Avaliação da suscetibilidade à fragilização por hidrogênio em aços avançados de alta resistência aplicados na indústria automotiva

Abstract

Hydrogen embrittlement has become a major challenge in the application of advanced high-strength steels (AHSS) in the automotive industry. Hydrogen uptake may occur throughout the material lifecycle, particularly during pickling, annealing, galvanizing, welding, and phosphating processes. The issue becomes more critical under mechanical shearing conditions, since the high dislocation density and microvoids generated at sheared edges promote localized hydrogen accumulation and abrupt fracture. Therefore, evaluating hydrogen effects under sheared-edge conditions is essential to assess the susceptibility of AHSS to hydrogen embrittlement. In this study, the hydrogen embrittlement behavior of DP1200 and TRIP1000 steels was investigated considering different edge-cutting conditions obtained by varying the punching clearance. A new methodology was proposed to enable ex-situ hydrogen charging at controlled levels, followed by constant load (CLT) and slow strain rate (SSRT) mechanical testing. Increased cutting clearance, associated with greater local deformation and the presence of microvoids, resulted in higher susceptibility to hydrogen embrittlement in both steels. Under favorable cutting conditions (12% clearance), the critical hydrogen contents were 0.27 ppm for DP1200 and 0.61 ppm for TRIP1000. However, when the clearance was increased to 25%, corresponding to reduced edge‑stretching capability, the critical hydrogen thresholds dropped significantly, reaching levels below 0.27 ppm for DP1200 and 0.24 ppm for TRIP1000. These findings highlight the importance of strict edge‑quality control, particularly for electro‑galvanized products. In this context, especially for DP1200, which showed greater sensitivity to this failure mode, post‑processing strategies, such as thermal desorption treatments, may be required to reduce hydrogen content and mitigate edge‑cracking risk during the service. The hydrogen effect on fatigue and weldability was also assessed. Stress‑controlled fatigue tests revealed hydrogen‑assisted embrittlement in both steels, although fatigue‑life reductions were more consistent for DP1200. Early crack nucleation was linked to the enhanced interaction between hydrogen and inclusions, which functioned as preferential initiation sites. In resistance spot welds (RSW), hydrogen promoted more brittle fracture modes without significantly affecting joint strength. Overall, these findings contribute to advancing the understanding of hydrogen embrittlement mechanisms in AHSS designed for automotive applications.