Precipitation Behavior and Microstructural Evolution of Ferritic Ti–V–Mo Complex Microalloyed Steel

Precipitation behavior of （Ti, V, Mo）C and microstructural evolution of the ferritic Ti-V-Mo complex microalloyed steel were investigated through changing coiling temperature （CT）. It is demonstrated that the strength of the Ti-V-Mo microalloyed steel can be ascribed to the combination of grain refinement hardening and precipitation hardening. The variation of hardness （from 318 to 415 HV, then to 327 HV） with CT （from 500 to 600-625 ℃, then to 700 ℃） was attributed to the changes of volume fraction and particle size of （Ti, V, Mo）C precipitates. The optimum CT was considered as 600-625 ℃, at which the maximum hardness value （415 HV） can be obtained. It was found that the atomic ratios of Ti, V and Mo in （Ti, V, Mo）C carbides were changed as the CT increased. The precipitates with the size of 〈 10 nm were the V-rich particles at higher CT of 600 and 650 ℃, while the Ti-rich particles were observed at lower CT of 500 and 550 ℃. Theoretical calculations indicated that the maximum nucleation rate of （Ti, V, Mo）C in ferrite matrix occurred around 630 ℃, which was consistent with the 625 ℃ obtained from experiment results.

A comparison of deformation, microstructure, mechanical properties and formability of SUS436L stainless steel in tandem and reversible cold rolling processes

A comparison was made for the deformation, microstructure, mechanical properties and formability of SUS436L stainless steel in tandem and reversible cold rolling processes. At first, the thermophysical parameters and stress-strain curves of SUS436L steel were measured in temperature range of 293-573 K and a flow stress model was regressed from the data of these curves. An analytical model based on the elasto-plastic finite element method was then established to simulate the tandem and the reversible cold rolling processes of SUS436L stainless steel strip where the flow stress model was introduced. The difference in shear strain distribution, microstructure, mechanical properties and formability of SUS436L steel strip in the two rolling processes was analyzed. The results showed that the larger shear strain, the enhanced intensity of γ fiber texture and the excellent formability of the strip can be easily obtained in the tandem rolling process with the larger work roll rather than the reversible rolling process with the smaller work roll.

Analysis on hot deformation and following cooling technology of 25Cr2Ni4MoVA steel

The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200℃ in the strain rate range of 0.001–10.0 s^(−1).And the dynamic continuous cooling transformation curves were obtained at the cooling rate range of 0.5–15.0℃ s^(−1) from the austenitization temperature of 1000℃ to the room temperature by pre-strain of 0.2 as well.The power dissipation map and the dynamic continuous cooling transformation diagram were constructed based on the data provided by these curves.Compared with the optical micrographs of the compressed samples,the full dynamic recrystallization region is located between 1000 and 1200℃ and at the strain rate range from 0.01 to 10.0 s^(−1) with the power dissipation efficiency not less than 0.33.In the full dynamic recrystallization region,the power dissipation efficiency increases and the dynamic recrystallization activation energy decreases with the temperature increasing.With the strain rate decreasing,the power dissipation efficiency increases firstly and then starts to decrease as the strain rate is less than 0.1 s^(−1),and dynamic recrystallization activation energy changes on the contrary.According to the dynamic continuous cooling transformation diagram,slow cooling is a better way for the hot-deformed piece with large size or complex shape to avoid cracking as the temperature of the piece is lower than 400℃,and different cooling ways can be used for the hot-deformed piece with small size and simple shapes to obtain certain microstructure and meet good compressive properties.

Analysis on Shear Deformation for High Manganese Austenite Steel during Hot Asymmetrical Rolling Process Using Finite Element Method

Based on the rigid-plastic finite element method（FEM）, the shear stress field of deformation region for high manganese austenite steel during hot asymmetrical rolling process was analyzed. The influences of rolling parameters, such as the velocity ratio of upper to lower rolls, the initial temperature of workpiece and the reduction rate, on the shear deformation of three nodes in the upper, center and lower layers were discussed. As the rolling parameters change, distinct shear deformation appears in the upper and lower layers, but the shear deformation in the center layer appears only when the velocity ratio is more than 1.00, and the absolute value of the shear stress in this layer is changed with rolling parameters. A mathematical model which reflected the change of the maximal absolute shear stress for the center layer was established, by which the maximal absolute shear stress for the center layer can be easily calculated and the appropriate rolling technology can be designed.

Modeling of strain-inducedγ→α′phase transformation for 201Cu metastable austenitic stainless steel and its verification in rolling processes

To model the strain-inducedγ→α′phase transformation for the Cr-Mn metastable austenitic stainless steel,the 201Cu steel was chosen as the analytical material and the cylindrical samples of this steel with size ofϕ5 mm×10 mm were compressed at strains of 0.2–0.6 in the temperature range of 25–150°C and in the strain rate range of 0.1–5.0 s^(−1).The flaky samples were prepared by wire cutting from the cylindrical samples and the volume fraction of the strain-inducedα′phase was detected in the test point of the flaky samples.The volume fraction changing with the process parameters was modeled,and the critical temperatures and the critical strains to preventγ→α′phase transformation were calculated as other different process parameters changed.The linear fitting goodness of the model between the calculated volume fraction values and the tested ones is 0.986 and the validity of the model was verified by application in cold and warm rolling experiments.