specimen is lower than that of the direct current plasma nitrided specimen. As the distance between the nitrided specimen and the metal screen increases from 50 mm, 100 mm to 200 mm, the thickness of the nitrided layer decreases from 18 mm, 15 mm to 6 mm, respectively. The nitrided layer has the same phases structure for speicmens 50 mm and 100 mm away from the metal screen, mainly consist of ε-Fe_2-3N、γ′-Fe₄N and α_N phases, while the nitrided layer which 200 mm away from the metal screen is composed of α-Fe and ε-Fe_2-3N phases. The surface hardness of the nitrided layer treated by two processes reaches 1305-1442 HV0.2, which is 3-4 times of the matrix hardness. The tribological properties and electrochemical corrosion behavior of the active screen plasma source nitrided layer are superior to those of the direct current plasma nitrided layer, with a friction coefficient maintained between 0.62-0.70 and a self corrosion potential between －0.11-－0.18 V.

In order to improve the surface hardness and wear resistance of high carbon H13 steel, carburizing+quenching and tempering processes were carried out, and the microstructure and hardness were analyzed. The results show that the carburizing+quenching and tempering processes can significantly improve the hardness of the steel. After carburizing at 920 ℃, quenching at 1050 ℃ and tempering at 510 ℃, the hardness of the high carbon H13 steel is the highest. Compared with that treated only by quenching-tempering, the high-carbon H13 steel cutter ring treated by this process can increase the tunneling distance by about 36% under the same wear conditions.

Surface mechanical rolling treatment (SMRT) with different loading methods (stress control and strain control) and processing passes was carried out on the annealed 2024 aluminum alloy to study the influence of SMRT on surface roughness and properties. The results show that after SMRT, with the increase of rolling pass, the surface roughness of the specimen first decreases and then increases, a hardness gradient structure is formed inside the specimens, as the distance from the surface increases, the microhardness shows a decreasing trend, and the strength of the specimen is improved, the plasticity decreases slightly, and the fatigue life is significantly enhanced. After stress-control rolled for 5 passes, the comprehensive performance of the 2024 aluminum alloy is the best, with minimum surface roughness of 0.280 μm, hardened layer depth of 600 μm, yield strength of 213 MPa, and tensile strength of 353 MPa. The average fatigue life is twice than that of annealed state, which is increased from 87 000 cycles to 174 000 cycles.

Failure analysis was conducted on the spalling problem of cam tip of a marine diesel engine camshaft after durability cycle testing, and a composite shot peening strengthening method was proposed to improve the contact fatigue strength of the camshaft. The results show the microstructure, hardness and hardened layer depth of the camshaft are all within the normal range, and the failure cause of the camshaft is contact fatigue spalling. After composite shot peening by using ceramic shot (0.15A)+glass shot (0.07A), the residual compressive stress distribution on the cam surface is uniform. The residual compressive stress in the surface layer is increased to 1284 MPa, and that in the subsurface layer is increased to 1322 MPa. The retained austenite content in the surface layer is reduced to 0.8%, and the surface hardness is increased to 971 HV0.05. This indicates that the composite shot peening strengthening can effectively solve the problem of contact fatigue spalling of the camshaft.

316L coating and SiC-316L composite coating on Q235 steel substrate were prepared using the laser-assisted cold spraying (LACS) technology, respectively, and the laser power for preparation of SiC-316L composite coating was determined according to the quality of 316L coatings under different laser powers, and then the microstructure, phase composition, hardness and wear resistance of the two coatings were studied and compared. The results show that the increase of laser power can significantly reduce the porosity of 316L coating and improve the bonding strength between the coating and the substrate. When the laser power is 500 W, the pores and microcracks of 316L coating are the least, the SiC particles are uniformly distributed in the SiC-316L composite coating, and no obvious oxidation and phase transformation occur in the two coatings which bonding mechanism between the coating and the substrate is the coexistence mechanism of mechanical bonding and metallurgical bonding. The average hardness of the 316L coating and SiC-316L composite coating reaches 437.7 HV0.3 and 490.3 HV0.3, respectively. The friction coefficient of the SiC-316L composite coating is 35% lower than that of the 316L coating under room temperature wear condition, and the friction coefficient of the SiC-316L composite coating is 18.4% lower than that of the 316L coating under 600 ℃ high temperature wear condition, showing that the SiC-316L composite coating exhibits more excellent wear resistance.

