Abstract
	Resistance of two heats of duplex stainless steels, containing 22% of Cr and 5% of Ni, to sulphide stress cracking (SSC) was studied. Steels were tested in initial state after solution annealing and after heat treatments, the aim of which was to provoke ? – phase formation. Annealing at temperatures in the range from 650 to 800°C resulted in a discontinuous ? – phase precipitation at the ferrite/austenite interface. The maximal volume fraction of ? – phase was about 0.04. SSC tests, performed in accordance to NACE TM 0177, showed that ? – phase deteriorated resistance of duplex steels to SSC considerably. In as-received state specimens failed only for stresses exceeding the yield strength of the material. If about 0.04 of ? – phase was present at the ferrite/austenite interface specimens withstood only stresses corresponding to about 70% of their yield strength. To establish the role of microstructure and applied stresses, hydrogen induced cracking (HIC) tests were performed as well. The results of HIC were different in comparison with SSC results. In the case of HIC, the presence of ??? phase did not deteriorate the resistance of duplex steels considerably. 
	The research was completed by hydrogen diffusion coefficient measurement in the studied duplex steels with the aid of electrochemical permeation method. Results showed that hydrogen diffusion coefficient of duplex steels depended mainly on the specimen orientation as the diffusion was easier if hydrogen diffused lengthwise of ferrite bands.