Effect of manganese on recrystallisation kinetics of niobium microalloyed steel

Cho, S.-H.; Kang, Ki Bong; Jonas, J. J.

doi:10.1179/026708302225001859

Cited by 35 publications

(13 citation statements)

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“…It is of particular note that, as long as DRX is initiated within the roll bite, MDRX will replace SRX during the next interpass interval. As the former softening mechanism is about an order of magnitude faster than the latter, 9,10) it can lead to interstand softening when there is no time for SRX. When DRX is not initiated within a particular rolling pass and no SRX takes place in the following interstand interval (as in Nb-modified and stainless steels), the strain is accumulated from pass to pass and DRX can still be initiated in later passes.…”

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confidence: 99%

Critical Strain for Dynamic Recrystallization in Variable Strain Rate Hot Deformation

Poliak¹,

Jonas

2003

ISIJ International

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124

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In rolling, the strain rate in a rolling pass is not constant but depends on pass reduction r p , decreasing or increasing along the arc of contact. In the present work, high temperature compression tests were performed with the rate varying according to strain rate profiles pertaining to various flat rolling pass reductions. Due to the high rate sensitivity of the stress at elevated temperatures, the stress follows such variations in strain rate. This can lead to peaks in the flow curves without regard to dynamic recrystallization (DRX). Nevertheless, critical strains for the onset of DRX can still be defined if the stresses and strains in variable strain rate deformation are normalized by the peak stresses and strains that would be observed if the deformation were being performed at a series of constant strain rates equal to that of successive points along the roll bite. Using plain carbon and Nb-bearing steels, it is demonstrated that the DRX critical strains are lower when r p Ͻ30 % and higher when r p Ͼ30% than in constant e˙deformation at the same initial strain rate. The present method permits the more accurate extrapolation of laboratory test results to industrial conditions and enables rolling loads to be analyzed with greater precision.

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confidence: 99%

Critical Strain for Dynamic Recrystallization in Variable Strain Rate Hot Deformation

Poliak¹,

Jonas

2003

ISIJ International

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124

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“…[12][13][14] Boron is well known to strongly depress the A r3 . 15,16) Boron raises the T nr and it has a synergistic effect when used in conjunction with Nb, effectively raising the T nr above that of either individual alloying element.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical Processing of Pipeline Steels with a Reduced Mn Content

Schambron

Phillips

O’Brien³

et al. 2009

ISIJ Int.

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Lowering the Mn content of hot rolled pipeline steel can economise the steel making process by eliminating costly desulphurisation and at the same time improve product properties, particularly toughness, by reducing the formation of MnS inclusions. Lower Mn contents, however, have significant implications for austenite recrystallization and austenite (g) to ferrite (a) transformation behaviour. This study compares the recrystallization start (T nr ) and g to a transformation (A r3 ) temperatures of two low Mn steels to those of a commercial steel with a conventional Mn content. Simulations of thermomechanical processing were carried out using a Gleeble 3500 testing machine. The T nr for the low Mn alloy design were found to be ϳ25°C higher than for the high Mn steel, while the A r3 of the low Mn steel were some 50°C higher. The higher A r3 promotes the formation of coarse ferrite grains, thus reducing the strengthening and toughening benefits of a fine grain size. However, this could largely be overcome by maximising the degree of deformation performed between T nr and A r3 and maintaining a combination of high cooling rates and low stop cooling temperatures below A r3 , thus providing a high density of nucleation sites and promoting high nucleation rates. Production trials validated the results from the Gleeble tests.KEY WORDS: pipeline steel; high strength low alloy; manganese; hot rolling; non-recrystallization temperature; thermo-mechanical control process.

