Change in shape of a cold formed and annealed stainless steel sheet and joining with use of this change

An austenitic stainless steel sheet with thickness 1.0 mm is V-bent, U-O press formed and roll-formed. Metastable austenitic stainless steel is partly transformed into martensite when cold formed and is reversed in annealing, followed by a volume change. Taking this into consideration, V-bend angle and outer diameter are measured before and after annealing of the V-channel and the pipe obtained. By evaluating the change, effects of the punch radius, reduction in outer diameter, stability of austenite, rolling direction and annealing temperature on the opening of the channel and the swelling of the pipe are made clear. For comparison a uniaxial tensile test is also performed and the volume fraction of martensite is measured. Maximum change in V-bend angle for 301 stainless steel is 5° when the punch radius is 10 mm and the V-channel is annealed at 1023K. For 301 stainless steel, 50% of the material is transformed into martensite and 80% of the transformed martensite is reversed at 1023K. Also for the roll-formed or U-O formed pipe, outer diameter of the pipe is changed by some 0.2%. Taking advantage of this change, the pipe can be joined with the carbon steel pipe and the obtained joining strength is about 25 MPa.