engleski

The effect of coolong rate on content hydrogen absorbed for low Cr-Mo-Nb steel

The low alloy Cr-Mo-Nb steel has been studied to determine the effect of cooling rate on the absorbed hydrogen content. Under the industrial conditions the billets were hot-rolled in pipes for oil country tubular goods. Specimens of 4 mm in diameter and 12mm in lenght were prepared for heat treatment by dilatometry method. To obtain the various microstructures the heat treatment of specimens was carried out using a high-speed dilatometer Adamel Lhomargy Type LK 02. The martensite microstructure was obtained by quenching of specimens (by blowing of argon) at the average cooling rate of 43°C/s in the temperature range from 870 to 500°C. The tempered martensite microstructure was obtained by tempering of specimens at 700°C for 40 min. The pearlite-ferrite microstructure was obtained by means of a slow cooling of specimens at the average cooling rate of 0.1°C/s by vacuum. After heat treatment the specimens were cathodic charged without load in 0.5M H2SO4 +10 mg/l As2O3 solution at the current density of 40 mA/cm2 for 60 min. Immediately after the cathodic charging the content of hydrogen was determined by hot vacuum extraction method. It was found that the martensite microstructure absorbed 17.0 ppm of hydrogen, while the pearlite-ferrite microstructure absorbed only 4.0 ppm of hydrogen. Thus, these results have shown that the ferrite-pearlite microstructure could be more resistant to the hydrogen embrittlement then the tempered martensite and/or untempered martensite microstructure.

steel; microstructure; cooling rate; hydrogen-embrittlement

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