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Metals
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Continuous Casting and Hot Ductility of Advanced High-Strength Steels
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Continuous Casting and Hot Ductility of Advanced High-Strength Steels

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 August 2023) | Viewed by 10354

Special Issue Editor

Prof. Dr. Barrie Mintz

E-Mail Website
Guest Editor
Mechanical and Aeronautical Engineering, City, University of London, Northampton Square, London EC1V OHB, UK
Interests: hot ductility of steels; structure/property relationships in steels
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

AHSS (advanced high-strength steels) are a very attractive option for the automobile industry. They have exceptional strength and ductility, which allow them to be fabricated without cracking, enabling thinner-gauge steel to be used. The weight reduction leads to a reduction in petrol consumption and harmful emissions, and for electrically operated automobiles, reduced energy requirements. However, their high production and material costs (e.g., high Mn level in TWIP steels) combined with their difficulty in continuous casting, restricts their more widespread usage. The aim of this Special Issue is to primarily select papers which deal with the ease of continuously casting these steels, but papers on their room-temperature properties will also be considered, as often the compositions giving excellent properties give poor hot ductility.

The AHSS involved are TWIP, TRIP-assisted and bainitic steels. High additions (>1%) of Al and Si are often added to give them their desired properties. However, Al additions greater than or equal to 1% cause problems with cracking on straightening, as AlN often forms as a thin coating over the austenite grain surfaces, leading to intergranular failure. Although much can be learned from the equilibrium thermodynamical predictions, little is known about the precipitation of AlN under the non-equilibrium conditions as they apply to industry, particularly as AlN precipitates so sluggishly; therefore, papers related to this problem are welcome.

The scope of this Special Issue covers the hot ductility of these steels and the latest innovations which may affect the ability to cast them. The influence of micro-alloying elements (e.g., Nb, V, Ti) for increasing the room-temperature yield strength via precipitation hardening and grain refinement, and the effect of these additions on their cracking susceptibility on straightening, need to be addressed, as does the influence of boron additions on improving their hot ductility.

Prof. Dr. Barrie Mintz
Guest Editor

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Keywords

  • continuous casting
  • hot ductility
  • Al
  • microalloying additions
  • Boron
  • TWIP
  • TRIP
  • AHSS

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Published Papers (9 papers)

