M50NiL钢中的δ-铁素体分布及其对强韧性的影响

Distribution ofδ-ferrite in M50NiL steel and its effect on strength and toughness

M50NiL轴承钢强韧性能特征与显微组织演变规律的研究结果表明,钢的显微组织由马氏体基体、残留奥氏体、碳化物和δ-铁素体所构成,其中δ-铁素体的面积分数在0.01%~0.125%之间;钢中Mo、V、Cr合金原子置换Fe原子固溶后,产生晶格畸变并提高内应力,δ-铁素体的硬度最高值为4.84 GPa,弹性模量的最高值为236.9 GPa。在冲击载荷作用下,冲击变形速度约为5 m·s^(-1),钢中δ-铁素体界面产生应力集中,导致δ-铁素体破碎且裂纹沿δ-铁素体界面扩展,降低钢的冲击性能,冲击吸收能量在47 J以上的试样缺口附近存在较少的小尺寸δ-铁素体相,形成宽度为600~1600μm的韧窝条带的断口形貌。在拉伸载荷的作用下,拉伸变形速度约为8μm·s^(-1),钢的基体与δ-铁素体界面经过协调塑性变形释放应力使得δ-铁素体形态、数量及分布对拉伸性能的影响不明显。

The study on the characteristics of strength and toughness and the evolution of microstructure of M50NiL bearing steel shows that the microstructure of the steel consists of martensite matrix,retained austenite,carbide andδ-ferrite,and the area fraction ofδ-ferrite is 0.01%-0.125%.After Mo,V,Cr alloy atoms in the steel replace Fe atoms for solid solution,lattice distortion will occur and internal stress will be increased.The maximum hardness ofδ-ferrite is 4.84 GPa,and the maximum elastic modulus is 236.9 GPa.Under the impact load,the impact deformation speed is about 5 m·s^(-1),and the stress concentration occurs at the interface ofδ-ferrite in the steel,resulting in the breaking ofδ-ferrite and the crack propagation along the interface ofδ-ferrite,and reducing the impact property of the steel;there are fewer small sizedδ-ferrite phases near the notch of the sample with impact absorption energy above 47 J,and the fracture morphology with a dimple band 600-1600μm wide is formed.Under the tensile load,when the tensile deformation rate is about 8μm·s^(-1),the steel matrix andδ-ferrite interface release stress through coordinated plastic deformation,so that the shape,quantity and distribution ofδ-ferrite have no obvious effect on the tensile properties of the steel.