大截面非调质预硬型塑料模具钢组织对硬度均匀性的影响

Effect of microstructure on hardness uniformity of non-quenched prehardened steel for large section plastic mould

采用光学显微镜,扫描电镜和透射电镜观察了截面尺寸为460mm×800mm的非调质预硬型塑料模具钢(NQP钢)模块心部和表层的组织,结果表明,心部组织较表层粗大,表层存在变形带特征,但精细结构均为位错密度较高的贝氏体铁素体板条和板条间不连续的碳化物或残余奥氏体组成,心部贝氏体铁素体板条稍宽于表层。结合NQP钢连续冷却时的相变特点,分析其截面硬度波动在±1.5HRC内的原因在于其有较好的贝氏体淬透性,模块整个截面上都得到了均匀的贝氏体组织,贝氏体板条宽度和位错密度的差异使得其表层硬度稍高于心部。

The microstructure of non-quenched prehardened steel（ NQP steel） for plastic mould with a cross-section of 460mm × 800mm was examined by optical microscopy, scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM）. The results show that grains at core are coarser and deformation bands are observed at surface, while microstructure both at core and at surface is composed of bainitic ferritc laths with high dislocation density and interlath cementite or residual austenite. Good uniforinity in hardness with a variation of ± 1.5 HRC throughout the section is due to high hardenability of baiaite formed in the NQP steel during cooling based on its continuous cooling transformation diagram.The difference of bainitic ferrite lath widths and dislocation density in bainitic ferrite lath makes hardness at surface a little higher than that at core.