Effect of previous plastic deformation on the resistance of chromium-manganese steels to cavitation erosion

The investigation described in this paper was concerned with austenitic chromium-manganese steels characterized by various resistances to the martensitic transformation during plastic deformation. It was established that the influence of previous plastic deformation on the resistance of these steels to cavitation erosion varies. In each case it is necessary to consider both the susceptibility of austenite to decomposition (accompanied by the formation of martensite and -phase) under the influence of cavitation and various phase and structural transformations taking place in the steel as a result of previous plastic deformation.     

Numerical analysis of cavitation erosion and particle erosion in butterfly valve

The investigation of butterfly valve applied in the circulation water filtration system (CWF) of one pressurized water reactor (PWR) nuclear power station is performed in the paper. A coupling computational fluid dynamics model combined multiphase, cavitation and discrete phase model has been built to simulate the cavitation erosion and particle erosion. The validity and rationality of the coupling model is sufficiently verified with the experiment of flow coefficient and effects of different factors including inlet pressure and valve opening angle are discussed in detail. The results reveal that the erosion of butterfly valve mainly occurs at the forward and backward part of valve disc. With the increase of inlet pressure, max velocity, mass flow rate, wall shear stress, turbulent intensity and particle erosion would increase. Mass flow rate, wall shear stress, turbulent intensity and particle erosion decrease with the decrease of valve opening angle. The simulation results are well consistent with the failure feature of butterfly valve applied in actual operation. The numerical analysis is expected to improve the erosion condition and reliability of butterfly valve.     

Research on cavitation erosion and wear resistance performance of coatings

Depending on the nature of the working medium and working conditions, corrosive and cavitation damage shall arise to pump’s components. In industrial applications the corrosion-reducing coatings are sprayed on hydraulic components. But it is questionable whether such products actually do help under wear or cavitation loads or not. Abrasive jet wear tests were carried out to determine the wear resistance of coating materials: polymers and ceramics, cast iron, and steel of various types. The samples were loaded for five hours, and finally the wear depth was measured as a determining indicator of the sample’s wear resistance. Results of investigation on anti-erosion performance of epoxy resin, ceramic and Polyurethane (PU) coatings brushed on alloy steel surface were also presented. Cavitation erosion tests were performed on the ultrasonic rig. The mass loss and surface morphology of the specimens were examined by balance analysis and 3-D laser microscopy, respectively. The investigations showed excellent wear-resisting performance of ceramic coatings, which is better than wear-resistance of stainless steel, cast iron and high chrome alloy steel. But the excellent wear-resisting performance could not guarantee a good erosion-resisting performance. The ceramic coatings’ anti-erosion performances were inferior to that of gray cast iron, and hardly comparable to those of stainless steels. The basic factors that influenced coating’s cavitation erosion endurance were adhesion and thickness of coatings. Analysis of coating’s degradation mechanism showed that PU coatings could withstand longer incubation period thus enhancing the materials’ cavitation erosion resistance. Several practical cases were analyzed, showing some guidance for coatings’ application.     

The erosion behaviour of TiN coatings on steels

The erosion behaviour of physical vapour-deposited titanium nitride has been studied using both blunt particle and angular particle erodent streams. The mechanisms of erosive loss have been identified and related to the microstructure and internal stress state of the coatings. High levels of internally stored energy (which scales with coating thickness and internal stress) induce spalling in erosion testing using blunt erodents. Consequently, it is found that thick coatings are more resistant to angular particle erosion whilst thin coatings have longer lifetimes when exposed to blunt erodents. Scratch adhesion testing has been performed on all erosion specimens and attempts made to correlate the critical load for coating failure, with the failure mechanisms observed in erosive wear. Whilst no correlation can be found between erosion resistance and critical load, good correlations between the failure mechanisms found in erosion and scratch testing can be made.     

新型耐空蚀Cr-Co-Ni-Mn奥氏体不锈钢研究

制备了一种Cr-Co-Ni-Mn含钴奥氏体不锈钢。与304不锈钢比较,研究了其抗空蚀性能,用TEM观察了空蚀试样的组织结构,并测定了该钢种的强度,利用时效处理研究其组织稳定性。结果表明Cr-Co-Ni-Mn含钴奥氏体不锈钢屈服强度、抗拉强度比常用的304不锈钢高,奥氏体组织稳定,空蚀孕育期长,耐空蚀效果好。TEM观察到试样空蚀作用层有ε马氏体组织,这些形变组织有利于吸收应变能,提高材料耐空蚀能力。综合该钢的性能,在耐空蚀领域有潜在的应用前景。     

材料表面抗空蚀涂层的研究进展

空蚀现象广泛存在于海洋平台、船舶机械和能源发电等领域.这种腐蚀现象不仅造成了巨大的经济损失,也成为相关从业人员的安全隐患.本文概述了抗空蚀涂层材料技术的研究进展,重点介绍了抗空蚀金属涂层技术和抗空蚀聚合物涂层技术.最后对目前抗空蚀材料存在的问题及未来发展进行了展望.     

