Galling Resistance Research Articles

Mechanical properties and galling resistance of API grade steels: A comparative study

Galling is a type of wear that affects the oil and gas industry causing loss of profits due to unexpected stops in the exploration and extraction process. In the present work, the galling resistance of three API grade steels (L80 type 1, T95 type 2, and P110) and one proprietary steel (125HC) used in the industry was evaluated by means of cross-cylinder tests. The surfaces were analyzed, and a Galling Tendency number was computed in order to rank the materials. Additionally, tensile and hardness tests were conducted to analyze the influence of the mechanical properties on galling. It was found that P110 exhibited the worst response and T95 the best one. For materials with the same ductility, an increase in strength is associated with higher galling resistance. A new index, based on the ductility and yield strength of the material, is proposed to predict the galling performance, demonstrating a strong correlation with the galling tendency.

Intermetallic and dispersoid structures in AA3104 aluminium alloy during two-step homogenisation

During homogenisation of the AA3104 cast ingot, a phase transformation of intermetallic particles from β-Al6(Fe,Mn) orthorhombic phase to harder α-Alx(Fe,Mn)3Si2 cubic phase occurs. The large constituent intermetallic particles, regardless of phase, assist in the recrystallisation nucleation process through particle stimulated nucleation (PSN). Ultimately, this helps to refine grain size. The sub-micron dispersoids act to impede grain boundary migration through a Zener drag mechanism. For this reason, the dispersoids that form during homogenisation are critical to the recrystallisation kinetics during subsequent rolling, with smaller dispersoids being better suited to instances where the minimisation of recrystallisation is required during hot rolling. This work simulates an industrial two-step homogenisation practice with variations in the peak temperature of the first step between 560 °C and 580 °C. The effect of this temperature variation on the intermetallic particle phase evolution is investigated. The aim is to identify the ideal intermetallic phase balance and the dispersoid structure that are best suited for the minimisation of recrystallisation during hot rolling through maximising Zener drag and maintaining galling resistance. The results indicate a trend where an increase in homogenisation temperature from 560 °C to 580 °C yields, firstly, an increase in the volume fraction of the α-phase particles to greater than 50% of the total volume fraction at both the edge and the centre of the ingot and, secondly, it yields an increased dispersoid size. Thus, a lower temperature homogenisation practice produces a near-ideal combination of intermetallic particle phase distribution, as well as dispersoid size, which is critical for Zener drag and the minimization of recrystallisation during the hot rolling processes.

Design and performance of nitrogen-alloyed iron-based coating for enhancing galling resistance by plasma transferred arc welding

Iron-based alloys have been widely used as high-temperature galling resistant coatings. In this study, we designed and prepared a galling-resistant coating using plasma transferred arc welding with cored wires of varying nitrogen content. Our approach was based on the concept that nitrogen alloying can lead to the formation of hard precipitates and promote strain-induced phase transformations. The coating was primarily composed of austenite, and as the nitrogen content increased, the grain size decreased and the amount of nitride precipitation increased. The threshold galling stress of this cobalt-free coating was found to reach 80% of that of a laser-clad Stellite 21 coating at 300 °C. Following the galling test, the hardness of the worn area increased and a phase transformation from austenite to martensite occurred beneath the worn surface. The improvement in galling resistance under dry heavy load sliding conditions can be attributed to the synergistic effect resulting from multiple strengthening mechanisms, including fine-grain strengthening, second phase strengthening and phase transformation strengthening.

High temperature friction and galling properties of nanolayered (Cr,V)N coatings and effect of V content

Chromium nitride (CrN) coating is considered as one of the best candidates for wear protection in many forming application where adhesive wear and galling dominate. However, its relatively high coefficient of friction against soft metals hinders its applicability. Vanadium nitride (VN), on the other hand has attracted increasing interest as VN is easily oxidized to form Magneli phase vanadium oxides with easy slipping shear planes, on one hand leading to self-lubricating properties but also to deteriorated wear resistance. This can be overcome by forming CrVN coatings. However, there is a lack of information how such coatings perform in terms of galling resistance and V-concentration in typical forming conditions and against soft metals.Therefore, the aim of this work was to study friction properties of nano-layered PVD (Cr,V)N coatings at room and elevated temperature and how V-content influences on friction and galling resistance against typical work materials. Nanolayered (Cr,V)N coatings with V in concentrations from 15 to 30 % were deposited by industrial DC magnetron sputtering system and tested using Load-Scanner against AA2024 aluminum alloy and low-carbon steel at room and elevated temperature of 300 °C and 600 °C, respectively. Results were evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation and volume of adhered work material. Results show that (Cr,V)N coatings do not necessarily improve galling resistance, being strongly dependent on V concentration and contact temperature. For forming Al alloys positive results are obtained with coatings containing 20–25 at.% V and for low-carbon steels above 25 at.%, with marked improvement obtained only at elevated temperatures.

