不同碳含量粉末烧结钢冷压流变致密化行为研究

摘要: 在材料万能试验机上对碳含量（质量分数）为0%、0.3%、0.6%、0.9%、1.2%的粉末烧结钢进行冷压变形试验，利用Hollomon方程对粉末烧结钢流变应力数据进行非线性拟合，结合显微组织形貌分析烧结钢冷压流变致密化行为和孔隙、晶粒变形机制。结果表明：烧结钢冷压应变硬化行为符合Hollomon方程，随着碳含量的增加，极限断裂应变量逐渐减小；在相同应变下，随着碳含量的增加，烧结钢应变硬化率逐渐上升，致密化效果先增强后减弱，在碳质量分数为0.9%时最佳；随着应变增加，烧结钢孔隙闭合，晶粒由等轴状变为片状；烧结钢的流变致密化过程在低应变下以致密化和致密化硬化为主，在高应变下以变形和基体加工硬化为主。
- 烧结钢 /
- 冷压 /
- 流变 /
- 致密化
Abstract: The cold compression tests of the powder sintered steels with the carbon mass fraction of 0%, 0.3%, 0.6%, 0.9%, and 1.2% were carried out on the universal material testing machine. The tested stress?strain data were nonlinearly fitted by the Hollomon equation. The behaviors of flow and densification and the deformation mechanisms of pore and grain were analyzed, combining with the microstructure analysis of the powder sintered steels. The results show that, the cold compression strain hardening behavior of the sintered steels conforms to the Hollomon equation, and the ultimate fracture strain decreases with the increase of the carbon content. In the same strain condition, the strain hardening rate of the sintered steels increases gradually with the increase of carbon content, and the densification effect first increases and then decreases, showing the best when the carbon content is 0.9%. With the increase of strain, the pores of the sintered steels are gradually closed, and the grains change from the equiaxed crystal into the flaky structure. During the flow and densification processes, the densification and densification hardening are dominant under the low strains, while the deformation and the matrix work-hardening are dominant under the high strains.
- powder sintered steels /
- cold compression /
- flow deformation /
- densification

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图 1 不同质量分数碳含量试样原始组织：（a）0%；（b）0.3%；（c）0.6%；（d）0.9%；（e）1.2%

Figure 1. Original microstructures of the specimens with the different carbon mass fractions: (a) 0%; (b) 0.3%; (c) 0.6%; (d) 0.9%; (e) 1.2%

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图 2 粉末烧结钢试样孔隙形貌和显微组织观察区示意图

Figure 2. Observation area diagram of the pore images and the microstructures in the powder sintered steel specimens

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图 3 粉末烧结钢在不同变形量下冷压真应力–真应变曲线

Figure 3. True stress-true strain curves of the powder sintered steels by cold compression at the different deformation

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图 4 粉末烧结钢应变硬化率–应变曲线

Figure 4. Strain hardening rate-strain curves of the powder sintered steels

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图 5 含碳质量分数为0.3%的冷压粉末烧结钢在不同变形量下的晶粒形貌: (a)15%；(b)25%；(c)35%；(d)极限应变

Figure 5. Grain morphology of the powder sintered steels by cold compression at the different deformation with the carbon mass fraction of 0.3%: (a) 15%; (b) 25%; (c) 35%; (d) ultimate strain

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图 6 不同碳含量烧结钢的轴向应变与周向应变的关系：（a）0%；（b）0.3%；（c）0.6%；（d）0.9%；（e）1.2%

Figure 6. Relationship between the axial strain and the circumferential strain of the powder sintered steels with the different carbon mass fractions: (a) 0%; (b) 0.3%; (c) 0.6%; (d) 0.9%; (e) 1.2%

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图 7 不同碳含量烧结钢的轴向应变与泊松比的关系

Figure 7. Relationship between the axial strain and the poisson's ratio of the powder sintered steels with the different carbon mass fractions

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图 8 不同碳含量烧结钢的变形量与相对密度的关系

Figure 8. Relationship between the deformation and relative density of the powder sintered steels with the different carbon mass fractions

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图 9 含碳质量分数为0.3%的冷压烧结钢不同变形量下的孔隙形貌：(a)0%；(b)15%；(c)25%；(d)35%

Figure 9. Pore images of the powder sintered steels by cold compression with the carbon mass fraction of 0.3% at the different deformation: (a) 0%; (b) 15%; (c) 25%; (d) 35%

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图 10 不同碳含量粉末烧结钢试样冷压变形量为15%时的孔隙形貌: （a）0%；（b）0.3%；（c）0.6%；（d）0.9%；（e）1.2%

Figure 10. Pore images of the powder sintered steels by cold compression with the different carbon mass fraction at the deformation of 15%: (a) 0%; (b) 0.3%; (c) 0.6%; (d) 0.9%; (e) 1.2%

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图 11 不同碳含量粉末烧结钢试样相对密度与轴向应力的关系

Figure 11. Relationship between the relative density and the axial stress of the powder sintered steels with the different carbon mass fraction

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表 1 Hollomon方程数值拟合结果

Table 1. Numerical fitting results of Hollomon equation

碳质量分数/ %	K	n	相关系数，R²
0.0	638.11	0.209	0.96391
0.3	694.29	0.203	0.96552
0.6	821.03	0.199	0.97736
0.9	982.54	0.192	0.97821
1.2	1080.35	0.189	0.97948

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