The present invention related to a structural steel sheet having excellent seawater resistance and having excellent corrosion resistance in environments in which corrosion is accelerated by seawater, and a method for manufacturing same.

The present disclosure relates to a thick steel material that can be appropriately used as a line pipe, a sour-resistant material and, more particularly, to a high-strength steel material having excellent sulfide stress corrosion cracking resistance and excellent resistance against propagation of sulfide stress corrosion cracking, and a method of manufacturing the steel material.

Provided are a high-strength wire rod having high hydrogen embrittlement resistance for cold heading, and a method for manufacturing the high-strength wire rod. The high-strength wire rod for cold heading has a chemical composition including, by weight %, C: 0.3% to 0.5%, Si: 0.01% to 0.3%, Mn: 0.3% to 1.0%, Cr: 0.5% to 1.5%, Mo: 0.5% to 1.5%, V: 0.01% to 0.4%, and a balance of Fe and other impurities, and the chemical composition satisfies the relational expression 1. The high-strength wire rod for cold heading has a microstructure including, by area %, 1% to 15% martensite, 0.1% to 5% pearlite, and a balance of bainite, and the fraction of martensite formed along grain boundaries of prior austenite in the martensite of the microstructure is 60% or more.

A steel material for a vacuum tube according to an aspect of the present disclosure may include C: 0.1˜0.2%, Si: 0.05∞0.5%, Mn: 1.0∞1.6%, Ni: 0.5∞1.0%, Cr: 1.5∞4.0%, and the balance of Fe and unavoidable impurities in percentage by weight, and may have a complex structure of ferrite and pearlite as a microstructure.

An embodiment of the present invention provides a wire rod and a method of manufacturing same. The wire rod comprises, by weight %, 0.3-0.5 wt % of C, 0.02-0.4 wt % of Si, 1.0-1.5 wt % of Mn, 0.3-0.7 wt % of Cr, 0.003 wt % or less (exclusive of 0 wt %) of B, less than 0.03 wt % (exclusive of 0 wt %) of Ti, 0.03 wt % or less (inclusive of 0 wt %) of P, 0.01 wt % or less (inclusive of 0 wt %) of S, 0.02-0.05 wt % of Al, 0.001-0.01 wt % of N, and the balance being Fe and inevitable impurities, wherein a microstructure is a complex structure having a main phase of ferrite+pearlite, with at least one of bainite or martensite accounting for 5 area % or less (inclusive of 0%), and has a cementite average aspect ratio of 35 or less in an area covering ⅖-⅗ of the diameter.

Provided is a hot rolled steel sheet having a predetermined chemical composition and a microstructure comprising, by area ratio, pearlite: 90 to 100% and pro-eutectoid ferrite: 0 to 10%, wherein the pearlite has an average lamellar spacing of 0.08 to 0.30 μm, and the percentage of cementite in the pearlite having a major axis length of more than 0.3 μm and an aspect ratio of less than 3.0 is less than 15%.

Provided are a non-heat treated wire rod having high drawability and impact toughness, and a method for manufacturing the non-heat treated wire rod. The non-heat treated wire rod includes, by wt%, C: 0.02% to 0.30%, Si: 0.05% to 0.8%, Mn: 0.5% to 2.0%, Cr: 1.0% or less, P: 0.03% or less, S: 0.03% or less, sol.Al: 0.01% to 0.07%, N: from greater than 0.01% to 0.02%, Nb: 0.1% or less, V: 0.5% or less, and Ti: 0.1% or less, and a balance of Fe and inevitable impurities, wherein the non-heat treated wire rod has a microstructure including ferrite and pearlite.

Disclosed is a bearing wire rod includes, in percent by weight (wt %), 0.8 to 1.2% of C, 0.01 to 0.6% of Si, 0.1 to 0.6% of Mn, 1.0 to 2.0% of Cr, 0.01 to 0.06% of Al, 0.02% or less (exclusive of 0) of N, and the balance of Fe and inevitable impurities, wherein a prior austenite grain size of a microstructure is from 3 to 10 μm, and a sum of lengths of high angle grain boundaries having a misorientation angle of 15° or more per unit area is from 1,000 to 4,000 mm/mm.sup.2.

Disclosed are a wire rod and a component, for cold forging, each having excellent delayed fracture resistance characteristics and applicable to high-strength bolts and the like and a manufacturing method therefor.

According to an embodiment, a heat-treated component having excellent delayed fracture resistance characteristics includes, in percent by weight (wt %), 0.3 to 0.5% of C, 0.01 to 0.3% of Si, 0.3 to 1.0% of Mn, at least two types selected from the group consisting of 0.3 to 1.5% of Cr, 0.3 to 1.5% of Mo, and 0.01 to 0.4% of V, and the balance being Fe and other impurities, includes, as a microstructure, a tempered martensite phase in an area fraction of 95% or more, and includes V-based carbides having a diameter of 300 nm or less at 10/100 μm.sup.2 or more.

An embodiment of the present invention provides a steel material, for a pressure vessel, comprising, in weight %, 0.06-0.25% of carbon (C), 0.05-0.50% of silicon (Si), 1.0-2.0% of manganese (Mn), 0.005-0.40% of aluminum (Al), 0.010% or less of phosphorus (P), 0.0010% or less of sulfur (S), 0.001-0.03% of niobium (Nb), 0.001-0.03% of vanadium (V), 0.001-0.03% of titanium (Ti), 0.01-0.20% of chromium (Cr), 0.05-0.15% of molybdenum (Mo), 0.01-0.50% of copper (Cu), 0.05-0.50% of nickel (Ni), 0.0005-0.0050% of magnesium (Mg), 0.0005-0.0050% of calcium (Ca), 0.0020% or less of oxygen (O), and the remainder being Fe and other unavoidable impurities. A microstructure comprises in terms of area fraction 30% or less of pearlite and the remainder being ferrite. A non-metallic inclusion contains Mg—Al—Ca—O composite oxide.