Transformation In Austenitic Steel Research Articles

Details of pearlite to austenite transformation in steel: Experiments and phase-field modeling

The austenitization of an initial pearlitic microstructure is simulated using the phase field model to achieve insight into White Etching Layer (WEL) formation in pearlitic railway steels. The simulations take into account the resolution of the cementite lamellae within a pearlite colony as well as the presence of pro-eutectoid ferrite. The austenite growth kinetics and morphology obtained via simulations are compared with dilatometry and microscopy observations. The influence of γ/θ and γ/α mobilities on the austenite growth morphology are studied. The simulations reproduce the microstructural features as well as the experimentally observed kinetics behavior of austenite formation, involving the correlation between mobilities and nucleation behavior.

Shear Transformation of Austenite in Steels Considering Stresses’ Effects

Shear Transformation of Austenite in Steels Considering Stresses’ Effects

Mechanism of FIB-Induced Phase Transformation in Austenitic Steel.

The transformation of unstable austenite to ferrite or α′ martensite as a result of exposure to Xe+ or Ga+ ions at room temperature was studied in a 304 stainless steel casting alloy. Controlled Xe+ and Ga+ ion beam exposures of the 304 were carried out at a variety of beam/sample geometries. It was found that both Ga+ and Xe+ ion irradiation resulted in the transformation of the austenite to either ferrite or α′ martensite. In this paper, we will refer to the transformation product as a BCC phase. The crystallographic orientation of the transformed area was controlled by the orientation of the austenite grain and was consistent with either the Nishiyama–Wasserman or the Kurdjumov–Sachs orientation relationships. On the basis of the Xe+ and Ga+ ion beam exposures, the transformation is not controlled by the chemical stabilization of the BCC phase by the ion species, but is a result of the disorder caused by the ion-induced recoil motion and subsequent return of the disordered region to a more energetically favorable phase.

Analytical models of austenite transformation in steels taking into account internal stresses

Analytical models of the transformation of austenite into steel are considered taking into account the influence of the stress state on structural transitions during heat treatment of steels A simple theoretical expression is proposed for calculating the amount of martensite formed as a function of the stresses in the gamma phase

АНАЛИЗ ФАЗОВО-СТРУКТУРНЫХ ПРЕВРАЩЕНИЙ ПРИ ОХЛАЖДЕНИИ СТАЛЕЙ С УЧЕТОМ ВОЗНИКАЮЩИХ ДЕФОРМАЦИЙ И НАПРЯЖЕНИЙ

The aim of the work is to study the phase-structural transformations during cooling of carbon and low-alloy steels, taking into account the resulting structural deformations and stresses. Low-alloyed steels with different content of alloying elements - chromium, molybdenum, nickel and steel, micro-alloyed with vanadium were chosen as the object of research. The dilatograms of steel samples were used to find the relative expansion of the steel sample before the start of austenite phase transformation (DA) and the relative expansion of the steel sample during austenite phase transformation (DFТ), which are associated with the relative elongation of the sample through a constant factor K. The parameter DA allows you to find structural stresses that arise in supercooled austenite steel in the presence of a temperature gradient. The parameter DFТ characterizes the stresses created by the phase transformation of austenite. As a result of the performed regression analysis, dependences were obtained that link the chemical composition of the steel, its cooling rate, and the parameters DА and DFТ. The analysis of phase-structural transformations during the cooling of the steel with the occurring deformations and stresses. An empirical relationship has been established between the temperatures of the beginning and end of the phase transformation of austenite in steel, the physicochemical parameters d and Zy, the cooling rate, and the deformation parameters when the austenite is cooled DA and the phase transformation DFТ. Confirmed the adequacy of the constructed equations. The obtained regression equations make it possible to calculate the deformation parameters DA and DFТ and critical points of the steel Ac1 and Ac3.

