Stainless steel deep drawing process cracking causes

Stainless steel has a small ductility, a large modulus of elasticity E, and a high hardening index. Stainless steel plate deep-drawing cracking sometimes occurs after deep-drawing deformation, and sometimes occurs immediately when the deep-drawing piece is withdrawn from the concave mold. Sometimes it occurs after deep drawing deformation by impact or vibration. It also sometimes occurs after a period of storage or in the process of use after deep drawing deformation.

Analysis of common problems in the process of stainless steel deep drawing.

1. The reasons for the formation of cracking

Austenitic stainless steel cold work hardening index is high (0.34 for stainless steel). Austenitic stainless steel is sub-stable, in the deformation of the phase change will occur, inducing the martensitic phase. The martensitic phase is brittle and therefore prone to cracking. In plastic deformation, with the increase of deformation, the induced martensite content will also increase with the increase of deformation, the greater the residual stress. The relationship between residual stress and martensite content: the higher the content of induced martensite phase, the greater the residual stress caused by the process will be more prone to cracking.

2. The reasons for the formation of surface scratches

Stainless steel deep-drawing surface scratches mainly due to the existence of workpiece and mold surface relative movement, under the action of a certain pressure, resulting in billet and mold local surface friction directly, coupled with the billet deformation of the heat so that the billet and the metal chips fused on the surface of the mold, so that the surface of the workpiece scratches produced by the surface of the abrasion scratches.

Stainless steel common molding defects of preventive measures.

1. Choose the right stainless steel material. The commonly used materials in austenitic stainless steel are 1Cr18Ni9Ti and 0Cr18Ni9Ti. 1Cr18Ni9Ti is more stable than 0Cr18Ni9Ti in the deep-drawing process, and has better resistance to cracking. Vì thế, 1Cr18Ni9Ti material should be selected as far as possible.
2. A reasonable choice of mold materials. Stainless steel in the deep drawing process hardening significantly, resulting in many hard metal points, resulting in adhesion, so that the surface of the workpiece and the mold is easy to scratch, wear and tear, so you can not use the general mold tool steel.
3. Choose reasonable convex and concave mold round angle. Concave mold angle and stress size and distribution has a great relationship. The radius of the round corner is large, the pressure area of the crimping circle is insufficient, and it is easy to produce instability and wrinkle; and if the round corner is too small, the resistance of the material to enter the concave mold during deformation will increase, and the material will not be easy to flow and transfer inward, which will increase the maximum tensile stress in the force transmission area, and it may lead to tensile cracking.
4. The use of belt thinning deep drawing. Previous explorers have also proved through tests that the use of belt-thinning deep-drawing can significantly reduce the maximum tangential residual stress of the deep-drawing parts, which can effectively prevent the occurrence of longitudinal cracking.
5. In the deep drawing process to join the intermediate annealing process can completely eliminate residual stress, and restore the organization of austenitic stainless steel. For high hardness stainless steel, intermediate annealing is required.
6. The use of appropriate lubricants for stainless steel deep-drawing has a significant effect.