Improvement of Continuously Cast Slab Surface and Performance of Rolling the Slab Free from Surface Conditioning

The aim of this work was to analyze the morphology and distribution of the microalloy precipitates in the slab surface zone of ULC/IF steel microalloyed with titanium. The slab was made by continuous casting using two different slab pulling rates. Transient slabs were pulled with pulling rate 0.4 m/min at the start and 0.8 m/min at the end of the slab. It was confirmed that morphology of the particles evaluated in the surface areas of slab were globular, cubical or elliptical shape and have been identified as of TiS, TiN and TiC. At the lower drawing rate particles from the middle cut-out from an area with coarse ferritic grains at the slab surface attained an mean size of 2r = 41.8 nm, and from an area with fine ferritic grains they attained an mean size of 2r = 32.5 nm. At the higher drawing rate particles in the middle cut-out attained an mean size of 2r= 63.5 nm. The coarser particles were found in areas with coarse ferrite grains and at higher pulling speed.

Download Full-text

Background of Branched Crack Formation in Surface Zone of Continuously-Cast Ti-Nb Microalloyed Steel Slab

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1127.143 ◽

2015 ◽

Vol 1127 ◽

pp. 143-149

Author(s):

Pavel Bekeč ◽

Margita Longauerová ◽

Marek Vojtko ◽

Ondrej Milkovič ◽

Jiří Kadlec ◽

...

Keyword(s):

Crack Formation ◽

Microstructural Analysis ◽

Thin Strip ◽

Thick Sheet ◽

Surface Zone ◽

Slab Surface ◽

Cast Slab ◽

X Ray ◽

Continuously Cast ◽

Oscillation Marks

Branched cracks are undesirable and dangerous, and under the oxidized surface of a continuously-cast slab they are mostly difficult to identify. They can cause the formation of defects in thick sheet or on thin strip. This work deals with the study of the background to the formation of branched cracks in a continuously-cast slab, at pulling rate 0.43 m.min-1. The results of the work show that branched cracks extended to a depth of 10 mm below the slab surface and occurred mostly below oscillation marks. Cracks were mostly present in the edge parts of the slab, where they were also deeper in comparison with locations in the middle of the slab width. Microstructural analysis confirmed heterogeneity of ferrite grain sizes in the slab surface skin. The microstructure was formed predominantly of polyhedral ferritic-pearlitic grains, and on the ferritic grain boundaries the presence of tertiary cementite was observed. In the area around the cracks mainly non-equilibrium microstructure of acicular character was observed. A typical feature of these cracks after their opening is intercrystalline fracture. Wavelength-dispersive X-ray analysis of a sample with a branched crack showed chemical heterogeneity of harmful elements, mainly S and As. Large amounts of these elements point to their significant segregation. The formation of branched cracks is conditioned not only by segregation of impurities, but possibly also by the presence of undesirable brittle cementite networks. The presence of cementite was confirmed not only by microstructural analysis, but also diffraction of hard X-ray radiation. Precipitation of microalloying elements in connection with the cementite can lead to higher probability of surface crack formation, as also confirmed in this study.Keywords: slab, branched cracks, oscillation marks, segregation, precipitation

Download Full-text

Influence of Scale Formation on Copper Enrichment Behaviour in Continuously Cast SLAB

2016 EPD Congress ◽

10.1002/9781119274742.ch1 ◽

2016 ◽

pp. 5-10

Author(s):

Nan Wang ◽

Yu Shan ◽

Li Xiaoao ◽

Xin Jianhua ◽

Chen Guanghao ◽

...

Keyword(s):

Scale Formation ◽

Cast Slab ◽

Continuously Cast

Download Full-text

Effect of the Penetration Depth of Casting Stream in Crater on the Accumulation of Large Oxide Inclusions in Continuously Cast Slab

Transactions of the Iron and Steel Institute of Japan ◽

10.2355/isijinternational1966.15.246 ◽

1975 ◽

Vol 15 (5) ◽

pp. 246-251

Author(s):

Yasuhiro HABU ◽

Hidenari KITAOKA ◽

Yutaka YOSHII ◽

Yoshiharu IIDA ◽

Takuo IMAI ◽

...

Keyword(s):

Penetration Depth ◽

Cast Slab ◽

Oxide Inclusions ◽

Continuously Cast

Download Full-text

Influence of Scale Formation on Copper Enrichment Behaviour in Continuously Cast Slab

EPD Congress 2016 ◽

10.1007/978-3-319-48111-1_1 ◽

2016 ◽

pp. 5-10

Author(s):

Nan Wang ◽

Shan Yu ◽

Xiaoao Li ◽

Jianhua Xin ◽

Guanghao Chen ◽

...

