The microstructure of 11%Cr ferritic/martensitic steel in the normally heat-treated state before and after irradiation was experimentally studied by using transmission electron microscopy and energy dispersive spectroscopy. The results show that the primary microstructure of the 11%Cr ferritic/martensitic steel before and after irradiation consists of tempered martensitic along with a small amount of δ-ferrite. Before irradiation, a small amount of precipitates with a relatively small size are present at martensite boundaries and within martensite laths. Some irregular, blocky, large black particles are present at the interface of δ-ferrite and matrix. There are no precipitates within δ-ferrite grains. After irradiation, a large number of rod-like and blocky precipitates appear at the boundaries and interior of the martensitic lath, while the number and size of precipitates significantly increase compared to that before irradiation. The number of irregular blocky black particles at the interface of δ-ferrite and matrix increase compared to that before irradiation. Inside the δ-ferrite, a large number of blocky and needle-like precipitates are formed which may be Cr-rich nitrides, Cr-rich carbonitrides and Fe-W type precipitates. After irradiation, the precipitates inside the martensitic laths are Cr-rich M₂₃C₆ phase. Compared with the Cr-rich M₂₃C₆ phase before irradiation, the Cr and Ta contents in the M₂₃C₆ phase slightly decrease, while the Fe and Nd contents slightly increase after irradiation. However, overall, the changes in the average metal element composition of the Cr-rich M₂₃C₆ phase are relatively small.

Using Python language to edit Thermal-Calc instructions for efficient calculation of alloy phase composition, two iron-based medium entropy alloys with L2₁ precipitation ratio greater than 15% were obtained according to design principles. Adopting large deformation cold rolling combined with medium temperature aging process for microstructure control to achieve excellent strength plasticity matching. The results show that the tensile strength and elongation of No.1 alloy are 1592 MPa and 17.50%, respectively, while that of No.2 alloy are 1682 MPa and 13.50%, respectively. At the same time, both the alloys form stable passivation films in a 3.5wt% NaCl solution, with a pitting potential close to 0 V(vs SCE) and good corrosion resistance. The main matrix phase of the two alloys is FCC solid solution, with a small amount of BCC phase. The combination of large deformation cold rolling and medium temperature aging results in the alloy having an incomplete recovery of fine grain structure, accompanied by the formation of multiphase and multi-scale precipitation phases, which form a soft and hard coordination with the FCC matrix to improve the strength and plasticity of the alloy. The combined effect of precipitation strengthening, dislocation strengthening and grain refinement strengthening enhances the strength of alloys. The high plasticity of the alloy is due to the relief of stress concentration during medium temperature aging. The good plasticity of the FCC matrix can effectively slow down the formation and propagation of cracks. In addition, the low mismatch between Heusler_L2₁ phase and the matrix can also slow down the formation of microcracks at the phase boundary, allowing the two medium entropy alloys to maintain high plasticity.

As a new generation of automotive steel, the Fe-Mn-Al-C system low-density steel is a potential material for future automotive light-weighting research due to its advantages of high strength, low density, and good plasticity and toughness. As a result of κ-carbide affect the comprehensive mechanical properties of the steel, the characteristics and formation mechanism of κ-carbides in Fe-Mn-Al-C low-density steels and the effect of differences in the content of alloying elements on κ-carbides were expounded, and the effect of solution and aging treatments on κ-carbides and the effect of κ-carbides on the toughening mechanism were described in detail. It is concluded that the mass fraction of Al and Mn in Fe-Mn-Al-C steel should be reasonably controlled to provide driving force for κ-carbide precipitation, and the solution treatment temperature should be 900-1100 ℃, after which the aging should be carried out in the range of 450-600 ℃, and the aging time should be 1-2 h, to avoid the precipitation of coarse κ-carbides at the grain boundaries to deteriorate the material properties.

Effect of different heating time (20, 40 min) on surface oxidation and decarburization of 60Cr13 stainless steel cutting tools at 1050 ℃ was studied. The results show that at heating temperature of 1050 ℃, a longer holding time results in severe internal oxidation and grain boundary oxidation on the surface of the 60Cr13 stainless steel cutting tools, with an oxide layer thickness of 15-17 μm. In addition, extending the heating time intensifies the oxidation reaction in high-temperature environments, the oxygen continuously diffuses into the interior of the steel, while the carbon atoms in steel migrate outward. Due to the diffusion rate of carbon atoms exceeding the oxidation rate, the surface decarburization process is intensified, reducing the carbon content in the surface layer, resulting in a decrease in the surface hardness of the 60Cr13 stainless steel cutting tools.

In order to study the role of vanadium in hypereutectoid tool steels, microstructure observation, mechanical property test, heat treatment test and abrasive wear test were used to compare and analyze the microstructure and properties of the two hypereutectoid tool steels with and without vanadium after hot rolling and heat treatment. The results show that under the same hot rolling process condition, fine VC particles with a diameter of not more than 10 nm are precipitated in the V-containing steel, the colony size of the pearlite are smaller and with finer lamellar spacing, the yield strength, tensile strength and hardness are 116 MPa, 179 MPa and 3.2 HRC higher than those of the V-free steel, respectively. When tempered at temperatures below 550 ℃, with the increase of tempering temperature, the hardness of the two tested steels gradually decreases and the wear rate gradually increases. Under the same heat treatment process conditions, the hardness of V-containing steel is higher, the wear rate is smaller, and the tempering resistance is better. The tempered hardness at 450 ℃ still reaches more than 53 HRC, and the wear rate is less than 23 mg·km^-1. Tempering at 500 ℃ is a turning point in the deterioration of wear resistance of the V-containing steel. When tempered at 500 ℃ and above, VC particles with a size of above 100 nm precipitate in the V-containing steel, resulting in a significant increase in wear rate and deterioration of wear resistance.