Modeling of Damage Evolution and Martensitic Transformation in Austenitic Steel at Cryogenic Temperature

Abstract In the present work, a constitutive model of materials undergoing the plastic strain induced phase transformation and damage evolution has been developed. The model is based on the linearized transformation kinetics. Moreover, isotropic damage evolution is considered. The constitutive model has been implemented in the finite element software Abaqus/Explicit by means of the external user subroutine VUMAT. A uniaxial tension test was simulated in Abaqus/Explicit to compare experimental and numerical results. Expansion bellows was also modelled and computed as a real structural element, commonly used at cryogenic conditions.

Plastic deformation and phase transformations in austenitic steels in the course of hydrogen charging and subsequent mechanical tests

This study aims to shed light on some uncertainty in the effect of hydrogen-induced ε-martensite on mechanical behavior of hydrogen charged austenitic steels. It is shown that cathodic charging of austenitic steels is accompanied by plastic deformation, which creates the crystallographic texture and decreases plasticity during subsequent tensile tests. This deformation is the main reason for the hydrogen-induced γ→ε transformation. The ε-martensite is formed in the hydrogen-rich areas of the austenite, which decreases the hydrogen content in the retained austenite. In case of a small fraction of the hydrogen-induced ε-martensite, it can be additionally formed during subsequent mechanical tests due to trip effect, which diminishes the hydrogen loss of plasticity.

Analysis of the strain induced martensitic transformation in austenitic steel subjected to dynamic perforation

An experimental and numerical analysis on the martensitic transformation in AISI 304 steel sheets subjected to perforation by conical and hemispherical projectiles is reported. Two target thicknesses are considered, 0.5 and 1.0 mm, and impact velocities range from 35 to 200 m/s. The perforation mechanisms are identified and the effect of the projectile nose-shape on the ability of the target for energy absorption is evaluated. Martensite has been detected in all the impacted samples and the role played by the projectile nose-shape on the transformation is highlighted. A 3D model implemented in ABAQUS/Explicit allowed to simulate the perforation tests. The material is defined through a constitutive description developed by the authors to describe the strain induced martensitic transformation taking place in metastable austenitic steels at high strain rates. The numerical results are compared with the experimental evidence and satisfactory matching is obtained. The numerical model succeeds in describing the perforation mechanisms associated to each projectile-target configuration analysed.

Thermo-mechanically coupled model of diffusionless phase transformation in austenitic steel

A constitutive model of thermo-mechanically coupled finite strain plasticity considering martensitic phase transformation is presented. The model is formulated within a thermodynamic framework, giving a physically sound format where the thermodynamic mechanical and chemical forces that drive the phase transformation are conveniently identifiable. The phase fraction is treated through an internal variable approach and the first law of thermodynamics allows a consistent treatment of the internal heat generation due to dissipation of inelastic work. The model is calibrated against experimental data on a Ni–Cr steel of AISI304-type, allowing illustrative simulations to be performed. It becomes clear that the thermal effects considered in the present formulation have a significant impact on the material behavior. This is seen, not least, in the effects found on forming limit diagrams, also considered in the present paper.

A constitutive model for the formation of martensite in austenitic steels under large strain plasticity

A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations is developed. The model takes basic thermodynamic relations as its starting point and the phase transition is treated through an internal variable (the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, along with the derivation of a consistent algorithmic tangent modulus. Simulations based on the presented model are shown to agree well with experimental findings. The proposed model provides a robust tool suitable for large-scale simulations of phase transformations in austenitic steels undergoing extensive deformations, as is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process.

Effect of hydrogen on the microstructure, mechanical properties and phase transformations in austenitic steels

Effect of high-pressure hydrogen charging on the microstructure, mechanical properties and phase transformations in austenitic steels has been investigated and discussed. The results show that the strength and impact toughness of the steels increase slightly and that the ductility decreases after hydrogen charging. The existence of δ-ferrite deteriorates the resistance to hydrogen embrittlement (HE) of the steels. The occurrence of carbide in the steel resulted from aging reduces the ductility of the steel and makes the steel sensitive to HE. The existence of sufficient hydrogen promotes the ϵ-martensitic transformation and suppresses the α'-martensitic transformation. The permeabilities and diffusivities of hydrogen in the steels have also been determined.

