Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10~(-4)s~(-1)to 1 s~(-1), the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions(n_2and n_1) and the transition strain(εL) decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.     

Effects of cold rolling deformation on microstructure,hardness, and creep behavior of high nitrogen austenitic stainless steel

Effects of cold rolling deformation on the microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel （HNASS） are investigated. Microstructure characterization shows that 70% cold rolling deformation results in significant refinement of the microstructure of this steel, with its average twin thickness reducing from 6.4 μm to 14 nm. Nanoindentation tests at different strain rates demonstrate that the hardness of the steel with nano-scale twins （nt-HNASS） is about 2 times as high as that of steel with micro-scale twins （mt-HNASS）. The hardness of nt-HNASS exhibits a pronounced strain rate dependence with a strain rate sensitivity （m value） of 0.0319, which is far higher than that of mt-HNASS （m = 0.0029）. nt-HNASS shows more significant load plateaus and a higher creep rate than mt-HNASS. Analysis reveals that higher hardness and larger m value of nt-HNASS arise from stronger strain hardening role, which is caused by the higher storage rate of dislocations and the interactions between dislocations and high density twins. The more significant load plateaus and higher creep rates of nt-HNASS are due to the rapid relaxation of the dislocation structures generated during loading.     

Grain refinement and strengthening of austenitic stainless steels during large strain cold rolling

The microstructure/texture evolution and strengthening of 316?L-type and 304?L-type austenitic stainless steels during cold rolling were studied. The cold rolling was accompanied by the deformation twinning and micro-shear banding followed by the strain-induced martensitic transformation, leading to nanocrystalline microstructures consisting of flattened austenite and martensite grains. The fraction of ultrafine grains can be expressed by a modified Johnson-Mehl-Avrami-Kolmogorov equation, while inverse exponential function holds as a first approximation between the mean grain size (austenite or martensite) and the total strain. The deformation austenite was characterised by the texture components of Brass, {011}<211>, Goss, {011}<100>, and S, {123}<634>, whereas the deformation martensite exhibited a strong {223}<110> texture component along with remarkable γ-fibre, <111>∥ND, with a maximum at {111}<211>. The grain refinement during cold rolling led to substantial strengthening, which could be expressed by a summation of the austenite and martensite strengthening contributions.     

Development of dislocation structure in Kh17N14M3B austenitic steel single crystals during rolling

The evolution of dislocation structure in single crystals of Kh17N14M3B austenitic steel with single and multiple orientations on rolling was studied. A quantitative analysis of the substructures at the stage of developed plastic strain was performed. The development of disoriented substructures in different stressed states of the crystal is discussed. The relation between the structure and texture at the stage of disoriented substructures is analyzed.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 6, pp. 94–101, June, 1990.     

Effect of electron irradiation on the structure and mechanical properties of 36% Ni, 12% Cr, 3% Ti, 1% Al age-hardened austenitic steel subjected to various modes of thermomechanical treatment

The effect of electron irradiation on the structure and mechanical properties of 36% Ni, 12% Cr, 3% Ti, 1% Al age-hardened austenitic steel after different modes of thermomechanical treatment, including quenching, rolling with a 99% degree of compression, and aging, is studied experimentally in the constant current mode with a fluence of 10¹⁹ freq cm^?2. Regularities of the changes in the structural phase composition and mechanical properties of the investigated alloy are established as a result of electron irradiation. Scientifically grounded recommendations are given for selecting modes of thermomechanical treatment, supplemented by irradiation and ensuring the optimum combination of strength and ductility in 36% Ni, 12% Cr, 3% Ti, 1% Al age-hardened austenitic steel.     

Annealing texture of a cold-rolled Fe–Mn–Al–Si–C alloy

The study of recrystallization texture of a cold deformed Fe–Mn–Al–Si–C alloy, with about 30% Mn, has been discussed in this paper. The alloy is fully austenitic at room temperature, and therefore, principal FCC rolling textures were developed in this material at different stages of cold rolling. The present study was undertaken to observe the transformation of FCC rolling texture during recrystallization of a heavily cold deformed specimen. It was observed that isothermal annealing at 750 °C led to a weak recrystallisation texture, which was quite similar to the deformation texture developed at the early stage of cold rolling. During recovery stage, a strong Bs/Goss-type texture was developed, which was identified as a new observation in this work.     

