Influence of microstructure on erosion resistance of steels

Erosive wear due to solid particle impingement is a very intensive degradation process of surface layers of metallic materials. Erosion resistance is influenced by the working conditions (impact angle, impact velocity of solid particles, size, shape, hardness and amount of impinging particles) and the parameters of the worn material like hardness and microstructure. In our experiments some structural and tool steels were tested by slurry with SiO₂ particles at a flow velocity of 20 m/s. The microstructures of the tested steels were modified in a broad range by changing the conditions of their heat treatment. Increasing pearlite share in the structure of annealed carbon and low-alloyed steels has a positive effect on their erosion resistance. The growing carbon content in the tested hardened steels increases their erosion resistance. Maximum erosion resistance was found in hardened chromium ledeburite steel. Hardened high-speed steel HS 11-0-4 in spite of its high hardness has lower erosion resistance than ledeburitic chomium steels. An increasing amount of retained austenite and decreasing carbide and martensite shares with growing quenching temperature of the tested ledeburitic chromium steels leads to the reduction of their erosion resistance.     

Corrosion and erosion performance of HVOF/TiAlN PVD coatings and candidate materials for high pressure gate valve application

The main objective of this paper is to study the slurry erosion and corrosion behavior of WC10Co4Cr, Armcore ‘M’ Stellite 6 and 12 HVOF coatings, TiAlN PVD coating, selected steels, such as X20Cr13, 17Cr–4Ni pH steel and Ti6Al4V titanium alloy alongwith conventional hard weld deposits of Stellite 6 and 21. The slurry erosion studies were carried out at 60° angle of impingement for the velocities in the range of 15–20 m/s using mineral sand of −40 to +80 mesh. The corrosion studies were carried out as per ASTM B 117-73 for 100 h. During slurry erosion testing, WC10Co4Cr HVOF along with TiAlN PVD coating are found out, to be the best coating materials followed by HVOF coating of Armcore ‘M’ material. However, for corrosion, Ti6Al4V, Stellite 6 and 21 hard weld deposits and 17Cr–4Ni pH steel turned out to be the best materials followed by HVOF coating of Stellite 6 and 12. HVOF coatings of WC10Co4Cr and Armcore ‘M’ materials corroded significantly, however, TiAlN PVD coating corroded very badly even after 24 h of testing.     

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.     

使用照相法测量汽轮机湿蒸汽中水滴尺寸的研究

为了蒸汽轮机的运行安全，准确可靠地测量蒸汽轮机中湿蒸汽水滴的粒径分布，利用图像测量的方法对湿蒸汽特征进行分析，采用Canny边缘检测算子准确检测水滴的边缘，然后根据水滴图片的放大倍数计算出水滴的实际尺寸，最后根据水滴的尺寸分布估计湿蒸汽的湿度及湿蒸汽的危害程度并发出报警信息。     

Development of a water droplet erosion model for large steam turbine blades

Water droplet erosion is one of major concerns in the design of modern large fossil steam turbines because it causes serious operational problems such as performance degradation and reduction of service life. A new erosion model has been developed in the present study for the prediction of water droplet erosion of rotor blades operated in wet steam conditions. The major four erosion parameter ; impact velocity, impacting droplet flow rate, droplet size and hardness of target are involved in the model so that it can also be used for engineering purpose at the design stage of rotor blades. Comparison of the predicted erosion rate with the measured data obtained from the practical steam turbine operated for more than 90.000 hours shows good agreement.     

Erosion durability of steels in steam boiler heat exchanger tubes

The erosion durability of three tube materials that are generally used in the heat exchangers of steam boilers was tested by having an air flow containing particles flowing through tube banks. The materials tested were St35.8, 15Mo3 and 10CrMo910. The last one was most resistive to erosion. The material 15Mo3 had a higher resistance than St35.8, but lower than 10CrMo910. Correlations between erosion resistance and the strength, and erosion resistance and the ductility of the steels were observed.     

35#钢35CrMnSi 钢激光淬火区耐磨性研究

重点对35^#钢和35CrMnSi 钢两种材料激光淬火组织耐磨性进行了研究.试验结果表明,激光淬火材料比原调质处理材料的耐磨性提高1—3倍.激光淬火层主要由马氏体组成,其高硬度是提高耐磨性的重要原因.     