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Research

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24 pages, 70786 KiB  
Article
The Hot Ductility, Microstructures, Mechanical Properties and Corrosion Resistance in an Advanced Boron-Containing Complex Phase Steel Heat-Treated Using the Quenching and Partitioning (Q&P) Process
by Antonio Enrique Salas-Reyes, Gerardo Altamirano-Guerrero, Rogelio Deaquino, Armando Salinas, Gabriel Lara-Rodriguez, Ignacio Alejandro Figueroa, Jesús Rafael González-Parra and Barrie Mintz
Metals 2023, 13(2), 257; https://doi.org/10.3390/met13020257 - 28 Jan 2023
Cited by 4 | Viewed by 2095
Abstract
The objective of this research work is to obtain the hot ductility behavior, and the structural, microstructural and mechanical characteristics of one of the latest generation of AHSS steels, a complex phase (CP) steel microalloyed with boron (0.006 wt.%), processed by hot and [...] Read more.
The objective of this research work is to obtain the hot ductility behavior, and the structural, microstructural and mechanical characteristics of one of the latest generation of AHSS steels, a complex phase (CP) steel microalloyed with boron (0.006 wt.%), processed by hot and cold rolling operations and heat-treated using two different quenching and partitioning (Q&P) treatments, a one-step partitioning (quenching to 420 °C) and the other a two-step partitioning (quenching to 420 °C and reheated to 600 °C). The results show that boron has a marked effect on the solidification process of the CP steel, refining the austenitic grain size. Due to its refinement, the boron-containing steel had better ductility throughout the temperature range examined (700–900 °C), i.e., the hot ductility trough. Thus, the minimum percentage of reduction in area (%RA) value occurring at 800 °C was 43% for the boron-free steel, compared with 58% for the boron-containing steel. Hence, cracking would not be a problem when straightening the strand on continuous casting. The benefit of boron addition on the room temperature properties was found to be very marked for the higher temperature two-step partitioning treatment, giving a yield stress of 1200 MPa, a UTS (ultimate tensile strength) of 1590 MPa and a total elongation above 11%. The final Q&P microstructure, in both one- and two-step partitioning conditions, consisted of retained austenite (RA-γ), martensite and ferrite islands in a bainitic matrix. Furthermore, the boron treated steel on quenching produced a greater amount of RA-γ, which accounted for its better room temperature ductility and produced a martensitic matrix rather than a bainitic one, giving it greater strength. The addition of boron improved the corrosion resistance of this type of third generation AHSS steel. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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14 pages, 7180 KiB  
Article
The Influence of High Vanadium and Phosphorus Contents on the Risk of Transverse Cracking during the Continuous Casting of Austenitic TWIP Steels
by Ingrid Morel, Blandine Remy, Anne Dez, Barrie Mintz and Colin Scott
Metals 2023, 13(1), 26; https://doi.org/10.3390/met13010026 - 22 Dec 2022
Viewed by 1554
Abstract
There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation [...] Read more.
There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation strengthening and grain refinement. However, the effect on slab quality during continuous casting has not been determined. In this study, the hot ductility of two twinning-induced plasticity (TWIP) steels, Fe-0.6C-22Mn and Fe-0.6C-22Mn-0.2V, was examined over the temperature range 650–1200 °C. Tensile samples were taken from continuous cast 225 mm slabs and from 36 mm transfer bars. The addition of V caused the ductility trough in the temperature range 650–900 °C to deepen and widen and the lowest reduction in area (RA) recorded in the as-cast condition was 30%. This deterioration of hot ductility was due to V(C,N) precipitation. Even though the minimum RA was below the value often accepted to avoid cracking, no transverse cracking was observed in industrial trials and the surface quality was acceptable. The RA values of Fe-0.6C-22Mn were found to be very sensitive to the P level. However, this sensitivity was less evident when V was added, possibly due to P trapping by VC at austenite boundaries. No transverse cracking was observed in industrially produced slabs with P in the range examined (0.02 to 0.04 wt.% P). Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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10 pages, 4363 KiB  
Article
Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces
by Dannis Rorisang Nkarapa Maubane, Roelf Johannes Mostert and Kevin Mark Banks
Metals 2022, 12(12), 2155; https://doi.org/10.3390/met12122155 - 15 Dec 2022
Cited by 3 | Viewed by 1328
Abstract
The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax [...] Read more.
The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax, followed by secondary cooling. The negative effect of a low Tmin on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the Ar3, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a Tmin of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when Tmin was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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20 pages, 5553 KiB  
Article
Thermomechanical and Microstructural Analysis of the Influence of B- and Ti-Content on the Hot Ductility Behavior of Microalloyed Steels
by Marina Gontijo, Arnab Chakraborty, Richard F. Webster, Sergiu Ilie, Jakob Six, Sophie Primig and Christof Sommitsch
Metals 2022, 12(11), 1808; https://doi.org/10.3390/met12111808 - 25 Oct 2022
Cited by 3 | Viewed by 1640
Abstract
The effects of the combined addition of B and Ti, as well as the influence of different strain rates on the hot ductility behavior of low carbon, continuously cast, microalloyed steels were investigated in this work. Tensile tests, microstructure analyses, and thermokinetic simulations [...] Read more.
