Effect of Annealing on Microstructure and Corrosion Behavior of Interstitial Free Steel

Interstitial free steels with various grain sizes and textures were prepared by cold-rolling followed by an annealing process. The effect of grain size, crystallographic orientations and stored energy on corrosion behavior of interstitial free steel was investigated. It was found that the deformed microstructure and dislocation boundaries were consumed by recrystallizing grains during annealing. The average grain size increase ranging from 0.61 μm to 11 μm and the volume fraction of recrystallized grains was about 96% after annealing for 64 h; meanwhile, the γ fiber was the dominated recrystallized texture component. The stored energy gradually decreased due to the reduction in dislocation density by annealing. The potentiodynamic polarization and Nyquist plots show that the corrosion potential exhibits a more positive shift and depressed capacitive semicircle radius increase with rising annealing time. The 64 h annealed specimens had the biggest depressed semicircle in the Nyquist plots and the highest positive corrosion potential, which indicates the enhancement of corrosion resistance. Such an improvement of corrosion resistance is attributed to the increase in the volume fraction of the γ fiber and decrease in the stored energy.

Development of Ultrafine Grain IF Steel via Differential Speed Rolling Technique

The aim of this paper was to investigate the microstructural development and properties of interstitial free (IF) steel fabricated using the DSR (differential speed rolling) process. Severe plastic deformation of the DSR passes was imposed on the sample for up to four passes, leading to ~1.7 total strain with a speed ratio of 1:4 between the two rolls. Microstructural observation revealed that the equiaxed grain size of ~0.7 µm, including the formation of grain boundaries with a high angle of misorientation, was reached after four operations of DSR, which was attributed to the grain subdivision of severely elongated ferrite grain. Since the deformation mode of the DSR operation was dominated by severe shear deformation, the main shear texture of the bcc components appeared in all DSR operations in which the α-fiber of the {110} slip became a main component in accommodating the severe plastic deformation of the DSR process. The intensity of the shear texture, the {110} and {112} slip, increased by increasing the number of passes. Moreover, the γ-fiber of the <112>-type planes was activated as a result of the alternation of the shear direction during sample rotation. The microhardness and room temperature tensile tests revealed that the strength of the IF steel improved as the amount of strain increased, and this was attributed to the grain refinement and texture characteristics of the samples after the DSR processing.

Characterisation of the plane anisotropy and its effect on interstitial free steel thin sheet metal forming simulation

The main purpose of this paper is to study the orthotropic plastic behaviour of the cold-rolled interstitial free steel HC260Y when it is submitted to various loading directions under monotonic tests. The experimental database included tensile tests carried out on specimens (in the as-received condition and after undergoing an annealing heat treatment) cut in different orientations according to the rolling direction. A model was proposed, depending on a plasticity criterion, a hardening law and an evolution law, which takes into account the anisotropy of the material. To validate the proposed identification strategy, a comparison with the experimental results of the planar tension tests, carried out on specimens cut parallel to the rolling direction, was considered. The obtained results allowed the prediction of the behaviour of this material when it is subjected to other solicitations whether simple or compound.

Enhancements in the Bonding Properties of a Friction Stir Lap-Welded Interstitial Free Steel and Al Alloy by Introducing a Ni Interlayer

A pure Ni interlayer with a thickness of 0.1 mm was introduced between high-strength interstitial free steel and Al–Mg–Si alloy, which were friction stir lap welded, producing an excellent welded joint. The interface layer consisted of a γ-Ni solid solution, and the mixed stirring zone contained alternate lamellae of γ-Ni and α-Fe solid solutions. The addition of a Ni interlayer strongly suppressed the reaction between Al and Fe because of the atomic arrangement of Ni. Furthermore, the insertion depth of the stirring pin has a significant influence on the Al/steel interfacial reaction. Under shallow insertion depth, the intermetallic compounds of both FeAl and Fe2Al5 were observed at the interface layer. A maximum tensile-shear fracture load of 4.3 kN was achieved, with fractures being present in the steel substrate far away from the Al/steel weld.

CrMnFeCoNi high entropy alloys with carbon and nitrogen: mechanical properties, wear and corrosion resistance

The use of interstitial elements has been a key factor for the development of different kinds of steels. However, this aspect has been little explored in the field of high entropy alloys (HEAs). In this investigation, the effect of carbon and nitrogen in a near-equiatomic CrMnFeCoNi HEA is studied, analyzing their impact on the microstructure, and mechanical properties from 77K to 673K, as well as wear, and corrosion resistance. Carbon and nitrogen are part of the FCC solid solution and contribute to the formation of precipitates. An increase in the yield and ultimate tensile strength accompanied with a decrease in the ductility are the main effects of C and N. The impact toughness of the interstitial-free material is higher than that of C and C+N alloyed systems. Compared to CrNi and CrMn austenitic steels, the wear resistance of the alloys at room temperature is rather low. The surface corrosion resistance of HEAs is comparable to austenitic steels; nevertheless HEAs are more susceptible to pitting in chloride containing solutions.