The effect of finish rolling temperature and tempering on the microstructure, mechanical properties and dislocation density of direct-quenched steel

Saastamoinen, Ari; Kaijalainen, Antti; Porter, David; Suikkanen, Pasi; Yang, Jer−Ren; Tsai, Yu-Ting

doi:10.1016/j.matchar.2018.02.026

Cited by 68 publications

(35 citation statements)

References 25 publications

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“…When the FRT decreases further, PF is also observed, and with very low FRT, the main phase is ferrite throughout the thickness. These results are consistent with the observations of Kaijalainen et al and Saastamoinen et al for ultrahigh‐strength strip steels. Lowering FRT, thereby increasing austenite pancaking, enhances the formation of PF and bainite at the expense of auto‐tempered martensite.…”

Section: Discussion Of Structure – Property Relationshipssupporting

confidence: 93%

The Influence of Microstructure on the Bendability of Direct Quenched Wear Resistant Steel

Kaijalainen

Hautamäki

Kesti

et al. 2019

steel research int.

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The influence of chemical composition and processing parameters on the microstructure and bendability of three thermomechanically rolled and directquenched wear resistant steel plates is studied. Overall, the bendability of the steels is good, but there are exceptions that are given special attention. The prior austenite condition and final microstructure is evaluated with respect to subsurface hardness and bendability. The possible effect of inclusions on bendability is taken into account. Away from the surfaces, the samples consisted mainly of auto-tempered martensite. Lowering the finishing rolling temperature (FRT) increased the total rolling reduction below the recrystallization temperature leading to pancaking of austenite and the formation of increasing fractions of polygonal ferrite (PF) and bainite near the plate surface together with an increased intensity of the shear texture component {112}<111>. Strength increased with increasing austenite pancaking provided the microstructure remained mostly martensitic. A homogeneous, largely martensitic microstructure extending across the plate thickness seemed to ensure good bendability. Microstructures that are inhomogeneous with respect to the hardness of the microconstituents, or highly ferritic, or microstructures with an intense {112}<111> shear texture component combined with elongated martensite-austenite (MA) plates in the subsurface layers resulted in the largest minimum useable bending radii.

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Section: Discussion Of Structure – Property Relationshipssupporting

confidence: 93%

The Influence of Microstructure on the Bendability of Direct Quenched Wear Resistant Steel

Kaijalainen

Hautamäki

Kesti

et al. 2019

steel research int.

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“…The dislocation density of a body‐centered cubic crystal can be represented as follows

ρ = 14.4 \frac{ε^{2}}{b^{2}}

where ρ is the dislocation density (m −2 ) and b is the Burger's vector of the dislocations in iron (0.248 nm).…”

Section: Resultsmentioning

confidence: 99%

Effect of Prestrain and Tempering on the Residual Stress of Low‐Carbon Microalloyed Steel

Ding

Liu

Xie

et al. 2019

steel research int.

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In this article a method that combines prestrain with tempering (PST) is used to study the effect of a thermomechanical treatment on the residual stress of high-strength steel and its underlying controlling mechanisms. The study results show that prestrain changes the material's dislocation distribution and carbide precipitation pattern and lowers the temperature controlling the residual stress. Compared with direct tempering (DT), 10% PST causes the temperature controlling the surface residual stress to decrease from 300 to 100 C, reducing the surface residual stress by 76.2%. The temperature controlling the elastic strain energy decreases from 600 to 450 C, and the elastic strain energy decreases by 75.2%. PST's action in controlling the residual stress involves two mechanisms. From room temperature to 300 C, the residual stress is controlled by the precipitation plasticity generated by cementite precipitation, and the effect is mainly focused on controlling the surface residual stress. For temperatures of 300 C and higher, the residual stress is controlled by precipitation-induced creep caused by carbide precipitation, and the effect is mainly focused on decreasing the elastic strain energy.

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“…Currently, the strength of the commercially available UHSS is about ~1.2 GPa. Great efforts are still continuing to develop steels with higher strength and toughness than the commercial ones [ 7 , 8 , 9 ].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, during the hot forming, dislocation density was also found to increase in the austenite phase. Such dislocation density and grain size changes in the hot forming process have an impact on the martensite fraction of the direct-quenched steel [ 8 , 9 ]. Thus, the steels produced via the DQ process have higher martensite fraction than the conventional re-austenitizing and quenching (RA/Q) steels., The steels produced via the DQ process have also been reported to possess excellent mechanical properties [ 16 , 17 , 18 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Hot-Rolling and a Subsequent Direct-Quenching Process Enable Superior High-Cycle Fatigue Resistance in Ultra-High Strength Low Alloy Steels

et al. 2020

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The current study investigated the effect of hot rolling reduction rate of ultra-high strength low alloy steel manufactured via the direct quenching process on microstructure, tensile and high-cycle fatigue properties of the alloy. In order to control the reduction rate of ultra-high strength steels (UHSSs) differently, the steels were produced with two different thicknesses, 6 mm (46.2%—reduction rate, A) and 15 mm (11.5%—reduction rate, B). Then, the two alloys were directly quenched under the same conditions. Both the UHSSs showed martensite in the near surface region and auto-tempered martensite and bainite in the center region. Tensile results showed that alloy A with higher fraction of finer martensite had higher yield strength by about 180 MPa (1523 MPa) than alloy B. The alloy A was also found to possess a higher tensile strength (~2.1 GPa) than alloy B. In addition, alloy A had higher strength than B, and the elongation of A was about 4% higher than that of alloy B. High-cycle fatigue results showed that the fatigue limits of alloys A and B were 1125 MPa and 1025 MPa, respectively. This means that alloy A is excellent not only in strength but also high-cycle fatigue resistance. Based on the above results, the correlation between the microstructure and deformation behaviors were also discussed.

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The effect of finish rolling temperature and tempering on the microstructure, mechanical properties and dislocation density of direct-quenched steel

Cited by 68 publications

References 25 publications

The Influence of Microstructure on the Bendability of Direct Quenched Wear Resistant Steel

The Influence of Microstructure on the Bendability of Direct Quenched Wear Resistant Steel

Effect of Prestrain and Tempering on the Residual Stress of Low‐Carbon Microalloyed Steel

Hot-Rolling and a Subsequent Direct-Quenching Process Enable Superior High-Cycle Fatigue Resistance in Ultra-High Strength Low Alloy Steels

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