Effect of O2 in Heating Atmosphere on Hydraulic Descaling in Hot Rolling of Low Carbon Steel

Abstract

Low carbon steel was oxidized over the temperature range 1 050-1 250°C in O 2 -CO 2 -H 2 O-N 2 gas mixtures. The oxidation times were 15-120 min, and the scales were 130-2 000 mm thick. The experimental parameters were chosen to approximate scale formation under conditions similar to those of reheating furnaces in hot strip mills. In the hydraulic descaling tests, two modes of scale removal were observed. In the first mode, observed in classical three-layer scales that developed an inner porous layer with low or medium porosity, the horizontal undercutting occurred at the boundary of the inner porous layer and dense scale. The second mode was observed in classical three-layer scales that developed an inner porous layer with high porosity, and in crystalline scales. In the second mode, the horizontal undercutting occurred at the first plane of large pores relative to the scale/steel interface. A rise in the concentration of free oxygen resulted in an increase in thickness of the residual scale at 1 050°C. At 1 100°C and 1 150°C, the increase in residual scale thickness with increasing free oxygen was significant in the initial 60 min of oxidation; after this period of time the differences in the thickness of the residual scale became smaller. At higher temperatures, the influence of free oxygen in the residual scale thickness was small at 1 200°C and negligible at 1 250°C. In general, the experiments showed that scale morphology controlled the removability of scale.

Characterization and Reduction Behavior of Mill Scale

“…[12][13][14] These studies showed that mill scale is a layered and brittle material, composed of iron oxides with wustite as a predominant phase. However, depending on parent steel composition some minor oxides are also detected in the mill scales.…”

Fast dynamic heat and mass balance model of walking beam reheat furnace with two-dimensional slab temperature profile

“…Li et al 4 merely comment that the beams can reduce the radiation by y83% around skids. Mogan 7 assumed that skids obstruct 80% of radiation to (34) the slab surface right above the skids. Therefore, the coefficients for this model were calculated using the concept proposed by Lindholm and Leden: 5 (i) coefficients at the distance x from the left hand edge of the computational domain were determined separately for the case of the slab resting on the stationary beam, equation (38), and the walking beam, equation (39) (ii) if the slab spends the portion of time W on the stationary beam, the overall shadowing coefficient at x is calculated using equation (40).…”

The effect of alloy compositions on the microstructure and the mechanical strength of oxide scales on four selected steels

“…A thin scale layer or some parts of the thick scale remain on the substrate surface [3]. The scale residues may grow further if O is available and will undergo structural changes even during cooling after coiling, which is the end of the process [1,7,8]. These scale residues significantly degrade the quality of the final products in several ways [1].…”

“…For this reason, it has been known that the weldability is strongly related to the amount of scale residues on the strip surfaces [12]. Research effort has been made to investigate the factors for the adhesion strength between the scales and the steels [7,14]. However, in reality, there are few parameters to vary in the hot rolling process [8].…”