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Effect of peak aging on compression properties of 7075 aluminum alloy produced by spray forming and extrusion

Li Yangyang, Yu Xinran, Meng Tao, Zhong Jiawen, Zhang Yaocheng

Heat Treatment of Metals 2025, 50 (1): 219-223. doi:10.13251/j.issn.0254-6051.2025.01.034

Abstract （405）

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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.

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Microstructure and texture evolution of cold-rolled deformed Fe-1.5%Si non-oriented silicon steel

Yang Jie, Hou Diwen, Wang Jiale, Fang Feng, Zhang Yuanxiang, Wang Yang, Zhang Xiaoming

Heat Treatment of Metals 2023, 48 (12): 166-174. doi:10.13251/j.issn.0254-6051.2023.12.028

Abstract （401）

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The influence of cold rolling reduction rate on microstructure and texture of Fe-1.5%Si non-oriented silicon steel at each process stage was analyzed. The results show that the initial structure of the hot-rolled plate is fine equiaxed crystal. The average grain size is 18 μm in the surface layer and 36 μm in the middle layer. After cold rolling at reduction rates of 25%-64%, the plate forms strong α and λ texture and weak α^* texture. After cold rolling at reduction rates of 64%-73%, the plate forms strong γ and sub-strong α texture. The cold-rolled Cube texture mainly rotates along four paths: ① rotating along the λ texture to {100}<021> and then along the α^* texture line; ② rotating along the λ texture to {100}<011> then along the α texture line; ③ rotating along {013}<031>, {110}<110> and nearby orientations; ④ rotating along the η texture line. In the early stage of annealing, Cube and Goss-oriented grains are preferentially nucleated, but with the extension of annealing time, their proportions are always small, the Cube recrystallization ratio is 0.55%-1.94%, and the Goss recrystallization ratio is 0.54%-2.85%, and the proportion of γ-oriented grains increases rapidly. After annealing, complete recrystallization occurs, and the recrystallization texture is mainly composed of strong γ texture, α texture and weak η texture. Unfavorable textures account for the main component.

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Effect of long-term aging on microstructure and properties of nickel-based superalloy

Cai Chenyang, Cao Tieshan, Wang Wei, Chi Qingxin, Cheng Congqian, Zhao Jie

Heat Treatment of Metals 2024, 49 (1): 9-15. doi:10.13251/j.issn.0254-6051.2024.01.002

Abstract （284）

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Microstructure of nickel-based superalloy with different aging time was observed to explore the evolution law of microstructure and properties in the process of high temperature aging. By using OM and SEM to observe and analyze the microstructure of the alloy before and after aging, a method for quantitative analysis of microstructure evolution was proposed, and the hardness of the alloy before and after aging was tested and analyzed. The results show that after aging at 900 ℃ for 20 h without loading, the γ′ phase is cuboidal and the size does not change obviously. When aging for 100 h, the γ′ phase changes from cube to circle. After aging for 500 h, the shape of γ′ phase becomes more irregular. Some γ′ phases are connected with neighboring γ′, showing a long strip shape, but some of them remain cubic shape. When aging for 2000 h, γ′ phase is coarsened obviously and cubed degree is decreased obviously. With the aging time, the size of γ′ phase grows gradually, and the hardness of the alloy shows a decreasing trend.

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Microstructure and wear resistance of AlCoCrFeMnZr near-eutectic high-entropy alloy

Wang Zhixin, Yang Cheng, Ma Mingxing, Wang Bozhen, Dong Chen, Li Shangzhi, Hou Runsen

Heat Treatment of Metals 2023, 48 (1): 1-5. doi:10.13251/j.issn.0254-6051.2023.01.001

Abstract （233）

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AlCoCrFeMnZr near-eutectic high-entropy alloy was prepared by vacuum melting, then its crystal structure, morphology, hardness and wear resistance were tested by means of XRD, SEM, microhardness tester and friction and wear testing machine. The results show that the phase structure of the AlCoCrFeMnZr alloy is BCC+HCP dual-phase structure, composing of primary phase and fine lamellar eutectic. The primary phase consists of the HCP phase enriched in Cr, Fe, and Zr, which grows in a dendritic manner. The main elements in the dendrite region (α phase) of the lamellar eutectic structure are Co, Cr and Fe, and the main elements in the intergranular (β phase) are Al and Zr, which conforms to the structure and element distribution of high-entropy alloys. The wear model changes from adhesive wear and abrasive wear to oxidative wear, and the friction factor shows a trend of increasing first and then decreasing, and the average friction factor is 0.5432, the microhardness is 768.8 HV0.5, that means the alloy has excellent hardness and wear resistance.