Martensitic transformations in ion implanted stainless steels

ABSTRACTUsing ion implantation it is possible to induce a variety of phase transformations in the surfaces of stainless steels. The implanted layer can be either amorphized, undergo an fee (γ) => bec (α') martensitic transformation, or compounds can be formed between implanted atoms and target atoms. Stress provides a dominant contribution to the driving forces for amorphization and martensitic transformations. Implantation-induced alloying is important for obtaining the right composition in the implanted layer, whereby the transformation conditions can be optimized. Amorphization is best achieved by implantation of metalloids or other conventionally known glass forming elements. Martensitic transformations in austenitic steels are most easily induced after implantations with noble gases — including helium, where highly pressurized noble gas inclusions are formed. Implantations at high fluences with compound forming species such as nitrogen, boron or phosphorus, will often produce an implanted layer with a structure resembling a ceramic glazing which, depending on the implant species, will be amorphous or crystalline.In order to understand and predict changes in the surface properties of implanted stainless steels, a detailed knowledge of the implantation induced microstructures is essential. The implanted surface will often have a multiphase structure giving only moderate improvements in corrosion properties, and in particular, resistance to pitting corrosion will often be reduced or only slightly improved. Surface hardness will, on the other hand, in many cases be increased, and large improvements will often be observed in wear and friction properties of the implanted surfaces. Under conditions where formation of a homogeneous surface layer is facilitated, the fatique life of implanted samples may also be extended.

Principle of the shift of the temperature of the instrumental onset of the austenite transformation in steels during high-speed and laser heating

It is shown that the shift of the temperature of the onset of the austenitic transformation in steels during high-speed heating can be interpreted as a time delay of the α→γ transformation relative to the rate of change of temperature. During heating of steels with laser radiation pulses the temperature shift may be considerable and this restricts the range of temperatures in which steels can be hardened without melting and can reduce the hardening efficiency. The calculated and experimental temperatures agree satisfactorily.

Transformation of austenite in steels of the 110G13L type containing chromium

1. The temperature of minimal stability of austenite in steel 110G13L of standard composition is ≈600°, and ≈540° for the steel with Cr. 2. For steels of the 110G13L type alloyed with chromium, the C curves shift to the right in comparison with the standard steel.

The effect of alternating stressing on the martensite transformation in austenitic steel

The effect of alternating stressing on the martensite transformation in austenitic steel

Hydrogen induced martensitic transformations in austenitic steels

Hydrogen induced martensitic transformations in austenitic steels

Structure and properties of die steels of the 5Kh2MF type

1. The high heat resistance (600–620°) of die steels in combination with good strength (σ0.2=135–140 kg/mm2) and toughness (an=4–5 kg-m/cm2) throught the section of large forgings (500×500 mm) after heat treatment is ensured by combined alloying within the following limits: 0.4–0.5% C, 0.5–1.0% Mn, 0.2–0.5% Si, 1.5–2.0% Cr, 0.8–1.2% Mo, 1.5–2.5% Ni, and 0.3–0.5% V. 2. In its combination of basic properties (heat resistance, strength, and toughness of large forgings), steel of the 5Kh2N2MF type surpasses standard steels 5KhNM (5KhNV) and 4Kh5V2FS (4Kh5MFS), and can be recommended for large heavily loaded drop-forging and pressing dies for hot working. 3. The partial transformation of austenite in steels of the 5Kh2MF type in the intermediate range during continuous cooling is accompanied by substantial reduction of the secondary hardness and toughness, and the highest secondary hardening occurs at higher tempering temperatures (580–600°).

Effect of dendritic segregation of manganese on the transformation of austenite in steel

1. We investigated the effect of manganese (0.58–2.45%) on the transformation of austenite under isothermal conditions after solidification and homogenizing annealing. 2. In the presence of manganese segregation the pearlite and bainite transformations in steel with 0.58–2.45% Mn occur over a longer time period and wider temperature range than in the homogenized steels. 3. The isothermal transformation of austenite begins in the axial sections of dendrites with a low stability due to the low concentration of manganese. Austenite later decomposes in sections between branches that are rich in manganese.

In termediate transformation of austenite in steels with silicon

In termediate transformation of austenite in steels with silicon