Cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability
The present disclosure provides a cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability, including, by weight: carbon (C): 0.0005 to 0.003%, manganese (Mn): 0.20 to 0.50%, aluminum (Al): 0.01 to 0.10%, phosphorus (P): 0.003 to 0.020%, nitrogen (N): 0.0005 to 0.004%, sulfur (S): 0.015% or less, niobium (Nb): 0.005 to 0.040%, chromium (Cr): 0.10 to 0.50%, tungsten (W): 0.02 to 0.07%, and a balance of iron (Fe) and other inevitable impurities, wherein C, Nb, and W satisfy the following relationship 1, a microstructure comprises 95 area % or more of polygonal ferrite and 5 area % or less of acicular ferrite, and the cold-rolled steel sheet comprises (Nb,W)C-based precipitates having an average size of 0.005 to 0.10 μm and a method for manufacturing the same: 0.00025≤(2×Nb/93)×(W/184)/(C/12)≤0.0015 [Relationship 1] where, C, Nb, and W are in weight %.
1. A cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability, comprising, by weight: carbon (C): 0.0005 to 0.003%, manganese (Mn): 0.20 to 0.50%, aluminum (Al): 0.01 to 0.10%, phosphorus (P): 0.003 to 0.020%, nitrogen (N): 0.0005 to 0.004%, sulfur (S): 0.015% or less, niobium (Nb): 0.005 to 0.040%, chromium (Cr): 0.10 to 0.50%, tungsten (W): 0.02 to 0.07%, and a balance of iron (Fe) and other inevitable impurities,
wherein C, Nb, and W satisfy the following relationship 1,
a microstructure comprises 95 area % or more of polygonal ferrite and 5 area % or less of acicular ferrite, and
the cold-rolled steel sheet comprises (Nb,W)C-based composite precipitates having an average size of 0.005 to 0.10 μm:
0.00025≤(2×Nb/93)×(W/184)/(C/12)≤0.0015 [Relationship 1]
where, C, Nb, and W are in weight %.
2. The cold-rolled steel sheet according to claim 1 , wherein the cold-rolled steel sheet comprises an alloyed plating layer on at least one surface thereof.
3. The cold-rolled steel sheet according to claim 2 , wherein the alloyed plating layer is a Fe—Ni alloyed plating layer.
4. The cold-rolled steel sheet according to claim 3 , wherein the Fe—Ni alloyed plating layer has an alloying rate of 5 to 25 area %,
where the alloying rate refers to a fraction of a compounded layer of Fe and Ni, composed of FeNi 2 generated at an interface between Fe and Ni among all Ni plating layers.
5. The cold-rolled steel sheet according to claim 1 , wherein the cold-rolled steel sheet has a thickness of 0.1 to 0.5 mm.
6. The cold-rolled steel sheet according to claim 1 , wherein the cold-rolled steel sheet is in a form of a battery case of a secondary battery.