Martensite Formation In Steel Research Articles

Structure and mechanical properties of high strength austenitic Mn–Ni–Cu–V–C dispersionally hardened steel

The paper presents the results of a study of the structure and mechanical properties of high-strength austenitic dispersionally hardened Mn–Ni–V–C steel with a yield strength of at least 700 MPa. Its composition and the hardening method were selected so that the steel meets the requirements for high strength and nonmagnetic properties. It is shown that the introduction of 1–2% Cu into Mn–Ni–V–C steel expands the region of existence of the γ-phase in the Fe–Ni–Mn phase diagram, narrows the two-phase γ+α-region and shifts it towards lower Mn contents, increasing stability of austenite to martensitic transformation during cold deformation. A numerical assessment of the influence of alloying austenite-forming elements Ni, Mn, Cu on the critical degree of cold plastic deformation, leading to the formation of deformation martensite in steel, is proposed. The temperature range of the reverse transformation of this martensite into austenite during annealing is established, depending on the nickel content in the steel. For precipitation hardened steel with a composition of 10%Mn; 10%Ni; 2%Cu; 0.3–0.4%C; ~1.4%V the regularities of dissolution upon heating for quenching and precipitation during aging of particles of the strengthening carbide phase VC were studied. It has been shown that the maximum strength is achieved after quenching from 1150°C and aging at 650°C for 15 hours. Taking into account the studies carried out on the stability of austenite, static and cyclic strength and durability, the optimal alloying range of steel with nickel, manganese and copper was substantiated, and the optimal mode of heat treatment was revealed, which provides a combination of high strength with good ductility and toughness of steel.

One‐Step Process for Press Hardened Steel–Carbon Fiber Reinforced Thermoset Polymer Hybrid Parts

A new one‐step process for manufacturing press hardened steel–carbon fiber reinforced (thermoset) polymer hybrid parts with potential for reduced cycle time, infrastructure requirements, and energy consumption compared with traditional two‐ and three‐step processes is developed. The process combines and optimizes the press hardening and prepreg compression molding technologies, traditionally used in isolation for manufacturing press hardened steel and carbon fiber reinforced polymer parts, respectively, to produce hybrid parts in a one‐step, fully integrated process. Heat required for curing and bonding prepreg to steel is provided by residual heat of the steel part immediately following hot forming and interrupted die‐quenching of steel. Thermal conductivity of tool material is investigated to achieve the optimal balance between die‐quenching rate for martensite formation in steel and temperature maintenance for complete curing and bonding of prepreg. Addition of epoxy adhesive and thickness ratio between steel and prepreg are also investigated. Benchmarking is conducted against parts manufactured by the traditional two‐step process, in which the press hardened steel part is formed in isolation before joining with the carbon fiber reinforced polymer part. No sacrifice of part quality is found from the new one‐step process with no loss of mechanical performance, despite clear economic and environmental advantages.

STRUCTURE TRANSFORMATION IN THE EXPLOSION WELDED BIMETAL STEEL 20 + STEEL 50Cr15Мo2V AFTER THERMAL TREATMENT

The results of studies of structural changes in a two-layer explosion-welded composite material are presented: carbon steel 20 + alloyed stainless steel 50Cr15Мo2V after normalization at temperatures of 800 - 1100 С and holding time 1 hour. It was found that at 800 ° C there is a “reverse” diffusion of carbon - from its lower to higher concentrations and the formation of a decarburized layer in steel 20, and with increasing temperature, carbon diffuses back into steel 20 together with chromium, changing the structure of the heat-affected zone: with an increase in the amount of perlite , the formation of the structure of Widmannstätt and carbide colonies in steel 20 and the formation of martensite in steel 50Cr15Мo2V. The features of structural changes in the alloys that were formed after explosion welding are considered.

Kinetic study on martensite formation in steels 1045 and 4340 under variable cooling rates

