低碳Nb-V微合金化高强度冷镦硼钢耐延迟断裂性的研究

A Study on Delayed Fracture Resistance of Low Carbon Nb-V Microalloying High Strength Cold Heading Boron Steel

试验用低碳硼钢(%:0.13～0.21C、0.000 5～0.003 7B)和低碳Nb-V微合金化硼钢(%:0.18～0.24C、0～0.033Nb、0～0.050V、0.000 5～0.002 2B)分别由实验室50 kg真空感应炉和碳管炉冶炼,轧-锻成φ13 mm圆棒,然后加工成拉伸和带缺口的延迟断裂试样。经950℃水淬+200℃回火处理后钢的延迟断裂性由延迟断裂强度比R=σ_n(延迟断裂强度)/σ_e(拉伸强度)表示。结果表明,0.028%Nb-0.032%V微合金化0.000 5%B钢的σ_e为1 480 MPa,R值为0.665,均高于880℃油淬+400℃回火40Cr钢和35CrMo钢的σ_e和R值(σ_e分别为1 460 MPa和1 530 MPa,R值0.583和0.556)。

Test low carbon boron steel （ % ： 0. 13 ～ 0. 21C, 0. 000 5 ～ 0. 003 7B） and low carbon Nb-V microalloying boron steel （ % ： 0. 18 - 0. 24C, 0 ～ 0. 033 Nb, 0 ～ 0. 050V, 0.000 5 ～ 0. 002 2 B） were melted respectively by laboratory 50 kg vacuum induction furnace and carbon tube furnace, and the tensile specimen and notched delayed fracture specimen were turned from φ13 mm rolled-forged rod. The delayed fracture resistance of test steels water-quenched at 950 ℃ and tempered at 200 ℃ is presented by delayed fracture strength ratio R = σn （ delayed fracture strength ） / σc （ tensile strength）. Results showed that the tensile strength of 0.000 5% B steel microalloying with 0. 028% Nb and 0. 032% V was 1 480 MPa and its R value was 0. 665 which was higher than that of 40Cr steel and 35CrMo steel queehed at 880 ℃, oil cold ＋ tempered at 400 ℃ （ both σc were respectively 1 460 MPa and 1 530 MPa, R value 0. 583 and 0. 556 ）.