Factors Influencing the Rate-of-Pickling Test on Tin-Plate Steel★
Abstract “Lag time” is a measure of the time of pickling necessary to produce a constant rate of weight loss from steel immersed in acid. This measurement has been used as a guide for improving the corrosion resistance of commercial electrolytic tin plate. It is determined by measuring either the rate of change of weight loss, hydrogen evolution, or corroding potential of a specimen in 6N hydrochloric acid at 90 C (194 F.) The lag time depends on surface effects inasmuch as removing the surface layers of steel by abrasion or by pickling destroys the lag. The influence of box-annealing atmospheres, cleanliness of steel, and time-temperature cycles on lag time have been investigated, and the complexity of these effects has been demonstrated. Explanations in terms of oxidation or decarburization of the steel surface during annealing are not feasible for the development of lag time under all the experimental conditions studied. Preliminary data demonstrating the high concentrations of certain elements on the steel surface before annealing, and the enrichment of the surface layer by some of these elements during annealing, are suggested as particularly promising areas for future work. In this way lag time phenomena in tin-plate steels may be better understood and further improvement in tin-plate corrosion resistance can be made. 2.3.4