Steel substrate for painted parts
AssigneeTata Steel Ijmuiden B.V.
InventorsMaxim Peter AARNTS, Job Anthonius VAN DER HOEVEN, Edgar Matthijs TOOSE
Life of this patent
Estimating the term…
Abstract
The invention relates to a steel strip, sheet or blank used for painted parts, wherein the steel strip, sheet or blank is optionally metallic coated. The steel is an Ultra Low Carbon (ULC) steel type having a composition of (in weight %): C: max 0.007 Mn: max 1.2 Si: max 0.5 Al: max 0.1 P: max 0.15 S: 0.003-0.045 N: max 0.01 Ti, Nb, Mo: if Ti≥0.005 and Nb≥0.005: 0.06≤4Ti+4Nb+2Mo≤0.60 otherwise 0.06≤Ti+2Nb+2Mo≤0.60 and one or more of the optional elements: Cu: max 0.10, Cr: max 0.06. Ni: max 0.08, B: max 0.0015, V: max 0.01, Ca: max 0.01, Co: max 0.01, Sn: max 0.01 resulting in a delta Waviness ΔWsa≤0.12 μm of the surface after the forming of the strip, sheet or blank.
Claims27
A method for producing a bake hardenable steel strip, sheet or blank used for painted parts, comprising
- hot rolling and cold rolling the steel strip, wherein the steel strip is cold rolled in a cold rolling mill and the last stand or the only stand of the cold rolling mill contains work rolls having a roughness Ra between 0.5 μm and 7.0 μm,
- wherein the steel strip, sheet or blank is optionally metallic coated,
- wherein the steel is an Ultra Low Carbon (ULC) steel type having a composition of (in weight %):
- C:
- max 0.007
- Mn:
- max 1.2
- Si:
- max 0.5
- Al:
- max 0.1
- P:
- max 0.15
- S:
- 0.003-0.045
- N:
- max 0.01
- Ti, Nb, Mo:
- if Ti≥0.005 and Nb≥0.005:
- 0.06≤4Ti+4Nb+2Mo≤0.60
- otherwise
- 0.06≤Ti+2Nb+2Mo≤0.60
- Cu:
- max 0.10
- Cr:
- max 0.06
- Ni:
- max 0.08
- B:
- max 0.0015
- V:
- max 0.01
- Ca:
- max 0.01
- Co:
- max 0.01
- Sn:
- max 0.01
- wherein C, Mn and Si are present, the remainder being iron and unavoidable impurities, having essentially equi-axed grains with a median grain size smaller than 11.0 micrometer,
- resulting in the optionally metallic coated steel strip, sheet or blank as an optionally metallic coated substrate such that a surface of a 145 mm×145 mm sample of the optionally metallic coated substrate, after forming of the sample into a cup, has a delta Waviness ΔWsa≤0.12 μm, according to a forming test wherein the cup is produced by pressing the 145 mm×145 mm sample of the optionally metallic coated steel strip, sheet or blank in a press with a hollow punch with diameter 75 mm and a blankholder force such that any material movement of the (coated) substrate between the blankholder and then die is completely suppressed, wherein deformation of the cup is such that thickness strain in a bottom of the cup is 9%+0.3%,
- wherein ΔWsa is defined as Wsa (Formed) minus Wsa (Flat), in which Wsa (Formed) is the Wsa value of the optionally metallic coated substrate surface after the forming and Wsa (Flat) is the Wsa value of the optionally metallic coated substrate surface before the forming,
- wherein Wsa is measured according to standard SEP 1941,
- wherein Wsa (Flat) is lower than 0.6 μm in rolling direction of the strip.
The method according to claim 1, wherein the work rolls of the last stand having a roughness Ra between 0.6 μm and 2.0 μm.
Dependencies are inferred from the claim text.