Relationship between the austenite recrystallized fraction and the softening measured from the interrupted torsion test technique

Fernández, A. Inés; López, Beatriz; Rodríguez-Ibabe, J.M.

doi:10.1016/s1359-6462(98)00452-7

Cited by 126 publications

(91 citation statements)

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“…1,20) In a recent work, a good correlation has been observed between the fractional softening quantified by this method and the metallographically measured recrystallized fraction. 20) On the other hand, for some specific deformation conditions, single-pass torsion tests were conducted, and the static recrystallized fraction was metallographically measured and compared with the softening quantified by mechanical procedure (two-pass torsion tests). Figure 1 shows the evolution of austenite grain size with reheating temperature for the steels analysed in the present work.…”

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confidence: 74%

“…In a previous work 20) it was demonstrated that in the case of plain sigmoidal softening curves the fractional softening determined by the 2 % offset method was linearly related to the volume fraction of static recrystallized grains, being the softening due to recovery adequately excluded. The good correlation between the recrystallized and softening fractions determined by this procedure can be observed in Fig.…”

Section: Effect Of Initial Grain Size and Strain Onmentioning

confidence: 99%

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Static Recrystallization Behaviour of a Wide Range of Austenite Grain Sizes in Microalloyed Steels.

et al. 2000

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The static recrystallization kinetics of four steels microalloyed with Nb, Ti and Nb-Ti have been investigated, covering conventional and hot direct rolling conditions. The influence of the grain size on the recrystallization time has been studied for a wide range of grain sizes (20-1000 mm). For the same deformation conditions it has been observed that the quadratic dependence on grain size works well in the range of finer grain sizes (Ͻ160 mm). In contrast, the recrystallization times measured at coarse grain sizes are significantly lower than those predicted by this dependence. However, when the whole grain size range analysed is considered, a linear dependence on grain size gives the best fit to experimental data. The effect of strain on the recrystallization kinetics has been also analysed for different initial grain sizes. It has been observed that the time to reach a 50 % recrystallized fraction (t 0.5 ) shows a dependence on strain of the type t 0.5 ϰe Ϫp , the exponent being influenced by the initial grain size. A unique equation has been proposed to describe the static recrystallization kinetics of Nb, Ti and Nb-Ti microalloyed steels. The predictions of the equations have been compared to previously published data on similar steels.KEY WORDS: static recrystallization; hot direct rolling; Nb; Ti and Nb-Ti microalloyed steels.austenite are not yet completely understood. These differences require an extension of the valid intervals of application for the equations already obtained. The slower recrystallization of the very coarse austenite in C-Mn and microalloyed steels in hot direct rolling processes, allied to the high supersaturation of microalloying elements, can modify the exponent values of Eqs. (1) and (2).A study has been carried out to determine the effect of initial austenite grain size on the 50 % recrystallization time, by using a wide range of grain sizes (20-1 000 mm) in one Nb, two Ti and one Nb-Ti low carbon microalloyed steels. The influence of the applied strain on the static recrystallization kinetics of these microstructures has also been investigated. Material and Experimental ProcedureThe chemical compositions of the steels analysed in wt% are listed in Table 1. Three grades of steel have been considered. The first steel is a Nb microalloyed steel (Nb steel). The second steel (Nb-Ti) has a similar Nb content to the first, but also contains 0.067 wt% of Ti. The other two steels (Ti-a and Ti-b) have Ti additions with different N levels, their Cu contents being similar to those steels produced in an electric arc furnace with scrap.In order to study the static recrystallization kinetics, twopass torsion tests were carried out, under isothermal conditions, to examine the softening behaviour of the austenite between intervals of hot working. The geometry of torsion specimens was a reduced central gauge section, 15.5 mm in length and 7.5 mm in diameter. The specimens are reheated at different soaking temperatures in the range from 1 100 to 1 460°C for 12-15 min. and cooled to test temperat...