The nanocomposite Nd₂Fe₁₄B/PrCo₅ melt-spun ribbons were prepared by induction melting and melt-spinning technique, and the effect of PrCo₅ addition on the phase structure, magnetic properties and exchange coupling was investigated. The XRD test results indicate that the ribbons has dual hard magnetic phases of Nd₂Fe₁₄B and PrCo₅, and no oxidation or formation of new phases occur during the preparation process. The content of PrCo₅ has an obvious effect on magnetic properties, and the appropriate addition of PrCo₅ can help improve coercivity. However, the remanent and maximum magnetic energy product decrease with the increase of PrCo₅ content. Research on the recoil loops shows that the "opening" phenomenon of the recoil loops is related to the content of PrCo₅, and the δ_M curve test shows that there is a strong exchange coupling effect in the Nd₂Fe₁₄B/PrCo₅ ribbons. Comprehensive analysis shows that optimal magnetic properties of the nanocomposite Nd₂Fe₁₄B/PrCo₅ ribbons can be obtained at 12%PrCo₅ content, with remanent M_r of 8.73 kGs, coercive H_cj of 11.03 kOe, and the maximum magnetic energy product (BH)_Max of 15.83 MGOe.

By adding rare earth cerium iron alloy in the 32MnMoNiCu cast steel, the effect of rare earth Ce on microstructure and mechanical properties of the cast steel was investigated by using scanning electron microscopy observation, tensile and impact testing methods. The results show that rare earth Ce can refine the ferrite phase, transform inclusions shape from long strip into nodular, and decrease the size of inclusions. Rare earth Ce mainly exists in the form of CeAlO₃, and does not react with MnS inclusions. Precipitation strengthening and fine-grained strengthening which are caused by rare earth Ce in the cast steel result in 12.3% and 23.4% increase in tensile strength and yield strength, respectively. However, the increase fraction of lath ferrite by adding rare earth Ce result in 11.1% and 7.4% decrease in elongation and impact absorbed energy, respectively.

Hot deformation behavior and microstructure evolution of Ti-44Al-5V-1Cr alloy deformed near the α-phase region (at 1250 ℃) under different conditions as various initial microstructure, strain rates and deformation were investigated by means of thermophysical simulation, SEM, EBSD and OM characterization. The results show that when the deformation temperature is 1250 ℃, the difference of flow stress variations in initial microstructure of the alloy under identical deformation rate are smaller. However, under the same microstructural condition, the strain rate has a relatively significant effect on the flow stress. As the strain rate decreases, the flow stress decreases noticeably. When the alloy is deformed near the α-phase region, the dynamic recrystallization of α phase is dominant, and the dynamic recovery is supplemented, while the β phase effectively suppresses the growth of α grains. In addition, increasing the deformation can facilitate the refinement of α grain size. After extrusion at 1250 ℃ with a high extrusion ratio, the alloy achieves a fine and uniform fully lamellar structure with average lamellar colony sizes of 12-23 μm.

Offshore platform steel EH36 was taken as the research object, and the welding process of the tested steel was simulated by DIL805L quenching dilatometer. The SHCCT curve of the tested steel was established by means of thermal expansion method combined with metallography method and Vickers hardness test, and the influence of different cooling rates on the microstructure transformation law of the welding heat affected zone was studied. The results show that in the whole cooling rate range, there are four types of microstructure transformation in the HAZ of the tested steel: ferrite+pearlite, ferrite+pearlite+bainite, bainite and martensite+bainite, and the hardness value increases from 164 HV10 to 277 HV10 with the increase of cooling rate. When the cooling rate is lower than 5 ℃/s, the hardness of the HAZ of the tested steel is lower than that of the base metal. In order to ensure that the tested steel obtains good welding joint properties, the cooling rate should be controlled in the range of 10-20 ℃/s (that is, the t_8/5 time is controlled in the range of 15-30 s).

The phase transformation characteristics of the SCM415H steel for automotive fasteners were studied by thermal simulation. The cooling rate of 0.25 ℃/s produces a microstructure of ferrite and pearlite, while the bainite and martensite occurs with the cooling rate reaches 0.5 ℃/s. The cooling rate of 5 ℃/s results in a microstructure of mainly martensite and bainite, and that of 15 ℃/s or above results in a microstructure of mainly martensite. The pearlitic transformation temperature is 700-575 ℃ during isothermal conditions. The nose tip temperature is about 660 ℃, and completion time of the phase transformation is about 428 s. Based on the tested results, the steel wires with a diameter of 24 mm were successfully produced, and then grade 10.9 automobile fasteners were successfully produced after one spheroidizing annealing and two drawing processes.

Continuous annealing hot-dip galvanizing process of a 780 MPa grade dual phase (DP) steel was studied by using hot-dip galvanizing simulation testing machine. Effects of four different heat treatment processes as direct quenching, quenching after slow cooling, post-galvanized martensite process and pre-galvanized martensite process on the microstructure and tensile properties of the steel were compared and analyzed. The results show that the slow cooling process after heating in the two-phase region can improve the hardenability of the untransformed austenite and obtain stable island-like martensite. A small amount of tempered martensite is obtained by the pre-galvanized martensite process. The Nb can improve the tempering stability of martensite and improve the mechanical properties of hot-dip galvanized DP steel. There is no significant change in precipitated phases of the steel after the post-galvanized martensite process and the pre-galvanized martensite process, the Nb-rich precipitates are prone to heterogeneous nucleation and precipitation at the interface of TiN precipitated firstly. The tensile strength of the DP steel obtained by the pre-galvanized martensite process is 867 MPa, and the elongation is 21.3%, which is close to the tensile strength (878 MPa) and elongation (24.0%) of the post-galvanized martensite process. However, the yield strength of the DP steel obtained by the pre-galvanized martensite process (564 MPa) is significantly reduced compared to the post-galvanized martensite (611 MPa). Therefore, the pre-galvanized martensite process can effectively reduce the yield ratio and improve the formability of the dual phase steel while ensuring its strength and plasticity.

Microstructure, mechanical properties, and fatigue property of 51CrMnV spring steel under the processes of 900 ℃×30 min quenching+450 ℃×90 min tempering and 900 ℃×30 min+350 ℃×30 min isothermal quenching were investigated by using optical microscopy (OM), scanning electron microscopy (SEM), universal tensile tester, impact tester, and fatigue tester. The results show that after quenching and tempering, the microstructure of the 51CrMnV steel consists of tempered martensite, and after isothermal quenching, the microstructure consists of bainite, martensite and retained austenite. Compared with quenching and tempering, the mechanical properties and fatigue properties of the 51CrMnV steel treated with isothermal quenching are better, with an increase in tensile strength of 53.6 MPa, elongation of 3.1%, impact absorbed energy of 7.3 J, and fatigue limit of 25 MPa.

