The effect of annealing process on the microstructures and properties of 2 000 MPa cold-drawn steel wire
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摘要: 利用扫描电子显微镜、透射电子显微镜，并结合常规的力学检测手段，采用退火模拟了一种冷拉钢丝的镀锌过程，研究了镀锌过程中冷拉钢丝组织和性能的变化。试验结果表明：退火时间是影响钢丝微观组织和力学性能的主要因素，随着退火时间的延长，冷拉钢丝的强度轻微波动后大幅度下降，扭转性能呈现先降低后上升的趋势，且其强度上升的阶段与其扭转性能显著恶化的阶段一致。钢丝表层组织首先出现退化，片层状的渗碳体断裂，形成渗碳体颗粒，且铁素体内部位错密度降低，而钢丝内部组织可保持相对完整的珠光体片层结构；经长时间保温处理后，其表层和内部的珠光体片层组织均出现全面退化。冷拉钢丝在镀锌过程中扭转性能剧烈恶化的原因是其表层组织与内部组织不一致，表层强度较高且扭转过程中变形最大，由此产生的应力集中迅速恶化扭转性能。Abstract: Annealing was used to simulate the galvanizing process of a kind of cold drawn steel wire, and the changes in the structure and properties of the cold drawn steel wire during the galvanizing process were studied utilizing a scanning electron microscope, transmission electron microscope, combined with conventional mechanical testing methods in this paper. The test results showed that the annealing time affected the steel wire′s microstructure and mechanical properties. With the extension of annealing time, the strength of cold drawn steel wire fluctuated first and then decreased significantly subsequently. Meanwhile, the torsional property showed a trend of decreasing first and then rising, and the stage of strength rising was consistent with the stage of significant deterioration of its torsional property. In addition, the surface structure of the steel wire firstly degenerated, the lamellar cementite breaks, forming cementite particles, and the internal dislocation density in the ferrite decreased, while the internal structure of the steel wire could maintain a relatively complete pearlite lamellar structure; after a long time of heat treatment, the surface and internal pearlite lamellar structures all degenerated. The severe deterioration of the torsional properties of cold drawn steel wire in the process of galvanizing was the surface structure inconsistent with the internal structure, and the surface strength was high, causing the deformation was the largest in the torsion process. As a result, stress concentration rapidly deteriorated the torsional performance.
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Key words:
- cold-drawn steel wire /
- annealing /
- strength /
- torsion property /
- microstructure
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图 1 退火温度对材料力学性能的影响
Figure 1. Effect of annealing temperature on the mechanical properties of materials
图 3 450 ℃不同退火时间对钢丝强度及扭转的影响
Figure 3. Effects of different annealing times on strength and torsional ductility of steel wire at 450 ℃
图 4 退火前后试样的横截面中心位置的典型TEM照片
Figure 4. Typical TEM photographs of the samples before and after annealing (the cross-sectional center)
图 5 各试样横截面表层及心部组织的非片层组织比例
Figure 5. The proportion of non-lamellar structures in surface and matrix structures for the cross sections of each specimen
图 6 450 ℃下不同时间保温后钢丝的硬度
Figure 6. Hardness of steel wires after holding at 450 ℃ for different times
表 1 试验材料的主要化学成分
Table 1. Main chemical compositions of tested material
% C Si Mn P S Cr V Ti 0.97 0.95 0.55 0.015 0.010 0.35 0.06 0.03 
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