Galling Resistance Research Articles

Laboratory test simulation of aluminium cold forming – influence from PVD tool coatings on the tendency to galling

Abstract Cold forming of aluminium is a group of very efficient methods used in a number of industrial applications. Two of the major factors limiting the tool life and restricting the complexity of the shapes produced, are galling, i.e. transfer of aluminium to the tool surface, which leads to problems in successive forming, and high stresses occurring when forming complex shapes. Both phenomena are closely related to friction and adhesion in the tool to workpiece interface. Earlier investigations have shown that aluminium is transferred to the tool steel surface regardless of the surface roughness of the tool. This has been proposed to be due to the hard native oxide on the soft aluminium leading to a mechanical gripping in the tool surface. The present paper investigates the influence of ceramic coatings on the tendency to galling. This is done by plastic forming of aluminium against coated tool steel rods in a lab test. The test scans over a wide load interval while monitoring the coefficient of friction. The transfer of work material to the tool is studied in the SEM. The test is focused on the friction level and on the number of contacts before a critical friction level is reached. The test set-up comprises two crossed cylinders in sliding contact, one made of coated tool material and the other of work material. Eight commercial coatings were included; DLC, TiAlN, TiN and TiCN as single layer or as multilayer combinations, with hardness values ranging from 800 HV to 3500 HV. All substrates were the same tool steel material (H13), prepared to two different surface finishes. The aluminium work piece cylinders of AA6082 were prepared by two different pre-treatments, soft-annealing followed by industrially used solid lubrication and pickling, respectively. The coating material, preparation of the tool surface finish and the aluminium surface pre-treatment all proved important with respect to galling tendencies and friction levels. Three of the DLC coatings showed very promising behaviour, also without lubricant, but surface roughness deteriorates the galling resistance. The other low-friction coatings tested neither improved the galling resistance nor reduced the friction significantly, compared to the uncoated tool steel.

UDDEHOLM VANCRON 40

Abstract Uddeholm Vancron 40 offers an excellent combination of galling resistance and adhesive wear resistance, which should be used in cold-work applications where the predominant failure mechanisms are adhesive wear or galling. Typical applications include blanking and forming, cold extrusion, deep drawing, and powder pressing. This datasheet provides information on composition, physical properties, and elasticity. It also includes information on heat treating, machining, surface treatment, and powder metal forms. Filing Code: TS-687. Producer or source: Böhler-Uddeholm North America.

Galling 50 , a Stochastic Measure of Galling Resistance

A new parameter called the Galling50 value is proposed to provide a statistically relevant measure of galling resistance. The Galling50 value represents the stress value where galling is expected to occur in 50% of the specimens tested. Galling50 is determined from the analysis of a series of tests that measure the probability of galling at different applied stresses. A method for graphically representing experimental galling data is presented. A sigmoidal function is used to mathematically represent the overall performance of the galling results. Similar to previous test methods, the proposed method provides a single parameter for reporting galling resistance results, making it suitable for comparison between different materials and test conditions. Test results for type 303, 304, and 316 stainless steels are given as an example of the testing and data reduction technique.

Dry dope-free premium connections: a zero discharge technology validated through laboratory and field testing and usage

Dope-free alternatives to standard thread compounds used for casing and tubing connections became commercially available around 2003. The challenges from galling resistance needs and handling and storage requirements were addressed. The lessons learnt from the initial uses and experiences with the dope-free solution were incorporated into products that are reliable and have proven their suitability in environments that vary from the extremely humid and cold North and Barents Seas to the sandy and hot environment of the Middle East. The experiences to date not only confirm the validity of initial drivers —mainly related to the environmental care—for the development of these alternatives, but also open up the possibility of the complete elimination of thread compound from the casing and tubing installation and storage processes. The dope-free solution has demonstrated suitability for application in all tubing and casing dimensional size ranges including: all type of steels (such as common carbon steel—both API grades and proprietary), 13Cr, and corrosion resistance alloys (CRA), premium connections with metal-to-metal seal both threaded and coupled (T&C), as well as integral connections. Experience with large outside diameter (OD) semi-premium connections indicates that this can be another area of application for dope-free solutions. This paper describes the different experiences related to the field use of dry, dope-free solutions, the improvements and adjustments incorporated after initial experiences and operators feedback and the verification activities in laboratory and especially in experimental rigs under actual field conditions. The intention of this presentation is to present the advantages and the value obtained through the use of this technology.

