新型低锰微铌钢与普通Q355钢焊接性能比较

Differences of weldability between novel low manganese niobium microalloying steel and ordinary Q355 steel

通过焊接热影响区最高硬度试验、斜Y形坡口焊接裂纹试验、典型对接接头性能评价试验及典型对接接头疲劳性能试验,结合金相显微镜(optical microscope,OM)和扫描电子显微镜(scanning electron microscope,SEM)两种表征手段,深入研究了新型低锰微铌钢(MnNb钢)与普通Q355钢(Q355钢)焊接性能差异及机理。结果表明,在不预热条件下,Q355钢表现出强烈的焊接淬硬倾向,而MnNb钢无淬硬倾向;MnNb钢和Q355钢均具备优良的防止焊接冷裂纹性能。相比于Q355钢接头,MnNb钢对接接头抗拉强度稍低,但其热影响区冲击吸收能量明显更优,这主要是由于Q355钢粗晶区中存在细小的晶内组织和侧板条铁素体组织,而MnNb钢粗晶区具有大量针状铁素体与较小的原始奥氏体晶粒。MnNb钢接头的条件疲劳极限强度比Q355钢接头高57 MPa,其扩展区疲劳辉纹间距更小,裂纹扩展速度更慢,MnNb钢对接接头的疲劳性能显著优于Q355钢对接接头。

The comparison of differences in weldability between novel low manganese niobium microalloying steel(MnNb steel)and ordinary Q355 steel(Q355 steel)was performed deeply and systematically by methods of the highest hardness test in welding heat-affected zone,welding crack test in oblique Y-bevel,weldability evaluation test in typical butt joints and fatigue resistance in typical butt joints with both optical microscopy(OM)and scanning electron microscopy(SEM).The results revealed that under the condition of no preheating,there was the strong weld hardening tendency in Q355 steel,while MnNb steel had no tendency to weld hardening.Also,there were excellent properties of cold crack prevention of welding in both MnNb steel and Q355 steel with no preheating.Compared with Q355 steel joints,MnNb steel had slightly lower tensile properties and significantly better impact toughness,which is mainly due to the presence of fine intra-grain microstructure and ferrite side plate ferrite in coarse-grained heat affected zones(CGHAZs)of Q355 steel,while there were abundant acicular ferrite and small prior austenite grain in CGHAZs of MnNb steel.Besides,the conditional fatigue ultimate strength of MnNb steel joints was 57 MPa higher than that of Q355 steel joints.There was smaller space of fatigue striations in the fatigue expansion zone of MnNb steel joints indicating the slower crack expansion rate.Therefore,the fatigue performance of MnNb steel butt joints was better than that of Q355 steel butt joints significantly.