On the hot-rolled recycled carbon steels: their oxide formation, pickling ability and scale adhesion

Abstract

Purpose The purpose of this study is to investigate the formation, pickling ability and adhesion of thermal oxide scales on the hot-rolled recycled steels produced from the medium and thin slabs. Because the scale on the steel produced from the medium slab was relatively thick of about 11 µm, it contained cracks after hot-rolling. Thus during pickling, the scale was uniformly attacked with the simultaneous dissolution of the inner scale because of the penetration of acid through cracks. However, the scale on the steel produced from the thin slab was thinner of about 6 µm and thus, nearly crack-free. The pickling solution thus attacked the scale surface uniformly. At longer pickling periods, pits were also nucleated and propagated. Concurrently, the tensile testing machine with a CCD camera has been applied to observe scale adhesion. Design/methodology/approach The formation, pickling ability and adhesion of thermal oxide scales on the hot-rolled recycled steels produced from the recycled slab, e.g. medium slab and thin slab, were investigated. The morphology and phase identification were examined by using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Furthermore, the adhesion behaviour of oxide scale was investigated by immersion test and tensile test with a CCD camera. Findings For the scale formation, it was found that the hematite and magnetite were formed on the hot-rolled recycled steels produced from the medium and thin slabs. For the immersion test, it was found that the scale on hot-rolled recycled steels produced from the medium slab was more difficult to be pickled as represented by the longer time for the complete pickling. This was consistent with the result of tensile test; the steel produced from the medium slab had better scale adhesion as represented by the higher strain initiating the first spallation of scale. Originality/value The effects of slab types and its alloying element were investigated to understand the scale adhesion behaviour. The empirical pickling mechanisms and the mechanical adhesion energy were proposed. It led to the understanding in the control of alloying element in the hot-rolled steel.

Experimental Study of Salicylic Acid as a Calcium Sulfate Dihydrate Scale Inhibitor, Analyzed from Surface Properties and Crystal Growth

“…Nucleation rate is defined as the number of formed nuclei per unit time per volume. It can be calculated according to the following relation: 21 where J is the rate of nucleation, and F is a frequency constant, is known as the pre-exponential factor, and has a theoretical value of 10 30 nuclei/(cm 3 s). β is a geometric (shape) factor of 16π/3 for the spherical nucleus, and f (θ) is a correction factor.…”

“…Nucleation rate is defined as the number of formed nuclei per unit time per volume. It can be calculated according to the following relation: 21 Ä…”

CHAPTER 4 High Temperature Oxidation of Stainless Steels

“…Because the ratio of oxygen and iron in magnetite is higher than that in wüstite, the formation of wüstite from magnetite then gives iron vacancy as follows: It is noted that at the temperature of 570 ºC, there exists the eutectoid reaction among wüstite, iron and magnetite. Thus when wüstite is cooled down from high temperatures to 570 ºC or lower temperatures, wüstite can decompose giving the eutectoid structure consisting of iron and magnetite, as typically observed in the thermal oxide on hot-rolled low carbon steel where the cooling rate of the strip is essentially slow [1,[5][6][7].…”

Analysis of the Effect of the Excess Air Combustion Ratio on the Loss of Steel and Scale Adhesion in the Process of Heating the Steel Charge Including Changes in Technology

“…The problem of too high scale adhesion occurs in the processes of hot rolling of steel products [10,11] and hot stamping of car body parts [12].…”