A method of inhibited acid pickling of metal cutting tools

Abstract

In tool plants 20% hydrochloric acid solutions are used as the pickling solution [1]. Tools are pickled (about i0 million per year) at temperatures of 20-25~ for 5-20 mln for full cleaning of them. Then follows the operation of hydrohoning (only hydrohoning without preliminary acid pickling does not remove all of the contaminants). The final operation is finishing of the tool by grinding of the teeth of taps and milling cutters, thread cutting, and relieving of taps [i]. Questions of inhibiting of acid corrosion of tool steel and the processes accompanying it have not been developed or investigated. In addition in many plants the temperature conditions of pickling are not always the optimum, frequently the temperatures are too low, and in addition immediately after rinsing the tools are immersed in the pickling bath without any cooling. In acid pickling the quite high tool temperature after rinsing (90-I00~ causes not only very intense cleaning of the surface of contaminants but also a high rate of corrosion, hydrogen impregnation, hydrogen embrittlement, and, as the result of this, crack fromation and decarburization of the steel. The temperature of the pickling solutions in the baths increases, reaching 50-60~ which, in turn, strengthens both subsequent pickling and the processes accompanying it. All of this increases the amount of scrap of the tools porduced and reduces their quality.