Influence of cold-rolling reduction on retained austenite texture in cold-rolled and intercritically annealed TRIP-assisted steel

The newly developed multiphase transformation-induced plasticity (TRIP) steels are of interest for industrial applications because of their excellent combination of high strength and ductility. Their performance can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite. The characteristics of the retained austenite are considered to be the main key to achieving the desired final properties. Against this background, the effects of retained austenite characteristics, such as volume fraction, carbon concentration, size and shape, on the behaviour of TRIP steels have been studied. The crystallographic orientation of the retained austenite was measured by electron backscattered diffraction (EBSD). The effect of initial cold-rolling reduction on the microtexture development of the retained austenite was studied on an aluminium-containing TRIP steel. The results show that, by increasing the cold-rolling reduction before the final austempering, the main components of the face-centred cubic phase, i.e. copper, brass and Goss, dominate the texture of the retained austenite. In contrast, the copper and Goss components of the retained austenite are absent in the texture of lightly deformed sheets. The features of the preferred orientation of the retained austenite are discussed and explained in terms of the annealing texture of the recrystallized ferrite and bainite

Modeling the magnetic properties of non-oriented electrical steels based on microstructural parameters

Magnetic properties of electrical steels such as magnetization behavior and electrical losses are mainly related to chemical composition, crystallographic orientation and microstructure. By now, several models have been proposed to empirically correlate magnetic properties and affecting parameters. A quantitative model based on physical understanding of the interaction between the magnetic field variables (e.g. domain structure) and local microstructural variables (e.g. grain orientation and misorientation, grain boundary plane inclination) is still missing. To obtain a better understanding of the interaction between grain boundaries and domain walls, the magnitude of free pole density at grain boundaries was taken into account. Experimental results from 3-dimentional EBSD experiments were employed to measure the grain boundary orientation for several samples with different chemical composition and grain size. The free pole density was calculated using the relative misorientation between adjacent grains, and was included in a model together with grain size, magnetocrystalline anisotropy energy and silicon equivalent. By comparison with the experimental results of the magnetic induction measured at low, medium and high magnetic fields, is shown that the magnetization behavior can be more accurately predicted when the above mentioned phenomena are taken into account

Mechanical and forming properties of AA6xxx sheet from room to warm temperatures

The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN AW-6061 has been investigated with a series of tensile tests. It is found that temperature has an effect on both the storage of dislocations and dynamic recovery. The results have been used to fit the dislocation based Nes work-hardening model. Simulations show that the model captures properly the dependence of yield stress and work-hardening rate with temperature and temper. The work-hardening model has been implemented into the Dieka FEM to simulate the warm deep drawing of cylindrical cups. Comparison of the simulated and experimental punch force and cup thickness reveals a good correspondence and validates the proposed modelling approach

Microstructural features controlling very high cycle fatigue of nitrided maraging steel

Maraging steels belong to the group of ultra-high strength materials and are often used in critical aerospace, automotive and tooling components. By applying a surface treatment such as nitriding, the fatigue and wear resistance can be improved. The microstructural features that influence the (very) high cycle fatigue response of nitrided maraging steels are studied in this work. Although the used steel has practically no inclusions, it was found that small surface imperfections, introduced during processing, may form potential fatigue initiation points. The samples are nitrided during aging in order to form nitrided layers with various thicknesses, microstructures and hardness profiles without formation of a continuous (compound) iron nitride layer. Data from microhardness tests, scanning electron microscopy, electron backscatter diffraction, x-ray diffraction and transmission electron microscopy were used to characterize the microstructure of the layers. Bending fatigue tests were employed to evaluate the fatigue response of the steel. It was found that the best fatigue behavior is obtained in samples with a thin diffusion zone with a narrow constant hardness region. In this zone, coherent disc-shaped nitride precipitates are detected with TEM

Surface energy controlled α-γ-α transformation texture and microstructure character study in ULC steels alloyed with Mn and Al

In this article, an ultralow-carbon steel grade alloyed with Mn and Al has been investigated during alpha-gamma-alpha transformation annealing in vacuum. Typical texture and microstructure has evolved as a monolayer of grains on the outer surface of transformation-annealed sheets. This monolayer consists of //ND and //ND fibre, which is very different from the bulk texture components. The selective driving force is believed to reside in the anisotropy of surface energy at the metal-vapour interface. The grain morphology is very different from the bulk grains. Moreover, 30-40% of the grain boundary interfaces observed in the RD-TD surface sections are tilt incoherent 70.5 boundaries, which are known to exhibit reduced interface energy. Hence, the conclusion can be drawn that the orientation selection of surface grains is strongly controlled by minimization of the interface energy; both metal/vapour and metal/metal interfaces play a roll in this

Modeling the recrystallization textures in particle containing al alloys after various rolling reductions

Various degrees of rolling reductions account for diverse recrystallization mechanisms and thus different microstructural and texture features. The development of deformation and recrystallization textures is discussed based on experimental data and results of finite element and crystal plasticity simulations. A recrystallization model is presented that incorporates the microstructural heterogeneities and changes in local stored energy. The experimental observations and results of crystal plasticity calculations testify that orientation selection during recrystallization is controlled by low stored energy nucleation which is incorporated in the recrystallization model. Results of texture simulations show that the evolution of {100} and {011} components is related to a particle stimulated nucleation mechanism