Physical Simulation of Press Hardening of TRIP Steel
Deformation-induced martensitic transformation is used for improving mechanical properties of AHS steels which contain metastable retained austenite. TRIP steels are one of the categories that fall into this group. Their microstructures consist of proeutectoid ferrite, bainite, and metastable retained austenite. Cold working causes retained austenite in these steels to transform to deformation-induced martensite. A technical complication to their treatment routes is the isothermal holding stage. At this stage, bainite forms and retained austenite becomes stabilized which is the key aspect of the process. A CMnSi-type low-alloy steel with 0.2% carbon was subjected to various experimental cooling sequences which represented press hardening operations at tool temperatures ranging from 500 °C to room temperature, followed by isothermal holding in the bainitic transformation region. By varying the cooling parameters, one can obtain a broad range of mixed martensitic-bainitic structures containing retained austenite, with strengths in the vicinity of 1300 MPa, and A20 elongation levels of 10%.
KeywordsPress hardening TRIP steel Retained austenite Two step etching EBSD
This paper includes results created within the project TG02010011 Promoting Commercial Opportunities of UWB, sub-project TRIPIAL Transformation Induced Plasticity Isothermal Annealing Less. The project belongs to the GAMA programme and is subsidised from specific resources of the state budget for research and development through the Technology Agency of the Czech Republic.
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