Behaviour of ferritic–martensitic steel and aluminium base coatings under demanding elevated temperature conditions

Abstract

Ferritic–martensitic steels are found in many elevated temperature applications due to their excellent strength properties and thermal conductivity. However, their resistance to elevated temperature corrosion, wear and combination of these is typically not at a desired level. One solution is to improve the surface properties by the application of a coating. In this study, aluminium diffusion coatings were deposited on 9Cr–1Mo steel and characterised in terms of microstructure and elevated temperature corrosion and erosion–corrosion behaviours. The two behaviours are then compared to those of an uncoated steel. The results from the tests indicate that aluminising shows great potential under the studied demanding elevated temperature conditions. The benefits and challenges of the deposition and use of aluminised coatings are discussed in this paper.     

High temperature erosion behavior of spark plasma sintered ZrB2-SiC composites

Damage of structural components of hypersonic vehicles by atmospheric particles demands thorough understanding on their wear behavior. In the present work, dense ZrB₂-SiC (10, 20, and 30 vol%) composites are prepared by spark plasma sintering at 55 MPa in two stages: 1400 °C for 6 min followed by 1600 °C for 2 min. With increase in SiC content, microstructures of sintered composites reveal strongly bonded ZrB₂ grains with SiC particles. A combination of maximum hardness of 23 GPa, elastic modulus of 398 GPa and fracture toughness of 5.4 MPa m^1/2 are obtained for the composite containing 30 vol% SiC particles. It is found that cracks are bridged or deflected by SiC particles in the composites. When the composites are subjected to SiC particle erosion at 800 °C, a 14% decrease in erosion rate is obtained with increase in SiC content from 10 to 30 vol%. The formation of large extent of boro-silicate rich viscous surface on eroded surfaces is attributed to reduced fracture or removal of ZrB₂ grains of the composites with increased SiC content.     

Designing erosion management plans in Lebanon using remote sensing, GIS and decision-tree modeling

Soil erosion by water represents a serious threat to the natural and human environment in Mediterranean countries, including Lebanon, which represents a good case study. This research deals with how to use Geographic Information Systems (GIS), remote sensing, and, more specifically, structural classification techniques and decision-tree modeling to map erosion risks and design priority management planning over a representative region of Lebanon. The structural classification organization and analysis of spatial structures (OASIS) of Landsat TM satellite imagery (30 m) was used to define landscapes that prevail in this area and their boundaries, depending on their spectral appearance. The landscape map produced was overlaid sequentially with thematic erosion factorial maps (i.e., slope gradient, drainage density, rainfall quantity, vegetal cover, soil infiltration, soil erodibility, rock infiltration and rock movement). The overlay was visual and conditional using three visual interpretation rules (dominance, unimodality and scarcity conservation), and landscape properties were produced. Rills and gullies were measured in the field, and a decision-tree regression model was developed on the landscapes to statistically explain gully occurrence. This model explained 88% of the variability in field gully measurements. The erosion risk map produced corresponds well to field observations (accuracy of 82%). The landscapes were prioritized according to anti-erosive remedial measures: preventive (Pre), protective (Pro), and restorative (Res). This approach seems useful in Lebanon, but can also serve in other countries with similar geo-environmental conditions or those lacking detailed geospatial data.     

Characteristics of Submerged Jets in Evolving Scour Hole Downstream of an Apron

This paper reports an experimental investigation on the velocity and turbulence characteristics in an evolving scour hole downstream of an apron due to submerged jets issuing from a sluice opening detected by an acoustic Doppler velocimeter. Experiments were carried out for the conditions of submerged jets, having submergence factors from 0.96 to 1.85 and jet Froude numbers from 2.58 to 4.87, over sediment beds downstream of a rigid apron. The distributions of time-averaged velocity vectors, turbulence intensities, and Reynolds stress at different streamwise distances are plotted for the conditions of initial flat bed, intermediate scour holes, and equilibrium scour hole downstream of an apron. Vector plots of the flow field show that the rate of decay of the submerged jet velocity increases with an increase in scour hole dimension. The bed-shear stresses are determined from the Reynolds stress distributions. The flow characteristics in evolving scour holes are analyzed in the context of self-preservation, growth of the length scale, and decay of the velocity and turbulence characteristics scales. The most significant observation is that the flow in the scour holes (intermediate and equilibrium) is found to be plausibly self-preserving.     