Experimental Studies on Galling Onset in OCTG Connections: A Review

With today’s high prices for natural gas and oil, the demand for oil and country tubular goods (OCTGs) with superior performance properties is very high. Failures in OCTG can be attributed to numerous sources, for example, makeup torque, corrosion, and galling. Thread galling is the most common mode of failure. This failure often leads to leakage, corrosion of the material, and loss of mechanical integrity. The failure of OCTG eventually amounts to excessive operational costs for the gas and oil industry. Numerous approaches have been taken to improve the galling resistance of OCTG connections. The advocacy of these approaches is often achieved through experimental studies using galling testers. There is a need to design and use effective galling testers to understand and improve the performance of OCTG connections. Thus, the objective of this paper is to present a concise review of literature related to the galling testers that may have applications to OCTG.

Comparison of two test methods for evaluation of forming tool materials

AbstractTwo test methods often used to simulate the tribological performance of forming tool materials are compared in this investigation through an evaluation of the friction and wear properties of four tool steels in dry sliding. One test (slider‐on‐flat‐surface (SOFS)) utilises a vertical disc sliding on a horizontal flat test surface, and the other (load scanner (LS) tests) utilises two crossed cylindrical rods. The test conditions were selected as equal as possible for the two tests, and the following conclusions are made.Somewhat unexpectedly, the friction and wear results differed substantially between the two tests. The SOFS test showed a better potential to evaluate wear resistance since one test sample is in continuous contact with the other. The LS test can generate higher contact pressures since the two rods contact each other in an unworn condition throughout the whole test stroke.LS indicate that two hard and smooth tool steels tested against each other generally give low friction and good galling resistance. The two hard couples tested sustained the highest loads without any detectable surface damage. For the same combinations of hard steels, SOFS gave a higher friction due to the wear of the disc. The carbides in the disc material resist wear better than the matrix and will consequently wear the disc by abrasion, which adds to the friction.The above conclusions are drawn from a rather limited examination using only one set of test parameters. In fact, the two tests are both very flexible as to the way they can be used, and they both have advantages and limitations in tribological studies. They should rather be considered complementary than competitive. Copyright © 2008 John Wiley & Sons, Ltd.

Development of a galling resistance test method with a uniform stress distribution

In this study, a new galling test method is presented along with results from a pilot testing program. The pilot program was performed on type 303 stainless steel. The new testing configuration consists of two concentrically aligned hollow cylindrical specimens loaded along their longitudinal axes. The specimens are held in alignment using a custom made alignment pin. The pin maintains concentricity between the mated surfaces while enabling the contact interface to self-align. The resulting contact surface is in the shape of an annulus and has a uniform stress distribution. The new testing configuration eliminates the stress concentration that exists in the ASTM G98 Standard Test Method for Galling Resistance of Materials. The results of this study show that the galling wear phenomena do not transition from non-galled to galled at a single value. Galling is shown to be stochastic in nature.

Development of Dope-Free Premium Connections For Casing and Tubing

Summary Removing API dope from the makeup process of threaded premium connections during casing and tubing operations not only reduces the risk of contamination of the local environment but also provides a cleaner and safer working area. Conversely, the removal of the antigalling property inherent in API dope greatly increases the risk of galling damage to connections during power-tight makeup. This paper describes various tests carried out to evaluate manufacturers' claims of having successfully improved the galling resistance of premium connections by electro-depositing a white bronze (45%Cu-55%Sn) alloy onto couplings manufactured from high-chrome materials. Galling resistance was measured by subjecting several test coupons plated with copper and various alloy compositions to a series of tests designed to generate high stresses to threaded surfaces. The paper also shows through experimentation how the correct amount of preload was achieved in a premium connection's gas-tight seal by applying a thin lubricating layer (also referred to as a protective film) to both pin and box threads.

