Over 200 million tons of Niobium-bearing steels were continuously cast and hot rolled globally in 2012. These Nb-bearing plate, bar and sheet... Show moreOver 200 million tons of Niobium-bearing steels were continuously cast and hot rolled globally in 2012. These Nb-bearing plate, bar and sheet products are manufactured throughout the world. The melting and casting practices to assure production of crack-free slabs, billets and blooms of high surface quality is presented. Much has been published about the traditional ductility trough associated with higher carbon equivalent steels with and without microalloy additions of Nb, V and/or Ti. The focus has primarily been on the chemistry and optimal composition based upon the literature review. However, the steelmaking and process metallurgy parameters are rarely correlated to the hot ductility behavior. Most studies involve laboratory produced heats, but this research is based upon industrial produced samples.The hot ductility troughs associated with simple carbon-manganese steels can also result in surface and internal quality issues if certain steelmaking and casting parameters are not followed. Although high carbon equivalent steels exhibit inherently lower hot ductility behavior, as measured by percent reduction in area at elevated temperature, these steels still exhibit sufficient ductility to satisfactorily meet the unbending stress and strain gradients existing in the straightening section of most casters. The % Reduction in Area significantly overstates the minimum ductility required for crack-free casting of Nb-bearing steels. The relationship between the steelmaking and caster operation and the resultant slab quality is related through the hot ductility behavior. This global Nb-bearing continuous casting steel research study introduces the strain energy as an improved xxi measure of the hot ductiity behavior. The incidence of cracking is primarily related to the steelmaking and caster process parameters and steel chemistry is secondary. These parameters include the elemental residual chemistry level, superheat variation, transfer ladle temperature stratification, oscillation frequency and stroke, mould flux incompatibility, casting speed fluctuation, and excessive secondary cooling. PH.D in Materials Science and Engineering, December 2013 Show less
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(-) mods_name_creator_namePart_mt:"Jansto, Steven George"