基于气-固双向耦合的输气管道最大冲蚀角度预测

弯管作为气田集输管道输送系统中的常用组件,极易受到固体颗粒对管壁的冲蚀破坏。为了研究输气管道的冲蚀规律、 预测弯管最大冲蚀位置,采用Eulerian-Lagrangian 方法计算了管内气、固两相的流动情况,在Eulerian 坐标系下求解气体连续相 流场,在Lagrangian 坐标系下求解颗粒离散相运动轨迹,利用Erosion/Corrosion Research Center（E/CRC）冲蚀模型以及Grant 和 Tabakoff 颗粒-壁面碰撞模型计算管壁冲蚀速率。数值计算过程中考虑了气、固两相之间的双向耦合作用,利用多种模型研究了在 不同弯径比及颗粒直径影响下的弯管冲蚀规律、颗粒运动轨迹及弯管最大冲蚀角度,并提出最大冲蚀位置预测方程。研究结果表明： ①固体颗粒对弯管的冲蚀存在着临界直径,在颗粒临界直径前后的冲蚀规律明显不同;②固体颗粒直接碰撞和滑动碰撞共同作用导 致弯管出现不同的冲蚀形貌,并影响最大冲蚀速率的出现位置;③根据临界颗粒直径以及管道中颗粒运动轨迹提出的冲蚀最严重位 置预测方程能很好地预测弯头处最大冲蚀角度,可以为输气管道冲蚀预测提供参考。     

掺炼俄油后常减压蒸馏设备的腐蚀问题处理

介绍了中国石油吉林石化公司炼油厂常减压装置掺炼俄油后出现的设备腐蚀问题,分析了硫腐蚀的机理,低温及高温硫腐蚀产生的部位及防止措施和收到的效果。     

Cavitation erosion resistance of stellite alloy weld overlays

Stellite alloys have excellent cavitation erosion resistance and are often used for liquid machinery, but the erosion properties of various stellite alloys have not been evaluated by a standard method. In this study, we evaluate the erosion resistance for various stellite alloy weld overlays of ST6 and ST21 in a vibrating method and in a cavitating liquid jet method. The grain size of the Co matrix affects the cavitation erosion resistance of stellite alloy weld overlays of ST6. The erosion rate of the maximum rate stage of stellite weld overlay alloys of ST6-1, ST6-2 and ST6-3 were found to be about 1/13 to 1/7 times that of SUS304. Moreover, we clarified the cavitation erosion mechanism of SUS304 and ST6 by scanning electron microscopy. Furthermore, by comparing the erosion behavior in a cavitating liquid jet method with that in a vibratory method, it was found that the erosion rate of the cavitating jet method and the vibratory method have a good correlation.     

Abrasion and erosion behaviour of manganese alloyed permanent moulded austempered ductile iron

Laboratory abrasion and erosion tests have been reported on permanent moulded austempered ductile iron with manganese as alloying element at three levels, i.e., 1%, 2% and 3%. The influences of Mn addition on the wear and tensile properties have been studied and discussed. The results indicate that with increase in Mn content from 1% to 2%, the abrasion and erosion volume losses are exhibiting decreasing trend. Further increase in Mn addition to 3% has resulted in an increase in wear losses. Same is the case with the tensile strength and percentage elongation properties. These data have been interpreted based on the structural features including graphite morphology.     

Erosive wear by silica sand on AISI H13 and 4140 steels

The erosive wear behaviour of AISI H13 tool steel and AISI 4140 steel has been investigated in this work using a sand blast-type rig. Samples of six different hardness levels (from annealed to 595 HV) were produced and subsequently tested using silica sand as the erodent material at impact angles ranging from 10° to 90°, air drag pressures of 0.689 and 1.38 bar (10 and 20 psi respectively), impact speeds ranging from 70 to 107 m s⁻¹ and various particle sizes. Results of erosion versus impact angle at different hardness levels showed three distinctive wear regions: (i) for impact angles of 10° and 20°, the amount of wear was higher at lower hardness values; (ii) for impact angles of 30° and 40° no significant changes were found in the amount of wear despite the increase in hardness; (iii) for impact angles of 60°, 75° and 90° the amount of wear was higher for higher hardness levels in the eroded material. Single curves showed typical ductile behaviour of these alloys, a transition towards brittle behaviour for the hardest specimens was also observed due to the formation of adiabatic shear bands. SEM analysis was conducted to identify the erosion mechanisms for each type of behaviour.     

Characterizing cavitation erosion particles by analysis of SEM images

Wear particles produced by vibratory cavitation erosion on stationary-aluminum Al-99.999 were analyzed using scanning electron microscope (SEM), forming a database for further analysis. The particle morphology features were first clarified based on the characteristic stages of the vibratory erosion rate-time pattern. Next, size, area, perimeter and shape factors (elongation and roundness) were determined for eroded particles, using image analysis software. In incubation period, the particles have distinctive characteristics which differed from that for the subsequent periods. These characteristics include the value of longitudinal ratio and roundness factor, limit size range and morphological features such as lamella shape, folding, curving with one of the particle surfaces as the virgin surface. In acceleration, steady-state and attenuation periods, the particles have a wide size range and larger thickness compared with that for the incubation period. The maximum particle size reached about 360 μm in acceleration and steady-state period. For all the cavitation erosion rate periods, the particles were out of sphericity and they have a roundness factor larger than 2. Detailed surface characteristics of the particles produced during cavitation erosion is significant and can open ways for monitoring the cavitation erosion progress.