大截面预硬型718MOD塑料模具钢的组织与力学性能

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 718MOD PRE-HARDENED PLASTIC MOULD STEEL LARGE BLOCK

通过洛氏硬度计、冲击及拉伸等方法对截面尺寸为510 mm×1 320 mm的大型预硬态718MOD塑料模具钢模块进行了力学性能检测,测定了该钢的CCT曲线,并对模块不同部位进行了成分分析与显微组织观察。结果表明:718MOD钢合理的成分设计使其临界冷速小于0.015℃/s,且模块成分均匀;模块边部组织是回火索氏体,1/8与1/4处是回火马氏体+回火贝氏体,心部为回火贝氏体,中部最大截面硬度差为3.8 HRC;模块力学性能优良,边部的强韧性最好,心部组织中的粗大碳化物与宽大铁素体片条导致其韧性降低。

The mechanical properties over the section of pre-hardened 718MOD plastic mould steel with a cross-section size of 510 mm × 1 320 mm were investigated by rockwell hardness,tensile and impact test.The CCT curve was measured and alloy composition of the steel analyzed,also the microstructure over the section observed by OM and SEM.The results showed that the 718MOD steel exhibited high hardenability,the critical cooling speed for formation of proeutectoid ferrite was lower than 0.015 ℃/s and the alloy composition was uniform in the whole block.The hardness fluctuation of the middle cross-section was no more than 3.8 HRC,and the microstructure of the block wastempered sorbite at the edge,mixed microstructure of tempered bainite with sorbite at 1/8 and 1/4 position,tempered bainite at the core.The mould block had excellent mechanical properties especially at the edge,and the reason for the toughness reduction of the core was that the microstructure was composed of coarse carbides and wide ferrite strips.