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Microstructure and mechanical properties of 9Cr heat-resistant steel strengthened by TiC nanoparticles

Zhu Xiaolong, Wang Zhenghui, Wang Wenyan, Xie Jingpei, Diao Xiaogang, Zhang Feiyang

Heat Treatment of Metals 2025, 50 (1): 187-194. doi:10.13251/j.issn.0254-6051.2025.01.029

Abstract （233）

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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 ℃.

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Hot deformation behavior and microstructure evolution of a novel Co-Ni-based superalloy

Fu Zhiqiang, He Guoai, Wu Yunjie, He Cunxiao

Heat Treatment of Metals 2024, 49 (2): 1-7. doi:10.13251/j.issn.0254-6051.2024.02.001

Abstract （221）

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Gleeble-3800 thermal simulation testing machine was used to perform hot compression tests on a novel Co-Ni-based superalloy to study its hot deformation behavior and microstructure evolution at deformation temperature of 950-1100 ℃, strain rate of 0.01-10 s^-1 and true strain of 0.693. The results show that the flow stress of the alloy decreases with the increase of deformation temperature or the decrease of strain rate. The average grain size of the alloy increases with the increase of deformation temperature and the dynamic recrystallization grains can be refined by reducing the deformation temperature and increasing the strain rate. The EBSD and TEM analysis results indicate that the discontinuous dynamic recrystallization (DDRX) is the main dynamic recrystallization (DRX) mechanism and the twin nucleation is the auxiliary nucleation mechanism during the hot deformation of the alloy.

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Isothermal phase transformation behavior and cooperative regulation of microstructure and properties and flat coil of hot rolling 65Mn steel strip

Tian Yaqiang, Yao Zhiqiang, Nian Baoguo, Zhang Junfen, Zhang Xiaolei, Song Jinying, Zhang Mingshan, Chen Liansheng

Heat Treatment of Metals 2024, 49 (9): 24-30. doi:10.13251/j.issn.0254-6051.2024.09.004

Abstract （211）

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Isothermal transformation curve (TTT curve) of 65Mn steel was obtained by quenching phase change machine. Based on this curve, the evolution of microstructure and mechanical properties at different coiling temperatures was studied, and the possible causes and control methods of flat coil were discussed. The results show that the typical microstructure of the 65Mn steel, namely proeutectoid ferrite and pearlite, is obtained between 600-750 ℃. The TTT curve presents a typical "C" shape, with a "nose tip" temperature of 550 ℃. The incubation period is relatively short at this temperature, only 0.25 s. Within the typical microstructure formation temperature range of the 65Mn steel, the incubation period gradually increases with the increase of temperature, and the content of proeutectoid proeutectoid ferrite increases, while the content of pearlite decreases. According to the actual production, the selected coiling temperature of the 65Mn steel is between 650-750 ℃, and the microstructure is proeutectoid ferrite and pearlite. With the coiling temperature decreases from 750 ℃ to 650 ℃, the proeutectoid ferrite content decreases from 19.4% to 4.1%, and the distribution gradually transitions from block distribution to network distribution. The pearlite lamellar spacing decreases from 277.0 nm to 178.0 nm, resulting in an increase in the yield strength of the 65Mn steel from 534 MPa to 637 MPa, an increase in ultimate tensile strength from 776 MPa to 899 MPa, an increase in hardness from 18.8 HRC to 24.3 HRC, and a decrease in percentage total extension at fracture from 28.9% to 19.4%. In actual production, the coiling temperature and the holding time before coil discharging are adjusted based on TTT curve and the evolution of microstructure and mechanical properties under different coiling temperatures can achieve synergistic regulation of microstructure, mechanical properties and flat coil defects.

