Recrystallization Kinetics of Microalloyed Steels Determined by Two Mechanical Testing Techniques

Airaksinen, K.; Karjalainen, L.P.; Porter, David; Perttula, Juha

doi:10.4028/www.scientific.net/msf.284-286.119

Cited by 17 publications

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“…Karjalainen et al 11) determined a relationship of t 0.5 ϰe Ϫ3.3 for a Nb microalloyed steel with a grain size of 60 mm, reporting exponent values between 3 and 4 for C-Mn steel with a fine grain size of 17 mm. For Ti, Ti-Ni-Nb and Ti-Ni-V microalloyed steels with grain sizes in the range 40 to 56 mm, exponent values between 2.5 and 3 were reported by Airaksinen et al 31) In contrast, the variations of p observed in the present work suggest that this parameter is influenced by the initial grain size D o . For the two coarse grain sizes of ϳ800 mm, a value of pϭ2 is obtained for both steels, while for the Nb-Ti steel with lower initial grain sizes of 60 and 109 mm the value of p is close to 3.…”

Section: ϫ4contrasting

confidence: 55%

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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Section: ϫ4contrasting

confidence: 55%

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

et al. 2000

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“…[22][23][24] All these values are relatively high compared to the values obtained for C and C-Mn steels (Ϫ0.11), medium carbon steels (Ϫ0.13) and also Ti-steels (Ϫ0.12). 8,25,26) Between these two values, the strain rate exponents for Nb and Nb-Ti and Mo steels are measured to be of the order of Ϫ0.23, 8,16) which value has also been used in the development of the regression models for kinetics and activation energy of SRX. 7,8) All these values point to the dependence of strain rate effect on the extent and type of alloying.…”

Section: Powers Of Strain and Strain Ratementioning

confidence: 99%

High Temperature Flow Stress and Recrystallization Behavior of High-Mn TWIP Steels

2007

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The flow stress behavior and recrystallization kinetics in the hot rolling temperature range have been investigated in five Fe-Mn-Al (Mn: 25 wt%, Al: 0-8 wt%) TWIP steels by compression testing on a Gleeble simulator. Results were compared with corresponding properties of carbon and austenitic stainless steels. Microstructures were examined by electron microscopy. The results show that the flow stress level of the TWIP steels is considerably higher than that of low-carbon steels and depended on the Al concentration close to 6 wt%, while the structure is austenitic at hot rolling temperatures. At higher Al contents, the flow stress level becomes significantly lowered due to the presence of ferrite. The static recrystallization kinetics is slower compared to that of carbon steels, but it is faster than typical of Nb-microalloyed or austenitic stainless steels. High Mn content is a reason for the high flow stress as well as for slow softening. Al has a minor role only, but in the case of austenitic-ferritic structure, softening of the ferrite phase occurs very rapidly that also contributes to overall faster softening. The grain size is effectively refined by the dynamic and static recrystallization processes.KEY WORDS: high-Mn steels; Al alloying; austenite; flow stress; recrystallization.ISIJ International, Vol. 47 (2007), No. 6, specimens were compressed in a single hit to the true strain of 0.8 at a constant true strain rate that was varied between 0.005 and 5 s Ϫ1. The SRX kinetics of the steels was studied by the double-hit compression technique using different temperatures (900-1 100°C), strains (0.11-0.4) and strain rates (0.01-5 s Ϫ1). The initial grain size of the steels was about 140 mm, as excluding the annealing twin boundaries. The flow stress at 5 % total reloading strain was adopted in computing the recrystallized fraction to exclude the effect of recovery from the softening data, as described elsewhere.9) Microstructures were examined in an optical microscope (OM) as well as in a scanning electron microscope equipped with an electron back-scattered diffraction device (SEM-EBSD). Results and Discussion Flow Stress and Dynamic RecrystallizationAs examples of the constitutive behavior of the steels, typical true stress-true strain curves for the high-Mn and reference steels are displayed in Fig. 1, as compressed at the strain rates of 0.1 s Ϫ1 and 5 s Ϫ1. In Fig. 1(a), it is seen that at 0.1 s Ϫ1, the 25Mn1Al steel exhibits peak stress behavior, even though the peaks are very broad, particularly at 950°C. The peak strain is rather small, about 0.25, 0.4 and 0.5 at 1 100, 1 000 and 950°C, respectively. 25Mn1Al steel possesses much higher deformation resistance than the low-C steel. Figures 1(b) and 1(c) clearly demonstrate that the flow resistance of high-Mn steels is increased by Mn and Al alloying. The flow stress of 25Mn steel is much higher than those of low-C and Nb-bearing steels, and among the Albearing steels, flow stress increases with Al content up to 3% ( Fig. 1(b)) or up to 6 % ( Fig. 1(c))....

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“…22) Figure 4 shows the resultant values of Qsrx for the seven steels studied vs. their silicon and aluminium contents.…”

Section: Activation Energy For Srxmentioning

confidence: 99%

Effect of Silicon and Aluminium on Austenite Static Recrystallization Kinetics in High-strength TRIP-aided Steels

et al. 2012

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Recrystallization Kinetics of Microalloyed Steels Determined by Two Mechanical Testing Techniques

Cited by 17 publications

References 0 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.

High Temperature Flow Stress and Recrystallization Behavior of High-Mn TWIP Steels

Effect of Silicon and Aluminium on Austenite Static Recrystallization Kinetics in High-strength TRIP-aided Steels

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