In this paper a thorough review of the literature on defects in beam blanks is carried out. The focus is on the formation mechanism and the solutions proposed to decrease their occurrence. Surface defects included are longitudinal cracks and transverse cracks, bleeding, pinholes and slag entrapment. Internal defects are blowholes and solidification cracks (web and wing end). The review includes the techniques used to investigate the defects: metallographical characterizations, CFD, thermodynamical and thermomechanical modelling, etc. The measures taken have to do with changes in casting system (i.e. SEN design), mold design, secondary cooling modifications and regulation, strand support.

1. REVIEW OF DEFECTS IN BEAM BLANK CASTING AND THE
MEASURES PROPOSED FOR THEIR ELIMINATION
Jorge Madias – metallon, San Nicolas, Argentina
Cristian Genzano – metallon, San Nicolas, Argentina
Marco Oropeza – Gerdau Corsa, Ciudad Sahagun, Mexico
Carlos Moss – Gerdau Corsa, Ciudad Sahagun, Mexico
04/10/2017

2.  Introduction
 Surface defects
 Internal defects
 Conclusions
Content

3.  metallon
 Consulting & training company based in San Nicolas, Argentina
 Technical assistance
 Short courses
 Met lab services
 Library services
 Gerdau Corsa Sahagun
 Start-up 2015
 Consteel EAF, LF, billet/bloom/beam blank caster, universal mill
 1.000.000 tpy crude steel capacity
 700.000 tpy rolled products capacity
Introduction

4. • Background for paper preparation
– Training on defects in beam blanks at Gerdau Corsa Ciudad Sahagun
plant some time after the start-up
Introduction

5.  Beam blank casting
 Mature process, born in 1968
 ≈60 casters installed worldwide
 Focus of the paper
 Defects formation mechanism
 Solutions proposed to decrease their occurrence
 Changes in casting system (i.e. SEN design)
 Mold design
 Secondary cooling modifications and regulation
 Strand support
 Techniques used to investigate the defects
 Metallographic characterizations
 CFD, thermodynamical and thermomechanical modelling
 Plant tests
Introduction

6.  Three casting modes
Introduction
Open casting (metering nozzles)
Semi submerged casting
(metering nozzles and funnels)
Submerged casting
(two or one SEN)

7.  Mold
 Tubular: small and medium
sections
 Lower cost
 Plates: larger sections
 More alternatives to manage
water cooling
 Slots, holes with spacer,
full hole, distance
between holes, distance
to hot face
 More rigidity of the assembly
 Stability of transverse
geometry of cooling
channels
 Easy achievement of
different taper modes
Introduction

8.  Pin holes
 Usual for casting with metering nozzle with oil lubrication
 May be deleterious for the final product if
 Concentrated in a particular zone (“nest”)
 Deep enough as to not disappear in the reheating furnace
 Visible if in the first rolling steps the materials has free spreading (it
is not contained) somewhere
 Almost scale-free in the beam blank, but then in the reheating
furnace they become filled with scale
Surface defects

9.  Pin holes
 Moisture in oil
 Moisture pick-up in oil circuit
 Too high oil rate
 Inhomogeneous transverse distribution
 Too thick oil slot gap (more than 0.5 mm)
 Partial obstruction of oil slot gap by splashing
 Sudden variations in steel mold level
 Use of pulsing bomb
 Lack of deoxidation
 Electromagnetic stirring helps in pinhole elimination
Surface defects

10.  Bleeding
 As in billets, this defect occurs when small strand breakout takes place,
healing immediately, without metal loss
 Annular stress may promote bleeding
Surface defects
670 mm wide beam blank
Bleeding in the inner surface of the wing

