钙处理对20CrMnTiH齿轮钢中非金属夹杂物的影响

Effect of calcium treatment on nonmetallic inclusions in 20CrMnTiH gear steel

铝脱氧齿轮钢中易生成大量的高熔点Al2O3类夹杂物,容易导致水口结瘤及钢材性能恶化,目前较常采用钙处理将钢中高熔点的Al2O3类夹杂物改性为低熔点的钙铝酸盐类夹杂物.合理的钙处理可以减轻水口结瘤并提高连铸过程钢液的可浇性,工业试验研究了喂钙前钢液中T.Ca含量、喂钙速度、喂钙量、净空高度及渣厚等参数对齿轮钢中钙收得率的影响,并在1.5 m·s^(−1)的喂钙速度条件下研究了不同喂钙量对钙处理过程中齿轮钢中非金属夹杂物改性的影响.研究结果表明,当喂钙前钢液中T.Ca的质量分数小于10×10^(−6),喂钙速度为1.5 m·s^(−1),适当降低喂钙量和净空高度和渣厚,钢液中钙收得率均高于20%.当钢液中T.Ca的质量分数高于17×10^(−6)时,钢中生成大量高熔点CaS型夹杂物,三元相图中夹杂物的平均质量分数远离液相区.随着齿轮钢中T.Ca含量的增加,夹杂物的平均尺寸和数密度逐渐增加.热力学计算结果与工业试验钙处理对钢中非金属夹杂物改性效果具有较好的一致性.

Obtaining high-quality gear steel calls for strict requirements on the oxygen content,shape,composition,size,and distribution of nonmetallic inclusions to ensure high-quality steel and castability of the molten steel during the continuous casting process.Al_(2)O_(3) inclusions with high melting point are easily generated in Al-deoxidized gear steel,and they easily result in nozzle clogging and deterioration in the properties of the steel.A reasonable calcium treatment can reduce the nozzle clogging and increase improving the castability of the molten steel,and thus it has been widely used in steel plants.Calcium treatment is often used to convert Al_(2)O_(3) inclusions with high melting point to calcium aluminate with low melting point.The factors of calcium treatment on nonmetallic inclusions in gear steel were investigated through industrial trials.The dependency of calcium yield on various factors,namely,the amount of calcium addition,feeding speed of calcium wire,and feeding position and slag thickness were discussed.The effect of the amount of calcium addition on nonmetallic inclusions in the molten steel was studied at a feeding rate of 1.5 m·s^(−1).With the initial mass fraction of T.Ca lower than 10×10^(−6) in the steel and a feeding rate of 1.5 m·s^(−1),the calcium yield can be higher than 20%if the amount of calcium addition,clearance height,and slag thickness during the refining process are appropriate.Large numbers of nonmetallic CaS inclusions with high melting point are formed in the molten steel with the mass fraction of T.Ca higher than 17×10^(−6),and the inclusions are formed far away from the liquidus region.With increase in the T.Ca content in the steel,the average size and number density of the nonmetallic inclusions gradually increase.The effect of calcium treatment on the modification of nonmetallic inclusions studied by thermodynamic calculation results agrees well with the measurements taken via industrial trials.