1, the yield strength of duplex stainless steel is twice as high as that of austenitic stainless steel, and the deformation amount should be smaller than that of austenite stainless steel. The proper speed and feed rate must be selected when cold rolling, so as to minimize the uneven longitudinal wall thickness and roll off. When drawing cold steel, the surface reduction rate of steel pipe should not be too large.
The middle pipe and finished softening heat treatment using continuous roller hearth type heating furnace.
2 duplex stainless steel (water cooling device with exit), prohibited the use of electric contact heating, which is not easy to control the temperature and the heating rate is very fast, easy temperature, ferrite phase number exceed the standard, especially in thin wall pipe rolling. Once the control is not good, easy to produce bamboo like uneven wall thickness, while the wall thickness is not mean little (less than 0.1mm). In electric contact heating, thin wall parts rapid warming, cause local overheating, the amount of ferrite increases greatly, and even the emergence of single-phase coarse grain ferrite, reduced corrosion resistance, then pickling, this part will produce local pickling, make steel scrap.
3, the solution treatment of duplex stainless steel pipe is critical, not only to eliminate the residual stress of duplex stainless steel pipe cold processing, but also to ensure the appropriate two-phase proportion and the surface quality of duplex stainless steel pipe. When heating treatment, it is necessary to pay attention to the uniformity of the material temperature and sufficient holding time, so as to avoid the high residual stress on the surface of the steel pipe caused by insufficient solution and lead to stress corrosion in some medium.
4. For duplex stainless steel pipes that are mainly used for stress corrosion resistance, solid solution pickling is required for delivery. When the steel pipe surface is distributed with small cracks and folding defects, the duplex stainless steel pipe after grinding needs to be re dissolved and pickled, and then delivered. The tangential stress in the residual stresses produced by grinding is the main stress to produce SCC damage.
Source: China Duplex Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)