On the Behavior of Hot Crack Formation During Solidification in Fe–Ni Alloys

Hansson, Karin; Fredriksson, Hasse

doi:10.1002/adem.200390011

Cited by 14 publications

(19 citation statements)

References 11 publications

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“…Figure 5 shows that critical strain is increased from 1.9 to 2.5 % by decreasing the cool side temperature of the specimen from 1 250 to 950°C. Since the various cool side temperatures were obtained with the same cooling rate, which implies the supersaturation of vacancies 7) of each specimen was equal, the variation in critical strain can be related to the area where liquid coexists with solid. Lower temperature on the cool side results in a smaller area of solid/liquid co-exist region due to a higher temperature gradient.…”

Section: Methodsmentioning

confidence: 99%

“…Kim, Hansson and Fredriksson have observed that an Invar alloy with a sulfur content of 14 ppm is more susceptible to hot cracking than an alloy with a sulfur content of 4 ppm. 15) They suggested that S atoms segregated to the boundaries could quantum mechanically weaken the boundaries and the work for crack nucleation decrease as a result of a reduction in the surface tension due to S segregation. Therefore, they suggested that hot cracking could occur even when liquid films are not present along the grain boundaries.…”

Section: Grain Growth Under Temperature Gradient Andmentioning

confidence: 99%

“…In the study on hot cracking, several experimental methods such as 'Submerged Split-Chill Tensile', 1,2) 'in-situ melt bending test' 3) and 'in-situ solidified test' [4][5][6][7] etc., have been used to measure critical strain for hot cracking during continuous casting. However, since the measured data varies widely 8) depending on the experimental conditions, reliable trend in cracking susceptibility with chemical compositions according to alloying elements has not been obtained by direct measurements.…”

Section: Introductionmentioning

confidence: 99%

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Hot Cracking Behavior of Fe-Ni Alloys via Direct Observation.

Lee

2003

ISIJ International

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Hot cracking behavior of Fe-Ni alloys was investigated by using a high-speed camera to observe hot cracking in samples that were temperature-gradient heated and tensile deformed. The susceptibility to hot cracking was reliably evaluated based on critical strain and crack propagation length as functions of Ni content and cool side temperature. Grain size and shape in the brittle temperature region depended on liquid boundary migration due to solute diffusion within the liquid boundary under temperature gradient. High susceptibility to hot cracking of Fe-Ni alloys could be explained by the high sulfur segregation near the grain boundary and the large grain size within the solid/liquid coexisting region due to the rapid migration of the liquid boundary.KEY WORDS: hot cracking; continuous casting; Fe-Ni alloys; grain growth; sulfur segregation; direct observation of hot cracking; temperature-gradient tensile test. ent direction, and examined metallographically. Samples with hot cracks were dipped in liquid nitrogen and fractured by impact to reveal the crack surface. Auger analysis was performed in a Physical Electronics Phi 600 Auger microprobe by slicing off the measured surfaces at a rate of 0.217 nm/s to investigate the microsegregation near the crack surface. Experimental Results Evaluation of Crack SusceptibilityFigure 2 shows hot crack occurrence followed by melt flowing into the crack near the hot surface during tensile deformation. Only a portion of the specimen's width is shown due to the cover that prevents heat loss. In order to evaluate critical strain for hot cracking, it is necessary to know the length of the uniform deformation zone, the exact time deformation started and the time the crack occurred. Figure 3 shows the measured displacements of various positions within the deformation zone using a program that allows tracking a movement in any position during hot deformation. From this result and the fact that only the upper jig in the tester moves up during the tensile test, the length of the uniform deformation zone could be defined by roughly ISIJ International, Vol. 43 (2003) assuming the curve of displacements and the relative positions of the measured points to be linear. The times of initial deformation and crack occurrence could also be determined through tracking the movements of points within the deformation zone. Figure 4 shows that the critical strain, using the above method, is sharply decreased from 5.3 to 2.2 % with increases of Ni content from 0.021 to 3.35 % and slowly decreased thereafter. Austenite phases formed during solidification cause larger microsegregation 12,13) due to much lower diffusivities of solute elements in Austenite phases than in Delta ferrite phases. The sharp decrease in critical strain up to ϳ3.5 % Ni may correspond to the fact that residence time during solidification within Delta ferrite phase decreases with increases in Ni content and according to the Fe-Ni phase diagram, the Austenite phase starts to form from Ͼϳ4.1 % Ni. Figure 5 shows that critical str...

