硅铁合金中金属钙元素对铝脱氧钢中夹杂物的影响

Effect of calcium in ferrosilicon alloys on inclusions in Al-killed steel

大尺寸CaO‒Al_(2)O_(3)类夹杂物容易引起轴承钢疲劳失效,大尺寸CaO‒Al_(2)O_(3)类夹杂物的控制是生产高端GCr15轴承钢的关键因素之一.精炼过程中合金引入杂质元素、渣精炼和精炼过程中卷渣是铝脱氧轴承钢中大尺寸CaO‒Al_(2)O_(3)类夹杂物的主要潜在来源.硅铁合金通常用来提高轴承钢的淬火和抗回火软化性.本文通过实验室实验、样品分析和热力学计算,研究了硅铁合金中金属钙元素对铝脱氧钢中夹杂物的影响.硅铁合金主要由深色的硅相和浅色的硅铁相组成,钙元素在硅相和硅铁相的界面处以金属化合物形式存在.研究发现,加入硅铁合金后,钢中总钙(T.Ca)含量增加,钢中的Al_(2)O_(3)和MgO·Al_(2)O_(3)夹杂物被改性为CaO‒Al_(2)O_(3)类夹杂物,夹杂物尺寸随着夹杂物中CaO含量增加而减小,钢中并未生成大尺寸CaO‒Al_(2)O_(3)类夹杂物.随着钢中T.Ca含量增加,夹杂物平均尺寸降低,钢中T.O含量增加,表明硅铁合金中金属钙元素不会直接引起钢中大尺寸CaO‒Al_(2)O_(3)类夹杂物的生成.但是生成的小尺寸固相CaO‒Al_(2)O_(3)类夹杂物在水口处粘附结瘤,结瘤物脱落后会成为钢中大尺寸CaO‒Al_(2)O_(3)类夹杂物的来源之一.

Large CaO‒Al_(2)O_(3)-type inclusions easily induce fatigue failure of bearing steels,so controlling large CaO‒Al_(2)O_(3)-type inclusions is the key to producing high-quality GCr15-bearing steel.Impurity elements in alloys added during refining,slag refining,and slag entrainment during the refining process are the main potential sources for forming large CaO‒Al_(2)O_(3)-type inclusions in Al-killed bearing steels.The ferrosilicon alloy is applied to improve the quenching and tempering softening resistance of Al-killed bearing steels.In this work,the effect of the calcium element in ferrosilicon alloys on inclusions in Al-killed bearing steel was studied through laboratory experiments,observations,and thermodynamic calculations.The ferrosilicon alloy mainly consists of the dark silicon and light ferrosilicon phases.The calcium element in ferrosilicon alloys exists as a metal compound at the interface between the silicon phase and the ferrosilicon phase.The total calcium(T.Ca)content in molten steel increases after adding the ferrosilicon alloy and modifying the Al_(2)O_(3)and MgO·Al_(2)O_(3)inclusions into CaO‒Al_(2)O_(3)-type ones.The size of inclusions in the molten steel decreases with an increase in the CaO content in the inclusions.Large CaO‒Al_(2)O_(3)-type inclusions are rarely generated.With the increase of the T.Ca in the molten steel,the T.O in the steel increases,whereas the average size of the inclusions decreases.It was observed that the calcium element in ferrosilicon alloys is not the direct cause for the formation of large size CaO‒Al_(2)O_(3)inclusions in the steel.However,the generated small,solid CaO‒Al_(2)O_(3)-type inclusions clog the wall of the submerged entry nozzle,leading to dislodging of the big clogging lump into the molten steel.This lump is one of the reasons for large and irregularly shaped CaO‒Al_(2)O_(3)type inclusions in the steel product.