架桥机大臂钢板开裂分析

架桥机大臂钢板在使用过程中发现表面呈方形开裂,但远未达到设计使用寿命。钢板材料为低合金结构钢Q345,其综合力学性能良好。为了弄清钢板开裂原因,通过宏观观察、扫描电镜及能谱仪分析、光学显微分析等对开裂钢板进行了深入探讨,结果表明:钢板失效属于疲劳断裂,疲劳起源于焊缝夹渣,并沿着方形焊缝路径扩展。焊缝中亦存在马氏体组织,马氏体组织较脆,裂纹遇到这种组织也较容易扩展。因此,在循环使用应力作用下,起源于焊渣的疲劳裂纹沿焊缝不断扩展,最终导致钢板呈方形断裂失效。可通过改善焊接工艺、增加焊接线能量以及焊前预热处理等途径来防止裂纹产生。

Cracks analysis of steel plate of large arm on bridging machine

Square cracks are found on the surface of steel plate of large arm on bridging machine in use,but it not reach the design service life.The steel plate material is low alloy steel Q345 and its comprehensive mechanical properties are good.In order to find why the cracks generate,the sample is analyzed by the means of macroscopic observation,scanning electronic microscope,energy disperse spectroscopy and optical microscope.The result shows that the failure of steel plate is fatigue fracture,and the fatigue originates from weld slag inclusion and extends along the square weld path.There is also brittle martensitic structure in the welds.Cracks are also easier to extend in this structure.Therefore,in the effect of cycle use stress,fatigue cracks extend along the weld,which leads to steel plate failures in the end.It can be prevented by improving welding technology,increasing welding heat input and preheating treatment before welding.