Characterization and Elimination of Solidification Hooks ... … · Hooks in Continuous Slab...
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Characterization and Elimination of Solidification Hooks in Continuous Slab Castings Samantha Chon-Briggs, Yuzhe Liu, Stephen Schriver, Fan Zhang Faculty Advisor: Prof. Matthew Krane Industrial Sponsor: Richard Gass Project Background ArcelorMittal at Indiana Harbor has expressed interest in the characterization and elimination of solidification hooks in their ultra-low carbon automotive steel slabs. The entrapped non-metallic inclusion at the solidification hook is a defect. Through literature review, metallographic optical microscopy, hook length and depth study, and experimental etchant trials, recommendations for ideal casting parameters for hook elimination and optimal sample preparation for microstructure study could be made. Hooks measured after Trial 3 had a near 45% decrease in depth and a 64% decrease in length. Experimental Procedure ● An increase in casting speed and oscillation frequency can relatively decrease solidification hook length and depth. ● Etching with Picric acid and Zephiramine bring out the clearest outline of the hook structures. Recommendations Discussion MSE 430- 440: Materials Processing and Design This work is sponsored by ArcelorMittal Indiana Harbor, East Chicago, IN Criterion for Identifying Solidification Hooks Etching Method Composition of Etchants Temperature Time 1 Ethanol 9.5ml Concentrated Nitric Acid 0.5ml Room Temp 45 s 2 Ethanol 96ml Picric Acid 4g Room Temp 31 hr 3 Water 100ml Picric Acid 1.1g Zephiramine (1%) 0.75ml Room Temp 13 hr 4 Cucl 2 2.5g Mgcl 2 10g Concentrated HCl 5ml Ethanol 250ml Room Temp 5 min Table II. Etchants and etching conditions Etching Method 3 Etching Method 4 Etching Method 2 Figure 4(a)&(b) Narrow face samples from Trial 1 casting parameters. Figure 6(a) Broad face samples from Trial 2 casting parameters. Figure 6(b) Broad face samples from Trial 3 casting parameters. Figure 7(a)&(b) Narrow face samples from Trial 3 casting parameters. Casting Direction Casting Direction Casting Direction Figure 8. Graph of sample Trial 1 and 3 (narrow face only)vs. the solidification hook depth and length. 1. Hook length 2. Hook depth (end of hook- OM) 3. Hook depth (OM-edge) 4. Hook depth (end of hook- edge) Casting Direction Figure 5(a) Narrow face samples from Trial 1 casting parameters. Figure 5(b) Broad face samples from Trial 2 casting parameters. Results a a b b a b Three separate casting trials were conducted by ArcelorMittal during the duration of this project, and their casting velocity and oscillation frequency inputs had a pronounced effect on hook length and depth. Trial 1 was the original, unchanged ArcelorMittal casting parameters for this steel grade, with its inputs listed in Table I. Research conducted by Brian Thomas et al. led to our first recommendation, listed as Trial 2. This trial proposed an increase in casting velocity in order to decrease hook length and depth. Trial 3 was similar, but increased oscillation frequency as well. Trials 1 and 3 were sampled from the ‘narrow’ face of the steel slabs, whereas Trial 2 was sampled from the ‘broad’ face. Narrow face refers to the thinner surface on the sides of the steel slab, while broad face refers to the longer top and bottom surfaces. For this reason, Trial 2 samples were unable to be compared directly with Trials 1 and 3. Figure 8 shows a significant decrease in hook length and depth from Trial 1 parameters to Trial 3 parameters. Figure 9 shows the comparison of hook measurements between the broad face samples and the narrow face samples. Hooks from the broad face have proven to be longer and deeper, on average, than the narrow face hooks. This might be due to the slab shell bulges in the spaces between the top side containment rolls and in the spaces between bottom side containment rolls. After the slab bulges, the next roll down in the caster pushes the bulge flat again, causing some amount of deformation to the hook. Etching Techniques The nital used in Figure 4 only reveals the segregation of different grain structures below and above the hook. This segregation of different hook structures may be due to the fact that the solidification rate differs on either side of the hook. But nital does not bring out the clear outline of the hook structure, making it difficult to identify the starting and ending points of the hook shape. In Figure 5 Picric acid and ethanol bring out clearer hook structures than nital etching. The limitation is that this process takes up to 31 hours. Picric acid with additions of Zephiramine reveals the clearest outline of the hook structure indicated in Figure 6(a). With this surfactant, the reaction of the etchants accelerates. But the limitation is it still takes up to 13 hours to reveal the hook shape. Mold Powder: The solidification temperature of mold powder from Trial 1 & 3 are the same. The mold powder from Trial 2 has higher solidification temperature. The hook dimensions and shape will be influenced by the high solidification temperature of the mold powder.