Papers by Author: Fu Tao Han

Abstract: Interstitial-free (IF) steel has excellent deep-drawability and was used widely in automotive industry. High strength IF-steel is that some phosphorus was put in common IF-steel to improve its strength without destroying the deep-drawability [1]. Microstructure and grain boundary character strongly affect the deep-drawability of high strength IF-steel, it is an obligatory task to test those characters. The technique of Electron Backscatter Diffraction (EBSD) can reveal the microtexture and detailed orientation distribution of grains from a single EBSD map, as a powerful instrument, EBSD was used widely in materials research from last decade [2]. Many researches have been focused on the texture evolution and recrystallization phenomena of high strength IF-steels [3,4], but the microtexture and grain boundary characters of warm-rolled high strength IF-steels was not fully investigated. The present study was aimed at researching the microtexture characters of a commercial high strength IF-steels under different warm-rolled temperature using EBSD technique, the microstructure and grain boundary character were analyzed systemically, and the relationship between the microstructure and deep-drawability was discussed.

Abstract: In this paper, effects of ferritic rolling process on microstructures and mechanical properties especially drawability of ultra-low carbon (ULC) and Ti-stabilized interstitial-free (Ti-IF) steels were investigated and the precipitates of ferritic-rolled Ti-IF steels were also analyzed. The results show that good deep drawability are achieved as IF steels are ferritic rolled in good lubricant condition; on the contrary, lubricant condition has less influence on the deep drawability of ULC steels. And with the decrease of rolling temperature in ferrite region, deep drawability of Ti-IF steels are improved, but for ULC steels, when ferritic rolled at low temperature, the r-value is still less than one, which means insignificant deep drawability.

Abstract: Precipitates have great influence on the recrystallization, texture evolution and thus the final mechanical properties of the Interstitial-Free (IF) steel sheets, however, very few studies have dealt with the precipitation behavior of IF steels warm rolled in ferrite region. In the present work, the precipitate characteristics (type, morphology, size and amount) of warm-rolled ordinary Ti-stabilized Interstitial-Free (Ti-IF) steel and p-added high-strength Ti-IF steel were investigated by Transmission Electron Microscope (TEM) and Energy Dispersion Spectrometer (EDS). The results show that most precipitates in warm-rolled ordinary Ti-IF steels are TiN, TiS, Ti4C2S2 and TiC. Besides these precipitates, a great amount of FeTiP precipitates exist in warm-rolled P-added high-strength Ti-IF steel. The precipitation of FeTiP retards the migration of grain boundary in the recrystallization annealing, so the {111} texture and thus deep drawability of warm-rolled high-strength Ti-IF steel is deteriorated.

Abstract: Warm-rolling can save the production cost and extend the production kind of hot-rolled IF steel strip, the precipitates strongly influence the annealing process and texture evolution so as to the final mechanical properties of the production, very few studies has relate to the precipitates of IF steels warm-rolled in ferrite region. In present work, two Ti- IF steels were warm-rolled in ferrite region under different rolling parameters and the precipitates were investigated. Transmission electron microscopy (TEM) and Energy dispersion Spectroscopy (EDS) microanalysis were carried out on carbon extraction replicas, the characteristics such as morphology, type, amount and size of precipitates were analyzed. The results show that different type of precipitates were appeared in two steels, TiN, TiS, Ti4C2S2 and TiC were found in common Ti-IF steel, but in high strength Ti-IF steel, the amount of TiS, Ti4C2S2 was very few and FeTiP precipitates appeared, the type and morphology of precipitates were not affected by rolling parameters, however, the number and size of precipitates were changed. Finally, the effect of different P content on the change of precipitates was analyzed, the precipitating mechanism was also discussed.

Abstract: In order to simplify production processes and to lower production cost of thicker coldrolled IF steel sheets for deep drawing applications, a new warm-rolled IF steel sheet was developed in our lab through hot-rolling in high-temperature ferrite range. In this paper, effect of processing parameters on properties, microstructures and precipitate morphology of warm-rolled IF steel sheets was investigated. It is found that firstly, good deep drawing properties and favorable textures were achieved as steels were warm-rolled in good lubricant condition. Secondly, most precipitates in steels were TiS, TiC, TiN and Ti4C2S2.