Optimum Morphology and Distribution of Borides in High-boron Austenitic Steel

Author of the article:CHEN Xiang 1,2 , WANG Mengxin 1 , LIU Zhongli 3

Author's Workplace：1. School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China; 2. Key Laboratory for Advanced Materials Processing Technology, Ministry of Education of China, Beijing 100084, China; 3. School of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai 264005, China

Key Words： boride; high-boron steel; morphology; distribution; high temperature mechanical property

Abstract： Borides in traditional high-boron-based alloys are generally located at the grain boundaries and distributed along the grain boundaries in a network or fish-bone shape with sharp edges and angles, which destroy the matrix continuity and greatly reduce the mechanical properties of the materials. The effect of carbon content on the microstructure of high boron austenitic steel was investigated by using optical microscope (OM), scanning electron microscope (SEM), transmission
electron microscope (TEM), time-of-flight secondary ion mass spectrometer (TOF-SIMS) and X-ray diffraction (XRD). The effect of carbon content on the mechanical properties of experimental steel at 850 ℃ was analysed by using a thermal mechanical simulation testing machine. The experimental results show that when the carbon content of high boron austenitic steel is high (0.37%~0.42%, mass fraction), the boride with round shape can be stably obtained, and the boride is evenly distributed in the matrix with granular dispersion, instead of network and fish-bone distribution along grain boundaries. The granular discrete boride is the complex compounds of Fe 1.1 Cr 0.9 B 0.9 , Mn 2 B 0.98 and Cr 2 B according to the XRD analysis. The addition of Cr and Mn in boride and the increase in matrix carbon content promote the roundness and granular dispersion of boride. The forging process also plays a direct role in promoting the granular dispersion of boride. The initial forging temperature of 1 150 ℃ is the basic condition for the granular dispersion of boride.