铝含量对TWIP钢中夹杂物特征及AlN析出行为的影响

采用扫描电镜、X射线能谱仪以及扫描电镜配置的夹杂物自动扫描统计软件(INCAFeature)表征了Fe-Mn-C(-Al)系TWIP钢中夹杂物的成分、形貌和数量,考察了Al质量分数在0.002%~1.590%的四种TWIP钢中夹杂物的特征和Al含量对AlN析出行为的影响.并在此基础上,采用了适合TWIP钢中高锰高铝特点的热力学参数对AlN夹杂物进行了系统的热力学分析.研究表明,在含有相似N质量分数(0.0078%~0.0100%)的TWIP钢中,当钢中Al质量分数升高至0.75%时,AlN夹杂物开始在钢中析出,并在MnS(Se)-Al2O3上局部析出形成MnS(Se)-Al2O3-AlN复合夹杂;当Al质量分数升高至1.07%时,热力学计算表明AlN已经可以在TWIP钢液相中形成,经不断长大后在MnS(Se)夹杂物表面局部析出形成MnS(Se)-AlN复合夹杂物;在Al质量分数为1.59%的TWIP钢中,AlN的平衡析出温度比其液相线温度高出42 ℃,在液相中形成的AlN可以作为异质核心,MnS(Se)夹杂在其表面包裹形成MnS(Se)-AlN复合夹杂物.另外,在Fe-18.21%Mn-0.64%C-1.59%Al体系的TWIP钢中,AlN在液相中析出所需的最低氮的质量分数仅为0.0043%.因此,在TWIP钢的冶炼过程中,应尽可能的降低钢中的氮含量,避免生成过量的AlN夹杂.

Influence of Al content on the characteristics of non-metallic inclusions and precipitation behaviors of AlN inclusions in TWIP steel

The morphology, composition, and number of inclusions in Fe-Mn-C(-Al) twining-induced plasticity (TWIP) steels were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and an automated program called "INCAFeature." The characteristics of the inclusions in four TWIP steels with different Al contents (0.002%-1.590%) as well as the influence of Al content on the precipitation of AlN inclusions were investigated.In addition, systematic thermodynamics calculations of AlN formed in TWIP steel were carried out using the appropriate thermodynamic data for high-Mn-Al TWIP steel.The results show that AlN would begin to precipitate and locally precipitate around the MnS(Se)-Al2O3 inclusions when the Al content in the steel reaches 0.75%.The thermodynamics calculations show that AlN could already form in the liquid TWIP steel at an Al content of 1.07%.Then, AlN would locally precipitate around the MnS(Se) inclusions, thus forming MnS(Se)-AlN aggregates.When the Al content increases to 1.59%, the precipitation temperature of AlN is 42℃ higher than the liquidus temperature of the TWIP steel.Furthermore, precipitated AlN inclusions in the liquid TWIP steel could act as heterogeneous nuclei for MnS(Se) inclusions, thus forming MnS(Se)-AlN inclusions.Moreover, according to the thermodynamics calculation, the lowest N content for AlN formation in the liquid Fe-18.21%Mn-0.64%C-1.59%Al steel is just 0.0043%.Therefore, the N content should be kept as low as possible to avoid the formation of excessive AlN inclusions during melting of Fe-Mn-C(-Al) TWIP steel.