RESUMO Os aços avançados de alta resistência (AHSS) têm evoluído nas últimas décadas, consolidando-se como materiais amplamente utilizados na indústria automotiva. Entre os AHSS, destaca-se o aço 22MnB5, que, por meio da estampagem a quente, é moldado em geometrias complexas, alcançando altos valores de resistência mecânica. O resultado é um aço com microestrutura formada por martensita e vestígios de bainita, conferindo elevada capacidade de absorção de energia, ideal para aplicações que exigem alta resistência e durabilidade. O presente trabalho apresenta a caracterização mecânica e microestrutural do aço 22MnB5 estampado a quente e soldado a laser, comparada ao material base. A soldagem propiciou um aumento da resistência à tração, especialmente no limite de escoamento, que apresentou incremento de cerca de 10%, enquanto o limite de resistência à tração aumentou aproximadamente 3%. A dureza da zona fundida e do material base variou em torno de 500 HV, enquanto a zona termicamente afetada apresentou um amolecimento, atingindo cerca de 350 HV. Apesar das mudanças localizadas na microestrutura e da redução de cerca de 50% no alongamento total, comprovou-se a viabilidade da soldagem do aço 22MnB5 com laser de fibra e dois passes opostos.

ABSTRACT Advanced high-strength steels (AHSS) have evolved over the past decades, establishing themselves as widely used materials in the automotive industry. Among the AHSS, the 22MnB5 steel stands out, which, through hot stamping, is shaped into complex geometries, achieving high mechanical strength values. The result is a steel with a microstructure formed by martensite and traces of bainite, providing high energy absorption capacity, ideal for applications requiring high strength and durability. This study presents the mechanical and microstructural characterization of hot-stamped and laser-welded 22MnB5 steel, compared to the base material. Welding led to an increase in tensile strength, especially in the yield strength, which showed an increase of approximately 10%, while the ultimate tensile strength increased by about 3%. The hardness of the fusion zone and the base material varied around 500 HV, while the heat-affected zone exhibited softening, reaching approximately 350 HV. Despite localized changes in the microstructure and a reduction of about 50% in total elongation, the feasibility of welding 22MnB5 steel with fiber laser and two opposite passes was demonstrated.

A new welding method which allows the assembly of two titanium nitride coated titanium parts is proposed. The welding procedure utilizes the possibility for pulse-shaping in order to change the energy distribution profile during the laser pulse. The pulse-shaping is composed of three elements: a) a short high power pulse for partial ablation at the surface; b) a long pulse for thermal penetration; and c) a quenching slope for enhanced weldability. The combination of these three elements produces crack-free welds. The weld microstructure is changed in comparison to normal welding, i.e. with a rectangular pulse, as the nitrogen and the microhardness are more homogenously distributed in the weld under pulse-shaping conditions. This laser pulse dissolves the TiN layer and allows nitrogen to diffuse into the melt pool, also contributing to an enhanced weldability by providing suitable thermal conditions.

The influence of laser parameters in welding aluminum alloys was studied in order to reduce hot cracking. The extension of cracks at the welding surface was used as a cracking susceptibility (CS) index. It has been shown that the CS changes with changing welding velocity for binary Al-Cu alloys. In general, the CS index increased until a maximum velocity and then dropped to zero, generating a typical lambda-curve. This curve is due to two different mechanisms: 1) the refinement of porosities with increasing velocity and 2) the changes in the liquid fraction due to decreasing microsegregation with increasing velocities.