Thermodynamic control of pearlite lamellar sheet spacing and its effect on mechanical properties of steel
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摘要: 利用实验室炼钢、轧制、热处理等手段获得了成分一致但珠光体片间距不同的两种材料，利用扫描电镜和万能试验机对比研究了珠光体片间距与力学性能之间的关系，得到以下结论：试验材料的珠光体片层间距的倒数Sp−1（μm−1）与其珠光体转变过冷度∆T（℃）满足线性关系Sp−1=9.0201+0.03358∆T，可知该材料进行550 ℃等温处理可获得理论上最细珠光体片间距（约61 nm）。随着极细珠光体片间距的细化，由105 nm降至72 nm时，材料强度上升的同时会出现塑性显著恶化，其极限变形应变值由0.18降至0.12，这与传统细晶强化理论不一致，其原因是细化的珠光体片层抑制了位错的自由运动。Abstract: A pearlite steel was prepared via laboratory steelmaking, and then after rolling and heat treatment to obtain two different samples with different pearlite lamellar spacing. The mechanical properties and microstructures of the materials were observed by scanning electron microscopy and universal testing machine. Results show that the reciprocal Sp−1(μm−1) of pearlite lamellae and transformation super cooling degree of pearlite ∆T(℃) satisfy the linear relationship of Sp−1=9.0201+0.03358∆T. This indicates that the theoretical minimum pearlite lamellae spacing(~61 nm) can be obtained by isothermal treatment at 550 ℃. With the thinning of the spacing between the very fine pearlite lamellar( from 105 to 72 nm), the strength increases but ductility will deteriorate significantly, and the ultimate deformation strain will decrease from 0.18 to 0.12. This result conflicts with the traditional grain refinement strengthening theory. The reason is that the refined pearlite lamellar restrains the free movement of dislocations.
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Key words:
- high strength steel /
- pearlite /
- lamellar spacing /
- strength /
- ductility /
- EBSD
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图 4 试样的晶粒取向，以及面积分数与颗粒直径的比例关系
Figure 4. The grain orientation and relationship between area fraction and particle diameter
(a)(c)1#; (b)(d)2#
表 1 试验材料主要化学成分
Table 1. Main chemical compositions of test materials
% C Si Mn P S Cr Mo Co 0.72 1.35 0.55 0.009 0.012 0.80 0.35 3.02 
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表 2 试样的力学性能结果
Table 2. Mechanical properties of the specimens with different pearlite lamellar spacing
编号 平均珠光体片间距/nm 屈服强度/MPa 抗拉强度/MPa 伸长率/% 1# 105 790 1155 17.7 2# 72 1075 1285 11.6
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