Effect of Martensite Volume Fraction on Strain Partitioning Behavior of Dual Phase Steel

Monotonic deformation behavior of ferrite-martensite dual phase steels with martensite volume of 13-43% have been analyzed in the current investigation using micromechanics based finite element simulation on representative volume elements. The effects of martensite volume fraction on the strain partitioning behavior between soft ferrite matrix and hard martensite islands in dual phase steels during tensile deformation have been investigated. As a consequence of strain incompatibility between hard martensite and soft ferrite phases, inhomogeneous deformation and finally deformation localization occur during tensile deformation. Restricted local deformation in ferrite phase caused by the adjacent martensite islands triggers the local stress triaxiality development. As the martensite volume fraction increases, the local deformation restrictions in ferrite phase also increases and which results in higher stress triaxiality development. Similarly the strain partitioning behavior between ferrite matrix and martensite island is also influenced by the volume fraction of martensite. The strain partitioning coefficient increases with increasing martensite volume fraction.     

Mechanism of homogenization of the martensite state of crystals with a shape memory effect

The mechanism of homogenization of the martensite state of crystals with a shape memory effect under mechanical stresses applied to a crystal is theoretically analyzed in the framework of the thermodynamic approach and the theory of smeared martensite transitions. The homogenization of the martensite state of the crystal is considered for two variants of martensite that differ in all parameters (the temperature and the heat of transformation, spontaneous strains, etc.) and for many variants of martensite that differ from one another in the orientation of the habit planes.     

Orientation relationship and the mechanism of martensite transformation in medium-carbon steel with batch martensite

Exact orientation relationship for martensite transformation in medium-carbon 37KhN3A steel with lath martensite are determined. The mechanism of deformation during the transformation of martensite in steel is described.     

CEMS of Sb+ implanted stainless steels

Martensitic transformations have been analysed in a series of antimony implanted austenitic stainless steels using CEMS. The implanted samples contain about 70 vols martensite, which is considerably more than can be formed conventionally by plastic deformation or cooling below the martensite start temperature. CEM spectra from implantation induced martensite and from martensite formed in conventional processes are virtually identical. In both cases the hyperfine field is ≈ 25T.     

Identification of epsilon martensite in a Fe-based shape memory alloy by means of EBSD

Ferrous shape memory alloys (SMAs) are often thought to become a new, important group of SMAs. The shape memory effect in these alloys is based on the reversible, stress-induced martensitic transformation of austenite to epsilon martensite. The identification and quantification of epsilon martensite is crucial when evaluating the shape memory behaviour of this material. Previous work displayed that promising results were obtained when studying the evolution of the amount of epsilon martensite after different processing steps with Electron BackScatter Diffraction (EBSD). The present work will discuss in detail, on the one hand, the challenges and opportunities arising during the identification of epsilon martensite by means of EBSD and, on the other hand, the possible interpretations that might be given to these findings. It will be illustrated that although the specific nature of the austenite to epsilon martensite transformation can still cause some points of discussion, EBSD has a high potential for identifying epsilon martensite.     

13C NMR study of carbon distribution in Fe−C,Fe−Ni−C and Fe−Mn−C martensite

The distribution of carbon atoms in martensite have been studied by NMR. It was established that in virgin martensite metalloid was located only in octahedral intersticies. The analysis of hyperfine fields on¹³C nuclei for various types of martensite local arrangement was carried out. Comparison of analysis results with experimental data let to determine the possible models of carbon clustering in martensite at steel aging.     

Carbon distribution in the martensite structure of structural steel

The martensite structure of a hardened pseudosingle crystal of grade 37KhN3A medium-carbon structural steel (0.37 wt % C, 1.50 Cr, 3.0 Ni, 0.33 Mn) had the form of coarse packets with dimensions of to 1 cm in the cross section. Every packet was composed of six-orientation martensite crystals arising on one common austenite plane of type {111}. The position of three texture maximums was determined using an X-ray diffractometer for every orientation. In addition, the position of four maximums of retained austenite was found. The periods of martensite lattices and retained austenite as well as the carbon concentration in martensite lattices and near the boundaries are determined.     

Aspects of thermal martensite in a FeNiMnCo alloy

Thermal martensite characteristics in Fe–29%Ni–2%Mn–2%Co alloy were investigated with scanning electron microscopy (SEM) and Mössbauer spectroscopy characterization techniques. SEM observations obviously revealed the lath martensite morphology in the prior austenite phase of examined alloy. As well, the martensitic transformation kinetics was found to be as athermal type. On the other hand, Mössbauer spectroscopy offered the paramagnetic austenite phase and ferromagnetic martensite phase with their volume fractions. Also, the internal magnetic field of the martensite was measured as 32.9 T from the Mössbauer spectrometer.     

