Effect of strain on formation of ultrafine ferrite in surface of hot rolled microalloyed steel

Priestner, R.; Alhorr, Yousef; Ibraheem, A.K.

doi:10.1179/026708302225004900

Cited by 33 publications

(22 citation statements)

References 4 publications

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“…The results published to date agree that a Ti/N ratio below the stoichiometric ratio (3.42) yields good results in to control austenite grain size, especially when precipitation takes place in the solid state as finer precipitates are obtained. [12][13][14] Previous studies on the influence of Ti on the hot flow stress during hot deformation in steels 15,16) established a quantitative dependence of the activation energy on the Ti content in the steels, without considering the precipitation state distribution, i.e. the precipitate size and precipitated volume.…”

Section: Introductionmentioning

confidence: 99%

Influence of the Size and Volume Fraction of TiN Particles on Hot Strength and Dynamic Recrystallisation in Structural Steels

Medina¹,

Vega²,

Gómez³

et al. 2005

ISIJ Int.

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The low solubility of titanium nitrides (TiN) in austenite is taken advantage of in structural steels to control the evolution of the microstructure in the hot rolling process and in the heat affected zone (HAZ) in processes involving the application of heat, such as welding. However, the quantitative influence of the precipitation state of these particles on hot strength and dynamic recrystallisation kinetics, given by the precipitate size distribution and the precipitated volume, is practically unknown. The present work studies the influence of various Ti and N compositions, which give rise to different precipitation states at the reheating temperatures, on the aforementioned phenomena. The influence of the precipitation state on hot strength has been quantified by changes in the peak stress and the activation energy. A maximum has been obtained for the activation energy which corresponds to a Ti/N ratio of approximately 1.3. The model used to predict the flow curve and dynamic recrystallisation kinetics has been improved, extending it to include microalloyed steels containing Ti.

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Section: Introductionmentioning

confidence: 99%

Influence of the Size and Volume Fraction of TiN Particles on Hot Strength and Dynamic Recrystallisation in Structural Steels

Medina¹,

Vega²,

Gómez³

et al. 2005

ISIJ Int.

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show abstract

“…The results reported in the literature agree that a Ti/N ratio of between 1 and 3, less than the stoichiometric ratio (3.42), provides good results in austenite grain size control, especially when precipitation takes place in the solid state, since finer precipitates are obtained. [10][11][12] Previous studies dealing with the influence of Ti on static recrystallisation kinetics 13,14) established a quantitative dependence of activation energy on the Ti content in the steel, without considering the precipitation state, i.e. the size and volume precipitated.…”

Section: Introductionmentioning

confidence: 99%

“…34) It should also be noted that the value of (Q x for steel S2 was negative, and this must be interpreted in the sense that a certain amount of TiN precipitates have acted as nucleation sites for recrystallised grains, due to their greater size compared with the precipitates of other steels, except for steel S3. (12) Expression (12) establishes that the influence of the precipitation state on the activation energy for static recrystallisation may be expressed as a function of the Ti/N ratio, except if the steel contains Ti in solution, since the drag solute effect is of a different nature. Therefore, expression (12) does not take into account the Ti content in solution and would only be valid if practically all of the Ti was precipitated, as occurs in all the studied steels with the exception of steel S3.…”

mentioning

confidence: 99%

“…(12) Expression (12) establishes that the influence of the precipitation state on the activation energy for static recrystallisation may be expressed as a function of the Ti/N ratio, except if the steel contains Ti in solution, since the drag solute effect is of a different nature. Therefore, expression (12) does not take into account the Ti content in solution and would only be valid if practically all of the Ti was precipitated, as occurs in all the studied steels with the exception of steel S3.…”

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confidence: 99%

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Influence of TiN Particle Precipitation State on Static Recrystallisation in Structural Steels

Vega¹,

Medina²,

Quispe

et al. 2005

ISIJ Int.

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This paper studies the influence of different Ti and N contents, which give rise to different precipitation states at the reheating temperatures, on the static recrystallisation of austenite in structural steels. The influence of the precipitation state has been quantified by the changes in the activation energy value (Q x ), which measures the greater or lesser facility for grain boundary self-diffusion, the mechanism that is responsible for recrystallisation. A maximum has been obtained for the activation energy which corresponds to the finest precipitate distribution and a Ti/N ratio close to unity, although the excess Ti content in solution also contributes to a considerable increase in Q x . The values obtained for the driving forces of recrystallisation have always been greater than the pinning forces, allowing static recrystallisation to take place irrespective of the chemical composition of the steel and the strain applied.KEY WORDS: Ti/N ratio; static recrystallisation; precipitation state; activation energy. austenite grain size, and an intrinsic magnitude of the material, related with the mechanism that regulates the process: the activation energy. [15][16][17] The aim of this work is to study the quantitative influence of the precipitation state of TiN particles, defined by the precipitated volume and size distribution, replacing the latter by the average precipitate size, on static recrystallisation kinetics in microalloyed steels with Ti. In particular, the activation energy value measures with good approximation the greater or lesser difficulty for the static recrystallisation of austenite to take place. Experimental ProcedureSix steels were manufactured in a vacuum induction furnace from high purity electrolytic iron. On the basis of their nitrogen content, the steels can be classified in two groups ( Table 1). The first group includes three steels with 40 ppm nitrogen (S1, S2 and S3) and the second group the other three steels with 80 ppm nitrogen (S4, S5 and S6). Steels S1 and S4 were not alloyed with titanium in order to serve as a reference in the assessment of the influence of the Ti content. The titanium and nitrogen contents of the steels guarantee that the precipitation of titanium nitride (TiN) particles takes place in the solid state, since their solubility temperatures are below 1 500°C, which is approximately the melting temperature of the studied steels (Fig. 1). The solubility temperature have been deduced according to Turkdogan's solubility product Hot deformation tests were carried out in a completely automatic torsion machine, with software for the programming of the tests and for data acquisition, respectively. The test specimens had a gauge length of 50 mm and a radius of 3 mm, and were protected during testing with an argon stream in order to prevent their oxidation. The magnitudes of torsion, torque and number of revolutions have been transformed into equivalent stress and strain values using Von Mises criterion. 18) In order to determine the static recrystallisation fraction...

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“…In the past years, it has been found that the strain, strain rate, deformation temperature and the grain size of primary austenite have great effect on the DIF during deformation or pre-deformation. [14][15][16] In addition, there are several factors such as hot holding time at high temperatures, cooling rates and annealing temperatures, might also influence on the conserving of DIF in practical hot mills. For example, the traditional finish rolling temperatures are normally higher than Ae 3 , there is a delay of about 2-5 s between deformation and subsequently cooling, and a laminar flow cooling at a rate about 20°C s Ϫ1 exists in the strip steels producing.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability of High Temperature Deformation Induced Ferrite in a Low Carbon Steel

et al. 2007

ISIJ Int.

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Effect of strain on formation of ultrafine ferrite in surface of hot rolled microalloyed steel

Cited by 33 publications

References 4 publications

Influence of the Size and Volume Fraction of TiN Particles on Hot Strength and Dynamic Recrystallisation in Structural Steels

Influence of the Size and Volume Fraction of TiN Particles on Hot Strength and Dynamic Recrystallisation in Structural Steels

Influence of TiN Particle Precipitation State on Static Recrystallisation in Structural Steels

Thermal Stability of High Temperature Deformation Induced Ferrite in a Low Carbon Steel

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