Juan Jia

Texture, Grain Boundary Characterization and Segregation of Phosphorus in an Annealed Interstitial Free Steel

The {111}//ND plane texture, grain boundary characterization and grain boundary segregation of phosphorus are investigated for the phosphorus added high strength interstitial free (IF) steel annealed at 810 °C for 60 s to 180 s. The results show that the maximum volume fraction of {111}//ND plane texture is about 85% and the grain boundary segregation peak of phosphorus is about 14 at.% for the steel annealed at 810 °C for 120 s. The Σ3 and other low-ΣCSL (coincident site lattice) boundaries are lowest for the steel annealed for 120 s. Segregation of phosphorus is also found at low angle grain boundaries.

Effect of Phosphorus Grain Boundaries Segregation and Precipitations on Mechanical Properties for Ti-IF Steel after Recrystallization Annealing

The cold-rolled (75% reduction ratio) Ti-IF (interstitial-free) steels of 1 mm thickness were recrystallized by annealing at 810°C for different times. The microstructure, mechanical properties and phosphorus segregation at grain boundary were investigated by means of optical microscopy (OM), tensile testing and field emission transmission electron microscopy (FE-TEM). It was observed that recrystallization was completed after annealing at 810°C for 180 s. The yield strength and tensile strength decreased as annealing time increased. The FE-TEM observation showed that after the annealing treatment, the grain boundary was broadened and the dislocations with higher density of phosphorus atoms and phosphide at grain boundaries became evident. The amount of phosphorus segregated at grain boundaries increased with annealing time.

Microtexture Evolution and Grain Boundary Character Distribution of Interstitial-Free Steels With Moderate Levels of Cold Rolling Reductions

High-strength interstitial-free steel sheets have very good deep drawability when processed to have {111} recrystallization texture. The microtexture evolution and grain boundary character distribution of interstitial-free steels as a function of moderate levels of cold rolling reductions were investigated by the metallographic microscopy and electron backscatter diffraction technique. The results showed that there was a close relationship between microtexture and grain boundary character distribution for interstitial-free steel, especially the distribution and features of some specific types of coincident-site lattice boundaries. In addition, α-fiber texture was weakened to vanish while γ-fiber texture strengthened gradually as cold rolling reduction was increased from 20% to 75% for cold rolled and annealed samples. Accordingly, increasing the rolling reduction from 20% to 75% would lead to a significant increase in the proportion of Σ3 boundaries. Also, it was found that the microtexture of 20% cold rolled sample would induce a high frequency of Σ11 grain boundaries, but the microtexture of 75% cold rolled sample would produce more Σ7 and Σ17 grain boundaries. It was suggested that texture played a significant role in the formation of grain boundary character distribution.

Precipitation Behavior of FeTiP in Ti-added Interstitial Free High Strength Steels

The precipitation behavior of FeTiP in interstitial free high strength (IFHS) steels has been studied by using a transmission electron microscope (TEM). The results show that the TiC particles, appearing at earlier stage, are more stable than the FeTiP ones during recrystallization annealing at the two given temperatures (810 °C and 840 °C). Therefore, the FeTiP particles can only be observed in the steels with sufficient amount of Ti. There is a critical forming time for the FeTiP, which is between 90 – 120 s at 810 °C and 60 – 90 s at 840 °C. The precipitation of FeTiP involves two steps, i. e. the formation of FeTi precursors and the diffusion of P. The former step determines the reliance of Ti content for the precipitation of FeTiP, whereas the latter step leads to the difference in the critical annealing time.

