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本文以阻力曲线法研究了两种Ms温度高于300℃的低碳钢的淬火态与低温回火态(20-300℃)试样(尺寸为10×12×58mm)的延性断裂韧度(J_(?c))。两种淬火态低碳马氏体(15MnB,Ms410℃;18Cr2Ni4W,Ms315℃)的延性断裂韧度,低温回火以后并未进一步提高,甚至有所降低。由J_(lc)计算的15MnB与18Cr2Ni4W淬火态试样的J_(lc)分别为280kgf·mm~(-3/2)与354kgf·mm~(-3/2),表明Ms温度高于300℃的淬火态低碳马氏体具有较好的断裂韧性。两种淬火态低碳马氏体具有高断裂韧性的组织形态,如仅仅在极少数位错马氏体的局部区域存在对断裂韧性无明显影响的不规则形态的孪晶亚结构,细小魏氏体型的自回火渗碳体弥散分布于全部位错马氏体内,板条马氏体间存在薄膜状残余奥氏体。自回火的淬火态低碳马氏体,低温回火以后碳化物长大,碳化物体积分数增加。回火温度进一步升高(例如15MnB钢250～300℃回火),板条间残余奥氏体消失,板条间碳化物沉淀,断裂韧性明显降低。
In this paper, the ductile fracture toughness (MPa) of quenched and low tempered (20-300 ℃) specimens (10 × 12 × 58mm) of low carbon steel with Ms> 300 ℃ J _ (? C)). The ductile fracture toughness of two kinds of quenched low carbon martensite (15MnB, Ms410 ℃; 18Cr2Ni4W, Ms315 ℃) did not increase further or even decreased after tempering at low temperature. The J_ (lc) of quenched samples of 15MnB and 18Cr2Ni4W calculated by J_ (lc) were 280kgf · mm ~ (-3/2) and 354kgf · mm ~ (-3/2), respectively, which indicated that the Ms temperature was higher than 300 ℃ The quenched low-carbon martensite has good fracture toughness. Two quenched low-carbon martensites with high fracture toughness of the organizational morphology, such as only in a small number of dislocation martensite in the local area there is no significant effect on the fracture toughness of the irregular morphology of twin sub-structure, small Wei The self-tempered cementite is diffusely distributed in all dislocation martensite, and there are thin film-like retained austenite between lath martensite. Self-tempering quenched carbon martensite, carbides after cryogenic tempering growth, increased volume fraction of carbides. Tempering temperature further increased (for example, 15MnB steel 250 ~ 300 ℃ tempering), the residual austenite between the slab disappears, the inter-lath carbide precipitation, fracture toughness decreased significantly.