Analysis of an ASTM interlaboratory study of the threshold galling stress

The result of performing the ASTM G98 Standard Test Method for the Galling Resistance of Materials is the determination of the threshold galling stress for a given pair of specimens. In the current study, the data from ASTM’s interlaboratory study (ILS) of G98 is reanalyzed using the data reduction technique from ASTM G196 Standard Test Method for Galling Resistance of Material Couples. The results of this study indicate that the assumption of a deterministic relationship in G98 between contact stress and galling is not supported by the results of ASTM’s interlaboratory study. A computer simulation was used to show the improvement in results and cost increase associated with completing multiple G98 tests to incorporate the stochastic nature of galling wear.

Comparative Study on Galling and Antiwear Behavior of Polyurethane Based Coatings Reinforced With Pristine and Alkylated MoS2 Nanosheets

Abstract The present investigation is focused on tribological studies of polyurethane (PU) based coatings doped with nano-MoS2, and MoS2 functionalized with octadecanethiol (i.e., MoS2-ODT) on steel substrate. The PU-based nanocomposite coatings showed enhanced hardness, scratch and galling resistance at room temperature. Tribological tests were carried out under two contact conditions, i.e., sliding contact for galling resistance and reciprocating wear studies. The PU-based nanocomposite coatings showed enhanced galling resistance at room temperature. The reciprocating wear studies showed a significant reduction in friction and wear with the addition of MoS2 and MoS2-ODT nanosheets in the polymer matrix. The PU-MoS2 coating showed a 46% and 77% reduction in coefficient of friction and wear, respectively. However, the PU-MoS2-ODT nanocomposite coatings showed up to 75% and 95% reduction in coefficient of friction and wear, respectively. The PU based nanocomposite coating also showed enhanced galling resistance up to 17.5 MPa, in contrast to 5 MPa of SS 304. Different tools like high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared radioscopy (FTIR), high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray (EDS), nanoindentation, stereo-zoom, and optical microscopies were used for the characterization and study of MoS2 nanosheets and PU based nanocomposite coatings.

Study of cracking and microstructure in Co-free valve seat hardfacing

• Through-thickness cracks were found on Co-free hardfacing with NOREM 02. • Brittle cracking propagate along the interdendritic network of carbides. • Solidification defects and lacking of ferrite phase was observed. For reducing the radiological hazard, Co-free hardfacing alternatives have been used to replace the traditional Co-based hardfacing alloys in nuclear power plant applications. However, manufacturing a defect-free Co-free hardfacing is challenging. Reduced galling resistance and mechanical properties exhibited by common replacement alloys in some conditions limit the application. This issue is important for the operating nuclear power plants with lifetime extension and also for the new builds. In this paper, a failed industrial hardfacing was studied. Through-the-thickness cracks of the Co-free hardfacing deposit with NOREM 02 on a nuclear swing check plug were detected. The potential cause of the brittle interdendritic cracking was studied and the detailed microstructure of the Co-free hardfacing analysed. The solidification defects during the manufacturing and the lacking of ferrite phase in the microstructure together with the potentially non-optimized handling procedures are concluded to be the causes of the observed cracking.

