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 reverse d in annealing, followed by a volume change. Taking this into consider ation, V-bend angle and outer diameter are measured before and after a nnealing of the V-channel and the pipe obtained. By evaluating the cha nge, effects of the punch radius, reduction in outer diameter, stabili ty of austenite, rolling direction and annealing temperature on the op ening of the channel and the swelling of the pipe are made clear. For comparison a uniaxial tensile test is also performed and the volume fr action of martensite is measured. Maximum change in V-bend angle for 3 01 stainless steel is 5 degrees when the punch radius is 10 mm and the V-channel is annealed at 1023K. For 301 stainless steel, 50% of the m aterial is transformed into martensite and 80% of the transformed mart ensite is reversed at 1023K. Also for the roll-formed or U-O formed pi pe, outer diameter of the pipe is changed by some 0.2%. Taking advanta ge of this change, the pipe can be joined with the carbon steel pipe a nd the obtained joining strength is about 25 MPa.