Effect of Co microalloying on microstructure and properties of M2 high speed steel

doi:10.13251/j.issn.0254-6051.2022.01.013

Abstract

Abstract: Effect of Co microalloying on its tempered microstructure and properties of the M2 high speed steel was studied by means of Rockwell hardness tester, scanning electron microscope and transmission electron microscope. The results show that the microstructure of the two tested steels after tempering is tempered martensite+a small amount of retained austenite+carbides. The addition of 0.82% (mass fraction, the same below) Co makes the peak hardness of M2 high-speed steel increasing by about 0.3 HRC and the hot hardness of M2 high-speed steel after holding at 600 ℃ for 48 h increasing by about 0.8 HRC. It can be seen that Co microalloying has little effect on the improvement of hardness and hot hardness of M2 high-speed steel, but makes the bonding strength increasing by about 950 MPa, while slightly decrease of the toughness of M2 high-speed steel, which is a brittle fracture mode. Through the observation of carbides in the tested steel, it is found that the primary carbides precipitated in the two tested steels are mainly large particle MC and M₆C carbides. After TEM analysis, it is found that the addition of 0.82%Co increases the number of long needle-like M₂C secondary carbides precipitated in martensitic lath of the tested steel.

Key words: M2 high speed steel, structure, hot hardness, bending strength, carbides

CLC Number:

TG142.1

Li Liangjun, Zhang Jiamin, Chi Hongxiao, Zhou Jian. Effect of Co microalloying on microstructure and properties of M2 high speed steel[J]. Heat Treatment of Metals, 2022, 47(1): 73-78.

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