汽轮机再热后级内颗粒冲蚀特性

汽轮机再热后级内叶片受到固体颗粒冲蚀,严重影响着汽轮机的安全经济运行。以某超临界汽轮机再热后第1+1/2级(第一级与相邻级的喷嘴)扭叶片为研究对象,通过拉格朗日法模拟不同粒径颗粒三维运动轨迹,并采用Finnie冲蚀模型,研究不同动静轴向间隙及不同负荷下颗粒对叶片的冲蚀特性。结果表明,由于动叶高速旋转,颗粒撞击到动叶时会获得与主流方向相反的速度,进而又反弹回静叶。较大粒径颗粒在动静叶片轴向间隙内"反复反弹"是造成再热后级内冲蚀的主要原因。适当增大动静轴向间隙可以有效地减少反弹回静叶的颗粒数量。当动静轴向间隙为5 mm时,反弹回静叶的颗粒为10%,轴向间隙增大为8 mm时,没有颗粒反弹回静叶。当机组负荷降低时,固体颗粒撞击叶片后的反弹角增大、反弹回静叶的数量增多,颗粒在动叶和下级静叶轴向间隙内反弹后,只有极少颗粒能够流出下级静叶。     

碳钢奥氏体不锈钢材料在水电工程中应用的局限性

通过对水电站典型应用材料(55钢、1Cr18Ni9Ti、0Cr13Ni5Mo)在冲蚀磨损过程中电化学腐蚀及抗冲蚀磨损性能研究,区分出纯磨损、纯腐蚀、磨损对腐蚀的促进分量及腐蚀对磨损的促进分量等在材料失效过程中各占的比例,考察了试验材料的抗冲蚀磨损特性及其磨损与腐蚀间的交互作用,分析了其失效机制。结果表明:不同的冲蚀速度下,0Cr13Ni5Mo不锈钢的冲蚀磨损失重率最小,55钢最大;纯磨损是材料失去的主要方式:55钢虽然纯磨损量较小,但腐蚀及其磨损与腐蚀的交互作用失去量大,1Cr18Ni9Ti不锈钢虽然纯腐蚀量小,但纯磨损量大,因而都有应用的局限性。     

Slurry Erosion Wear Resistance and Impact-Induced Phase Transformation of Titanium Alloys

Erosion wear resistance and impact-induced phase transformation of titanium alloys TA2 (pure Ti), TC4 (Ti–6Al–4V) and TC11 (Ti–6.5Al–3.5Mo–1.5Zr–0.3Si) were investigated using a slurry jet tester. The slurry erosion wear resistance of TA2 is comparable to that of 304 stainless steel, especially at the impingement angle 90°. Although TC4 and TC11 have higher hardness, TA2 possesses the best erosion wear resistance except TC11 at 15°. With the increasing erosion time, the eroded surface hardness of TC11 at the impingement angle 90° increases and then decreases, while the volume loss rate drops in the first 15 min, then increases until 30 min, and then slightly decreases again. With XRD characterization and SEM observation, erosion-induced phase transformation from metastable β-phase to α-phase is proved on the surface of titanium alloy TC11. And the thickness of visible phase transformation layer is about 10 μm. Phase transformation influences the erosive wear mechanism of titanium alloys. At the impingement angle of 30°, the material removal of TC4 and TC11 can be described as micro-plowing and lip extruding, while plowing mark is not a typical surface morphology of TA2, indicating a better work-harden ability. So, stabilizing β-phase can be an effective way to improve the erosion wear resistance of titanium alloys.     

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.     

钛合金冷风切削表面粗糙度试验研究

为了探索汽轮机低压锁扣叶片材料Ti6Al4V钛合金的切削表面粗糙度变化规律,采用均匀设计方法设计了钛合金切削参数,在冷风降温条件下,对表面粗糙度进行试验研究。运用最小二乘法原理,对试验数据进行多元线性回归分析,建立了适用于钛合金材料在冷风切削条件下的表面粗糙度经验公式,从而找到冷风条件下切削表面粗糙度的变化规律。     

Slurry Erosion–Corrosion of Carburized AISI 5117 Steel

The erosion–corrosion of carburized and untreated low alloy steel (AISI 5117) has been investigated using slurry whirling-arm test rig. Erosion–corrosion tests were carried out in slurries composed of sand particles and either tap water or 3 % NaCl solution. The tests were carried out with particles concentration of 1 wt% and slurry stream impact velocity of 15 m/s. Silica sand having a nominal size range of 250–355 μm was used as an erodent. It has been shown that the erosion and erosion–corrosion resistance of AISI 5117 low alloy steel can be effectively improved by carburizing for all impact angles. However, the effectiveness of carburizing was the highest for an impact angle of 45°, where the erosion and erosion–corrosion resistance were increased by 60–40 %, respectively, compared with that of the untreated material. The results showed that the treated and untreated specimens behaved as ductile materials under erosion and erosion–corrosion tests, and the maximum mass loss occurred at an impact angle of 45°. SEM analysis showed that the erosion tracks developed on the untreated specimens were wider and deeper than that formed on the carburized specimens for erosion and erosion–corrosion tests.     

