Tribo-Behavior and Corrosion Properties of Welded 304L and 316L Stainless Steel

The present study investigates the electrochemical corrosion response and tribo-behavior of 304L and 316L stainless steel welded by gas metal arc welding (GMAW), which offered a high deposition rate. During this research, the metallurgically prepared welded samples were subjected to a tribological test and a corrosion test. The wear results were favorable for 316L steel, and it showed a lower coefficient of friction than the 304L specimen. These samples also underwent characterization studies, such as X-ray diffractometry (XRD) and scanning electron microscopy (SEM), to identify the different phases obtained on the cooling of the weld pool. Finally, both specimens were compared against their mechanical properties. Owing to the above properties, the 316L sample showed lasting durability, as compared to the 304L steel. The primary compositional difference is the higher presence of molybdenum and chromium in the 316L steel, compared to the 304L stainless steel.

Metallurgy and Mechanism of Underwater Wet Cutting Using Oxidizing and Exothermic Flux-Cored Wires

This paper considers the metallurgical processes of dissociation, ionization, oxidation, deoxidation, and dissolution of oxides during underwater wet cutting. A multiphase mechanism of underwater wet cutting consisting of working and idle cycles of the electrical process in a pulsating vapor gas bubble is proposed. A model of arc penetration into metal due to metal oxidation and stabilization of the arc by the inner walls of a narrow kerf is proposed. For underwater cutting of 10 KhSND, 304L steel, CuAl5, and AlMg4.5Mn0.7 alloy, we provide a principle of modeling the phase composition of the gas mixture based on high oxygen concentration, improving ionization, enthalpy, heat capacity, and thermal conductivity of plasma through the use of a mixture of KNO3, FeCO3, and aluminum. The method of improving the thermophysical properties and ionization of plasma due to the exothermic effect when introducing Fe3O4, MoO2, WO2 oxides and Al, Mg, Ti deoxidizers is proposed. Although a negative effect of refractory slag was revealed, it could be removed by using the method of reducing surface tension through the ionic dissolution of refractory oxides in Na3AlF6 cryolite. In underwater cutting of 10 KhSND and 304L, the steel welding current was 344–402 A with a voltage of 36–39 V; in cutting of CuAl5 and AlMg4.5Mn0.7 alloy, the welding current was 360–406; 240 A, with a voltage of 35–37; 38 V, respectively, with the optimal composition of flux-cored wire: 50–60% FeCO3 and KNO3, 20–30% aluminum, 20% Na3AlF6. Application of flux-cored wires of the KNO3-FeCO3-Na3AlF6-Al system allowed stable cutting of 10KhSND, AISI 304L steels, and CuAl5 bronze with kerf width up to 2.5–4.7 mm.

Exhaust system piping made by hydroforming: relations between stresses, microstructure, mechanical properties and surface

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.