PURPOSE: To obtain a superior descaling agent for stainless steel by adding a specified halogen compd. to an aq. soln. of nitric acid having a specified concn.

CONSTITUTION: A halide of an alkali metal or alkaline earth metal such as the chloride, bromide or fluoride of K, Na, Li, Mg or Ca or an ammonium salt contg. halogen such as NH4Cl, NH4Br or NH4F is added to an aq. soln. contg. 1.5-5.0wt.% HNO3, e.g. by 1-3wt.%. Proper amts. of a nonionic surfactant and a thickener such as polyacrylic salts are further added as required. Though the concn. of the HNO3 is low, a treating agent having superior ability to remove scale sticking to stainless steel is obtd.