热处理工艺对4Cr3Mo2Si1V钢组织与性能的影响

Effect of heat treatment process on microstructure and properties of 4Cr3Mo2Si1V steel

利用热膨胀相变仪测定了新型热作模具钢4Cr3Mo2Si1V的奥氏体连续冷却转变(CCT)曲线,研究了其在不同淬火、回火工艺下的力学性能和显微组织。结果表明:4Cr3Mo2Si1V钢的珠光体与贝氏体的临界冷速分别为0.03℃·s^(-1)和0.8℃·s^(-1)。经淬火试验,发现该钢种在1030℃和1060℃油淬后具有较高的硬度,且晶粒未发生明显长大。随着回火温度的提高,其硬度呈现先增后降的趋势,在500℃回火时由于第二相粒子大量析出,析出强化作用增强,促使二次硬化现象产生,硬度达到峰值,约57 HRC。经过多组工艺对比后,发现1030℃淬火和600℃回火后的平均冲击吸收能量达到最大值,为265 J,且硬度值仍保持在52 HRC,故最终选定1030℃×30 min油淬+600℃×2 h回火两次作为4Cr3Mo2Si1V钢的最佳热处理工艺。

Continuous cooling transformation(CCT) diagram of hot work die steel 4 Cr3 Mo2 Si1 V was measured by thermal dilatometry. Mechanical properties and microstructure of the steel under different quenching and tempering processes were studied. The results show that the critical cooling rates of pearlite and bainite of the steel are 0.03 ℃·s^(-1)and 0.8 ℃·s^(-1), respectively. Through quenching test, it is found that the steel has high hardness after oil quenching at 1030 ℃ and 1060 ℃, and the grain size does not grow obviously. The hardness of the steel increases firstly and then decreases with the increase of tempering temperature, reaching peak value of about 57 HRC at 500 ℃ due to a high volume fraction and density of second phase particles precipitate which enhances the precipitation strengthening effect and results in the secondary hardening phenomenon. After quenching at 1030 ℃ and tempering at 600 ℃, the average impact absorbed energy of the steel reaches the maximum value of 265 J, as well as the hardness remains 52 HRC. By evaluating the combination of strength and toughness, the optimal heat treatment process of the 4 Cr3 Mo2 Si1 V steel is quenching at 1030 ℃ for 30 min with oil cooling and then tempering twice at 600 ℃ for 2 h with air cooling.