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Creep property and microstructure evolution at 700 ℃ of a novel Fe-Ni based superalloy

Jiao Chunhui, Pan Yanjun, Li Shengzhi, Bai Du, Li Bei, Deng Ge, Jia Xiaoshuai

Heat Treatment of Metals 2025, 50 (2): 1-7. doi:10.13251/j.issn.0254-6051.2025.02.001

Abstract （207）

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A novel Fe-Ni-based superalloy, intended for ultra-supercritical thermal power generating units, was evaluated under constant load conditions at 700 ℃ with varying stress levels of 250 MPa and 200 MPa. The service limit and creep life of the alloy were predicted, and the microstructure evolution during creep was analyzed. The results indicate that the creep life of the alloy at 700 ℃/250 MPa and 700 ℃/200 MPa is 2378 h and 12 716 h, respectively. Based on the Larson-Miller equation, the alloy can withstand stresses of approximately 152 MPa after 100 000 h and 134 MPa after 260 000 h at 700 ℃, fully meeting the service requirements (stress of 35 MPa, creep life of 100 000 h). Microstructure analysis reveals that high-density dislocations are distributed in the 700 ℃/250 MPa specimen, whereas fewer dislocations are observed in the 700 ℃/200 MPa specimen. The MC carbides with larger size within the grains predominantly exhibit blocky or rod-like morphologies, with faster growth rates under higher stress conditions. The smaller M₂₃C₆ carbides at grain boundaries precipitate primarily in chain form, and their width increases with prolonged creep exposure. The γ′ phase within the grains remains spherical but undergoes coarsening during creep. Notably, some grain boundary γ′ phases exhibit abnormal growth, forming PFZs/DCZs, which adversely affect the alloy's high-temperature creep performance.

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Fatigue properties and influencing factors of carburized gear steel 18CrNiMo7-6

Zhang Xiaolu, Hai Xianü, Gui Weimin, Yu Wenchao, Shi Jie, Wang Maoqiu

Heat Treatment of Metals 2023, 48 (1): 60-67. doi:10.13251/j.issn.0254-6051.2023.01.011

Abstract （195）

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Taking 18CrNiMo7-6 gear steel as base steel, a tested 18CrNiMo7-6 gear steel was prepared by traditional vacuum degassing smelting + Nb microalloying + electroslag remelting smelting, then the fatigue properties and influencing factors of both steels were comparatively studied by rotary bending fatigue test combined with analyses and characterization of microstructure, hardness distribution, inclusions and fatigue fracture. The results show that the fatigue limit of the tested steel smelted by electroslag remelting and Nb microalloyed is 90 MPa higher than that of the base steel, the service life under the same load is significantly increased, the grain size of the carburized layer of the tested steel is refined from grade 7.5 of the base steel to grade 9, but the surface hardness is decreased due to the increase of retained austenite content. The Aspex inclusion characterization shows that the number of inclusions in the tested steel is significantly lower than that in the base steel, and there are fewer hard oxide inclusions, which is consistent with the fracture characterization results. The comprehensive analysis shows that the grain refinement and decrease of non-metallic inclusion level are the main influencing factors to improve the fatigue properties of the tested steel.

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Effect of long-term aging on microstructure and properties of GH4169 alloy

Tao Tiancheng, Zang Kai, Zhu Zhiyuan

Heat Treatment of Metals 2024, 49 (4): 83-88. doi:10.13251/j.issn.0254-6051.2024.04.014

Abstract （194）

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After standard heat treatment of 960 ℃×1 h+720 ℃×8 h+620 ℃×8 h, GH4169 alloy was subjected to long-term aging at 650 ℃ for 100-4000 h. The microstructure evolution law mechanical properties and their relationship of the alloy during long-term aging was explored. The results show that after aging at 650 ℃ for 100-800 h, a large number of γ″ and γ′ phases precipitate in the grain, δ phase precipitates at the grain boundary, and the hardness of the alloy increases. After aging for 1600-2400 h, γ″ and γ′ phases grow up gradually, δ phase coarsens gradually and γ″ poor zone appears around the δ phase, and the alloy hardness increases slowly. After aging for 3200-4000 h, γ″ and γ′ phases coarsen obviously and a large number of γ″ phases change into δ phase, and the hardness of the alloy decreases. Meanwhile, the tensile strength and yield strength of the alloy after long-term aging are consistent with the change of hardness, and the plasticity shows a decreasing trend.

