Cem Örnek

An experimental investigation into strain and stress partitioning of duplex stainless steel using digital image correlation, X-ray diffraction and scanning Kelvin probe force microscopy

The evolution of microstructure strain partitioning during quasi in situ tensile loading of grade 2205 duplex stainless steel has been investigated. Digital image correlation revealed the development of tensile strain initially in austenite and at interphase boundaries, and further extending into the ferrite with increasing load. Higher resolution digital image correlation observations indicated strain hardening of austenite, followed by deformation of the ferrite. Digital image correlation analysis of a 20% cold-rolled microstructure revealed tensile strain development at interphases, with discrete tensile and compressive strain pockets observed within the austenite. X-ray diffraction measurements indicated the presence of tensile stresses primarily developing in the ferrite, with full-width at half maximum values indicating plastic strain accumulation primarily in the austenite. The effect of tensile loading on Volta potential differences, obtained via scanning Kelvin probe force microscopy, highlighted the development of discrete anodic and cathodic sites with the introduction of strain. A Volta potential roughness parameter (ΨRa) is introduced describing Volta potential changes as a function of strain. This observation supports the concept of an enhanced propensity of local electrochemical activity with increasing applied strain in duplex stainless steel.

Low-Temperature Environmentally Assisted Cracking of Grade 2205 Duplex Stainless Steel Beneath a MgCl2:FeCl3 Salt Droplet

The corrosion and environmentally assisted cracking susceptibility of grade 2205 duplex stainless steel beneath a FeCl3:MgCl2-containing salt deposit has been investigated. Long-term exposure to atmospheric environment at 50°C and 30% relative humidity resulted in different forms of corrosion and the formation of cracks depending on the location under the salt-laden droplet. Selective dissolution with closely-spaced microcracks of the ferrite suggested hydrogen embrittlement toward the center of the droplet, with chloride-induced stress corrosion cracking and selective dissolution of the austenite observed toward the rim of the deposit. Cracks in the ferrite had cleavage-like appearances, typically forming within existing cracks, whereas the austenite had branched cracks, initiating from crevices and pits. These observations are discussed in light of expected electrochemical potential variations beneath the droplet.

Probing propensity of grade 2205 duplex stainless steel towards atmospheric chloride- induced stress corrosion cracking

Abstract The propensity of grade 2205 duplex stainless steel towards atmospheric chloride-induced stress corrosion cracking at 50°C has been investigated. Electron backscatter diffraction has been used to characterise as received and 750°C heat-treated microstructures. Screening tests in chloride-containing aqueous environments were employed to investigate the corrosion behaviour of both microstructures. These tests indicated significantly increased corrosion rates when exposed to HCl or FeCl3-containing environments. Stress corrosion cracking tests with atmospheric exposures for up to 12 months showed selective dissolution of the ferrite, accompanied by stress corrosion microcracks in the austenite. This work demonstrates that grade 2205 duplex stainless steel microstructure may be rendered susceptible to stress corrosion cracking under atmospheric exposure conditions at 50°C.

475°C Embrittlement of Duplex Stainless Steel—A Comprehensive Microstructure Characterization Study

The effect of 475 degrees C embrittlement on microstructure development of grade 2205 duplex stainless steel was investigated. Spinodal decomposition products and associated precipitates in ferrite ...

Time-dependent in situ measurement of atmospheric corrosion rates of duplex stainless steel wires

Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 °C (12–15 M Cl− and pH ~5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires.Stainless steel: Comprehending corrosionThe corrosion of two grades of stainless steel has been studied, in situ, under atmospheric exposure conditions. Grade ‘2205’ duplex stainless steel (DSS) has been suggested as a possible container material for the storage of intermediate-level radioactive nuclear waste in the UK because of its high resistance to corrosion and stress corrosion cracking (SCC). Now a team led by D. Engelberg from The University of Manchester, United Kingdom, have used time-lapse X-ray computed tomography to determine the corrosion rates of strained grade ‘2202’ and ‘2205’ DSS wires—over the course of 21 months—that had been exposed to a chloride-containing thin-film electrolyte. They saw that although the corrosion rate of grade 2202 DSS wires increased with time, the corrosion rate for grade 2205 decreased, confirming its superior corrosion resistance. They also observed the nucleation of SCC cracks in both grades of wire and demonstrated that duplex stainless steels can suffer from low-temperature SCC.

Additive manufacturing – a general corrosion perspective

ABSTRACT Metallic additive manufacturing will replace some materials produced by conventional fabrication methods in the nearest future. However, corrosion will remain an important aspect needed to be prevented. The corrosion behaviour of additively manufactured alloys has been sparsely studied and very little work has been published so far. In this article, a general discussion about materials produced by additive manufacturing will be provided.

Towards Understanding the Effects of Strain and Chloride Deposition Density on Atmospheric Chloride-Induced Stress Corrosion Cracking of Type 304 Austenitic Stainless Steel under MgCl2 and FeCl3:MgCl2 Droplets

Type 304 (UNS S30400) austenitic stainless steel was exposed for 6 months under elastic (0.1%) and elastic/plastic (0.2%) strain to MgCl2 and mixed MgCl2:FeCl3 droplets with varying chloride deposi...