Effect of bismuth content on the microstructure and properties of free cutting steels
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摘要: 含铋环保型易切削钢具有广阔应用前景。通过制备铋锰铁合金将铋合金化，再在真空感应熔炼过程中将铋锰铁合金加入钢液，浇铸并热轧变形，获得三种含铋易切削钢。研究铋含量对钢中第二相、钢材力学性能和切削性能的影响。结果表明，随着铋含量由0.013%增加至0.069%，钢中MnS第二相的尺寸下降约45%，外形由杆状向球状转变；钢材的屈服强度、基体和第二相的硬度以及冲击功降低，抗拉强度小幅增加，延伸率大幅度提升，钢材的综合力学性能略有降低；切削试验表明，铋含量的增加，使铣削刀具的磨损显著减小，钢材表面平整度和光洁度增加，切屑由长带状向短螺旋状转变，碎断程度提高，切削性能显著改善。Abstract: The bismuth-containing free-cutting steel served as an environment-friendly material has a broad application prospect. Bismuth was alloyed by preparing bismuth ferromanganese alloy, which was then added to the molten steel in the process of vacuum induction melting. After casting the melt and hot rolling, three kinds of bismuth-containing free cutting steels were obtained. The effect of bismuth content on the second phase, mechanical properties and cutting properties of steels was studied. With the increase of bismuth content from 0.013% to 0.069%, the size of MnS decreased by about 45% and the shape changed from rod to ball. The yield strength, the hardness of matrix and second phase, and the impact energy of the steels decreased. The tensile strength increased slightly, and the elongation of the experimental steel increased greatly. The comprehensive mechanical properties of the steel decreased slightly. The results of cutting experiments showed that with the increase of bismuth content, the wear of milling tools decreased significantly; the surface flatness and smoothness of the steels increased; the chip shapes changed from long strip to short spiral; the chip breakage degree was greater; and the cutting performance was significantly improved.
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Key words:
- free cutting steel /
- bismuth /
- manganese sulfide /
- machinability /
- mechanical property
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图 1 三种钢中第二相的显微形貌
(a) 1#钢; (b) 2#钢; (c) 3#钢
Figure 1. Microstructure of inclusions in three kinds of steels
图 2 三种钢中第二相的面积、当量直径及长宽比的标准化频率
(a) 面积；(b) 当量直径；(c) 长宽比
Figure 2. Standardized frequencies of area, equivalent diameter and length width ratio of inclusions in three experimental steels
图 3 三种钢组织中第二相的SEM形貌
(a) 1#钢; (b) 2#钢; (c) 3#钢
Figure 3. Morphology of inclusions in three kinds of steels
图 4 第二相形貌及EDS能谱分析结果
(a) 显微组织; (b)、(c) EDS能谱
Figure 4. Inclusion morphology and EDS energy spectrum analysis results
图 5 钢中第二相的背散射图像和元素面扫描
(a) 背散射电子像; (b) Bi元素; (c) Mn元素; (d) S元素
Figure 5. Backscattering images of inclusions and surface scanning of elements in the experimental steels
图 6 MnS的三维形貌
(a) 球形; (b) 杆棒状; (c) 纺锤体形; (d) 长条状
Figure 6. Three dimensional morphology of MnS
图 7 Bi-MnS的三维形貌
(a) 1#钢; (b)、(c) 2#钢; (d) 3#钢
Figure 7. Three dimensional morphology of Bi-MnS
图 9 三种钢室温拉伸断口形貌
(a)、(b) 1#钢; (c)、(d) 2#钢; (e)、(f) 3#钢
Figure 9. Tensile fractography of three kinds of steels at room temperature
图 10 三种钢的冲击断口形貌
(a、b) 1#钢; (c、d) 2#钢; (e、f) 3#钢
Figure 10. Impact testing fractography of three kinds of steels
图 11 三种钢铣削后刀具的显微形貌
(a)、(b)、（c) 刀具1; (d)、(e)、(f) 刀具2; (g)、(h)、(i) 刀具3；其中(b)、(e)、(h)为刀具的边部，(c)、(f)、(i)为刀具的角部
Figure 11. Micromorphology of tools after milling by three kinds of steels
图 12 三种钢切削试验后工件表面的二维和三维形貌
(a)、(b) 1#钢; (c)、(d) 2#钢; (e)、(f) 3#钢
Figure 12. Two-dimensional and three-dimensional morphology of workpiece surface after cutting experiments of three kinds of steels
图 13 三种钢不同粗糙度参数值的变化曲线
Figure 13. Variation curves of different roughness parameter values in three kinds of steels
图 14 三种钢的切屑照片
(a) 1#钢; (b) 2#钢; (c) 3#钢
Figure 14. Photos of three kinds of steel chips
表 1 含铋易切削钢的实际化学成分
Table 1. Actual chemical compositions of the bismuth containing free cutting steels
% 钢种编号 C Si Mn S P Bi Fe 1# 0.063 0.010 1.07 0.28 0.052 0.013 Bal 2# 0.070 0.014 1.14 0.30 0.057 0.034 Bal 3# 0.067 0.017 1.15 0.28 0.058 0.069 Bal 
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