Papers by Keyword: Softening

Abstract: Three different heat input combinations for the medium carbon alloy steels 5CrMoV are compared in terms of the heat affected zone of microstructures, hardness, and tensile properties. The microstructures in the heat affected zone are predominately ferrite and bainite, with grain size variation in different sub-zones and different heat input. Analyses of the micro-hardness profiles indicated that softening phenomenon occurs in the entire heat affected zone, and high heat input resulted in the greatest decrease in hardness. The results of the tensile tests reveal tensile properties of the heat affected zone deteriorate with the increase of heat input, and the region at temperatures near Ac1 is the weakest part of heat affected zone.

Abstract: A semi-empirical approach to the modeling of the microstructural evolution during the hot rolling of austenite including grain growth, hardening and softening has been discussed in the frame of a generalized energetic expression for related structural processes. The current concept suggests the activation energy of iron self-diffusion in austenite and its dependence upon the chemical composition of the steel for prediction of the particular phenomena. Additionally, the precipitation sequences, the size distribution, Oswald ripening and interaction with softening are also included in the model of the microstructural evolution. The simulation results are reliable to the structural evolution of the low carbon steels microalloyed with Nb and Ti during hot rolling.

Abstract: The paper describes the structure, properties and heat stability of white cast irons containing 2.5 – 3.0 %C, 14 and 20 %Cr, 3 %V after the secondary hardness treatment (quenching from 1150 °C and double tempering at 560 °C). It is shown that after the secondary hardness treatment M₂₃C₆ carbides appear along with the M₇C₃ phase. Heat stability of the alloys is estimated according to GOST 19265-73 standard. The effect of the temperature and duration of holding at 520–620 °C on structural changes and softening of secondary hardness treated cast irons is considered in comparison with high-speed steel and cast irons of the same composition quenched for the maximum hardness (from 1050 °C). The processes occurring at higher temperatures and long holdings that are responsible for softening of secondary hardness treated cast irons are studied. It is shown that the alloys under consideration after the secondary hardness treatment achieve the hardness of HRC 60 and more, and are able of pertaining it when heated up to 540 °C for 20 hours. This allows using these alloys as wear-resistant materials in the said temperature range.

Abstract: Reinforced concrete (RC) jacketing is becoming increasingly common among the different retrofit techniques for poor RC members, due to its economical and practical advantages. Experimental investigations in the literature have shown that the actual axial capacity of RC jacketed members can be substantially lower than that analytically evaluated by adapting the most common theoretical models for confined concrete. This fact can be explained by taking into account the presence of tensile stresses developing in the concrete, due to a mutual interaction between the inner core and the external jacket. This phenomenon is relevant especially in members where the concrete properties of the jacket are different with respect to those of the core, causing the premature failure of the external layer. This paper presents a simplified approach able to evaluate these effects. Circular RC jacketed sections are studied and a model is presented to predict the concrete softening effect. The section is modeled by joining circular hollow layers and circumferential and radial stresses are firstly calculated under the assumption of linear elastic behaviour and plane strain state. The model is extended in the non-linear range by adopting a secant constitutive law. Finally, comparisons are made with experimental data available in the literature, showing good agreement.

Abstract: Strain localization in low carbon steel DC04 undergoing uniaxial tension is investigated by Electronic Speckle Pattern Interferometry (ESPI). The necking in the sheet specimens occurs by forming two narrow crossing bands. A model of strain rate distribution is used to extract quantitative information about the localization bands, such as bandwidths, bands orientations and their maximum strain rates. Thus, their evolutions are followed from the diffuse necking up to the rupture. The influence of specimen geometry on localization phenomenon is studied.

Abstract: The law and mechanism of hydrogen induced softening in Ti6Al4V alloy in the temperature range 400 °C to 1010 °C are researched by lots of isothermal hot compression experiment in this paper. The relationship between σ_h (the true stress when the test is compressed to half of its original height) and C_H (hydrogen content) is investigated to describe the law. The results show that, Between 400 °C and 450 °C, the plasticity increases at first, and then decreases and the strength is almost changeless with the C_H rising. Between 480 °C and 950 °C, the strength decreases at first, and then increases with the C_H rising. In α+β phase region, the strength decreases with the C_H rising. In β phase region, the strength increases with the C_H rising. Hydrogenation induced α phase high temperature softening and hydrogenation promoting α→β phase transition are the main reasons for hydrogen induced titanium alloy softening. Hydrogenation induced β phase solution strengthening is the reason for hydrogen induced titanium alloy strengthening. And the relationship between furnace temperature and vacuum is investigated during dehydrogenation heat treatment.

Abstract: The main objective of the present work is to assess the influence of several parameters relevant for Finite Element Analysis (FEA) in modelling Friction Stir Welding (FSW) processes on AA2024-T3 plates. Several tests were performed including variations on the type of shell elements, number of integration points across thickness direction and mesh refinement levels, aiming for good accuracy and low computational cost. On the one hand, several setups of the mechanical boundary conditions, modelling the clamping systems, were also tested, leading to the conclusion that the results, in terms of longitudinal residual stresses, are significantly affected by this factor. On the other hand, variations on the heat input distribution showed a reduced effect, or almost null, on the final results.

Abstract: The influences of 1-MCP on AC tomato fruit softening were investigated. Ethylene production, flesh firmness, protopectin content, soluble pectin content and polygalacturonase (PG) activity were used to evaluate the quality of tomato fruit. It was shown that 1.0 and 1.5 μL/L 1-MCP treatment significantly decreased the levels of ethylene production, and inhibited flesh firmness and protopectin content decline and polygalacturonase activity increase. At last, it was concluded 1.0 μL/L 1-MCP treatment on AC tomato fruit was the best determining economy.

Abstract: The paper presents a model that splits the material cross section into a number of parallel fractions each of them having a different elastic-perfectly brittle characteristic. The idea is that the summation of all parallel fractions provides an approximation of the overall continuum softening curve. Softening is interpreted as a gradual reduction of the cross-sectional area, which it actually is from a physical point of view. Disorder and heterogeneity are introduced by assigning the fractions i different values of Young’s modulus E_i , strength f_i and area A_i such that the overall fracture energy is consumed properly. The model blends well with a scaled sequentially linear solution procedure at global level tracing structural failure via successive snapping/cracking of critical fractions. Examples are included for tension, compression, combined tension-shear and combined tension-compression. The tension-shear case shows the ability of the model to capture a gradually shifting crack orientation. Preliminary structural examples are included in this paper and further results will be presented at the conference. These relate to push-over analysis of Groningen masonry building stock subjected to man-induced earthquakes from gas depletion, a currently serious problem in The Netherlands. The results show an increased robustness and stability of the post-peak response as compared to conventional incremental-iterative procedures.

Abstract: Zero-point spin fluctuations are shown to strongly influence the ground state of ferromagnetic metals and to impose limitations for the fully spin polarized state assumed in half-metallic ferromagnets, which may influence their applications in spintronics. This phenomenon leads to the low-frequency Stoner excitations and cause strong damping and softening of magnons in magnetoresistive manganites observed experimentally.