Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel

Luo, Yiwa; Guo, Hongjian; Sun, Xiaolin; Mao, Mingtao; Guo, Jingjie

doi:10.3390/met7010027

Cited by 33 publications

(21 citation statements)

References 24 publications

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“…The as-cast structure of AISI M42 HSS can be divided into two types of constructions: a dendritic matrix of ferrite with small carbides and a ledeburite of carbides and ferrite. A previous study 19 demonstrated that the smaller carbides were mostly V-rich MC or M(C,N), while the large primary carbides were Mo-rich M 2 C. In conventional M42 steel, the morphology of M 2 C carbides presents a lamellar shape with dimensions of 5 to 20 μm in length and 1 to 2 μm in width (Fig. 3(a) ).…”

Section: Resultsmentioning

confidence: 87%

Influence of the Nitrogen Content on the Carbide Transformation of AISI M42 High-Speed Steels during Annealing

Luo

Guo

Sun

et al. 2018

Sci Rep

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Attempts were made to elucidate the effect of nitrogen on primary eutectic carbides in as-cast and annealed AISI M42 high-speed steel. Particular emphasis was placed on the transformation of carbides during forging and annealing in steels with different nitrogen concentrations and the influence of final carbides on the impact toughness of the steel. Microstructural observation, electrolytic extraction method, X-ray diffraction analysis, automated inclusion analysis (INCASteel), and impact toughness measurement combined with fractographic observation were conducted on the specimens. Primary M2C carbides were found to be dominant precipitates in the as-cast ingot, with a certain amount of V(C,N). Nitrogen addition promoted the formation of fibrous M2C, whereas lamellar M2C predominated in M42 steel with a low nitrogen concentration (w[N]% = 0.006). Fibrous carbides M2C tend to decompose into more stable carbides M6C and MC during forging and annealing compared to lamellar M2C. Nitrogen alloying only affected the morphologies and dimensions of carbides, but did not change the types of carbides. These improvements in the dimensions and fractions of carbides naturally increased the impact toughness of annealed steel. Hence, it was suggested that the addition of nitrogen to AISI M42 high-speed steel was required to achieve homogeneous distribution of carbides and sufficient impact toughness.

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Section: Resultsmentioning

confidence: 87%

Influence of the Nitrogen Content on the Carbide Transformation of AISI M42 High-Speed Steels during Annealing

Luo

Guo

Sun

et al. 2018

Sci Rep

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“…The typical microstructure in the as-cast alloy consists of dendrites surrounded by coarse M 2 C-type eutectic carbides with a networked structure. These coarse primary carbides undergo decomposition, dissolution, transformation, and precipitation during hot deformation, and transform into a more stable form that can be expressed as M 2 C + matrix→M 6 C + MC [6,7,8,9]. Nogueira et al [10] reported that undecomposed reticular carbides could provide routes for crack propagation and make cracks deeper.…”

Section: Introductionmentioning

confidence: 99%

Gleeble-Simulated and Semi-Industrial Studies on the Microstructure Evolution of Fe-Co-Cr-Mo-W-V-C Alloy during Hot Deformation

Luo

Guo

et al. 2018

Materials

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Fe-Co-Cr-Mo-W-V-C alloy is one of the most important materials for manufacturing drills, dies, and other cutting tools owing to its excellent hardness. However, it is prone to cracking due to its poor hot ductility during continuous hot working processes. In this investigation, the microstructure characteristics and carbide transformations of the alloy in as-cast and wrought states are studied, respectively. Microstructural observation and first-principles calculation were conducted on the research of types and mechanical properties of carbides. The results reveal that carbides in as-cast Fe-Co-Cr-Mo-W-V-C alloy are mainly Mo2C, VC, and Cr-rich carbides (Cr7C3 and Cr23C6). The carbides in wrought Fe-Co-Cr-Mo-W-V-C alloy consist of Fe2Mo4C, VC, Cr7C3, and a small amount of retained Mo2C. For these carbides, Cr7C3 presents the maximum bulk modulus and B/G values of 316.6 GPa and 2.48, indicating Cr7C3 has the strongest ability to resist the external force and crack initiation. VC presents the maximum shear modulus and Yong’s modulus values of 187.3 GPa and 465.3 GPa, which means VC can be considered as a potential hard material. Hot isothermal compression tests were performed using a Gleeble-3500 device to simulate the flow behavior of the alloy during hot deformation. As-cast specimens were uniaxially compressed to a 70% height reduction over the temperature range of 1323–1423 K and strain rates of 0.05–1 s−1. A constitutive equation was established to characterize the relationship of peak true stress, strain rate, and deformation temperature of the alloy. The calculated results were in a good agreement with the experimental data. In order to study the texture evolution, the microstructures of the deformed specimens were observed, and an optimal deformation temperature was selected. Using the laboratorial optimal temperature (1373 K) in forging of an industrial billet resulted in uniform grains, with the largest size of 17 µm, surrounded by homogenous spherical carbides.

