AN IMPROVED MARSHALL'S REAGENT FOR ETCHING OF COLD ROLLED AND ANNEALED INTERSTITIAL FREE (IF) STEEL SHEET

摘要

The main object of the present invention therefore, is to provide an improved Marshall"s reagent for controlling the rate of etching reaction. Another object of the present invention is to avoid etching pits introduced by the echants. Yet another object of the invention is to avoid over etching for preventing the darkening of the surface. These and other objects of the invention are achieved as summarized in Table 2. Etching for extended period may cause darkening of the surface. A moderate amount of graying can be cleaned through ultrasonic cleaning using ethylene-diamine tetra-acetic acid (EDTA), it is a method of cleaning the surfaces of a metallographic sample using certain solution and an ultrasonic vibrator. The specimen is generally kept in a suitable container (breaker etc.) full of solution and then the entire container along with specimen in it is placed in the ultrasonic vibrator. The liquid solution in contact with the specimen cleans the surface from oil, dirt and other impurities very effectively when the ultrasonic vibration is applied 3 % ethylene-diamine tetra-acetic acid (EDTA) solution is a specific solution that can be used for ultrasonic cleaning of metallographic sample of steel. The present invention provides a method for etching of cold rolled and annealed interstitial free (IF) steel sheet, comprising the steps of: preparing a chemical etchant in two parts, a first part comprising oxalic acid, sulphuric acid and distilled water at room temperature, and a second part comprising 30% solution of H2O2 at a temperature of 15-20° C for controlling the rate of etching; mixing freshly made solutions of said first and second part in equal proportion; etching samples of said steel sheets with said chemical etchant for 30- 40 seconds; and ultrasonic cleaning of the etched surface for about 15-20 minutes.