Co微合金化对M2高速钢组织和性能的影响

采用洛氏硬度计、扫描电镜和透射电镜等方法研究了在M2高速钢中添加微量Co对其回火组织和性能的影响。结果表明,两种试验钢回火之后的组织都为回火马氏体+少量残留奥氏体+碳化物。添加0.82%(质量分数,下同)Co使得M2高速钢的峰值硬度提高了约0.3 HRC,使600 ℃保温48 h之后的红硬性提高了约0.8 HRC,可以看出微量Co添加对M2高速钢的硬度和红硬性的提升效果不大,抗弯强度提高了约950 MPa,而使得M2高速钢的韧性略有降低,均为脆性断裂。通过对试验钢中的碳化物进行观察发现,两种试验钢析出的一次碳化物主要为大颗粒的MC型和M₆C型碳化物,通过TEM分析之后发现,添加0.82%的Co使得试验钢中马氏体板条上长条针状M₂C型的二次碳化物析出数量增多。

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

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.