The effects of the combined addition of B and Ti, as well as the influence of different strain rates on the hot ductility behavior of low carbon, continuously cast, microalloyed steels were investigated in this work. Tensile tests, microstructure analyses, and thermokinetic simulations were performed with in situ melted samples. Furthermore, prior austenite grain evaluations were carried out for the two different microalloyed steels. Increasing the strain rate brought improvements to the ductility, which was more significant in the steel with the leanest composition. The steel containing more B and Ti presented a better hot ductility behavior under all conditions tested. The main causes for the improvements rely on the precipitation behavior and the austenite–ferrite phase transformation. The preferential formation of TiN instead of fine BN and AlN was seen to be beneficial to the ductility, as well as the absence of MnS. Grain boundary segregation of free B that did not form BN retarded the ferrite formation, avoiding the brittleness brought by the thin ferrite films at the austenite grain boundaries. Furthermore, it was revealed that for the steels in question, the prior austenite grains have less influence on the hot ductility behavior than the precipitates and ferrite formation. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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15 pages, 5164 KiB  
Article
Deep Learning to Predict Deterioration Region of Hot Ductility in High-Mn Steel by Using the Relationship between RA Behavior and Time-Temperature-Precipitation
by Ji-Yeon Jeong, Dae-Geun Hong and Chang-Hee Yim
Metals 2022, 12(10), 1689; https://doi.org/10.3390/met12101689 - 10 Oct 2022
Cited by 4 | Viewed by 1738
Abstract
Reduction of area (RA) measurement in a hot ductility test is widely used to define the susceptibility of surface crack of cast steel, but the test is complex because it entails processes such as specimen fabrication, heat treatment, tensile testing, and analysis. As [...] Read more.
Reduction of area (RA) measurement in a hot ductility test is widely used to define the susceptibility of surface crack of cast steel, but the test is complex because it entails processes such as specimen fabrication, heat treatment, tensile testing, and analysis. As an alternative, this study proposes a model that can predict RA. The model exploits the relationship between precipitation and RA behavior, which has a major effect on hot ductility degradation in high-Mn steels. Hot ductility tests were performed using four grades of high-Mn steels that had different V-Mo compositions, and the RA behavior was compared with the precipitation behavior obtained from a time-temperature-precipitation (TTP) graph. The ductility deterioration of high-Mn steels shows a tendency to start at the nose temperature TN at which precipitation is most severe. Using this relationship, we developed a model to predict the hot ductility degradation temperature of high-Mn steels. TN was calculated using J-matpro software (version 12) for 1500 compositions of high-Mn steels containing the precipitating elements V, Mo, Nb, and Ti, and by applying this to a deep neural network (DNN), then using the result to develop a model that can predict TN for various compositions of high-Mn steel. The model was tested by comparing its predicted RA degradation temperature with RAs extracted from reference data for five high-Mn steels. In all five steels, the temperature at which the RA decreases coincided with the value predicted by the DNN model. Use of this model can eliminate the cost and time required for hot ductility testing to measure RA. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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13 pages, 3410 KiB  
Article
Influence of Cu and Ni on the Hot Ductility of Low C Steels with Respect to the Straightening Operation When Continuous Casting
by Osvaldo Comineli, Abdullah Qaban and Barrie Mintz
Metals 2022, 12(10), 1671; https://doi.org/10.3390/met12101671 - 5 Oct 2022
Cited by 6 | Viewed by 2366
Abstract
Cu-containing steels can suffer from hot shortness unless Ni is added to protect them but whether this problem also influences the straightening operation is not clear. Previous work on hot ductility has found that only when the tensile samples from Cu-containing steels are [...] Read more.
Cu-containing steels can suffer from hot shortness unless Ni is added to protect them but whether this problem also influences the straightening operation is not clear. Previous work on hot ductility has found that only when the tensile samples from Cu-containing steels are oxidised can any deleterious influence of copper be found. However, this paper shows that oxidation is not essential. It is more complex than that and, as Cu has been suggested for TRIP steels at levels up to 2.5% Cu to increase their strength and ductility, a greater understanding is required, both of hot shortness and cracking during straightening. The present paper explores the hot ductility behaviour of steels alloyed with Cu and Ni in the straightening temperature range, 700–1000 °C, when tested in air and in an argon atmosphere. Segregation of Cu to the sulphides and grain boundaries occurred allowing the formation of fine Cu2S particles at the austenite grain boundaries favouring intergranular failure and this was more pronounced under oxidising conditions and required strain. It was concluded that a Cu addition, as well as causing hot shortness at higher temperatures will also cause cracking problems in the straightening temperature range in the more sensitive to cracking grades of steel and although the problems are different they are nevertheless interrelated and provided there is sufficient Ni, both may be avoided. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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Review

