Near Net Shape Casting: Is It Possible to Cast Too Thin?
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RODUCTION
NEAR net shape casting technologies such as twin roll and belt casting have both made huge strides in commercialization in the past decade. Ventures such as the joint SMS Seimag/Salzgitter Flachstahl,[1] the new Castrip facilities in China (completed 2019) and the USA (building commenced 2016),[2–4] have all seen step changes towards commercial production through these rapid, more cost-effective methods. A major attraction for development and increasing implementation of these processes lies in their energy efficiency, with technologies such as horizontal belt casting showing potential energy savings > 3 GJ/ton of steel produced.[5,6] Another advantage is the system size and casting speed with near net shape casters being 8 to 10 times smaller and capable of casting speeds up to 9 150 faster compared to thick slab continuous casting routes.[1,6] One of the additional potential drivers of these techniques is the ability to produce new or exotic alloys that previously were ‘‘uncastable’’ by conventional continuous casting. These alloys included high
CARL SLATER and CLAIRE DAVIS are with the WMG, University of Warwick, Warwick CV4 7AL, UK. Contact e-mail: [email protected] Manuscript submitted May 24, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
manganese TWIP/TRIP grades,[1,7–10] high silicon electrical steels,[11–13] high carbon energy efficient sheets,[14] as well as ultra-thin HSLA grades.[15] However, with the exception to the TWIP/TRIP, these have been lab/pilot scale in the majority. While each of these show promising developments, none are without their problems (such as surface quality, centreline position etc.[16]), but also the expected production volumes (with the exception to maybe the electrical steel) are low in comparison to the more commodity grades. Current usage of some of the commercial net shape production has been for the more commodity grades, which although proves that the technology will not compete with the larger scale mass production of continuous casters. The question remains that for these new casting methods to become more commercially viable and for greater adoption, do they need to be able to produce a wider range of higher value conventional grades (HSLA, AHSS etc.) to at least the same quality of conventional continuous casting? As the majority of the work on these processes have been lab based, there is little in the way of benchmarking against conventional continuous casting; however, some literature suggest that the net shape route produces a coarser microstructure as seen by Kwon et al.[17] in ferritic high-aluminum alloys, where the conventional ingot route showed nearly a 10 pct higher UTS compared to the a twin roll cast counterpart.
The batch type production of the near net shape processes lends itself well to switching between alloys, and therefore, understanding the metallurgical impact of producing the commodity grades through this route is needed.
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MATERIALS AND METHODOLOGY
A benchmark AHSS material was selected to compare to belt cast production
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