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Technical Paper
The objective is to examine the conditions under which the layer of scale on the surface of 430 stainless steel strips during hot rolling is capable of reducing the coefficient of friction. The independent parameters are the thickness of the layer of scale, the temperature, the speed, the reduction and the origin of the sample, whether slab or strip.
The roll forces and the coefficients of friction depend on the thickness of the scale layer in a significant manner. The rolling speed, the temperature and the reduction also affect both variables. The forces and the coefficients drop as the scale thickness increases at 900 deg and 1000 deg C. The opposite is observed at 1100 deg C. Both parameters decrease as the temperature and the roll velocity increase.
In the speed range of 1 m/s and at temperatures less than 1100 deg C increasing scale thickness appears to reduce the frictional resistance. At lower speeds and higher temperatures the opposite phenomenon has been observed.
KEY WORDS
Hot Rolling; Stainless Steel; Friction
INTRODUCTION
Since the technical literature concerning the effects of scaling during hot rolling of ferritic stainless steels on friction is not voluminous, some insight may be gained by examining the behaviour of plain carbon steels (Beynon et al., 2000). The scale is usually less ductile than the steel and the rolling process tends to break the interface bond between it and the steel (Ginzburg, 1989).
The layer of scale then cracks and small spaces form in between the scale particles. Hot steel is extruded through these spaces under high pressures (Blazevic, 1983a, 1983b, 1983c; Li and Sellars, 1999). At the same time, the steel is deformed in the rolling direction, resulting in the simultaneous roughening and smoothing of the steel surface (Munther and Lenard, 1997). A schematic diagram of the cross section of the hot steel, the cold roll and the broken-up layer of scale has been presented (Li and Sellars, 1999) in which the hot steel, contacting the cold roll is clearly indicated.
Previous studies discuss the effect of several parameters on friction in hot, flat rolling of carbon steel strips. The coefficient of friction has been shown to decrease with increasing temperature (Munther and Lenard,...