In order to study the effect of cryogenic treatment on mechanical properties and microstructure evolution of nuclear grade mild steel, the mechanical properties and microstructure of 20 steel after different heat treatments were characterized by means of microhardness tester, XRD, SEM and TEM. The results show that the tempering treatment promotes the transformation of partial retained austenite into martensite and the precipitation of carbon atoms leading to martensite refinement, resulting in an increase in hardness from 468.5 HV0.1 of the quenched steel to 480.3 HV0.1 of the tempered steel. The cryogenic treatment promotes the transformation of the retained austenite into fine lath martensite in the tested steel, and at the same time, the cryogenic treatment causes lattice distortion in the martensite, which leads to the increase of stresses and defects such as dislocations in the microstructure, which in turn promotes the precipitation of carbon atoms in the martensite, leading to the enhancement of precipitation strengthening, resulting in the increase of hardness of the tested steel to 495.3 HV0.1 after quenching-cryogenic-tempering treatment.

Effects of quenching temperature and low temperature tempering temperature on microstructure and mechanical properties of a Cr-Mo wear-resistant steel were investigated. The results show that the lath of tempering martensite of the tested steel after tempering is coarsened with the increase of quenching temperature, leading to the decrease of the strength, ductility and toughness. The hardness of the steel after quenching at 1060 ℃ and tempering is higher than that of quenching at 860 ℃ and tempering, which is due to the higher solution strengthening caused by more solution element during quenching isothermal stage. When the quenching temperature is 860 ℃, the strength and toughness first increase and then decreases with the increase of tempering temperature. The optimal tensile strength and impact absorbed energy at -40 ℃ are obtained when tempered at 200 ℃, which are 1607 MPa and 43.9 J, respectively, while the product of strength and elongation decreases to the lowest grade when tempered at 280 ℃. With the tempering temperature further increasing, the strength and toughness increase slightly. When the quenching temperature is 1060 ℃, the strength gradually decreases with the tempering temperature increasing, while the toughness first decreases and then has a little increment. The optimal tensile strength and impact absorbed energy at -40 ℃ are obtained when tempered at 160 ℃, which are 1494 MPa and 45.4 J, respectively.

Effect of aging under pulsed magnetic field on microstructure and mechanical properties of ZL205A aluminum alloy was studied by means of scanning electron microscope, X-ray diffractometer and universal testing machine. The results show that the pulsed magnetic field increases the vacancy formation energy ΔS_V during the aging process of the ZL205A aluminum alloy, and the atomic diffusion is easier, which leads to the appearance of uniform and fine precipitation phases in the matrix after aging. After the pulsed magnetic field aging treatment (195 ℃×4 h), the tensile strength and elongation are 408 MPa and 11%, respectively. Compared with the conventional aging treatment (155 ℃×9 h) in a factory, the tensile strength is basically the same, the elongation is 64% higher and the aging time is 55% shorter.

Microstructure and mechanical properties of a high strength oil casing steel under different heat treatment conditions as hot rolling, quenching at 860 ℃, and quenching at 860 ℃+quenching at two phase region of 800 ℃+tempering at 200 ℃ and 660 ℃(QTL), respectively, were analyzed, and the relationship between microstructure and mechanical properties of the steel after low temperature QLT and high temperature QLT treatment was studied by means of EBSD and TEM. The results show that the microstructure of the hot-rolled steel is granular bainite+pearlite+a small amount of polygonal ferrite. After quenching at 860 ℃, the microstructure consists of lath martensite and a small amount of bainite. After low temperature QLT treatment, the microstructure transforms into tempered martensite and ferrite, the yield strength is 936 MPa, the tensile strength is 1260 MPa, the yield ratio is 0.74, and the impact absorbed energy at 0 ℃ is 40 J, meanwhile, the proportion of LAGB is 34.9%, the dislocation tensity of GND is 10.2×10¹⁴ m^-2, and the equivalent grain size is 1.43 μm. After high temperature QLT treatment, the microstructure transforms into tempered sorbite and ferrite, yield plateau appears in the stress-strain curve, the yield strength is 833 MPa, the tensile strength is 912 MPa, the yield ratio is 0.91, the impact absorbed energy at 0 ℃ increases to 93 J, all of which show best strength and toughness matching, however, the proportion of LAGB decreases to 30.9%, the dislocation density of GND decreases to 9.6×10¹⁴ m^-2, the equivalent grain size decreases to 1.39 μm, which makes the strength of the tested steel decrease and the plasticity increase.

In order to study the main factors affecting the microstructure and low temperature toughness of a 500 MPa grade offshore engineering steel, quenching and tempering process was carried out to explore the effect of quenching temperature on microstructure and mechanical properties of the as-hot-rolled tested steel, and to identify the propagation mechanism of cracks in different microstructure. The results show that the microstructure is dominated by ferrite and martensite after subcritical quenching at 800 ℃ and 850 ℃, and with the increase of quenching temperature, the volume fraction of ferrite decreases. After higher temperature quenching at 910-1010 ℃, the microstructure is completely composed of lath martensite, and the size of martensitic lath increases with the increase of quenching temperature, resulting in the increases of strength, and the decrease of low temperature toughness and uniform elongation. The best heat treatment process for the tested steel to obtain the best strength and toughness is quenching at 910-960 ℃ and tempering at 500 ℃. Most of the cracks in the tested steel originate at the interface of the soft and hard phases in the tempered microstructure, propagate in straight line along the interface between ferrite grains and martensitic laths, and end at the prior austenite grain boundary. The increase of the proportion of large angle grain boundary is helpful to improve the low temperature toughness of the tested steel.

Effects of intercritical quenching temperature on the microstructure and mechanical properties of Cr-Mn-Si low-alloy ultra-high strength steel were investigated by using optical microscope (OM), scanning electron microscope (SEM), tensile tester and impact tester. The results show that when the tested steel is quenched within 790-850 ℃, the carbides gradually dissolve, the ferrite content decreases, the martensite content increases and the strength increases with the increase of quenching temperature within 790-820 ℃. When the quenching temperature is 830 ℃, the ferrite basically disappears, and the strength reaches the peak. When the quenching temperature is ≥850 ℃, the carbides disappear, and the microstructure is mainly composed of martensite+retained austenite, the strength and toughness basically remain unchanged. The best mechanical properties of the tested steel can be obtained by quenching at 850 ℃+tempering at 230 ℃ with the tensile strength of 1770 MPa, yield strength of 1447 MPa, elongation after fraction of 12%, reduction of area of 53% and impact absorbed energy of 71 J.

