Papers by Keyword: TRIP Steel

Abstract: Metal-matrix composite materials, based on a metastable austenitic stainless steel reinforced with a magnesia partially stabilised zirconia have been prepared by a ceramics-derived extrusion technology. Using this powder metallurgical method enables the shaping of lightweight cellular structures as well as bulk specimens with a variety of steel/ceramic ratios at room temperature. However, the extrusion of composite structures is limited by the uniform cross section throughout its entire length. Joining of these metal-matrix composite preforms after sintering by conventional welding techniques is a challenging task. The presence of ceramic fractions may lead to several complications and the subsequent heat exposure during joining may initiate phase transformations in both metastable components resulting in a deterioration of the mechanical properties of the composite material. An adapted ceramics-derived joining technology allows the combination of varying TRIP-steel/zirconia composite materials. The main features are the machining and joining of the parts in their dry green state at room temperature before their thermal treatment. Thus, the material’s consolidation and the formation of the joint take place simultaneously. The ability of joining different parts offers the possibility to create structures for complex applications and testing conditions. The key to advanced properties of the joining zone are the base materials, the surface treatment of the parts, and the paste used for joining. The joining process of different base materials, the mechanical properties, and the microstructure of sinter-joint samples are presented.

Abstract: The current contribution deals with metal-matrix composites prepared by paper manufacturing technology. In contrast to conventional techniques, this technology is an energy-and cost-efficient process for the shaping of thin sheets using solid powder mixtures. Conventional and pre-ceramic as well as pre-metallic paper-manufacturing have in common that cellulose (pulp) fibres are loaded with inorganic fillers. The present study is focused on the paper web formation using a metastable austenitic steel powder (16-7-3 %Cr-%Mn-%Ni) and a magnesia partially stabilised zirconia powder as inorganic fillers. The paper web formation was investigated. During filtration of the aqueous fibre-filler suspension the steel particles were incorporated in-between the fibre network and steel clusters were formed. Thus, solid retentions of > 90 wt.% were achieved. Calendering had a positive influence on porosity, bulk density, and tensile strength of the green paper sheets. The development of an optimized debinding process is presented and the microstructural changes as well as phase formations during firing are discussed in response to the residual carbon content. The sintered composites attained ultimate tensile strengths of up to 177 N/ mm2 at a total porosity of 66 %. These metal-matrix composites are promising materials for the shaping of light-weight structures.

Abstract: Ceramic particle reinforced metal matrix composites (PRMMCs) combine the strength and brittleness of ceramics with the toughness of a metallic matrix. In order to use these materials in construction and operational design their fracture mechanical behavior must be evaluated. In this study, a 30 vol.-% Al₂O₃ reinforced austenitic TRIP steel processed by powder metallurgical technique was investigated using precracked miniature SENB-specimens in 3-point-bending. An elastic-plastic analysis by means of the J-integral method in combination with optical crack observation showed the materials ability of stable crack growth, i. e. R-curve behavior. In addition to the mechanical tests microstructural studies were performed, whereby particle debonding and fracture as well as martensitic phase transformation and crack bridging within the matrix were identified as fracture energy dissipating mechanisms.

Abstract: The effects of the stress state and temperature on the martensitic phase transformation behavior in TRIP 780 steel were investigated using multi-axial experimental techniques. Various mechanical experiments are performed to differentiate the stress state and temperature effects. For this purpose, five different stress states were considered; i.e., uniaxial tension, uniaxial compression, equibiaxial tension, plane strain tension and simple shear. A temperatures both 25 and 60 °C for each stress state condition except the simple shear test were investigated. In-situ magnetic measurements were performed to mesure the evolution of the martensite content throughout each experiment. Finally, a new martensitic transformation kinetics model for the TRIP 780 steel is proposed to take the effect of stress state and temperature into account.

