Steel material having excellent hydrogen induced cracking resistance, and manufacturing method therefor
The present invention relates to a steel material for a pressure vessel, which is used in a hydrogen sulfide atmosphere, and, more specifically, to a steel material having excellent hydrogen induced cracking (HIC) resistance, and a manufacturing method therefor.
1 . A steel material having excellent hydrogen induced cracking resistance, comprising:
by wt %, 0.10 to 0.25% of carbon (C), 0.05 to 0.50% of silicon (Si), 1.0 to 2.0% of manganese (Mn), 0.005 to 0.1% of aluminum (Al), 0.010% or less of phosphorus (P), 0.0015% or less of sulfur(S), 0.001 to 0.03% of niobium (Nb), 0.001 to 0.03% of vanadium (V), 0.001 to 0.03% of titanium (Ti), 0.01 to 0.20% of chromium (Cr), 0.01 to 0.15% of molybdenum (Mo), 0.01 to 0.50% of copper (Cu), 0.05 to 0.50% of nickel (Ni), 0.0005 to 0.0040% of calcium (Ca), a balance of Fe, and other inevitable impurities,
wherein a length ratio of a short side portion to a long side portion (short side portion/long side portion) of a void formed at a central portion of the steel material is 0.7 or more, and
wherein the steel material has a tensile strength of 515 MPa or more, and a Charpy impact absorption energy at −50° C. of 239 J or more.
2 . The steel material of claim 1 , wherein the steel material comprises a composite structure of ferrite having an area fraction of 70% or more and the balance pearlite.
3 . The steel material of claim 2 , wherein an average crystal grain size of the ferrite is 40 μm or less.
4 . The steel material of claim 1 , wherein the steel material has a hydrogen induced cracking crack length ratio (CLR) of 5% or less.
5 . The steel material of claim 1 , wherein the steel material has a thickness of 50 to 200 mm.
6 . The steel material of claim 3 , wherein the steel material has a hydrogen induced cracking crack length ratio (CLR) of 5% or less,
wherein the steel material has a thickness of 50 to 200 mm, and
wherein the steel material is manufactured (i) at a reduction ratio per pass of 5% or less, (ii) by cooling to a temperature of 400 to 600° C. at a cooling rate of 27 to 60° C./s, and (iii) by a normalizing heat treatment.