Effect of cryogenic-solution-aging treatment on microstructure and mechanical properties of a vacuum die-cast aluminium alloy and its corrosion behavior after immersion in 3.5%NaCl solution for different time were studied. The results show that the cryogenic-solution-aging treatment can effectively improve the mechanical properties of the vacuum die-cast alloy, and the tensile strength is increased from 184.8 MPa to 249.5 MPa, the hardness is increased from 90.3 HV0.1 to 124.6 HV0.1, and the elongation is increased from 6.3% to 7.7%. The cryogenic-solution-aging treatment promotes the α-Al phase, Si phase and Al₅FeSi phase in the aluminum alloy to become fine and distribute evenly, which is conducive to the formation of a denser and more uniform passivation layer during immersion, indirectly hindering the invasion of chloride ions into the internal structure of the aluminum alloy. Compared with the as-cast aluminum alloy, the corrosion progress of cryogenic-solution-aging treated alloy is slow, and the corrosion resistance is significantly improved.

Al-Zn-Mg-Cu matrix composites reinforced with 0.5wt% GNPs were prepared by vacuum hot pressing sintering and hot extrusion process with Al-Zn-Mg-Cu alloy powder as matrix and graphene as reinforcing phase. The effect of aging treatment on the properties of composites and the strengthening mechanism of graphene on the Al-Zn-Mg-Cu matrix were studied. The results show that the mechanical properties of the composites are the best after aging at 120 ℃ for 24 h, and the tensile strength reaches 505.92 MPa. From the microscopic characterization, it can be seen that the black block second phase in the composite material is the most, mainly graphene and a small amount of precipitated phase after aging at 120 ℃ for 24 h. The reinforced phase graphene is dispersed at the grain boundary of the large grain, which can pin the grain boundary and reduce the merging of the subgrain boundaries, thus hindering the dislocation movement. The MgZn₂ and Mg₂Si phases in the composites aged at 120 ℃ for 24 h are the most. The addition of graphene is also beneficial to the precipitation of the second phase, which is easier to pin the grain boundary and improve the mechanical properties.

Continuous annealing tests were conducted on tinplate with different nitrogen contents at different temperatures (595-710 ℃) using a continuous annealing testing machine. The microstructure, grain size, hardness, and tensile properties of the annealed tinplate were analyzed. The results show that the increase in nitrogen content raises the recrystallization temperature of the tinplate, while also refines grain size and inhabits grain growth. The hardness and strength of tinplate with higher nitrogen content are both higher than those with lower nitrogen content. The main nitrogen precipitates are dispersed rectangular TiN and AlN, which increase with the increase of nitrogen content. When the annealing temperature is raised to above 690 ℃, the lamellar pearlite in tinplate with different nitrogen contents is distributed along grain boundaries, replacing the granular pearlite distributed along the rolling direction. Based on the experimental results, controlling the continuous annealing temperature for the production of high-hardness tinplate in the industrial production within the range of 645-660 ℃ can reduce the hardness fluctuation and improve the canning efficiency.

Effect of continuous annealing temperature on tensile properties, hydrogen permeability, microstructure and precipitates of Ti-containing ultra-low carbon steel was studied. The results show that with the increase of annealing temperature, the strength of the tested steel decreases gradually, the formability and hydrogen permeability increase gradually, the average grain size increases gradually, and the proportion of small size precipitates within 50 nm increases obviously. When the annealing temperature is 830 ℃, the tensile strength is 290 MPa, the yield strength is 130 MPa, the elongation is 46.5%, the n value is 0.25, the r value is 3.0, the hydrogen permeation time is 12.0 min, and the average grain diameter is 14.3 μm, showing the best of formability and hydrogen permeation performance.

Effects of solution treatment temperature (1030-1190 ℃), aging temperature (460-530 ℃), and holding time (0.5-2 h) on the microstructure of N03360 Ni-Be alloy with Ti addition were studied by optical microscope and microhardness tester. The results show that the grain size of the N03360 alloy tends to increase when the solution treatment temperature exceeds 1100 ℃. When the temperature exceeds 1170 ℃, it will cause overburning, local grain boundary melting and NiBe compounds agglomeration. The rich-Be phase generated during the discontinuous precipitation process of the N03360 alloy at the grain boundaries will reduce the hardness. The higher the solution treatment temperature is, the more violent the discontinuous dissolving process will be. If the aging temperature is too high or the holding time is too long, the discontinuous dissolving process at the grain boundaries of the N03360 alloy will be out of control.

In order to improve the properties of the pinch roller and extend its service life, the current Delstain-442 welding wire and the proposed Multipass-249 and Multipass-224HC welding wires were studied. The microstructure and properties changes of the surfacing layers prepared by the three types of welding wires after annealing at 500 ℃ and 540 ℃ were compared. The results indicate that after annealing, the retained austenite in the three types of surfacing layers transformed into martensite, and the transformation of the Delstain-442 layer is more complete. The Multipass-249 layer annealed at 540 ℃ has better toughness, more stable microstructure, and better high-temperature wear resistance. The Delstain-442 layer annealed at 540 ℃ can also achieve better high-temperature hardness and high-temperature wear resistance. The Multipass-224HC layer has higher brittleness, while obtains good wear resistance after annealing at both the temperatures, where the wear rate is reduced by one order of magnitude compared to that of the Delstain-442. The comprehensive properties of the Multipass-249 layer annealed at 540 ℃ are good, but due to doubts about its impact toughness, further verification is needed to determine whether it can replace the Delstain-442.

Effect of annealing temperature on the corrosion resistance of 1060Al/TA2/CCSB steel explosive clad plate in artificial seawater was studied by natural immersion method, corrosion electrochemical method and micro-electrochemical test. The results show that pitting corrosion mainly occurs in the explosive clad plate in the artificial seawater solution. With the increase of annealing temperature, the corrosion resistance of the explosive clad plate changes. When annealing at 350 ℃, the radius of the AC impedance spectrum is the largest, the passivation zone appears in the polarization curve, the current density is the lowest, the potential difference between the two bonding interfaces of 1060Al/TA2 and TA2/CCSB steel is the smallest, and the explosive clad plate has the best corrosion resistance. The micro-electrochemical test results show that the TA2/CCSB steel interface has better corrosion resistance. Therefore, the corrosion resistance of the composite plate is improved after annealing treatment.

