DELAYED FRACTURE OF STEEL 15Kh3MFA UNDER THE INFLUENCE OF HYDROGEN AFTER NEUTRON BOMBARDMENT

Ferritic--pearlitic steel 15Kh3MFA [7] (0.12% C, 0.45% Mn, 0.26% Si, 0.011% P,0.015% S, 2.50% Cr, 0.62% Mo, 0.26% V, 0.17% Ni, 0.12% Cu) in the form of plates 130 mm thick was tested after oil quenching from 1000~ and tempering at 700~ for i0 h. The effect of neutron bombardment on the mechanical properties in tension was determined on five samples with a reduced section 3 mm in diameter and samples with a ring notch (3 mm in diameter at the notch, notch depth 0.5 mm, 0 = 0.25 mm) at room temperature. The second group of samples was also used for delayed fracture tests. Irradiation was conducted in a VVR-M reactor with doses of 2 �9 i02~ and i �9 i02~ neutrons/cm 2 (E > 1 MeV) at temperatures of I00-150~ and 300-350~ respectively. , Delayed fracture tests were made in spring-loaded apparatus by two different methods. In the first method the samples were electrolytically hydrogenated to obtain 7-10 cmS/100 g in a 4% solution of sulphuric acid with 25 mg/liter of arsenic oxide added. The anode was platinum wire. To prevent desorption of hydrogen in the course of subsequent tests, the samples were coated with copper from a solution of K4P207. They were then held under load for i000 h. The experiments were conducted with continuous hydrogenation of the loaded samples. The electrolyte was not stirred during the tests, but was changed once a day. The concentration of hydrogen in the metal was determined in the reduced section of the samples by means of vacuum extraction at 200~ immediately after fracture or after the test ceased if the sample did not fracture. The test results for delayed fracture of hydrogenated samples are shown in Fig. 1. The lack of a time dependence of the breaking load indicates that the steel is not susceptible to delayed fracture under the given expermental conditions. Both in the original condition and after irradiation, fracture occurs at stresses practically equal to the ultimate tensile strength determined in brief tests. Hydrogenation of the steel irradiated under the conditions given leads to a reduction of the breaking load by approximately 50 kg/mm 2, while this value does not change under the influence of hydrogen in the original condition.