[3] Figure 9. Comparison of hook dimensions between broad face and narrow face sample of Trial 3. Trial Casting Speed (mm/min) Oscillation Stroke Length (mm) Oscillation Frequency (cycles/min) Superheat (℃) Mold Fluctuation (mm) Negative Strip Time (seconds /cycle) Mold Powder Solidification Temp(℃) 1 1303 5.47 159 21 1 0.128 1035 2 1504 5.98 159 30 2 0.124 1115 3 1499 4.99 210 24 3 0.099 1035 Table I. Casting Parameters for 3 separate trials Trial 1 is the original ArcelorMittal process, while Trial 2 and Trial 3 were process parameters recommended by the senior design team. The equation predicts the average hook depth from the casting conditions: V c is casting speed, F is oscillation frequency, T s is superheat temperature difference, L F is mean level fluctuation during sampling, T sol is the solidification temperature of mold powder. [ a b The micrographs below represent experimental etchant testing on steel samples from Trials 1, 2, and 3. Four etching techniques listed in Table 2 were tested in order to achieve and document the optimal method for revealing solidification hook structures within the steel microstructure. The red arrow indicates the casting direction of the samples. The red curve line indicates the solidification hook shape. Etching Method 1 Casting Direction Molten steel flows from a ladle, through a tundish into the mold. Slag cover over the liquid surface prevents oxygen from reacting to form detrimental oxide inclusions. Solidification Hooks are distinct subsurface microstructural features that accompany oscillation marks and can entrap gas bubbles, oxides, and other defects. Hooks form and result in microstructure grains curving up and away from the oscillation mark and casting direction. Characterization of Hooks The predictive hook equation shown in the following section correlates casting parameters with hook dimensions, so in order to study these hooks within the microstructure, optimal etching techniques had to be developed and tested. References 1. Intro to Continuous Casting - CCC - U of I . ( n . d . ) . Retrieved April 19 , 2016 , from http : //ccc . illinois . edu/introduction/overview . html#techniques 2. Sengupta , Joydeep . ( 2006 ) . A New Mechanism of Hook Formation during Continuous Casting of Ultra - Low - Carbon Steel Slabs . Metallurgical & Materials Transactions . Part A, 37 A ( 5 ), 1597 - 1612 . 3. Lee, G.-G. (2009). Prediction and control of subsurface hooks in continuous cast ultra-low-carbon steel slabs. Ironmaking & Steelmaking, 36(1), 39-50. Figure 1. Schematic of continuous casting process [1] Figure 2. Etched sections of curved hooks (left) and straight hooks (right) [2] Figure 3. Curved hooks from narrow face samples. [3]
Transcript of Characterization and Elimination of Solidification Hooks ... … · Hooks in Continuous Slab...
Characterization and Elimination of Solidification Hooks in Continuous Slab CastingsSamantha Chon-Briggs, Yuzhe Liu, Stephen Schriver, Fan Zhang Faculty Advisor: Prof. Matthew KraneIndustrial Sponsor: Richard Gass
Project Background
ArcelorMittal at Indiana Harbor has expressed interest in the characterization and elimination of solidificationhooks in their ultra-low carbon automotive steel slabs. The entrapped non-metallic inclusion at the solidificationhook is a defect. Through literature review, metallographic optical microscopy, hook length and depth study,and experimental etchant trials, recommendations for ideal casting parameters for hook elimination and optimalsample preparation for microstructure study could be made. Hooks measured after Trial 3 had a near 45%decrease in depth and a 64% decrease in length.
Experimental Procedure
● An increase in casting speed and oscillationfrequency can relatively decrease solidificationhook length and depth.
● Etching with Picric acid and Zephiramine bring out the clearest outline of the hook structures.
Recommendations
Discussion
MSE 430-440: Mater ials Processing and Design
This work is sponsored by ArcelorMittal Indiana Harbor, East Chicago, IN
Criterion for Identifying Solidification Hooks
Etching Method Composition of Etchants Temperature Time
1 Ethanol 9.5mlConcentrated Nitric Acid 0.5ml
Room Temp 45 s
2 Ethanol 96mlPicric Acid 4g
Room Temp 31 hr
3 Water 100mlPicric Acid 1.1g
Zephiramine (1%) 0.75ml
RoomTemp
13 hr
4 Cucl2 2.5gMgcl2 10g
Concentrated HCl 5mlEthanol 250ml
Room Temp 5 min
Table II. Etchants and etching conditions
Etching Method 3
Etching Method 4
Etching Method 2
Figure 4(a)&(b) Narrow face samples from Trial 1 casting parameters.
Figure 6(a) Broad face samples from Trial 2 castingparameters. Figure 6(b) Broad face samples fromTrial 3 casting parameters.
Figure 7(a)&(b) Narrow face samples from Trial 3casting parameters.
Casting Direction
Casting Direction
Casting Direction
Figure 8. Graph of sample Trial 1 and 3 (narrow face only)vs. the solidification hook depth and length.
1. Hook length 2. Hook depth
(end of hook-OM)
3. Hook depth (OM-edge)
4. Hook depth (end of hook-edge)Casting Direction
Figure 5(a) Narrow face samples from Trial 1 castingparameters. Figure 5(b) Broad face samples fromTrial 2 casting parameters.