In order to solve the problem of coarse grains remained in hot forging rings of a Cr-Ni-Mo-Ti maraging stainless steel, the temperature range of inheriting of forged coarse grains was investigated, and the recrystallization temperature for grain size refinement was determined. Moreover, the effect of repeated solution treatment on the grain size refinement and mechanical properties was determined. The results show that the forged coarse grains are inherited in a wide temperature range above Af of the steel. After solution treatment near 950 ℃, the austenite grains with completely closed grain boundaries and obvious refinement are formed, indicating that the recrystallization temperature T_re is approximately equal to 950 ℃, moreover, further increasing the solution temperature leads to grain growth. Repeated heating and cooling slightly below 950 ℃ lead to large grain boundary migration and forming the fine grain with open boundries. The repeated heating and cooling at 950 ℃ can still fine the grains, while the effect is weakened with the further increase of temprature, untill the effect vanish at 1050 ℃. The grain refinement by repeated heating and cooling at 875 ℃ significantly improves the impact properties, but the tensile strength and yield strength decrease, showing that the strength decreases with the grain refinement. The strength and toughness when heating and cooling once at 925, 975 ℃ (near T_re) are close to those of repeated heating and cooling for 3 cycles at 875 ℃, while the grains are slightly refined with the increase of repeated heating and cooling times, and there is no significant change in mechanical properties.

Effect of isothermal quenching process at 240-320 ℃ near Ms on the phase transformation characteristics and mechanical properties of 300M steel was studied by means of thermal dilatometer, color metallography, scanning electron microscopy and transmission electron microscopy. The results show that the isothermal quenching below Ms result in athermal martensite produces first and the incubation period of bainite transformation shortened of the 300M steel. Compared with the isothermal quenching process at 320 ℃ above Ms, the isothermal quenching process at 260 ℃ below Ms makes the retained austenite transform from blocky M/A islands to film between bainite laths, the average width of bainite lath decreases, the tensile strength increases from 1550 MPa to 1930 MPa and the total elongation increases from 7.7% to 9.2%, showing that the strength and plasticity increase simultaneously.

Effects of addition of rare earth Ce and tempering process on microstructure, precipitation behavior of the second phase and hardness of air-cooled bainite steel for oil casing were compared and studied. The phase transition points of the rare earth and non-rare earth bainite steels were determined by thermal dilatometer, the microstructure and the second phase after tempering were observed and analyzed by using metallographic microscope and TEM, the precipitation behavior of the second phase was simulated by thermodynamic calculation software, and the hardness of the tested steels was tested by using Rockwell hardness tester. The results show that after tempering at 200, 450 and 650 ℃, respectively, for different time, the microstructure of the non-rare earth bainite steel is tempered martensite, tempered troostite and tempered sorbite, respectively, however, the microstructure of the rare earth bainite steel is tempered martensite, tempered troostite and tempered troostite+tempered sorbite, respectively. When tempered at 650 ℃ for 60 min, the second phases in the bainite steels are (Fe, Cr)₃C and Cr₂₃C₆ carbides. With the increase of tempering temperature and time, the hardness of the rare earth and non-rare earth bainite steel decreases overall, while the secondary hardening phenomenon is found when tempered at 450 ℃ for 120 min, and the hardness of the rare earth bainite steel is higher than that of the non-rare earth bainite steel. In conclusion, the addition of rare earth Ce can increase the temperature of the phase transition point, delay the pearlite transformation and improve the hardness of bainite steel.

In order to improve the high temperature strength of heat-resistant steel for steam turbine, 9Cr heat-resistant steels with different contents of TiC nanoparticles (mass fraction of 0%, 0.01%, 0.05% and 0.1%) were prepared. The microstructure of the tested steel with 0.01%TiC nanoparticles was analyzed by using high temperature laser scanning confocal microscopy (LSCM), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the mechanical properties were studied by tensile and impact tests. The results show that the addition of TiC nanoparticles can significantly enhance the high-temperature strength at 600 ℃ of the 9Cr heat-resistant steel, and when the addition amount is 0.01%, the maximum tensile strength is 356 MPa, and the strain at fracture is 38%. The martensite structure is obtained for the tested steel with 0.01% TiC nanoparticles under air-cooling conditions, the second-phase carbide category is M₆C, and the distribution of TiC nanoparticles in the grains plays a role in dispersive strengthening. The tested steel with an addition of 0.01%TiC nanoparticles has excellent comprehensive mechanical properties after annealing at 1040 ℃+normalizing at 990 ℃+tempering at 740 ℃, with the hardness, tensile strength, yield strength, elongation and reduction of area of 177 HBS, 734 MPa, 538 MPa, 15.45% and 31.15%, respectively, and a large number of dimples are observed in the tensile fracture, indicating ductile fracture. The impact absorbed energy at room temperature is 116 J, and the ductile-brittle transition temperature FATT₅₀ is -15 ℃.

Microstructure chang of metastable austenitic stainless steel 022Cr18Ni8N with varying nitrogen contents (0%, 0.02%, 0.05% and 0.14%) before and after cold rolling was investigated, and the effect of nitrogen on the microstructure and properties was characterized by using OM, EBSD, XRD, and room temperature tensile tests.The results indicate that nitrogen can improve the stability of austenite of the tested steel and reduce the formation of deformation induced martensite during cold deformation. The strain-induced martensite nucleates at the intersections of deformation bands, within solitary deformation bands, and at the intersections of deformation bands and grain boundaries. An appropriate nitrogen content endows metastable austenitic stainless steel with enhanced comprehensive mechanical properties through the regulation of two strengthening mechanisms, namely phase transformation strengthening and solution strengthening.

GH4720Li alloy bars were solid solution treated at different temperatures of 1100, 1090, 1080, and 1070 ℃ to obtain four different microstructure with average grain sizes of 24, 18, 15 and 3-5 μm, respectively. The effect of grain size on the high-temperature tensile properties of the alloy at 650 ℃ was investigated. The results show that with the reduction of grain size, the 650 ℃ strength of the GH4720Li alloy increases, accompanied by a decrease in plasticity. When the grain size is further reduced to 3-5 μm, the plasticity begins to increase, and at this time, the alloy exhibits the optimal comprehensive tensile properties at 650 ℃. This is attributed to the pinning effect of primary γ′ strengthening relative to grain boundary, resulting in a fine grain structure that not only provides a large number of grain boundaries and improves strength, but also disperses plastic deformation, reduces stress concentration, and improves plasticity. Simultaneously, an appropriate amount of secondary and tertiary γ′ strengthen phase can further ensure the strength of the alloy.

