Cavitation damage incubation with typical fluids applied to a scroll expander system

During the operation of a scroll expander system overpressure may occur resulting in cavitation damage. Impacts due to implosion of cavitation bubbles near to suction ports can result in damage to the scroll plate in the expander. The accumulation of cavitation pits across the scroll plate leads to cavitation erosion hence efficiency drop. An experimental analysis to identify the mechanical damage of the cavitation on various steel surfaces with different liquid environments was conducted.Three liquid environments and four steel grades were utilised experimentally. The liquids used for the tests were distilled water, used as a reference liquid, and the two working fluids of the scroll expander a synthetic lubricant and a high molecular refrigerant. The steel grades were a high carbon (AISI 1085) and low carbon (AISI 1010) martensitic steel with retained austenite, a chromium martensitic steel (AISI 52100) and a martensitic scroll plate (SP) sample. An ultrasonic transducer was utilised to produce cavitation conditions using a 5 mm diameter probe. The comparison of the results revealed the most hostile liquid environment according to the morphology evaluation of the incubation pits. The cavitation mechanisms are discussed and the cavitation resistance of the steel grades is evaluated. The best performing steel material against cavitation is determined for the conditions described.     

An experimental study on cavitation erosion-corrosion performance of ANSI 1020 and ANSI 4135 steel

Cavitation erosion is quite complex, containing corrosion-erosion interaction effect. High temperature oxidization may be aroused after bubble collapse, accompanied by hot gas contacting with the pump component surface. The analysis of the erosion pits can be an effective way to know the mechanism of cavitation erosion. In present paper, the cavitation erosion resistance of carbon steel (ANSI 1020) and alloy steel (ANSI 4135) were tested in an ultrasonic vibration apparatus. By using energy dispersive X-ray spectroscope and three dimensional laser microscope, the chemical composition around erosion pits and the oxidation film structure were analyzed. By using metallographic microscope and scanning electronic microscope, the metallographic structure of specimens (e.g., carbon steel and alloy steel), the nano structured iron oxide and corresponding influence on specimen’s anti-erosion performance were discussed. Based on the comparison between the different tests performed in distilled water and tap water respectively, results can be obtained that erosion rate of carbon steel and alloy steel varies with the component of water which had close correlation to the oxidation effect. Erosion rate of alloy steel 4135 was much lower in distilled water compared to tap water while the difference of carbon steel 1020 was not that large. The remarkable different responses of these two materials had close relationship with oxidation effect. The oxidation effect transferred the original structure of alloy steel surface which had high anti-erosion capability, into newly generated iron oxide structure, which was preferentially to be attacked. The pumping of slightly corrosive fluids frequently leads to erosion-corrosion damage on impellers, and corrosion can further amplify the erosion process.     

Performance of environment-friendly hydraulic fluids and material wear in cavitating conditions

The cavitation performance of various metals and hydraulic fluids used in a hydraulic system was evaluated using the vibratory test method. Mineral oil, vegetable oil and oil-in-water emulsions were used in the experiments. The materials were selected based on the general components employed in a hydraulic system—AA 5005 aluminium alloy, ASTM A536-84 ductile spheroidal graphite (SG) cast iron, ASTM A48-83 grey cast iron, AISI 303 stainless steel and BS 1400 LG2 bronze. It was observed that vegetable oil exhibits the best medium for erosion resistance for all metals due to its high viscosity index. Emulsions having higher oil concentration produced lesser erosion damage. It was seen that an increase in viscosity led to a decrease in the rate of growth and collapse of bubbles and hence reduced erosion on the surfaces of the specimens. The experiments also revealed that materials with high hardness had less cavitation damage for all lubricants. A comparison of cavitation performance revealed that materials and hydraulic fluids have a dependent relationship. Results indicate that AISI 303 stainless steel would be the best choice in the construction of a hydraulic system and this is especially the case when using a hydraulic fluid that has a high viscosity index.     

The Role of Reversible Martensitic Transformation in the Wear Process of TiNi Shape Memory Alloy

It has been established that the superelastic effect of TiNi alloy is related to a reversible martensitic transformation; that is, stress-induced transformation. The high elastic recovery of TiNi alloy has made it a potential candidate for high wear resistance applications. In the present study the tribological behavior of superelastic TiNi alloy was studied and compared to Ni, Ti, and AISI 304 stainless steel using dry sliding wear and friction tests. The effect of normal load and testing temperature on superelasticity has been investigated. It has been found that although AISI 304 stainless steel and superelastic TiNi alloy have similar hardness, TiNi exhibits superior wear resistance. The wear rate of AISI 304 stainless steel is over four times higher than TiNi. The superior wear resistance of TiNi and the effect of load and temperature on wear were discussed and related to the reversible martensitic phase transformation, as well as self-accommodation and stabilization of martensite.     

