Corrosive wear behaviour of various stainless steel alloys and a Stellite 6 weld cladding

This study has comprised an investigation the corrosive wear behaviour of UNS S31600, a low hardness (280Hv) UNS S42000, a high hardness (480Hv) UNS S42000 and a single layer Stellite 6 (UNS R30006) weld cladding on a low alloy carbon steel (UNS G43400). Erosion-corrosion testing was conducted using a submerged jet of 3.5% NaCl aqueous solution with spherical silica sand particles. The sand concentration was 2.4g/l, the velocity of the jet was 18m/s and the testing temperature range was 16°C-27°C. Both normal incidence (90°) and low angle (20°) tests were performed. Mass losses, wear scar depths and a volumetric analysis technique were used to assess the damage in the direct impinged zone (DIZ) and the outer area (OA) of the specimens. For all materials, it was found that mass loss was higher at 20° tests than that of 90°. However, when comparing wear scar depths the opposite trend was found. The results are discussed in terms of comparative material behaviour, the influence of material hardness and the corrosive wear mechanisms in different regions formed during slurry jet impingement

Enhanced approach of assessing the corrosive wear of engineering materials under impingement

Corrosive wear phenomena are apparent in hydraulic machinery that handle slurries. This study focuses on the development of an integrated methodology of material assessment that is employed to understand the mechanisms of deterioration and effectively compare materials’ performance under impinging slurry. The technique involves mass loss measurements and post-test analysis of the surface, which comprises measurement of wear scar depths and volumes, that yield the quantification of the various material degradation processes that occur directly under, and adjacent to, the impinging jet. A medium carbon steel and a stainless steel have been investigated, since they exhibit different corrosive wear behaviour

Effect of corrosion on abrasive wear in a range of materials

Engineering components, such as those which are employed in fluid sealing systems, experience abrasive wear deterioration, which is often significantly enhanced by corrosion processes and the interaction of corrosion with the mechanical damage. Broader understanding and quantification of the corrosive abrasion is appropriate to combat this complex degradation phenomenon. This paper discusses the influence of corrosion on abrasive wear and utilises a recently developed experimental technique which enables the quantification of corrosive abrasion damage of materials subjected to impingement by a saline aqueous solution containing suspended sand particles. The materials reviewed in this study were Zirconia, a Diamond-Like Carbon (DLC) Coating, High Velocity Oxygen Fuel (HVOF) WC-12Co, HVOF WC-10Ni, medium carbon steel (UNS G10400) and martensitic stainless steel (UNS S42000). UNS S31600 was used as a comparator material. The influence of acidic conditions was also investigated on the tribo-corrosion resistance of the martensitic stainless steel. Volume loss ratios, microscopy and surface roughness measurements were employed to expand the assessment of corrosion abrasion damage. The ceramic (Zirconia and DLC coating) and cermet (HVOF WC-12Co and HVOF WC-10Ni) materials exhibited excellent abrasion resistance, however, the cermets suffered extensively from corrosion related damage. The engineering steels, on the other hand, were extensively attacked by corrosion abrasion wear. Through this comparative study, material considerations, associated with the different mechanisms that occur in fluid seals, were also formulated

Erosion-Corrosion Mechanisms of Engineering Steels in Different NaCl Concentrations

This study utilises a recently developed, enhanced approach to assess detailed aspects of the corrosive wear behaviour of different steel grades in aqueous slurries containing three NaCl concentrations (0.05%NaCl, 3.5%NaCl and 10%NaCl). Erosion-corrosion testing was conducted using a slurry impingement test rig and damage was quantified using volume loss, potentiodynamic polarisation scans and surface topography. Single- and segmented specimens were adopted to yield the contribution of the degradation mechanisms in the two hydrodynamic zones (directly impinged and surrounding area). The overall material losses from the two zones of the stainless steels were observed to increase with increasing salinity. However, the overall material loss for the low-alloy steel was found to increase from 0.05%NaCl to 3.5%NaCl, before reducing when the salinity was further increased to 10%NaCl. Changes in salinity were observed to have the most effect on the corrosion-enhanced mechanical damage mechanism. The in-house developed technique demonstrated good linkage between single samples and the outer area damage region. However, it also showed that the use of single samples can be less successful when assessing highly turbulent (directly impinged) damage regions

A study on the erosion-corrosion behaviour of engineering materials used in the geothermal industry

Erosion-corrosion can be a significant issue for engineering components used in the geothermal industry. This study assesses the erosion-corrosion behaviour of a wide range of engineering alloys which are used in various parts of geothermal power plants. The evaluated materials comprised a carbon steel, low-alloy steel, three grades of stainless steel together with Ni–Cr alloy (Inconel 625) and Ti–6Al–4V. Tests were conducted by utilising a submerged 90° impinging slurry jet consisting of silica sand particles suspended in an acidic (pH 4) aqueous solution consisting of 3.5% NaCl. Gravimetric mass losses, in-situ potentiodynamic polarisation scans and an enhanced volumetric analysis technique were used to assess the influence of hydrodynamic conditions on the erosion-corrosion behaviour of the test materials. The effect of applied cathodic protection was also examined. Post-test metallurgical examination was also conducted via SEM. The results showed the distinct differences between low alloy steels and "corrosion resistant" alloys – with the former demonstrating substantial material loss in the low-angle corrosive wear region due to large amounts of corrosion-related damage. Both superaustenitic stainless steel (UNS S31254) and Inconel 625 (UNS N06625) exhibited the greatest erosion-corrosion resistance of the test materials – with Inconel 625 demonstrating the greatest resistance to high angle corrosive wear. The relevance of the findings to materials selection and other methods of protection against surface degradation in geothermal power plants is discussed