Evaluation of the cavitation and erosion resistance of surfacing materials

The results of investigations of the cavitation and erosion resistance of chromium steels are given, the influence of alloy elements on the degree of strengthening of materials is considered, and an engineering method of evaluation of the resistance of surfacing materials is proposed.Translated from Problemy Prochnosti, No. 12, pp. 79–86, December, 1990.     

Microstructures and mechanical properties of boride-dispersed precipitation-hardening stainless steels produced by RST

Two commercial precipitation-hardening (PH) stainless steels were modified with 2.64 to 2.86 wt% Ti and 1.2 to 1.3 wt% B via rapid solidification technology (RST) and powder metallurgy (PM). The resulting alloys exhibited improved tensile and yield strengths over their commercial PH stainless steel counterparts at room and elevated temperatures. Ductility improvements at elevated temperatures were also observed. The improved mechanical properties were due to extremely fine microstructures stabilized by a fine dispersion of boride phases.     

Features of cavitation and cavitation erosion of waveguides of powerful ultrasonic units at higher-than-average pressure of the media

The features of the acoustic effects of cavitation created by the rod waveguides of powerful ultrasonic magnetostriction units in different liquid media at a pressure to 5 MPa have been investigated. It has been established that, under the conditions of maximum acoustical activity of cavitation realized at the medium's higher-than-average pressure, the erosion damage to the waveguides is of an unusual structurized character and develops from the central part of the end to its periphery. A result of the erosion damage may be the total loss of operating capacity by the waveguides manufactured from the most erosion-resistant materials (stainless steel and titanium alloys) even after a few hours of tests. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 690–696, July–August, 2008.     

Characteristics of rolling contact fatigue of steels produced by thermomechanical processing

0.27C-1.97Cr-1.65Mn-0.30Mo-0.21Ni steels produced by thermomechanical processing were rolling contact fatigue tested in the elastohydrodynamic lubricating condition at the rotating speed of 8,000 rpm under the applied load in the range of 25–100 kgf. A mixture of lower bainite and martensite was formed during thermomechanical processing, and it was found in transmission electron microscopy that fine lower bainite was formed by splitting in two after formation of martensite. The zone of maximum shear stress was found to be 195.0–339.3 m in depth from the contact surface by comparing the regions of hardness increase, microstructural change and the contact width during rolling contact fatigue. Resistance to crack initiation during rolling contact fatigue is the main reason for improved fatigue life. This is confirmed from the result that the shortest fatigue life was shown in the specimen with the largest crack length and crack depth.     

Hot-cracking of high-alloyed steels evaluated by wedge rolling test

We present a new methodology of determination of hot-cracking of metallic materials, which is based on laboratory application of the wedge rolling test and computer processing of the results obtained. The experiment was made with selected new types of high-alloyed free-cutting (ferritic and austenitic) steels. The initial specimens underwent an additional modification enabling easier development of cracks which consisted in milling out of the defined V-shaped notches on a side wall of a specimen. After taking specimens from the rolled material, we performed the metallographic analysis of microstructures by means of optical microscopy as well as a SEM analysis of the cracks. The resulting microstructure in the propagating crack vicinity was markedly influenced by this fracture. In the crack vicinity, a noticeable refinement of grains was observed due to the stress-induced recrystallization and occurrence of deformation zones that were pronounced by the rolled-out and stretched sulphides. As a rule, fractures were created by the ductile failure with visible pits, caused by tearing of sulphides from the material. Susceptibility of the studied steels to hot-cracking was evaluated and compared. __________ Translated from Problemy Prochnosti, No. 1, pp. 60–63, January–February, 2008.     

马氏体冷轧-回火制备超细晶钢及其热稳定性

在低碳钢和低碳加铌、钒、钛微合金钢中,通过马氏体冷轧--回火的方法获得了尺寸为数百纳米的超细晶粒铁素体组织,研究了超细晶粒组的形成机制和热稳定性.通过马氏体相交在这些钢中引入了大量高密度位错,马氏体冷轧后位错进一步增殖,形成大量位错胞状结构;在500-600℃进行的60min回火将上述胞状结构转变成具有清晰大角晶界的超细晶粒.在回火过程中形成的微合金元素碳化物对位错运动和晶界移动具有有效的"钉扎"作用,有助于获得超细晶组织并明显提高其热稳定性.     

Effect of boron addition on the cavitation erosion resistance of Fe-based hardfacing alloy

The cavitation erosion behavior of Fe–Cr–C–Si–xB (x = 0, 0.3 and 0.6 wt.%) alloys were investigated up to 50 h by using 20 kHz vibratory cavitation erosion test equipment. The boron-added alloys showed the improved cavitation erosion resistance compared to the boron-free alloy. This improvement was attributed to that the boron addition enhanced the grain boundary strength and refined the grain size of the matrix. However, the cavitation erosion rate of the 0.6 wt.% boron specimen was higher than that of the 0.3 wt.% boron specimen. The higher erosion rate of the 0.6 wt.% boron was due to the larger carbide volume in the matrix.