含钛齿轮钢中CaO-Al2O3-TiOx+TiN系夹杂物形成机理

Formation mechanism of CaO-AlO-TiO+TiN system inclusions in Ti-bearing gear steel

为了研究20CrMnTi齿轮钢中特殊夹杂物(CaO-Al2O3-TiOx包裹TiN的复合夹杂物)的形成机理,结合工业试验和实验室合金化试验,借助热力学计算推断了TiN直接生成的可能性。研究发现,钛铁合金的洁净度较差,合金中含有较多的Al2O3和TiN夹杂物。在炼钢温度条件下,钢中的溶解钛与氮反应生成TiN在热力学上是不可能的。复合夹杂物的TiN核不可能是由钢中的溶解钛和氮直接反应生成,而应该是由合金带入的。当CaOAl2O3-TiOx系夹杂物与未溶解完全的TiN碰撞到一起后,液态的夹杂物将TiN包裹,从而形成较大尺寸的CaOAl2O3-TiOx包裹TiN的夹杂物。要控制这类夹杂物,需采用氮质量分数更低的钛铁合金。

Industrial and laboratory experiments were carried out to investigate the formation mechanism of a special kind of complex inclusions(TiN surrounded by CaO-Al2O3-TiOx)in 20CrMnTi gear steel,and thermodynamic calculations were also conducted to check the possibility of the formation of TiN by the dissolved elements in the liquid steel.It is found that Ti-Fe alloy has poor cleanliness and contains many Al2O3 and TiN inclusions.At the steelmaking temperature,the reaction of dissolved Ti and N in steel to form TiN is thermodynamically impossible.The TiN core of the complex inclusions cannot be generated by the direct reaction between dissolved Ti and N in the steel but should be sourced from the Ti-Fe alloy.When the liquid CaO-Al2O3-TiOx inclusions collide with the undissolved TiN,TiN inclusions would be wrapped by the liquid inclusions,thus forming larger CaO-Al2O3-TiOx inclusions with a TiN core inside.Ti-Fe alloys with lower nitrogen content are suggested to control these inclusions.