Mechanical and Corrosion Properties of a Duplex Steel Welded using Micro-Arc or Laser

Abstract

Duplex stainless steels have been extensively used in parts that are subject to corrosive environments and that have high mechanical strength requirements. Welding usually distorts the well-balanced austenite-ferrite ratio, and can produce brittle intermetallic phases; therefore, post-welding heat treatments are usually required. For applications where post-welding treatments are not possible, low heat input methods, such as micro-tungsten inert gas welding (TIG) and laser beam welding (LBW), can be used. The present investigation analyzed the microstructure, mechanical, and corrosion properties of 2507-classduplex steel tubes after welding. The microstructures of the heat-affected zones and the fusion zones contained variable amounts of ferrite and austenite. In the heat-affected and fusion zones in the TIG samples, the microstructures were primarily composed of ferrite grains with allotriomorphic austenite at the grain boundaries, intragranular Widmanstätten needles and plate-like precipitates. The LBW samples showed much finer microstructures, which contained austenite in the grain boundaries and fine austenite precipitates in the ferrite grains. Deleterious intermetallic phases, such as σ-phases, were not observed using X-ray diffraction. The tensile strength properties were very similar for the TIG and LBWsamples, reaching tensile strengths of approximately 840 MPa and total elongations between 61 and 87%. The heat-affected zone of the TIG welds were particularly susceptible to corrosion (0.05 mm/year) compared to the base metal (0.007 mm/year) and the laser welds (0.01 mm/year). Therefore, laser welding is a promising technique for the welding of 2507-class duplex tubes.

Microstructural and Corrosion Properties of Cold Rolled Laser Welded UNS S32750 Duplex Stainless Steel

“…Microhardness evolution in the welded region, in the heat affected zone and in the base material is depicted in Figure 7. Microhardness of the base material (blue line) it is clear the ascending trend due to strain hardening which lead to generation and interaction of dislocations, causing an inevitable increase in hardness [30,43,44]. The microhardness in the welded region is approximately 300 HV and it is not related to the different thickness reduction.…”

“…Because of this remarkable cooling rate, the HAZ (region between dashed lines in Figure 3) was almost undetectable. The temperature reached in the weld zone was supposed to be approximately 1400 °C [8] even though some researchers found to be as high as 1800 °C [30]. One of the weld's critical regions is the HAZ, depicted in Figure 3.…”

Influence of Ferrite Phase Content on the Electrochemical Properties of Duplex Stainless Steels

“…11,12 From an economical viewpoint it is therefore of great importance to develop alloys with a lower content of this element. In the duplex stainless steels, a small decrease in the amount of Ni in the alloy affects the relationship between the austenite and ferrite phase, increasing the content of the latter.…”

Effect of Heat Sink and Cooling Mediums on Ferrite Austenite Ratio and Distortion in Laser Welding of Duplex Stainless Steel 2205

“…Figure 5(a) shows the presence of very narrow heat affected zone formed during the laser welding process. Due to the faster cooling rate, the HAZ is invisible in laser welding of DSS sheets [32]. Due to the sudden cooling in laser welding, the microstructure has small equiaxed ferrite with allotriomorphic austenite.…”