Effect of nitriding on the corrosive wear performance of a single and double layer Stellite 6 weld cladding

This study investigates the corrosive wear behaviour of single and double layer Stellite 6 (UNS R30006) weld claddings and the effectiveness of nitriding on their erosion-corrosion resistance. Tests were conducted by utilising an impinging slurry jet. The slurry consisted of 3.5% NaCl aqueous solution which contained 500 µm spherical silica sand with a concentration of 2.4 g/l. The velocity of the jet was 18 m/s and the testing temperature ranged from 16–27°C. The erosion-corrosion tests were conducted at low angle (20°) and at normal incidence (90°). Mass losses, wear scar depths and a volumetric analysis technique were used to assess the damage in the Direct Impinged Zone (DIZ) and the Outer Area (OA) of the specimens. Electrochemical monitoring was also utilised to assess the inherent corrosion resistance of the materials. Although nitriding was found to reduce the pure corrosion resistance of the Stellite 6 weld claddings and did not appear to affect the 90° direct impingement damage, nitriding did yield benefits in terms of low angle sliding abrasion resistance

Influence of metallic matrix on erosion-corrosion behaviour of high chromium cast irons under slurry impingement conditions

Chromium cast irons (CCI) comprise versatile materials that encompass a range of compositions and microstructures often chosen to promote good wear resistance. There are, however, issues that arise when the cast iron is required to operate in conditions where corrosion, as well as, wear is a factor. This scenario usually results in adapting the composition of the CCI in order to achieve higher chromium content in the metallic matrix and, thereby, to attain the corrosion resistance exhibited by high-Cr stainless steels. This paper comprises a comparison of the corrosive wear behaviour of an austenitic-based hypoeutectic cast iron and a martensitic-based, near-eutectic cast iron with the associated stainless steels, in a saline water under solid-liquid submerged jet conditions. A comprehensive experimental methodology has been adopted including evaluation of the behaviour of the materials in free erosion-corrosion conditions and with the application of cathodic protection. This approach has extended the understanding of the fundamental deterioration mechanisms in different hydrodynamic conditions and has highlighted the complexities of the mechanical/electrochemical interactions occurring during erosion-corrosion. An important feature is the influence of micro-galvanic interactions at phase boundaries. The impact of the findings has been discussed in terms of CCI alloy selection and corrosion control strategies

Electrochemical evaluation of the effect of different NaCl concentrations on low alloy- and stainless steels under corrosion and erosion-corrosion conditions

The main objective of this study was to assess the influence of salt concentration on the corrosion behaviour, including the role of hydrodynamic conditions, of two broad classes of ferrous engineering materials. These are comprised of alloys, typified by a low-alloy steel (UNS G43400) that corrodes actively in aqueous conditions and a range of passive-film-forming stainless steels (UNS S31600, UNS S15500 and UNS S32760). Corrosion monitoring employed electrochemical (potentiodynamic polarisation) techniques. Three concentrations of aerated sodium chloride were utilised: 0.05 wt% NaCl, 3.5 wt% NaCl and 10 wt% NaCl. In quiescent, liquid impingement and solid/liquid impingement conditions, the corrosion rate of the low-alloy steel was observed to peak at 3.5 wt% NaCl, followed by a reduction in 10 wt% NaCl solution. These findings expand the range of previously reported trends, focused on static conditions. Such corrosion rate/salinity trends were observed to be dictated by the progress of the anodic reaction rather than influence on the cathodic reaction. Detailed studies were undertaken using segmented specimens to facilitate comparisons of the influence of hydrodynamic variations on corrosion behavior; these revealed that such variations influence the corrosion rates of low-alloy steel to a much lesser extent than the effect of changes in salinity. For the stainless steels, in quiescent and flowing conditions, when surface passive films are stable, there was a constant increase in corrosion rate with salinity. In solid-liquid conditions, however, the periodic film-destruction/repassivation events resulted in a similar corrosion rate/salinity trend to that displayed by the low-alloy steel, but with a much larger effect of hydrodynamic conditions. Additonally, the study revealed an underlying influence of stainless steel composition that mirrored, to an extent, the corrosion behaviour in pitting/re-passivation situations

Comparison of hot wire TIG stellite 6 weld cladding and lost wax cast stellite 6 under corrosive wear conditions

This study compares Hot Wire Tungsten Inert Gas Stellite 6 weld cladding on a low carbon steel substrate with a lost wax cast Stellite 6 in impingement erosion-corrosion conditions. Austenitic stainless steel samples were used as a reference material. Tests were conducted in a closed loop impinged slurry vessel with a jet velocity of 18 m/s with 3.5%NaCl aqueous solution containing 500 µm spherical silica sand particles (0.5 g/l sand concentration). The testing temperature was 40 °C. Mass loss measurements and a volumetric analysis as well as microstructural evaluation were used as post-test analysis techniques. Results showed that weld cladding and lost wax cast Stellite 6 performed better than the stainless steel, with the weld cladding marginally outperforming the lost wax cast technique

Experimental investigation of engineering materials under repetitive impact with slurry conditions

In some industrial situations, components are subject to repetitive impact in the presence of a slurry. A novel repetitive impact-with-slurry test rig was developed to evaluate the behaviour of a wide range of engineering materials in such conditions. The test materials could be categorised into five main groups – heat treated steels, stainless steels, chromium cast irons, hardfacing coatings and superalloys. Three-dimensional surface topography was used to quantify the depths and volumes of the produced wear scars. Post-test metallurgical examination was also conducted to further evaluate the wear processes. The wear mechanisms could be split into two main groups of materials; ductile materials were observed to plastically deform and hard/brittle materials demonstrated cracking/spalling mechanisms. Hardened martensitic-type materials exhibited the greatest resistance to repetitive impact wear