Service Performance of ER8C and ER8 Wheels for High-Speed Electric Multiple Unit
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摘要:
为全面掌握高速动车组用ER8C和ER8车轮服役性能，使用OBLFQSN750型电火花直读光谱仪等设备分别实测了新旧车轮材料的化学成分、常规力学性能、疲劳特性、冲击性能及韧脆转变温度、断裂韧性、疲劳裂纹扩展门槛值和疲劳裂纹扩展速率等，并进行了金相组织观测，综合评价分析了两种材质车轮服役性能. 结果表明：1） ER8C材质车轮比ER8材质车轮中Si含量高2.74倍，Mn含量高1.29倍，Cr+Mo+Ni总含量低45%，C含量略低，其抗拉强度和屈服强度提高5%，疲劳强度提高15%. 2） 车轮显微组织为珠光体+少量铁素体，踏面下相同深度，ER8C材质车轮中铁素体更均匀细小，晶粒度大于8.5级，ER8材质车轮铁素体粗大，晶粒度为8级. 3） ER8C材质车轮韧脆转变温度为84.30 ℃，ER8材质车轮韧脆转变温度为71.97 ℃，车轮运用工况处于两种材质的脆性区. 4） ER8C材质车轮断裂韧性比ER8材质车轮高约6%，其阻止裂纹产生的能力优于ER8材质车轮；ER8材质车轮裂纹扩展门槛值比ER8C材质高17%，其阻止裂纹扩展的能力优于ER8C材质车轮；两种材质车轮的裂纹扩展速率相当. 5） 服役过程中ER8C材质车轮踏面垂直磨耗速率略大于ER8材质车轮.
Abstract:In order to fully understand the service performance of ER8C and ER8 wheels for high-speed electric multiple units (EMUs), the chemical composition, the conventional mechanical properties, the fatigue properties, the impact properties, the ductile-brittle transition temperature, the fracture toughness, the fatigue crack growth threshold, the fatigue crack growth rate and etc of in-serving and over-served wheels materials were measured by electric spark direct reading spectrometer(OBLFQSN 750). The metallographic structure of the both wheels materials was analyzed,and the service performance of the both wheels were assessed. The results show as follows: 1） Compared with the ER8 wheel, the ER8C wheel has 2.74 times higher Si content, 1.29 times higher Mn content, 45% lower total Cr + Mo + Ni content and slightly lower C content; their tensile and yield strengths have increased by 5%, and their fatigue strength has increased by 15%. 2）The microstructure of the wheels contains pearlite and a small amount of ferrite, the same depth under the tread, the ferrite in the ER8C wheel is more uniform and fine, the grain size is greater than 8.5, and the ferrite wheel in the ER8 material is coarse and the grain size is grade 8. 3) The ductile-brittle transition temperature of the ER8C wheel is 84.30 ℃ and that of the ER8 wheel is 71.97 ℃. The working condition of wheels is in the brittle zone of two materials. 4) The fracture toughness of the ER8C wheel is about 6% higher than that of the ER8 wheel. However, the crack propagation threshold of the ER8 wheel is 17% higher than that of the ER8C wheel, where their crack growth rates are almost the same. 5) During service, the vertical wear rate of the ER8C wheel is slightly higher than that of the ER8 wheel.
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Key words:
- high-speed EMU wheel /
- mechanical performance /
- microstructure
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图 2 ER8和ER8C材质轮辋/轮辐室温时应力-寿命（S-N）曲线
Figure 2. ER8 and ER8C rim / spoke stress-life curves at room temperature
表 1 化学成分的质量分数
Table 1. Mass fraction of chemical components
% 车轮材质 C Si Mn P S Cr Cu Mo Ni V Al Cr+Mo+Ni ER8C 0.533 0.959 0.907 0.009 0.001 0.089 0.089 0.025 0.068 0.001 0.014 0.182 ER8 0.547 0.350 0.700 0.0085 0.001 0.174 0.199 0.038 0.120 0.001 0.016 0.332 
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表 2 两种材质金相组织对比
Table 2. Comparison of crack growth rate of two kinds of material axles
材质 名义滚动圆处 滚动圆下15 mm 滚动圆下 35 mm ER8C 
ER8 
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表 3 ER8和ER8C两种材质常规力学性能对比
Table 3. Comparison of conventional mechanical properties between ER8 and ER8C
车轮材质 抗拉强度/MPa 屈服强度/MPa 延伸率/% 断面收缩率/% 轮辋 轮幅 轮辋 轮幅 轮辋 轮幅 轮辋 轮幅 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 新轮 磨耗轮 ER8 869 869 741 743 542 543 408 403 20.56 20.13 20.48 20.95 51.31 50.72 39.42 43.20 ER8C 913 926 787 779 595 589 428 427 19.17 19.92 22.28 22.26 54.66 54.03 45.14 44.83
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表 4 车轮断裂韧性试验值
Table 4. Wheel fracture toughness test value
MPa•m1/2 材质 试样编号 新轮 磨耗轮 ER8C C1 83.1 71.0 C2 71.9 89.3 C3 85.5 77.3 C4 87.7 79.0 平均值 82.1 79.15 ER8 R1 74.0 73.4 R2 79.7 74.9 R3 76.0 82.4 R4 79.7 68.7 平均值 77.35 74.85
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表 5 车轮疲劳裂纹扩展门槛值
Table 5. Fatigue crack growth threshold
MPa•m1/2 材质 车轮类型 试样编号 门槛值 ΔKth 平均门槛值 ER8C 新轮 CN1 7.7949 7.55 CN2 6.9228 CN3 7.8247 CN4 7.8500 CN5 7.3400 磨耗轮 CW1 8.9815 8.61 CW2 8.6810 CW3 9.0462 CW4 7.5393 CW5 8.7782 ER8 新轮 RN1 8.9700 8.88 RN2 8.7500 RN3 9.0600 RN4 8.7300 磨耗轮 RW1 8.9700 9.02 RW2 9.4800 RW3 8.5060 RW4 9.1393
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