Low Alloy Stainless Steels Research Articles

A Mechanistic Approach to Understanding Microbiologically Influenced Corrosion by Metal-Depositing Bacteria

Iron (Fe)- and manganese (Mn)-oxidizing bacteria are often cited individually and collectively as putative microorganisms for microbiologically influenced corrosion (MIC). The two groups of microorganisms have in common the ability to attach to surfaces and produce macroscopic accumulations (deposits) of metal oxides/hydroxides/oxyhydroxides that can influence corrosion of some metals and alloys in some environments. In all cases, once initiated, the corrosion is independent of the activities of the colonizing species. Despite the phylogenetic diversity of Fe-oxidizing bacteria (FeOB), the following sections will deal with corrosion mechanisms attributed to neutrophilic, lithotrophic, microaerophilic FeOB. The mineralogy of biologically oxidized Fe is consistent over a wide range of environments. All FeOB produce dense deposits that can cause corrosion of low alloy stainless steels (SS) directly, i.e., under-deposit corrosion. Association of Mn-oxidizing bacteria (MnOB) and other microorganisms may stabil...

Effect of N, Mo, and Si on Local Corrosion Resistance of Unstabilized Cr–Ni and Cr–Mn–Ni Austenitic Steels

Features of the effect of both individual and combined alloying with nitrogen, molybdenum and silicon of unstabilized cold-worked and heat-treated austenitic Cr–Ni and Cr–Mn–Ni steels on pitting and intercrystalline corrosion (ICC) resistance in weakly oxidizing media are studied. On the basis of corrosion and electrochemical test results (electrochemical method), an ambiguous effect of alloying cold worked Cr–Mn–Ni steels with nitrogen and molybdenum on pitting corrosion resistance is revealed. It is established that a necessary condition for intergranular corrosion resistance of chromium-nickel steels after prolonged tempering at 550–750°C is the presence of silicon in addition to nitrogen and molybdenum, which participates in improving the passivity of chromium-depleted boundary zones. Silicon added to nitrogen-containing steel alloyed with molybdenum and 0.03 wt.% carbon with a balanced content of Cr, N, Mo and Si facilitates an improvement of passivity for boundary zones impoverished in chromium. Introduction of silicon into nitrogen-containing chromium-nickel steel (0.03% C) alloyed with molybdenum with a balanced content of Cr, Ni, Mo, and Si makes its ICC resistance equal to specially low-alloy stainless steel containing 0.003% C.

Corrosion testing in superheated geothermal steam in Iceland

Corrosion testing was conducted in a superheated geothermal steam from the IDDP-1 well in Iceland at 360°C for 113 days. Severe silica scaling occurred in the test. The average corrosion rate was extremely low; less than 0.1mm/year for all the metals tested which can be explained by the combined protective effect of the silica and the high superheat in the steam preventing any condensation. Despite the low average corrosion rate, the microstructural analysis show that even the most corrosion resistant materials tested, such as UNS N06625 and titanium UNS R52400 show localized corrosion damage after the test. Only the low alloy stainless steels UNS S30403, UNS 31603 and UNS 31803 showed evidence of Stress Corrosion Cracking.

Current State of Developing Creep Damage Constitutive Equation for 0.5Cr0.5Mo0.25V Ferritic Steel

This paper reports a critical summary of literature review of creep damage constitutive equations. Firstly, it introduces the general background on the creep damage in low alloy stainless steel and weldment. Then, it summarizes the typical creep damage constitutive equations for this material available from public literature and discusses the deficiencies existed in the popular creep damage constitutive equations. Finally it outlines the approach to be used in the developing a new set of creep damage constitutive equation and the directions of future work.

Phase composition of nitrogen-containing low-alloy stainless steels of the system Fe–Cr–Ni–N–Si

The limiting solubility of nitrogen at atmospheric pressure in low-carbon stainless steels containing not more than 0.03% carbon, 13–25% chromium, 5–13% nickel, 0–5% silicon is calculated. Using Scheffler diagrams and the calculated limiting nitrogen content within steels of the system Fe–Cr–Ni–N–Si limits are determined for phase areas in relation to values of nickel and chromium equivalents. Temperatures are calculated for the start of martensitic transformation during cooling and plastic deformation of steels containing a different amount of chromium, nickel, nitrogen, and silicon.

Localized Corrosion Resistance Of Welded Austenitic And Lean Duplex Stainless Steels

Weld oxides are known to decrease the pitting resistance of welded stainless steel, so post- weld cleaning is needed for optimum corrosion performance. The drop in corrosion resistance is larger for low-alloyed stainless steels than the higher alloyed grades, but corrosion testing of the former is more difficult due to their low corrosion resistance. Residual weld oxides can cause an initial current peak during electrochemical corrosion testing according to ASTM G150, with the result that the test is terminated prematurely and interpreted as poor corrosion performance. The objective of this work was to investigate the effect of weld oxide on the austenitic stainless steels 304 (EN 1.4301), 304L (EN 1.4307), 316L (EN 1.4404) and the lean duplex LDX 2101® (EN 1.4162). Pitting potentials have been measured based on the ASTM G61 standard and compared with critical pitting temperatures using ASTM G150. The aim was to rank the grades based on the pitting resistance of base metal, polished and pickled welds, but it was found that the pitting potential ranking did not match that typically seen with critical pitting temperatures. The larger sensitivity to surface roughness of the ASTM G61 method was identified as a contributing factor. In addition, it is demonstrated that oxide dissolution, but no visible pitting attack could be identified after the first current peak for both ASTM G61 and ASTM G150 testing. This indicates that the corrosion resistance of as-welded samples is actually higher than the standard measuring techniques indicate.