Abstract: Austenitic FeMnCr steels have high strength, high toughness and formability because of the stress-and strain-induced γ→α and γ→ε martensitic phase transformations. These are the so-called TRIP (Transformation Induced Plasticity) and TWIP (Twining induced Plasticity) effects. TWIP steels deform by both glide of individual dislocations and mechanical twinning [1]. The type and mechanism of the austenite→martensite transformation depends on the composition, deformation rate and temperature. The ratio and quantity of the resulting phases determine the properties of the product. It is known that austenitic steels can transform into α and/or ε martensite phases during plastic deformation The characteristics of the martensitic transformations induced by uni-axial tensile tests between room temperature and 200°C in a FeMnCr steel with 2,26 w% Cr content were examined. Mechanical properties as, yield stress were determined from tensile tests. Metallographic examinations, quantitative and qualitative phase analysis by X-ray diffraction were carried out on the uniformly elongated part of the samples (cross, longitudinal sections).

Abstract: The presented paper is devoted to the study of hydrogen diffusion characteristics in the C-Mn-Si TRIP 800 steel. The steel was tested in three different states: in as-received state after hot and cold rolling and subsequent heat treatment; and furthermore after 5% and 10% tensile deformation. Hydrogen diffusion characteristics were studied by means of electrochemical permeation method. Two build up transients corresponding to lower and higher charging current densities as well as a decay transient were recorded during experiment. The lowest values of hydrogen diffusion coefficient (from 1 to 3.5.10^-7 cm².s^-1) were observed during the first build up transient; the value of 3.5.10^-7 cm².s^-1 corresponded to 10% tensile deformation. During the 2^nd build up transient corresponding to the higher charging current density, hydrogen diffusion coefficients increased markedly reflecting thus the fact that hydrogen trapping was less pronounced. For decay transients hydrogen diffusion coefficients were situated between values obtained for the 1^st and 2^nd build up transients. In all studied states, a rather high sub-surface hydrogen concentration was observed during the 1^st build up transient rising to 12.6 ppm of hydrogen in as-received state. The obtained results are explained taking into account steel microstructure and hydrogen trapping.

Abstract: For the numerical analysis of TRIP steel wire drawing process, the Drawing 2d programme based of finite element method, has been used. The process was run following two variants, with small and large partial drafts for two drawing speeds: 1.11; 0.23 m/s. The investigations carried out allowed a relationship between temperature of drawing wires and the amount of retained austenite for wire surface and for wire axis.

Abstract: The article deals with the comparison of thickness change of spherical cup made from TRIP steel RAK40/70 after hydraulic bulge test. The thickness has been measured by timing gauge and by apparatus Argus. Experimental material thickness has been 0.75 mm. From measured values of thickness of experimental material has been calculated the dependence stress-strain by models of several authors.

Abstract: The hot-rolling deformation resistances of a TRIP Steel were studied by using a Gleeble-3500 thermal simulator. The true stress-true strain curves of the TRIP steel is determined under different hot-rolling deformation conditions, and the effect of deformation temperature, strain rate and deformation amount on the deformation resistance was evaluated. Based on experimental results, the mathematic model for the calculation of the deformation resistance of the TRIP Steel has been set up by the regression analysis by means of the origin software. It is found that the simulated stress-strain curves have good curve-fitting performance.

Abstract: Transformation induced plasticity (TRIP) steels is a kind of low-alloying high strength steel with good combination of strength and plasticity. To investigate the material behavior of TRIP steel, the multiscale simulation method was used in this paper. Through the investigation we can see that, multiscale simulation model of TRIP steel can be setup by combining finite element and microscope technology together, and the simulation results agree with the experimental results greatly. Both for uniaxial tension and biaxial tension, the micro stress distribution was unevenly for the difference of material behavior of bainite, ferrite and retained austenite, which create local stress concentration, and for uniaxial tension and biaxial tension, the stress distribution of biaxial tension was relative average, for the boundary condition biaxial tension was a kind of relative even boundary condition, the stress on different direction was balance.