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Precipitation behavior and mechanical properties of Inconel 718 alloy prepared by selective laser melting

Wang Yingzhi, Zheng Liuwei, Yang Fei, Nie Yujin, Meng Lixin, Yin Lei, Liang Wei

Heat Treatment of Metals 2024, 49 (3): 141-146. doi:10.13251/j.issn.0254-6051.2024.03.024

Abstract （188）

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Inconel 718 alloy was prepared by selective laser melting (SLM), and the as-deposited alloy was double aged (DA) and solution+double aged (SA). The precipitation behavior and tensile properties of the alloy under different heat treatment states were studied by means of scanning electron microscope, electron backscattered diffraction, transmission electron microscopy, and universal testing machine. The results show that aging alone cannot eliminate the Laves phase. After direct aging, the Laves phase still exists in the alloy, but the content of γ' and γ″ strengthened phase is higher than that of the deposited state. The strength of the material significantly increases, and the plasticity significantly decreases. After high-temperature solid solution treatment at 1150 ℃ followed by double aging, the alloy is completely recrystallized, and the substructure disappears. The brittle Laves phase dissolves completely, and the content of the strengthened phases γ' and γ″ phases increases significantly. The strength increases and plasticity decreases compared to the as-deposited specimen. The tensile strength, yield strength and elongation of the alloy reaches 1330 MPa, 1110 MPa and 16.73%, respectively. The solution+double aging process, while enhancing the material's strength, ensures plasticity, which makes the Inconel 718 alloy to have excellent comprehensive mechanical properties.

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Process optimization and microstructure of C250 maraging steel prepared by SLM process

Liu Zaixi, Lu Dehong, Wang Changjun, Liu Yu

Heat Treatment of Metals 2023, 48 (3): 143-150. doi:10.13251/j.issn.0254-6051.2023.03.025

Abstract （177）

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C250 maraging steel was prepared by SLM process. Effect of SLM process parameters on relative density and microstructure of the C250 maraging steel by means of metallographic microscopes (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and density measurement devices. Morphology and microstructure of the C250 maraging steel prepared by optimizing SLM process were analyzed. The results show that when the energy density is 85-120 J/mm³, relative density is higher than 99.5%, and the microstructure is dense without obvious defects. When the laser power is 270 W, the scanning rate is 700 mm/s, the scanning spacing is 0.11 mm, and the powder layer thickness is 0.03 mm, the density of the C250 maraging steel reaches 100%. Under the optimal SLM process, main phase composition of the C250 steel is martensite, which reaches 97.13%, and its internal grains are extremely fine, about 2.7 μm. In the martensite matrix there are also strengthening phases and dislocations to strengthen the C250 steel.

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Effect of heat treatment process and copper content on texture of high-silicon non-oriented silicon steel

Xue Rundong, Fang Xizhen

Heat Treatment of Metals 2024, 49 (4): 78-82. doi:10.13251/j.issn.0254-6051.2024.04.013

Abstract （176）

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Effect of copper content on the texture of two high-silicon non-oriented silicon steels without Cu and with trace Cu was analyzed by EBSD technology, and the microscopic mechanism was also investigated. The results indicate that after high temperature annealing at 1000 ℃, the addition of trace Cu element has an obvious harmful effect on the texture of finished silicon steel product. The high temperature annealing process plays a more full role in optimizing the texture by the shear bands, while such optimizing effect is inhibited obviously by adding of trace Cu to the non-oriented silicon steel, which is attributed to the dispersive distribution of the copper precipitates in the steel matrix.

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Microstructure and properties of high hardenability high-carbon chromium bearing steel

Wang Bingnan, Jia Yuxin, Wang Shanshan, Zhang Yahui

Heat Treatment of Metals 2024, 49 (9): 31-35. doi:10.13251/j.issn.0254-6051.2024.09.005

