Descaling Behavior of 430 Hot-rolled Stainless Steel in HCl-based Solution

Descaling of hot-rolled stainless steel is generally implemented through pickling process in HNO3-HF mixed acids, which induces severe environmental concerns of nitrogen oxide (NOx) gases and nitrites. According to the electrochemical measurement, the mass loss test and the appearance analysis, a new pickling process which employed HCl-based solution was proposed and evaluated to provide theoretical basis for the development of environment-friendly and highly effective pickling process. Under the experimental condition, the HCl-based solution can compete with ordinary HNO3-HF mixed acids in terms of pickling efficiency, surface integrity and the removal of Cr-depleted layer. The descaling process of 430 hot-rolled stainless steel in the HCl-based solution consisted of three steps. The descaling solution penetrated the oxide scales into the underlying metal, dissolving the Cr-depleted layer and part of substrates. The oxide scales peeled off from the stainless steel and a polished and smooth surface was exposed. The descaled stainless steel was dissolved uniformly in the HCl-based solution; therefore, the pickling duration was vital for desired surface integrity. Under the static condition, the appropriate descaling time of 430 hot-rolled stainless steel in HCl-based solution was 400 s.