Effect of Quenching Holding Time on Microstructure and Hardness of High Boron High Speed Steel

Author of the article:CHEN Hantao 1 , MA Shengchao 2 , LUO Yang 1 , WANG Jie 1 , XING Jiandong 1 , MA Shengqiang 1

Author's Workplace：1. Xi'an Jiaotong University, State Key Laboratory For Mechanical Behavior Of Metarials, Xi'an 710049, China; 2. Avic Shaanxi Aero Electric Co.LTD, Xingping, 710065, China

Key Words： high-boron high-speed steel; alloying element; borides; hardness

Abstract：The microstructure and properties of high boron high speed steel with B content 1.5% and C content 0.4% were
studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and Rockwell hardness tester. The
results show that the as-cast high boron high speed steel is composed of ferrite, pearlite, boride and a small amount of
martensite. The borides are distributed in the metal matrix in the form of mesh and fishbone. The hard phase in the
structure is mainly composed of M 2 B, Fe 3 (C,B) and M6(C,B). After quenching, part of the hard phase appears broken and
dissolved. When the quenching holding time is less than 2 h, some small boron carbide particles dissolve into the matrix,
passivation occurs at the edge, and the hardness of the alloy is significantly increased. When holding time exceeds 3 h, the
boron carbide dissolves seriously, the residual austenite increases, and the macro hardness decreases.