School of Materials Science and Engineering, Nanchang University, Nanchang 330031
Cite this article:
XUE Yingyu, TANG Jiancheng, ZHUO Haiou, YE Nan, WU Tong, ZHOU Xusheng. MICROSTRUCTURES AND PROPERTIES OF LEAD-FREE FREE-CUTTING GRAPHITE-BRASS PREPARED BY GRAPHITIZATION OF CEMENTITE. Acta Metall Sin, 2015, 51(2): 223-229.
Graphite is believed to be an attractive candidate substituting for lead to produce free-cutting brasses, because of its lubricating property and the role in chip breaking. The major hindrances of developing graphite-brass are the large density difference and nonwetting characteristic between graphite and copper. In this work, eutectic cast iron (ECI) was added into brasses instead of other form of carbon source. Cementite particles were in situ formed during casting, then annealing treatment was conducted to facilitate the graphitization of cementite particles, and finally uniformly dispersed graphite particles with the size of 3~6 mm were obtained in brass alloys. SEM and EDS observation indicate that the microstructures of the graphite-brass are refined with the cast iron content increased from 1% to 7%. The tensile strength and microhardness are increased, and the chip morphologies are improved gradually with the cast iron content increased from 1% to 7%. However, the graphite brass with 7% addition shows suboptimal chip morphologies because of the segregation of graphite particles. The chips of graphite brasses with 5% addition are desired, which are short and discontinuous. Its tensile strength, elongation and Vickers hardness are 502.00 MPa, 22.6% and 148.9 HV, respectively. The graphite brass shows comparable machinability to conventional lead brass HPb59-1。
Fig.1 SEM images of as-cast (a) and annealed (b) brass added with 5% eutectic cast iron (ECI) and EDS corresponding to points i (c), ii (d), iii (e) and iv (f) in Figs.1a and b
Fig.2 Schematics of solidification and annealing of graphite-brass (L—liquid)
Fig.3 SEM images of annealed graphite-brass added with 1% (a), 3% (b), 5% (c) and 7% (d) ECIs
Fig.4 Particle size distributions of graphite in annealed graphite-brass added with different ECIs
ECI / %
sb / MPa
s0.2 / MPa
d / %
Hardness / HV
1
432.36
212.07
27.5
134.5
3
468.66
238.60
22.7
140.7
5
502.00
249.00
19.2
148.9
7
543.31
276.38
16.8
168.3
HPb59-1[27]
≥440
≥10
Table 1 Mechanical properties of annealed graphite-brass added with different contents of ECIs and HPb59-1
Fig.5 The chips morphologies of annealed graphite-brass added with 1% (a), 3% (b), 5% (c) and 7% (d) ECIs
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