RESISTANCE OF DIFFERENT VARIANTS OF THE TRIP 800 STEEL TO HYDROGEN EMBRITTLEMENT IN SOUR ENVIRONMENT

The presented paper evaluates resistance to hydrogen embrittlement of two variants of the TRIP 800 steel prepared in laboratory conditions at FMME VSB - Technical University of Ostrava. The first type of investigated steels is based on C-Mn-Si composition. The second variant corresponds to C-Mn-Si-Al composition. Both studied TRIP steels are characterized by the yield strength in the range from 420 to 450 MPa and by the tensile strength between 880 and 900 MPa. The TRIP steels were studied in the form of sheets with thickness of 1.5 mm. The resistance to hydrogen embrittlement was tested in a sour environment, containing hydrogen sulphide, by means of HIC and SSC tests performed in accordance with NACE standards. Both variants of the TRIP 800 steel showed high resistance to hydrogen embrittlement. SSC cracks were not observed at all. Some cracking corresponded to the HIC mechanism was revealed in both variants. The measured parameters (CLR, CTR and CSR) were rather dispersive. In some cases they were lower than recommended limits but in other cases the measured parameters were higher (CLR up to 70%). Cracks were initiated preferentially on non-metallic inclusions, either on elongated manganese sulphides, or on stringers of oxides rich in Al.