20CrMnTiH1齿轮钢中CaS夹杂的形成与控制

Formation and control of CaS inclusion in gear steel 20CrMnTiH1

利用Factsage软件,对20CrMnTiH1齿轮钢中(CaO)m(Al2O3)n与CaS夹杂形成进行了热力学分析。结果表明:当钢中w(Al)S=0.035%时,要使钢中夹杂物完全转变为液态(CaO)12(Al2O3)7,应控制钢中w(S)低于0.006 7%,w(Ca)/w(Al)高于0.12;本钢液成分条件下,在炼钢温度下不会自发生成CaS夹杂,当钢液温度下降到1 739.8 K时,凝固前沿的w(S)达到0.015 9%,此时会与低熔点(CaO)12(Al2O3)7夹杂表面的CaO反应析出CaS夹杂。通过对某钢厂生产的20CrMnTiH1齿轮钢铸坯中夹杂物的检验发现,实际情况与热力学计算相符合。同时,通过硫偏析方程计算得到:20CrMnTiH1齿轮钢在凝固过程中不析出CaS夹杂的条件为将硫的初始质量分数控制在0.000 318%以下。

The themodynamic analysis on formation of （A1203）m （CaO）, and CaS inclu- sions in gear steel 20CrMnTiH1 using the Factsage. The result shows that when the mass fraction of solute aluminium is 0. 035 %, the mass fraction of sulfur is lower than 0. 006 7 G and the value of w（ Ca） /w（A1） is higher than 0. 12, the liquid approximate （CAO）12 （A1203）7 inclusions will produce in the molten steel. The calcium sulfide inclu- sions can not be produced inself in molten steel under the condition of this composition experimental steel. The CaS inclusions are precipitated by the reaction of sulfur with CaO of the surface layer of lower melting pointing （CaO）12 （A1203）7 inclusions with the temperature of molten steel drop to 1 739. 8 K and the sulfide content reached 0. 015 9 % at the frontier of solidification. With analysis of the steel sample,it is found that the result is consistent with theoretical calculations. It is obtained by calculation that the mass fraction of sulfur must be controlled below 0. 000 318% when the gear steel 20CrMnTiH1 can not precipitate CaS inclusion in solidification processing.