Cooling rate dependence of properties in a Si rich advanced high strength steel

ABSTRACT

The possibility to produce third-generation advanced high strength grades from a Fe-0.22C-2.1Mn-1.0Si steel through continuous cooling was explored. A large amount of retained austenite is formed at medium cooling rates ranging from 1°C/s to 15°C/s due to the fact that C enrichment in the austenite occurs because the high content of Si inhibits the formation of pearlite. A multi-phase microstructure including ferrite, bainite, martensite and retained austenite is obtained when the cooling rate is in between 5°C/s and 40°C/s. A grade of steel with an ultimate tensile strength of 1200 MPa, a total elongation of 8% and a hole expansion capacity of 20% can be obtained with a cooling rate of 15–20°C/s. Third generation high strength grades with enhanced formability cannot be obtained through continuous cooling process with the current composition as the size of the bainitic ferrite are too large and the stability of the retained austenite is too low.

KEYWORDS:

• Advanced high strength steel
• continuous cooling transformation
• CCT diagram
• tensile property
• hole expansion capacity

Disclosure statement

No potential conflict of interest was reported by the author(s).