High strength low alloy steels are employed in structural elements and, despite presenting good weldability, the welded joint is always a critical issue and its evaluation is fundamental in guaranteeing structural integrity. The mechanical properties of weld beads can be significantly different from the base material's properties due to metallurgical alterations caused by the welding process. One of the factors leading to significant impact is the heat input. This paper evaluates the hardness, fracture toughness and fatigue crack growth in weld beads obtained via a Laser process with two different heat inputs, which resulted in weld beads with distinct microstructures: one composed of ferrite presenting different morphologies and the other composed of martensite and bainite. The aims of this work are evaluating the effect of Laser welding heat input on microstructures in the weld beads, and the correlation of the microstructure with fatigue crack growth and crack-tip opening displacement fracture toughness. Fracture toughness presented itself to be more sensitive to the microstructural alterations caused by the heat input than hardness and fatigue crack growth. Weld beads showed higher resistance to fatigue crack growth when compared to the base metal, even though there were no significant differences between them.

高强度低合金钢用于结构元件，尽管具有良好的可焊接性，但焊接接头始终是关键问题，其评估对保证结构完整性至关重要。由于焊接工艺引起的冶金变化，焊缝的机械性能可能与基材的性能显着不同。导致重大影响的因素之一是热量输入。本文通过两种不同的热量输入，对通过激光工艺获得的焊道的硬度，断裂韧性和疲劳裂纹扩展进行了评估，结果发现焊道具有不同的微观结构：一种由呈现不同形态的铁素体组成，另一种由马氏体和贝氏体组成。这项工作的目的是评估激光焊接热输入对焊道中显微组织的影响，以及显微组织与疲劳裂纹扩展和裂纹尖端开口位移断裂韧性的关系。与硬度和疲劳裂纹扩展相比，断裂韧性对热输入引起的微观结构变化更敏感。与母材相比，焊缝显示出更高的抗疲劳裂纹扩展能力，即使它们之间没有显着差异。与硬度和疲劳裂纹扩展相比，断裂韧性对热输入引起的微观结构变化更敏感。与母材相比，焊缝显示出更高的抗疲劳裂纹扩展能力，即使它们之间没有显着差异。与硬度和疲劳裂纹扩展相比，断裂韧性对热输入引起的微观结构变化更敏感。与母材相比，焊缝显示出更高的抗疲劳裂纹扩展能力，即使它们之间没有显着差异。