Development and use of combined wear testing equipment for evaluating galling and high stress sliding wear behaviour

Galling is a severe form of wear characterized by localized, macroscopic material transfer or removal of material when two solid surfaces experience relative sliding under load. The current paper describes the development of a wear testing machine capable of testing both galling resistance and sliding wear behaviour (pin-on-disc) at high stress levels. For evaluating galling resistance using this equipment, a stationary button is placed in contact with a rotating flat block at a desired pressure by means of a hydraulic system. The block is rotated through one revolution and both the specimens are inspected for the presence of galling as per ASTM G98-91 galling procedure. In this, button axis coincides with the rotating block axis. Surface damage as a result of galling is also evaluated by applying the desired load to the button specimen and rotating the block about its vertical axis, back and forth 10 times through 120° in 90 s. To evaluate sliding wear behaviour, button axis is offset to a required distance and it is used as pin-on-disc apparatus. The apparatus developed in this work could be successfully used for assessing the sliding wear behaviour, as also the galling resistance. Various features of this apparatus and results from the tests are discussed in this paper.

Galling resistance and wear mechanisms – cold work tool materials sliding against carbon steel sheets

One of the major causes for tool failure in sheet metal forming is transfer and accumulation of adhered sheet material to the tool surfaces, generally referred to as galling. In the present work, the galling resistance of several tool materials was investigated against two-phase ferritic-martensitic carbon steel under dry sliding test conditions. Tribological evaluation was carried out at different contact pressures by using a slider-on-flat-surface (SOFS) tribometer.

Analysis of the stress field in a threshold-galling test

The wear phenomena of galling is characterized by macroscopic roughening and deformation of the surfaces of mated materials. Currently, the ASTM G98 button-on-block test method is the only standardized testing procedure for determining the galling resistance of material couples. The pattern of surface damage resulting from performing the ASTM test tends to be predicable. In particular, the galling generally occurs near the outer edge of the button and migrates inwards. In this study, the stress distribution between the mated specimens leading up to the onset of galling was investigated. A suitable analytical model of the system geometry and loading conditions was developed and applied. The results of the model show that a stress concentration exists along the edge of the button specimen when loaded. The stress concentration is believed to contribute to the initiation of galling at this site. The results of the analytical model have also shown that the magnitude of the stress concentration is dependent on the size of the corner radius. An alternative testing arrangement is presented and preliminary results are shown.

Surface analysis of laser cladded Stellite exposed to self-mated high load dry sliding

Materials from the Stellite family of Co-based alloys are commonly used as low friction, galling resistant materials in high load dry sliding contact applications. In the present investigation, the surface region of a Co-based material (Stellite 21) exposed to self-mated high load dry sliding at room temperature has been analysed in detail. During sliding, an approximately 30 nm thick Co-enriched tribofilm is created. It exhibits low friction properties and a high galling resistance. The transformation from an face-centred-cubic structure to easily sheared hexagonal-closed-packed basal planes in the tribofilm combined with the high load carrying capacity of the underlying deformation hardened zone is suggested to explain the excellent low friction properties and galling resistance of this material.

CARLSON NITRONIC 33

Abstract Carlson alloy Nitronic 33 has twice the yield strength of 304 stainless with comparable corrosion resistance. The low magnetic permeability of the alloy is retained after severe cold working. The resistance to chloride stress-corrosion cracking is superior to Type 304. Nitronic 33 has excellent strength and ductility at cryogenic temperature, and wear and galling resistance is superior to the standard austenitic grades. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on low temperature performance and corrosion resistance as well as forming and joining. Filing Code: SS-931. Producer or source: G.O. Carlson Inc., Electralloy.