Results
a
a
b
b
a b
Three separate casting trials were conducted byArcelorMittal during the duration of this project, andtheir casting velocity and oscillation frequency inputshad a pronounced effect on hook length and depth.Trial 1 was the original, unchanged ArcelorMittalcasting parameters for this steel grade, with itsinputs listed in Table I. Research conducted by BrianThomas et al. led to our first recommendation, listedas Trial 2. This trial proposed an increase in castingvelocity in order to decrease hook length and depth.Trial 3 was similar, but increased oscillationfrequency as well.Trials 1 and 3 were sampled from the ‘narrow’ faceof the steel slabs, whereas Trial 2 was sampled fromthe ‘broad’ face. Narrow face refers to the thinnersurface on the sides of the steel slab, while broadface refers to the longer top and bottom surfaces.For this reason, Trial 2 samples were unable to becompared directly with Trials 1 and 3. Figure 8shows a significant decrease in hook length anddepth from Trial 1 parameters to Trial 3 parameters.Figure 9 shows the comparison of hookmeasurements between the broad face samples andthe narrow face samples. Hooks from the broad facehave proven to be longer and deeper, on average,than the narrow face hooks. This might be due to theslab shell bulges in the spaces between the top sidecontainment rolls and in the spaces between bottomside containment rolls. After the slab bulges, the nextroll down in the caster pushes the bulge flat again,causing some amount of deformation to the hook.Etching TechniquesThe nital used in Figure 4 only reveals thesegregation of different grain structures below andabove the hook. This segregation of different hookstructures may be due to the fact that thesolidification rate differs on either side of the hook.But nital does not bring out the clear outline of thehook structure, making it difficult to identify thestarting and ending points of the hook shape. InFigure 5 Picric acid and ethanol bring out clearerhook structures than nital etching. The limitation isthat this process takes up to 31 hours. Picric acidwith additions of Zephiramine reveals the clearestoutline of the hook structure indicated in Figure 6(a).With this surfactant, the reaction of the etchantsaccelerates. But the limitation is it still takes up to 13hours to reveal the hook shape.Mold Powder:The solidification temperature of mold powder fromTrial 1 & 3 are the same. The mold powder from Trial2 has higher solidification temperature. The hookdimensions and shape will be influenced by the highsolidification temperature of the mold powder.[3]
Figure 9. Comparison of hook dimensions between broad face and narrow face sample of Trial 3.
Trial Casting Speed
(mm/min)
Oscillation Stroke
Length (mm)
Oscillation Frequency
(cycles/min)
Superheat (℃)
Mold Fluctuation
(mm)
Negative Strip Time
(seconds/cycle)
MoldPowder
Solidification Temp(℃)
1 1303 5.47 159 21 1 0.128 1035
2 1504 5.98 159 30 2 0.124 1115
3 1499 4.99 210 24 3 0.099 1035
Table I. Casting Parameters for 3 separate trials
Trial 1 is the original ArcelorMittal process, while Trial2 and Trial 3 were process parameters recommendedby the senior design team.
The equation predicts the average hook depth fromthe casting conditions: Vc is casting speed, F isoscillation frequency, Ts is superheat temperaturedifference, LF is mean level fluctuation duringsampling, Tsol is the solidification temperature of moldpowder.
[
a b
The micrographs below represent experimentaletchant testing on steel samples from Trials 1, 2, and3. Four etching techniques listed in Table 2 weretested in order to achieve and document the optimalmethod for revealing solidification hook structureswithin the steel microstructure. The red arrowindicates the casting direction of the samples. Thered curve line indicates the solidification hook shape.
Etching Method 1 Casting Direction
Molten steel flows from aladle, through a tundish intothe mold.Slag cover over the liquidsurface prevents oxygenfrom reacting to formdetrimental oxide inclusions.
Solidification Hooks aredistinct subsurfacemicrostructural featuresthat accompany oscillationmarks and can entrap gasbubbles, oxides, and otherdefects.
Hooks form and resultin microstructuregrains curving up andaway from theoscillation mark andcasting direction.
Characterization of HooksThe predictive hook equation shown in the followingsection correlates casting parameters with hookdimensions, so in order to study these hooks withinthe microstructure, optimal etching techniques had tobe developed and tested.
References1. Intro to Continuous Casting - CCC - U of I. (n.d.). Retrieved April 19, 2016, from http://ccc.illinois.edu/introduction/overview.html#techniques2. Sengupta, Joydeep. (2006). A New Mechanism of Hook Formation during Continuous Casting of Ultra-Low-Carbon Steel Slabs.
Metallurgical & Materials Transactions. Part A, 37A(5), 1597-1612.3. Lee, G.-G. (2009). Prediction and control of subsurface hooks in continuous cast ultra-low-carbon steel slabs. Ironmaking & Steelmaking,
36(1), 39-50.
Figure 1. Schematic of continuous casting process [1]
Figure 2. Etched sections of curved hooks (left) and straight hooks
(right) [2]
Figure 3. Curved hooks from narrow face samples.
[3]
