Influence of heat and thermochemical treatment on abrasion resistance of structural and tool steels

Abrasive wear is responsible for intensive degradation of machine parts or tools. This process starts as an interaction between hard, mostly mineral, particles and the working surface. Methods of increasing the lifetime are based on application of abrasion resistant materials or creation of hard, wear-resistant surface layers or coatings on the surfaces of machine parts or tools. Carbon and low-alloy steels with different types of thermochemical treatment (case hardening, nitriding) are used in cases of low abrasion. Another method of increasing lifetime is the application of ledeburitic steels. The wear resistance of these steels depends on their chemical composition and heat treatment. The results of laboratory tests of thermochemically treated steels, heat-treated ledeburitic chromium steels and high-speed steels show the effect of the microstructure of these steels on their abrasion resistance. Abrasion resistance of carburized low-alloy steels is on the same level as in high-carbon structural and tool steels. In ledeburitic chromium steel maximum abrasion resistance was achieved by quenching from 1100 °C whilst in ledeburitic chromium–vanadium steel the optimum quenching temperature was 1150 °C. Growing abrasion resistance was caused by increasing amounts of retained austenite.     

The erosion of heat-treated steels

The erosion behavior of a plain carbon steel (AISI-SAE 1020), an austenitic stainless steel (type 304) and a low alloy steel (AISI-SAE 4340) in various heat-treated conditions was determined. The testing was conducted at room temperature using aluminum oxide particles with an average size of 140 μm in an air stream. An attempt was made to characterize the erosion behavior as it relates to the mechanical properties obtainable in these alloys by conventional heat treatments. It was found that the ductility of the steels had a significant effect on their erosion resistance which increased with increasing ductility and that hardness, strength, fracture toughness and impact strength had little effect on erosion behavior. The platelet mechanism of erosion occurred in all the steels tested at all conditions.     

Assessment of the erosion resistance of steels used for slurry handling and transport in mineral processing applications

The wear environment of steels used for containing, transporting and processing erosive mineral slurries is often such that fluid borne particles form a layer moving at high speed across the wearing surface. Information on the performance ranking of such materials is limited, particularly with respect to the influence of steel hardness and microstructure on the resistance to erosion. This is particularly important for the oil sands industry of Northern Alberta where handling and processing of essentially silica-based solids results in extremely severe wear conditions. This paper presents slurry erosion data obtained on 11 commercially available wear resistant plate and pipeline steels with hardness values up to 750 HV. These data were obtained using a Coriolis erosion tester operated at 5000 rpm with an aqueous slurry containing 10 wt.% of 200–300 μm silica sand particles.

The Coriolis erosion tester was selected because it provides a low-angle scouring action that simulates the erosive conditions encountered in oil sands and tailings pipeline transport and in some related processing operations. Results show that this test method is able to discriminate clearly between the erosion resistance of these steels, expressed in terms of specific energy (the energy necessary to remove unit volume of test material), with the most erosion resistant steel being more than five times superior to the least resistant. A graphical relation between steel hardness and erosion resistance is given. A comparison is also made between slurry erosion data and the performance of the materials in the ASTM G65 dry sand rubber wheel (DSRW) sliding abrasion test. Comments on the influence of the macro- and microstructures of the steels on their wear behaviour are included.     

Wear behaviour of some low alloyed steels under combined impact/abrasion contact conditions

The wear behaviour of some low alloyed steels has been investigated using a laboratory impeller–tumbler wear test equipment in which the steel samples are worn by angular granite particles under combined impact/abrasion wear contact conditions. The wear of the steels was evaluated by weight loss of the steel samples while the wear mechanisms of the steels were investigated by post-test light optical microscopy (LOM), scanning electron microscopy and energy dispersive X-ray analysis. The worn steel surfaces display a very rough surface topography with pronounced craters and distinct grooves caused by high and low angle impacts, i.e. abrasive wear, respectively. Besides, fragments of embedded granite particles are frequently observed in the worn surface of the steels. The wear of the steels tends to decrease with increasing steel hardness. However, instead of using the bulk hardness value the hardness of the worn/plastically deformed surface layer should be used when modelling the wear resistance. Further, the wear resistance of the steels was found to be dependent on the microstructure and chemical composition. Steels with similar type of microstructure show a linear decrease in weight loss with decreasing grain size and increasing carbon content.     

