Steel sheet having excellent image clarity after painting
Provided is a steel sheet having excellent image clarity after painting, including: carbon (C): 0.001% to 0.03%, silicon (Si): 0.001% to 0.35%, manganese (Mn): 0.05% to 2.2%, phosphorus (P): 0.003% to 0.1%, sulfur (S): 0.001% or 0.025%, aluminum (Al): 0.01% to 0.1%, nitrogen (N): 0.001% to 0.007%, and a remainder of iron (Fe) and inevitable impurities. The microstructure of the steel sheet mainly is ferrite phases. An R-cube texture of a surface layer of the steel sheet is 5% or less by area %.
1. A steel sheet having excellent image clarity after painting, the steel sheet comprising, by wt %:
carbon (C): 0.001% to 0.03%, silicon (Si): 0.001% to 0.35%, manganese (Mn): 0.05% to 2.2%, phosphorus (P): 0.003% to 0.1%, sulfur (S): 0.001% or 0.025%, aluminum (Al): 0.01% to 0.1%, nitrogen (N): 0.001% to 0.007%, and a remainder of iron (Fe) and inevitable impurities,
wherein a microstructure of the steel sheet comprises 95% or more of ferrite phases by area %, and
an R-cube texture of a surface layer of the steel sheet is 5% or less by area %, wherein the surface layer is defined by an area from a surface of the steel sheet to a predetermined position in a thickness direction of the steel sheet.
2. The steel sheet of claim 1 , wherein the steel sheet further comprises at least one selected from the group consisting of niobium (Nb): 0.005% to 0.03% and titanium (Ti): 0.005% to 0.10%.
3. The steel sheet of claim 1 , wherein an average grain size of the surface layer is 30 μm or less.
4. The steel sheet of claim 1 , wherein a standard deviation of grain size of the surface layer is 8 μm or less.
5. The steel sheet of claim 1 , wherein, in the surface layer, a ratio of a first area fraction of a grain having a grain size of 10 μm or less to a second area fraction of a grain having a grain size of 30 μm or more is 0.5 or above, and
wherein the first area fraction and the second area fraction represent an area fraction measured in a given observable field/cross-section of the surface layer using an electron back scattered diffraction method.
6. The steel sheet of claim 1 , wherein, in the surface layer, an area fraction of a grain having an aspect ratio of 0.3 or less accounts for 15% or less, and
wherein the area fraction represents an area fraction measured in a given observable field/cross-section of the surface layer using an electron back scattered diffraction method.
7. The steel sheet of claim 1 , wherein the steel sheet further comprises a coating layer on the surface thereof,
wherein the coating layer is one of an Al-based coating layer, a Zn-based coating layer and a Zn—Al—Mg alloy-based coating layer.