Abstract （175）

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Martempering and austempering treatments were conducted on three types of high-hardenability high-carbon chromium bearing steels, namely GCr18MnMo steel, GCr18MnMo1 steel and GCr19SiMnMo1 steel. The differences in their microstructure, maximum hardenability size, retained austenite and impact properties were compared. The results show that the hardenability is ranked from high to low as GCr19SiMnMo1 steel > GCr18MnMo1 steel > GCr18MnMo steel. If the hardenability standard is that the core hardness is greater than or equal to 55 HRC, the maximum hardenability size of GCr18MnMo steel is approximately 70 mm, the maximum hardenability size of GCr18MnMo1 steel is approximately 100 mm, and the maximum hardenability size of GCr19SiMnMo1 steel is approximately 130 mm. When these three tested steels undergo austempering, the retained austenite content can be guaranteed to be less than 1%. During martempering, the retained austenite content of GCr18MnMo and GCr18MnMo1 steels is less than 15%, and for GCr19SiMnMo1 steel, the retained austenite content can be reduced to less than 1% by additional tempering while ensuring high hardness. The impact properties of these three specimen steels are very close, and the impact property after austempering is approximately 70% higher than that after martempering. Only GCr19SiMnMo1 steel can be used for parts with wall thickness or diameter more than ϕ100 mm to ensure that the core troostite meets the requirements.

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Interfacial microstructure of diffusion bonded joints of TC4 titanium alloy and additive manufactured 17-4PH stainless steel and effect of process parameters

Wang Lixiang, Liu Kun, Li Jie, Lu Sheng, Xu Cong, Chen Dongjun

Heat Treatment of Metals 2024, 49 (11): 53-59. doi:10.13251/j.issn.0254-6051.2024.11.008

Abstract （175）

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TC4 titanium alloy and atomic diffusion additive manufactured(ADAM) 17-4PH( stainless steel were diffusion bonded with different interlayers at different temperatures. The microstructure characteristics and properties of the joint interface were analyzed by means of optical microscope, scanning electron microscope, EDS analysis and microhardness testing. The results show that a well formed TC4 titanium alloy/ADAM 17-4PH stainless steel diffusion bonded joint is obtained by using a Cu foil+Ni foil composite interlayer at 960 ℃ and 920 ℃, with holding time of 60 min and welding pressure of 2 MPa. The interfacial area mainly includes four different zones, namely the diffusion affected zone on the TC4 titanium alloy side (DAZ 1), the interface reaction zone (IRZ 1 and IRZ 2) generated by the diffusion reaction of Cu foil+Ni foil and the diffusion affected zone on the ADAM 17-4PH stainless steel side (DAZ 2). When the diffusion bonding temperature is 960 ℃, CuTi+CuTi₂ eutectic phase and CuTi₂, Ti (Cu, Ni), α-Ti phases are generated in the IRZ 2, with the highest shearing strength of 163 MPa. With the diffusion bonding temperature increases from 920 ℃ to 960 ℃, the width of interface increases from 243.5 μm to 278.2 μm and the maximum microhardness of IRZ 2 decreases from 693 HV0.1 to 612 HV0.1 in the case of Cu foil+Ni foil as interlayers. When the diffusion bonding temperature remains constant (960 ℃), the peak microhardness of the diffusion bonded joint with Cu foil+Ni foil as interlayers is the highest, about 612 HV0.1, while that with Ni foil as interlayer is the lowest, approximately 495 HV0.1, in the IRZ.

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Microstructure and mechanical properties of ultrafine grained heterostructured dual-phase steel prepared by warm rolling and intercritical annealing

Yan Wenchao, Gao Bo, Xiao Lirong, Zhou Hao

Heat Treatment of Metals 2024, 49 (7): 54-62. doi:10.13251/j.issn.0254-6051.2024.07.009

Abstract （173）

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Comprehensive mechanical properties of the low-carbon steel were greatly improved by producing the ultra-fine grained heterostructured dual-phase (UFG-HSDP) structure. First, the initial structure of the low carbon dual-phase structure is refined by warm rolling at 300 ℃, and then the ultra-fine grained heterostructured dual-phase steel with high martensite content (volume fraction of77%) is obtained by intercritical annealing at 740 ℃. The average grain size of ferrite and martensite is 0.78 and 0.39 μm, respectively. The UFG-HSDP steel shows excellent comprehensive mechanical properties, with yield and tensile strengths of 1.26 and 1.75 GPa, respectively, while maintaining a uniform elongation of 6.2%. The mechanical incompatibility between ferrite and martensite in the UFG-HSDP steel during tensile deformation results in significant hetero-deformation induced hardening, which enhances the total strain hardening rate and thus improves the strength-ductility match of low-carbon steel.

