屈服强度460MPa级耐候钢及其焊接性能

Weathering Steel With a Yield Strength of460MPa and Its Weldability

通过连续冷却相转变行为的研究,利用试验轧机成功试制了24mm厚,屈服强度460MPa级耐候钢板,并分析了钢板微观组织、力学性能、腐蚀性能以及焊接性能。连续相转变行为和钢板试制结果表明：精轧温度不大于850℃,厚度压下率不小于0.6,冷速为4-15℃/s和终冷温度不大于465℃可得到以针状铁素体（3-10μm）和多边形铁素体（5-15μm）为主的钢板,其屈服强度不小于480MPa,抗拉强度不小于635MPa,伸长率不小于23%,-40℃冲击功不小于209J。对试制钢板进行了热输入量为72kJ/cm的双丝埋弧焊接试验,无焊前预热和焊后热处理,得到了无缺陷焊接接头,焊接热影响区-40℃冲击功不小于100J;粗晶区的高韧性与其晶内铁素体为主以及少量晶界铁素体和上贝氏体的微观组织有关。72h周浸试验结果表明：试制钢种的耐大气腐蚀能力比普碳钢Q345B提高了46%。

A weathering steel with a thickness of 24 mm and an yield strength of 460MPa was successfully hot rolled based on the study of continuous cooling transformation （CCT） behavior, and then microstructure, mechanical property, corrosion property and weldability of the plate were examined. Results of both CCT and hot rolling suggest that a combination of finish rolling temperature （- 850 ℃）, thickness reduction ratio （-0.6）, cooling rate （4--15 ℃/s） and cooling finish temperature （-465 ℃） results in a plate consisting of mostly acicular ferrite （3--10/am） and polygonal ferrite （5-15μm）, which has an yield strength not below 480MPa, a tensile strength not below 635 MPa, an elongation not below 23% and an impact toughness not below 208J at -40 ℃. Tandem submerged arc welding with heat input of 72 kJ/cm was employed to butt weld the plate without prehea- ting and post weld heat treatment, and defect-free weld joint with satisfactory impact property at heat-affected zone was obtained. The high impact toughness of coarse grain heat-affected zone is due to its microstrueture of in tra-granular ferrite, few grain boundary ferrite and upper bainite. The rolled plate shows an increase of 46% in corrosion resistance relative to conventional Q345B judged from 72h periodical dry wet immersion test result.