NiAl合金翼型空蚀破坏行为的试验研究

在收缩-扩散型空蚀磨损试验水洞中对NiAl合金翼型进行空蚀破坏试验,使用扫描电镜(SEM)对受空蚀破坏的翼型上表面进行了观测,结果表明翼型上表面有大量的空蚀针孔出现,并随着试验时间的不断延长而扩展成空蚀坑,蚀坑内有微裂纹出现,蚀坑间也出现了微裂纹,从而导致蚀坑的扩展和表面材料的去除.     

Cavitation Erosion and Sliding Wear to Assess Carbide Integrity in AISI D2 Tool Steel

Ultrasonic cavitation and ball-on-disk wear tests were conducted in order to assess the carbide integrity in AISI D2 steel specimens with different heat treatments and carbide orientations on the exposed surface. The response of the tested materials under cavitation erosion was clearly distinguishable for each carbide orientation and heat treatment. Particularly, carbide predominant orientation can be successfully associated with the incubation period of cavitation damage. Validity of the cavitation erosion tests as a useful characterization technique in materials with reinforcement phases is discussed based on the small contact areas associated with the microjets generated in the ultrasonic cavitation test. On the other hand, ball-on-disk tests in conjunction with conventional wear analysis (coefficient of friction graph, wear volume) did not provide a clear relationship between research variables. However, by using discrete Fourier analysis from friction coefficient data, it was possible to establish a correlation between integrity of primary carbide, its orientation and matrix hardness.     

Failure analysis of melt urea pump impeller

Abstract

A melt urea pump is out of work after only 6 days in service. The failure of the melt urea pump impeller is analysed using different methods including chemical composition analysis, metallographic observation, SEM and energy dispersive spectroscopy analyses, etc. The results show that the material of the impeller is not the reported AISI 321 stainless steel but AISI 316 stainless steel. There are many honeycombed holes on its impeller, which is the typical feature of cavitation damage. Therefore, the main failure reason of the impeller is the cavitation erosion, and the electrochemical corrosion of the medium also accelerated the failure of the impeller. The failure of the impeller is not related with the as casted defects of the material because no obvious as casted defects are found in the material.     

A study on the cavitation resistance of ion-nitrided steel

Cavitation is a common deterioration process of a material resulting from high-speed fluid attack. Surface treatments are usually preferably considered to promote cavitation resistance because economic reason and longer durability consideration. The cavitation behaviors of ion-nitrided carbon steel, the response of nitriding layer to various cavitation environments, in particular, were studied. An ASTM G32-85 standard method was conducted to proceed cavitation test in fresh water, 3.5 wt.% NaCl and 3.5 wt.% HCl aqueous electrolytes, respectively.Experimental results show that nitriding of steel would reduce the cavitation rate of the S48C steel in fresh water due to the hard nitrided surface which could resist mechanical damage. Electrochemical corrosion plays a part in the case of 3.5 wt.% NaCl and 3.5 wt.% HCl electrolytes. Ion-nitrided specimens in the former electrolyte, therefore, become less protective than in fresh water with, however, lower cavitation rate than blank steel. Ion-nitrided specimen in the later electrolyte subjecting primarily to electrochemical attack to the nitriding layer, which has high corrosion current, shows inferior cavitation resistance than blank substrate. Therefore, the method of surface modification should be properly determined depending on what electrolyte would be used. Ion nitriding of carbon steel in our case is suitable for fresh water and 3.5 wt.% NaCl electrolyte, but not for 3.5 wt.% HCl electrolyte.     

Tribological Behavior of New Martensitic Stainless Steels Using Scratch and Dry Wear Test

This paper focuses on the tribological characterization of new martensitic stainless steels by two different tribological methods (scratch and dry wear tests) and their comparison to the austenitic standard stainless steel AISI 316L. The scratch test allows obtaining critical loads, scratch friction coefficients, scratch hardness and specific scratch wear rate, and the dry wear test to quantify wear volumes. The damage has been studied by ex situ scanning electron microscopy. Wear resistance was related to the hardness and the microstructure of the studied materials, where martensitic stainless steels exhibit higher scratch wear resistance than the austenitic one, but higher hardness of the martensitic alloys did not give better scratch resistance when comparing with themselves. It has been proved it is possible to evaluate the scratch wear resistance of bulk stainless steels using scratch test. The austenitic material presented lower wear volume than the martensitic ones after the dry wear test due to phase transformation and the hardening during sliding.     