11.  Bleeding
 Classic formation mechanism
Surface defects

12.  Trapped scum
 Typical of open casting
 Due to thorough reoxidation of
the liquid steel in contact with air
and oxidizing slag
 Usually a liquid manganese
silicate, but if a solid precipitates,
viscosity increases and
entrapment may occur
 If silicon content is too high
(due to a low Mn/Si ratio),
silica precipitation occurs,
 If aluminum wire injection in
the mold is practiced,
alumina precipitation may
occur if it is excessive or it is
not in the right point
Surface defects

13.  Casting powder entrapment
 Similar to scum entrapment
 Higher viscosity may occur in this case through
 Alumina pick-up
 Reduction reactions between elements in the steel and oxides in the
casting powder
 Example, dissolved titanium reacting with silica in the slag
 Enhanced through turbulence
 Excessive electromagnetic stirring
 Short SEN / funnel submersion
Surface defects

14.  Network cracks
 Related with high copper content in the steel
 High copper scrap charge
 Where gap between strand and mold becomes large, grain size
increases and if copper content is high, network cracking may occur
Surface defects
Rolled H Beam, Dragon Steel Corporation

15.  Longitudinal facial cracks
 Fairly common for beam blanks
 Formed in the mold
 Similar to longitudinal cracks in slabs and blooms
 In rolled product, its metallographic features are
 Internal oxidation (as polished, no etching)
 Decarburization (etching with Nital 2%)
 Oxygen penetration (hot etching with alkaline sodic chromate)
 Influencing factors
 Chemistry of the liquid steel
 Properties of the casting powder
 Deviations of caster radius caused by mold oscillation
 Primary cooling: Water flow rate and temperature
 Secondary cooling: Water flow rate
Surface defects
1050 mm wide beam blank
Longitudinal crack between web and fillet

16.  Longitudinal facial cracks
 Steel chemistry
 Sulphur content
 Carbon content
 Peritectic transformation
needs to be avoided
 POSCO scarfed beam
blanks corresponding to
2,000 heats
 0.12 – 0.13% carbon
the more sensible
range
 Stahlwerke Thüringen
 C 0.08% max
Surface defects

17.  Longitudinal facial cracks
 Casting powder
 Stahlwerke Thüringen
 Low viscosity mold flux for
small beam blanks at low
speed (<1 m/min)
 “Soft” cooling at meniscus
level was obtained
 Lower capacity for
infiltration and lubrication
compensated by low
viscosity
 JFE Steel Mitsushima
 Different set of casting
conditions
 Low viscosity gave place to
longitudinal cracks (among
other reasons)
Surface defects

18.  Longitudinal facial cracks
 Casting powder
 In cold zones of the
meniscus (i.e., close to the
SEN), casting powder may
reach the limit of its
performance and give place
to surface cracks
Surface defects

19.  Longitudinal facial cracks
 Casting speed
 Posco experience
 As the casting speed increases
 Solidifying shell is thinner
 Heat flow increases
 Strain is larger
 Result: More cracks
Surface defects

20.  Longitudinal facial cracks
 Secondary cooling
 More secondary cooling intensity, more cracking risk
Surface defects

21.  Longitudinal facial cracks
 Secondary cooling
 Extensive use of mathematical modeling
 Jin Yi Iron & Steel: optimization of secondary cooling to avoid these
cracks
 ANSYS for the thermo mechanical model
 MATLAB for parameter optimization
 Maanshan Steel: thorough modeling of secondary cooling with the
same purpose, taking into account all the mechanisms involved in heat
transfer
Surface defects

22.  Longitudinal facial cracks
 Summary of plant experiences
Surface defects
Company/Plant Year Corrective actions
JFE Steel Mizushima 1975 Decrease sulphur; increase mold flux viscosity; improve mold alignment
JFE Steel Mizushima 1981 Decrease sulphur; adequate mold flux; minimize mold misalignment; adequate
primary cooling; soft secondary cooling in first segments; better distribution of
sprays in transverse section
Stahlwerke Thüringen 1998 High basicity low viscosity casting powder
JFE Steel Fukuyama 1996 Decrease sulphur; decrease secondary cooling flow rate
Stahlwerke Thüringen 1997 C<0.08% (Mn 0.60 to ensure mechanical properties)
Posco 2002 Avoid 0.12-0.13% C; lower casting speed
Stahlwerke Thüringen 2002 Avoid 0.12% C
Jinyi Iron & Steel 2013 Lower water flow rate in all secondary cooling segments
Maanshan Steel 2014 More secondary water to fillet; less to wing ends and web center. -10%
segment 1; -7% segment 2

