Title

STEELMAKING AND CONTINUOUS CASTING PROCESS PARAMETERS AND PHYSICAL METALLURGY RELATIONSHIPS AFFECTING HOT DUCTILITY BEHAVIOR OF NIOBIUM-BEARING STEELS

STEELMAKING AND CONTINUOUS CASTING PROCESS PARAMETERS AND PHYSICAL METALLURGY RELATIONSHIPS AFFECTING HOT DUCTILITY BEHAVIOR OF NIOBIUM-BEARING STEELS

Authorship

Jansto, Steven George

Jansto, Steven George

I am this author

DOI

10.5151/2594-5300-22838

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Abstract

Over 200 million tons of Nb-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. However, the steelmaking and process metallurgy parameters are rarely correlated to the hot ductility behavior. 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 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 concludes that the incidence of slab cracking during casting is related to the steelmaking and caster process parameters. These parameters include the elemental residual chemistry level, superheat variation, transfer ladle temperature stratification, mould flux incompatibility, casting speed fluctuation, and excessive secondary cooling. This paper defines these operational root causes supported by physical metallurgy hot ductility data.

Over 200 million tons of Nb-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. However, the steelmaking and process metallurgy parameters are rarely correlated to the hot ductility behavior. 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 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 concludes that the incidence of slab cracking during casting is related to the steelmaking and caster process parameters. These parameters include the elemental residual chemistry level, superheat variation, transfer ladle temperature stratification, mould flux incompatibility, casting speed fluctuation, and excessive secondary cooling. This paper defines these operational root causes supported by physical metallurgy hot ductility data.

Keywords

Continuous casting; Hot ductility; Niobium; Steelmaking.

Continuous casting; Hot ductility; Niobium; Steelmaking.