EFFECT OF SHOT PEENING ON OXIDATION RESISTANCE OF AUSTENITIC ALLOYS IN SUPERCRITICAL WATER CONDITIONS

摘要

Austenitic stainless steels are attractive candidate materials for the SCWR (Supercritical Water Reactor) concept, with long and successful history in nuclear power generation. Unfortunately their relatively high oxidation rate at estimated peak temperatures of 650 - 850°C may severely limit their use as fuel cladding material. However, it has been shown that cold working of the exposed surfaces by shot peening can beneficially retard high temperature oxidation of austenitic steels. This paper describes the effect of shot peening on the oxidation behaviour of three commercially available austenitic steels, 316NG, 347H and 347HFG in supercritical water (SCW) at 650°C/25 MPa for up to 1800 h. The beneficial effect of shot peening on oxidation resistance appeared to be more effective for grade 347H with a larger average grain size than for 347HFG. In comparison, shot peened grade 316NG showed an order of magnitude faster oxidation. The shot peened specimens exhibited surface regions where the shot peening effect had not reached the bottom of crevices or other irregularities of the surface. Such locations showed an enhanced oxidation rate, demonstrating limitations of shot peening on irregular metal surfaces. In general, a moderate decrease in oxidation rate at 650°C by shot peening was observed.