Stress rupture tests with 40 ton tester were conducted at 500 and 600°C for large welded specimens of stainless clad steel, Mn-Mo-Ni steel ASTM A 302 B claded with AISI 304 L, which is essential to nuclear applications. The large specimen, 38 mm thick and 40 mm wide, showed much inferior property to usual small welded specimen.
The results of test at 600°C under a stress of 12 kg/mm
2 are : (1) The rupture time of transverse as-welded specimen was 55 % of base metal. (2) The rupture times of transverse welded specimens decreased through heat treatment after welding at 550, 650 and 870°C × 1.5 hr as low as to 40, 60 and 90 %, respectively, of as welded specimen. (3) Machining the reinforcement flush with the surface of base metal increased the rupture time of 550°C × 1.5 hr heat treated specimen by 1.5 times. (4) Longitudinal welded specimen was approximately equivalent to base metal in rupture time. (5) Transverse specimen manually welded showed about 50% longer rupture time than submerged-arc welded specimen.
Macroscopic and microscopic examinations showed that cracking in rupture occurred along bond in the graphitized heat-affected zone of base metal. The initiation of cracking occurred mostly at the intersection between the surface of bond of stainless weld metal and the cladding surface, viz., the line along which concentration of strees and local strain were most extreme. Crack initiation in backing steel ocurred frequently at the toe of carbon steel weld metal. If the bottom of stainless weld metal were made smooth with cladding surface, the rupture time of transverse welded specimen would become identical to base metal.
The test results at 500°C, however, showed 45 degrees shear type fracture which is different from that at 600°C in which fracture occurred along bond.
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