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Section: Methodsmentioning

confidence: 99%

Section: Grain Growth Under Temperature Gradient Andmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hot Cracking Behavior of Fe-Ni Alloys via Direct Observation.

Lee

2003

ISIJ International

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“…It is difficult to advise an experimental method to verify this assumption. In an earlier investigation 9,10 of peritectic steels , no difference was observed in the stress-strain behaviour between steels solidifying primarily austenite and steels solidifying to ferrite. In the present study, a new experimental method was developed in order to verify the above assumption.…”

Section: Introductionmentioning

confidence: 80%

Hot crack formation during peritectic reaction in steels

Korojy

Nassar

Fredriksson

2010

Ironmaking & Steelmaking

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Hot crack formation during solidification was investigated during the peritectic reaction in steels. A series of in situ solidification experiments was performed using a MTS tensile testing machine combined with a mirror furnace. Sample temperature and force change were measured during the solidification process. The force measurements showed a sudden drop during the solidification of samples, which occurred around the peritectic temperature of the alloy, were accompanied by cracks or refilled cracks in the microstructure. Furthermore, the peritectic reaction types were studied theoretically and experimentally to understand their effects on the force change during solidification. The theoretical analyses showed that the volume change due to the peritectic transformation is one of the reasons for crack formation. In addition, when the peritectic reaction occurs in a diffusionless (partition less) manner in an alloy with sufficiently high primary precipitation, crack formation is more probable.

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“…It is often formed at a location of stress concentration associated with a sudden change in the transversal cross section or hot spots due to the obstructed contraction of the solidifying material. In recent years, many studies have been conducted to investigate the hot tearing susceptibility (HTS) and the underlying mechanisms of the different alloy systems, such as steel, Al alloys, and Mg alloys …”

Section: Introductionmentioning

confidence: 99%

Hot Tearing Susceptibility of Binary Mg–Gd Alloy Castings and Influence of Grain Refinement

et al. 2018

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The hot tearing susceptibility (HTS) of binary Mg-Gd alloys is tested from 1.0 to 8.0 wt% using a constrained rod casting (CRC) mold. It is found that the curve of the HTS versus Gd content follows a typical "Λ" curve: HTS increases firstly, reaches a maximum at 1.5% Gd, and then decreases, which is in good agreement with the results predicted by Clyne-Davies model. Microstructure observations and thermodynamic calculations show that grain structure (size and morphology), the susceptible freezing range, the volume fraction of eutectic liquid, and the amount of intermetallics (Mg 5 Gd) are the main factors influencing the HTS of Mg-Gd experimental alloys. The highest HTS observed in Mg-1.5Gd alloy is attributed to its coarse columnar grains, the high freezing range, and the thin and continuous liquid film as well as the hard and brittle intermetallics precipitated along the grain boundaries. In contrast, the lowest HTS observed in Mg-8Gd alloy is mainly related to the fine equiaxed grains, which can effectively accommodate the strain during solidification, and the tear healing by eutectic liquid. Furthermore, the effect of grain refinement by Zr addition on the HTS is also studied, and the results show that grain refinement can significantly reduce the HTS.

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On the Behavior of Hot Crack Formation During Solidification in Fe–Ni Alloys

Cited by 14 publications

References 11 publications

Hot Cracking Behavior of Fe-Ni Alloys via Direct Observation.

Hot Cracking Behavior of Fe-Ni Alloys via Direct Observation.

Hot crack formation during peritectic reaction in steels

Hot Tearing Susceptibility of Binary Mg–Gd Alloy Castings and Influence of Grain Refinement

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