A laser shock processed(LSPed) thermal barrier coating model was established by changing the growth rate and morphology of thermally grown oxide (TGO), and the interfacial stress of the LSPed coating was simulated in comparison with those of the non-LSPed coating, so as to analyse the effect of laser modification on the high-temperature thermal cycling of the thermal barrier coating from the view of the stress evolution, and the cohesion units at the TC/TGO interface was introduced to study the effect of laser modification on the interfacial crack of the thermal barrier coating. The results show that for the same TGO morphology, the stress value of LSPed specimens is smaller than that of Non-LSPed specimens on the TGO surface, and the laser modification reduces the risk of fold warping, layer cracking, and shear damage in this region. At the TGO/BC interface, the stress value of LSPed specimens in the pre-oxidation period is larger, but in the late stage of the oxidation period, the stress values of Non-LSPed and LSPed specimens are close to each other, suggesting that the effect of LSP modification on the stress at the TGO/BC interface is relatively small. Under different TGO morphologies, the overall stress of LSPed specimens is smaller than that of Non-LSPed specimens, indicating that LSP modification can effectively reduce the stress value of the coating interface. After 35 thermally cycles, cracks appear at the wave peak position of the TC/TGO interface in the Non-LSPed specimen. As the number of cycles increases, the cracks extend towards the wave valley. However, no cracks appear in the LSPed specimen after 50 thermal cycles.

Aiming at the problem of planar warping distortion of a G-type lid made of ZL101A alloy after heat treatment, numerical simulation method was used to predict the easy-distorted part of the lid, and then anti-distortion measures were conducted. Firstly, a multi field coupling model of temperature-heat transfer-stress and strain was established, the thermal physical parameters such as the specific heat capacity and thermal conductivity of ZL101A alloy was calculated by JMatPro software, and the heat transfer coefficient of water and AQ260 aqueous solution were tested. Based on these, the influence of furnace loading method and quenching medium on the quenching distortion of the G-type lid was simulated using ANSYS finite element method, meanwhile a series of experiments were conducted by combining the simulation results. The simulation results show that the distortion of the lid treated by hanging+PAG aqueous solution quenching is the smallest, with a planar warping distortion value of 3.5603 mm. Considering that there is a distortion of about 1 mm in the as-cast state lid, which cannot meet the machining requirement of ≤4 mm in actual production, a scheme of enhancing structural rigidity is adopted to control the lid distortion. The experiments results show that the methods of point welding stiffeners or attaching stiffeners can both reduce the planar warping distortion during the heat treatment of the lid, and the scheme of hanging+PAG aqueous solution quenching+attaching stiffeners achieves the best distortion control, with the planar warping distortion of all three tested lids ≤2.5 mm, meeting the machining requirements.

Electromagnetic field-temperature field coupling mathematical model between the induction coil and the induction quenching workpiece was established by using the finite element software Ansys Maxwell. The magnetic field distribution and the temperature field distribution of the workpiece during the induction heating process were obtained, and the simulation results were verified by the induction quenching test. The results show that the induction coil can make the magnetic field gather on the surface of the quenching area of the workpiece to realize induction heating. The effect of induction heating with 3 turns coil for 10 s is the best, and the maximum temperature of the workpiece surface is about 903 ℃, which meets the design expectation. The induction quenching test results are in good agreement with the simulation results. The hardened layer depth of the screw blank is 4.6 mm, the hardness distribution is semi-saddle-shaped, and the surface hardness is significantly improved to 61.5 HRC, which meets the process requirements, indicating that the induction coil design is reasonable and the induction quenching process is appropriate. It can be applied to the production of high-precision retention ball screw blanks.

Based on comparison with GB/T 7216—2009, GB/T 7216—2023 was interpreted from standard application scope, terms and definitions, inspection items, rating images, and result representation. In GB/T 7216—2023, the application scope of the standard, the measurement methods and reference images for various types of microstructure are changed. Terms and definitions, the calculation method of graphite content, and examples of graphite shape length expressions are added. In the appendix part, the comparison with ISO 945-1: 2019, the typical flake graphite distribution patterns, and image analysis identification methods for graphite types are added.