铌微合金化对低合金高强钢模拟焊接热影响区粒状贝氏体相变及SH-CCT曲线的影响

Effect of Nb micro-alloying on granular bainite transformation and SH-CCT curves in simulated heat-affected zone of high strength low alloy steel

设计了4种铌含量的低合金高强钢,采用Gleeble-3500热模拟机,研究铌微合金化对模拟焊接热影响区粒状贝氏体相变的影响,并通过SH-CCT(Simulated heat-affected zone continuous cooling transformation)进行表征。结果表明,添加铌元素后,连续冷却相变温度降低,中等焊接热输入的连续冷却相变温度区间约在700~500℃之间,发生的是贝氏体相变。随着铌含量的增加,粒状贝氏体相变的t_(8/5)(表征焊接热输入的参量)范围逐渐增大,当铌含量达到0.180wt%时,发生粒状贝氏体转变的t_(8/5)扩大到3~150 s之间,即铌含量的增加促进了连续冷却粒状贝氏体转变、且扩大了t_(8/5)的范围。显微硬度随着试验钢中铌含量的增加而增加,即铌含量越高,在相同的t_(8/5)时间下,显微硬度也越高。铌含量为0.085wt%时,在较大的热输入范围内(t_(8/5)=15~80 s),显微硬度变化最小。显微硬度变化范围为183~192 HV。SH-CCT曲线为铌微合金化钢基于焊接性设计提供了理论依据。

Four kinds of high strength low alloy steels with niobium content were designed,and the effect of niobium microalloying on the granular bainite transformation in the simulated weld heat affected zone was studied by using the Gleeble-3500 thermal simulator,which was characterized by SH-CCT(Simulated heat affected zone continuous cooling transformation).The result shows that the transformation temperature of continuous cooling transformation decreases with the addition of Nb.The continuous cooling phase transformation temperature is about 700 ℃ to 500 ℃ at the range of medium welding heat input,where the granular bainite transformation takes place.The t_(8/5) range of the granular bainite transformation increases with the increase of Nb content.When the Nb content in the tested steel is increased to 0.180wt%,the range of cooling rate t_(8/5) for transformation of granular bainite is around 3-150 s.The increase of Nb content promotes the continuous cooling granular bainite transformation and expands the t_(8/5) range.The microhardness increases with the increase of Nb content.The higher the Nb content,the higher the microhardness at the same t_(8/5 )condition.When the content of Nb is 0.085wt%,the change of microhardness value is the smallest in the large heat input range(t_(8/5)=15-80 s).The microhardness value varies from 183 HV to 192 HV.The SH-CCT curves provides a theoretical design of niobium microalloyed steel based on the weldability.