Environmental Cracking Of HY-130 Steel

ABSTRACT Plate's of HY-130 steel produced commercially by both electroslag remelt (ESR) and air melt vacuum degassed (AM.VD) steelmaking practice have been tested for resistance to environmental cracking (EC). When subjected to cathodic protection in 3.5% NaCl solution the stress intensity for EC is about 100 MPa.ml/2 compared to 130 to 160 MPa.m1/2 for dry fracture of specimens of the same size. Gas Ireta1 arc (G1A) weld metal may exhibit EC at stress intensities as low as 50 MPa.m1/2 under the same cathodic conditions. Circular patch weld restraint specimens have developed radial cracks in the weld metal and heat-affected zone when subjected to environments having extremely high hydrogen activity. INTRODUCTION A research project on the environmental cracking (EC*) of high-strength alloys has been under way at the Physical Metallurgy Research Laboratories of the Canadian Department of Energy, Mines and Resources for a number of years. The project originated because of problems with EC encountered during the hydrofoil development program of the Canadian Department of National Defence. Most recently this research project has concentrated on determining the EC resistance of commercially produced HY-130 steel. This alloy was developed by the United States Steel Corporation under contract for the United States Navy and was intended for use as the pressure hull of advanced submarines. HY-130 steel contains 5% Ni and significant amounts of chromium, mo1ybdenum and vanadium. It is a quenched and tempered alloy with a minimum yield strength of 900 MPa designed to be welded in the quenched and tempered condition and to require no heat treatment after Welding. The specifications for the alloy are given in the U.S. Department of Defense Standard MIL-S-24371A (Ships) 21 Aug. 1975. *Environmental cracking is used as a general term and includes hydrogen embrittlement cracking and stress-corrosion cracking. Sandoz (1), in 1972, summarized the literature on the EC of HY-130. This review shows that the threshold stress intensity for EC, termed KISCC, may fall to about 100 MPa.ml/2 from dry fracture values of 149 to 180 MPa.m1,2. For EC of weld metal he reported values as low as 88 MPa.ml/2 Work at PMRL by Biefer (2) using a specimen stressed by a slowly rising load gave a stress intensity for EC of 72 MPa.ml/2 when the parent metal was coupled to zinc in 3.5% NaCl solution. For weld metal, Biefer reported values as low as 48 MPa.ml/2 However, the alloy used by Biefer was obtained in 1968 and is not considered typical of current HY-130. Smith (3) found a threshold stress intensity for EC of about 104 MPa.ml/2 for parent metal HY-130 coupled to zinc in 3.5% NaCl solution and 92 MPa.m1/2 for a specimen coupled to magnesium. Recently Loginow and Phelps (4) reported a thresh-old stress intensity of only 36 MPa.ml/2 for EC of HY-130 in 21 MN/m2 hydrogen gas. Although there are great differences in environment between aqueous solutions and high-pressure hydrogen gas, this result is cause for concern about the suitability of HY-130 for use in any environment having a high hydrogen activity.