Effect of Toughness and Ductility on the Cavitation Erosion of Martensitic Stainless Steel (original) (raw)
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During their operation, the components of hydraulic equipment are exposed both to special mechanical and technological loads and to the corrosive action of the working environment, which affect the normal functioning of the machinery. After decades of activity, hydro turbines from Romania hydropower plants, respectively their components have been subjected to vast refurbishment processes. On these occasions, frequently cavitation erosion has been found on the surfaces of Kaplan and Francis turbine blades. The stainless steel grade X3CrNiMo13-4 (1.4313), alloyed with chromium, nickel and molybdenum and presenting a martensitic structure with a low content ferrite is widely used for the casting of Kaplan blades and Francis runners designed to equip Romanian power plants. In this paper, the authors realized a comparative study regarding the cavitation resistance of several samples of soft martensitic stainless steel type 13-4, having different compositions and microstructures. The material samples were taken from cast components used in five Romanian hydropower plants. The results obtained may be used to support the refurbishment program for hydraulic turbines set on Romanian rivers.
IOP Conference Series: Earth and Environmental Science, 2010
The paper follows the evolution of cavitation erosion on two stainless steels with structures in which the martensite and austenite have similar ratios, using the characteristic curves for the medium depth of erosion (MDE) and the medium depth of erosion ratio (MDER), and also using images of the eroded surfaces which were taken using a microscope. The goal of the tests was to find the reason for which materials with similar microstructures have different behaviors to cavitation erosion. This way, the influence of chromium and the influence of the other alloying elements can be observed. The results show that the steel with higher contents of alloying elements like manganese, silicon and titanium have a superior cavitation erosion resistance. Also, the results validate the manufacturers' trend to use stainless steels with carbon contents of about 0.1% for the manufacturing of hydraulic machines and equipment. The tests were conducted on a vibratory apparatus with piezoceramic crystals T2, built in accordance with to the ASTM G32-10 international standard, found in the Hydraulic Machines Laboratory in Timişoara. The studied stainless steels cast after specific recipes for hydraulic rotors and blades. After the casting process, the steels were subjected to an annealing treatment and a hardening process.
Cavitation Erosion Behaviour of Stainless Steels with Constant Nickel and Variable Chromium Content
Materials Testing, 2012
The paper highlights new aspects in the evaluation of cavitation erosion resistance based on the chromium content variation and implicit on the Cr/Ni equivalent which constitutes the microstructure development using the information given by the Schaeffler diagram. The presented and analysed results show that it is possible to establish an optimum relation between the chromium and nickel content, in order to obtain a substantial increase of the cavitation erosion resistance. For this purpose, four stainless steels used in manufacturing of machinery parts, heavily subject to cavitation such as hydraulic turbine runners and pump impellers, were analyzed from the point of view of cavitation erosion. The cavitation erosion behaviour was evaluated by the microstructure behaviour investigated through optic and electronic microscopy and by comparisons with the characteristic curves for reference steels.
Cavitation Erosion Resistance Tests Performed on Some Stainless Steels for Turbine Runner Blades
Revista de Chimie
The paper presents cavitation erosion testing results of three stainless steels that may be used in making hydropower turbine parts. Two of these steels have a chemical composition close to that of some other stainless steels previously employed in producing these parts. They are updated steel grades of the former ones. The third one is newly conceived. Aiming better mechanical and corrosion resistance characteristics as well as an inclusion - free structural state, steels were produced in an induction furnace with cold copper crucible under vacuum and argon atmosphere. Quenching and tempering heat treatments were subsequently applied.
