钢材层状撕裂及抗层状撕裂焊接接头的设计

钢材层状撕裂是焊接钢桥中一种非常危险的缺陷,通常发生在角焊接头处。钢材中夹杂物的数量、分布和形态以及基体金属的塑性和韧性是影响层状撕裂的钢材因素。钢材中含硫量越多,夹杂物以片状形态大量密集于同一平面,发生层状撕裂的倾向就越大。钢材的刚度越大、板越厚,越容易产生层状撕裂。相同板厚、相同焊接方法条件下,焊缝断面越大,越易产生层状撕裂。角焊缝接头中选择贯通板,T型或十字型焊接接头中选择不熔透或部分熔透角焊缝,热加工时避开蓝脆温度和红脆温度,冷加工时确保一定的曲率半径(大于15倍板厚),改善隅角焊的坡口形式,用小线能量焊接取代大能量焊接,采用低强度焊道打底、焊前预热等,均可抑制层状撕裂的发生。同时,给出日本和Eurocode3的层状撕裂评定方法和Z向钢的选材标准,以便设计和制造人士准确把握。

Lamellar Tearing of Steel and the Welding Joint Design to Avoid Lamellar Tearing

Lamellar tearing of steel is a kind of very dangerous defect of the welding steel bridge and normally takes place at the fillet welding joint.The amount,distribution and configuration of the inclusions and the plasticity and toughness of the metal matrix are all the factors that can influence the lamellar tearing.If there is more sulfur in the steel and the steel contains many inclusions with flake configuration in the same plane with high density,lamellar tearing tends to happen with high probability.The lamellar tearing is easier to occur if the steel plate has higher stiffness and greater thickness.And with the same plate thickness and weld technology,lamellar tearing is easier to occur if the weld section has larger size.Measures to restrain lamellar tearing are as follows: selecting integrity plate in the fillet weld joint,selecting fillet weld without penetration or with partial penetration in T type or type weld joint, avoiding blue brittleness and red brittleness temperature during heat machining,keeping curvature radius which must be greater than 15 times plate thickness during cold machining,improving groove type of the fillet weld,replacing large energy welding with low energy welding,using low strength weld bead,pre-heating before welding,and etc..Japanese and Euro Code3 methods for evaluating lamellar tearing and the standards for selecting Z direction steel are presented for designers and manufacturers as references.