TTT curves for the formation of austenite

Lenel, U. R.

doi:10.1016/0036-9748(83)90334-4

Cited by 19 publications

(12 citation statements)

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“…This point is currently under investigation. The enthalpy change associated with the α → γ transformation in aged samples is slightly less than the corresponding value recorded for pure iron, and this is certainly due to the presence of the carbide phase that serves to retard the kinetics of the α → γ structural change [28]. In the case of the martensite, the carbide volume fraction formed during continuous heating being relatively less, the α → γ structure change is facilitated to a little more extent with the concomitant effect of recording a slightly higher value for enthalpy change (Table 1).…”

Section: Discussionmentioning

confidence: 61%

“…The determination of the calibration factor (J · µV −1 · s −1 ) for converting the peak area into appropriate enthalpy units is enabled from a knowledge of the known value of the enthalpy associated with similar phase changes taking place in pure iron and the corresponding peak area-all measured under identical experimental conditions. It is reasonable to assume in the case of pure iron that for a heating rate of about 10 K · min −1 , the α → γ allotropic transformation goes to near completion; but in the case of high chromium steels, the presence of carbides and its sluggish dissolution in austenite, results in an incomplete realization of the α → γ transformation at the transformation off-set Ac 3 temperature [21,28,29]. Because of this fact, there is a mild underestimation of the true enthalpy change that is associated with austenite formation reaction under equilibrium conditions.…”

Section: Principal Transformation Characteristicsmentioning

confidence: 99%

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A Study on the Effect of Thermal Ageing on the Specific-Heat Characteristics of 9Cr–1Mo–0.1C (mass%) Steel

et al. 2009

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The effect of thermal ageing on the heat-capacity behavior of 9Cr-1Mo-0.1C (mass%) ferritic/martensitic steel has been studied using differential scanning calorimetry (DSC) in the temperature range from 473 K to 1,273 K. The DSC results in the case of slow cooled, normalized and tempered, and subsequently thermally aged samples (500 h to 5,000 h at 823 K (550 • C) and 923 K (650 • C), clearly marked the presence of both magnetic and α-ferrite + carbide → γ -austenite phase transformations that take place successively upon heating. Furthermore, for the case of fully martensitic microstructure, an additional exothermic transformation at about 920 K (647 • C), arising from carbide precipitation is noticed. This event is characterized by a sharp drop in C P . It is found that the α-ferrite + carbide → γ -austenite phase transformation temperature is only mildly sensitive to microstructural details, but the enthalpy change associated with this phase transformation, and especially the change in specific heat around the transformation regime, are found to be dependent on the starting microstructure generated by thermal ageing treatment. Prolonged ageing for about 500 h to 5,000 h in the temperature range from 823 K to 923 K (550 • C to 650 • C) contributed to a decrease in heat capacity, as compared to the normalized and tempered sample. This is due to the increase in carbide volume fraction. The martensitic microstructure is found to possess the lowest room-temperature C P among different microstructures.

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Section: Discussionmentioning

confidence: 61%

Section: Principal Transformation Characteristicsmentioning

confidence: 99%

A Study on the Effect of Thermal Ageing on the Specific-Heat Characteristics of 9Cr–1Mo–0.1C (mass%) Steel

et al. 2009

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“…Thus, we may infer from Fig. 9 that the process of isothermal austenitisation involves certain well defied time dependent microstructural changes, such as carbide dissolution [92,93], which as the present experimental results suggest, is progressive in nature. Depending on the homogeneity of the starting microstructure at sub-micron level, the carbide dissolution process gets initiated at different time intervals.…”

Section: Carbide Dissolution In Austenite and Its Effect On Martensitmentioning

confidence: 79%

“…This is subsequently followed by a continuous decrease in a manner that is much like the case of 1323 K austenitised samples. Obviously, this difference in the initial response of the hardness curve between these two annealing temperatures stems from the sluggish nature of carbide dissolution step at 1253 K [92,93]. For smaller time holds at 1253 K, the parent austenite phase still contains quite an extent of undissolved carbides as compared to 1323 K. Further, the lack of carbide dissolution means that the austenite is not getting that much enriched in chromium which is a known ferrite stabiliser.…”