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“…Austenitization temperature plays an important role in these steels since it influences several microstructural features e.g. ; prior austenite grain size, morphology of martensitic lath structure, volume fraction of primary carbides (carbides retained after austenitizing treatment are called primary carbides whereas carbides formed during tempering are called secondary carbides), amount of alloying elements dissolved in the austenite and the amount of retained austenite [4][5][6][7][8]. Higher the austenitizing temperature, a greater amount of alloying elements is expected to be dissolved in the austenite [9]; therefore full potential of these alloying elements can be exploited during subsequent quenching-tempering process in which secondary hardening precipitates form.…”

Section: Introductionmentioning

confidence: 99%

“…Higher the austenitizing temperature, a greater amount of alloying elements is expected to be dissolved in the austenite [9]; therefore full potential of these alloying elements can be exploited during subsequent quenching-tempering process in which secondary hardening precipitates form. However higher austenitizing temperatures also results in increasing the prior austenite grain size [7,[10][11][12][13][14]. At the same time, lower the austenitization temperature, finer is the prior austenite grain size, and greater is the fraction of undissolved primary carbides in the austenite which decreases the secondary hardening effect and also reduces the fracture toughness of the steel [4,15,16].…”

Section: Introductionmentioning

confidence: 99%

Austenite stability and M2C carbide decomposition in experimental secondary hardening ultra-high strength steels during high temperature austenitizing treatments

Veerababu

Prasad

Phani

et al. 2018

Materials Characterization

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The present study deals with the austenite stability and M 2 C carbide decomposition in three secondary hardening ultra-high strength (SHUHS) steels with varying levels of Cr and Mo (2Cr-1Mo, 2Cr-3Mo and 5Cr-5Mo) investigated using Vicker's hardness, optical and electron microscopy. These steels were subjected to high temperature austenitizing treatments at 1000, 1050, 1100 and 1150 o C. It has been established that increasing both Cr and Mo to 5wt. % as well as increasing the austenitizing temperature in this class of SHUHS steels is stabilizing the austenite such that almost 100% austenite is produced upon oil quenching. Further, higher Cr and Mo is also found to influence the stability of metastable M 2 C carbide formed during processing of the steels. While the M 2 C carbide in 2Cr-3Mo steel remained untransformed, it was found to transform partially to M 6 C during austenitization of 5Cr-5Mo steel. Hardness measurements on these steels revealed that hardness is relatively insensitive to austenitizing temperature in 2Cr-1Mo steel, decreased in 2Cr-3Mo and decreased more drastically in 5Cr-5Mo steel with austenitizing temperature. This dependence has been correlated to the influence of composition on M s temperature and hence on retention of austenite as well as primary carbides. The experimental results were compared against theoretical calculations using ThermoCalc, which predict the presence of only M 6 C in both 2Cr-3Mo and 5Cr-5Mo steels. The apparent discrepancy between theoretical and experimental observations has been correlated to kinetic factors.

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Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel

Cited by 33 publications

References 24 publications

Influence of the Nitrogen Content on the Carbide Transformation of AISI M42 High-Speed Steels during Annealing

Influence of the Nitrogen Content on the Carbide Transformation of AISI M42 High-Speed Steels during Annealing

Gleeble-Simulated and Semi-Industrial Studies on the Microstructure Evolution of Fe-Co-Cr-Mo-W-V-C Alloy during Hot Deformation

Austenite stability and M2C carbide decomposition in experimental secondary hardening ultra-high strength steels during high temperature austenitizing treatments

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