A Technology for the Prediction and Control of Microstructural Changes and Mechanical Properties in Steel.

Kwon, Oh-Heum

doi:10.2355/isijinternational.32.350

Cited by 95 publications

(60 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Overall, these values of n are very low compared to the typical values measured in torsion, which range from 1 to 2. 21,22) The low n values correspond to a "flattening" of the fraction recrystallized versus time profile; this is illustrated in Fig. 9, in which an Avrami plot with a "normal" exponent (nϭ1) is compared to one with a value similar to that observed above (here a hypothetical t 50 of 100 s has been used).…”

Section: Resultsmentioning

confidence: 82%

Static and Dynamic Strain Aging at High Temperatures in 304 Stainless Steel

Stewart

Jonas

2004

ISIJ International

View full text Add to dashboard Cite

Commercial 304 austenitic stainless steel was deformed at high temperatures. The experiments involved 2-hit hot compression and multi-pass hot torsion testing; the experimental variables included strain rate, temperature and interpass time. The relationship between these variables and the degree of interpass softening produced unexpected results. Specifically, the normal effect of temperature on the static softening kinetics was reversed at intermediate interpass times: the fractional softening decreased with increasing temperature for these times. The diffusion kinetics and segregation mechanics of the substitutional impurities in the material, combined with the experimental results, suggest that the temporary non-equilibrium segregation of phosphorus (and/or sulphur) to dislocations is responsible for the observed behaviour. Additionally, the observed trend in strain rate sensitivity with increasing deformation temperature indicates that dynamic strain aging was taking place.KEY WORDS: recrystallization; non-equilibrium segregation; stainless steel; static strain aging; dynamic strain aging.rate to vacancy concentration. It has been observed that, under specific thermal and straining conditions, the nonequilibrium segregation of substitutional solutes will occur in steel. 7) This involves the segregation of solute atoms to features such as grain boundaries in concentrations well in excess of equilibrium values. The non-equilibrium segregation is temporary; back diffusion from areas of excess concentration to adjacent regions of solute depletion will return the solute distribution to its equilibrium state given sufficient time. 8) Materials and MethodsThe material used for virtually all the experiments in this work was a 304 austenitic stainless steel obtained from a single billet produced by Atlas Stainless Steel in Tracy, Quebec. In addition, a small amount of ultra-high purity 18Cr-12Ni-Fe 9,10) alloy was obtained and tested. The compositions of these steels are given in Table 1, along with the 304 specifications. Austenitic stainless steel has a low stacking fault energy, 11) in the range 21 mJ m Ϫ2 . Numerous studies of the recrystallization behaviour of such materials have been conducted over the past thirty years (especially involving torsion testing). [12][13][14] The stainless steel tested was obtained in the form of a billet 30-cmϫ15-cmϫ15-cm. The billets were sectioned parallel to the transverse direction and the sections sliced along the normal direction. After machining, the resulting cylindrical samples had their longitudinal axes parallel to the normal direction of the billet. The initial grain size was not a variable of interest in this work, but was essentially constant and in the range 80-100 mm. Torsion samples (Dϭ6.3 mm, Lϭ22 mm) were also machined from the same billet. These were machined such that the longitudinal axis of the samples were aligned along the rolling direction of the billet.Two-hit compression tests were performed primarily for the study of static softening. The tests were co...

show abstract

Section: Resultsmentioning

confidence: 82%

Static and Dynamic Strain Aging at High Temperatures in 304 Stainless Steel

Stewart

Jonas

2004

ISIJ International

View full text Add to dashboard Cite

show abstract

“…It is well known that the static recrystallisation of austenite in microalloyed steels is different before and after strain-induced precipitation. Before, all the elements are in solution and recrystallisation kinetics occur in the same way as in low alloy steels, whereby the various alloying elements contribute to delaying recrystallisation to a greater or lesser degree [2][3][4]. As the temperature drops, a critical temperature is reached, after which static recrystallisation is momentarily inhibited by the effect of strain-induced precipitates.…”

Section: Introductionmentioning

confidence: 99%

From heterogeneous to homogeneous nucleation for precipitation in austenite of microalloyed steels

