To study the influence of different deformation parameters of the hot working process on the microstructure of 20Cr2Ni4A gear steel during the plastic forming process, the heat deformation experiment of 20Cr2Ni4A gear steel was carried out using the Gleeble-3500 Thermal Machanical Simulator, and the heat deformation behavior of hot 20Cr2Ni4A gear steel under different deformation conditions was investigated. Through the dislocation density model, recrystallization nucleation and grain growth model, we innovatively wrote the cellular automaton program to simulate the dynamic recrystallization behavior during the heat deformation process. The simulation results were verified through EBSD and metallographic diagrams.
This paper studied the high-temperature stability of dissimilar steel welded joints between G115 and Sanicro25 steel. The joints were exposed to 700 C-degrees for time up to 2000h. The microstructure evolution of base metal (BM) and fine-grain heat-affected zone (FGHAZ) were analyzed. Tensile, microhardness, and impact experiments were conducted on the joints, and the explanations for the changes in mechanical performance are derived from the microstructure. The results showed that the Laves phase were precipitated after aging for 100 h, which has two nucleation methods. Nucleation adjacent to M23C6 is the main way in this research. Laves phase mainly grows up to consume M23C6. The microstructure in BM and FGHAZ is obviously different after aging. After aging for 1000 h, mechanical properties such as tensile strength, Vickers hardness, impact energy, elongation and area reduction are reduced, except for the yield strength. The softening caused by the microstructure evolution of FGHAZ is the main reason for the joint fracture in FGHAZ.
Effect of aging rolling on the microstructure,texture and magnetic properties of the low-temperature oriented silicon steel was studied by conducting aging rolling tests at 250 ℃ for different time using a single cold rolling method.The results indicate that the aging rolling has no significant effect on the cold rolling and primary recrystallization microstructure of low-temperature oriented silicon steel,but it can significantly improve the primary recrystallization texture.The contents of favorable Goss and { 111 }<112>textures in the primary recrystallization microstructure increase first and then decrease with the increase of aging rolling time,reaching the maximum value at 5 min.An increase in favorable texture content can improve the secondary recrystallization microstructure and enhance the magnetic properties of the final sheet.The magnetic induction intensity of the final sheet increases first and then decreases with the prolongation of aging rolling time,and the iron loss shows the opposite trend.When the aging rolling time is 3-7 min,the final sheet has excellent magnetic properties.
The recrystallization and inhibitor precipitation behaviors of rare earths under water cooling after holding for different times of oriented silicon steel hot rolled at 1200°C in the ferrite zone with 30% deformation were analyzed using Gleeble 1500D, SEM,TEM and ICP. The results showed that: during the hot rolling of oriented silicon steel in the high temperature ferrite zone, only dynamic reversion occurred, no dynamic recrystallization occurred, and the amount of precipitates did not increase significantly; after deformation at 1200°C, static recrystallization occurred after holding for about 20s, and the inhibitor started to precipitate and grow. The higher the recrystallization rate, the faster the volume fraction of precipitates. After the deformation, the amount of Cu 2 S and MnS in the precipitates was similar. At 64% recrystallization rate, MnS increased by about 8% and Cu 2 S increased by about 23%. At the same time, most of the precipitates were precipitated in the crystal, and gradually nucleated and grew at the grain boundary when the holding time was extended. After rare earth lanthanum and cerium were added, the precipitation amount of inhibitor was reduced. The higher the degree of static recrystallization, the more obvious the effect of rare earth on the precipitation of inhibitor.
通过等温热压缩试验研究了新型亚稳β钛合金Ti-1500在750～910℃、0.001～10 s-1条件下的热变形行为.建立了耦合应变的双曲正弦型Arrhenius本构方程,基于动态材料模型及Prasad流变失稳准则构建了热加工图,分析了变形后的显微组织.结果表明,随着变形温度升高、应变速率降低,合金的流变应力降低,相同条件下合金的峰值流变应力略高于Ti55531合金,低于M28合金.合金在两相区的平均热变形激活能为291.36 kJ/mol,远高于纯钛的自扩散激活能,β单相区为153.96 kJ/mol,与纯钛的自扩散激活能接近.两相区能量耗散效率峰值位于低应变速率(0.001 s-1);单相区能量耗散效率峰值位于中低应变速率(0.01～0.1 s-1);所有试验温度下,应变速率高于1 s-1时发生变形失稳.结合显微组织分析可以将变形分为3个区域,即低温低应变速率下的β→α相变区、中高温低应变速率下的β再结晶区以及高应变速率下变形不均匀的失稳区.
