屈服强度450 MPa级新型耐候钢研制

 通过连续冷却相转变行为研究，成功试制了20 mm厚屈服强度450 MPa级耐候钢板，并对钢板的显微组织、力学性能、耐腐蚀性能及焊接性能进行了分析。连续冷却相变行为和钢板试制结果表明：精轧温度约为850 ℃、累计压下率不小于0.6、轧后冷速为15～30 ℃/s、终冷温度不大于579 ℃可以得到以多边形铁素体（晶粒尺寸为3～10 μm）和退化珠光体为主并含有少量马奥岛（M-A组元）的钢板，其屈服强度和抗拉强度分别为458和557 MPa，伸长率不小于 28%，－60 ℃冲击功不小于 287 J，其优异的低温冲击韧性与钢板有效晶粒尺寸较小以及大角度晶界所占比例较高有关。72 h亚硫酸氢钠和氯化钠溶液周期性浸润试验结果显示，试制钢板的耐蚀性能比Q345B分别提高了约49%和40%。对试制钢板进行线能量为30 kJ/cm的埋弧焊焊接试验，得到的焊接接头热影响区熔合线处－40 ℃冲击功为156 J。

Development of a New Weathering Steel With Yield Strength of 450 MPa

20 mm thick yield strength 450 MPa weathering steel was successfully hot rolled based on continuous cooling transformation (CCT) behavior study, and its microstructure, mechanical properties, corrosion-resistance and weldability were analyzed. Both CCT and hot rolling test results suggest that a combination of finish rolling temperature of about 850 ℃, thickness reduction ratio≥0.6, cooling rate of between 15-30 ℃/s and cooling finish temperature ≤ 579 ℃ resulted in a plate consisting of polygonal ferrite (3-10 μm), degenerate pearlite and small amounts of M-A. The rolled plate exhibited a yield strength of 458 MPa, and tensile strength of 557 MPa, elongation ≥ 28% and impact absorbed energy ≥ 287 J at －60 ℃. The excellent low temperature toughness was derived from the small effective grain size of and high proportion of high-angle boundary. 72 h periodical dry-wet immersion corrosion test in NaHSO3 and NaCl solutions show that the corrosion resistance of the hot rolled plate was 49% and 40% higher than Q345B, respectively. Submerged arc welding with heat input of 30 kJ/cm was employed to the hot-rolled plate, and the heat affected zone shows an impact absorbed energy ≥ 156 J at －40 ℃.