Kinetic study on martensite formation in steels 1045 and 4340 under variable cooling rates Dimitry V. Bubnoff1, Mariana M. O. Carvalho2, Thiago R.M. Lourenço1, Jose Adilson de Castro1 1 PPGEM, Industrial Engineering School/UFF, Volta Redonda/RJ, Brazil 2 Lappeenranta University of Technology/LUT, Skinnarilankatu, Lappeenranta Finland2 DOI: https://doi.org/10.33017/RevECIPeru2015.0011/ Abstract The experiments were carried with two steels with different chemical compositions, aiming at understanding and comparison with the available literature. The microstructures of steels 1045 and 4340 were characterized and quantified using scanning electron microscopy (SEM) and optic microscopy (OM) with quantitative methods. Based on the experimental results, the amount of martensite, the hardness and the microhardness were determined, as a function of the distance from the quenching end, under different cooling conditions. For predicting the evolution of martensitic fraction along the sample, Koistinen-Marburger’s (K-M) model was adopted. It was found that the parameters recommended in the literature for the traditional K-M model do not represent accurately the results obtained for the steel samples under investigation. According to indications found in recent literature, parameter corrections were proposed, leading to a modified K-M model which better represents the transformations observed in the different examined steels. Keywords: Kinetics, martensite, Koistinen-Marburger model.

Kinetic Study on Martensite Formation in Steels 1045 and 4340 under Variable Cooling Rates

The experiments were carried with two steels with different chemical compositions, aiming at understanding and comparison with the available literature. The microstructures of steels 1045 and 4340 were characterized and quantified using scanning electron microscopy (SEM) and optic microscopy (OM) with quantitative methods. Based on the experimental results, the amount of martensite, the hardness and the microhardness were determined, as a function of the distance from the quenching end, under different cooling conditions. For predicting the evolution of martensitic fraction along the sample, Koistinen-Marburger’s (K-M) model was adopted. It was found that the parameters recommended in the literature for the traditional K-M model do not represent accurately the results obtained for the steel samples under investigation. According to indications found in recent literature, parameter corrections were proposed, leading to a modified K-M model which better represents the transformations observed in the different examined steels.

Investigation of Martensite Transformation in 316L Stainless Steel

A large number of parameters affect martensite formation in steel, such as composition, applied stress, plastic strain and temperature. Low cycle fatigue tests on 316L austenitic stainless steel have been carried outwith different strain amplitudesat room temperature and cryogenic temperatures. The influences of deformation and temperature have been investigatedby carrying out in-situ and ex-situ neutron diffraction measurements in the ENGIN-X diffractometer at ISIS (UK) to analyze the volume fraction and strain in the martensite phase. Increasing plastic deformation and decreasing temperature were shown to promote martensite transformation and increase the hardness of the material. The influence of the appearance of martensite due to deformation and temperature will be discussed.

Stabilization of the tetragonal distortion of FexCo1−xalloys by C impurities: A potential new permanent magnet

We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m${}^{3}$ and a saturated magnetization field of 1.9 T.

Crystallographic analysis of martensitic transformation in an iron-nickel alloy with twinned martensite

A variant of the crystallographic theory of martensitic transformations is proposed, based on a mechanism of lattice deformation in which the angle of rotation of a martensite plate is reduced to a minimum. In an iron-nickel alloy with twinned martensite, the least angle of rotation corresponds to the deformation of the austenite lattice by shear on the (111) plane in the $$\left[ {11\bar 2} \right]$$ direction proposed by Kurdyumov and Sachs as the first shear in the two-shear theory of martensite formation in steel.

The kinetics of bainite and martensite formation in steels during cooling

The kinetics of bainite and martensite formation in steel 41Cr4 has been determined using dilatometry for a range of cooling rates. It is demonstrated that all fraction curves can be adequately described with a previously proposed model using a single set of input parameters. This validation shows that the model can give accurate predictions of the CCT diagram of bainitic steels provided the model can be tested against a single experimental fraction curve to determine the model parameters for the given composition.

Martensitic transformation in iron

1. The formation of martensite in iron (0.03% C) occurs at high temperatures (700–650°) and obeys well-known [5] rules established for the formation of martensite in steels—in particular, the initial martensitic transformation temperature is independent of the austenite grain size and the cooling rate. 2. The growth rate of martensite crystals is low (∼3 μ/sec for iron and 2 μ/sec for low-carbon steel) and does not depend on the temperature. 3. Martensite formation is not a thermally activated process—the low rate at which martensite is formed at high temperatures is due to the fact that the growth of martensite platelets occurs in a narrow range in which relaxation processes occur rapidly. Evidently the occurrence and relaxation of stresses is the principal factor determining the mechanism and rate of the martensitic transformation.

The kinetics of martensite formation in steel

The main features of martensite transformation kinetics observed in steels are surveyed. The quantitative analysis of the data relating to isothermal transformation is emphasized as the starting point for a more general understanding of other types of kinetic behavior. It is concluded that the distinction between athermal and isothermal kinetics is purely empirical, and that athermal transformation should be regarded as a rapid isothermal reaction.