UNS S31803 Duplex Stainless Steel Research Articles

In Situ Local Dissolution of Duplex Stainless Steels in 1 M H 2 SO 4 + 1 M NaCl by Electrochemical Scanning Tunneling Microscopy

Local dissolution behavior of duplex stainless steel UNS S32304, UNS S31803, and UNS S32750 in was studied in situ by electrochemical scanning tunneling microscopy (STM). Submicrometer features could be resolved and events occurring at phase/grain boundary regions could be monitored in the solution. By STM imaging, severe local dissolution was observed on UNS S32304 in the form of both pitting-like dissolution occurring at the active potential region, and selective dissolution of ferrite phase that already started at the corrosion potential. On UNS S31803, no pitting-like corrosion was observed, but a small amount of selective dissolution occurred at anodic potentials in the active region. The phase boundary region seemed to be prone to local dissolution. No noticeable local dissolution was observed on UNS S32750 in this solution in active and passive potential regions. The results show that a sufficient amount of both Mo and N in duplex stainless steel resulted in more homogeneous dissolution of the two phases and strengthened phase boundaries, and thus decreased the risk for local dissolution. © 2002 The Electrochemical Society. All rights reserved.

The Influence of Basic vs. Rutile Electrode on the Composition of Duplex Stainless Steel Weldments

Abstract The effects of the type of electrode coating – basic or rutile – on the composition of a welded structure made of duplex stainless steel UNS-S31803 have been investigated. It was found that when welding with an electrode having a basic coating (“basic electrode”) the covering of the slags affords better protection of the melt against the entrapment of air but is less effective in de-oxidizing it. There is, therefore, more dissolved oxygen when welding with a basic electrode, and consequently more ∊-Fe2O3 is created. On the other hand, the entrapment of air when a rutile-coated electrode (“rutile electrode”) is used leads to considerable porosity and a higher nitrogen content.

475 °C Embrittlement in a duplex stainless steel UNS S31803

The susceptibility of a duplex stainless steel UNS S31803 to thermal embrittlement at 475 °C was evaluated by means of mechanical tests (impact energy and hardness), magnetic measurements (hysteresis and thermomagnetic analysis) and scanning electron microscopy. The results show that the material undergoes severe embrittlement and hardening in the first 100 h. The corrosion resistance of the ferrite phase in a 10%HNO3 + 0.05%HF solution deteriorated after 500 h of ageing. The Curie temperature (Tc) was the most sensitive magnetic property to the microstructural changes that promote embrittlement. Tc increases with ageing time due to the progressive reduction of chromium in the Fe-rich matrix during spinodal decomposition.

Microstructure and properties following welding of duplex stainless steel using coated electrodes

The effects of the type of electrode coating – basic or rutile – on the microstructure, and strength and impact properties of a welded structure constructed from duplex stainless steel UNS–S31803 were investigated. It was found that the use of a rutile coated electrode leads to considerable porosity and a higher nitrogen content but lower oxygen, and hence less ε-Fe2O3 is created compared with weldments produced using an electrode having a basic coating. These phenomena, in turn, cause a higher volume fraction of austenite and thus a higher low temperature impact energy, as well as improved ductility; however, the yield strength is reduced compared with that following basic coated electrode welding.

Magnetic property changes during embrittlement of a duplex stainless steel

Changes in magnetic properties were used to investigate the ferrite decomposition that occurs in wrought duplex stainless steel (DSS) UNS S31803 at high (800°C) and low temperatures (475°C). At 800°C the saturation and residual induction, the coercive force and the differential permeability decrease with time, due to the increase in the austenite content. Firstly, secondary austenite (γ 2) forms in the α/α grain boundaries causing embrittlement, but not hardening. Ferrite then decomposes into σ and austenite phases (α→σ+γ 2), producing hardening and severe embrittlement. During embrittlement at 475°C, only a small increase in the coercivity was observed, even on aging up to 500 h. On the other hand, the Curie temperature increased with aging time, as a consequence of spinodal decomposition (α→α+α′). The results obtained show that the mechanical property changes of DSS UNS S31803 due to exposures at 475 and 800°C may be monitored by magnetic measurements.

Analysis of plastic deformation processes at fatigue crack tip in 18Cr10Ni austenitic stainless steel (304L): Brahmi, S., Chappuis, G. and Lehr, P. Mem. Etud. Sci. Rev. Metall. Jan. 1992 89 (1) 49–61 (in French)

This paper brings together and analyzes recent work based on the interpretation of the electrochemical measurements made on a modified micro-abrasion-corrosion tester used in several research programmes. These programmes investigated the role of abradant size, test solution pH in abrasion-corrosion of biomaterials, the abrasion-corrosion performance of sintered and thermally sprayed tungsten carbide surfaces under downhole drilling environments and the abrasion-corrosion of UNS S32205 duplex stainless steel. Various abrasion tests were conducted under two-body grooving, three-body rolling and mixed grooving-rolling abrasion conditions, with and without abrasives, on cast F75 cobalt–chromium–molybdenum (CoCrMo) alloy in simulated body fluids, 2205 in chloride containing solutions as well as sprayed and sintered tungsten carbide surfaces in simulated downhole fluids. Pre- and post-test inspections based on optical and scanning electron microscopy analysis are used to help interpret the electrochemical response and current noise measurements made in situ during micro-abrasion-corrosion tests. The complex wear and corrosion mechanisms and their dependence on the microstructure and surface composition as a function of the pH, abrasive concentration, size and type are detailed and linked to the electrochemical signals. The electrochemical versus mechanical processes are plotted for different test parameters and this new approach is used to interpret tribo-corrosion test data to give greater insights into different tribo-corrosion systems. Thus new approaches to interpreting in-situ electrochemical responses to surfaces under different abrasive wear rates, different abrasives and liquid environments (pH and NaCl levels) are made. This representation is directly related to the mechano-electrochemical processes on the surface and avoids quantification of numerous synergistic, antagonistic and additive terms associated with repeat experiments.