There is an increasing demand for welding of steel pipes meant for pressure purposes. P355NH (1.0473) steel became an important construction material used for structuring and restructuring of a medium-pressure gas pipeline due to its properties, such as significant tensile strength at the level of 600 MPa and increased yield point. These properties ensure appropriate service life of the principal pipeline structures. When welding P355NH steel, processes that enable high-quality welds without significant changes in the chemical composition of the base material, are applied. It is recommended to use the TIG welding process to produce joints, although P355NH steel joints are considered as difficult to weld. During welding, various welding defects might appear, which mainly include sticking and lack of fusion. Creation of joints with the desired properties, including those used in the construction of medium pressure gas pipelines, with the required class B quality, requires selection of appropriate parameters and compliance with the welding process practice. This is very important for the service life of the structure. Therefore, the article aims to select the most appropriate parameters and thermodynamic conditions for welding P355NH steel in order to obtain the best mechanical properties. The most important of the tested welding parameters of P355NH steel is welding speed, welding current, preheating temperature, interpass temperature and, above all, the role of various shielding gases. (Three different shielding gases containing argon and helium additives were tested.) The obtained joints were tested by: non-destructive tests, such as VT—visual examination; MT—magnetic particle testing, PT—penetration tests, UT—ultrasonic testing and by the destructive methods, such as tensile strength, impact toughness, bending test, light microscopy and scanning electron microscopy. The cause-and-effect relationships between the obtained joint structure and its mechanical properties were determined. The considerations were supported by the nucleation model and the mechanisms of formation of the acicular ferrite phase in the joint material. The chosen parameters of TIG process allow to obtain joint with adequate strength for the production of the gases pipeline, without welding defects. The results have a practical implication, the developed production technology for the obtaining the joints. The presented solution gives the possibility of producing correct welded joints, which can be used in the responsible steel construction. The originality of manuscript is the presentation the newly, uncomplicated solution of obtaining joint with good mechanical properties included the thin-walled tubular structure with a thickness of 3.6 mm. A novelty in the article is a clear indication of the importance of detailed thermodynamic welding conditions and obtained weld structure on the mechanical properties of the P355NH steel joint, which lead to the formation of various non-metallic titanium inclusions, which have a decisive impact on the mechanical properties of the joint, especially its strength and impact strength.

对用于压力用途的钢管焊接的需求不断增加。 P355NH（1.0473）钢因其具有600 MPa级的显着抗拉强度和较高的屈服点等特性，成为中压天然气管道结构和改造的重要建筑材料。这些特性确保了主要管道结构的适当使用寿命。焊接 P355NH 钢时，所采用的工艺可实现高质量焊接，且不会显着改变母材的化学成分。尽管 P355NH 钢接头被认为难以焊接，但仍建议使用 TIG 焊接工艺来生产接头。焊接过程中可能会出现各种焊接缺陷，主要包括粘连和未熔合等。创建具有所需性能的接头（包括用于建造中压天然气管道的接头）以及所需的 B 级质量，需要选择适当的参数并遵守焊接工艺实践。这对于结构的使用寿命非常重要。因此，本文旨在选择最合适的焊接参数和热力学条件来焊接P355NH钢，以获得最佳的力学性能。 P355NH钢的测试焊接参数中最重要的是焊接速度、焊接电流、预热温度、层间温度，以及最重要的是各种保护气体的作用。 （测试了三种不同的含有氩气和氦气添加剂的保护气体。）所获得的接头通过以下方式进行测试：无损测试，例如VT——目视检查； MT—磁粉检测、PT—渗透测试、UT—超声波测试以及破坏性方法，如拉伸强度、冲击韧性、弯曲测试、光学显微镜和扫描电子显微镜。确定了所获得的接头结构与其机械性能之间的因果关系。这些考虑得到了接头材料中针状铁素体相的成核模型和形成机制的支持。 TIG 工艺的所选参数允许获得具有足够强度的接头来生产气体管道，并且没有焊接缺陷。结果对于获得接头所开发的生产技术具有实际意义。所提出的解决方案提供了生产正确焊接接头的可能性，该焊接接头可用于负责任的钢结构。手稿的独创性在于提出了获得具有良好机械性能的接头的新的、简单的解决方案，包括厚度为 3.6 毫米的薄壁管状结构。本文的新颖之处在于清楚地表明了详细的热力学焊接条件和获得的焊缝结构对 P355NH 钢接头机械性能的重要性，导致各种非金属钛夹杂物的形成，对接头的力学性能，特别是其强度和冲击强度具有决定性的影响。