As-cast microstructure and mechanical properties of Y12Cr18Ni9 free-cutting steel
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摘要: 以Y12Cr18Ni9易切削钢为研究对象，借助Factsage热力学计算软件、扫描电镜、Phenom Partical X扫描电镜-能谱仪对其铸态组织及力学性能进行研究。结果表明：Y12Cr18Ni9易切削钢中的平衡相主要有Liquid、MnS、δFerrite、Austenite、M23C6、Ferrite与Sigma。平衡凝固和冷却相变路径为：Liquid→Liquid+δFerrite→Liquid+δFerrite+Austenite→Liquid+δFerrite+MnS+Austenite→δFerrite+MnS+Austenite→MnS+Austenite→MnS+M23C6+Austenite→MnS+M23C6+Austenite+Ferrite→MnS+M23C6+Sigma+Austenite+Ferrite。试验钢中的硫化物呈球形、椭球形、纺锤形或短棒状并以簇状沿晶界分布，属于第Ⅱ类硫化物，长宽比≤3的硫化物占比达到了94.75%，尺寸≤3 μm的硫化物所占比例为80.22%，最大弦长≤3 μm的硫化物所占比例为76.02％。簇状硫化物会影响Y12Cr18Ni9易切削钢的力学性能，沿晶界分布的簇状硫化物是形成准解理面的主要原因。经室温拉伸及冲击试验测试，其抗拉强度、屈服强度、断后伸长率、断面收缩率和冲击功分别为597 MPa、233 MPa、17.7%、19.5%和21.8 J。
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关键词:
- Y12Cr18Ni9易切削钢 /
- FactSage软件 /
- 硫化物 /
- 力学性能 /
- 显微组织
Abstract: The as-cast structure and mechanical properties of Y12Cr18Ni9 free-cutting steel were studied by means of thermodynamic calculation software FactSage, SEM and Phenom Partical X SEM-EDS. The results show that the main equilibrium phases in Y12Cr18Ni9 free-cutting steel are Liquid, MnS, δFerrite, Austenite, M23C6, Ferrite and Sigma. The equilibrium phase transition path is as follows: Liquid→Liquid+δFerrite→Liquid+δFerrite+Austenite→Liquid+δFerrite+MnS+Austenite→δFerrite+MnS+Austenite→MnS+Austenite→MnS+M23C6+Austenite→MnS+M23C6+Austenite+Ferrite→MnS+M23C6+Sigma+Austenite+Ferrite. The sulfides in the test steel are spherical, ellipsoidal, spindle shape or short-bar-like, and distributed in clusters along the grain boundary, belonging to a type II sulfide. The proportion of sulfides with length-width ratio≤3 reaches 94.75%, the proportion of sulfides with size ≤3 μm is 80.22%, and the proportion of sulfides with maximum chord length ≤3 μm is 76.02%. The cluster sulfides affect the mechanical properties of Y12Cr18Ni9 free cutting steel. The cluster sulfides distributed along the grain boundary is the main reason for the formation of quasi cleavage surface. The tensile strength, yield strength, elongation after fracture, reduction of area and impact toughness of the steel are 597 MPa, 233 MPa, 17.7%, 19.5% and 21.8 J, respectively.-
Key words:
- Y12Cr18Ni9 free-cutting steel /
- FactSage software /
- sulfide /
- mechanical property /
- microstructure
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图 1 Y12Cr18Ni9易切削钢FactSage软件模拟平衡相图
Figure 1. Equilibrium phase diagram of Y12Cr18Ni9 free-cutting steel predicated by FactSage software
图 2 Y12Cr18Ni9易切削钢的平衡凝固及冷却相变路径
Figure 2. Phase transition path of the Y12Cr18Ni9 free-cutting steel during equilibrium solidification and cooling
图 3 规格为Ø230 mm的Y12Cr18Ni9易切削钢横截面低倍组织
Figure 3. Macrostructure of Ø230 mm Y12Cr18Ni9 free-cutting steel on cross-section
图 4 Y12Cr18Ni9易切削钢中典型硫化物SEM形貌及元素分布
Figure 4. The SEM micrograph(a) and element mapping(b~d) typical sulfides in the Y12Cr18Ni9 free-cutting steel
图 5 Y12Cr18Ni9易切削钢中硫化物长宽比分布
Figure 5. Distribution of length-width ratio of sulfides in the Y12Cr18Ni9 free-cutting steel
图 6 Y12Cr18Ni9易切削钢中夹杂物尺寸与最大弦长分布
Figure 6. Distribution of size and maximum chord length of sulfides in the Y12Cr18Ni9 free-cutting steel
图 7 Y12Cr18Ni9易切削钢铸态工程应力-应变曲线
Figure 7. Engineering stress-strain curves of the as-cast Y12Cr18Ni9 free-cutting steel
图 8 Y12Cr18Ni9易切削钢拉伸试样扫描断口形貌
Figure 8. Scanning fracture morphology of tensile specimen of the Y12Cr18Ni9 free-cutting steel
图 9 Y12Cr18Ni9易切削钢冲击试样扫描断口形貌
Figure 9. Scanning fracture morphology of impact specimen of the Y12Cr18Ni9 free-cutting steel
表 1 Y12Cr18Ni9易切削钢的化学成分
Table 1. Chemical composition of the Y12Cr18Ni9 free-cutting steel
% C Mn Si Ni Cr Mo Al P H O N S Sn Ca Mg Fe 0.035 1.83 0.273 7.79 16.24 0.198 0.0011 0.012 0.00047 0.0071 0.011 0.175 0.0036 <0.0005 <0.0005 Bal. 
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