23.  Longitudinal facial cracks
 Corrective actions
 Metallurgy
 Low sulphur
 Avoid peritectic transformation
 Mold flux
 High basicity
 Even heat transfer
 Mold design
 To avoid longitudinal cracks in the shoulder
 Secondary cooling
 Less water, mostly for the first segments
 Better transverse distribution
Surface defects

24.  Blowholes
 Depending on the root cause,
they may be concentrated in
the first heat of the sequence
or in some given heat, or all
along the sequence
 Start: close to the beam blank
surface, when there is enough
gas segregation to the
interdendritic spaces
 End: when somewhere below
the meniscus, the ferrostatic
pressure is higher than the gas
pressure
Internal defects

25.  Blowholes
 Excess of gases dissolved in the steel (oxygen, nitrogen, hydrogen),
enough to produce a bubble
 Compromise between clogging and blowholes
Internal defects

26.  Blowholes
 Typical industrial cases
 High oxygen
 Lack of deoxidation
(coordination, slag carry
over)
 High oxygen and nitrogen
 First heat of the
sequence
 High hydrogen
 Moisture in new lining of
ladle or tundish
 High nitrogen
 Ladle with long
treatment, when nitrogen
is used for stirring
Internal defects

27.  Blowholes
 Dragon Steel Corp. case
 Casting with metering nozzle
 80 kg Al addition during tapping
 40 kg CaFe to get O<10 ppm
 Oxygen injection in tundish if temperature too low
 Thorough study of LMF and caster variables
 High moisture in tundish repair refractory material
Internal defects

28.  Web central cracks
 Equivalent to centerline
segregation in slabs
 Not enough support length
 Insufficient secondary cooling
 Bulging, and in severe cases, an
internal opening in the web
 Rolled H beam
 Central segregation
 Crack formation
 Some countermeasures
 Efficient use of roll checker
 Equipment for segment
alignment
Internal defects

29.  Web central cracks
 JFE Steel Mitzushima
 Caster 12.5 m radius, funnel
casting
 400 x 460 x 120 mm
 287 x 560 x 120 mm
 Influence of sulphur content
and casting speed
 Solutions
 Intensive spray cooling
on the web portion
 Strict maintenance of
roll gap
Internal defects

30.  Inner crack in wing end
 May promote strand breakout
 Resemble off-corner cracks in billets and slabs
Internal defects

31.  Inner crack in wing end
 JFE Steel Kurashiki case
 Strand breakout in some heats
 Improvement plan
 Solution: optimization of mold taper in wing ends
Internal defects
Study Objective
Observation of breakout boxes Research solidification in mold; find cause
Solidification macrostructure Mechanism of formation of inner cracks in wing end
Sulphur addition test Measurement of shell thickness in normal operation
Mold temperature Estimation of heat flow in several parts of the mold

32.  Beam blank casting is an established process with a 50 years history
 Not free of surface and inner defects
 Some of them share features with billet defects; other has more to do with
slab defects
 Complex shape induces specific solidification defects
 Occurrence of defects requires improvement plans
 Defect characterization is important
 Modeling is thoroughly used to elucidate formation mechanisms and to
suggest corrective measures
Conclusions

33. • jorge.madias@metallon.com.ar +54 9 336 421 1990
Thank you!
Jorge Madias (1), Cristian Genzano (1), Marco Oropeza (2), Carlos Moss (2)
(1) metallon, San Nicolas, Argentina
(2) Gerdau Corsa, Ciudad Sahagun, Mexico