Crystallographic specific features of the martensitic structure of Ni<Subscript>47</Subscript>Mn<Subscript>42</Subscript>In<Subscript>11</Subscript> alloy

The structure of Ni₄₇Mn₄₂In₁₁ alloy after annealing has been investigated. It is shown that the martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy upon cooling is accompanied by the formation of 14M modulated martensite. Crystallographic analysis of the martensite structure has been performed. The orientation relationships between the high-temperature austenitic phase and martensite and habit planes of the martensite plates have been determined.     

Violation of the sequence of martensite crystals formation on cooling and their shrinking on heating during B2 ↔ B19′ martensitic transformation in Ti40.7Hf9.5Ni44.8Cu5 shape-memory alloy

An in situ transmission electron microscopy study of the B2 ? B19′ martensitic transformation in Ti_40.7Hf_9.5Ni_44.8Cu₅ shape memory alloy was carried out. It was observed that the sequence of the martensite crystals shrinking on heating differed from the sequence of the martensite crystal appearance on previous cooling. This was shown that strain nanodomain formation on cooling prior to the forward martensitic transformation resulted in accumulation of the elastic energy. This led to the dependences of the elastic energy stored on cooling or released on heating on the volume fraction of the martensite phase became different. In this case, at the same volume fraction of the martensite phase, the configuration of the martensite crystals on cooling and heating was different and it was a reason for a violation of the sequence of the martensite crystal formation on cooling and its shrinking on heating.     

Characterization of martensite in Fe-25%Ni-15%Co-5%Mo alloy

Kinetic, morphological, crystallographical, magnetic and thermal characteristics of thermally induced martensite in Fe-25%Ni-15%Co-5%Mo alloy have been investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), Mössbauer spectrometer, and differential scanning calorimeter (DSC). Kinetics of the transformation was found to be athermal. Also only lenticular martensite morphology was observed during microscope observations. In addition, martensite start temperature (M_s) was determined as −63 °C from differential scanning calorimeter. On the other hand, Mössbauer spectra revealed a paramagnetic character for the austenite phase and a ferromagnetic character for thermally induced martensite phase.     

Surface influence on the behavior of stabilized zirconia nanoparticles under pressure

The surface state of partially stabilized zirconia with nanoparticles of sizes 10–30 nm after temperature and pressure treatments was investigated by Fourier transform infrared spectroscopy, X-ray diffraction and small-angle X-ray scattering. It is shown that the synthesized nanoparticles are surface fractals and the fractal dimensions non-monotonically change with nanoparticles size change. The martensite tetragonal-to-monoclinic transition of the partially stabilized zirconia nanoparticles under hydrostatic pressure (100–1000 MPa) was investigated. It was shown that the character of the martensite transition in nanoparticles’ system depends on the pressure values. Three ranges of pressures were revealed. It was shown that the stability of martensite tetragonal–monoclinic transition decreases with the increase in size of the nanoparticles only for the pressures range of 300–500 MPa. Below 200 MPa, the character of the martensite transition is extreme and has a maximum for the particle size of 17 nm. In pressure range of 600–1000 MPa, the degree of martensite transition is dependent on the fractal dimension of the surface.     

Martensitic transformation in heterogeneous austenite

The dependence of the martensite structure on the volume fraction of coherent inclusions inherited from aged austenite has been studied. An explanation for the considerable martensite lattice tetragonality in the case of thin martensite twins in comparison with their inclusion diameter is suggested. A reason for surface relief height decreasing for alloys with narrow temperature hysteresis of transformation has been discovered.     

马氏体相变过程中低频内耗的研究

本文测出了金镉(Au-Cd)合金在正反马氏体相变过程的低频内耗峰,内耗极大值与变温速率有线性关系,但比Fe-Mn等非热弹性马氏体相变内耗的速率依赖要小得多,稳定内耗峰(变温速率为零)在每一温度的内耗值与频率无关,是静滞型损耗。内耗峰高与马氏体晶粒尺寸有关。等温转变过程也出现一个内耗-时间峰。根据以上诸实验事实,我们认为,低频马氏体相变内耗是由那些在振动应力作用下可以运动的相界面所引起的。 关键词：     

Crystallographic patterns of the shape memory effect in non-ordered solid solutions

A method is proposed to estimate the possibility of achieving shape memory effects in martensite alloys with disordered lattices. The analysis of orientational relationships between the lattices of austenite and martensite allows one to detect those which are able to form self-accommodation complexes, an important part of the memory effect mechanism. This method has been applied to the Ti₄₈Zr₄₈Nb₄ alloy in which two martensite phases are formed: hexagonal α′ and orthorhombic α″ martensites.     

