淬火温度对7Ni钢低温力学性能的影响

Effect of Quenching Temperature on Cryogenic Mechanical Properties of a 7Ni Steel

使用OM、SEM、TEM和XRD等手段观察并表征在不同温度淬火的7Ni钢的组织形貌和逆转奥氏体含量的变化,研究了淬火温度对7Ni钢的低温强度和低温韧性的影响。结果表明:当淬火温度从830℃提高到930℃时钢的低温韧性急剧下降,低温抗拉强度和屈服强度明显降低。同时,随着淬火温度的提高延伸率下降,与低温强度的变化趋势基本一致。在830℃淬火的试验钢,原奥氏体晶粒和马氏体板条束最为细小。而当淬火温度超过830℃时钢中的原奥氏体晶粒和马氏体板条束都显著长大,钢的低温强度和低温韧性随着晶粒尺寸与板条束宽度的增大而下降,粗化的组织对钢的低温强度与低温韧性都有不利的影响。随着淬火温度的提高钢中的逆转奥氏体含量基本上呈下降趋势,在830℃淬火的试验钢中逆转奥氏体含量最高,其低温冲击功也最高。

The effect of quenching temperature on cryogenic strength and toughness of a 7 Ni steel was investigated. The microstructure and volume fraction of reversed austenite were characterized by means of OM, SEM, TEM, XRD. Results show that cryogenic toughness of the steel sharply decreased when quenching temperature increased from 830℃ to 930℃. And cryogenic tensile strength as well as yield strength were obviously decreased with increasing quenching temperature. What＇s more, elongation also decreased at higher quenching temperature, and has a consistent variation tendency with cryogenic strength. Grains of prior austenite and martensite packets were fine in the steel quenched at 830℃, but grains and packets grew significantly at higher quenching temperature. Cryogenic strength and toughness decreased with growth of grain sizes and packet width. Coarsen microstructure has a adverse effect on cryogenic strength and toughness. The amount of reversed austenite showed downtrend basically by increasing quenching temperature. The steel quenched at 830℃ has a maximum of reversed austenite amount and impact energy.