Stainless steel products often have various cracking phenomena during the deep drawing process. The lateral or point-like cracking of the side wall is a common processing failure form of the 304 stainless steel products with relatively deep drawing of the heat preservation cup and the pressure cooker. In particular, in recent years, the continuous reduction of the cost reduction of product processing procedures, such as the number of deep drawing of the vacuum cup has been reduced from 5 times to 3 times currently used, from intermediate annealing to stamping after annealing or no annealing. Therefore, higher requirements are imposed on the formability of stainless steel materials. The lateral or point-like cracking defects of the side wall of stainless steel products may be caused by intergranular defects such as inclusions of materials, δ ferrite and the like, or may be caused by factors such as deep drawing process and deep drawing oil in the processing of stainless steel products.
The lateral or point cracking of the side wall of the 304 stainless steel vacuum flask is mainly caused by the inclusions or delta ferrite present in the material matrix. Therefore, the following two points should be controlled in the production process of stainless steel:
(1) Improve the purity of the material and reduce the content of inclusions in the matrix of the stainless steel material.
(2) Improve the composition design and hot and cold rolling annealing process to reduce the content of δ ferrite in the matrix of stainless steel.
However, due to the inevitable existence of these two manufacturing defects in the production process of stainless steel materials, appropriate process measures can be taken during the processing of products such as vacuum flasks to reduce or avoid defects caused by inclusions or delta ferrite defects. Cracking phenomenon:
(1) Change the forming method from thinning and drawing to equal thickness drawing.
(2) Increase the depth of the pass, increase the fillet radius of the die, and reduce the deformation difficulty of the material.
(3) Appropriately increase the viscosity of the drawn oil, promote uniform deformation of the material, and avoid excessive concentration of stress.