Effect of tempering on microstructure and mechanical properties of a Ta-added 9%Cr steel with high B and low N contents

E Tkachev,A Belyakov

doi:10.1088/1757-899x/525/1/012049

Abstract

Ta was added to a modified 9%Cr steel with high B and low N content to achieve an optimal dispersion of second phase particles. The effect of tempering on the microstructure and mechanical properties of an Fe-0.1C-9Cr-1.8W-0.6Mo-3Co-Nb-V-0,0013B-0,007N-0,085Ta steel was investigated. Typical martensite lath structure was observed after normalization at 1323 K for 0.5 h. The M23(C,B)6 and complex (Nb,Ta)(C,N) particles formed during tempering at 1023-1053 K. An increase in the hardness after tempering at 1038 K was attributed to the precipitation of the fine (Nb,Ta)(C,N) particles. The impact toughness depended significantly on tempering temperature. The impact toughness increased from 25 to 181 J/cm2 with increasing the tempering temperature from 1038 to 1053 K.

Highlights

Ta was added to a modified 9%Cr steel with high B and low N content to achieve an optimal dispersion of second phase particles
A small amount of B was found useful to improve the stability of tempered martensite lath structure (TMLS) under creep conditions especially due to fine dispersion of M23(C,B)6 particles [6,7,8]
The microstructures of the present steel were analysed by optical microscopy and transmission electron microscopy (TEM) using Jeol JEM-2100 microscope operating at 200kV equipped with an INCA energy-dispersive X-ray (EDX) spectrometer

Summary

Introduction

Ta was added to a modified 9%Cr steel with high B and low N content to achieve an optimal dispersion of second phase particles. A small amount of B was found useful to improve the stability of tempered martensite lath structure (TMLS) under creep conditions especially due to fine dispersion of M23(C,B) particles [6,7,8]. Since the newest B-containing steels contain 910%Cr and 2-2,5%(W+Mo), the optimum Co content required to avoid the δ-ferrite formation was found to be ~3% [1,11,12] Following this alloying design, several 9-10%Cr steels with increased creep strength were developed [13,14,15]. The precipitation behavior and mechanical properties of high-chromium martensitic steels are closely connected with tempering temperature. The present work describes the effect of tempering on microstructure and mechanical properties of a modified Ta-added 9% Cr steel with high B and low N contents.

Methods

Results

Conclusion