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28 pages, 7139 KiB  
Review
The Influence of Small Additions of Alloying Elements on the Hot Ductility of AHSS Steels: A Critical Review Part 2
by Barrie Mintz, Abdullah Qaban and Shin Eon Kang
Metals 2023, 13(2), 406; https://doi.org/10.3390/met13020406 - 16 Feb 2023
Cited by 6 | Viewed by 1871
Abstract
In this paper, the influence of small additions of Cr, Mo, Cu, Ni, B, Ca, Zr, and Ce on the hot ductility of advanced high-strength steels (AHSS) has been reviewed. Most of these small additions have a positive effect in improving hot ductility [...] Read more.
In this paper, the influence of small additions of Cr, Mo, Cu, Ni, B, Ca, Zr, and Ce on the hot ductility of advanced high-strength steels (AHSS) has been reviewed. Most of these small additions have a positive effect in improving hot ductility on straightening during continuous casting operations and should be considered when problems with cracking in continuous casting are encountered. In many of these cases, the reason for these generally small but important improvements in hot ductility is not known with certainty, but the segregation of these elements to the austenite grain boundaries, strengthening the bonding, is often suggested. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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10 pages, 4988 KiB  
Review
The Hot Ductility of TWIP and TRIP Steels—An Alternative Interpretation
by John Campbell
Metals 2022, 12(12), 2134; https://doi.org/10.3390/met12122134 - 13 Dec 2022
Cited by 1 | Viewed by 1506
Abstract
There is significant evidence from light metals that turbulence in casting leads to bifilm defects; enfolded, doubled-over oxide films which act like cracks in the liquid, and are inherited as cracks by the solid. This population of introduced cracks is now known to [...] Read more.
There is significant evidence from light metals that turbulence in casting leads to bifilm defects; enfolded, doubled-over oxide films which act like cracks in the liquid, and are inherited as cracks by the solid. This population of introduced cracks is now known to significantly influence the tensile failure behaviour of light alloys. There is evidence that analogous defects exist in steels. This paper examines the possibility that bifilms may control the hot ductility of TWIP and TRIP steels, and therefore the problems of straightening during continuous casting. Techniques for overcoming these problems are indicated. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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31 pages, 102999 KiB  
Review
The Influence of Precipitation, High Levels of Al, Si, P and a Small B Addition on the Hot Ductility of TWIP and TRIP Assisted Steels: A Critical Review
by Barrie Mintz and Abdullah Qaban
Metals 2022, 12(3), 502; https://doi.org/10.3390/met12030502 - 16 Mar 2022
Cited by 14 | Viewed by 2966
Abstract
The hot ductility of Transformation Induced Plasticity (TRIP) and Twinning Induced Plasticity (TWIP) steels is reviewed, concentrating on the likelihood of cracking occurring on continuous casting during the straightening operation. In this review, the influence of high levels of Al, Si, P, Mn [...] Read more.
The hot ductility of Transformation Induced Plasticity (TRIP) and Twinning Induced Plasticity (TWIP) steels is reviewed, concentrating on the likelihood of cracking occurring on continuous casting during the straightening operation. In this review, the influence of high levels of Al, Si, P, Mn and C on their hot ductility will be discussed as well as the important role B can play in improving their hot ductility. Of these elements, Al has the worst influence on ductility but a high Al addition is often needed in both TWIP and TRIP steels. AlN precipitates are formed often as thin coatings covering the austenite grain surfaces favouring intergranular failure and making them difficult to continuous cast without cracks forming. Furthermore, with TWIP steels the un-recrystallised austenite, which is the state the austenite is when straightening, suffers from excessive grain boundary sliding, so that the ductility often decreases with increasing temperature, resulting in the RA value being below that needed to avoid cracking on straightening. Fortunately, the addition of B can often be used to remedy the deleterious influence of AlN. The influence of precipitation hardeners (Nb, V and Ti based) in strengthening the room temperature yield strength of these TWIP steels and their influence on hot ductility is also discussed. Full article
(This article belongs to the Special Issue Continuous Casting and Hot Ductility of Advanced High-Strength Steels)
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