Study on galling behaviour of HiPIMS deposited Mo/DLC multilayer coatings at ambient and elevated temperature

Galling has been a severe concern in oil – gas, automotive, and nuclear sectors. SS 304 steel is used in these industries despite its low galling resistance because it possesses good corrosion resistance properties. The threads of bolt, nut or a tapped hole and fasteners made of SS 304 experience severe damage due to galling or cold working. Therefore, the galling characteristics of the coated SS 304 samples were studied against the uncoated counterpart. A multilayer coating of molybdenum (Mo) and diamond like carbon (DLC) was deposited through dual sputtering using a high power impulse magnetron sputtering (HiPIMS) power source for graphite target and pulsed DC power source for Mo target. The Mo/DLC multilayer coating was optimized for antiwear and low friction properties. The evaluation of friction properties was done through a nanotribometer. The galling samples of SS 304 steel were prepared following the ASTM G196 standard, and the optimized coating was deposited on the galling samples. The adhesion strength of the coating was analyzed with the help of a nanoscratch tester. The galling behavior of coated and uncoated samples was investigated at room temperature (RT) and 300 °C. Galling damage was quantified by calculating the galling area on the galled sample. Image processing and computer vision tools were used to calculate the galled area. The tribopair having coated (Mo/DLC multilayer coating on SS 304) and the uncoated sample (SS 304) showed lower galled area than the tribopair containing both uncoated samples in every test conditions. At RT the coated sample failed at 15 MPa, whereas the uncoated samples failed at 5 MPa. Similar type of results were obtained when the samples were tested at 300 °C. The characterization of the coating and the mechanism of galling were studied in detail with the help of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, stereo-zoom optical microscopy, and scanning electron microscopy (SEM).

UDDEHOLM VANCRON SUPERCLEAN

Abstract Uddeholm Vancron SuperClean is a chromium-molybdenum-vanadium-nitrogen alloy cold-work tool steel that is produced by the powder metallurgy process. It offers an excellent combination of galling resistance and adhesive wear resistance, which makes the steel ideal for severe production conditions and/or long run production in applications where a surface coated tool steel is needed. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on heat treating and machining. Filing Code: TS-824. Producer or source: Uddeholms AB.

Effect of Deep Cryogenic Treatment on Wear and Galling Properties of High-Speed Steels.

New approaches to improving wear resistance with an affordable and noncomplex technology, such as deep cryogenic treatment, (DCT0), are receiving attention. The aim of this study is to investigate the effect of DCT on the friction and wear performance of high-speed steels. AISI M2, AISI M3:2 and AISI M35 were heat-treated under different conditions, and then investigated under dry sliding conditions. Tribological testing involved different contact conditions, prevailing wear mechanisms and loading conditions. The DCT effect on sliding wear resistance depends on HSS steel grade, as well as contact conditions and wear mode, whereas it improves the dynamic impact of the wear and galling resistance.

Measurement of friction in galling testing – An example of its use in characterising the galling behaviour of hardfacings at ambient and elevated temperature

Galling is a category of severe adhesive wear that is defined by surface damage arising between sliding solids, distinguished by macroscopic, usually localized, roughening and creation of protrusions above the original surface. The identification of galling is through a visual observation of the tested surface and is therefore inherently subjective. Due to the microscopic processes behind the onset of galling being poorly understood, further work is needed to understand the behaviour of different materials under galling conditions, both at room temperature and at elevated temperature.The current paper describes the development of a new galling testing apparatus, broadly under the ASTM G196 configuration with the addition of in-situ torque measurements, an automated worm drive for sample rotation as well as band heaters providing capability for testing at elevated temperatures up to a maximum applied stress of 950 MPa. Results from galling tests conducted at room temperate and 300 °C for both Stellite 6 (Co-based) and Tristelle 5183 (Fe-based) hardfacings are presented.The results show that the galling resistance of Tristelle 5183 is significantly reduced at elevated temperature (<52.8 MPa) compared to room temperature (158.3 MPa). In the case of Stellite 6, galling was not observed at either room temperature or 300 °C up to the maximum tested stress of 950 MPa.

Galling categories investigations in stainless steels

This paper focuses on the galling mechanisms occurring in stainless steels and aims to provide a better comprehension of the effects of microstructure on galling resistance. Five stainless steels are studied in this paper, namely Nitronic60, AISI660, 316L, 316LN (austenitic stainless steels) and Uranus45 N (duplex austenite-ferrite). Both surface topography and in-depth microstructure are characterized in order to determine the consequences of galling apparition. Experimental investigations at macroscopic and microscopic scales show that galling can occur following several mechanisms. Galling leads to either adhesive wear spots randomly distributed on the surface (tolerant galling), adhesive wear initiated on the periphery of the pin (moderate galling) or abrasive wear and smearing (severe galling). Depending on these categories, the galling threshold and severity are highly variable. Studying these specific mechanisms can help us predict and eventually increase galling resistance for a given material couple. Thus, several microstructural investigations have been performed in order to discuss about the possible origins of these galling categories.

