In Situ Study of Phase Transformations during Non-Isothermal Tempering of Bainitic and Martensitic Microstructures

Talebi, Seyyed Hesamodin; Ghasemi-Nanesa, Hadi; Jahazi, Mohammad; Melkonyan, Haikouhi

doi:10.3390/met7090346

Cited by 33 publications

(19 citation statements)

References 32 publications

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“…For distances of 200 mm or above from the surface of the sample, bainite volume fractions were very similar in both simulations. This could be explained in terms of the precedence of bainite transformation over martensitic transformation at slower cooling rates (i.e., far from the surface zone) as also reported by other authors through experimental work on similar steels [10,29,30].…”

Section: Effect Of Carbon Contetntsupporting

confidence: 74%

Numerical Simulation of Water Quenching of Large Size Steel Forgings: Effects of Macrosegregation and Grain Size on Phase Distribution

Lyassami

Shahriari

Fredj

et al. 2018

JMMP

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In this paper, water quenching of large ingots was simulated using FORGE NxT 1.1 ® Finite Element code. Simulations were carried out for as-forged medium-carbon low-alloy steel. A novel method is proposed to simulate the different parts of a large size forged block with different chemical compositions and grain sizes using the multiple materials method. The effects of macrosegregation, grain size variation and cooling rate on phase distribution through the volume of the forged block were investigated. The delay in transformation kinetics, which is due to the effect of grain size variation and carbon content, was analyzed. Results show that macrosegregation and grain size variations significantly influence transformation start points and the volume fraction of phases that are present in each location of the forged ingot. The proposed prediction method was validated using high-resolution dilatometry experiments and X-ray diffraction measurements to evaluate accurately the volume fraction of martensite, bainite and the percentage of retained austenite for each condition.

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Section: Effect Of Carbon Contetntsupporting

confidence: 74%

Numerical Simulation of Water Quenching of Large Size Steel Forgings: Effects of Macrosegregation and Grain Size on Phase Distribution

Lyassami

Shahriari

Fredj

et al. 2018

JMMP

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“…Therefore, during the quench process, significant temperature gradients are produced that result in a variety of microstructures, such as martensite, bainite and retained austenite through the thickness of the large-size block [ 4 , 5 ]. The hard martensitic phase is generally located near the surface region with the proportions of bainite and retained austenite increasing with the thickness [ 6 ]. Such heterogeneity in the microstructure translates into variable mechanical properties from one location to another of the block and could impact the machinability and service durability of the mold.…”

Section: Introductionmentioning

confidence: 99%

Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium-Carbon Low-Alloy Bainitic Steel

2018

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The effect of isothermal tempering on retained austenite decomposition and carbide precipitation were investigated in a medium-carbon low-alloy bainitic steel. High-resolution dilatometry was used to perform isothermal tempering at 350 °C, 550 °C and 600 °C for different holding times up to 16 h. The decomposition of retained austenite, morphology and composition of carbides were investigated by analyzing the dilatometric curves and were confirmed through scanning and transmission electron microscopy observations. The decomposition behavior of retained austenite varied significantly as a function of the tempering temperature with a full decomposition observed at 600 °C. It was also found that by increasing the tempering temperature from 550 °C to 600 °C, carbides precipitate approximately twice as fast, and evolve from M3C type to Cr7C3 and Cr23C6 after 16 h of tempering at 600 °C.

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“…The first stage is from 50 °C to 200 °C, and it is associated with carbon segregation and clustering, as well as cementite I precipitation; during this stage, carbon was precipitated from ferrite and carbide formation, leading to a slight shrinkage in the length of the specimen. The selected area diffraction pattern at 200 °C (Figure 4(b)) shows that unlike the tempering process of martensite [6,21], transition carbides did not precipitate from 700 L in this temperature range; however, the cementite did directly precipitate. This is mainly due to the low carbon content in 700 L. The second stage involved the decomposition of retained austenite from 200-300 °C.…”

Section: Stages In the Tempering Processmentioning

confidence: 98%

Effect of Carbide Precipitation on the Evolution of Residual Stress during Tempering

Ding

Liu

Xie

et al. 2019

Metals

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The evolution of microstructure and residual stress during the tempering of 700 L low-carbon micro-alloyed steel was studied using a crack compliance method for measuring residual stress. Additionally, a non-isothermal tempering dilatation test, Vickers micro-hardness test, and transmission electron microscopy were used. The evolution of residual stress during tempering consists of two stages. The first stage coincided with cementite precipitation. Under the initial residual stress, the transformation plasticity due to cementite precipitation leads to partial relaxation of the micro-stress evoked by the austenite-to-ferrite transformation during quenching. It also caused the material surface and the core to exhibit different residual stress evolution trends. After tempering at 300 ∘ C for 30 min, the residual stress was reduced from 487 MPa to 200 MPa; however, the elastic strain energy remained unchanged. The second stage coincided with alloy carbide precipitation and Mn partitioning, but the precipitation of the alloy carbide only reduced the elastic strain energy by 8.7%. Thus, the change in activation energy was the main reason for the relaxation of residual stress at this stage. After tempering at 600 ∘ C for 30 min, the residual stress was reduced to 174 MPa, the elastic strain energy was reduced by 72.72%, and the residual stress was controlled.

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In Situ Study of Phase Transformations during Non-Isothermal Tempering of Bainitic and Martensitic Microstructures

Cited by 33 publications

References 32 publications

Numerical Simulation of Water Quenching of Large Size Steel Forgings: Effects of Macrosegregation and Grain Size on Phase Distribution

Numerical Simulation of Water Quenching of Large Size Steel Forgings: Effects of Macrosegregation and Grain Size on Phase Distribution

Retained Austenite Decomposition and Carbide Precipitation during Isothermal Tempering of a Medium-Carbon Low-Alloy Bainitic Steel

Effect of Carbide Precipitation on the Evolution of Residual Stress during Tempering

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