Effect of Tempering on the Bainitic Microstructure Evolution Correlated with the Hardness in a Low-Alloy Medium-Carbon Steel

Ståhlkrantz, Adam; Hedström, Peter; Sarius, Niklas; Sundberg, Hans-Åke; Kahl, Sören; Thuvander, Mattias; Borgenstam, Annika

doi:10.1007/s11661-020-06030-6

Cited by 7 publications

(3 citation statements)

References 41 publications

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“…The martensite start temperature for the material has previously been determined with dilatometry to 259°C. [37] The transformation time for the formation of bainite was also determined with dilatometry, and all samples were confirmed to be fully transformed after 1 hour of isothermal holding.…”

Section: Methodsmentioning

confidence: 99%

Revealing the Unexpected Two Variant Pairing Shifts Due to Temperature Change in a Single Bainitic Medium Carbon Steel

Ståhlkrantz

Hedström

Sarius

et al. 2021

Metall Mater Trans A

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The microstructure of a low alloy medium carbon bainitic steel, austempered in the temperature range 275 °C to 450 °C has been investigated by detailed electron backscatter diffraction and variant pairing analysis. It is observed that the variant pairing tendency has two distinct changes with varying temperature. At low temperature V1-V6 is the most frequent, whereas V1-V2 is the most frequent at intermediate temperature and at the highest temperature, V1-V4 dominates. This is distinct from the literature on low carbon steel where only two dominant variants pairs, related to the common distinction of bainite into lower and upper bainite, are typically reported. The change of the variant pairing in bainite also has many similarities with the change of variant pairing in martensite when its carbon content changes. Another observation is that the morphological orientation of cementite in the bainite has a strong relation with the variant pairing at lower austempering temperatures.

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Section: Methodsmentioning

confidence: 99%

Revealing the Unexpected Two Variant Pairing Shifts Due to Temperature Change in a Single Bainitic Medium Carbon Steel

Ståhlkrantz

Hedström

Sarius

et al. 2021

Metall Mater Trans A

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“…In an earlier work by the present authors the unexpected two distinct shifts in the variant paring in a 64Ni4 steel with increasing austempering temperature [24] was revealed and the microstructure was characterized in-depth. [24,33] For that specific steel it is clear that the bainitic microstructure is more complex than inferred by the standard division into upper and lower bainite. However, further investigations on additional steels after austempering at various temperatures are needed in order to improve the understanding of the effect of austempering temperature and carbon content on variant pairing in bainite.…”

Section: Introductionmentioning

confidence: 98%

Effect of Carbon Content on Variant Pairing in Bainitic Low Alloy Steel

Ståhlkrantz

Hedström

Sarius

et al. 2022

Metall Mater Trans A

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Variant pairing in bainite was evaluated in four different commercial low alloy steels with medium to high carbon content. The steels investigated were austempered in the temperature range 275 °C to 450 °C to obtain a bainitic microstructure. It was found that the V1–V6 is the most frequent variant pairing at lower temperature, while it gradually decreases towards intermediate temperatures, and at the highest austempering temperatures the variant pairing with low misorientation boundaries such as V1–V4 and V1–V8 is the most frequent. The preferred variant pairing is the least pronounced after austempering of steels with higher carbon contents at intermediate temperature. Nonetheless, a continuous increase of variant pairing within the same Bain group was observed with increasing austempering temperature for all steels. Furthermore, it was observed that the deviation from the theoretical Kurdjumov–Sachs orientation relationship increases with increasing austempering temperature for all steels.

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“…When choosing the optimal material for a particular component, geometric constraints and desired properties are the determining factors. Alloys should have features such as the desired hardenability, economic feasibility, and resistance to unwanted phase formation, which can lead to poor mechanical properties or thermal cracking [1].…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions

Shin

Kim

et al. 2021

Metals

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In this study, the changes in the microstructure and mechanical properties during isothermal heat treatment of cast steel before and after hot deformation were investigated using medium-carbon steel with low alloy content. The microstructural characteristics of the cast and hot-rolled medium-carbon steel under isothermal heat-treatment conditions were examined using optical microscopy and scanning electron microscopy in conjunction with electron backscatter diffraction. The variation in the mechanical properties was evaluated using Rockwell hardness and tensile tests. After maintaining an austenitizing condition at 1200 °C for 30 min, an isothermal heat treatment was performed in the range 350–500 °C, followed by rapid cooling with water. Both the cast steel and hot-rolled steel did not completely transform into bainitic ferrite during isothermal heat treatment. The partially untransformed microstructure was a mixture of martensite and acicular ferrite. At 500 °C, the prior austenite phase changed to Widmanstätten ferrite and pearlite. At 450 °C, bainitic ferrite and cementite were coarsened by the coalescence of ferrite and subsequent diffusive growth. The mechanical properties increased as the isothermal heat-treatment temperature decreased, and the hardness of the cast steel was generally higher than that of the hot-rolled steel. Hardness and strength showed similar trends, and overall mechanical properties tend to decrease as the isothermal heat-treatment temperature increases, but there are slight differences depending on complex factors such as various phase fractions and grain size.

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Effect of Tempering on the Bainitic Microstructure Evolution Correlated with the Hardness in a Low-Alloy Medium-Carbon Steel

Cited by 7 publications

References 41 publications

Revealing the Unexpected Two Variant Pairing Shifts Due to Temperature Change in a Single Bainitic Medium Carbon Steel

Revealing the Unexpected Two Variant Pairing Shifts Due to Temperature Change in a Single Bainitic Medium Carbon Steel

Effect of Carbon Content on Variant Pairing in Bainitic Low Alloy Steel

Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions

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