钙处理对DZ2高速铁路车轴钢中夹杂物的影响

Effect of calcium treatment on inclusions in DZ2 high-speed railway axle steel

采用钙处理来改善铝脱氧DZ2高速铁路车轴钢在连铸过程中的可浇性。为此,向钢中添加不同含量的钙,并利用扫描电镜(SEM)和能谱分析仪(EDS)观察和统计冶炼过程和连铸坯中夹杂物的形貌、类型和尺寸,通过这些观察和统计结果研究钢中夹杂物的演变规律以及钙含量对夹杂物的影响。研究表明,低喂钙量钢A和高喂钙量钢B的冶炼过程中夹杂物的演变规律大致相同。从LF结束到中间包这一阶段中,夹杂物由低CaO含量的Al_(2)O_(3)-CaO-MgO类夹杂物逐渐转变为高CaO含量的CaO-Al_(2)O_(3)-MgO类夹杂物,但是在钢B的中间包中还存在较多的CaO类夹杂物。在钢A的连铸坯中,夹杂物主要为在钢液降温和凝固过程中形成的小尺寸、低CaO含量的Al_(2)O_(3)-CaO-MgO类夹杂物,只存在少量来源于精炼过程中的大尺寸(>10μm)、高CaO含量的CaO-Al_(2)O_(3)-MgO类夹杂物。而在钢B的连铸坯中,夹杂物主要为钙处理后形成的CaO类夹杂物,且这些夹杂物的尺寸较大。在钢A和钢B中,夹杂物的类型和尺寸存在差异的原因与钢中钙含量有关。只有合理的钙含量才能将钢中的Al_(2)O_(3)类夹杂物改质为纯液态夹杂物,过高的钙含量会导致CaO和CaS类固态夹杂物的出现。FactSage热力学软件的计算结果表明,在DZ2车轴钢中,钙处理时钢中的最佳钙质量分数为0.0005%~0.0018%。需要谨慎地进行钙处理来确保钢液的可浇性,同时也需要优化冶金工艺来去除钙处理后以及在其他精炼阶段形成的大尺寸液态CaO-Al_(2)O_(3)-MgO类夹杂物。

Calcium treatment is employed to enhance the castability of aluminum-deoxidized DZ2 high-speed railway axle steel during continuous casting.Through the introduction of varied Ca content into steel,scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS)are employed to scrutinize and count the morphologies,types,and sizes of inclusions in the smelting procedure and continuous casting billet.This endeavor aims to investigate the evolution patterns of inclusions and the effect of Ca content on the inclusions.Research indicates that the evolution patterns of inclusions during the smelting process exhibit a general similarity between low calcium feeding Steel A and high calcium feeding Steel B.From LF end to the tundish,the inclusions undergo a progressive transformation from Al_(2)O_(3)-CaO-MgO with diminished CaO content to compositions characterized by elevated CaO content,specifically CaO-Al_(2)O_(3)-MgO.Nonetheless,a notable emergence of CaO persists in the inclusions within the tundish of B.In the continuous casting billet of Steel A,the inclusions are mainly small-sized,low-CaO-content Al_(2)O_(3)-CaO-MgO formed during the cooling and solidification process of the molten steel.The large-sized(>10μm)CaO-Al_(2)O_(3)-MgO inclusions,characterized by elevated CaO content,are present in only modest quantities.In the continuous casting slab of Steel B,the prevailing inclusions primarily consist of CaO induced by calcium treatment,exhibiting a larger size.The difference in the type and size of inclusions in the continuous cast slabs of Steel A and Steel B is intricately tied to the Ca content in the steel.Only a rational Ca content has the capacity to modify Al_(2)O_(3) inclusions into purely liquid states.Excessive Ca content,however,leads to the emergence of solid inclusions,such as CaO and CaS.The calculation results from FactSage thermodynamic software reveal that the optimal Ca content for DZ2 axle steel,following calcium treatment,falls within the range of 0.0005%to 0.0018%.Prudent application of calcium treatment is imperative to secure the castability of molten steel.Furthermore,it is essential to optimize the metallurgical processes to eliminate large-sized liquid CaO-Al_(2)O_(3)-MgO inclusions formed after calcium treatment and during other refining stages.