采用热力学模拟试验机研究了铜合金压铸模具钢在850 ℃下的高温力学性能, 采用Uddeholm自约束法研究了模具钢在室温至800 ℃时的热疲劳性能, 采用光学体视显微镜和SEM研究了模具钢热疲劳试样的表面热疲劳裂纹和断面裂纹纵深扩展状态. 分析了B对材料室温及高温力学性能、热疲劳性能的影响. 结果表明, 添加B后, B在实验钢基体内以M₂B (M为Fe, Cr或Mn)型硼化物的形式分布在奥氏体基体上, 有效提高了材料的高温力学性能, 材料硬度由200 HV提高到302 HV, 850 ℃拉伸屈服强度由144.3 MPa提高到190.3 MPa, 压缩屈服强度由139.7 MPa提高到167.9 MPa; 300 cyc室温至800 ℃循环热疲劳实验结果表明, 含B模具钢的热疲劳级别为2~3级, 大大优于用于对比的经电渣重熔的ESR-H13钢的7~8级, 其主要原因是硼化物能够终结热疲劳裂纹扩展或使裂纹扩展方向改变, 并避免热裂纹发生散射状扩散.

Copper die-casting die steel is usually used in severe rugged environment. Liquid metal flows with high temperature and high pressure during injection and provides rapid filling of the die cavity. The copper die-casting steel should has excellent combination of the properties of high toughness, wear resistance, hardness, thermal fatigue resistance, oxidation resistance and corrosion resistance at high temperature for the cavity surface of die-casting die suffers high pressure, scour, erosion and thermal shock. A new kind of copper alloy die-casting die steel with pure austenitic matrix was conducted in this work, wherein the boride with high thermal stability and high hardness distributes in the austenitic matrix. The mechanical properties of copper alloy die-casting die steel at high temperature of 850 ℃ were studied using dynamic thermal-mechanical simulation testing machine. The thermal fatigue behavior of die steel at room temperature to 800 ℃ was performed using self-restraint Uddeholm thermal fatigue test method, and the depth extension status of surface thermal fatigue cracks and cross-sectional cracks in die steel thermal fatigue specimens was measured using stereo microscope and SEM. The effects of B content on the mechanical properties at room temperature and high temperature and on the thermal fatigue resistance were evaluated. The experimental results showed that boride distributes in austenitic matrix in the form of M₂B-type boride (M represents Fe, Cr or Mn) after adding B in the tested steels, and the comprehensive performances of steel at high temperatures were effectively improved, the hardness of the steel at room temperature increased from 200 HV to 302 HV, the tensile yield strength at 850 ℃ increased from 144.3 MPa to 190.3 MPa, and the compressive yield strength increased from 139.7 MPa to 167.9 MPa. Evaluation of the degree of heat checking on 300 cyc of thermal fatigue testing at room temperature to 800 ℃ showed that the die steel containing B was rating 2~3, much better than rating 7~8 of electroslag remelting ESR-H13 steel for comparison, which mainly because the thermal fatigue cracks were blunted or deflected by boride, and then the cracks spread as scattering shapes was avoided.