Properties of Tool Steels and Their Importance When Used in a Coated System

The introduction of new light-weight high-strength materials, which are difficult to form, increases demands on tool properties, including load-carrying capacity and wear resistance. Tool properties can be improved by the deposition of hard coatings but proper combination and optimization of the substrate properties are required to prepare the tool for coating application. The aim of this paper is to elaborate on tool steel substrate properties correlations, including hardness, fracture toughness, strength and surface quality and how these substrate properties influence on the coating performance. Results show that hardness of the steel substrate is the most influential parameter for abrasive wear resistance and load-carrying capacity, which is true for different types of hard coatings. However, high hardness should also be accompanied by sufficient fracture toughness, especially when it comes to very hard and brittle coatings, thus providing a combination of high load-carrying capacity, good fatigue properties and superior resistance against impact wear. Duplex treatment and formation of a compound layer during nitriding can be used as an additional support interlayer, but its brittleness may result in accelerated coating cracking and spallation if not supported by sufficient core hardness. In terms of galling resistance, even for coated surfaces substrate roughness and topography have major influence when it comes to hard ceramic coatings, with reduced substrate roughness and coating post-polishing providing up to two times better galling resistance.

Influence of surface roughness and phosphate coating on galling resistance of medium-grade carbon steel

The aim of this research work was to investigate the influence of surface roughness and presence of phosphate coating on the galling resistance of medium-grade carbon steel. Galling resistance was evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation, surface quality, and volume of adhered material, analysed by load-scanner test rig as a function of load. Results of the investigation show that best galling resistance is not provided by very smooth surfaces but with semi rough ones (Ra = 0.21–0.28 μm), obtained by fine turning. Furthermore, by phosphating and formation of low-friction Mn–P coating superior galling resistance for medium-grade carbon steel is provided, at the same time diminishing effect of surface roughness.

The roles of adhesion, internal heat generation and elevated temperatures in normally loaded, sliding rough surfaces

The thermal effects of plastic and frictional heat generation and elevated temperature were examined along with the role of adhesion in the context of galling wear, using a representative crystal plasticity, normally loaded, sliding surface model. Galling frequency behaviour was predicted for 316L steel. Deformation of the surfaces was dominated by the surface geometry, with no significant effect due to variations in frictional models. Plastic and frictional heating were found to have a minimal effect on the deformation of the surface, with the rapid conduction of heat preventing any highly localised heating. There was no corresponding effect on the predicted galling frequency response.Isothermal, elevated temperature conditions caused a decrease in galling resistance, driven by the temperature sensitivity of the critical resolved shear stress. The extent of deformation, as quantified by the area of plastically deformed material and plastic reach, increased with temperature. Comparisons were made with literature results for several surface amplitude and wavelength conditions. Model results compared favourably with those in the literature. However, the reduction in predicted galling resistance with elevated temperature for a fixed surface was not as severe as observations in the literature, suggesting other mechanisms (e.g. phase transformations, surface coatings and oxides) are likely important.

Galling resistance of nanostructured CVD tungsten/tungsten carbide coatings

Nanostructured tungsten/tungsten carbide (W/WC) coatings produced by chemical vapour deposition are promising WC based coatings for applications where galling wear is prevalent due to the high hardness, toughness and stacking fault energy which the coatings possess despite low hardness to elastic modulus ratio (H/E). In this work the galling resistance of W/WC coatings has been studied through tibometer tests using sliding speeds of 0.014 m s−1 and contact pressures of up to 810 MPa. The study investigates the effects of surface finish and the use of similar and dissimilar material combinations on galling wear. Results show that self-mated stainless steel AISI 316 behave poorly under dry sliding wear conditions whilst uncoated stainless steel tested versus W/WC coating combinations are affected by galling due to material transfer forming a stainless steel on stainless steel tribosystem. The best performance was recorded for self-mated W/WC which did not develop any signs of galling even at the highest contact pressures (810 MPa) contradicting the common practice that the use of dissimilar materials can help prevent galling.