Influence of thermomechanical processing on shear bands formation and magnetic properties of a 3% Si non-oriented electrical steel

The effect of thermomechanical processing on the formation of shear bands and on the magnetic properties of a 3.0 wt% silicon non-oriented steel was investigated by hot rolling samples with different thicknesses at different temperatures, in order to obtain a variation in hot band grain size and cold strain. All the samples were processed in a single-stage cold rolling and finally annealed at 1020 °C. It was found that the increase of the hot band grain size decreases the γ fiber volume fraction and increases the η fiber volume fraction after the final annealing. The increase of the cold strain strongly contributed to this result. A good combination of intense generation of shear bands, and proper crystallographic texture, due to higher nucleation of grains with favorable orientations to magnetization in these bands, can be obtained for the samples hot rolled at 1000 and 1120 °C and submitted to cold strain of 64.3% and 72.2% respectively. However the best combination of B₅₀, W_15/60 and μ_r can be obtained by hot rolling the samples at 1000 °C to the thickness of 1.4 mm, corresponding to 64.3% of cold strain.     

Formation mechanism of nanostructures in austenitic stainless steel during equal channel angular pressing

An ultra-low carbon austenitic stainless steel was successfully pressed from one to eight passes by equal channel angular pressing (ECAP) at room temperature. By using X-ray diffraction, optical microscopy and transmission electron microscopy, the microstructural evolution during ECAP was investigated to reveal the formation mechanism of strain-induced nanostructures. The refinement mechanism involved the formation of shear bands and deformation twins, followed by the fragmentation of twin lamellae, as well as successive martensite transformation from parent austenitic grains with sizes ranging from microns to nanometres through the processes γ(fcc)?→?ε(hcp)?→?α′(bcc). After pressing for eight passes, two types of nanocrystalline grains were achieved: (a) nanocrystalline austenite with a mean grain size of ～31?nm and (b) strain-induced nanocrystalline α′-martensite with a size of ～74?nm. The formation mechanisms are discussed in terms of microstructural subdivision via deformation twinning and martensite transformation.     

Small-angle neutron scattering study on the cold rolled steel sheets

The effect of cold rolling on the small-angle neutron scattering (SANS) pattern was investigated for low-carbon steels. Several cold rolled steel samples with different reduction ratios and annealed samples after cold rolling were respectively measured by SANS. The cold rolled samples presented anisotropic two-dimensional (2D) SANS patterns. From the 2D SANS patterns two kinds of 1D pattern were calculated: one was for the Q⊥RD (rolling direction), the other for the Q//RD. The scatterer sizes calculated from the 1D patterns by using a model fitting increased with the reduction ratio, for the Q⊥RD section only. The annealed sample presented an isotropic SANS pattern. It can be concluded that the dislocations produced during the cold rolling process accumulated around the precipitates and then caused anisotropic 2D SANS patterns.     

多层奥氏体钢中超声相控阵辐射声场分析

针对一维线性超声相控阵透过楔块,在多层不同晶轴取向的奥氏体钢中的声场辐射问题,结合高斯声束等效点源模型以及基于时间最小原理的射线追踪法,给出了各层介质中透射声场的计算方法。将奥氏体钢近似为横向各向同性介质,计算了相控阵透过楔块,在晶轴取向为0°的奥氏体钢中的无延时纵波声场,计算结果与COMSOL仿真结果相吻合,从而验证了所用方法的正确性。通过加入不同的延迟法则,仿真计算了三层含有不同晶轴取向(0°,30°,100°)的奥氏体钢中的纵波声场,实现了相控阵声场的偏转与聚焦,分析了偏转声场与聚焦声场的传播特性。仿真结果表明,不同的晶轴取向将导致不同的声束偏转以及聚焦效果。通过延迟激励各阵元,虽然可以控制声束偏转或聚焦到预定位置,但是晶轴取向仍会对声束宽度以及幅值产生一定的影响。      

A model of grain refinement and strengthening of Al alloys due to cold severe plastic deformation

This paper presents a model which quantitatively predicts grain refinement and strength/hardness of Al alloys after very high levels of cold deformation through processes including cold rolling, equal channel angular pressing (ECAP), multiple forging (MF), accumulative roll bonding (ARB) and embossing. The model deals with materials in which plastic deformation is exclusively due to dislocation movement within grains, which is in good approximation the case for many metallic alloys at low temperature, for instance aluminium alloys. In the early stages of deformation, the generated dislocations are stored in grains and contribute to overall strength. With increase in strain, excess dislocations form and/or move to new cell walls/grain boundaries and grains are refined. We examine this model using both our own data as well as the data in the literature. It is shown that grain size and strength/hardness are predicted to a good accuracy.     