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confidence: 74%

Section: Effect Of Initial Grain Size and Strain Onmentioning

confidence: 99%

Static Recrystallization Behaviour of a Wide Range of Austenite Grain Sizes in Microalloyed Steels.

et al. 2000

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“…In order to quantify the amount of softening between these extremes, the 2 % offset method was used. With that method the softening effects by recovery can be neglected 17,18) and consequently the calculated softening fraction is linearly related to the statically recrystallized volume fraction. Double-hit compression tests were performed with the four experimental alloys, using deformation temperatures between 850 and 1 075°C and interpass times between 1 and 5 000 s. The results of the softening analysis are shown in Fig.…”

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Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

et al. 2009

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A good combination of strength and toughness in HSLA steels can be achieved by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at lower temperatures by solute drag or by precipitation pinning. In this study, the recrystallization behavior of four Nb-microalloyed model alloys which were designed to show either extensive or almost no precipitation, was compared by multi-hit torsion tests and double hit compression tests. A good consistency between the different types of tests was found and the results were verified by optical micrographs. Further, by construction of softeningtime-temperature diagrams the recrystallization behavior was linked to the precipitation state of the material which was investigated by thermodynamical equilibrium calculations and by experimental observations from TEM-EDX, Inductively Coupled Plasma Mass Spectroscopy and X-ray Diffraction. Quantitative agreement between the experimental measurements and the calculations for precipitated mass fraction and precipitate composition as a function of temperature and steel composition is demonstrated.KEY WORDS: recrystallization; microalloyed steels; precipitation; solute drag. 911© 2009 ISIJ tions with experimental data from Craven et al. 13)The objective of the present paper is to separate both retarding mechanisms, i.e. solute drag and precipitation pinning, by investigating model alloys designed to show either extensive or almost no precipitation. Moreover, the recrystallization kinetics of four Nb-microalloyed steels during hot deformation is linked to the morphology and composition of the precipitates and the amount of Nb-solutes found in these materials. The recrystallization kinetics were investigated combining different hot deformation testing techniques while information on the precipitation state of the material was obtained from thermodynamic equilibrium calculations and from a combination of experimental observation techniques. With this work, a contribution to the understanding of the fundamental mechanisms responsible for the retardation of austenite recrystallization in Nb-microalloyed steels is achieved. Experimental ProcedureFour model alloys were designed and casted as 100 kg ingots in a Pfeiffer vacuum furnace operated under argon gas atmosphere. The chemical composition of these alloys can be found in Table 1. The C-Mn-reference alloy, without additional Nb, represents a reference steel. The second alloy, a lowC-Mn-Nb alloy containing only a few ppm C, allowed to study the effect of Nb in solid solution. The third alloy (C-Mn-Nb) was designed to study the effect of NbC-precipitates on the recrystallization kinetics. To have the highest fraction of NbC precipitates possible, a stoichiometric Nb/C-ratio of 8/1 was chosen. Finally, the fourth alloy (C-Mn-Nb-N) was designed to study the influence of N on the recrystallization and precipitation behavior. The cast blocks were thermomechanically processed under conditions comparable to those during industrial steel plate rolli...

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“…The softening fraction which occurred during inter-pass time can be calculated by several methods [23].…”

Section: Recrystallization Softeningmentioning

confidence: 99%

Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

Ahmadabadi

Naderi

Mohandesi

et al. 2018

Canadian Metallurgical Quarterly

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The metadynamic softening behavior and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5 to300s after achieving a strain of 0.3. The results indicated that at deformation temperatures lower than 1050 ºC, the final average grain size decreases with increasing time, attaining a minimum value at 15s,. However, grain coarsening was observed at deformation temperatures of 1150 and 1100 ºC. Based on the experimental results, a model was established for estimation of the softening fraction at different deformation parameters. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of ASTM 5.5 decreased down toASTM7 to ASTM 8.5 at the deformation temperatures of 1020 ºC and 940 ºC, respectively. More uniform grain distribution was obtained with decreasing initial grain size especially at lower deformation temperatures.

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Relationship between the austenite recrystallized fraction and the softening measured from the interrupted torsion test technique

Cited by 126 publications

References 10 publications

Static Recrystallization Behaviour of a Wide Range of Austenite Grain Sizes in Microalloyed Steels.

Static Recrystallization Behaviour of a Wide Range of Austenite Grain Sizes in Microalloyed Steels.

Austenite Recrystallization–Precipitation Interaction in Niobium Microalloyed Steels

Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

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