Effect of annealing treatment on deep drawing behavior of hot-rolled Q235 carbon steel/410/304 stainless steel three-layer composite plate was investigated. Deep drawability of the unannealed composite plates exhibits a sharp difference for various contact surfaces with the die. The limit drawing ratio (LDR) of the composite plate with the carbon steel contacting the die is 1.75, while it is 1.83 with the stainless steel contacting the die due to the different mechanical responses to the tensile stress at the corner of the die. After annealing at 900°C for 2 h, however, the deep drawabilities of the composite plates both for various contact surfaces with the die are significantly improved and becomes almost identical, which are attributed to the stress relief, the enhanced ductility and the improved interface bonding strength of the hot-rolled component plates during annealing.

The 0.05 mm-thick 304 stainless steel foil was annealed within the temperature range from 950℃-1100℃ for 10 minutes to obtain different microstructures. And micro-deep drawing experiments of stainless steel foils with different tissue structures were conducted to obtain relevant material forming properties influenced by dimensional effects. On this basis, the influence of the microstructure characteristics on the forming performance of 304 stainless steel foil and the quality of the cup formed by using micro-drawing was studied, and its mechanism was discussed. It can be seen from the results that the stainless steel foil annealed at 950℃ exhibits poor forming performance, and the wrinkle phenomenon of the deep-drawn cup is obvious. At the annealing temperature of 1050℃, the quality of the deep drawing cup is significantly improved. When the annealing temperature reaches 1100℃, with the increase of the annealing temperature, the crystal grains size increase sharply, and the coarse-grain effect causes the uneven plastic deformation effect to be obvious. Besides, the drawing quality is obviously deteriorated. The observation of the microstructure of the deep drawing cup shows that the forming effect of the drawing cup is poor due to the rolling defects and the coarse grain effect. The 304 stainless steel drawing cup annealed at 1050℃ enjoys the best forming effect.

The analysis of the development of the microstructure of deep drawn automotive B pillar, as well as the analysis of deformation based on numerical simulation and experiment, was performed. The microstructure of steel sheet as well as Al-Si coating after various stages of B pillar production was investigated. It was found that the obtained microstructure of the B pillar was significantly different from that described in many studies as a proper one. The microstructure of the investigated material consisted of martensite, bainite, and a small amount of ferrite. Al-Si coating, despite its morphological changes, remained on the surface of B pillar and, in spite of this, did not fully eliminate oxidation and decarburization of B pillar material. The analysis of the state of strain allowed to evaluate the deformation safety of the process, as well as to verify the simulation results through measurements of sheet thickness variations.