Adhesion behaviour of scales on hot-rolled steel strips produced from continuous casting slabs

Abstract

The objective of this research was to study the adhesion behaviour of scales on the as-received hot-rolled steel strips produced from continuous casting slabs, i.e. medium and thin slabs. The adhesion test was conducted by the tensile testing machine equipped with a CCD camera to instantaneously observe the scales failure during the test. The adhesion test was also conducted by pickling test via immersion in a 10%v/v HCl solution at 80°C for observing the scales removing rate. There were two approaches that can be used to evaluate the scales adhesion on the studies steels. This was due to during the hot rolling process the steel strips covers with oxide scales. This scales must be removed by the acid pickling process before further process, e.g. cold rolling process. The results shown that the as-received hot-rolled steel strips produced from medium slab was exhibited higher scales adhesion more than the steel produced from thin slab for both tests. The scales thicknesses on the as-received hot-rolled steel strips produced from medium and thin slabs were 9 and 8 μm respectively. A result from tensile test, the mechanical adhesion energies of the scales actually formed on the hot-rolled steel strips produced from medium and thin slabs were 38 and 11 J.m-2 respectively. A result from pickling test, the scales dissolution rate on the as-received hot-rolled steel strips produced from medium and thin slabs were 0.0025 and 0.008 mg.cm-2.s-1. The result was also shown that the time for the complete pickling of scales on the hot-rolled steel strips produced from medium and thin slabs were 25.5 and 23 seconds respectively. This was due to the presence of high amounts of interfacial silica, which was promoted scales adhesion, indicating that longer time needed for scales removal.