Journal of Materials Science Letters, 2003
The cavitation erosion (CE) of a high nitrogen stainless steel (HNS) and a low nitrogen CrMnN stainless steel in both distilled water and 3%NaCl solution at 20¡1uC was investigated by using a magnetostrictive induced cavitation facility. The evolution of CE with test time was analysed by morphology observation by SEM and roughness measurement after different CE intervals. The possible phase transformation of austenite to martensite due to cavitation was analysed by XRD, and cross-sectional microhardness after cavitation was also measured to evaluate the work hardening ability. The role of corrosion was analysed by polarisation curve. The test results indicated that HNS had a relatively higher CE resistance than CrMnN steel, which was mainly attributed to its higher work hardening ability, thicker wok hardening layer and lower stacking fault energy. Different from that of the HNS, many tiny cracks could be clearly seen in the cross-section of eroded CrMnN steel especially at the ferrite zones. The pure erosion dominated the whole cavitation damage process, and the synergistic effect between corrosion and erosion was relatively small for both steels. The CE behaviour of HNS was relatively more sensitive to the corrosion media than that of CrMnN steel. Therefore, it should be a little bit careful when HNS was used in corrosive media.
Cavitation erosion resistance of 13/4 and 21-4-N steels
Sadhana. Academy Proceedings in Engineering Sciences, 2013
Nitrogen strengthened austenitic stainless steel (termed as 21-4-N steel) in as cast and hot rolled conditions has been investigated as an alternative to 13/4 steel (termed as CA6NM) to overcome the problems of cavitation erosion in hydro turbine underwater parts. The cavitation erosion of 21-4-N and 13/4 steels was investigated by means of an ultrasonic vibration processor. The cavitation erosion is highly dependent on microstructure and mechanical properties. The results show that hot rolled 21-4-N steel is more cavitation erosion resistant than the 13/4 and 21-4-N steels in as cast condition. The eroded surfaces were analysed through optical microscope and scanning electron microscope for study of erosion mechanisms.
Cavitation Erosion and Friction Behavior of Stainless Steel as a Function of Grain Size
MRS Proceedings, 2003
ABSTRACTResearch conducted on steels is motivated by a technological need to further improve their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a low yield strength. One way of increasing the yield strength is by grain refining. This work presents a study on the cavitation erosion and friction behavior of AISI 304 austenitic stainless steel characterized by two different grain sizes: 2.5 μm and 40 μm. The cavitation erosion behavior in water with different pH values and at room temperature has been studied by using a 20 kHz ultrasonic vibratory apparatus. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH value; decrease of this value pr...
Cavitation wear behaviour of austenitic stainless steels with different grain sizes
Wear, 2005
The cavitation erosion behaviour of two different austenitic stainless steels in water with different pH values and room temperature have been studied by means of a 20-kHz ultrasonic vibrator operating at a peak-to-peak amplitude of 40 m. The austenitic stainless steels used were AISI 304 (18Cr-10Ni) steel and a high nitrogen (HN) containing steel. Each of the steels were fabricated to yield three different grain sizes: 2.5 m, 20 m and 45 m. The grain size in both steels was adjusted by inducing an austenite-martensite-austenite phase transformation. Grain refining results in an improvement of the mechanical properties: hardness, yield strength, tensile strength, fatigue strength as well as an enhancement in the corrosion resistance. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases continuously with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH: a decrease of this value produces an increase in surface damage. This work shows that the HN steel exhibits better cavitation erosion resistance than AISI 304 steel. Also, hardness, tensile strength, yield strength and grain size of both steels can be correlated with the cavitation resistance R e .
Cavitation erosion of thermomechanically processed 13/4 martensitic stainless steel
Wear, 2014
This investigation is concerned the cavitation erosion resistance of 13/4 martensitic stainless steel that was processed in a Gleeble s 3800 simulator using thermomechanical treatments at two different temperatures (1000 1C and 1100 1C) and with two strain rates (0.01 s À 1 and 0.1 s À 1). Microstructures of the as-received and thermomechanically processed 13/4 martensitic stainless steel specimens were documented by light optical microscopy, and worn surfaces were examined using scanning electron microscopy. The erosion behavior was quantified using cumulative volume loss, volume loss rate, and roughness parameters plotted as a function of exposure time. The erosion characteristics were correlated with microstructure and mechanical properties. The best cavitation erosion resistance was exhibited by the specimen that was thermomechanically processed at 1000 1C using a strain rate of 0.1 s À 1. This result is attributed to microstructural refinement and higher hardness that led to a longer incubation period.