Characterizing the ordering of thermomechanically processed high-Si steel by Mössbauer effect techniques

The processing of high-Si steels remains challenging. The development of ordered phases is the reason for the deteriorated workability which makes not feasible its production. The influence of the hot and the cold work on the order degree in high-Si steel is investigated by TMS (Transmission Mössbauer spectroscopy) and ILEEMS (Integrated low-energy electron MS). The Si-addition favors the creation of an order gradient in the hot rolled sheets; this accounts as an extra strengthening mechanism. In order to have a successful cold rolling the degree of order must be as low as possible; this is difficult to obtain when the Si-content is too high.     

Strain-induced martensite to austenite reverse transformation in an ultrafine-grained Fe–Ni–Mn martensitic steel

Research was conducted to evaluate the effect of heavy cold rolling on microstructural evolution in an Fe–10Ni–7Mn (wt.%) martensitic steel. The chemical driving force for the strain-induced martensite to austenite reverse transformation was calculated using thermodynamic principles and a model was developed for estimating the effect of applied stress on the driving force of the martensite to austenite reverse transformation through heavy cold rolling. These calculations show that, in order to make a reverse transformation feasible, the applied stress on the material should supply the total driving force, both chemical and non-chemical, for the transformation. It is demonstrated that after 60% cold rolling the required driving force for the reverse transformation may be provided. Experimental results, including cold rolling and transmission electron microscopy images, are utilized to verify the thermodynamic calculations.     

Effect of thermomechanical processing on microstructural evolution and deformation behaviour of polycrystalline magnesium under quasi-static and high strain rate conditions

Abstract

The effect of thermomechanical processing on microstructure evolution and room temperature flow behaviour of polycrystalline magnesium in compression at strain rates of ~10^?2 and ~10³ s^?1 was investigated. Different initial microstructures were produced by optimising rolling and annealing cycles. Prior to annealing for 1 h at 350 °C, Mg samples were processed by two different treatments such as (i) hot rolling at 350 °C and (ii) hot rolling at 350 °C plus cold rolling at room temperature. Introduction of cold working step led to an increased fraction of hard oriented grains with a marginal grain size difference in post-annealed samples. A profound effect of thermomechanical processing on strain hardening rate as well as rate-sensitive flow behaviour of Mg was observed. The influence of prior processing history and strain rate on flow behaviour of Mg was clearly reflected in terms of texture strengthening/weakening phenomena and formation of microstructural deformation bands.     

Development Kinetics of the Plastic Wave Front at the Metal Interface

Russian Physics Journal - The paper considers an inhomogeneous development of plastic strain at the Chernov–Lüders band front in the bimetal consisting of carbon and austenitic steel...     

The influence of elastic deformation on the properties of the magnetoacoustic emission (MAE) signal for GO electrical steel

Magnetic properties of the grain oriented (GO) electrical steels are strongly affected by the stresses, both external and internal. The change is important even for the deformation resulting in stress level much lower than their yield limits. In this paper we present the results of investigation of the influence of compression and tension on the magnetoacoustic emission (MAE) signal properties. The experiment was performed with the help of bending machine in which the samples (0.3 mm thick, M140-30 S GO electrical steel) glued to the non-magnetic (austenitic steel) 8 mm thick bars were bent. The samples cut out in two directions (parallel and perpendicular to the rolling direction) were investigated. The elongation was measured directly with the help of tensometric bridge. Various parameters of the MAE signal, such as e.g. signal intensity and MAE peaks separation, have been examined.     