Cavitation erosion of cobalt-based Stellite® alloys,cemented carbides and surface-treated low alloy steels

A number of Stellite^® alloys, cemented carbides and surface-treated alloy steels have been evaluated for erosion resistance. The ability of the Stellite alloys to withstand erosion is primarily a function of the cobalt-rich solid solution phase while erosion of cemented carbides is controlled predominantly by the binder phase. The nickel-based tungsten carbides are more resistant to erosion than the cobalt-based samples.Investigation of industrial surface treatments has demonstrated that erosion rates of hardened low alloy steels can be improved. For example, a hardened electroless nickel coating on BS 817M40 steel erodes at one-third the rate of uncoated BS 817M40 steel. A Tufftriding treatment, which is a proprietary method of carbonitriding, applied to the same steel caused a similar improvement in performance but only after an initial loss of the compound layer. Hard chrome coating is, in general, less effective than the above treatments in combating cavitation erosion.     

Friction and Wear of Metals in Gases Up to 600 C

Apparatus is described for measuring friction and wear in controlled atmospheres. A comparison is made of the room temperature behavior of copper, mild steel and brass, rubbed against a hardened tool steel, in four environments—vacuum (10^?3 mm Hg), dry helium, dry carbon dioxide, and dry air. The effect of varying the water vapor content in air is also discussed.

The initial selection of rubbing pairs for service at elevated temperatures is gaseous environments under unlubricated conditions, is based on their long-term resistance to corrosion and their ability to give low wear rates. In general, therefore, the materials must be hard. Several alloys having chromium contents of between 1% and 30%, and hardness values in the range 200–1000 vpn have been investigated. These included two low-chromium nitrided steels, a tungsten-chromium tool steel and a series of four Co-Cr-W alloys. Specific wear rates and friction coefficients varied markedly with temperature, and values in the ranges 10^?13–10^?8 cm³/cm kg and 0.1–0.8, respectively, were obtained in both dry carbon dioxide and dry helium. Lowest wear rates were observed with the nitrided steels. The diverse characteristics observed are discussed on the basis of current theories of adhesive wear.     

Erosive wear behaviour of weld hardfacing high chromium cast irons: effect of erodent particles

Five commercial hardfacing high chromium cast iron alloys were deposited by flux cored arc-welding method. The solid particle erosion studies were carried out using air blast type erosion test rig with 125–150 μm cement clinker, 125–150 μm blast furnace sinter, 100–150 μm silica sand and 125–150 μm alumina particles at a velocity of 50 m s⁻¹ and at impingement angles of 15–90°. The observed erosion rates were rationalised in terms of relative hardness of erodent particles and ability of erodent particle to cause gross fracture of the carbides. The dependence of erosion rate on impingement angle was found to be quite weak for hardfacing high chromium cast iron alloys. However, significant differences were observed in the ranking of the alloys when eroded with different erodent particles. The presence of large volume fraction of carbides proved to be beneficial to the erosion resistance when the erodent particle were softer than the carbides. With silica sand particles at normal impact and with alumina particles large volume fraction of carbides proved detrimental to the erosion resistance. The operating erosion mechanisms involved small-scale chipping, edge effect, indentation and fracture and fatigue.     

