硼对低合金高强钢大热输入焊缝韧性的影响

Effects of Boron on Toughness in High Heat Input Welds of High Strength Low Alloy Steel

对不同硼(B)的质量分数的低合金高强钢大热输入焊缝进行组织性能研究,分析、讨论B对低合金高强度(High strength low alloy,HSLA)钢焊缝韧性的影响规律。研究表明,低合金高强钢焊缝中适量增加B元素质量分数可提高组织中针状铁素体质量分数,有效细化焊缝组织,而当B元素过量时则使焊缝组织中的针状铁素体质量分数下降,组织粗化。同时,适量B元素还可抑制晶界先共析铁素体的产生;随着焊缝中B质量分数的增大,贝氏体转变得到促进,M-A组元总量提高,从不含B时的2.4%提高到B质量分数为0.008 8%时的5.7%,且其尺寸也相应增大,由平均尺寸2.14μm增加至2.83μm。由于B质量分数增加先促进针状铁素体后促进贝氏体形成,因此其对焊缝韧性的影响呈现抛物线变化规律,即低温冲击吸收能量随着B质量分数的增加先上升后下降。在焊缝Ti质量分数约为0.03%的条件下,B质量分数为0.005 2%时,焊缝获得了最佳的低温冲击韧度。

The microstructure and toughness are investigated to elucidate the influence of boron on toughness in the high heat input welds of high strength low alloy（HSLA） steel. The result indicates that appropriate addition of boron effectively promotes the formation of acicular ferrite, and as a result microstructure is refined. Whereas the percentage of acicular ferrite decreases and microstructure is coarsen as the boron content further increases. Meanwhile, moderate amount of boron obviously suppresses proeutectoid ferrite, and bainite is favored. The fraction and size of M-A constituent accordingly increases from 2.4% and 2.14 μm with no addition of boron to 5.7% and 2.83 μm with 0.008 8%B. As result, the weld toughness is improred at first and then detoriorat as the boron overdoses. When the boron content is 0.005 2% with the titanium content of 0.03%, the highest toughness can be attained at low temperature for the high heat input welds of HSLA.