35CrMnSi低合金钢淬火直径与微观组织的关系

对不同直径的35CrMnSi低合金钢棒进行900 ℃油冷淬火+230 ℃回火处理,通过分析钢棒直径与横截面硬度、横截面中心显微组织的关系,探索了35CrMnSi低合金钢油冷淬火临界直径。结果表明,由于贝氏体的存在使淬火马氏体量与硬度的相关性不再符合SAE J406标准提供的对应关系,其中Ø60 mm钢棒马氏体含量仅约40%,但轴线中心硬度接近于按SAE J406标准90%马氏体对应的硬度,轴线中心强度和韧性考核证明符合超高强度钢强韧性要求,可以判定35CrMnSi低合金高强度钢淬火临界直径不小于Ø60 mm;Ø90 mm钢棒轴线中心粒状贝氏体和上贝氏体对硬度影响有限,450 HV10(46 HRC)的硬度远高于SAE J406标准50%马氏体对应的硬度,同样证明若用SAE J406标准淬火马氏体量预测35CrMnSi钢的淬火临界直径远低于实际值。

Relationship between quenching diameter and microstructure of 35CrMnSi low alloy steel

35CrMnSi low alloy steel bars with different diameters were quenched by oil cooling at 900 ℃ and tempered at 230 ℃. The quenching critical diameter of the 35CrMnSi low alloy steel was explored by analyzing the relationship between the diameter of the steel bar and the hardness of the cross section and the microstructure of the center of the cross section. The results show that the correlation between quenched martensite volume and hardness is no longer consistent with the corresponding relationship provided by SAE J406 standard due to the presence of bainite. The martensite content of Ø60 mm steel rod is only about 40%, but the hardness of the center of the axis is close to the hardness corresponding to 90% martensite according to SAE J406 standard. The strength and toughness of the center of the axis are proved to meet the requirements of the strength and toughness of ultra-high strength steel, it can be determined that the quenching critical diameter of the 35CrMnSi low alloy high-strength steel is not less than Ø60 mm. The microstructure at the center of the axis of the Ø90 mm steel bar is granular bainite and upper bainite, which have limited influence on the hardness, and the hardness of 450 HV10 (46 HRC) is much higher than that of 50% martensite of SAE J406 standard, which also proves that quenching critical diameter of the 35CrMnSi steel predicted by the quenched martensite content of SAE J406 standard is much lower than the actual value.