The Influence of Both Functioning Time and the Service Temperature on the Mechanic Characteristics and Metallographic Structure of Some Steels

Abstract

The paper determines the influence of both functioning time and the service temperature on mechanic characteristics of 12H1MF steel. In this purpose, the results of mechanical tests, performed at temperatures ranging from 510 to 590 ^oC, have been correlated with those of the optical microscopy analysis.
Due to the prolonged exposure to high temperatures, a slight degradation of the mechanical behaviour has been noticed that has been ascribed to the structural changes produced during functioning. The microstructural study of the steel has emphasized that after prolonged functioning several irreversible changes have occurred such as the increase of the ferrite grains, the dispersion of pearlite areas as well as the precipitation and coalescence of carbides. Yet, since neither decarburation nor network formation tendencies for the precipitated carbides have been observed, it has been concluded the 12H1MF steel can be kept in service even after more than 71000 functioning hours in live steam, at temperatures of 570 ^oC and pressures of 155 atmospheres.