The effects of work material on tool wear

Wear maps showing the wear behaviour of titanium carbide (TiC)-coated cemented carbide tools during dry turning of various types of steel have been presented in earlier studies. The maps have demonstrated that tool wear rates vary with cutting speeds and feed rates used. They have also shown that there is a range of cutting conditions, called the safety zone, within which tool wear rates are the lowest. This paper further examines, using the wear mapping methodology, the effects of different grades of steel workpieces on the wear of TiC-coated carbide tools. Wear maps constructed for the machining of AISI 1045 and 4340 steels show that flank wear is generally more severe when machining the AISI 4340 grade, especially at high cutting speeds and feed rates. Nevertheless, the contour and location of the safety zone on the wear maps for both grades of steels correspond to that revealed in previous work on general steel grades.     

Erosion–corrosion of engineering steels—Can it be managed by use of chemicals?

One significant contributory factor in the degradation of both pipelines and downhole tubulars in the oil and gas industry is erosion–corrosion. An erosion–corrosion investigation was carried out with three different steels—carbon steel, martensitic stainless steel and superduplex stainless steel. The materials were chosen to represent “active” and “passive” corrosion materials and are the same materials used in completions. Tests were carried out under three different regimes spanning a range of fluid velocities to simulate the severity of the mechanical erosion effect. A commercial corrosion inhibitor was used to investigate the inhibitor ability to reduce damage due to erosion–corrosion. In each of the conditions, pure corrosion and combined erosion–corrosion were studied by electrochemical and gravimetric techniques. The experiments were conducted using a jet impingement rig capable of producing jet velocities up to 20 m/s in a CO₂-saturated environment with sand. Erosion–corrosion mechanisms were determined from microstructural studies by SEM and inhibitor adsorption tests. The paper shows that the inhibitor effectively reduced erosion–corrosion damage for carbon steel; it was only in severe erosion–corrosion conditions that inhibitor has any noticeable effect for martensitic stainless steel and there were no conditions where the inhibitor offered a benefit for the superduplex stainless steel.     

Application of hot press forming process to manufacture an automotive part and its finite element analysis considering phase transformation plasticity

An automotive flex plate that is installed in the automotive engine and delivers a torque to a transmission is manufactured by hot press forming technique. By this technique, significant increase of strength through quenching of heated high carbon SK5 steel sheet and higher dimensional stability after forming through the press operation at high temperature can be attainable. The indirect method with a pre-forming step and direct oil quenching to attain uniform and fast cooling rate are employed considering cooling characteristics of the SK5 steel and large thickness of the flex plate. A new tool design is proposed for the hot press forming process, and an optimized heat treatment condition is determined by studying two frequently utilized heat treatments: austempering and quenching with tempering heat treatments. By introducing designed tools and selected heat treatment condition, the target product can be successfully manufactured, which satisfies two main manufacturer's specifications: high hardness and good dimensional accuracy. Moreover, finite element analysis, which considers transformation induced plasticity (TRIP) during phase transformations, is performed to understand the thermo-mechanical behavior of hot press formed sheet. The analysis verifies that phase transformations play significant roles in strengthening by transforming hard martensitic phase and in reducing dimensional change by additional plastic deformation during phase transformations.     

钢制阀门常用主体材料

介绍了适用于各种不同工况条件的钢制阀门主体材料常用的普通碳钢、普通低温钢、铬钼高温钢和奥氏体不锈钢等钢种所适用的标准。在简单介绍各类钢种的主要性能及其化学元素对材料的性能影响的基础上，对各类钢种又分别以铸件、锻件、板材和管材等4种材料类型对其化学成分和力学性能等进行了分析和比较。     

Three-dimensional atom probe characterization of alloy element partitioning in cementite during tempering of alloy steel

Hardness measurements confirm that the martensitic microstructure of an alloy steel, AISI/SAE 4340, is significantly more resistant to softening, compared to the martensitic microstructure of a high-purity Fe-0.4% C alloy, at tempering temperatures, 300-400 degrees C, just above the temperatures where cementite replaces transition carbides in the martensitic matrix. Three-dimensional atom probe (3DAP) analyses of the 4340 steel show that Si rejection from the cementite is first detected after low-temperature tempering for times of 1 h. After 10-h tempering at 400 degrees C, Mn and Cr contents are increased, and Ni contents decreased, in cementite according to their carbide- and non-carbide-forming tendencies, respectively. The results are discussed with respect to the diffusivity of the substitutional alloying elements in the 4340 steel, and the effect that such diffusion-controlled redistribution would have on maintaining fine distributions of cementite that resist softening during tempering.     

