Influência de Ti e Nb no comportamento microestrutural e propriedades mecânicas de aços maraging submetidos a tratamentos de ciclagem térmica

Abstract

This study investigated the influence of thermal cycling above the austenitization temperature and the addition of niobium (Nb) and titanium (Ti) on grain refinement and mechanical performance of maraging steel M300. Three alloy variants (Ti, Ti+Nb and Nb) were subjected to repeated thermal cycles at 900 °C (5 and 10 cycles). Microstructural characterization was carried out using EBSD, XRD, and EDS, while mechanical behavior was evaluated through tensile testing, hardness test and fractographic analysis. EBSD results showed that five thermal cycles promoted effective refinement of prior austenite grains (< 20 μm) and an increase in high-angle grain boundaries, although Nb-containing alloys exhibited reduced refinement due to grain boundary pinning. XRD confirmed strain accumulation and crystallite refinement after five cycles, followed by partial recovery after ten cycles. EDS analyses revealed a transition from Ti-based precipitates to Nb–Mo intermetallics during cycling, with indications of incomplete dissolution in alloys containing only Nb. From a mechanical standpoint, Ti-containing alloys exhibited a significant increase in ductility (≈ 9% elongation), whereas Nb additions favored higher strength. The Ti+Nb variant stood out by providing a superior balance between hardness, strength, and toughness. Overall, these results demonstrate that controlled thermal cycling combined with Nb and Ti additions is an effective strategy to tailor microstructure and mechanical behavior for demanding engineering environments, offering promising alternatives for aerospace, offshore, and high-performance tooling applications, where refined grains and balanced mechanical properties are essential.