Effect of aging temperature (150, 180, 210 ℃) on intergranular corrosion susceptibility of 7055 aluminum alloy was studied by means of optical microscope (OM), transmission electron microscope(TEM), hardness test and intergranular corrosion test. The results show that under the same hardness condition, intergranular corrosion occurs in the under-aged alloy, while pitting corrosion occurs in the peak-aged and over-aged alloys. With the increase of aging temperature and time, the intergranular corrosion susceptibility of the alloy decreases and the corrosion morphology changes from intergranular corrosion to pitting corrosion. With the aging temperature increasing from 150 ℃ to 210 ℃, the grain boundary precipitates (GBPs) change from continuous distribution to discontinuous distribution, the Cu content in GBPs increases from 3.82% to 5.02%, and the width of precipitate free zones (PFZs) increases from 37 nm to 55 nm. The change of intergranular corrosion susceptibility of the alloy is due to the combined effect of coarsening and discontinuous distribution of GBPs, the broadening of PFZs, and the segregation of Cu element in GBPs.

Based on the process of thin slab continuous casting and rolling, the effect of various cooling temperatures after hot rolling on the microstructure and properties of a hot-rolled dual-phase steel was studied by using optical microscope, universal tensile machine, microhardness tester, and X-ray diffractometer. The results show that the yield strength and tensile strength first decrease and then increase, while the total elongation gradually decreases with the cooling temperature increases from 640 ℃ to 720 ℃. In addition, the hardness decreases first and then increases with the increase of cooling temperature, which is consistent with the trend of strength changes, indicating that higher strength and hardness can be obtained after cooling at 720 ℃. The grain size of ferrite first increases and then decreases with the increase of increasing cooling temperature, and the martensite content gradually increases. It is shown from the calculation according to the strengthening mechanism of the dual-phase steel that the difference in strength of the specimens under different cooling temperatures is mainly due to the differences in grain refinement strengthening, transformation strengthening and dislocation strengthening, among which the grain refinement strengthening and dislocation strengthening are the main mechanisms, and the theoretical strength calculation results are in agreement with the experimental results.

Solution+peak aging treatment (470 ℃× 2 h, water cooling, 120 ℃× 24 h, air cooling) was carried out on spray formed and extruded 7075 aluminum alloy, and microstructure and compressive properties of the alloy were characterized. The results show that the microstructure of the alloy consists of aluminum matrix and coarse rod-shape η(MgZn₂) phase distributed along the extrusion direction. After solution and peak aging treatment, the recrystallization occurs and the recrystallized grain size is 20-30 μm, and a large number of nanoscale strengthening phases η′(MgZn₂) and GP zones are precipitated. The compressive stress of the alloy slowly increases with the increase of strain. The compressive strength and compressive stress of the spray formed and extruded and peak aged alloy (at a compressive strain of 0.5) are 475.8-540.6 MPa and 700.1-807.7 MPa, respectively. The nanoscale strengthening phase in peak aged alloy inhibits dislocation movement, significantly improving the compression properties of the alloy. The compressive stress of the alloys in two states at room temperature is insensitive to the quasi-static strain rate. The fracture mechanism of the spray formed and extruded alloy is a mixed mode of transgranular fracture and intergranular fracture, and the peak aged alloy shows an intergranular fracture. The key to ensuring the ultra-high strength and overcoming the poor plasticity of the 7075 aluminum alloy is the uniform microstructure and the supersaturated solid solution obtained by spray forming and extrusion, and the fine recrystallized grains obtained by the solution and peak aging treatment.

Effect of different annealing time at 850 ℃ on the microstructure and texture of 1.0%Si non-oriented silicon steel cold-rolled sheets was investigated by means of characterization techniques such as EBSD and XRD. The results indicate that the cold-rolled sheets undergo recrystallization when annealed at 850 ℃ for 90 s. The texture type transforms from strong α and rotated cube texture {001}<110> to γ texture {111}<112> and α^* texture. When annealed from 90 s to 180 s, the grain size gradually increases, with the average grain size growing from 14.2 μm to 21.3 μm. The α^* texture and rotated cube texture {001}<120> strengthen gradually, the magnetic induction B₅₀₀₀ increases from 1.55 T to 1.63 T, and the iron loss P_1.5/50 decreases from 4.213 W/kg to 3.832 W/kg.

Microstructure transformation of the clamping section (aging), deformation section (creep), and necking position (rupture) of P92 steel elbows during creep rupture at 630 ℃ and different stresses (175, 140, 130, and 100 MPa) was studied by using scanning electron microscopy, transmission electron microscopy, EBSD, etc. The results indicate that strain-induced precipitation coarsening occurs in the P92 steel elbows under creep conditions. After long-term aging, the morphology of the P92 steel changes from martensite lath to edge dislocation. The cracks near the rupture of the P92 steel initially expand into elliptical holes. After the Laves phase precipitates, the grain boundary strength decreases compared to the early stage, and the cracks transform into wedge and flower shapes.

In order to optimize the induction heating process of ball screw and improve the uniformity of its surface temperature distribution, thereby improving its manufacturing precision and performance, a finite element model was constructed by means of electromagnetic simulation software to analyze the influence of different process parameters on the surface temperature distribution of the ball screw during both static and dynamic induction heating. The results show that an excessively small internal diameter of the induction coil results in a narrow gap between the workpiece and the coil, which can easily lead to overheating of the workpiece surface. Conversely, an excessively large internal diameter results in a wide gap, reducing heating efficiency and resulting in a shallow heating layer. Therefore, selecting an induction coil with an appropriate internal diameter is essential for ensuring the quality of heating. The double-turn coil demonstrates superior performance in terms of heating efficiency and temperature uniformity. Employing high voltage and an appropriate current frequency can improve heating efficiency and control the depth of heating layer. For dynamic heating, a scanning speed of 6-10 mm/s is recommended to achieve a balance between heating efficiency and process stability.