A comparative assessment of iron and cobalt-based hard-facing alloy deformation using HR-EBSD and HR-DIC

Three iron-based alloys (Nitronic 60, Tristelle 5183 and RR2450) and a cobalt alloy (Stellite 6) are studied using bend-testing to induce progressive straining and both high resolution DIC and EBSD are utilized to provide quantitative characterization of the deformation mechanisms. The roles of austenite, ferrite and carbide/silicide phases are investigated, together with how each contributes to slip activation and localisation, GND development and hardening through to particle pull-out and fracture. The observed mechanisms are discussed in the context of galling performance.The results suggest that a distribution of fine precipitates, both intra-granular and at grain/phase boundaries, promote more homogeneous and distributed slip, and the development of distributed higher densities of GNDs. The latter promotes hardening which in turn also facilitates homogeneity of deformation and potentially better galling resistance. A uniform size of fine precipitates is also helpful; large silicides lead to particle fracture and pull-out, likely highly damaging under conditions of sliding contact and galling.

A comparison of the galling wear behaviour of PVD Cr and electroplated hard Cr thin films

Electroplated hard chromium (EPHC) is used in many industries as a wear and corrosion resistant coating. However, the long term viability of the electroplating process is at risk due to legislation regarding the toxic chemicals used. The physical vapour deposition (PVD) process has been shown to produce chromium and chromium-based coatings that could be a possible alternative for EPHC in some applications. This study investigates the microstructure and properties of two PVD chromium coatings as a possible alternative to EPHC to provide resistance to galling. Two PVD deposition processes are investigated, namely electron beam PVD (EBPVD) and unbalanced magnetron sputtering (UMS). Galling wear tests were performed according to ASTM G98-17. The results show that the two PVD coatings are of similar hardness, surface roughness and exhibit similar scratch behaviour. However, the galling wear resistance of the coating deposited by UMS is approximately ten times that of the EBPVD coating, and similar to that of the EPHC. X-ray diffraction reveals that the EBPVD chromium coating has a strong preferred orientation of the {200} planes parallel to the coating surface whilst in the UMS PVD coating, preferred orientations of the {110} and {211} planes parallel to the surface are observed. The EPHC does not exhibit relative peak intensities which conform to the International Centre for Diffraction Data (ICDD) powder diffraction pattern consistent with chromium. The crystal orientation of the PVD chromium coatings appears to play a significant role in influencing galling resistance.

Galling characterization for the pair composed by aluminium and M2 steel under dry and lubricated conditions by using load-scanning test method

Galling or severe adhesive wear is a well-known failure mechanism caused by adhesion between sliding surfaces and is frequently found in sheet metal forming (SMF) operations. In SMF operations of materials such as aluminium, transfer and accumulation of sheet material to the stainless steel forming tool surface happens for certain conditions and can result in severe scratching of produced parts and toll steel damage. The aim of the present research work was to assess if load-scanning test rig can be used to evaluate and compare the galling resistance of different engineered surfaces, namely the material couple aluminium—M2 steel under dry and lubricated sliding conditions, for single- and multi-passing tests with increasing normal loads. In order to determine the galling resistance, a new test method resorting to a Computer Numerical Control (CNC) machine was used. It was found that the galling resistance increases through the use of the proper lubrication, as well as for low applied loads.

Development of a gall-resistant stainless-steel hardfacing alloy

This work details the development of a new cobalt-free stainless steel powder metallurgy hardfacing alloy designed to replace Stellite 6, a cobalt-based hardfacing alloy used in nuclear valve applications. The fundamental strategy centers on alloying stainless steels with up to 0.5 wt% nitrogen, which is shown to increase both the volume fraction of hard phase precipitates and the strain-hardening rate of the matrix. The resultant alloy, Nitromaxx, exhibits galling performance that is comparable to Stellite 6, up to 350 °C. This performance is attributed to the suppression of strain localization events associated with galling. In particular, transmission electron microscopy and diffraction measurements from tensile tests show that the nitrogen addition decreases the calculated matrix stacking fault energy and enhances both deformation-induced martensite transformation at room temperature and deformation twinning at elevated temperature. These strain-hardening mechanisms, coupled with the increase in precipitate volume fraction, effectively suppress localization and enhance galling resistance up to 350 °C. The enhanced galling resistance cannot be rationalized in terms of tensile stress-strain response alone.