Boron-manganese steel 22MnB5 is extensively used in structural automotive components. Knowledge about its microstructural evolution during hot stamping and resistance spot welding (RSW) is extremely relevant to guarantee compliance with application requirements. Particularly, corrosion properties are critical to the application of uncoated sheet steels. However, microstructural studies are usually simplified to top-hat geometries, which might not be fully representative of the complex thermomechanical cycles locally faced by a real component. Therefore, the present work brings an extensive characterization of a hot-stamped 22MnB5 automotive B-pillar in terms of microstructure, hardness and corrosion resistance, which were correlated with a reverse engineering of the process using numerical simulation. Physical simulations of the subcritical heat affected zone (SCHAZ) of RSW were done to assess the influence of microstructure on martensite tempering. Results showed that the component undergoes a complex strain distribution along its body during hot stamping. Most heavily strained regions presented higher amounts of ferrite, leading to poorer corrosion resistance, since ferrite behaves as an anode. Physical simulations of the SCHAZ showed that the softening degree due to martensite tempering is solely affected by peak temperature, while other microstructural features appear to exert negligible or no influence.

Super-duplex stainless steels (SDSSs) were introduced in the oil and gas industry due to their high resistance to pitting corrosion, promoted by the high content of alloying elements. The welding process can cause an unbalanced ferrite/austenite microstructure and, consequently, the possibility of deleterious phases, increasing the risk of failure. The aim of this work is to investigate the behavior of the heat-affected zone (HAZ) of SDSS UNS S32750 steel produced with different thermal inputs simulated in a Gleeble^® welding simulator and correlate these findings with its corrosion properties. The pitting resistance was investigated by electrochemical techniques in sodium chloride solution, and the critical pitting temperature (CPT) was calculated for each evaluated microstructure. The material as received presents 46.19 vol% ferrite and a high corrosion resistance, with a CPT of 71.54 °C. HAZ-simulated cycles resulted in similar ferrite percentages, between 54.09 vol% and 57.25 vol%. A relationship was found between heat input, ferrite content, and CPT: increasing the heat input results in greater ferrite content and lowers the CPT, which may favor the pitting corrosion process. Therefore, it is concluded that the ferrite content directly influences the pitting behavior of the material.

This study investigates the influence of ferroniobium (FeNb) lump size and dissolution temperature on the dissolution kinetics, microstructure, and resulting mechanical and corrosion properties of a Nb-stabilized austenitic stainless steel (AISI 347). FeNb was added to an AISI 304 base steel under three distinct dissolution conditions involving variations in lump size (25–30 mm and 45–50 mm) and temperature (1560–1590 °C and 1610–1630 °C). Dissolution kinetics were monitored via time-resolved chemical analysis, while microstructural evolution was characterized by scanning electron and optical microscopy and thermodynamic simulations. Mechanical performance was assessed through tensile and impact testing, and corrosion resistance was evaluated via potentiodynamic polarization in chloride solution. Results indicate that lump size and dissolution temperature affect features such as niobium carbonitrides morphology, delta ferrite stability and austenitic matrix composition. These features strongly influence mechanical behavior, with the best combination of strength, ductility and toughness observed in the condition containing fragmented carbonitrides, retained delta ferrite and solid solution strengthening enhanced by niobium and silicon, yielded by coarse lump dissolution at lower temperatures. Corrosion resistance presented a complex dependence on these features, being strongly affected by the presence of microgalvanic cells. The findings highlight the critical role of dissolution conditions in tailoring the performance of Nb-stabilized stainless steels.