Medina

2015

Acta Materialia

View full text Add to dashboard Cite

This paper studies the influence of strain on precipitate nucleation in austenite for three is dependent not only on the strain magnitude but also on the driving force for precipitation. When the driving force is high, or low in absolute terms, the influence of the strain, i.e. the increase in the dislocation density, gives rise to a notable reduction in the t 0.05 value due to heterogeneous nucleation on the dislocation nodes. In contrast, when the driving force is low, or high in absolute terms, the influence of the strain on t 0.05 decreases considerably and the nucleation of precipitates becomes preponderantly homogeneous. Therefore, the driving force value is responsible for the transition from heterogeneous nucleation to homogenous nucleation.

show abstract

“…According to the review paper by Kwon,1) recent progress in developing the austenite grain size (AGS) prediction models in plate rolling process and improving the mechanical properties of the rolled products based on such prediction models has been reported. One of the most important contributions was first made by Sellars and Whiteman 2) and their pioneering work was followed by many researchers for two decades.…”

Section: Introductionmentioning

confidence: 99%

Numerical Prediction of Austenite Grain Size in Round-Oval-Round Bar Rolling

et al. 2003

View full text Add to dashboard Cite

In bar or rod rolling process, improvement of mechanical properties of the hot rolled products requires numerical prediction of austenite grain size (AGS) for better controlling the microstructural evolution. In this study, a fully three-dimensional finite element (FE) program, which can simulate three-dimensional deformation and heat transfer was integrated with an AGS evolution model available in the literature. It was applied to a four-pass round-oval-round rolling sequence to characterize the AGS distributions depending on the change of roll gap and rolling speed. The predicted AGS distribution obtained from the FE based approach was compared with that obtained from the approximate analytical approach based on elementary theory of plasticity, developed for practical purpose. It was found out that reducing roll gap and increasing the rolling speed leads to fine and uniform grain distribution and recrystallization behavior divided into meta-dynamic and static recrystallization region, respectively. In addition, AGS predicted from the approximate analytical approach was in agreement with that from the FE based approach, but showed discrepancies at higher rolling speed conditions investigated in the present work.KEY WORDS: austenite grain size; bar or rod rolling; finite element method; rolling speed; approximate analytical approach.parameters for each pass in an average sense were used as input values for the AGS evolution model proposed by Hodgson and Gibbs. 6) In this study various strategies to achieve grain refinement were discussed but only average value of the AGS was predicted.Compared to plate rolling, it is well known that deformation mechanics for shape rolling is rather complex in the roll gap because of the material flow in all three directions. To predict the microstructural change in shape rolling process by utilizing the AGS evolution model, the deformation of material during rolling must be accurately determined in couple with temperature and then the AGS model should be integrated with it. In this aspect, the FE method, which can provide the detailed information on material flow during rolling, has been widely employed. Several research groups applied the FE analysis to model the deformation in shape rolling and to predict the AGS distribution in rolled sections. Glowacki et al. 10) predicted the AGS distribution using two-dimensional FE simulations based on the generalized plane strain assumption in consideration of computational efficiency. The predicted AGS distribution for a square-oval rolling pass was compared with the experimental results.To make better prediction of the AGS distribution, more accurate information of the material flow and temperature distribution during rolling is required. With this in mind, in this study, a fully three-dimensional FE analysis, which can calculate the three-dimensional heat transfer, was conducted and the results were integrated with an AGS evolution model proposed by Hodgson and Gibbs. 6) The proposed approach was then applied to four-pass round-oval...

show abstract

A Technology for the Prediction and Control of Microstructural Changes and Mechanical Properties in Steel.

Cited by 95 publications

References 0 publications

Static and Dynamic Strain Aging at High Temperatures in 304 Stainless Steel

Static and Dynamic Strain Aging at High Temperatures in 304 Stainless Steel

From heterogeneous to homogeneous nucleation for precipitation in austenite of microalloyed steels

Numerical Prediction of Austenite Grain Size in Round-Oval-Round Bar Rolling

Contact Info

Product

Resources

About