By combining analytical and numerical methods, the convective heat transfer coefficient of 2195 aluminum lithium alloy hemispherical shell was approximately calculated, and the variation law of convective heat transfer coefficient with temperature under air cooling and water cooling conditions was analyzed. Using ABAQUS finite element simulation software, a thermo-mechanical coupling model was constructed, and the quenching process of the 2195 aluminum lithium alloy hemispherical shells with diameters of ø200 mm and ø100 mm was simulated by finite element method, and the stress and strain laws during the quenching process were analyzed. The results show that during the water cooling process, the heat transfer coefficient of the aluminum lithium alloy hemispherical shell increases first and then decreases with the surface temperature of the workpiece from low to high, and the peak point appears at around 175 ℃. During the air cooling process, the convective heat transfer coefficient increases with the increase of workpiece temperature. The simulation results of the quenching process indicate that stress concentration occurs at the mouth of the hemispherical shell, and plastic strain mainly occurs at the surface of the hemispherical shell mouth. The stress and strain distribution patterns of hemispherical shells with different sizes after cooling at different inlet water temperatures are similar.

In order to study the heating characteristics of steel plate in the heating furnace during heating process, a high-precision computational fluid dynamics (CFD) model of the heating furnace was established by using FLUENT based on a roller hearth furnace with radiant tube heating. The heating process of the steel plate, heating temperature of 873.5 K and heating time of 135 min, was numerically simulated, and the simulation results were experimentally verified. The simulation results show that the temperature of the steel plate in heating stage rises rapidly, with a higher surface temperature, but the overall temperature of the steel plate does not show significant differences, indicating that the overall heat transfer of the steel plate is relatively uniform. The comparison between the CFD heating model results and the experimental results shows that the maximum error in the average temperature of the steel plate is only 5 K, with an error of less than 1%, indicating good consistency between the experiment and simulation.

Application of machine learning in materials research is extensive. However, the task of designing alloys based on many composition and process factors remains a significant difficulty. A machine learning approach to develop alloys by considering the physicochemical qualities, composition, and process of the material was proposed. The property prediction of the Cu-Ni-Co-Si alloy was then optimized by using a genetic algorithm. The recursive elimination method was employed to investigate the potential correlation between the characteristics and alloy properties. The results show that the primary factors influencing the hardness and conductivity characteristics of the alloys are the aging treatment and cold rolling deformation. Furthermore, the physicochemical properties primarily influence the conductivity of the alloy by impacting the density of free electrons and the free path of free electron migration. It affects the hardness of the alloy by exerting influence on solution strengthening and dislocation strengthening.

In order to reveal the complex relationship between mechanical properties and heat treatment process of SUS321 stainless steel, a prediction model between annealing temperature, annealing time and mechanical properties of the SUS321 stainless steel was established by machine learning method based on random forest model. The results show that the prediction validity parameter R² of the model for the tensile strength, yield strength and elongation of the SUS321 stainless steel exceeds 0.8, showing a good prediction effect. The analysis based on partial dependence plots and individual conditional expectation plots shows that with the increase of annealing temperature and annealing time, the tensile strength and yield strength of the SUS321 stainless steel decrease, while the elongation increases, and the annealing temperature is the main feature parameter.

Three-dimensional morphological characterization and automatic statistical quantification of typical inclusions such as large-size Al₂O_3,MnS, conventional oxysulfides and nitrides were conducted in the ultra-low carbon steel, free cutting steel, pipeline steel and spring steel by using electrolytic etching and automated inclusion analysis technique. The in-situ electrolytic etching mechanism and the effects of electrolytic experimental parameters and analysis parameters of scanning electron microscope on the three-dimensional characterization of inclusions were discussed. The results show that different inclusions in the tested steels appear to be protruded on the flat matrix by controlling the electrolytic parameters of the constant potential electrolytic etching of the steel specimens, and then the real three-dimensional morphologies of the inclusions can be observed by the scanning electron microscope, and the inclusions in a certain area can be quantified statistically. When the electrolytic voltage increases or the electrolytic time prolongs properly, the etching of the electrolyte on the matrix increases accordingly, which is beneficial to the more exposure of the inclusions. However, the pearlite, bainite and martensite microstructures of the steel matrix are easy to cause serious interference to the statistical quantitative results of inclusions, therefore some measures such as the filtration of matrix composition or inhibiting the appearance of matrix structure can be taken to prevent its unfavorable effects. Scanning electron microscope parameters such as magnification, image mode, image contrast and inclusion gray threshold also have an important influence on the three-dimensional statistical quantification of inclusions, therefore these parameters should be set appropriately to ensure that inclusions are accurately identified and quantified. The in-situ electrolysis method can quickly obtain the in-situ three-dimensional morphology of non-metallic inclusions in the steels, and realize the automatic statistical quantification of inclusions in the steels with different matrix microstructures. Compared with the two-dimensional analysis, the three-dimensional morphology of inclusions obtained by the in-situ electrolysis method is more complete, and the statistical quantitative data of the inclusions obtained from a certain depth area of the steel specimens are more representative.

Effect of induction hardening on the microstructure, hardness, and hardened layer thickness was analyzed of a high-end CNC machine tool guide rail formed by HT300. The causes of cracks during the quenching process were also analyzed. The results show that after intermediate frequency induction hardening, the surface hardness of the machine tool integrated guide rail of cast iron HT300 can reach over 700 HV (60 HRC), and the depth of the harded layer can reach 5.5 mm. After induction hardening heat treatment, the surface layer of the cast iron guide rail mainly forms cryptocrystalline martensite, the transition layer mainly consists of martensite+pearlite structure, and the core is mainly composed of pearlite structure. Crack analysis shows that the graphite in cast iron is mainly E-type graphite, and the phosphorus eutectic structure present in the cast iron dissolves and precipitates during quenching, reducing the surface strength of the cast iron. After deep layer induction hardening, the tensile stress formed on the surface layer exceeds the strength of the cast iron, which is the main reason for the cracking of the cast iron during quenching. The cracking source is located on the surface, and the cracking location is mostly in the phosphorus eutectic region.

