高Co-Ni二次硬化钢的设计准则与时效工艺分析

Design Standard and Analysis of Ageing Process in High Co-Ni Secondary Hardening Steel

通过对已有高Co-Ni二次硬化钢实验结果的分析,提出了基于纳米级奥氏体层的相变诱导塑性(TRIP)效应和纳米级M_2C碳化物析出的强韧化机理,并根据Aer Met100钢大量已有的实验数据,建立了综合考虑奥氏体相变摩尔体积增量、奥氏体层稳定性、奥氏体层厚度、奥氏体平衡含量、M_2C尺寸、M_2C平衡含量、成本控制等多个因素的设计准则。通过控制时效工艺,将高Co-Ni二次硬化钢中的M_2C相尺寸控制在1~5 nm,奥氏体层厚度控制在10~20 nm。M_2C和奥氏体的平衡含量被分别控制在19.5%和3.8%。根据设计准则分析了新型高Co-Ni二次硬化钢M54的时效工艺制度,模拟设计结果与显微组织实验观察结果基本吻合。设计得到的新型高Co-Ni二次硬化钢具有较好的强度(2021 MPa)和韧性(115 MPa·m1/2)。

High Co-Ni secondary hardening steels have received great attention for a long time. In several decades, many previous studies were made to improve their strength, toughness, corrosion resistance ability and even stress corrosion sensibility. Although many new kinds of high Co-Ni secondary hardening steels were developed by researchers, the mechanisms of strength and toughness were still a problem, which would inhibit the further development of high Co-Ni secondary hardening steels. In this work, both microstructure and mechanical properties of high Co-Ni secondary hardening steels were analyzed by simulation and experiment. The strengthening and toughening mechanism was explained, which included the transformation induced plasticity（TRIP） effect of austenite layer in nanometer size and the precipitation of M2C in nanometer size. According to the previous studies about Aer Met100 steel, the design standard for high Co-Ni secondary hardening steels was established, which included the mole volume change for austenite, the stability of austenite, the austenite thickness, the austenite equilibrium content, the M2C size, the M2C equilibrium content and cost control. Based on this design standard, the ageing process for a new high Co-Ni secondary hardening steel was analyzed. By controlling the ageing process as 515 ℃ for 10 h, based on the design standard, M2C with the size of 1~5 nm and austenite layers with the thickness of 10~20 nm was formed in new high Co-Ni secondary hardening steels. The equilibrium content of M2C and austenite layers were controlled as 19.5% and 3.8%, respectively. The simulation results were basically consistent with the microstructure observation results. The high Co-Ni secondary hardening steel treated by the designed heat treatment process has considerable strength（2021 MPa）and toughness（115 MPa·m1/2）. Both simulation and experimental results showed that this design standard of ageing process for high Co-Ni secondary hardening steels can help to obtain steels with high strength and toughness.