Effect of the composition and heat treatment of high-strength steels on hydrogen cracking of them after cyanide cadmium plating

Abstract

ples with a notch [1]. The values of the long-term tensile strengths found were compared with the original tensile strengths of the steels. The samples were made of sheet and the notch was perpendicular to the rolling direction. The effect of hydrogen absorption on the long-term tensile strength of the steels is shown by the data of Table 1. The figures in parentheses also show the minimum time (with an accuracy of *30%) necessary for practically complete restoration of (to 0.SCrb) long-term strength of the steel with heating of it at 200~ in air (dehydrogenation time). With an increase in tempering temperature the sensitivity of steel to hydrogen content drops and tempering at 400~ and higher causes a sharp drop in the sensitivity of the steels to hydrogen cracking. With the same temper the long-term tensile strength of the various steels depends upon the steel composition with a definite role played by the carbon content, an increase in which increases the sensitivity of the steels to hydrogen cracking. Individual attention should be paid to the sensitivity of patented U8A steel to hydrogen cracking. Experiments were made on samples prepared from 5-ram-diameter patented wire (grade IIA of GOST 9389-60, tensile strength 140-165 kgf/mm 2) by grinding it to a thickness of 25 ram with subsequent making of a notch. The width of the sample was equal to the wire diameter. Cyanide cadmium plating of such samples of patented wire in the as-received condition causes practically no decrease in the long-term strength of the steel. If samples of the same wire are hardened in oil with tempering at 200-300~ for 2 h, then after cyanide cadmium plating they fail at stresses of more than 30% of the tensile strength, as for samples made of sheet with normal heat treatment (Table 1). The minimum dehydrogenation time of the steels after cyanide cadmium plating increases with an increase in carbon content in the steel and decreases with an increase in tempering temperature. TABLE 1. Long-Term Strength (in % of ~b) and Time for Dehydrogenation (in Parentheses) of Heat-Treated Steels after Cyanide Cadmium Plating (15#)