研究了等温处理对中碳超高强度弹簧钢组织与力学性能的影响。结果表明，在325~375 ℃等温可以获得无碳化物贝氏体/马氏体复相组织；奥氏体化温度对贝氏体/马氏体复相组织的影响很大，从875 ℃升高到930 ℃，强度升高，但其塑性、冲击韧性和断裂韧性显著降低。试验范围内，在875 ℃保温30 min，325 ℃等温120 s油淬后，在300 ℃ 进行回火处理2 h，可获得强韧性配合良好的贝氏体/马氏体复相组织，其断裂韧性KIC值为83 MPa·m1/2，是相同强度水平下常规淬火回火马氏体组织的1.5倍。
The effect of isothermal heat treatment on microstructure and mechanical properties of a mediumcarbon ultra high strength spring steel (U) was studied. The results show that a carbidefree bainite/martensite duplex microstructure could be obtained by austempering at 325375 ℃. The austenitizing temperature before austempering has obvious influence on both the microstructure and mechanical properties of bainite/martensite duplex microstructure of steel U. With increasing austenitizing temperature from 875 ℃ to 930 ℃, the strength of steel U increases, while its toughness decreases markedly. Bainite/martensite duplex microstructure with good combination strength and toughness was obtained by austempering at 325 ℃ for 120 s after austenitizing for 30 min at 875 ℃ followed by tempering at 300 ℃ for 2 h.The fracture toughness of specimens was 83 MPa·m1/2,1.5 times higher than that of single tempered martensite with same strength level.
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