Computational Design of a Novel Medium-Carbon, Low-Alloy Steel Microalloyed with Niobium

Abstract

The design of a new steel with specific properties is always challenging owing to the complex interactions of many variables. In this work, this challenge is dealt with by combining metallurgical principles with computational thermodynamics and kinetics to design a novel steel composition suitable for thermomechanical processing and induction heat treatment to achieve a hardness level in excess of 600 HV with the potential for good fracture toughness. CALPHAD-based packages for the thermodynamics and kinetics of phase transformations and diffusion, namely Thermo-Calc ® and JMatPro ® , have been combined with an interdendritic segregation tool (IDS) to optimize the contents of chromium, molybdenum and niobium in a proposed medium-carbon low-manganese steel composition. Important factors taken into account in the modelling and optimization were hardenability and as-quenched hardness, grain refinement, and alloying cost. For further investigations and verification, the designed composition, i.e. in wt.% 0.40C, 0.20Si, 0.25Mn, 0.90Cr, 0.50Mo, was cast with two nominal levels of Nb: 0 and 0.012 wt.%. The results showed that an addition of Nb decreases the austenite grain size during casting and after slab reheating prior to hot rolling. Validation experiments showed that the predicted properties i.e. hardness, hardenability and level of segregation for the designed composition were realistic. It is also demonstrated that the applied procedure could be useful in reducing the number of experiments required for developing compositions for other new steels.

Dissimilar Laser Welding of Austenitic Stainless Steel and Abrasion-Resistant Steel: Microstructural Evolution and Mechanical Properties Enhanced by Post-Weld Heat Treatment

“…We utilized MATLAB software, along with the MTEX texture and the crystallographic toolbox, to reconstruct the original austenite grains, i.e., prior austenite grain (PAG), which transformed into martensite during solidification of the melt pool of the weld zone, as described in [ 20 , 21 ].…”

Characterization of the Microstructure and Precipitates Formed During the Thermomechanical Processing of a CrNiMoWMnV Ultrahigh‐Strength Steel

“…The filtering value is 3 pixels, which means that the smallest grain size included in the calculation of the mean EGS is 0.22 μm. Using EBSD data, the original prior austenite grains were reconstructed using MATLAB software with the aid of the MTEX texture and crystallographic analysis toolbox, as described by Javaheri et al . and Nyyssönen et al …”

Effect of cooling rate and composition on microstructure and mechanical properties of ultrahigh-strength steels

“…To determine the prior austenite grain size, different EBSD runs were performed at low magnification with an accelerating voltage of 15 kV, a magnification of 500 and a step size of 0.65 lm. To reveal prior austenite grain (PAG) structure, EBSD orientation data were used to reconstruct the prior austenite using MATLAB software combined with the MTEX texture and crystallographic analysis toolbox [16][17][18]. The linear intercept method was then used to determine prior austenite grain size (PAGS) from the reconstructed image.…”