厚规格35CrMo预硬型模具钢板的回火组织与硬度研究

Research on Tempering Microstructure and Hardness of Larger Thickness Pre- hardened Die Steel Plate 35CrMo

通过扫描电镜的分析手段,研究了莱钢生产35CrMo预硬型模具钢板厚度方向显微组织对硬度分布的影响。结果表明：80mm厚度钢板经过900℃淬火和550~560℃回火后,钢板近表面硬度为HRC32~36,心部硬度超过HRC28,厚度方向硬度波动控制在HRC5以内;120mm厚度钢板经过920℃淬火和570℃回火后,钢板近表面硬度为HRC32~34,心部硬度下降到HRC28~30。回火态钢板表面硬度下降幅度大于心部硬度的下降幅度,钢板近表面处组织中的回火马氏体呈板条状,原始奥氏体被晶界不同取向的板条马氏体分割细化,组织中碳化物呈短棒状,数量相对较少;板厚1/2处组织为回火贝氏体和数量较多的碳化物。随着钢板厚度增加和回火温度升高,显微组织中回火马氏体体积分数逐渐减少,回火贝氏体体积分数逐渐增多,组织中的碳化物析出量逐渐增加,聚集长大趋势明显。

The effect of through- thickness microstructure on hardness distribution of pre- hardened die steel plate 35 CrMo produced by Laigang has been studied by means of scanning electronic microscopy in this paper. The results show that after 900 ℃ quenching and 550 ~ 560 ℃ tempering,the near surface hardness of 80 mm thickness plate reaches HRC32 ~ 36,the center hardness exceeds HRC28 and the variation of through- thickness hardness is controlled to a value less than HRC5; after 920 ℃ quenching and 570 ℃ tempering,the near surface hardness of 120 mm thickness plate reaches HRC32 ~ 34,the center hardness decreases to HRC28 ~ 30. After tempering,the surface hardness decreases more than the center hardness,the microstructure show that the near surface microstructure consists of tempered lath martensite,the prior austenite are segmented and refined by the lath martensite of different orientation,the carbides in microstructure are in the shape of short bar with less quantity. The microstructure at 1 /2 plate thickness composes of tempered bainite and more carbides. With increasing of plate thickness and tempering temperature,the fraction of tempered martensite decreases,the fraction of tempered bainite gradually increases,the carbide content also increases gradually with significant tendency of aggregation and growth.