Initial Evaluations of Metallurgical Variables as Possible Factors Controlling the Radiation Sensitivity of Structural Steels

摘要

Experimental investigations for the isolation and assessment of metallurgical factors causing variable radiation embrittlement sensitivity of reactor structural steels were undertaken, using both large-tonnage commercial heats and special laboratory heats of steel. Metallurgical variables being evaluated include the identity and quantity of major alloying elements and of residual elements, steel-making practice--both melting (refining) and heat treatment practice, microstructure, and gas content. Experimental results from the initial series of the exploratory screening studies demonstrate that the radiation sensitivity of a steel can be altered appreciably through heat treatment practices and that microstructure plays a dominant, if not the most influential, role in radiation sensitivity development. A tempered martensite structure was noted to be generally less radiation sensitive than tempered upper bainite and ferrite structures. The data also indicate that vacuum melting and the minimization of residual element content yields steels having a superior irradiation performance compared with steels produced by conventional open hearth melting. However, long-term stress relieving heat treatments were not found to alter the irradiation response of A302-B steel. (Author)