P20塑料模具钢淬火及回火组织性能的研究

Research on Microstructure and Property of P20 Plastic Die Steel After Quenching and Tempering

利用扫描电镜、金相显微镜、洛氏硬度计研究了P20塑料模具钢淬火及回火组织,并测定了硬度随淬火温度以及回火温度的变化。P20钢经830～920℃淬火得到板条马氏体,淬火后晶粒尺寸随淬火温度的升高有粗化的趋势但并不明显,直到890℃以后才明显粗化,因此,淬火温度应在830～890℃,以860℃为宜。P20钢硬度随回火温度升高而降低,碳化物析出增多并逐渐球化,马氏体板条边界逐渐变得模糊,有些板条合并变宽。P20钢经620℃×1h回火后其硬度为32.8～35.8HRC,能满足预硬化硬度要求,而且经830～890℃淬火+620℃×1h回火,硬度基本不随淬火温度变化,这将有利于工厂组织生产,因此最终选择预硬化工艺为860℃×30min淬火+620℃×1h回火。

P20 plastic die steel was treated at different quenching and tempering temperature. The quenching and tempering microstructure of P20 plastic die steel was investigated with scanning electronic microscope,metallurgical microscope and its hardness was measured with rockwell hardmeter. The experimental results show that the lath martensite is attained after the steel quenched from 830 ℃ to 920 ℃ and the grains of steel gradually increase with the elevation of quenching temperature,however the increase of the size is not obvious until the temperature is higher than 890 ℃. So quenching temperature can be set at 830 ～890 ℃ and 860 ℃ is a better choice. Tempering hardness decreases with the elevation of tempering temperature,precipitated carbide gradually spheroidizates and the amount gradually increases,martensite lath boundaries gradually become blurry and some laths are mergered and broadened with the elevation of tempering temperature. When 620 ℃ for 1 h is selected as tempering process,the tempering hardness is from 32.8 HRC to 35.8 HRC and it can satisfy pre-hardening hardness requirement. In addition,tempering hardness remains almost constant when the steel is quenched at 830 ～890 ℃ and tempered at 620 ℃,which is benefit for actual production in factory. So quenching at 860 ℃ for 30 min plus tempering at 620 ℃ for 1 h is finally selected as pre-hardening processes.