Materials Science Forum Vols. 702-703

Abstract: Effects of steel composition and coiling temperature on textures of a series of high strength IF steels were studied. An intermediate coiling temperature (6200C), instead of a high coiling temperature (7100C), was found most beneficial for the steels containing moderate to high phosphorus content. On the other hand, high coiling temperature was found beneficial for the steels containing low amount of phosphorus.

Abstract: The recrystallization texture of highly cold deformed IF steels is addressed. The latter is characterized by the //ND fibre and a certain spread towards the {311} orientation. The //ND fibre is the optimum texture for enhanced deep-drawing properties whereas the presence of any other component, such as {311}, will deteriorate the plastic anisotropy of the material. Previous works concluded that the recrystallized {311} orientation results from an oriented nucleation process related to the plastic instability of {001} deformed grains. In the present work, the microstructural nature of such plastic instability is investigated by high resolution orientation scanning microscopy on an annealed IF sample after cross-rolling. Present data indicate that localized deformation in near {001} grains plays an essential role in the nucleation of {311} orientations.

Abstract: Annealing behaviour of ferritic HT-9 stainless steel plates was investigated through evolution of microstructural, textural and mechanical properties. Microstructural observations showed two important findings: (a) abnormal grain growth occurs at higher annealing temperatures, (b) drop in in-grain misorientation with increasing annealing temperature. However, textural results showed an increase in texturing till 500oC annealing and a clear drop in texturing beyond 500oC annealing. The strength (both yield and tensile) decreased with increase in testing temperature and the micro-hardness values decreased with increase in annealing temperature. Dynamic strain ageing was observed at certain strain rates and testing temperatures. The onset of the serrated yielding at low temperature limit estimated from the strain rate-temperature plot was found out to be ~ 94kJ/mol identifiable with that for migration of C and N.

Abstract: Texture formation during annealing of a 95% cold rolled HSLA steel with 10°C/s and ~3000°C/s was studied with the purpose to investigate the interaction between the recrystallization and the austenite formation as well as the possibility of grain refinement. The recrystallization and austenite formation were monitored by means of optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). It was found that at extreme reheating rates of 1000°C/s and higher, the α-γ phase transformation starts before the completion of recrystallization and the deformation texture is partially retained in the samples after annealing. The crystallographic texture observed in the martensitic phase which is the product of intercritical austenite transformation in as-quenched samples, i.e. after the double α-γ-α’ transformation, is the same as the initial cold rolling texture, which is an indication for the texture memory effect. After ultra fast reheating with average reheating rates of 1000°C/s and higher a significant grain refinement was observed with an average ferrite grain size of ~1µm. The obtained final ferrite grain size depends significantly on both the reheating temperature and the reheating rate.

Abstract: The evolution of microstructure with degree of deformation in a deformed wedge shaped hypereutectoid steel implement, containing 1.84 C, 0.06 Si, 0.01 S, 0.14 P, 0.11 Cu, 0.017 Zr and 0.05 Ce, has been characterized using optical and scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). Microstructures consisted of bulky carbides dispersed in a matrix of pearlitic, with grain boundary proeutectoid cementite, side plate Widmanstatten cementite and intragranular cementite were noted in region of low strain. The cast structure was broken down with increasing degree of deformation. The mechanism for the formation of spheroidization of cementite in hypereutectoid steel has been proposed. Microstructural analysis of high strain region consists of fine equiaxed ferrite grains surrounded by high angle boundaries.

Abstract: Severe cold rolling and short intercritcal annealing is often used to produce ultra-fine grained ferrite and martensite dual phase steels. In this paper, microstructure and texture of Nb-microalloyed steel following cold rolling and short intercritical annealing is investigated. The results show that cold rolling and annealing resulted in ultra-fine grained dual phase steel consisted of polygonal ferrite in the range of ~1-2 μm in size. In cold rolled material, the texture components are γ fiber (//normal direction) and α fiber (//rolling direction). Partial recrystallization texture was observed following intercritical annealing.

Abstract: Texture formation during uniaxial compression at elevated temperatures in Fe-3mass%Si and 430 stainless steel is studied. The behavior is analyzed in relating to the understanding on the texture development in Al-Mg solid solution alloy at high temperatures. It is found that the fraction of {001} (compression plane) is much higher than that of {111} both in Fe-3%Si and 430 steel, which is different from the deformation at room temperature. In Fe-3%Si, the fraction of {001} becomes higher at higher temperatures and with lower strain rates. EBSD measurement suggests that the development of {001} is attributed to the preferential growth of {001} oriented grains. In the case of 430 steel, no obvious deformation condition dependence of {001} development is seen, probably due to the fine particles pinning the grain boundaries.

Abstract: It is well known that clogging constitutes one of the main issues encountered during casting in the steel industry. To clarify how clogging deposits are formed and to minimize their impact in the process, their microstructure and relationship between the different constituents need to be studied. In the tundish well the studied deposits consist predominantly of Al2O3 inclusion fans but are found interspersed with islands of pearlite along the margins. These islands of coarse pearlite, i.e. thick cementite/ferrite plates surrounded by large ferrite grains are formed even in Ti-rich ultra low carbon steels and the orientation relationships are used to track the initial composition of the deposit when it was formed. The crystallographic orientation relationship (ORS) between ferrite and cementite in pearlite can follow Isaichev (I), Bagaryatskii (B) or Pitsch-Petch (PP). Results showed that the pearlite islands are formed with ORS relatively close to PP and are intersected by alumina particles which show a specific relation with the islands and with the ferrite matrix. It was concluded that an external carbon source and temperatures just above the eutectoid are needed to form those islands.

Abstract: The effect of heating path and heating rate on the microstructure and texture development in cold-rolled continuously annealed DP steel was studied by SEM and EBSD. A methodology to separate the individual phases present in mixed microstructures, and thus to enable quantification of the individual contributions to the bulk texture has been applied. It was observed that a higher heating rate may promote strengthening of {111} textures in DP steels as observed in low carbon grades.

Abstract: Ultra fine grained (UFG) pure titanium fabricated by severe plastic deformation techniques has been recently considered for biomedical applications. In this study, the effects of grain size and crystallographic orientation on the biocompatibility of commercially pure titanium have been evaluated. Samples having significant differences in terms of average grain size (from 0.4 to 20 mm) and crystallographic textures have been produced using equal channel angular pressing (ECAP) and compared. X-ray diffraction and electron back scattered diffraction (EBSD) were used to document the texture and microstructural properties. Cell attachment tests were done to study the biocompatibility of the samples using MC3T3 pre-osteoblast cells. The number of attached cells was found to be higher on the samples having more (0002) plane parallel to the surface regardless of their grain sizes. It was concluded that the texture plays a more significant role than the grain size in the biocompatibility of pure titanium.