Abstract
Development of high strength or even ultra-high strength steels is mainly driven by the automotive industry which strives to reduce the weight of individual parts, fuel consumption, and CO2 emissions. Another important factor is to improve passenger safety. In order to achieve the required mechanical properties, it is necessary to use suitable heat treatment in addition to an appropriate alloying strategy. The main problem of these types of treatments is the isothermal holding step. For TRIP steels, the holding temperature lies in the field of bainitic transformation. These isothermal holds are economically demanding to perform in industrial conditions. Therefore new treatments without isothermal holds, which are possible to integrate directly into the production process, are searched. One way to produce high-strength sheet is the press-hardening technology. Physical simulation based on data from a real-world press-hardening process was tested on CMnSi TRIP steel. Mixed martensitic-bainitic structures with ferrite and retained austenite (RA) were obtained, having tensile strengths in excess of 1000 MPa.
Highlights
Advanced high-strength steels (AHSS) are a promising group of materials for the automotive industry
Development of high strength or even ultra-high strength steels is mainly driven by the automotive industry which strives to reduce the weight of individual parts, fuel consumption, and CO2 emissions
3 Results and discussion The regime, which was a physical simulation of press hardening in a tool at room temperature (RT), where the cooling rate was 100°C, produced a martensitic microstructure with some ferrite and 3% retained austenite (RA) (Fig. 3a)
Summary
Advanced high-strength steels (AHSS) are a promising group of materials for the automotive industry. Since most of them are multiphase materials that benefit from a number of strengthening mechanisms, considerably wide ranges of mechanical properties can be attained [1,2,3] They enable the car body weight and fuel consumption to be reduced while improving crash safety [4, 5]. TRIP (TRansformation Induced Plasticity) steels, which possess a good combination of strength and ductility, fall into this group [8, 9] Their microstructures consist of ferrite, carbide-free bainite and retained austenite (RA) [8,9,10,11,12,13,14,15]. If the multiphase microstructure and the desired mechanical properties are to be obtained, various cooling regimes in press hardening need to be tested
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