Comparison between different test methods for evaluation of galling properties of surface engineered tool surfaces

In forming operations, galling is a tribological process associated with pick-up of formed material by the surface of the tool and subsequent damage of the work material surface. In lubricated operations, it is associated to lubricant film breakdown. Currently the main focus in development of forming tools is on improving their galling resistance, mainly by including new forming tool steels, improving surface finish, and applying surface treatments and coatings. However, in order to qualitatively rank the galling resistance of material couples, a proper test method for galling evaluation is needed. During the years several methods for determining the galling resistance have been reported in the literature. In the present investigation three different test methods were compared and evaluated as to their ability to assess the galling tendencies of coated and un-coated forming tool steel. The study included the pin-on-disc configuration, a modified cylinder-on-cylinder test with a spring loading system, and a new load-scanning test method, which involves two crossed cylinders. It was proved that the load-scanning test rig is both a very simple and the most suitable method to evaluate galling properties of tool steels. It gives the capability to compare different tool steels, tool surface finishes and treatments, and hard coatings in terms of friction level, amount of material transfer, and critical load for galling initiation.

The influence of phase transformations and oxidation on the galling resistance and low friction behaviour of a laser processed Co-based alloy

The effect of oxide formation on the tribological properties of a CO 2-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions in air and in an oxygen free environment. The tests were carried out by sliding two identical specimens against each other in a load-scanning test. A friction coefficient at a level of about 0.20 was observed for both test environments. However, the wear of the Co base material is accelerated when the sliding is performed in an oxygen free environment. The friction level appears to be controlled by the shearing of hcp {0 0 0 1} planes rather than by the presence of an oxide layer.

A galling-resistant substitute for silicon nickel

Silicon nickel, a cast nickel alloy containing about 3% silicon, had been used for threaded couplings in chemical delivery systems for over 40 years because it had necessary corrosion resistance and did not gall when mated with 316 and other stainless steels. In 2001, it was learned that this material was no longer available from long-time sources, and a laboratory study was undertaken to find a substitute alloy. Laboratory tests evaluated the threshold galling stress (using a modified ASTM G98 procedure) of six stainless steels against two titanium alloys and two proprietary alloys that allegedly (by their manufacturer) have good galling resistance. Silicon nickel was also tested as the material to “beat” in galling tests. The silicon nickel exhibited poor galling characteristics against all test counterfaces. Titanium with 6% A1 and 4% V showed good galling resistance against all counterfaces, but produced significant transfer to some counterfaces. One of the galling-resistant alloys exhibited good galling characteristics but transferred less. The galling-resistant alloy, which was essentially an austenitic stainless steel with increased nitrogen, silicon and manganese, was recommended as the substitute for the silicon nickel. It is thought that the silicon nickel worked in service because its porosity and silicide inclusions produced very high surface roughness in machining, and it was the porous, rough surface that provided its apparent galling resistance.

Effect of temperature on friction and galling of laser processed Norem 02 and Stellite 21

The Stellite family of Co-based alloys is known to offer superior performance in many demanding sliding contact applications. However, alternative materials with corresponding properties are searched for, e.g. due to the fact that wear and corrosion products of Co run the risk of activation in nuclear plant applications. Furthermore, due to the high price of Co, a competitive, less expensive alloy would be very welcome for use in many applications. The present investigation examines the frictional behaviour and galling resistance of the laser processed Fe-based alloy Norem 02 at temperatures ranging from room temperature (RT) to 250 °C. Friction and galling testing was performed by sliding two crossed test rods in a load-scanning test rig. The results are compared with those previously attained from laser processed Stellite 21, one of the best low friction, galling resistant Co-based alloys. At RT Norem 02 exhibited excellent sliding performance, comparable to that of Stellite 21, showing a low and stable friction coefficient at a level of 0.25, and no tendencies to gall. However, at temperatures of 150 °C or above, the friction coefficient raised to a level of 0.5–0.7 and massive galling was observed for Norem 02. Stellite 21, however, maintained its excellent friction performance at those temperatures. Consequently, laser processed Norem 02 might not be suitable as a candidate material to replace Stellite in valves and seals in the primary circuit of nuclear power plants, which usually operate at temperatures considerably higher than RT.

