Chemically-patterned steels

A new type of microstructure design concept for high strength steels, consisting of a nanolaminate of martensite and austenite, was recently proposed using an approach termed ‘chemical patterning’. This approach generates a controlled chemical pattern in the austenite and then uses that pattern as the template for subsequent phase transformations during austenite decomposition. This approach allows access to new types of microstructures not previously utilised for alloy design. In this contribution, a computational thermodynamic and kinetic model to simulate the chemical patterning process is presented and it is shown to describe well the experimental variation in retained austenite fraction as a function of the temperature of the chemical patterning process. This model is sufficiently robust that it can be used for coupled alloy and process design and is used to design two new chemically-patterned alloys containing 30% and 50% retained austenite, respectively. The success of the model has been experimentally confirmed with two new chemically-patterned steels with higher austenite fraction, ∼30% for Fe-0.5C-6Mn-1.5Si (wt.%) and ∼50% for Fe-0.65C-6Mn-0.5Si-1Al (wt.%). Tensile, compressive and abrasive wear results are shown to demonstrate the interesting performance that can be obtained from these new types of microstructures.