Section: Carbide Dissolution In Austenite and Its Effect On Martensitmentioning

confidence: 87%

A study on martensitic phase transformation in 9Cr–1W–0.23V–0.063Ta–0.56Mn–0.09C–0.02N (wt.%) reduced activation steel using differential scanning calorimetry

Raju

Ganesh

Kumar

et al. 2010

Journal of Nuclear Materials

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“…Moreover, another feature shown in Figure 8 is that a longer time is required to increase the austenite volume fraction by 5% at a later stage of the transformation, which reveals the impingement mechanism in the steel. As described by Lenel (1983), towards the end of the reaction when a large amount of austenite has been formed, impingement of neighbouring growth centres (or their diffusion fields) will occur, which slows down the reaction rate and increases the time taken to reach equilibrium. Figure 8 Effect of heating rate on the transformation time to increase austenite volume fraction by 5% from 80%, 85% and 90% during soaking at 1173K.…”

Section: Effects Of Heating Rate On Isothermal Austenite Formationmentioning

confidence: 99%

Experimental characterisation of the effects of thermal conditions on austenite formation for hot stamping of boron steel

Lin

Balint

et al. 2016

Journal of Materials Processing Technology

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The formation of austenite in manganese-boron steels during selective heat treatment has great significance in the application of innovative hot stamping processes. Heat treatment tests were designed according to the thermal cycle of industrial heating and hot stamping processes and were conducted on a Gleeble 3800 thermomechanical testing system. Specimens were subjected to non-isothermal (heating rates: 1K/s-25K/s) and isothermal (soaking temperatures: 1023K-1173K) temperature profiles. A high-resolution dilatometer was employed to detect the dimensional change of the specimens associated with austenitization. The dilatometric measurement was quantitatively related to the volume fraction of austenite. By analysing the evolution curves of austenite fraction, the effects of heating rate and temperature on the progress of austenite formation under both non-isothermal and isothermal conditions were investigated and characterised, improving the current understanding of the mechanisms that control austenite formation in manganese-boron steels. Imperial College London Reviewer #1: General:This submission presents new and significant results on austenite formation during heating cycles for a commercial Mn-B steel (22MNB5). The data and insights presented will be valuable in the design of selective heating and quenching processes for hot stamping of this steel grade. However, the Discussion is deficient. The need to analyse the (same) dilatometer data several different ways is not obvious. See responses to the specific comments below -in particular, see the response to specific comment 5. Specific:1. p.6: Section 2 is a lengthy description of 'textbook material'. It should be deleted and replaced with a brief summary of the issues/knowledge gaps which were addressed in the present study. This revised summary should be included in Section 1. Section 2 has been reduced and incorporated into a revised Section 1 (p. 6-8). The information that remains is necessary for later discussion Thank you for these corretions. All have been updated according to the suggestions. The comments from Reviewer #3:In order to gain a better understanding of the kinetics of the austenite formation in boron steels, in this work the formation of austenite in a manganese-boron steel has been investigated by the authors through dilatometry and theoretical analysis. The authors have conducted heat treatment tests on a Gleeble 3800 thermomechanical testing system. Specimens were subjected to non-isothermal heating rates (1K/s, 5 K/s and 25K/s) and different isothermal soaking temperatures (1023K, 1073K,1123K and1173K) . A high resolution dilatometer was employed to detect the dimensional change of the specimens associated with austenitization and a method was proposed to quantitatively relate the dilatometric measurement to the volume fraction of austenite. The effects of heating rate and soaking temperature on the progress of austenite formation under both non-isothermal and isothermal conditions were investigated by analyzing the evolu...

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TTT curves for the formation of austenite

Cited by 19 publications

References 1 publication

A Study on the Effect of Thermal Ageing on the Specific-Heat Characteristics of 9Cr–1Mo–0.1C (mass%) Steel

A Study on the Effect of Thermal Ageing on the Specific-Heat Characteristics of 9Cr–1Mo–0.1C (mass%) Steel

A study on martensitic phase transformation in 9Cr–1W–0.23V–0.063Ta–0.56Mn–0.09C–0.02N (wt.%) reduced activation steel using differential scanning calorimetry

Experimental characterisation of the effects of thermal conditions on austenite formation for hot stamping of boron steel

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