Effect of Silicon Nitride Ball on Adhesive Wear of Martensitic Stainless Steel Pyrowear 675 and AISI M-50 Races with Type II Ester Oil

Advanced bearing materials for future military and commercial gas turbines are required to operate at high speeds, high temperature, and higher thrust loads. At elevated operating conditions, the bearing and gear materials must be able to operate with ultrathin oil films without suffering detrimental effects of adhesive wear. The development of materials with rolling-element fatigue and corrosion resistance properties without deterioration in adhesive wear attributes is a significant challenge. To meet those performance requirements, the forerunner, martensitic stainless steel Pyrowear 675 (AMS 5930), has been in development for aerospace bearing and gear applications. This article addresses the adhesive wear performance of three variants of Pyrowear 675 with silicon nitride ball material simulating a hybrid bearing evaluated using a WAM8 machine. Baseline testing was conducted using conventional bearing steel AISI M-50. Adhesive wear testing was conducted at a temperature of 200°C and at different contact slips (15, 30, 50, and 70%) and entraining velocities (1.3 to 10.2 m/s). Posttest specimens were analyzed by scanning electron microscopy (SEM) and auger electron spectroscopy (AES). All the hybrid material pairs demonstrated very good adhesive wear performance compared to the baseline AISI M-50–AISI M-50 pair.     

低层错能FeMnSiCrCu形状记忆合金的空蚀

对低层措能Fe—26Mn—6Si—7Cr—lCu形状记忆合金和0Crl3Ni5Mo不锈钢进行了空蚀试验。结果表明，Fe—26Mn—6Si—7Cr—lCu形状记忆合金杭空蚀性能优于0Crl3Ni5Mo不锈钢。空蚀过程中应变诱发马氏体转变是该形状记忆合金具有良好杭空蚀性能的主要原因。     

Friction and wear behavior of diamond-like carbon coating on plasma nitrided mild steel under boundary lubrication

The friction and wear properties of synthetic ionic liquid functionalized borate esters as additives in poly-alpha-olefin (PAO) were measured for diamond-like carbon (DLC) coating on plasma nitrided AISI 1045 steel. Results show that the borate esters gave much better friction–reduction and antiwear properties for DLC coating/steel and DLC coating/DLC coating sliding pairs than zinc dialkyldithiophosphate (ZDDP). In addition the DLC coating had much better wear resistance than the nitrided mild steel substrate, indicating that duplicate surface modification was more effective in significantly increasing the wear resistance of mild steel.     

Lower bainite bearings for adverse environments

The conventional heat treatment processes used in the manufacture of rolling bearings are normally specified to produce a martensitic structure in high carbon bearing steel. An alternative process in which lower bainite is produced offers a tougher steel which is particularly advantageous in conditions where lubrication is poor. The improved performance of lower bainite bearings in mine conveyor applications and where fire-resistant fluids are used as lubricants is discussed in this paper.     

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.     

The Effect of Different Temperatures on Friction and Wear Properties of CFRPEEK against AISI 431 Steel under Water Lubrication

The tribological behavior of 30 vol% carbon fiber–reinforced polyetheretherketone (CFRPEEK) against AISI 431 steel under different temperatures of water lubrication was investigated. Friction and wear tests were carried out on a disc-on-disc contact test apparatus under different operating conditions. The results reveal that the lubricant temperature has a significant effect on the friction and wear properties of CFRPEEK sliding against AISI 431 steel. The average friction coefficient and wear rate of CFRPEEK increase with increasing lubricant temperature. However, the wear rate of AISI 431 steel did not have a positive correlation with the wear rate of CFRPEEK under different temperatures of water lubrication. Moreover, the original and worn surfaces of CFRPEEK and AISI 431 steel were imaged by environmental scanning electron microscopy and optical microscopy, respectively. The main tribological mechanisms of CFRPEEK sliding against AISI 431 steel were adhesive wear, and increasing the temperature of the lubricant could accelerate wear.