两步法等温淬火球墨铸铁型材的组织与性能

Micro structure and Properties of Two-Step Austempering Ductile Iron Bars

针对Φ35 mm水平连铸球铁型材进行了两步法等温淬火。通过金相观察、X射线衍射分析、硬度冲击韧性及抗拉强度测试,研究了奥氏体化温度、奥氏体化时间、第一步等温淬火温度及淬火时间、第二步等温淬火温度及淬火时间等因素在该工艺中对等温淬火球墨铸铁(ADI)组织性能的影响。结果表明:球铁型材经两步法等温淬火工艺处理后可以获得组织更为细密的ADI,材料强度显著提高,且残余奥氏体具有较高的含碳量。第一步等温淬火温度会显著影响针状铁素体晶粒的大小和残余奥氏体的含量,随着第一步淬火温度的升高,铁素体逐渐变得粗大,残余奥氏体含量逐渐增加,ADI的抗拉强度和硬度均呈先增加后降低的趋势。当两步法工艺为900℃+60 min+310℃+15 min+340℃+60 min和940℃+60 min+290℃+15 min+360℃+60 min时,相对综合力学性能最好。

The two-step austempering process ofΦ35 mm horizontal continuous cast ductile iron bars was carried out.The metallographic observation,X-ray diffraction(XRD)analysis and the testing of hardness,impact toughness and tensile strength were conducted to investigate the effect of some heat treatment parameters on the microstructure and mechanical properties of ADI in the two-step austempering process,such as the austenitizing temperature,austenitizing time,the first step austempering temperature and time,the second step austempering temperature and time,etc.The results show that fine-grained of ADI can be fabricated by the two-step austempering process with higher tensile strength and high carbon content of residual austenite.The first step austempering temperature presented great influence on the size of ferrite grain and the content of residual austenite.As the first step austempering temperature increased,ferrite became coarser,tensile strength and hardness showed a trend of increasing firstly,then decreased.The better comprehensive mechanical properties of ADI were obtained in the process of 900℃+60 min(austenitizing)+310℃.(first step austempering)+15 min+340℃.(second step austempering)+60 min and 940℃+60 min+290℃.+15 min+360℃+60 min.