Stability and stabilization of 2H martensite in Cu–Zn–Al single crystals

The stabilization of the 2H martensitic phase in Cu–Zn–Al single crystals with an electron concentration e/a?=?1.53 was investigated. This orthorhombic 2H martensite was first induced from the cubic β phase by the direct β?→?2H or the indirect β?→?18R?→?2H transformations. On loading the 2H martensite, a transition without hysteresis is observed at a stress which was denoted σ_T1. It was found that this stress is associated with a change in the behaviour of the 2H martensite. A high stabilization of the 2H martensite, around 300?K, is only obtained if an ageing is performed at a stress above σ_T1. Additionally, the stresses of the transformation to another martensitic phase, called 18R₂, were found to be constant when the value of σ_T1 is below the retransformation stress. The 2H martensite and its behaviour on ageing were studied by dilatometry, calorimetry, mechanical testing, optical microscopy and transmission electron microscopy (TEM). Models accounting for the stabilization of the 2H martensite on ageing are proposed.     

Evolution of the phase composition and defect substructure of rail steel subjected to high-intensity electron-beam treatment

The morphology, structure-phase states, and defect substructure of annealed rail steel subjected to electron-beam treatment in the surface-layer melting mode are studied by scanning and transmission electron microscopy methods. The formation of the lath martensite structure, as well as cellular and dendritelike structures, containing nanoscale martensite crystals, is revealed.     

Deformation-induced martensite and nanotwins by cryogenic laser shock peening of AISI 304 stainless steel and the effects on mechanical properties

Laser shock peening (LSP) of stainless steel 304 was carried out at room and cryogenic temperature (liquid nitrogen temperature). It was found that the deformation-induced martensite was generated by LSP only when the laser-generated plasma pressure is sufficiently high. Compared to room temperature laser shock peening (RT-LSP), cryogenic laser shock peening (CLSP) generates a higher volume fraction of martensite at the same laser intensity. This is due to the increase in the density of potential embryos (deformation bands) for martensite nucleation by deformation at cryogenic temperature. In addition, CLSP generates a high density of deformation twins and stacking faults. After CLSP, an innovative microstructure, characterised by networks of deformation twins, stacking faults and composite structure (martensite and austenite phases), contributes to material strength and microstructure stability improvement. The combined effect of higher surface hardness and a more stabilised microstructure results in greater fatigue performance improvement of the CLSP samples compared to that of the RT-LSP samples.     

Updating a software package for the simulation of diffraction patterns and the computation of the parameters of the twinning and self-accommodation of martensite crystals

An updated software package for the simulation of point diffraction pictures and the computation of several crystallographic characteristics of martensite crystals in alloys with the shape-memory effect is presented. Optimization was carried out for the procedure of the analysis of the orientation relationships between the lattices of austenite and martensite from the viewpoint of the possibility of the formation of self-accommodation complexes.     

Crystallographic features of the structure of a martensite packet of the NiMn intermetallic compound

Optical microscopy, scanning electron microscopy, and X-ray diffraction are used to show that a pseudosingle crystal forms upon cooling of an alloy Ni₄₉Mn₅₁ single crystal below the temperature of the β→θ (bcc → fct) transformation. At room temperature, this pseudosingle crystal has the structure of tetragonal L1₀ martensite with parameters a = 0.3732 nm and c = 0.3537 nm and a tetragonality c/a = 0.94775. The temperatures of the forward and reverse B2 → L1₀ transformations are determined. The crystallographic features of martensite packet formation are analyzed. As shown by EBSD, neighboring martensite packets always have three kinds of tetragonal martensite plates, which are in a twin position and have different tetragonality axis directions. Repeated heating and quenching of the pseudosingle crystal result in recrystallization with the formation of coarse grains. The packet structure of the tetragonal martensite is retained in this case, and the sizes of the packets formed within a grain decrease by a factor of 2–3 as compared to the initial pseudosingle crystal.