Erosion–corrosion behavior of Zr-based bulk metallic glass in saline-sand slurry

Bulk metallic glass (BMG) is supposed to have a good erosion–corrosion (E–C) resistance due to its high hardness and good corrosion resistance. To reveal the E–C behavior, Zr₅₅Cu₃₀Ni₁₀Al₅·BMG is investigated using a slurry pot erosion tester. Experimental results show the volume loss rate of BMG increases with an increase in the particle size, sand concentration or impact velocity. The corrosion current density and the synergism rate increase with the increasing impact velocity. During E–C process, the surface microstructure transforms gradually from pure amorphous to composite mixture of crystalline and amorphous phases. The E–C resistance of BMG is better than that of 304 stainless steel, but not as expected as its high hardness.     

Experimental assessment of droplet impact erosion resistance of steam turbine blade materials

The droplet impact erosion resistance of five different but highly relevant steam turbine blade materials is investigated with the help of an erosion test rig. The rig adapts wetness and droplet impact speed conditions in the last stages of condensing steam turbines in such a way that the material degradation is greatly accelerated in order to establish monotonic saturating material loss gradients—ideally within a testing time interval of 50 h. Repeatability and reproducibility of the evaluation method is ensured to facilitate the representative ranking of materials based on droplet impact erosion resistance being a key material property for durable steam turbine blade designs.A selection of three blade steels (X20Cr13, a steel similar to X5CrNiMoCuNb 14-5, X5CrNiCuNb 16-4) and one titanium alloy (Ti6Al4V) is tested and analysed. Additionally, X5CrNiCuNb 16-4 in a laser-hardened condition is investigated. Besides the influence of droplet impact speed and droplet impact angle on erosion, the generated surface jaggedness, the level of material degradation as well as the material loss gradients are discussed and utilised for further deductions. Among the high yield strength blade steels, the laser-hardened X5CrNiCuNb 16-4 exhibits the best erosion resistance while Ti6Al4V exhibits a higher erosion resistance than all the steel alloys tested.Finally, a simplified but functional model is inferred from the test data to estimate the droplet impact erosion resistance of alternative steel and titanium blade materials relative to the materials discussed in this text.     

Effects of vanadium and carbon on microstructures and abrasive wear resistance of high speed steel

The effects of vanadium and carbon on microstructures and abrasive wear resistance of high speed steel were studied. The results show that the microstructures are characterized by VC, M₇C₃ and Mo₂C in the martensite and austenite matrix. Typical morphologies of vanadium carbides are found to be spherical, lumpy, strip, and short rod. On the other hand, the vanadium carbides have three kinds of distributions, i.e. grain boundary, chrysanthemum-like, and homogeneous distributions. The abrasive wear resistance of high speed steel depends on the hardness and microstructures. When the hardness is lower than HRC58, the abrasive wear resistance of the high speed steel mainly depends on its hardness. But when the hardness is higher than HRC58, it mainly depends on the amount, morphology and distribution of VC in the matrix. Many spherical or lumpy VC carbides are obtained when vanadium and carbon content is up to 8.15–10.20 and 2.70–3.15%. The excellent abrasive wear resistance would be obtained if such VC carbides disperse uniformly in the hardened matrix of high speed steel after quenched at 1050 °C and tempered at 550 °C.     

Mechanical properties and features of erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attributed to differences in their resistance to fracture. The present paper discusses some features of the material removal process during the particle–wall collision. Solid particle erosion tests on eight materials have been performed using silicon carbide and silica abrasive particles within a range of erodent size of 0.1–0.3 mm, impact angles from 30 to 90° and particle velocity from 30 to 80 m s⁻¹. In order to clarify the details of the impact, the process of interaction of solid particles with cermet targets was studied using a laser Doppler anemometer (LDA) measuring technique. Systematic studies of the influence of the impact variables on the collision process have been carried out.     

