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Title: Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology

Abstract

The mechanical properties and development of microstructure and texture of a low carbon steel produced by Flexible Thin Slab Rolling (FTSR) with warm rolling technology were investigated using scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction and X-ray diffraction etc. The microstructural features in the hot strip are mainly large polygonal ferrite grains with very few or hardly any pearlite colonies. The values of yield strength and tensile strength are in the range of 215-240 MPa and 305-335 MPa, respectively, and the elongation is in the range of 33-41%. The ferrite softening can be attributed to ferrite recrystallization. Even though the dominant bulk texture is the typical recrystallization texture, which can be grouped into the ND fibre ({l_brace}111{r_brace}<110-112>) having a <111> axis parallel to the normal direction, a weak {l_brace}110{r_brace}<112> transformation texture was also observed in the final microstructure by electron back-scattered diffraction. By analysis, the large grain size is explained in terms of ferrite recrystallization and relevant growth mechanisms, and the ferrite recrystallization can be considered to play a major role in determining the grain size in the microstructure of the low carbon steel produced by FTSR with warm rolling technology.

Authors:
 [1];  [2];  [2];  [2];  [3]
  1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China). E-mail: yhzhmr@sina.com
  2. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)
  3. Tangshan Iron and Steel Co. LTD., Tangshan 063016 (China)
Publication Date:
OSTI Identifier:
20833192
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 56; Journal Issue: 2; Other Information: DOI: 10.1016/j.matchar.2005.10.008; PII: S1044-5803(05)00239-1; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CARBON STEELS; FERRITE; GRAIN SIZE; RECRYSTALLIZATION; ROLLING; SCANNING ELECTRON MICROSCOPY; TENSILE PROPERTIES; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; YIELD STRENGTH

