The subject of research is car exhaust system piping made of chromium–nickel steel of grade AISI304L with a unique, complex shape that was obtained by hydroforming technology. The purpose of the research was to determine the relation between the microstructure features, surface condition, hardness and the stresses on the external surface as determined by the sin²ψ X-ray method. We found that the stresses were tensile and correlated with the steel hardness, i.e. they were greater where the hardness was higher. Moreover, longitudinal stresses showed a relationship with pipe wall thickness, while circumferential stresses did so only partially. According to our data, the greatest value of stress determined in the pipe amounted to 290 MPa, and was close to the yield point of the strain hardened 304L steel. As depicted via XRD and SEM examination, the pipe stress level and hardness were influenced by the transition γ→α’. Furthermore, in the region of higher stress and hardness, the amount of martensite was 10 vol.%. We also noted that the pipe’s outer surface when subjected to friction against the die shows lesser roughness compared to its inner surface upon exposure to water under pressure.

研究的主题是由AISI304L等级的铬镍钢制成的汽车排气系统管道，其独特而复杂的形状是通过液压成型技术获得的。该研究的目的是确定由sin ²确定的微观结构特征，表面状况，硬度和外表面应力之间的关系。X X射线法。我们发现应力是拉伸应力，并且与钢的硬度相关，即，硬度越高，应力越大。此外，纵向应力显示出与管壁厚度的关系，而周向应力仅部分显示出这种关系。根据我们的数据，在管道中确定的最大应力值为290 MPa，接近应变硬化304L钢的屈服点。如通过XRD和SEM检查所描绘的那样，管道的应力水平和硬度受转变γ→α'的影响。此外，在应力和硬度较高的区域中，马氏体的含量为10体积％。我们还注意到，与压力作用下的管子内表面相比，管子的外表面在与模具摩擦时表现出的粗糙度要小。