Correlation Between Thermoelectric Power (TEP) and Martensite Start Temperature (Ms) Measurements of 9Cr-W-V-(Ta) Martensitic Steels

Abstract

Low Activation Martensitic (9Cr-W-V,Ta) steels are studied for Fusion reactor applications. This paper deals with the experimental results obtained by using Thermoelectric Power (TEP) technique and Martensite Start (Ms) temperature measurements by dilatometry performed after partial austenite=>femte phase transformations of merent LAM steels. Six 9-llCrf0.7-3WN,Ta base steels have been studied with different nominal concentrations of interstitial (C+N) elements ranging from 0.1 to 0.2 weight percent. TEP and Ms values have been correlated with the residual interstitial (C+N) concentration in solid solution of the non transformed austenite, which generates martensite during cooling to the ambient temperature. These experimental results seem to evidence that there is a decrease of the C and N concentration within the non transformed austenite during both isothermal and anisothermal (i.e. during continuous cooling from the auste~te phase field) austenite to ferrite transformations. Some complements$ microstructural examinations show that this decrease is associated with a heavy precipitation of chromium rich carbides and/or nitrides during the early stages of the femte growth.