Citation Formats

Yu Hao, Kang Yonglin, Zhao Zhengzhi, Wang Xin, and Chen Libin. Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology. United States: N. p., 2006. Web. doi:10.1016/j.matchar.2005.10.008.
Yu Hao, Kang Yonglin, Zhao Zhengzhi, Wang Xin, & Chen Libin. Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology. United States. doi:10.1016/j.matchar.2005.10.008.
Yu Hao, Kang Yonglin, Zhao Zhengzhi, Wang Xin, and Chen Libin. Wed . "Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology". United States. doi:10.1016/j.matchar.2005.10.008.
@article{osti_20833192,
title = {Microstructural characteristics and texture of hot strip low carbon steel produced by flexible thin slab rolling with warm rolling technology},
author = {Yu Hao and Kang Yonglin and Zhao Zhengzhi and Wang Xin and Chen Libin},
abstractNote = {The mechanical properties and development of microstructure and texture of a low carbon steel produced by Flexible Thin Slab Rolling (FTSR) with warm rolling technology were investigated using scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction and X-ray diffraction etc. The microstructural features in the hot strip are mainly large polygonal ferrite grains with very few or hardly any pearlite colonies. The values of yield strength and tensile strength are in the range of 215-240 MPa and 305-335 MPa, respectively, and the elongation is in the range of 33-41%. The ferrite softening can be attributed to ferrite recrystallization. Even though the dominant bulk texture is the typical recrystallization texture, which can be grouped into the ND fibre ({l_brace}111{r_brace}<110-112>) having a <111> axis parallel to the normal direction, a weak {l_brace}110{r_brace}<112> transformation texture was also observed in the final microstructure by electron back-scattered diffraction. By analysis, the large grain size is explained in terms of ferrite recrystallization and relevant growth mechanisms, and the ferrite recrystallization can be considered to play a major role in determining the grain size in the microstructure of the low carbon steel produced by FTSR with warm rolling technology.},
doi = {10.1016/j.matchar.2005.10.008},
journal = {Materials Characterization},
number = 2,
volume = 56,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • Coupons with the same composition and thickness (4.0 mm nominal gauge) obtained from hot strips of low carbon steel underwent a series of investigations to analyze the microstructural characteristics and mechanisms responsible for their differences in mechanical properties. Two different industrial technologies were adopted, although the strips used in this research were produced on the same Compact Strip Production (CSP) line. One of the strips was produced with a routine {gamma}{yields}{alpha} CSP thermal history, but the other with a {gamma}{yields}{alpha}{yields}{gamma}* conventional thermal history. The only difference between them was that one technology had a {alpha}{yields}{gamma}* thermal history. Different specimens ofmore » both types of strips were prepared for metallographic observation, tensile tests, electron back-scattered diffraction tests and positron annihilation technique tests. Experimental results showed that the differences in mechanical properties could be ascribed to dissimilarities not only in the grain size and textural components but also in dislocation density.« less
  • The microstructure and texture evolution of a strip cast and of a hot rolled austenitic stainless steel (18% Cr, 8.5% Ni) during cold rolling was studied (maximum thickness reduction {Delta}d/d{sub 0} = 80%). The microstructure of the hot band was homogeneous through the sheet thickness, except that in the center layer a small volume fraction of martensite appeared. The hot band texture revealed a through-thickness gradient which was discussed in terms of the shear distribution during hot rolling. The microstructure of the cast strip showed globular grains with martensite in the center layer and blocks of austenitic dendrites in themore » other layers. The formation of martensite was attributed to the deformation of the solidified films in the rolling gap. The strip cast sample revealed a weak texture fiber close to {l_brace}001{r_brace} uvw which was interpreted in terms of growth selection during solidification. During cold rolling in both types of samples the volume fraction of martensite increased up to ca. 50 vol.% (80% reduction). The cold rolling texture of the austenite was in both cases characterized by {l_brace}011{r_brace}<211> and {l_brace}111{r_brace}<100>. The cold rolling texture of the hot band was stronger than that of the strip cast sample which was attributed to the influence of the starting texture and of the grain size. The cold rolling texture of the austenite was simulated by means of a Taylor type model considering grain interaction and the so-called card glide mechanism. The martensite texture was characterized by {l_brace}211{r_brace}<011> and {l_brace}111{r_brace}<211>. The former component was interpreted in terms of the relaxation of shear constraints. The latter was attributed to selective phase transformation of {l_brace}011{r_brace}<211> (austenite) to {l_brace}332{r_brace}<113> (martensite) which then rotated towards {l_brace}111{r_brace}<112>. The rolling textures of the martensite were simulated using a Sachs type deformation model.« less
  • The microstructural evolution during hot-strip rolling has been investigated in four commercial high-strength low-alloy (HSLA) steels and compared to that of a plain, low-carbon steel. The recrystallization rates decrease as the Nb microalloying content increases, leading to an increased potential to accumulate retained strain during the final rolling passes. The final microstructure and properties of the hot band primarily depend on the austenite decomposition and precipitation during run-out table cooling and coiling. A combined transformation-ferrite-grain-size model, which was developed for plain, low-carbon steels, can be applied to HSLA steels with some minor modifications. The effect of rolling under no-recrystallization conditionsmore » (controlled rolling) on the transformation kinetics and ferrite grain refinement has been evaluated for the Nb-containing steels. Precipitation of carbides, nitrides, and/or carbonitrides takes place primarily during coiling, and particle coarsening controls the associated strengthening effect. The microstructural model has been verified by comparison to structures produced in industrial coil samples.« less
  • The dynamic restoration mechanisms of metals during hot working have been one of the main topics in the past two decades. In most cases, it has been found that dynamic recovery is the sole dynamic restoration mechanism in ferrite ([alpha]-iron) due to its high stacking fault energy. Dynamic recrystallization is found to occur only in high purity ferrite and in ferritic interstitial free steels. In the latter case, the nucleation of dynamic recrystallization takes place via the bulging of grain boundaries. However, all of the above work has been done on single-phase ferrite, and the dynamic restoration behavior of ferritemore » in coarse two-phase structures is still unclear. In a previous study on the hot deformation of low carbon steel in the ferrite-austenite (F+A) two-phase range, the authors found that the nucleation mechanism of dynamic recrystallization in the austenite phase was greatly influenced by the presence of F/A phase boundaries. In this paper, the dynamic restoration of ferrite in (F+A) two-phase structures and the role of F/A phase boundaries were investigated.« less
  • Wedge-shaped slab rolling was employed to investigate the microstructural evolution of an interstitial-free (IF) steel during warm working in the temperature range 500--800 C. Mean flow stress-strain curves calculated from load-time data of rolling tests reasonably correspond to work hardening and dynamic recovery behavior. The development of substructures in the deformed material was investigated using optical and electron microscopy. A close correlation was observed between mechanical behavior and microstructural development during deformation. Microbands in directions of {+-} 35{degree} with respect to the rolling direction, independent of strain, temperature and initial grain orientations are the most noticeable features in the microstructuralmore » observations. The sequences of substructural changes from the appearance of early microbands at very low strains, their development with strain, to the formation of equiaxed subgrains at higher strains and temperatures were followed by TEM.« less