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采用水平连续铸造工艺制备了矩形截面120 mm×100 mm灰铁型材,对比研究了不同温度奥氏体化对正火组织与性能的影响.结果表明,该灰铁型材表层10 mm处为D型石墨,1/2R为E型石墨,心部为A型石墨,基体中的珠光体分别为5％,15％和15％.880、900和920 ℃分别保温2h后出炉空冷的正火组织,表层10 mm处珠光体含量均接近80％;1/2R处的珠光体含量分别为40％ 、50％和60％;心部的珠光体含量分别为30％、40％和50％.铸态表层硬度为92 HRB,1/2R处和心部硬度低于表层,硬度差为6.4 HRB,正火热处理能够提高灰铁型材心部力学性能,降低不同部位的硬度差和拉伸强度差.正火温度越高,越有利于石墨片附近获得高碳奥氏体,有利于珠光体的形成,有利于灰铁型材断面组织与性能均匀性的提高.920℃×2 h正火,表层的拉伸强度超过350 MPa,断面性能均匀性得到提高,表层和心部的拉伸强度差仅为30 MPa.

Rectangular section of 120 mm× 100 mm gray cast iron bars were prepared by the horizontal continuous casting (HCC) method,and the effect of different austenitizing temperature on microstructure and properties of the normalizing sample was studied.The results show that the typical flake graphite microstructure is type D in the distance of 10 mm from surface,type E in the distance of 1/2R and type A in the center,and the contents of pearlite in the matrix are 5％,15％ and 15％,respectively.After normalizing at 880 ℃,900 ℃ and 920 ℃ for 2 h and cooling in air,the contents of pearlite in the distance of 10 mm from surface are all close to 80％,and those are 40％,50％ and 60％ in the 1/2R,and 30％,40％ and 50％ in the center,respectively.The hardness of as-cast HCC gray iron bars in the surface is 92 HRB,and is 6.4 HRB higher than that of in the 1/2R and center.Normalizing can improve the center mechanical properties of the HCC gray iron bars,and reduce the difference of hardness and tensile strength in the different parts of the bars.Increasing the normalizing temperature,it is more conducivc to obtain high carbon austenite close to the flake graphite,and the formation of pearlite is easy,and the section uniformity of the microstructure and properties of HCC gray iron bars are improved.After normalizing at 920 ℃ for 2 h,the tensile strength of the HCC gray iron bars in the surface is over 350 MPa,and the section uniformity is also improved,and the difference of tensile strength is only 30 MPa between the surface and the center.