Effect of Micro-Alloying Elements of Ti, Nb and B on Recrystallization Behavior of Cold-Rolled Interstitial-Free Steel Sheets

The effect of micro-alloying elements of niobium and boron and titanium on recrystallization behavior is researched after the cold rolled IF steels are annealed at high temperature. The results show that there is high density dislocation in the cold rolled steel and the microstructure is fibrous tissue. The recrystallization grains appear when the cold steel annealed at 655 °C and then the grains grow up with the annealing temperature increased to 840 °C. The recrystallization temperature and time of B-Ti-IF steel is lower than that of Nb-Ti-IF and Ti-IF steels. The recrystallization activation energy of Nb-Ti-IF steel is 181.7KJ/mol which is 56.6KJ/mol larger than that of B-Ti-IF steel.

Effect of Phosphorus Contents on Texture and Grain Boundary Character for the Annealing High Strength Ti-IF Steels

The effect of phosphorus contents on texture and grain boundaries character for the high strength Ti-IF annealed for 120sec at 810oC are researched by electron backscatter diffraction technique（EBSD）. The recrystallization texture is approximated by the γ-fiber texture whose components are {111} and {111} orientation texture. The highest volume fraction of //ND texture is almost 80% for the sample containing 0.056%P. A large amount of coincidence site lattice(CSL) grain boundaries ∑3，∑5, ∑7，∑9，∑11 and ∑13b are obtained.

Effect of Annealing Temperature on Phosphorus Segregation at Grain Boundary in a Ti-IF Steel

The concentration of phosphorus at grain boundary of the Ti-IF steel annealed for 180sec at 780°C、810°C and 840°C respectively is measured by auger electron spectroscopy (AES). The results show that the segregation concentration of phosphorus at grain boundary decreases with increasing annealing temperature from 780 to 840°C. The maximum phosphorus concentration at grain boundary is 13.5at% or so for the specimen annealed for 180sec at 780°C. Most of the grains are intergranular crack and there are a few secondary crack for the samples annealed at 780°C and 810°C. The grains grow up and the cleavage planes increase with increasing the annealing temperature from 780 to 840°C.

Work Hardening of the Isotactic Polypropylene during Rolling

The crystallinity of the isotactic polypropylene during rolling is measured by the wide angle X-ray method. And then the influence of the crystallinity and true rolling strain on the work hardening is analyzed comprehensively. The work hardening index of the crystallinity part is 2, and the index of the amorphous part is 4. Deformation in the crystallinity part is more difficult than the amorphous part; however, the work hardening rate is smaller. The work hardening contribution of the crystalline part is higher than the amorphous part in the early rolling stage, but lower as the true strain is higher than 1.0.

Microstructure and Texture Evolutions in a Short-Time-Annealed Interstitial-Free Steel

One kind of high strength interstitial free steel sheets are annealed in a salt bath at 810 C for different times (1-30 s). The microstructure and recrystallized texture evolution during annealing are investigated using the optical microscopy and the Electron Back Scattered Diffraction technique. The results show that beginning and finishing of recrystallization are observed in the sample annealed at 810 C for 8 and for 20 s, respectively. The recrystallized grains nucleate in the order of ‹111›//ND, ‹110›//ND and ‹100›//ND. Recrystallized grains with ‹111›//ND orientation nucleate firstly in the ‹111›//ND deformed grains as well as at their boundaries and grow up by consuming the ‹111›//ND deformed grains at the initial stage of recrystallization. The ‹111›//ND recrystallized grains grow up by depleting the remained formed ‹100›//ND grains after the full consumption of the ‹111›//ND deformed grains. The overall recrystallization texture is mainly the ‹111›//ND component in the steel.

Development of Texture and Grain Boundary Character in a Boron Bearing IF Steel after Recrystallization Annealing

The development of texture and grain boundary character are researched for a boron bearing IF steel after recrystallization annealing for different times at 810°C. The results show that the main texture components are {111}<110> and {111}<112> after the cold rolling samples annealing different times. The maximal volume fraction of <111>//ND texture is about 78% for the sample annealing for 120sec. The main CSL boundaries are ∑3，∑5，∑7，∑9，∑11，∑13b and ∑17b. And the ∑3 grain boundary increase with increasing the annealing times from 60sec to 180sec.