Mechanical and tribological properties of duplex treated TiN, nc-TiN/a-SiN x and nc-TiCN/a-SiCN coatings deposited on 410 low alloy stainless steel

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiN x or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiN x , TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and ε-Fe 2N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiN x and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H 3/ E r 2 ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiN x coatings: this includes excellent adhesion, low friction ( C f = 0.17) and low wear rate ( K = 1.6 × 10 − 7 mm 3/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/ E and H 3/ E r 2 ratios and the tribological performance of the nano-composite coatings is discussed.

Estimating localised corrosion resistance of low alloy stainless steels: comparison of pitting potentials and critical pitting temperatures measured on lean duplex stainless steel LDX 2101 after sensitisation

Two different methods for estimating the corrosion resistance of low alloy stainless steels are compared: critical pitting temperature according to a modified ASTM G150 with a low chloride concentration (0·1M), and pitting potentials from polarisation curves acquired using the novel Avesta multicell. The methods were tested on the lean duplex stainless steel grade LDX 2101, which has a corrosion resistance in the low end of the standard critical pitting temperature scale. The results from both methods correlated well with Charpy V impact energies and with the formation of carbides and intermetallics in the microstructure after annealing. In this study, the most consistent results for the sensitised material were obtained using pitting potentials.

SUPPRESSION OF AXIAL NONUNIFORMITY IN CONTINUOUS-CAST STEEL BY INOCULATING IT WITH A CLAD POWDER INOCULANT

Improving the quality of rolled plates is one of the main goals of the metallurgical industry. This goal can be achieved through treatment of the steel outside the furnace ‐ especially in the pouring ladle or tundish ‐ with the use of chemically active elements that will refine, inoculate, and micro-alloy the melt. Such a practice is most efficiently carried out by introducing master alloys in the form of clad powder inoculants (cored wires). These materials consist of an infinite thin-walled metal tube packed with a pressed powder of suitable chemical and granulometric composition. The use of cored wires with chemically active elements allows measured, controlled introduction of refining and alloying components with a high degree of assimilation and without adverse environmental consequences [1]. Plates of low-alloy stainless steels are characterized by anomalously low ductility in the Z-direction (through their thickness). The nonuniform cooling of the semifinished product and an increase in the concentration of certain elements (carbon, the alloying elements manganese, silicon, etc.) and impurities (sulfur, phosphorus) in the liquid phase ahead of the crystallization front lead to the formation of an axial segregation zone. The formation of this zone makes the structure of the st eel more nonuniform through the thickness of the plate and affects the morphology of the nonmetallic inclusions in the axial zone. The structural features of the resulting slab are reflected in the structure of the finished rolled product, which is cha racterized by structural and chemical axial nonuniformity. As a result, the properties of the axial region differ significantly from the properties of the matrix of the metal. Despite the thinness of the segregation zone (10‐250 μm), it has a decisive effect on the mechanical characteristics of the product in the Z-direction in connection with the formation of microcracks in that zone. The presence of the microcracks can lead to low-energy fracture. One method of alleviating axial nonuniformity is microalloying the melt with master alloys containing rare-earth metals (REMs) and calcium [2]. This article examines the effect of calcium and cerium introduced into steel through cored wire on the structure of the steel in the axial segregation zone and the mechanical characteristics of the rolled product in the Z-direction. We studied series of trial heats of two steels: steel 09G2S (0.09% C; 1.48% Mn; 0.56% Si; 0.008% S; 0.017% P; 0.03% Ti; 0.043% Al; 0.01% Nb; 0.009% N; 0.02% Cu); steel St 52.3 (0.20% C; 1.38% Mn; 0.36% Si; 0.006% S; 0.013% P; 0.04% Ti; 0.035% Al; 0.03% Nb; 0.011% N; 0.03% Cu). Each steel was treated with 10-mm-diam. cored wire during casting on a continuous caster. The wire contained REMs and calcium-silicon in a 1:1 ratio. The coefficient characterizing the fullness of the tube had a value of 42‐46%. Pinch rollers were used to introduce the wire into a tundish near the stopper at a rate of 0.6‐0.7 m/sec, which was sufficient to produce finished steel with 0.003‐0.004% Ca and 0.008‐0.010% Ce. To evaluate the effect of the treatment of steel with cerium and calcium, we determined the rates of crystallization of experimental and comparison (non-inoculated) continuous-cast metal from the change in the density of the dendritic structure. The results show that microalloying had almost no effect on crystallization rate in the axial zone of the

Use of low-alloy stainless steels for the production of castings in chemical and petroleum engineering

Use of low-alloy stainless steels for the production of castings in chemical and petroleum engineering