マルテンサイト型13%クロムステンレス鋼の熔接組織および急熱急冷による組織の挙動

Abstract

Metallographic studies have been performed on the structures of weld metal and the heat-affected zone of 13% chromium martensitic stainless steel. The heat-affected zone was obtained by single bead welding, in which a single bead 10∼12 cm in length was placed on a 13% chromium stainless steel plate of 200×75×20 mm3. The isothermal austenitization diagrams (T-T-A diagram, Time-Temperature-Austenitization diagram) were determined for two specimens differently pre-heat treated. The specimen was heated in a salt bath, followed by rapid quenching in water, and then the T-T-A diagram was obtained from changes in hardness (Hv) and in matrix structure.The results may be summarized as follows: (1) In the specimen heated at 1050°C for 30 min and then oil quenched, the heat-affected zone is shaply divided into two parts; one is heated over the Ac1 point and the other is tempered at a lower temperature than the Ac1 point. This is characterized by hardness. (2) The hardness of the heat-affected zone approaches that of base metal by a short-time annealing at 700°C, but the chromium carbide is aggregated in the heat-affected zone. (3) By rapid heating and cooling, the 13% chromium stainless steels with varying carbon contents show a different hardness and an almost identical Ac1 point. The hardness curve exhibits a peak at a maximum heating temperature. (4) From the T-T-A diagrams of the specimens differently treated, it is clear that, in the rapid heating and quenching, a very short holding time is sufficient for hardening when the specimen is heated up to a specified temperature. (5) As to the different pre-heat treatment of the 13% chromium martensitic stainless steel, the austenitization time of the specimen that received only solid solution treatment is shorter than that of the annealed specimen.