Quantitative evaluation of ultrasonic C-scan image in acoustically homogeneous and layered anisotropic materials using three dimensional ray tracing method

Quantitative evaluation of ultrasonic C-scan images in homogeneous and layered anisotropic austenitic materials is of general importance for understanding the influence of anisotropy on wave fields during ultrasonic non-destructive testing and evaluation of these materials. In this contribution, a three dimensional ray tracing method is presented for evaluating ultrasonic C-scan images quantitatively in general homogeneous and layered anisotropic austenitic materials. The directivity of the ultrasonic ray source in general homogeneous columnar grained anisotropic austenitic steel material (including layback orientation) is obtained in three dimensions based on Lamb’s reciprocity theorem. As a prerequisite for ray tracing model, the problem of ultrasonic ray energy reflection and transmission coefficients at an interface between (a) isotropic base material and anisotropic austenitic weld material (including layback orientation), (b) two adjacent anisotropic weld metals and (c) anisotropic weld metal and isotropic base material is solved in three dimensions. The influence of columnar grain orientation and layback orientation on ultrasonic C-scan image is quantitatively analyzed in the context of ultrasonic testing of homogeneous and layered austenitic steel materials. The presented quantitative results provide valuable information during ultrasonic characterization of homogeneous and layered anisotropic austenitic steel materials.     

Effect of annealing prior to cold rolling on magnetic and mechanical properties of low carbon non-oriented electrical steels

The effects of annealing prior to cold rolling on the microstructure, magnetic and mechanical properties of low-C grain non-oriented (GNO) electrical steels have been investigated. The grain structure of hot-rolled electrical steel strips is modified by annealing at temperatures between 700 and 1050 °C. Annealing at temperatures less than the ferrite to austenite+ferrite transformation temperature on heating (Ac₁) causes a marginal effect on the grain size. However, annealing in the intercritical region at temperatures between Ac₁ and Ac₃ (the ferrite+austenite to austenite transformation temperature on heating) causes rapid decarburization and development of large columnar ferrite grains free of carbide particles. This microstructure leads, after cold rolling and a fast annealing treatment, to carbide free, large ferrite grain microstructures with magnetic and mechanical properties superior to those observed typically in the same steel in the industrially fully processed condition. These results are attributed to the increment in grain size and to the {1 0 0} fiber texture developed during the final annealing at temperatures up to 850 °C. Annealing at higher temperatures, T>Ac₃, results in a strong {1 1 1} fiber texture and an increase of the quantity of second phase particles present in the microstructure, which lead to a negative effect on the final properties. The results suggest that annealing prior to cold rolling offers an attractive alternative processing route for the manufacture of fully processed low C GNO electrical steels strips.     

Influence of cold rolling on the anisotropy of the shear modulus and the poisson coefficient of polycrystalline copper and silicon steel

We consider a method for calculating the anisotropy of the shear modulus and the Poisson coefficient in the rolling plane for textured polycrystalline materials with a cubic lattice, which makes use of the integrated texture characteristics for averaging over the single-crystal properties, which are a certain combination of direction cosines in the sample coordinates, averaged with respect to orientation. The integrated texture characteristics are determined from two experimentally opposite polar figures of the plates. We study the influence of the amount of deformation during cold rolling on the anisotropy of the plate properties listed above for copper and silicon steel. The accuracy in the calculations is better than 5%. The results are compared with data from other authors. K. D. Ushinskii Institute, Odessa. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 25–29, February, 1993.     

Manufacturing near dense metal parts via indirect selective laser sintering combined with isostatic pressing

To fabricate metal parts via indirect selective laser sintering (SLS), isostatic pressing technology, including hot isostatic pressing (HIP) and cold isostatic pressing (CIP), are exploited to reform SLS green parts and make them near dense. The processes of SLS/HIP and SLS/CIP/HIP technologies are investigated respectively and the densification of AISI304 stainless steel specimens is mainly discussed. It is indicated that green parts made by indirect SLS can be pressed into near dense parts with the relative densities of 67.3% and more than 80% in SLS/HIP and SLS/CIP/HIP routes, respectively, and their densities rise if much higher CIP pressure is employed. Compared with SLS/HIP, SLS/CIP/HIP technology is regarded as a better method to manufactured dense parts, and it enlarges the application domain of indirect SLS simultaneously. PACS 81.20.Ev; 81.20.Hy; 81.40.Lm; 81.40.Vw