Effect of tempering on the precipitation behavior of a Ta-alloyed 9%Cr steel with high B and low N contents

Abstract

The size and distribution of second phase particles are key factors governing the mechanical properties of creep-resistant 9–12% Cr steels at elevated temperatures. As the M23C6 carbide and MX carbonitrides are the major precipitates in these steels the efforts should be focused on increase in the stability and obtaining the optimum number density of these particles. A Ta-alloyed 9%Cr steel with high B and low N contents was examined by using SEM and TEM methods to characterize the microstructure and precipitates after tempering at different temperatures. The results obtained from experimental observations and thermodynamic calculations reveal that Ta promotes the precipitation of fine MX particles in lath interiors during tempering at T ≥ 750 °C while its effect on M23C6 carbide is negligible. The precipitation and growth kinetics of MX particles at different tempering temperatures were simulated and discussed.