Structure-property relationship in a 2 GPa grade micro-alloyed ultrahigh strength steel

Mandal, G.; Roy, Chiranjit; Ghosh, S. K.; Chatterjee, S.

doi:10.1016/j.jallcom.2017.02.164

Cited by 34 publications

(12 citation statements)

References 49 publications

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“…The morphology of ductile tearing was observed in Figure a, whereas cleavage facets existed in Figure b. It is well known that brittle fracture yields cleavage facets and leads to an inferior tensile toughness . In contrast, ductile fracture causes ductile tearing and provides a high tensile toughness.…”

Section: Resultsmentioning

confidence: 96%

Effects of Nb on Bainite Transformation Behavior and Mechanical Properties of Low‐Carbon Bainitic Steels

Chen

et al. 2019

steel research int.

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The bainite transformation behavior and the mechanical properties of lowcarbon bainitic steels with and without niobium (Nb) are investigated by two different heat-treatment methods À isothermal transformation process (ITP) and continuous cooling process (CCP). The results indicate that for ITP, the kinetics of bainitic transformation for the Nb-added sample is accelerated at the beginning of the isothermal holding process due to more nucleation sites followed by its further deceleration as a consequence of the formation of ferrite prior to austempering. For all ITPs, Nb addition resulted in a decrease in the final amount of transformed bainites. In addition, different from the generally accepted result, the tensile strength of the steel is degraded by Nb addition during both ITP and CCPs, and the addition of Nb did not improve the final comprehensive properties of the steels. Moreover, Nb addition caused an increase in the critical temperature of high-temperature transformation (Ar 3 ); however, it yielded no significant effects on critical temperatures of Ac 1 and Ac 3 . Materials and Methods MaterialsNb-free (Fe-0.22C-1.55Si-2.01Mn (wt%); used as a reference sample) and 0.025Nb-bearing (wt%) steels were first refined in a vacuum induction furnace and then cast into 50 kg ingots. The

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Section: Resultsmentioning

confidence: 96%

Effects of Nb on Bainite Transformation Behavior and Mechanical Properties of Low‐Carbon Bainitic Steels

Chen

et al. 2019

steel research int.

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“…Ductile tearing is regarded as a feature of the ductile fracture mode, which implies high tensile toughness. On the contrary, cleavage facet represents the feature of brittle fracture, which expresses the inferior tensile toughness [32]. The fracture surface of specimen held for 15 h contains a lot of cleavage facets, whereas more volume of ductile tearing morphology appears in the specimen held for 30 h, indicating that the tensile toughness increases with prolonging the holding time.…”

Section: Microstructure and Xrd Resultsmentioning

confidence: 99%

Effect of Ni Addition on Bainite Transformation and Properties in a 2000 MPa Grade Ultrahigh Strength Bainitic Steel

Tian

Jiang

et al. 2018

Met. Mater. Int.

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The effects of Nickle (Ni) addition on bainitic transformation and property of ultrahigh strength bainitic steels are investigated by three austempering processes. The results indicate that Ni addition hinders the isothermal bainite transformation kinetics, and decreases the volume fraction of bainite due to the decrease of chemical driving force for nucleation and growth of bainite transformation. Moreover, the product of tensile strength and total elongation (PSE) of high carbon bainitic steels decreases with Ni addition at higher austempering temperatures (220 and 250 °C), while it shows no significant difference at lower austempering temperature (200 °C). For the same steel (Ni-free or Ni-added steel), the amounts of bainite and RA firstly increase and then decrease with the increase of the austempering temperature, resulting in the highest PSE in the sample austempered at temperature of 220 °C. In addition, the effects of austempering time on bainite amount and property of high carbon bainitic steels are also analyzed. It indicates that in a given transformation time range of 30 h, more volume of bainite and better mechanical property in high carbon bainitic steels can be obtained by increasing the isothermal transformation time.

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“…However, in order to use Equation (4), the magnitudes of the lath sizes were converted from ECD to mean linear intercept (MLI) with the aid of Equation (5) [41] and both values are given in Table 8. The precipitation strengthening contribution (σ p ) was calculated using Equation (6), i.e., the Ashby-Orowan equation, [42].…”

Section: Mechanical Propertiesmentioning

confidence: 99%

The Effect of Electroslag Remelting on the Microstructure and Mechanical Properties of CrNiMoWMnV Ultrahigh-Strength Steels

Ali

Porter

Kömi

et al. 2020

Metals

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The effect of electroslag remelting (ESR) with CaF 2 -based synthetic slag on the microstructure and mechanical properties of three as-quenched martensitic/martensitic-bainitic ultrahigh-strength steels with tensile strengths in the range of 1250-2000 MPa was investigated. Ingots were produced both without ESR, using induction furnace melting and casting, and with subsequent ESR. The cast ingots were forged at temperatures between 1100 and 950 • C and air cooled. Final microstructures were investigated using laser scanning confocal microscopy, field emission scanning electron microscopy, electron backscatter diffraction, electron probe microanalysis, X-ray diffraction, color etching, and micro-hardness measurements. Mechanical properties were investigated through measurement of hardness, tensile properties and Charpy-V impact toughness. The microstructures of the investigated steels were mainly auto-tempered martensite in addition to small fractions of retained austenite and bainite. Due to the consequences of subtle modifications in chemical composition, ESR had a considerable impact on the final microstructural features: Prior austenite grain, effective martensite grain, and lath sizes were refined by up to 52%, 38%, and 28%, respectively. Moreover, the 95th percentiles in the cumulative size distribution of the precipitates decreased by up to 18%. However, ESR had little, if any, the effect on microsegregation. The variable effects of ESR on mechanical properties and how they depend on the initial steel composition are discussed.The prior austenite grains are divided into packets, which consist of blocks of laths with the same habit plane. These blocks contain sub-blocks in which the laths have similar crystal orientations. The boundaries between packets and blocks have high-angle misorientations while the boundaries between sub-blocks and laths have low-angle misorientations [8][9][10].Strength and toughness properties can be improved simultaneously by grain refining, which can be achieved, for example, by the pinning of the austenite grain boundaries by fine precipitates, which are stable at high temperatures [11]. A high number density of fine precipitates leads to enhanced pinning of the grain boundaries, which subsequently leads to a reduction of the final prior austenite grain, packet, and block sizes and a significant effect on the mechanical properties of the steel. It was observed by Wang et al. [12] that the yield strength of 17CrNiMo6 martensitic steel is increased by 235 MPa by reducing the prior austenite grain size (PAGS) by 33% and the Charpy U-notch impact energy at 77 K was enhanced more than eight-fold.In addition to the above strengthening factors, additional strengthening can be achieved through precipitation. In the case of dislocation bowing between precipitates, the Orowan relationship [13] shows that the yield strength increment from precipitation increases with increasing volume fraction and decreasing size of the precipitates. In the case of tempered martensite, the optimum combinati...

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Structure-property relationship in a 2 GPa grade micro-alloyed ultrahigh strength steel

Cited by 34 publications

References 49 publications

Effects of Nb on Bainite Transformation Behavior and Mechanical Properties of Low‐Carbon Bainitic Steels

Effects of Nb on Bainite Transformation Behavior and Mechanical Properties of Low‐Carbon Bainitic Steels

Effect of Ni Addition on Bainite Transformation and Properties in a 2000 MPa Grade Ultrahigh Strength Bainitic Steel

The Effect of Electroslag Remelting on the Microstructure and Mechanical Properties of CrNiMoWMnV Ultrahigh-Strength Steels

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