Revisiting passivation II: electronic conduction of transition metal oxides, Mott-Schottky plots, and root cause of stainless steel grades and nickel based alloys

2018 ◽  
Vol 106 (1) ◽  
pp. 108 ◽  
Author(s):  
Jean-Louis Crolet

The novel views on passivation and passivity are briefly reviewed, with further explanation of some key details. First, the most common polymerisation mechanism directly transforms an insoluble hydroxide into a cross-linked oxide gel. The Al type passivation corresponds to insulating oxides, and this directly leads to a nearly sealed off gel with just a residual access of the electrolyte to the metal surface. In Fe type passivation, the electronic 3d shells are incomplete, which induces a coexistence of bi- and trivalent monomers, and from elsewhere well-known quantum (or magnetic) effects, a complete ordering can suddenly induce an electronic conduction at the interatomic scale. The different grades of stainless steels or Ni based alloys, and a few other paradoxical observations, are thus explained by the required conjunction of magnetic, chemical and electrochemical features. In parallel, any applied polarisation induces a junction potential at the electrolyte boundary, with electric field, ionic space charges, and local electromigration. All are cancelled in the Faraday cage of a conductive gel, but its adaptation to each potential takes some time. Therefore, the alleged “Mott-Schottky” plots do not detect the electronic space charges of a supposedly semiconductor, but just the local ionic space charges induced by artificial polarisations.

Materials ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2235
Author(s):  
Hailong Wang ◽  
Yuanjian Wu ◽  
Xiaoyan Sun ◽  
Jiayan Ling ◽  
Daoqin Zou

To evaluate the corrosion resistance of a novel stainless steel intended for use within reinforced concrete (RC) structures exposed to aggressive environments, the threshold chloride concentration of three stainless steels (316, 2205, novel 2205) and two carbon steels (HRB400, HRB500) exposed to pore solutions of fresh concrete was experimentally studied by means of electrochemical methods. The effect of steel surface state on the corrosion resistance was also experimentally investigated. The results showed that the novel stainless steel has a much higher corrosion resistance than those of the carbon steels and stainless steels when subjected to chloride environments. The presence of surface damage leads to significant decrease of corrosion resistance for carbon steel, however the corrosion can be certainly inhibited with the accumulation of rust on the steel surface. Although the oxide layer was worn, the novel 2205 stainless steel still has a great corrosion resistance.


Author(s):  
G. Ubertalli ◽  
M. Ferraris ◽  
P. Matteis ◽  
D. Di Saverio

Lean duplex stainless steels have similar corrosion and better mechanical properties than the austenitic grades, which ensure their extensive spreading in industrial applications as a substitute of austenitic grades. In the construction of liquid tanks, however, it is often necessary to weld such steels with a range of fittings which are commonly fabricated with austenitic stainless steel grades. Therefore, this paper examines dissimilar welded joints between LDX 2101 (or X2CrMnNiN22-5-2) lean duplex stainless steels plates and austenitic stainless steel pipes, carried out by different arc welding processes. The investigation focuses on the correlation between the welding procedures and the microstructural and mechanical properties of the welded joints.


Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 731 ◽  
Author(s):  
Zitelli ◽  
Folgarait ◽  
Di Schino

In this paper, the capability of laser powder bed fusion (L-PBF) systems to process stainless steel alloys is reviewed. Several classes of stainless steels are analyzed (i.e., austenitic, martensitic, precipitation hardening and duplex), showing the possibility of satisfactorily processing this class of materials and suggesting an enlargement of the list of alloys that can be manufactured, targeting different applications. In particular, it is reported that stainless steel alloys can be satisfactorily processed, and their mechanical performances allow them to be put into service. Porosities inside manufactured components are extremely low, and are comparable to conventionally processed materials. Mechanical performances are even higher than standard requirements. Micro surface roughness typical of the as-built material can act as a crack initiator, reducing the strength in both quasi-static and dynamic conditions.


Author(s):  
H. Ertugrul Karabaki ◽  
Jussi Solin ◽  
Marius Twite ◽  
Matthias Herbst ◽  
Jonathan Mann ◽  
...  

The cyclic behavior and endurance of austenitic stainless steels tested under NPP-relevant laboratory conditions has been studied. It had been earlier shown that long intervals between fatigue transients can affect the fatigue performance in stainless steels that are generally used in NPP primary piping. If this can be confirmed, then the transferability between laboratory results, design curves and the fatigue behavior of NPP components during plant operation shall be addressed. In addition to coolant water environmental effects, the material response during steady state normal operation should also be accounted for. Advanced Fatigue Methodologies (AdFaM), a joint project of European research laboratories, vendors and plant operators was focused on empirical and mechanistic investigations to confirm the claimed effects of hold times on fatigue life. Strain-controlled fatigue tests incorporating accelerated hold times at temperatures between 290°C and 420°C were performed on stabilized and non-stabilized stainless steel grades, which are used in Germany and the UK. Two material batches of both alloy types (304L and 347) were studied. The mechanisms responsible for the observed variations in stress response and fatigue life have been investigated using a range of microscopy techniques. The results confirmed the extension of fatigue life due to hold times in both stabilized and non-stabilized grades. This life extension appears to be linked to hold hardening observed in the cyclic behavior of both alloys. Tests incorporating hold times may be more representative of material behavior in NPPs, where temperature transients due to start-ups, shutdowns and major power changes may be separated by long periods of steady state operation. This gives reason to consider the transferability of standard laboratory test data to fatigue assessments of NPP components, and to propose a new factor ( Fhold ) as part of an advanced fatigue methodology and realistic transferability factor: Freal = Fen × Fhold.


