Development of ultrafine bainite+martensite duplex microstructure in SAE 52100 bearing steel by prior cold deformation

Chakraborty, Jayanta; Bhattacharjee, D.; Manna, I.

doi:10.1016/j.scriptamat.2009.05.035

Cited by 87 publications

(42 citation statements)

References 7 publications

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“…Zhang et al [47] showed that ausforming decreased the Ms, thereby enabling isothermal transformation at lower temperatures, thus facilitating the formation of nanostructured bainite. Besides this, decreasing the ausforming temperature and increasing the This same technique has received attention as a means of accelerating the sluggish bainitic transformation of (low temperature) nanostructured bainite and hence, different deformation routes have been tested, not only revealing accelerated transformation kinetics but also achieving an extra refinement of the microstructure [47][48][49][50][51][52][53][54][55][56][57][58][59]. While extensive work has been done on a single alloy containing 0.5 C wt.…”

Section: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

García‐Mateo

Paul

Somani

et al. 2017

Metals

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Abstract:The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the transformation, are the two factors controlling the final scale of the bainitic microstructure. Usually, those two parameters can be tailored by means of selection of chemical composition and transformation temperature. However, there is also the possibility of introducing plastic deformation on austenite and prior to the bainitic transformation as a way to enhance both the austenite strength and the driving force for the transformation; the latter by introducing a mechanical component to the free energy change. This process, known as ausforming, has awoken a great deal of interest and it is the object of ongoing research with two clear aims. First, an acceleration of the sluggish bainitic transformation observed typically in high C steels (0.7-1 wt. %) transformed at relatively low temperatures. Second, to extend the concept of nanostructured bainite from those of high C steels to much lower C contents, 0.4-0.5 wt. %, keeping a wider range of applications in view.Keywords: bainite; ausforming; kinetics; plate thickness Structural Refinement of Bainitic Steels: General ConsiderationsBainitic steels can be designed on the basis of the theory that predicts the highest temperature at which bainite (Bs) and martensite (Ms) can start to form in a steel of a given composition. These two temperatures constitute the upper and lower limits at which the isothermal heat treatment can be performed to generate bainite.It has been reported that bainitic ferrite plate thickness depends primarily on three parameters, i.e., (1) the strength of the austenite at the transformation temperature, (2) the dislocation density in the austenite and (3) the chemical free energy change accompanying transformation [1][2][3]. In accord, a strong austenite possessing a high dislocation density and a large driving force results in finer plates. Austenite strength and dislocation density refine the structure by increasing the resistance to interface motion, and the thermodynamic driving force refines the structure by increasing the nucleation rate. All three factors-austenite strength, dislocation density and driving force-increase

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Section: Deformation Of Austenite (Ausforming)mentioning

confidence: 99%

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

García‐Mateo

Paul

Somani

et al. 2017

Metals

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“…[10][11][12] One of the best combinations of strength and toughness was achieved in a bainitic steel exhibiting 1600 MPa and 130 MPa ffiffiffiffi m p , respectively, by meeting this criterion. [7,8] Chakraborty et al [13] recently showed improved mechanical properties of 52100 steel (1.1C, 1.46Cr, 0.27Si, 0.33Mn, 0.14V, 0.04Ni, 0.02P, balance Fe, all in wt pct) with a dualphase structure made of bainite and martensite over quenched and tempered structure by adopting the austempering route. Some prior cold deformation was given to refine the thickness and size of the bainitic sheaves.…”