Micro-abrasion resistance of thermochemically treated steels in aqueous solutions: Mechanisms, maps, materials selection

The area of micro-abrasion is an interesting and relatively recent area in tribo-testing methodologies, where small particles of less than 10 μm are employed between interacting surfaces. It is topical for a number of reasons; its direct relation to the mechanisms of the wear process in bio-tribological applications, ease in conducting tests and the good repeatability of the test results. It has widespread applications in conditions used in the space and offshore industries to bio-engineering for artificial joints and implants.There have been many recent studies on the micro-abrasion performance of materials, ranging from work basic metals to nano-structured coatings. However, no significant work is reported on the micro-abrasion resistance of thermochemically treated steels. Hence, this paper looks at the performance of two thermochemically treated steels, Tenifer bath nitride stainless steel (T-SS) and vanadized carbon steel (V-CS) in such conditions with reference to the stainless steel (SS) by varying the applied load and sliding distance.The results indicated that T-SS demonstrates exceptionally poor resistance to micro-abrasion. It was observed that the heat treatment process and properties of the hardened layer (hardness and thickness) are extremely important in determining the micro-abrasion resistance of such steels. Finally, the results were used to develop micro-abrasion mechanism and wastage maps, which can be used to optimize the surface treated materials for micro-abrasion resistance.     

Studying wear resistance of carbon steels strengthened by plasma hardening

The wear resistance of carbon steels strengthened by plasma hardening in an UDGZ-200 setup is studied using a friction machine. It has been found that the wear resistance of hardened low-carbon steel 15 is equal to ～70% of normalized steel 45, as well as the wear resistances of the hardened medium-carbon steel 45 and the hardened high-carbon U8A steel exceed the wear resistance of the normalized steel 45 by ～60 and ～90 times, respectively.     

Revision of cavitation erosion database and analysis of stainless steel data

Cavitation erosion data have been accumulated in our laboratory for about 32 years since 1970. The database was constructed as electronic data in MS Excel files. The data files are able to offer quick search in terms of the test material, test method and test conditions from among 859 data. In this study, 131 data since 2003 were newly added to the database constructed in our previous study. The stainless steel data were analyzed, including various stainless steels such as ferritic, austenitic, duplex and martensitic stainless steels. Vibratory cavitation test results for different stainless steels, obtained with varying test conditions of frequency, amplitude and attachment of specimen, were converted analytically to obtain average erosion rates under assumed standardized conditions of a stationary specimen test with 1 mm standoff distance, and with frequency and amplitude as specified by ASTM G32. The average of erosion rate under the standardized condition (ASTM G32, stationary specimen method, standoff distance 1 mm) was determined for different stainless steels. The erosion resistance was defined as a reciprocal of erosion rate, and the correlation between erosion resistance and hardness of the specimen after erosion test was better than with the other mechanical properties. The erosion resistance is equal to 2.6E?07 × (HV × F_mat)^2.4 (HV; Vickers hardness, F_mat; material factor), and the correlation coefficient is 0.98. It was concluded that the erosion resistance of different stainless steels could be estimated with high reliability from the material hardness and the material factor.     

The wear-resistant coating of steel by chemical vapour deposition

There is a steady increase in the use of chemical vapour deposition to deposit carbides of the transition metals onto the surface of steel. In this process the transition metal, in the form of a volatile chloride, is normally carried to the surface in a controlled manner by a carrier gas together with a carbon-containing reactant such as a gaseous hydrocarbon. These react at the steel surface to form a carbide layer on it which is smooth, hard, continuous and wear and corrosion resistant. The general features of the process are described for the specific coatings of titanium carbide and chromium carbide on high alloy ledeburitic carbon steels. By way of illustration three examples are discussed which are of industrial significance.     

General aspects for tribological applications of hard particle coatings

Hard coatings, consisting of WC, TiC or Cr₃C₂ particles with a nickel or cobalt matrix were compared with conventional wear-resistant materials like hardened steel 100 Cr6, Ferro TiC P143, WC-Co hard metal and a widely used thermal spray layer NiCrBSi. The coating procedure was flame spraying and diffusion welding. Some layers were remelted using an electron beam to improve their microstructural properties, porosity and binding to the bulk material.

