Development of Mn-Cr-(C-N) Corrosion Resistant Twinning Induced Plasticity Steels: Thermodynamic and Diffusion Calculations, Production, and Characterization

In this work, the development of corrosion-resistant twinning induced plasticity steels is presented, supported by thermodynamic and diffusion calculations within the (Fe-Mn-Cr)-(C-N) alloy system. For the calculations, ambient pressure and primary austenitic solidification were considered as necessary to avoid nitrogen degassing in all processing steps. Manganese is used as an austenite stabilizer, chromium is used to increase nitrogen solubility and provide corrosion resistance, and carbon and nitrogen are used as interstitial elements to provide mechanical strength. Isopleths of the different elements vs temperature as well as isothermal sections were calculated to determine the proper amount of Mn, Cr, total interstitial content, and the C/N ratio. Scheil and diffusion calculations were used to predict the extent of microsegregations and additionally to evaluate the effect of diffusion annealing treatments. The materials were produced in laboratory scale, being followed by thermomechanical processing and the characterization of the microstructure. Tensile tests were performed with three different alloys, exhibiting yield strengths of 460 Mpa to 480 MPa and elongations to fracture between 85 pct and 100 pct.