Abstract: Due to its low cost, environmental protection, and excellent machinability, graphite free-cutting steel has attracted extensive attention from metallurgical and materials scholars at home and abroad in recent years. In this work, the effects of two kinds of carbon content (0.20wt% and 0.52wt%) on the microstructure changes of 1.9wt%Si-1.1wt%Al high-silicon and high-aluminum steel during hot-rolling, quenching-tempering process and the precipitation behavior of graphite particles after tempering were studied by metallography microscope, scanning electron microscope and energy spectrum analyzer. The results showed that the microstructure of 0.20wt%C experimental steel after hot rolling→quenching→tempering was transformed into ferrite+pearlite→ferrite+"island" bainite→ferrite+graphite particle+a small amount of cementite. The microstructure of the experimental steel at 0.52wt% C after hot rolling→quenching→tempering changes to ferrite+pearlite→martensite→ferrite+graphite particles+a small amount of cementite. At the same tempering temperature, the quantity and size of graphite particles in 0.52wt% C experimental steel are larger and more precipitated in grain boundary nucleation mode than that in 0.20wt% C experimental steel. When the tempering temperature increased from 680℃ to 710℃, the density of graphite particles precipitated on the grain boundary of 0.20wt% C steel decreased from 2337/mm2 to 1710/mm2, and the average size increased from 1.50 μm to 2.27 μm. At 0.52wt% C, the density of precipitated graphite particles at the grain boundary of the experimental steel decreased from 5244/mm2 to 1938/mm2, and the average size increased from 2.36 μm to 3.45 μm. The increase of carbon content from 0.20wt% to 0.52wt% can effectively promote the nucleation and growth of graphite particles in the tempering process. Compared with the tempering at 710℃, the number of graphite particles in the tempering at 680℃ is more and the distribution is more uniform, which is more conducive to the improvement of the overall machinability of the experimental steel.

Key words: carbon content, high silicon high aluminum steel, tempering temperature, graphite particle, grain boundary nucleation

摘要： 石墨易切削钢因具有低成本、环保及优良可切削性等优点，近年来引起了国内外冶金和材料学者的广泛关注。本工作采用金相显微镜、扫描电镜和能谱分析仪等方法，系统研究了两种碳含量(0.20wt%和0.52wt%)对1.9wt%Si-1.1wt%Al高硅高铝钢热轧-淬火-回火过程组织变化及回火后石墨粒子析出行为的影响。结果表明，0.20wt% C的实验钢热轧→920℃淬火→回火后的组织演变为铁素体+珠光体→铁素体+“小岛”状贝氏体→铁素体+石墨粒子+少量渗碳体，而0.52wt% C的实验钢热轧→920℃淬火→回火后的组织演变为铁素体+珠光体→马氏体→铁素体+石墨粒子+少量渗碳体。在相同回火温度下，相比0.20wt% C的实验钢，0.52wt% C的实验钢中石墨粒子的数量更多、尺寸更大且更多以晶界形核方式析出。当回火温度从680℃提高至710℃，0.20wt% C的实验钢晶界上析出的石墨粒子密度从2337个/mm2降至1710个/mm2，其平均尺寸从1.50 μm增大至2.27 μm；0.52wt% C的实验钢晶界上析出的石墨粒子密度从5244个/mm2降至1938个/mm2，其平均尺寸从2.36 μm增大至3.45 μm。钢中碳含量从0.20wt%增加至0.52wt%，可有效促进实验钢回火过程石墨粒子的形核和长大。相比710℃回火，680℃回火后的实验钢中石墨粒子数量更多且分布更为均匀，更有利于其整体切削性能的提高。

关键词: 碳含量, 高硅高铝钢, 回火温度, 石墨粒子, 晶界形核