Study of corrosive fatigue and life enhancement of low pressure steam turbine blade using friction dampers

The paper investigates the causes of failure of low pressure steam turbine blade of the last stage and suggests few techniques to overcome the failure causes is presented in this paper. The blade under investigation is made of chrome alloy steel. The fracture occurred at the airfoil region of the blade. The investigation included visual inspection, micro structural characterization, SEM-EDS microanalysis and spectroscopy test to identify the causes of failure. The paper also suggests the methods to reduce the blade fatigue subsequently through computation and to enhance the fatigue strength of the steam turbine blade. In order to reduce the blade fatigue susceptibility and to enhance the fatigue life of the steam turbine blade, the wedge shape friction damper is proposed.     

The role of adiabatic shear in solid particle erosion

A comparison is made of the deformation produced when titanium and mild steel target specimens are impacted obliquely by flat-ended cylindrical projectiles. The impact process is studied by high speed photography; it is shown that whereas in mild steel material is not removed from the surface but merely displaced, in titanium, the displaced material detaches by a process involving the formation of adiabatic shear bands. Attention is drawn to the influence of susceptibility to adiabatic shear on resistance to solid particle erosion.     

High-temperature erosion tests on materials for fluidized bed combustor heat-exchanger tubes

In order to simulate and predict the erosion damage suffered by in-bed tubes in fluidised bed combustors, dedicated test equipment was set up at CISE's tribology laboratory with ENEL S. p. A (Italian National Electricity Board) support. This erosion rig was used to test and characterise the behaviour of AISI 310, P9, and P22 steels, candidate materials for this type of heat-exchanger tube. Tests were carried out at room temperature to characterise the erosion behaviour of these materials and at higher specimen (350°C and 500°C) and air (840°C) temperatures to simulate and characterise their behaviour in service. From this experimental work it turned out that, while at room temperature, the erosion behaviour of the three materials did not differ significantly, at high temperature P9 showed the best resistance in both test conditions and AISI 310 displayed an optimum behaviour at normal impact angles, but had the higher erosion rate at 30° impact angle.     

Particle-surface interactions during the erosion of aluminide-coated MarM002

Particle-surface interactions during the erosion of a nickel aluminide coating were assessed using a single-impact technique. It is shown that the erosive response is a function of the surface scale thickness and the temperature, with the temperature not only influencing the surface scale plasticity but also determining the contribution of the coating substrate to the impact process. In this respect the ductile-to-brittle transition temperature of the coating is of particular importance.Under a wide range of conditions typical of those found in gas turbines the erosion of aluminide coatings is shown to be controlled by the formation and removal of surface scales. This implies that the use of aluminide coatings will increase the erosion resistance of typical turbine blade materials because of the superior oxidation and corrosion resistance of this coating. This increase in erosion resistance will be particularly significant at higher operating temperatures, above 900 °C.     

Liquid drop impact on solid surface with application to water drop erosion on turbine blades,Part I: Nonlinear wave model and solution of one-dimensional impact

Water drop erosion is regarded as one of the most serious reliability concerns in the wet steam stage of a steam turbine. The most challenging aspect of this problem involves the fundamental solution of the transient pressure field in the liquid drop and stress field in the metal substrate, which are coupled with each other. We solve the fundamental problem of high-speed liquid–solid impact both analytically and numerically. In Part I of this paper, the governing equations based on a nonlinear wave model for liquid are derived. Analytical and approximate solutions of one-dimensional liquid–solid impact are given for both linear and nonlinear models, which provide critical insights into the water drop erosion problem. Both continuous and pulsant impacts on rigid and elastic substrates are analyzed in detail. During continuous impact, the maximum impact pressure is always higher than the water hammer pressure. Upon pulsant impact and at a particular instant related with the impact duration, the maximum tensile stress appears at a certain depth below the solid surface, which can be readily related with the erosion rate. In Part II of this paper, two-dimensional (axisymmetric) liquid–solid impact is solved numerically, from which the most dangerous impact load/duration time and the most likely crack positions are deduced. Based on our recent solution of the water drop impact statistics (associated with the fluid flow in the blade channel), a comprehensive numerical study of the water drop erosion (fatigue) on a turbine blade is carried out.     

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.     

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.