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Acta Metall Sin  2007, Vol. 43 Issue (3): 315-320     DOI:
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Refinement of Grain and Enhancement of Impact Energy Absorption for Low-Alloy Ultra-High Strength Bainite Steels Containing Silicon
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Abstract  Through judiciously using the silicon, manganese and nickel as the alloying elements and effectively controlling the transformation temperature, cooling and tempering parameters for a series of low alloy ultrahigh strength bainitic steels (LUHSBS), the combination of strength and toughness are very excellent and the impact energy absorption (AKV ≥185 J) has been tripled compared to the previously advanced martensitic steel 23MnNiCrMo with the same strength level (>1500 MPa). The basic reasons giving rise to the enhancement of strength and toughness consist in the increase of carbon content and the refinement of sublaths in the bainitic ferrite (BF) and the very thin films of retained austenite (AR). It is confirmed by the atomicforce microscope (AFM) and scanning tunneling microscope (STM) that there was no any large bulky areas of AR in the structure which is less stable and will reduce the impact toughness of bainitic steels. Not only is the sublaths is significantly refined, but also the average size of subgrains is less than 20 nm and the average thickness of shear units in a BF lath is only about 1.6 nm. The refinement of microstructure, the enrichment of interstitial atom carbon in BF and the increase of both the dislocation density and the volume fraction of AR are some critical factors that affect the ultimate tensile strength, the stability of AR and the impact energy absorption. Furthermore, the physical mechanism on the improvement of the combination of strength and toughness is in depth discussed.
Key words:  bainitic ferrite      bainitic laths      sub-units      refined microstructure      
Received:  29 June 2006     
Corresponding Authors:  GAO Kuan     E-mail:  purely_1007@163.com
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. Refinement of Grain and Enhancement of Impact Energy Absorption for Low-Alloy Ultra-High Strength Bainite Steels Containing Silicon. Acta Metall Sin, 2007, 43(3): 315-320 .

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https://www.ams.org.cn/EN/     OR     https://www.ams.org.cn/EN/Y2007/V43/I3/315

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