Vanadium Microalloying for Ultra-high Strength Steel Sheet Treated by Hot-dip Metallising
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摘要: 对超高强度钢板进行热处理,模拟热浸镀锌和合金化镀锌工艺的热循环,并考察获得的力学性能和微观组织。研究用钢含有适量的碳(~0.2%)、锰(1.2%)和铬(0.4%),保证钢板在奥氏体化后在镀锌前的连续退火线上进行快速冷却时能够完全转变成马氏体。采用不同的钒含量(0~0.1%)和氮含量(0.002%~0.012%),研究这些微合金化元素对回火马氏体强度的影响。尤其与高氮相配合情况下,钒有助于抵抗回火效应,因此在镀锌后大部分原始强化贡献被保留下来,使得钢的抗拉强度超过1 000 MPa。使用铝或硅进行不同脱氧试验,发现在同一碳含量下两者具有相同的强度水平,但是Si镇静钢的弯曲性能明显优异。对退火钢板进行微观组织观察,但是钒产生有益作用的原因还未完全掌握。通过研究得出这样结论:钒微合金化对耐腐蚀超高强度钢板的开发而言是一种极具前景的途径。Abstract: Ultra-high strength steel sheets have been subjected to heat treatments that simulate the thermal cycles in hot-dip galvanising and galvannealing processes and evaluated with respect to their resulting mechanical properties and microstructures. The steels contained suitable contents of carbon(~0.2%),manganese(1.2%) and chromium(0.4%) to ensure that they could be fully transformed to martensite after austenitisation followed by rapid cooling in a continuous annealing line,prior to galvanising. Different contents of vanadium(0~0.1%) and nitrogen(0.002%~0.012%) were used to investigate the possible role of these microalloying elements on the strength of the tempered martensite. Vanadium,especially when in combination with a raised nitrogen content,helps to resist the effect of tempering so that a larger proportion of the initial strengthening is preserved after the galvanising cycle,giving tensile strength levels exceeding 1 000 MPa. Different deoxidation practices using aluminium or silicon have also been included. These showed similar strength levels at corresponding carbon contents but the bendability of the Si-killed steel sheet was considerably superior. Microstructural examinations have been made on the annealed steels but the reason for the beneficial effect of vanadium is still not fully explained. It is concluded that microalloying with vanadium is a very promising approach in the development of corrosion-resistant ultra-high strength steel sheet products.
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Key words:
- sheet steel /
- vanadium /
- microalloying /
- alvanising /
- strength /
- ductility /
- bendability /
- microstructures
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