Section: Introductionmentioning

confidence: 99%

Development of New High-Strength Carbide-Free Bainitic Steels

Sharma

Sangal

Mondal

2011

Metall Mater Trans A

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An attempt was made to optimize the mechanical properties by tailoring the process parameters for two newly developed high-strength carbide-free bainitic steels with the nominal compositions of 0.47 pct C, 1.22 pct Si, 1.07 pct Mn, 0.7 pct Cr (S1), and 0.30 pct C, 1.76 pct Si, 1.57 pct Mn, and 0.144 pct Cr (S2) (wt pct), respectively. Heat treatment was carried out via two different routes: (1) isothermal transformation and (2) quenching followed by isothermal tempering. The results for the two different processes were compared. The bainitic steels developed by isothermal heat treatment were found to show better mechanical properties than those of the quenched and subsequently tempered ones. The effect of the fraction of the phases, influence of the transformation temperatures, the holding time, and the stability of retained austenite on the mechanical properties of these two steels was critically analyzed with the help of X-ray diffraction, optical metallography, scanning electron microscopy, and atomic force microscopy. Finally, a remarkable combination of yield strength of the level of 1557 MPa with a total elongation of 15.5 pct was obtained.

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“…As explained in section 3.1, increasing the austenitizing temperature causes increase in bainite width. According to Eq.3, increasing the bainite width (L 3 ) decreases the yield and tensile strength of the mixed microstructure of lower bainite -martensite in comparison with the single phase martensite microstructure 22,24 . Where σ y Mix is yield strength of lower bainite -martensite mixed microstructure, σ y M and σ y B are yield strength of martensite and lower bainite microstructure, respectively.…”

Section: (2)mentioning

confidence: 99%

“…On comparison, in the present experimental results, σ y Mix deviates more from equation 1. As shown in Fig 4, by increasing the volume fraction of lower bainite up to 28%, where σ Fe is the strength of pure annealed iron, σ C is the contribution of solid solution strengthening due to carbon, Σσ SS is the summation of solid solution strengthening due to all substitutional solutes, L 3 is the ferrite plate thickness, ρ d is the dislocation density, Δ is the distance between the carbide particles (or precipitates) and K 1 , K 2 , K 3 are constants 22,24 . The variations of elongation, reduction of area and charpy impact energy with austenitizing temperature for various microstructures obtained from different heat treatment cycles are shown in figures 6 -8, respectively.…”

Section: (2)mentioning

confidence: 99%

“…Also the bainite length and width was increased in the range of 16-115µm and 2.5-9µm for samples austenitized at 910°C to 1200°C, in which the average error for grain size, bainite length and bainite wedth are ±3 µm, ±2µm and ±1µm, respectively. Chakraborty et al 22 reported that refinement of the austenite grains led to enhancement of the heterogeneous nucleation rate of bainite but the extent of the overall transformation was limited by a slow growth rate. In other words, lowering of the prior austenite grain size may generate additional nucleation sites for bainite and enhance nucleation rate, but restrict the growth of ferritic sheaves by grain boundaries.…”

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confidence: 99%

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Effect of Austenitizing Temperature on Mechanical Properties of the Mixed Bainite - Martensite Microstructure in CrMoV Steel

2017

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The effect of austenitizing temperature on mechanical properties of the mixed bainite -martensite microstructure in CrMoV steel was studied in the present work. The result showed that at low austenitizing temperature (910°C -1000°C), the mixed microstructures containing 12-28% volume fraction of lower bainite showed higher yield and tensile strength than fully martensitic microstructure. The partitioning of the prior austenite grain by lower bainite was found to cause a refinement of the martensite packet size. In addition the strength of the lower bainite in the mixed microstructure is enhanced by plastic constraint induced by the surrounding stronger martensite. By increasing the austenitizing temperature from 1000°C to 1200°C (40min), the YS, UTS, %EL, %RA and CVN impact energy decreased for all samples. This is attributed mainly to the increase in austenite grain size and width of bainite sheaves.

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Development of ultrafine bainite+martensite duplex microstructure in SAE 52100 bearing steel by prior cold deformation

Cited by 87 publications

References 7 publications

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective

Development of New High-Strength Carbide-Free Bainitic Steels

Effect of Austenitizing Temperature on Mechanical Properties of the Mixed Bainite - Martensite Microstructure in CrMoV Steel

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