EFFECT OF STEELMAKING ON THE HYDROGEN ATTACK OF CARBON-STEEL

Four normalized carbon steels made in different ways (Si-killed, Al-killed, REM-treated, and electroslag refined) were studied to determine the role of differing fine inclusions on the early stages of hydrogen attack (HA). Hydrogen exposures were made at 450°C (6.5 MPa) and 375°C (7.6 MPa). The first stage of HA is shown to be the development of a closely spaced (1 to 2 μm) array of small bubbles over the ferrite/pearlite, or occasionally the ferrite/ferrite boundaries. These bubbles grew together to form tears, primarily in the rolling plane, leading to more rapid expansion normal to this plane than parallel to it. Fracture planes followed high solute layers in banded steel but only rarely if ever did the fine bubbles form on inclusions. At 450°C REM-treated steel was attacked the fastest and Al-killed steel required exposures two to four times as long for attack. © 1979 American Society for Metals and the Metallurgical Society of AIME.