Standard Guide for Preparation of High-Carbon Steel for coating.<br />Preparation of Steel, General<br />1. Preparatory Treatments, a wide variety of surface conditions are encountered in high-carbon steel articles to be electroplated. The surface may require the removal of one or more of the following contaminants: grease, oil or drawing compounds, burned-in oil scale, light to heavy treatment scale, permeable oxide films, emery and fine steel particles resulting from the grinding operation. The removal of such contaminants is accomplished by one or more of the following pretreatment procedures where applicable:<br />. Substantial removal of oil, grease, and caked-on dirt by precleaning before the part enters the electroplating cycle.<br />. Mechanical treatment of the surface by tumbling, sand or grit blasting, vapor blasting, or grinding.<br />. Final and complete anodic cleaning in an electrolytic alkali cleaner.<br />. Acid treatment in HCl to remove the last trace of oxide and scale. This should be avoided for spring temper and case-hardened parts. This treatment also removes residual traces of lead that may be present following proper lead-bath quenching.<br />2. Smut removal by cyanide dipping or by anodic treatment in cyanide or alkali.<br />* Final preparation for coating may be accomplished by an anodic etching treatment in H2SO4.<br />Final Pretreatment Procedures:<br /> Final cleaning, oxide removal, and anodic acid treatment are fundamental steps required for preparing high-carbon steel for electroplating. These pretreatment steps are designed to assist in the control of hydrogen embrittlement and in securing the maximum adhesion of the electroplated coating.<br />First, Electrolytic Anodic Cleaning:<br />1. All work, except work to be barrel electroplated, should preferably be cleaned in an electrolytic anodic alkaline cleaner. Anodic cleaning is recommended to avoid hydrogen embrittlement that is likely to result from cathodic cleaning. <br />2. The purpose of this cleaning step is to remove completely the last traces of contaminants.<br />3. The electrolytic anodic cleaner should be used at a temperature of 90°C or higher, and at a current density of 5 A/dm2 or higher, in order that the required degree of cleanliness be obtained in a time period not exceeding 2 min.<br />4. On removal from the cleaner, the work should be thoroughly rinsed, first with water warmed to 50°C, and then in a cold-water spray at room temperature, prior to the acid dip.<br />Important Rinsing:<br />1.The most thorough fresh-water rinsing operation possible is mandatory after each processing step if the best results in electroplating high-carbon steel are to be obtained. The purpose of rinsing is to eliminate drag-over by complete removal of the preceding solution from the surface of the work.<br />2. Warm to hot rinses should be used following alkaline solutions or where the subsequent processing solution is hot. The rinse temperature should not be so high as to induce drying of the steel surface between processing steps.<br />3. The recommended rinsing practice includes the use of an immersion rinse, always followed by a spray rinse of fresh water at the required temperature. Not using a spray rinsing is an invitation to trouble in the electroplating of high-carbon steel.<br />Second, Hydrochloric Acid Treatment, the purpose of the HCl treatment is to remove completely the last trace of oxide from the surface of the high-carbon steel. The use of H2SO4 instead of HCl is not recommended for descaling high-carbon steel because of its smut-forming tendency.<br />Third, Treatment for Smut Removal, When the HCl treatment of the high-carbon steel results in the presence of smut, the smut must be removed before the surface is electroplated. Light oxides formed on exposure to air after acid treatment must likewise be removed. This can be done by an anodic cyanide or alkaline treatment. Air-formed oxide, if not too heavy, can be removed by a cyanide dip after the rinse following the acid treatment. A concentration of 22 g/L of NaCN is sufficient for the cyanide dip. Where a severe smut condition exists, it can be eliminated by a 1⁄2 to 1-min anodic treatment at 1.5 to 2 A/dm2 in a solution of a NaCN of the noncritical concentration of 45 g/L used at room temperature. An alternative treatment for a somewhat lighter smut condition is electrolytic anodic treatment in the noncyanide alkaline cleaning solution above 70°C, for 15 to 30 s at 2.5 to 5 A/dm2. The current density is not critical.<br /><br />