Causes and solutions of lateral cracks on the sidewalls of 304 stainless steel products
304 stainless steel products often appear various cracking phenomena during the stretching process. Among them, lateral or point cracks on the sidewalls are common processing failure modes of 304 stainless steel products with relatively large stretching. Especially in recent years, the cost-reduction work of stainless steel products processing procedures has continued to advance. The number of stretching passes has been reduced from 5 times to 3 times currently commonly used. The intermediate annealing is changed to one annealing or no annealing after stamping. The formability of the material puts forward higher requirements. The lateral or point cracking defects of the side wall of stainless steel products may be caused by material inclusions, delta ferrite and other material intergranular defects, or may be caused by factors such as the stretching process and stretching oil in the processing of stainless steel products.
The lateral or pitting cracking of the side wall of 304 stainless steel pipe is mainly caused by inclusions or delta ferrite in the material matrix. Therefore, the following points should be controlled during the production of stainless steel:
(1) Improve the purity of materials and reduce the content of inclusions in stainless steel materials.
(2) Improve the composition design and hot rolling and cold rolling annealing process to reduce the content of δ ferrite in stainless steel materials.
However, because stainless steel pipe materials inevitably have these two manufacturing defects during the production process, appropriate process measures can also be taken during the processing of stainless steel products to reduce or avoid cracks caused by inclusions or delta ferrite defects phenomenon:
(1) Change the forming method from thinning drawing to equal thickness drawing.
(2) Increase the number of stretching passes, increase the radius of the die fillet, and reduce the difficulty of material deformation.
(3) Properly increase the viscosity of the drawing oil to promote uniform deformation of the material and avoid excessive stress concentration.