Measurement of the threshold galling stress of hardfacing alloys

Galling is a severe type of wear that occurs when relative motion exists between contacting surfaces with extensive local adhesion. The ASTM button-on-block test method for galling resistance of a material couple requires a large number of specimens and an apparatus with very high load capacity for testing at a range of different loads to find the threshold galling stress. In contrast, the galling test method of sliding two crossed cylinders over each other has the advantages of determining the galling resistance by using a small number of samples and utilizing a standard metallurgical/mechanical test apparatus. In this study, the crossed cylinder method is used to test cobalt- and iron-based hardfacing alloys with very high threshold galling stresses. How to measure or calculate the threshold galling stress in the crossed cylinder method is also studied.

Effect of niobium on structure and properties of PM high-speed steels : H. Chung et al. (Ajou University, Gyunggi, Korea)

Tools and dies used in hot metal forming are exposed to very demanding contact conditions, including elevated temperatures, high contact pressures and abrasive flow of work material, which lead to different types of tool damage. However, the most critical ones are wear and fatigue fracture. As the focus shifts toward the use of new lightweight high-strength materials, also requirements on tool properties are becoming more demanding. This requires use of surface engineering techniques like nitriding and PACVD coating and proper balance between hardness and fracture toughness. Vacuum heat treatment allows the optimization of the tool steel microstructure, which may result in increased fracture toughness while maintaining or even increasing hardness, which enhances possibilities of using coated forming tools.The aim of this work was to investigate the effect of austenitizing and tempering temperature on properties of AISI H11 hot work tool steel, including fracture toughness and hardness and how these properties effect on wear resistance and load-carrying capacity of plasma nitrided and PACVD-coated tool steel. Results indicate that through optimized vacuum heat treatment and surface engineering resistance of tool steel can be greatly improved. Increasing core hardness improves the resistance of nitrided AISI H11 tool steel to abrasive wear, but sufficient level of fracture toughness needs to be obtained first. Change in fracture toughness/hardness ratio has up to 40% influence on wear resistance. On the other hand, galling resistance mainly depends on the surface condition, with plasma nitrided surface without compound layer providing the very best results. Although TiN/TiB2 coating has no beneficial effect on galling resistance, it gives up to two orders of magnitude better wear resistance than nitride surface. However, for proper coating support high core hardness needs to be provided.

Some observations of the influence of δ-ferrite content on the hardness, galling resistance, and fracture toughness of selected commercially available iron-based hardfacing alloys

Iron-based weld hardfacing deposits are used to provide a wear-resistant surface for a structural base material. Iron-based hardfacing alloys that are resistant to corrosion in oxygenated aqueous environments contain high levels of chromium and carbon, which results in a dendritic microstructure with a high volume fraction of interdendrite carbides which provide the needed wear resistance. The ferrite content of the dendrites depends on the nickel content and base composition of the iron-based hardfacing alloy. The amount of ferrite in the dendrites is shown to have a significant influence on the hardness and galling wear resistance, as determined using ASTM G98 methods. Fracture-toughness (K IC) testing in accordance with ASTM E399 methods was used to quantify the damage tolerance of various iron-based hardfacing alloys. Fractographic and microstructure examinations were used to determine the influence of microstructure on the wear resistance and fracture toughness of the iron-based hardfacing alloys. A crack-bridging toughening model was shown to describe the influence of ferrite content on the fracture toughness. A higher ferrite content in the dendrites of an iron-based hardfacing alloy reduces the tendency for plastic stretching and necking of the dendrites, which results in improved wear resistance, high hardness, and lower fracture-toughness values. A NOREM 02 hardfacing alloy has the most-optimum ferrite content, which results in the most-desired balance of galling resistance and high K IC values.