2007 ◽  
Vol 539-543 ◽  
pp. 4891-4896 ◽  
Author(s):  
P. Antoine ◽  
B. Soenen ◽  
Nuri Akdut

Transformation of austenite to martensite during cold rolling operations is widely used to strengthen metastable austenitic stainless steel grades. Static strain aging (SSA) phenomena at low temperature, typically between 200°C and 400°C, can be used for additional increase in yield strength due to the presence of α’-martensite in the cold rolled metastable austenitic stainless steels. Indeed, SSA in austenitic stainless steel affects mainly in α’-martensite. The SSA response of three industrial stainless steel grades was investigated in order to understand the aspects of the aging phenomena at low temperature in metastable austenitic stainless steels. In this study, the optimization of, both, deformation and time-temperature parameters of the static aging treatment permitted an increase in yield strength up to 300 MPa while maintaining an acceptable total elongation in a commercial 301LN steel grade. Deformed metastable austenitic steels containing the “body-centered” α’-martensite are strengthened by the diffusion of interstitial solute atoms during aging at low temperature. Therefore, the carbon redistribution during aging at low temperature is explained in terms of the microstructural changes in austenite and martensite.


2020 ◽  
Vol 854 ◽  
pp. 16-22 ◽  
Author(s):  
Artem D. Davydov ◽  
Olga O. Erokhina ◽  
Sergey Vladimirovich Ryaboshuk ◽  
Pavel Valer'evich Kovalev

Austenitic stainless steels are widely used in industry. Increased requirements for the quality of products from these steel grades, the difficulties associated with the implementation of technological processes, as well as the high cost of steel, determine the necessity to assess probable causes of defects. This article presents an analysis of the influence of main process parameters on the quality of products from the grade 08X18H10T steel. Based on the results of statistical analysis and thermodynamic modeling, it was concluded that the increased content of titanium and nitrogen affects the quality of products, which is caused by the formation of titanium carbonitrides in the process of steel solidification.


2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Saeed Ghali

Three stainless steel grades with different vanadium content were produced in open induction furnace. The base chemical composition of investigated stainless steel has contained 18.48–18.75% Cr, 5.17–5.62% Mn, 2.47–2.58% Mo, and 6.39–6.64% Ni. The vanadium contents of the three stainless steel grades were 0.009%, 0.112%, and 0.189%. The proposed stainless steels were casted at temperatures 1753 K and 1833 K. The nitrogen contents were determined for the produced steel grades at every cast temperature. The determined nitrogen contents were compared with those calculated from the developed equation of Grigorenko and Pomarin. The influence of cast temperature and vanadium content on nitrogen solubility was investigated. Interpretation between experimental and calculated nitrogen content was carried out. Increasing vanadium content and decreasing cast temperature were found to have positive significant effect on the nitrogen solubility. There were great deviations between experimental results and those calculated by Grigorenko and Pomarin equation.


Author(s):  
L.E. Murr ◽  
J.S. Dunning ◽  
S. Shankar

Aluminum additions to conventional 18Cr-8Ni austenitic stainless steel compositions impart excellent resistance to high sulfur environments. However, problems are typically encountered with aluminum additions above about 1% due to embrittlement caused by aluminum in solid solution and the precipitation of NiAl. Consequently, little use has been made of aluminum alloy additions to stainless steels for use in sulfur or H2S environments in the chemical industry, energy conversion or generation, and mineral processing, for example.A research program at the Albany Research Center has concentrated on the development of a wrought alloy composition with as low a chromium content as possible, with the idea of developing a low-chromium substitute for 310 stainless steel (25Cr-20Ni) which is often used in high-sulfur environments. On the basis of workability and microstructural studies involving optical metallography on 100g button ingots soaked at 700°C and air-cooled, a low-alloy composition Fe-12Cr-5Ni-4Al (in wt %) was selected for scale up and property evaluation.


2018 ◽  
Vol 106 (1) ◽  
pp. 107 ◽  
Author(s):  
Jean- Louis Crolet

All that was said so far about passivity and passivation was indeed based on electrochemical prejudgments, and all based on unverified postulates. However, due the authors’ fame and for lack of anything better, the great many contradictions were carefully ignored. However, when resuming from raw experimental facts and the present general knowledge, it now appears that passivation always begins by the precipitation of a metallic hydroxide gel. Therefore, all the protectiveness mechanisms already known for porous corrosion layers apply, so that this outstanding protectiveness is indeed governed by the chemistry of transport processes throughout the entrapped water. For Al type passivation, the base metal ions only have deep and complete electronic shells, which precludes any electronic conductivity. Then protectiveness can only arise from gel thickening and densification. For Fe type passivation, an incomplete shell of superficial 3d electrons allows an early metallic or semimetallic conductivity in the gel skeleton, at the onset of the very first perfectly ordered inorganic polymers (- MII-O-MIII-O-)n. Then all depends on the acquisition, maintenance or loss of a sufficient electrical conductivity in this Faraday cage. But for both types of passive layers, all the known features can be explained by the chemistry of transport processes, with neither exception nor contradiction.


Alloy Digest ◽  
2012 ◽  
Vol 61 (4) ◽  

Abstract Stoody AP stainless steel wires are all-position wires. The nickel in this product will achieve a good balance of austenite and ferrite in lean duplex stainless steels. This datasheet provides information on composition and tensile properties as well as fracture toughness. It also includes information on forming and joining. Filing Code: SS-1118. Producer or source: Stoody Company.


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