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Variant selection of α phase in β-type Ti-15Mo alloy

Ren Cheng, Min Xiaohua, Fei Qi

Heat Treatment of Metals 2024, 49 (9): 1-10. doi:10.13251/j.issn.0254-6051.2024.09.001

Abstract （160）

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SEM and EBSD were used to investigate the variant selection behaviour of the α phase in the β matrix and at the β grain boundaries in the Ti-15Mo alloy after solution treatment and aging. The results show that the solution treated specimen consists of single β grains without any preferred orientation. In the solution treated and aged specimen, the intragranular α phase does not undergo variant selection, instead, self-accommodation occurs among α variants, leading to a cross distribution of α phase variants at 60°. The variant selection of the film-like grain boundary α phase is influenced by the misorientation of adjacent β grains. A minor misorientation causes α phase to retain a Burgers orientation relationship with β grains on either side, whereas a major misorientation affects the precipitation of the α phase due to the interface orientation. The variant selection of the grain boundary Widmanstätten microstructure relies on the nucleation site. When the nucleation takes place at the film-like grain boundary α phase, it selects the same variants as the film-like grain boundary α phase. Nonetheless, when the nucleation occurs at the interface between the film-like grain boundary α phase and the β matrix, it is influenced by both.

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Effect of cooling temperature on microstructure and mechanical properties of a hot-rolled dual-phase steel

Wang Cheng, Liu Yajun, Chen Zhihui, Tong Shankang, Gan Xiaolong

Heat Treatment of Metals 2025, 50 (1): 213-218. doi:10.13251/j.issn.0254-6051.2025.01.033

Abstract （152）

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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.

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Heat treatment process and mechanical properties of low alloy wear-resistant steel

Zhang Zhichun, Wen Jia, Chen Guorui, Wu Guanghui, Weng Zeju, Gu Kaixuan

Heat Treatment of Metals 2023, 48 (9): 220-224. doi:10.13251/j.issn.0254-6051.2023.09.037

Abstract （152）

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CCT curves of a low alloy wear-resistant steel were measured by using a DIL805 quenching dilatometer to study its phase transformation law during continuous cooling. The microstructure of the specimens at different cooling rates was observed by using OM. In addition, the low alloy wear-resistant steel was heat treated by using quenching+tempering process, quenching+cryogenic treatment+tempering process, and the specimens were analyzed by using SEM characterization, tensile and impact tests to study the effect of cryogenic treatment on the microstructure and properties of the tested steel. The results show that the critical cooling rate of martensite transformation of the tested steel is 5 ℃/s. The tensile strength and yield strength of the low alloy wear-resistant steel are increased by 136.5 MPa and 141.5 MPa, respectively, with the addition of cryogenic treatment. The impact property is decreased slightly while the plasticity remains unchanged after cryogenic treatment. The main mechanism of improvement of the strength and plasticity of low alloy wear-resistant steel caused by cryogenic treatment is to promote the refinement of martensitic lath.

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Microstructure and fatigue properties of SCM435 steel for engines

Jiang Chang, Lu Hengchang, Wei Xicheng, Dong Han

Heat Treatment of Metals 2024, 49 (3): 159-163. doi:10.13251/j.issn.0254-6051.2024.03.027

Abstract （142）

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Microstructure and mechanical properties of SCM435 steel quenched at 870 ℃ and tempered at 350-650 ℃ were studied by means of SEM, TEM and tensile test. The results show that when tempering temperature is 350 ℃, the structure is martensite lath and a small amount of carbide. With the increase of tempering temperature, the lath morphology of martensite gradually disappears, and carbides precipitate and grow along the direction of lath. The microstructure tempered at 525 ℃ still has obvious martensite lath morphology and short rod cementite is dispersed. By controlling the mechanical properties of the SCM435 steel within the studied tempering temperature range, it can meet the mechanical performance requirements of 8.8-12.9 level fasteners. The fatigue properties of the steel quenched at 870 ℃ and tempered at 525 ℃ is experimentally verified, with a median fatigue limit of 425 MPa, indicating good fatigue properties.

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