稀土对HRB400E螺纹钢低温冲击韧性的影响

采用工业试验生产了稀土质量分数为0%、0.016 8%、0.028 5%和0.037 0%的HRB400E螺纹钢,使用DVN(Direct V-notched)冲击试样进行了低温冲击试验,以研究稀土含量对HRB400E螺纹钢低温冲击韧性的影响,并借助OM、SEM、EDS和全自动夹杂物分析仪表征了稀土处理前后螺纹钢的微观组织和夹杂物的形貌、化学成分和尺寸。结果表明,在-20、-40、-60 ℃ 3个试验温度下,试验钢的低温冲击韧性随稀土含量的增加呈现出先升高后降低的趋势。其中,稀土质量分数为0.016 8%的试验钢低温冲击韧性最佳,-20 ℃时其冲击功为276 J,相比未添加稀土的试验钢提高了117%。未添加稀土时,试验钢中的夹杂物主要为MnS、MnO-SiO₂和Al₂O₃,添加0.016 8%稀土后试验钢中MnO-SiO₂和Al₂O₃的比例(数量)大幅降低,MnS的比例明显提高,并生成了小尺寸、形状相对规则的稀土复合夹杂物,从而阻碍裂纹的萌生与扩展,改善了试验钢的低温冲击韧性。然而,过量添加稀土会导致试验钢中稀土夹杂物的尺寸增大,大尺寸的稀土夹杂物促进裂纹扩展,对试验钢的低温冲击韧性具有不利影响。

Effects of rare earth on low temperature impact toughness of HRB400E rebar

Industrial tests were carried out to produce HRB400E rebar with rare earth mass fraction of 0%, 0.016 8%, 0.028 5% and 0.037 0%, and low temperature impact tests were carried out using DVN (Direct V-notched) impact specimens to investigate the effect of rare earth content on low temperature impact toughness of HRB400E rebar. The microstructure and inclusion characteristics, chemical composition and size of rebar before and after rare earth treatment were characterised with the aid of OM, SEM, EDS and Explorer 4 Analyzer. The results show that low-temperature impact toughness of test steels at -20, -40, -60 ℃ tends to increase and then decrease with increasing rare earth content. Test steel with 0.016 8% rare earth mass fraction has the best low temperature impact toughness. The impact energy of test steel with 0.016 8% rare earth at -20 ℃ is 276 J, an increase of 117% compared to the test steel without rare earth. Without the addition of rare earth, the inclusions in test steel are mainly MnS, MnO-SiO₂ and Al₂O₃, while the addition of 0.016 8% rare earth results in a significant decrease in the quantity percentages of MnO-SiO₂ and Al₂O₃ and a significant increase in the quantity percentage of MnS in the test steel. Small size and relatively regular shape of rare earth composite inclusions are formed, which prevent the emergence and expansion of cracks and improve the low temperature impact toughness of test steel. However, addition of excessive rare earths leads to an increase in the size of rare earth inclusions in test steel, and the large size of rare earth inclusions promotes crack expansion, which has a negative effect on low temperature impact toughness of test steel.