Cold rolled and annealed steel sheet and method of manufacturing the same
AssigneeArcelorMittal
InventorsKangying Zhu, Astrid Perlade, Coralie Jung, Frederic Kegel
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Abstract
A cold-rolled and heat-treated steel sheet having a microstructure of, in surface fraction: between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite Austenite islands having a size above 0.5 μm, at most 10% of fresh martensite and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A manufacturing method thereof is also provided.
Claims21
A cold-rolled and heat-treated steel sheet, made of a steel having a composition comprising by weight percent:
- C:
- 0.03-0.25%
- Mn:
- 3.5-8%
- Si:
- 0.1-2.0%
- Al:
- 0.03-2.0%
- Ti≤0.080%
- Nb≤0.080%
- V≤0.2%
- V+Ti+Nb>0.01%
- S≤0.010%
- P≤0.020%
- N≤0.008%
- and optionally including at least one of the following elements, in weight percentage:
- Mo:
- 0.1-0.5%
- Cr:
- 0.01-1%
- B:
- 0.0005-0.004%
- a remainder of the composition being iron and unavoidable impurities resulting from processing,
- the cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction:
- between 10% and 30% of retained austenite, the retained austenite being present as austenite films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite Austenite islands having a size above 0.5 μm,
- at most 10% of fresh martensite, and
- balance with recovered martensite containing precipitates of at least one element chosen from the group consisting of:
- niobium, titanium and vanadium.
Dependencies are inferred from the claim text.