Steel sheet and method for producing same
AssigneeHyundai Steel Company
InventorsChun Ku Kang, Jin Sung Park, Nam Hoon Goo, Seong Ju Kim
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Abstract
Disclosed herein are a steel sheet having excellent aging resistance and low yield ratio properties, and a method for producing the same. The disclosed sheet comprises, by weight, 0.005-0.06% carbon (C), 0.2% or less silicon (Si), 1.0-2.0% manganese (Mn), 0.08% or less phosphorus (P), 0.01% or less sulfur (S), 0.2-2.0% aluminum (Al), one or more of chromium (Cr) and molybdenum (Mo) in an amount satisfying 0.3≤[Cr wt %]+0.3[Mo wt %]≤2.0, and 0.008% or less nitrogen (N), with the remainder being iron (Fe) and inevitable impurities, and has a single-phase structure of ferrite in a hot-rolled state, and a two-phase structure of ferrite and martensite in a cold-rolled state.
Claims14
A steel sheet comprising, by weight, 0.005-0.025% carbon (C), 0.2% or less silicon (Si), 1.0-2.0% manganese (Mn), 0.08% or less phosphorus (P), 0.01% or less sulfur (S), 0.2-2.0% aluminum (Al), chromium (Cr) and molybdenum (Mo) in an amount satisfying 0.8≤[Cr wt %]+0.3[Mo wt %]≤1.5, and 0.008% or less nitrogen (N), with a remainder being iron (Fe) and inevitable impurities, the steel sheet having a two-phase structure of ferrite and martensite in a cold-rolled state,
- wherein the steel sheet shows a yield ratio (YP/TS) of 0.45 or less,
- wherein the steel sheet comprises 0.3-1.5 wt % chromium (Cr) and 0.05-0.4 wt % molybdenum (Mo), and
- wherein the steel sheet has an elongation of 38% or more and the two-phase structure has 5.0-10.0% by area of martensite with the remainder being ferrite.
A steel sheet comprising, by weight, 0.005-0.025% carbon (C), 0.2% or less silicon (Si), 1.0-2.0% manganese (Mn), 0.08% or less phosphorus (P), 0.01% or less sulfur (S), 0.2-2.0% aluminum (Al), greater than 0% chromium (Cr) and greater than 0% molybdenum (Mo) in an amount satisfying 0.8≤[Cr wt %]+0.3[Mo wt %]≤1.5, and 0.008% or less nitrogen (N), with a remainder being iron (Fe) and inevitable impurities, the steel sheet having a two-phase structure of ferrite and martensite in a cold-rolled state, wherein the steel sheet shows a yield ratio (YP/TS) of 0.45 or less,
- wherein the steel sheet has an elongation of 38% or more and the two-phase structure has 5.0-10.0% by area of martensite with the remainder being ferrite.
A method for producing a steel sheet, comprising the steps of:
- reheating a steel slab having an alloy composition by weight of 0.005-0.025% carbon (C), 0.2% or less silicon (Si), 1.0-2.0% manganese (Mn), 0.08% or less phosphorus (P), 0.01% or less sulfur (S), 0.2-2.0% aluminum (Al), one or more of chromium (Cr) and molybdenum (Mo) in an amount satisfying 0.5≤[Cr wt %]+0.3[Mo wt %]≤1.5, and 0.008% or less nitrogen (N), with a remainder being iron (Fe) and inevitable impurities, the steel sheet having a two-phase structure of ferrite and martensite in a cold-rolled state;
- hot-rolling the reheated steel slab at a temperature equal to or higher than an Ar3 point to obtain a hot-rolled steel sheet;
- coiling the hot-rolled steel sheet at a temperature between 680° C. and 750° C.;
- pickling the coiled steel sheet, then cold rolling the pickled coiled steel sheet;
- and
- annealing the cold-rolled steel sheet at a temperature between 820° C. and 850° C., followed by cooling.
Dependencies are inferred from the claim text.