Abstract
	Presented paper compares resistance of selected types of quenched and tempered steels to sulphide stress cracking (SSC). Experiments were made with use of micro-alloyed steel grades X52 and X60 according to API and super-martensitic steel 13Cr6Ni2.5Mo. Heat treatment was realised in laboratory conditions. The samples were subjected to tensile tests, during which the samples were exposed to stress corresponding to a certain degree of yield strength and time to rupture of individual samples of steels was measured. Detailed description of the testing method is given in [1]. Fractures areas of the samples were then investigated in detail with use of scanning electron microscopy, namely of the scanning electron microscope JEOL JSM 50-A.
	Mutual comparison of resistance of steels to sulphide stress cracking showed that the worst was super-martensitic steel 13Cr6Ni2.5Mo, in spite of the fact that it has great structural advantage, since it contains high portion of reverse austenite (approx. 30 %). Chemical composition could have also played certain role in influencing this low resistance to SSC, particularly nickel contents, which is generally considered as a factor deteriorating resistance of steels to hydrogen embrittlement.
	Quenched and tempered steels X52 and X60 are structurally dependent what concerns their resistance to sulphide stress cracking, and in spite of increase of strength characteristics, when resistance of steel should decrease according to usual criteria, it contrariwise increases due to favourable micro-structural characteristics.