连续退火炉露点对汽车用高强钢磷化处理特性的影响

Effect of Dew Point in Continuous Annealing Furnace on Phosphatability of High-Strength Steel for Automobile

对含0.18%C、1.6%Si、2.2%Mn(质量分数)的汽车用高强钢板在露点为-40、-20、-10、-5、0和10℃的炉气氛中进行了830℃保温2 min后氢气冷却的退火,随后对钢板进行了磷化处理。采用辉光放电光谱仪、扫描电子显微镜和表面电位检测等方法研究了退火气氛露点对汽车用高强钢板磷化特性的影响。结果表明:随着退火气氛露点的提高,钢板的磷酸盐膜覆盖率上升,在露点≤-20℃的气氛中退火的钢板磷酸盐膜覆盖率仅为30%,而在露点≥0℃的气氛中退火的钢板磷酸盐膜覆盖率达90%以上;钢板表层形成Si、Mn氧化物是退火气氛露点提高时钢板磷化处理特性改善的重要原因。

High-strength steel plate with 0.18%C,1.6%Si and 2.2%Mn(by mass)for automobile was annealed by heating at 830℃for 2 min then hydrogen cooling in furnace atmosphere with dew points of-40,-20,-10,-5,0 and 10℃,and then was subjected to phosphate treatment.The effect of dew point of annealing atmosphere on phosphatability of the steel plate was investigated by means of glow-discharge spectrograph,scanning electron microscope and detection of surface potential.The results showed that(a)with the increase in dew point of annealing atmosphere,the coverage fraction of phosphate film on the steel plate increased,the coverage fraction of phosphate film was as little as 30%on the steel plate annealed in atmosphere with dew points not higher than-20℃,and was more than 90%on the steel plate annealed in atmosphere with dew points not lower than 0℃;and(b)the formation of Si and Mn oxides in the surface layer of steel plate proved to be a significant cause for improvement in phosphatability of the steel plate as the dew point of annealing atmosphere became higher.