钇、锆对非调质钢中MnS及组织力学性能的影响

Effect of Y and Zr on MnS and microstructure and mechanical properties of non-quenched and tempered steel

MnS调控一直是高品质非调质钢开发的重点和难点。为改善钢中MnS形态和分布同时提高其力学性能,在实验室利用真空感应炉熔炼3炉试验钢,并对钢锭进行锻造,以研究Y、Zr对钢中夹杂物、显微组织及力学性能的影响。采用扫描电镜对铸态(A1~A3)和锻态(B1~B3)试样中夹杂物进行了统计分析;利用金相显微镜对锻态钢组织进行了观察;利用万能材料试验机和冲击试验机对试验钢性能进行了测试。结果表明,添加Y、Zr后,A2和A3铸态钢中夹杂物多为Ⅲ类和Ⅰ类MnS,平均直径为2.9μm和1.8μm。氧含量不是影响MnS形态和分布的主要因素,钢中生成的YAlO_(3)、Y_(4)Zr_(3)O_(12)与MnS具有较小晶格错配度,凝固过程中MnS易以氧化物为核心异质形核析出。以氧化物为核心的MnS在锻造过程中表现出良好的抗变形能力。Y、Zr合金化后,试验钢晶粒尺寸减小,晶内铁素体所占比例增加,平均晶粒尺寸由36.5μm(B1)降低至22.8μm(B2)和11.4μm(B3);晶内铁素体比例由2.4%(B1)提高至6.2%(B2)和11.1%(B3)。晶粒尺寸最小、晶内铁素体比例最高、MnS尺寸最小的B3钢具有最优的力学性能,其屈服强度为840 MPa,室温冲击功为52 J。研究结果为改善非调质钢中MnS和力学性能提供了理论参考。

The regulation of MnS has always been the focus and difficulty in the development of high-quality non-quenched and tempered steel.In order to improve the morphology and distribution of MnS in steel and enhance its mechanical properties,three furnaces of experimental steel were melted by vacuum induction furnace in the laborato-ry,and the ingot was forged to study the effects of Y and Zr on inclusions,microstructure and mechanical properties in steel.Inclusions in both as-cast(A1-A3)and as-forged(B1-B3)samples were quantified and analyzed via scanning electron microscopy.Microstructural examination of the forged steel was conducted using metallographic micro-scope.The mechanical properties of the experimental steel were assessed using universal material testing machine and impact testing machine.Results indicate that the addition of Y and Zr lead to class III and class I MnS inclusions in A2 and A3 as-cast steels predominantly,with average diameters of 2.9μm and 1.8μm,respectively.The oxygen content is not the primary determinant of MnS morphology and distribution in the steel.YAlO and Y,Zr Oi2 formed within the steel exhibit a slight lattice disregistries with MnS,facilitating heterogeneous nucleation and pre-cipitation with oxide as the core during solidification.MnS with oxide as the core demonstrates enhanced deforma-tion resistance during forging.Following Y and Zr alloying,the experimental steel experiences reduced grain size,heightened intragranular ferrite proportion,with average grain sizes decreasing from 36.5μm(B1)to 22.8μm(B2)and 11.4μm(B3).Intragranular ferrite proportion increases from 2.4%(B1)to 6.2%(B2)and 11.1%(B3).