Some Aspects of Bainite Transformation in Fe-Based Alloys

Tsuzaki, Kaneaki; Maki, Tadashi

doi:10.1051/jp4:1995807

Cited by 8 publications

(8 citation statements)

References 12 publications

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“…[9] A different mechanism for the incomplete transformation has also been proposed: carbon enrichment in untransformed austenite up to the T 0 ¢ line, which is the upper limit of diffusionless growth affected by the elastic strain energy, occurs with carbide-free bainitic ferrite formation, and thus lowers the driving force. [10,11] However, the incomplete transformation observed in Fe-Ni-C alloys, [8] in which the bainite transformation occurs with cementite precipitation and Ni does not have a strong interaction with carbon, complicates the discussion of the mechanism. It is necessary to look more closely at the nucleation and growth of bainite transformation to reveal alloying effects on the incomplete transformation.…”

Section: Introductionmentioning

confidence: 99%

“…[3] Such transformation stasis is caused by the incomplete transformation of bainite [4] and has been observed in Fe-C-Mo ternary alloys [5,6] as well as other alloy systems. [7,8] It has been proposed that transformation stasis is caused by the segregation of alloying elements with a strong affinity for carbon to the ferrite/austenite interphase boundary, [6] and an increase in Mo segregation was revealed by STEM-EDX analysis in Fe-C-Mo ternary alloys. [9] A different mechanism for the incomplete transformation has also been proposed: carbon enrichment in untransformed austenite up to the T 0 ¢ line, which is the upper limit of diffusionless growth affected by the elastic strain energy, occurs with carbide-free bainitic ferrite formation, and thus lowers the driving force.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Transformation Stasis in Low-Carbon Steels Microalloyed with B and Mo

Tsuzumi

Miyamoto

Amino

et al. 2014

Metall Mater Trans A

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TADASHI FURUHARA, KENJI TSUZUMI, GORO MIYAMOTO, TAKAFUMI AMINO, and GENICHI SHIGESATO In the present study, bainite transformation kinetics was examined in low C-Mn steels with the addition of small amounts of B and Mo. This addition delays the onset of the bainite transformation. Mo addition causes transformation stasis at temperatures between 873 K and 823 K (600°C and 550°C) just below the bainite-start (B s ) temperature, resulting from an incomplete bainite transformation. Post-stasis transformation after a prolonged hold proceeds by the formation of ferrite with a low dislocation density, and in Mo-containing alloys, often the formation of carbides. The volume fraction at which the transformation stops is higher for lower carbon contents and lower transformation temperatures. By contrast, at 773 K (500°C), the bainite transformation accompanying cementite precipitation occurs regardless of microalloying and is completed after shorter hold times. EDX measurement performed on the Mo-added 0.15 pct C alloy with aberration-corrected STEM revealed that segregation at the bainite/austenite interphase boundary is small for Mn and negligible for Mo in the early stages of stasis, which does not support the incomplete transformation mechanism based on the solute drag theory for the alloys used.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characterization of Transformation Stasis in Low-Carbon Steels Microalloyed with B and Mo

Tsuzumi

Miyamoto

Amino

et al. 2014

Metall Mater Trans A

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“…Figure 12 shows the subsurface of the 300 °C specimens produced with salt-bath times of 30 min and 120 min. When the matrix was composed of a fine feather structure and martensite and subjected to a short duration (30 min) of austempering, the brittleness became significant and caused the subsurface to become irregular (Figure 12a) [12,20]. Figure 12b shows the flat fracture characteristic that was obtained with a longer austempering time (120 min).…”

Section: Resultsmentioning

confidence: 95%

“…In addition, the salt-bath specimen at 300 °C, became coarser was the austempering duration increased (Figure 4). A fully bainite matrix with finer primary carbides can be achieved with a longer austempering time [5,[12][13][14]. However, if the tempering time was insufficient, then no feathery structure was seen in the matrix after etching.…”

Section: Resultsmentioning

confidence: 99%

Microstructures and Mechanical Properties of Austempering SUS440 Steel Thin Plates

Chen

Hung

Lui

et al. 2016

Metals

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SUS440 is a high-carbon stainless steel, and its martensite matrix has high heat resistance, high corrosion resistance, and high pressure resistance. It has been widely used in mechanical parts and critical materials. However, the SUS440 martempered matrix has reliability problems in thin plate applications and thus research uses different austempering heat treatments (tempering temperature: 200˝C-400˝C) to obtain a matrix containing bainite, retained austenite, martensite, and the M7C3 phase to investigate the relationships between the resulting microstructure and tensile mechanical properties. Experimental data showed that the austempering conditions of the specimen affected the volume fraction of phases and distribution of carbides. After austenitizing heat treatment (1080˝C for 30 min), the austempering of the SUS440 thin plates was carried out at a salt-bath temperature 300˝C for 120 min and water quenching was then used to obtain the bainite matrix with fine carbides, with the resulting material having a higher tensile fracture strength and average hardness (HRA 76) makes it suitable for use as a high-strength thin plate for industrial applications.

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“…Robertson [7] investigated the transformation rate of the microstructures that formed upon quenching from austenite and proposed that the slow growth of the ferrites constituent of bainite is best explained by transformation being controlled by carbon diffusion. Other work emphasised the similarity to martensite, and it was understood that bainite formed with a supersaturation of carbon [8][9][10][11]. Vilella [12] and Bain [13] proposed that transformation involved the formation of flat plates which form abruptly, before decarburising at a rate depending on the temperature.…”

Section: Literature Surveymentioning

confidence: 99%

Modeling And Characterization Of High Carbon Nanobainitic Steels

Sidhu¹

2021

Preprint

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Analytical models have been developed for the transformation kinetics, microstructure analysis and the mechanical properties in bainitic steels. Three models are proposed for the bainitic transformation based on the chemical composition and the heat treatment conditions of the steel as inputs: (1) thermodynamic model on kinetics of bainite transformation, (2) improved thermo-statistical model that eliminates the material dependent empirical constants and (3) an artificial neural network model to predict the volume fraction of bainite. Neural networks have also been used to model the hardness of high carbon steels, subjected to isothermal heat treatment. Collectively, for a steel of given composition and subjected to a particular isothermal heat treatment, the models can be used to determine the volume fraction of bainitic phase and the material hardness values. The models have been extensively validated with the experimental data from literature as well as from three new high carbon experimental steels with various alloying elements that were used in the present work. For these experimental steels, data on the volume fraction of phases (via X-ray diffraction), yield strength (via compression tests) and hardness were obtained for various combinations of isothermal heat treatment times and temperatures. The heat treated steels were subjected to compression and hardness tests and the data have been used to develop a new correlation between the yield stress and the hardness. It was observed that while all three experimental steels exhibit a predominantly nanostructured bainite microstructure, the presence of Co and Al in one of the steels accelerated and maximized the nano-bainitic transformation within a reasonably short isothermal transformation time. Excellent yield strength (>1.7 GPa) and good deformability were observed in this steel after isothermal heat treatment at a low temperature of 250C for a relatively short duration of 24 hours.

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Some Aspects of Bainite Transformation in Fe-Based Alloys

Cited by 8 publications

References 12 publications

Characterization of Transformation Stasis in Low-Carbon Steels Microalloyed with B and Mo

Characterization of Transformation Stasis in Low-Carbon Steels Microalloyed with B and Mo

Microstructures and Mechanical Properties of Austempering SUS440 Steel Thin Plates

Modeling And Characterization Of High Carbon Nanobainitic Steels

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