Effect of powder metallurgy technology on properties of pure iron soft magnetic material
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摘要: 利用粉末冶金技术制备纯铁软磁材料，在不同温度和压力下将不同粒径铁粉压制成生坯，并在保护气氛下进行烧结。结果表明：不同粒径铁粉混合有助于压坯密度的增加，适宜的压制温度可以有效地促进粉末流动，避免大尺寸孔洞的形成，优化组织。140℃、800 MPa温压条件下雾化铁粉压坯密度最高可达7.35 g·cm-3。对比常温压制，温压压坯烧结后孔洞分布均匀。烧结体密度随温度的升高而上升，雾化铁粉压坯在1250℃烧结后密度最高可达7.47 g·cm-3。在一定范围内，软磁材料磁性能与密度成正比，混粉压制试样的密度接近理论值，但在混合铁粉中，较细的铁粉夹杂于粗粉中，阻碍磁畴壁移动，造成饱和磁化强度（Ms）偏小、矫顽力（Hc）偏大的现象，Ms为205.51 emu·g-1，Hc为7.9780 Oe。Abstract: Powder metallurgy technology was proposed to prepare the pure iron soft magnetic material. The green of iron powders in different size distribution was compacted at different temperatures and pressures, and then was sintered in protective atmosphere. The results show that the appropriate size proportion of iron powders is helpful to increase compaction density. The suitable pressing temperature can effectively promote the powder flowability, avoid the formation of large-sized pores, and finally optimize the microstructures of iron powder green. The highest compaction density of atomized iron powders can achieve 7.35 g·cm-3 in the warm compaction condition of at 140℃ and 800 MPa. Compared with the normal temperature compaction, the pore distribution of sintered body prepared by warm compaction is uniform. The density of sintered body increases with the increase of temperature. After sintered at 1250℃, the highest density of atomized iron powder compaction can reach 7.47 g·cm-3. The magnetic properties of soft magnetic material are proportional to the density. The density compacted by iron powders in different size distribution is close to the theoretical. But in the mixed iron powders, the fine iron powders are mixed in the coarse powders, which hinder the movement of the magnetic domain wall, resulting in the phenomenon that the saturation permeability (Ms) is smaller (205.51 emu·g-1) and the coercivity (Hc) is higher (7.9780 Oe).
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Key words:
- powder metallurgy /
- soft magnetic materials /
- density /
- magnetic property
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图 1 铁粉物相组成（a）与显微形貌（b）
Figure 1. Phase composition (a) and microstructures (b) of iron powders
图 3 800 MPa常温压制不同粒径铁粉所得压坯密度
Figure 3. Compaction density of iron powders in different particle size proportion at room temperature and 800 MPa
图 4 压坯密度与压制压力及温度的关系
Figure 4. Compaction density of iron powders at different temperatures and pressures
图 5 不同压制压力和温度下压坯显微组织：（a）600 MPa，常温；（b）600 MPa，140 ℃；（c）700 MPa，常温；（d）700 MPa，140 ℃；（e）800 MPa，常温；（f）800 MPa，140 ℃
Figure 5. Microstructures of compaction at different pressures and temperatures: (a) 600 MPa, room temperature; (b) 600 MPa, 140 ℃; (c) 700 MPa, room temperature; (d) 700 MPa, 140 ℃; (e) 800 MPa, room temperature; (f) 800 MPa, 140 ℃
图 6 压坯烧结体显微组织（常温压坯、1250 ℃烧结）: （a）金相显微组织；（b）扫描电子显微组织
Figure 6. Microstructures of normal temperature compaction sintered at 1250 ℃: (a) metallographic microscopy; (b) scanning electron microscopy
图 7 不同压制压力下压坯烧结体磁滞回线（常温压坯、1250 ℃烧结）
Figure 7. Magnetic hysteresis loop of normal temperature compaction sintered at 1250 ℃ in different pressures
图 8 不同压制温度的压坯烧结体磁滞回线（800 MPa）
Figure 8. Magnetic hysteresis loop of sintered body at different compaction temperatures (800 MPa)
表 1 原料铁粉化学成分及性能
Table 1. Chemical composition and properties of raw iron powders
元素质量分数/% 氢损 松装密度/(g·cm-3) 流动性/[s·(50 g-1)] Fe C S P Si Mn 99.500 0.008 0.008 0.010 0.040 0.080 0.15 2.7~3.1 26 
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表 2 不同粒径粉末配比方式
Table 2. Proportion of iron powders in different size distribution
单一铁粉/目 不同粒径铁粉 60%100目+其他粒径铁粉 60%200目+其他粒径铁粉 60%300目+其他粒径铁粉 100（1#） 1# 40%200目（6#） 40%300目（11#） 40%400目（16#） 200（2#） 40%300目（7#） 40%400目（12#） 40%500目（17#） 300（3#） 40%400目（8#） 40%500目（13#） 20%200目+20%400目（18#） 400（4#） 40%500目（9#） 20%100目+20%400目（14#） 20%200目+20%500目（19#） 500（5#） 20%200目+20%300目（10#） 20%100目+20%500目（15#） 20%400目+20%500目（20#）
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表 3 生坯压制工艺条件
Table 3. Compaction conditions of iron powder green
温度/℃ 压力/MPa 常温、100、110、120、
130、140、150400、500、600、
700、800
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表 4 不同烧结条件试样的磁性能
Table 4. Magnetic properties of samples in different sintering condition
烧结温度/
℃烧结条件 饱和磁化强度，
Ms/(emu·g-1)矫顽力，
Hc/Oe1050 真空 197.89 7.46 1150 真空 198.93 7.36 1250 真空 205.50 7.98 1250 氩气 204.44 7.48
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