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“…This observation is again consistent with literature data regarding the change in softening mechanism from SRX to MDRX as the preloading strain is increased. [5][6][7]14) As follows from Eq. (5), the activation energy for softening by MDRX is determined by the activation energy for deformation since, at k t ϭ0, Q s ϭqQ def .…”

Section: Resultsmentioning

confidence: 99%

“…(4) and (6), when the preloading strain is equal to the peak strain, the temperature-compensated time t 50 is solely a function of Z, i.e., the strain dependence of t 50 vanishes when e f1 ϭe p . The same applies when preloading is interrupted at the beginning of steady state flow.…”

Section: Effect Of Preloading Strain Hardening Rate On Thementioning

confidence: 99%

“…The kinetics of SRX are known to exhibit fairly weak strain rate dependence (small q), but are strongly influenced by the preloading strain and are also quite sensitive to temperature due to the relatively high activation energy. [4][5][6] By contrast, MDRX does not depend on the preceding strain and initial grain size (p, b→0) and has a somewhat lower activation energy; concurrently, it is much more strain rate sensitive. [4][5][6][7][8][9] Within certain ranges of processing conditions (T, e, ė), there can be a gradual transition from SRX-to MDRX-controlled softening, where the respective coefficients can assume intermediate values.…”

Section: Introductionmentioning

confidence: 98%

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Prediction of Interpass Softening from the Strain Hardening Rate Prior to Unloading

Poliak¹,

Jonas

2004

ISIJ International

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It is shown experimentally that the kinetics of interpass softening, normally described in terms of the strain, strain rate and temperature, can be more conveniently specified as a function of the strain hardening rate, strain rate and temperature prior to unloading. This approach significantly reduces the number of experiments required to generate sufficient data for modeling purposes. It also eliminates the need to determine the retained strain to predict the softening kinetics in multi-hit deformation and simplifies the extrapolation of laboratory data to the conditions of industrial processing.KEY WORDS: hot deformation; interpass softening; strain hardening.puted from experimental values of X; it is then related to the experimental variables (e, ė, T def , T s , D 0 ) so that values of the coefficients in Eq. (2) can be derived. These can subsequently be employed in process control. Since the set of Eqs. (1) and (2) involves a large number of parameters that also vary with the conditions of prestraining, laboratory simulations require a considerable amount of experimental work.7) Moreover, further difficulties can be faced when the experimental results are applied to industrial processing, because the sensitivity of the various softening parameters to the prestraining conditions can be different in the simulations and in the mill.In the present work, the parameters of post-deformation softening are evaluated by utilizing the data from conventional flow curves. This permits a significant reduction in the experimental work necessary to establish the softening kinetics and simplifies the application of the results of laboratory simulations to industrial hot working conditions. As will be seen below, the method is based on the current value of the (normalized) rate of work hardening. In a subsequent work, this approach will be extended to deformation under conditions of varying strain rate, as in the roll bite of industrial mills. ExperimentalThe present study was concerned with a plain low C-Mn steel (wt%: 0.04 % C, 0.22 % Mn, 0.012 % Si, 0.05 % Al) that was shown earlier 10) to undergo DRX during high-temperature, constant strain rate deformation. Therefore, various mechanisms of post-deformation softening can be expected.Laboratory melt ingots were hot rolled to 20 mm thick plates using a laboratory rolling mill. Standard cylindrical compression specimens with initial heights of 15 mm and initial diameters of 10 mm were machined from the plates with the specimen axes parallel to the plate transverse direction.Fractional softening was determined by means of interrupted uniaxial compression testing using a Gleeble ® 1 500 thermomechanical simulator. In the tests, specimens were reheated to 1 100°C for 30 s and then cooled to the test temperature (900-1 050°C) at 5°C/s. After 20 s of soaking at the test temperature, the specimens were compressed in a single hit to a true strain of 1.2 (70 % height reduction) and in the double-hit tests to first-hit strains of e f1 ϭ0.11Ϫ0.5 (10-40 %). In all the tests, constant...

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Effect of manganese on recrystallisation kinetics of niobium microalloyed steel

Cited by 35 publications

References 11 publications

Critical Strain for Dynamic Recrystallization in Variable Strain Rate Hot Deformation

Critical Strain for Dynamic Recrystallization in Variable Strain Rate Hot Deformation

Thermomechanical Processing of Pipeline Steels with a Reduced Mn Content

Prediction of Interpass Softening from the Strain Hardening Rate Prior to Unloading

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