车轴钢铸锭中MnS的生成、长大、熟化规律分析

 为降低大尺寸MnS夹杂物引起的车轴磁粉探伤不合格率,利用第二相析出理论以及铸锭凝固数值模拟计算相结合,计算分析了车轴钢铸锭中MnS生成、长大、熟化规律。计算结果显示,MnS形核核心尺寸与熟化过程尺寸增加均为纳米级,凝固过程MnS的长大决定凝固完成时MnS粒子直径,理论计算得到车轴钢铸锭竖直中心线上冒口、中心、底部位置对应的MnS长大后尺寸分别为156.35、107.37和94.96 μm,中心处MnS尺寸为连铸工艺条件下的2倍,与实际检测结果相符。钢锭凝固过程缓慢是MnS易于长大的直接原因,显著区别于连铸过程。在现有工艺条件下,为控制车轴钢模铸钢MnS尺寸,关键在于降低钢液硫质量分数以及控制硫偏析。控制车轴成品中MnS夹杂物不超过1.5级,需降低钢液中w(S])至0.004 3%以下。

Nucleation,growth and maturation analysis of MnS during solidification in axle steel ingots

To reduce the non-compliance rate of magnetic particle detection of axles caused by large-size MnS inclusions, the formation, growth, and maturation of MnS in ingot of axle steel were calculated and analyzed based on the second phase precipitation theory and the numerical simulation of ingot solidification. The calculation results show that both the core size of the MnS nucleus and the size increase during the maturation process are in the nanometer. The growth of MnS throughout the solidification process determines the diameter of MnS particles after solidification. The theoretical calculation results show that in the riser, center, and bottom of the vertical center-line of the ingot, the corresponding MnS grew to a size of 156.35,107.37 and 94.96 μm, respectively, which is twice the size of MnS in continuous casting slab and consistent with the practice. The slow solidification process of the ingot is the direct cause of easy MnS growth, which is significantly different from the continuous casting process. Under the existing process conditions, in order to control the MnS size in axle steel ingot, it is critical to reduce the S content of the molten steel and control the S segregation. In order to control the MnS inclusions in the finished product of the axle not exceeding 1.5 grades, it is necessary to reduce w(S]) of the molten steel to below 0.004 3%.