Keyword(s):

Scale Formation ◽

Cast Slab ◽

Continuously Cast

Download Full-text

Evolution of Austenite Grain Size in Continuously Cast Slab during Hot-Core Heavy Reduction Rolling Process Based on Hot Compression Tests

steel research international ◽

10.1002/srin.201800025 ◽

2018 ◽

Vol 89 (7) ◽

pp. 1800025 ◽

Cited By ~ 2

Author(s):

Meina Gong ◽

Haijun Li ◽

Tianxiang Li ◽

Bin Wang ◽

Zhaodong Wang

Keyword(s):

Grain Size ◽

Rolling Process ◽

Hot Compression ◽

Compression Tests ◽

Cast Slab ◽

Austenite Grain Size ◽

Austenite Grain ◽

Continuously Cast

Download Full-text

Effect of Stirring on Crystal Morphologies and on Macro-Segregation

Journal of Materials Science Research ◽

10.5539/jmsr.v7n3p37 ◽

2018 ◽

Vol 7 (3) ◽

pp. 37

Author(s):

Toshio Fujimura ◽

J. K. Brimacombe

Keyword(s):

Solid Fraction ◽

Cast Steel ◽

Liquid Core ◽

Cast Slab ◽

Analogue Study ◽

Fraction Solid ◽

Continuously Cast ◽

Steel Slabs

To minimize the macro-segregation in continuously cast steel slabs, the effects of the stirring on the macro-segregation were studied. Industrial findings by the metallographic observations of the steel slabs showed macro-segregation was improved by the refinements of crystals. It was also found that the stirring at low fraction solid refined crystals. The unsolidified liquid core of the continuously cast slab with the optimum stirring was well packed with the refined crystals whereas it was not with coarse equiaxed crystals. The analogue study with experiments of Pb-Sn alloy showed, similarly as with steel slabs, the stirring at low solid fraction refined crystals. Also, the artificially created cavity in a mush was well packed with the refined, globular, crystals whereas it was not with the coarse dendritic crystals. Thus, it is considered the stirring at the low solid fraction is advantageous to refine crystals and to improve macro-segregation.

Download Full-text

Reduction in Surface Defect in Continuous Cast Slab through Intervention in Process Parameters

Materials Science Forum ◽

10.4028/www.scientific.net/msf.978.91 ◽

2020 ◽

Vol 978 ◽

pp. 91-96

Author(s):

Snehangshu Roy ◽

R.K. Singh ◽

Kiran Kumar Keshari ◽

N. Pradhan ◽

M. Kumar ◽

...

Keyword(s):

Continuous Casting ◽

Surface Defects ◽

Systematic Investigation ◽

Route Optimization ◽

Critical Parameters ◽

Hot Strip Mill ◽

Cast Slab ◽

Process Route ◽

Mould Flux ◽

Continuously Cast

Occurrence of defects like crack on the surface of the cast products has long been recognized as a critical challenge for steelmakers in the continuous casting. Cracks on the surface can severely reduce yield and required further operations like salvage and scarfing. Depending on the severity of defect slabs can be diverted or in worst cases a slab can be rejected altogether if the defect cannot be removed by surface conditioning. Rourkela Steel Plant (RSP) of Steel Authority of India Limited (SAIL) produces continuously cast slabs as feed material for plate mills and hot strip mill. Sometimes the slabs produced through continuous casting are faced issues intermittently due to presence surface defects like midface longitudinal cracks (LC) and transverse edge crack (EC) etc. A systematic investigation of the operating parameters of these casters e.g. monitoring of oscillation parameters, slabs and mould flux, simulation and analysis of fluid flow inside mould, steel chemistry and role of dissolve gases in steel. Based on the investigation critical parameters responsible for crack formation have been identified and key areas identified where modification need to be done. Modifications has been done in terms of mould flux addition practice, optimization of the grade chemistry, optimization of process route, optimization of casting speed, checking of strand thermal profile, mould & machine allignment etc. It was observed that the crack incidences are significantly lower after the modifications were done.

Download Full-text

Characterisation of Bimodal Grain Structures and Their Dependence on Inhomogeneous Precipitate Distribution during Casting

Materials Science Forum ◽

10.4028/www.scientific.net/msf.500-501.613 ◽

2005 ◽

Vol 500-501 ◽

pp. 613-622 ◽

Cited By ~ 7

Author(s):

D.J. Chakrabarti ◽

Claire L. Davis ◽

Martin Strangwood

Keyword(s):

Grain Size ◽

Peak Height ◽

Visual Observation ◽

Peak Height Ratio ◽

Cast Slab ◽

Grain Structures ◽

Thermo Calc Software ◽

Grain Size Distributions ◽

Continuously Cast ◽

Nb Microalloyed Steel

Bimodal grain size distributions were found in continuously cast slab and thermomechanical controlled rolled (TMCR) samples of Nb-microalloyed steel. Scanning electron microscopy (SEM) revealed inhomogeneous distributions of Al- and Nb-containing precipitates, which were found to pin prior austenite grain boundaries during reheating. An effort has been made to establish parameters to quantify the extent of bimodality of reheated and rolled microstructures. Quantification of bimodality using peak grain size range, (PGSR) and peak height ratio, (PHR), is found to match closely with the visual observation of bimodality. Thermo-Calc software was used to predict the sequence of precipitation for different compositions and that could explain the formation of bimodality during reheating.

Download Full-text