G50超高强度钢大规格锻件退火工艺优化

以30CrMnSiA钢作为对比，研究了典型成分G50超高强度钢在Ac₁附近加热和冷却的相变过程，及退火硬度和退火制度的关系。结果表明，针对现行成分控制要求的G50钢，在稍低于膨胀法测定的Ac₁温度退火时形成的奥氏体，冷却后形成未回火马氏体导致硬度上升，原680℃退火温度已不适用，出现退火时间越长硬度越高的现象。多炉号试验验证表明，660℃×6 h退火虽有部分奥氏体形成，但原始正火马氏体相软化程度更大，能有效降低G50钢锻件硬度，具有普遍适用性。

Optimization of annealing process of G50 ultra-high strength steel large forgings

Take 30CrMnSiA steel as comparison, phase transition process of the G50 ultra-high strength steel with typical chemical composition when heated and cooled near Ac₁ was studied, meanwhile the relationship between annealing hardness and annealing specification was analyzed. The results show that the present G50 steel annealed at the temperature slightly below the Ac₁ measured by means of the expansion method forms austenite and consequently cooling forms untempered martensite which leads to the hardness rise, and the original 680 ℃ annealing temperature is no longer applicable, resulting in the phenomenon of the longer the annealing time, the higher the hardness. Verification experiment of multiple batches shows that although some austenite is formed by annealing at 660 ℃ for 6 h, more softening degree of the original normalized martensite can effectively reduce the hardness of the G50 steel forgings, and it has universal applicability.