Wear tests were performed under different degrees of severity to qualify the resistance of the coating, using abrasive, sliding and impact test methods representing different wear mechanisms. It is shown that the benefit of the hard particle content depends on the acting loading situation. Under abrasive and sliding conditions the advantage of a high hardness level, i.e. a high concentration of hard phases, could be demonstrated. For impact loading, causing severe surface fatigue, homogeneous materials with high toughness, such as martensitic steels, are beneficial; followed by coatings with a high concentration of ductile matrix. In some cases, the weaknesses, such as brittleness and limited strength of binding to the bulk, could be improved by electron beam remelting.     

Erosive wear of selected metals in coal washing environments

A slurry erosive wear apparatus developed by the authors has been used to test the erosive wear behaviour of selected metals in coal washing environments. The erosive wear test machine was employed to determine the effects of (1) carbon content in carbon steels, (2) chromium content in alloy steels, and (3) corrosion of aqueous solutions on the erosive wear behaviour of metals. The test results revealed that the carbon content in annealed carbon steels slightly affects the erosive wear resistance of metals, while the increase in chromium content of alloy steels apparently improves the erosive wear resistance of metals and, when a corrosion inhibitor is added to slurries, the erosive wear rates of metals reduces significantly. Two types of micro-mechanism were deduced from the observation of eroded surfaces by SEM: (1) local exfoliation, and (2) micro-cutting. The corrosion inhibitor can alter the micro-mechanism from local exfoliation to micro-cutting. The analyses show that the erosive wear of selected metals in slurries results from the synergistic effects of wear by solid particles plus fluid corrosion.     

Characterization of erosion of gas pipelines by dry sand

In oil and gas industry, the economic considerations determine the selection of low cost materials, in general, carbon steel, for pipelines. However, another type of deformation that is not well understood is its erosion resistance. The objective of this study was to investigate the factors affecting the erosion of carbon steel in a dry sand stream. In this work, a laboratory built test rig was used to erode representative carbon steel plates with accelerated sand streams. The results revealed that the normal incidence sand stream of larger particles and higher impact velocities causes more erosion of the carbon steel. The highest erosion rate of 6.75 ± 0.16 was predicted at an impact angle of 90°, which was three times higher than the erosion rate at impact angle of 30°. Similarly, the erosion caused by the smaller particles was not as severe as the larger particles. The cross-section profiles revealed that the crater depth was increased from 7° to 32.8° with an increase in sand size from 200 µm to 600 µm. The deepest crater of 32.8° was induced by the largest sand size of 600 µm.     

Wear of cast chromium steels with TiC reinforcement

Wear resistance of a series of new titanium carbide reinforced cast chromium steels was investigated under various wear conditions. The steels which were melted in a vacuum induction furnace contained 12 Cr, 3–5 Ti, 1–2 C in weight percent. Microstructure of these materials was characterized using scanning electron microscopy, light optical microscopy, and X-ray diffraction. Microstructure of steels consisted of TiC phase dispersed in a martensitic matrix. High-stress and low-stress abrasion tests, and an erosion test, were utilized to understand the wear behavior of these materials under different environments. The steels were tested in as-cast and heat treated conditions. Wear rates of the cast Cr/TiC steels were compared to those of an AISI type 440C steel and P/M composites reinforced with TiC.     

An evaluation of the wear behaviour of a dual-phase low-carbon steel

Wear behaviour of dual-phase AISI 1020 steel was investigated. The steel was austenitized at critical transformation temperature and rapidly quenched. Thus, the structure of the steel consists of martensite and ferrite phases in different proportions. Heat treated samples were subjected to wear with a cylinder-on-cylinder sample configuration under dry sliding conditions. Wear resistance was determined as functions of hardness and proportion of martensite phase, and elongation of the steel. The wear resistance of the dual-phase 1020 steel was also compared with those of hardened and tempered AISI 1040 and 8640 steels. It was indicated that the wear resistance of the test steel decreases with martensite proportions, and increases with martensite hardness and elongation of the steel.