微量钒对紧固件用SA-540合金强韧性的影响

Effect of trace vanadium on strength and toughness of SA-540 alloy for fasteners

在SA-540合金中添加了钒以改善其强韧性,并研究了钒含量和回火温度对合金强韧性的影响规律,同时采用JMatPro软件和钢中第二相热力学模型研究了加入钒后SA-540合金中的物相变化机制。结果表明:加入钒元素可提高SA-540合金强度,但冲击性能明显降低,但通过回火处理可改善冲击性能;加入0.1%钒的合金在570℃以上回火后冲击性能明显改善,而加入0.2%钒的合金在600℃回火仍不能改善冲击性能;加入0.1%钒的SA-540合金在860℃淬火+590~600℃回火可获得最佳强韧性匹配。热力学分析计算结果表明:SA-540合金平衡相中碳化物类型主要有M_(23)C_(6)、Fe_(3)C、M_(7)C_(3),加入钒后合金中生成了MC型碳化物,并导致了部分含钼碳化物由M_(23)C_(6)型转变为更加稳定的MC型;VC生成量的影响因素主要是合金中钒含量,其次为淬火温度,而回火温度的影响较小。

Vanadium was added to SA-540 alloy to improve its strength and toughness,and the effect of vanadium content and tempering temperature on strength and toughness of the alloy was studied.The phase change mechanism in the SA-540 alloy with addition vanadium was studied by using JMatPro software and the second phase thermodynamic model in steel.The results show that the strength of the SA-540 alloy can be improved by adding vanadium,but the impact properties are obviously reduced,but the impact properties can be improved by tempering treatment.The impact properties of the alloy with 0.1%vanadium are improved obviously after tempering at above 570℃,but the impact properties of the alloy with 0.2%vanadium can not be improved after tempering at 600℃.The SA-540 alloy with 0.1%vanadium can obtain the best strength toughness matching by quenching at 860℃and tempering at 590-600℃.The results of thermodynamic analysis and calculation show that the main types of carbides in the equilibrium phase of the SA-540 alloy are M_(23)C_(6),Fe_(3)C and M_(7)C_(3).MC type carbides are formed in the alloy after vanadium is added,which leads to the transformation of some molybdenum containing carbides from M_(23)C_(6) type to more stable MC type.The main influencing factor of the formation of VC is the vanadium content in the alloy,followed by the quenching temperature,while the tempering temperature has little effect.