Causes of surface bare defects of alloyed galvanized DP980GA strip were analyzed by means of macro and micro morphology observation and composition analysis. The results show that a large number of manganese oxide and iron oxide particles are found inside the plating pit, and a small amount of alumina and chromium oxide are also found, which is due to the enrichment and selective oxidation of manganese on the surface of the steel strip in the continuous annealing furnace, and the aluminothermic replacement reaction in the zinc pot is incomplete, thus reducing the wettability of the strip surface and causing the bare defects. It is suggested that through moderately reducing the dew point temperature of the heating section in the continuous annealing furnace to reduce the manganese oxide film formed by selective oxidation on the surface and its thickness, and moderately increasing the Al content in the zinc pot to promote the aluminothermic replacement reaction, the manganese oxide on the surface of the strip can be fully replaced by alumina and sunk into the zinc pot, thereby the wettability of the strip surface can be improved and the problem of surface bare defects can be solved.

In response to the problem of fracture of 20CrMoH alloy steel reducer bevel gear shaft during installation and tightening, the macroscopic morphology, microstructure, and hardness of the fracture specimen were tested and analyzed using optical microscopy, microhardness tester, scanning electron microscopy, and other detection methods to identify the cause of the fracture. The results show that the cracks in the 20CrMoH steel bevel gear shaft originate from poor machining of the thread start stop groove, with multiple points of fracture and severe wear in the source area. Subsequently, under the action of bending shear stress, the cracks propagate along the carburized transition layer and fracture, with the fracture morphology showing intergranular features. The chemical composition and hardness of the parts basically meet the requirements, but there is a significant variation in hardness at the core of the parts. Overall, the parts exhibit characteristics of high stress overload fracture, which is caused by stress concentration due to poor machining tool marks and material conditions, leading to the fracture. It is recommended to investigate the stress state during tightening and improve the heat treatment process conditions to reduce the depth of the induction annealing layer and narrow down the heat affected zone.

To improve the surface hardness, wear resistance, and corrosion resistance of stainless steel, the effects of single ion nitriding and ion nitriding/physical vapor deposition (PVD) composite treatments on the microstructure, hardness and tribological and corrosion properties of 316L austenitic stainless steel were studied. The results show that the specimen treated by single ion nitriding forms a high-nitrogen hardened layer with a thickness of about 20 μm and hardness of about 802 HV0.05. The specimen treated by nitriding/PVD composite treatment forms a modified layer with a thickness of about 25 μm and nanohardness of about 29 GPa. Both processes form the γ_N phase, and the amorphous film formed on the surface of the nitriding/PVD composite treated specimen does not affect the phase of the intermediate layer. Compared to that of the substrate steel, the friction coefficients of the single nitrided specimen decrease to 0.520 and 0.311 under dry friction and corrosive friction conditions, respectively, while that of the nitriding/PVD composite treated specimen decrease to 0.074 and 0.119, respectively. The self-corrosion current density of the single nitrided and the nitriding/PVD composite treated specimens decrease from 4.602×10^-8 A/cm² to 4.084×10^-8 A/cm² and 3.318×10^-8 A/cm², respectively, and the self-corrosion potentials increase from -0.213 V to -0.195 V and -0.182 V, respectively. Comprehensively, the composite treatment can significantly improve the surface hardness, wear resistance, and corrosion resistance of the 316L austenitic stainless steel.

Induction heat treatment technology and its application in key components of machine tool were summarized from the two aspects of induction heat treatment technology and equipment, the specific induction heat treatment process and equipment design for spindle, ball screw and guideway of the machine tool were introduced, and the prospects for future promotion were prospected.

Aiming at the high surface requirement when applying QPQ treatment to improve titanium alloy surface properties, centrifugal barrel finishing before QPQ treatment was carried out. The effect of centrifugal barrel finishing/QPQ combined treatment on the surface morphology, phase composition, microhardness and wear resistance of TC4 titanium alloy were studied by means of XRD, SEM, ultra-depth of field optical microscope, white light interferometer, roughness meter, micro-Vickers hardness tester and friction and wear tester. The results show that more uniform titanium nitrides and oxides are formed on the surface of TC4 titanium alloy after centrifugal barrel finishing composite QPQ treatment, and the surface quality is improved as the surface roughness Ra decreases by 35.7% than that of only grinding, the microhardness increases by 42.74%, the average friction coefficient decreases by 6.56%, the wear rate decreases by 38.89%, and the wear scar depth decreases by 49.81%, indicating that the wear resistance increased significantly.

To improve the hardness and wear resistance of H13 steel, surface treatment of H13 steel was carried out by hollow cathode ion discharge nitrocarburizing (520, 530 and 540 ℃ for 5 h), and the microstructure, hardness and friction and wear properties of the H13 after nitrocarburizing were analyzed. The results show that an iron-nitride compound diffusion layer is formed on the surface of the H13 steel after nitrocarburizing, which results in significantly improvement of the hardness and wear resistance. The surface hardness of the specimen after nitrocarburizing at 530 ℃ is the highest, which is 999.3 HV0.1, 120% higher than that of the specimen after quenching and tempering, and the depth of the hardening layer is about 175 μm based on the measurement of hardness gradient. The friction and wear test under oil lubrication condition shows that the wear volume of the specimen after nitrocarburizing at 540 ℃ is 83% lower than that of the specimen after quenching and tempering.

The duplex platinum-aluminum coatings were prepared by electroplating platinum, vacuum diffusion and embedded aluminization. Effects of different diffusion and annealing treatments on the thickness, element content and hardness of the duplex platinum-aluminum coatings were studied. The results show that the Pt content of the outer layer decreases with the increase of diffusion temperature, the Al content slowly increases with the increase of diffusion temperature, the hardness of the outer layer of the coatings slowly decreases with the increase of diffusion temperature, and the hardness of the middle layer does not change much. At the same time, adding annealing treatment after coating preparation can reduce the hardness of the outer layer of the duplex platinum-aluminum coatings and decrease the brittleness of the coatings.

The existing curriculum system for metal-related majors provides students with perfectly solid training in both theoretical knowledge and practical skills. However, it is difficult for students to integrate the knowledge points scattering across different courses into a complete knowledge system. This indicates that there is still a lack of an integrated application course that enables students to flexibly apply all their professional knowledge. Therefore, the elective course "Materials Engineering and Performance" has been designed. It covers microstructure control, strengthening mechanisms, and ductility and toughness mechanisms, which helps students to integrate the theoretical knowledge of materials science. Importantly, it can cultivate their ability to design new metal materials. Thus, this course will enable students to effectively address practical issues in the fields of science and engineering.