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The cavitation behavior of a metastable Cr–Mn–Ni Steel
Wear 240 Ž2000. 231–234 www.elsevier.comrlocaterwear
The cavitation behavior of a metastable Cr–Mn–Ni Steel Yi Zhang ) , Zhechang Wang, Yan Cui Ceramic and Composite Department, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shengyang 110015, People’s Republic of China Received 28 November 1999; received in revised form 8 March 2000; accepted 24 March 2000
Abstract The cavitation behavior of metastable Cr–Mn–Ni steel was investigated in a rotating disk machine. The microstructure of the cavitated area was investigated by X-ray diffraction ŽXRD., scanning electron microscopy ŽSEM. and optical microscopy. The results of XRD showed that the g a phase transformation and hNi 3Ti precipitation had occurred during cavitation testing. Cavitation damage of the material occurred by combined thermal–mechanical fatigue failure. It was deduced that the high-temperature behavior and properties should be taken into account in evaluating the cavitation resistance of such materials. q 2000 Elsevier Science S.A. All rights reserved.
™
Keywords: Cavitation; Erosion; Thermal effects
1. Introduction
2. Experiment details
Though cavitation damage of materials is probably the oldest known effect of cavitation, its mechanism has been a matter of controversy. The consensus opinion nowadays is that it is largely mechanical in nature. Many efforts have been applied to correlate cavitation resistance with the mechanical properties of materials, for example, strain energy w1,2x, and ultimate resilience w3x. Syamala Rao et al. w4x studied the cavitation erosion behind blunt bodies with varying hydrodynamic factors of flow and geometrical parameters of the system. They found that there was no general correlation between the cavitation damage and mechanical properties of a material, including the density, yield strength, tensile strength, engineering strain energy, hardness, percentage elongation, elastic modulus and so on. Recently, more material properties were taken into account to investigate the mechanism of cavitation damage, such as bonding energy w5x and dynamic hardness w6x. In fact, most research works has been focussed on correlating the cavitation resistance of a material with its roomtemperature properties. A material in a cavitation environment would be expected to exhibit different behavior from that at room temperature. In this work, the cavitation behavior of metastable austenite steel was studied.
2.1. Apparatus
)
Corresponding author. Tel.: q86-24-23843531-55287. E-mail address: [email protected] ŽY. Zhang..
The cavitation experiments were conducted with a rotating disk machine as shown in Fig. 1. The test disk was 360 mm in diameter; 12 mm thick and contained six 15 mm diameter through holes on both sides of disk to induce cavitation as shown in Fig. 2Ža.. There were two fixed grids consisting of spokes on both sides of disk. The test disk was powered by a 30-kW d.c. electric motor and its rotating rate could vary up to 3000 rpm. In order to make the fluid flow symmetrically in the chamber, the fluid was supplied through the hole in the center and drained from four holes at the rear edge. The pressure in the chamber was measured with a standard pressure gauge and regulated by a pump and valve. In this work, the speed of the test disk was 2900 rpm and the temperature of the water was kept at 12 " 18C. 2.2. Experimental procedure The steel used in this study was supplied in the form of rolled plate. Its nominal chemical composition was 0.15 wt.% C; 13 wt.% Mn; 18 wt.% Cr; 3 wt.% Ni; 0.5 wt.% Ti; Fe balance. After solution heat treatment at 10508C, the material was machined into specimens as shown in Fig. 2Žb.. The specimens were polished with 800-emery paper. XRD method and SEM were used to investigate the mi-
0043-1648r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 0 4 3 - 1 6 4 8 Ž 0 0 . 0 0 3 8 8 - 4
232
Y. Zhang et al.r Wear 240 (2000) 231–234
Fig. 1. Schematic diagram of rotating disk unit. Dimensions are shown in mm.
crostructural changes on the surfaces of the specimens both before and after the cavitation tests. The duration of the cavitation test was 18 h. Fig. 3. SEM micrograph of specimen surface after exposure to cavitation field.
3. Results and discussion Fig. 3 shows SEM micrographs of the cavitated surface with typical fatigue characters such as steps and striations.
Fig. 4 shows that many slip bands had appeared in and around the grains. This indicates that the deformation had occurred in the surface and subsurface. Fig. 5 shows the XRD patterns from the surface for specimens before and after the cavitation test, and shows that the g a phase
™
Fig. 2. Schematic diagram of Ža. rotating test disk and Žb. specimen. Dimensions are shown in mm.
Fig. 4. Optical micrographs of cross sections of specimens Ža. before and Žb. after the cavitation test.
Y. Zhang et al.r Wear 240 (2000) 231–234
Fig. 5. XRD patterns from surfaces of specimens Ža. before and Žb. after the cavitation test.
transformation and hNi 3Ti precipitation had occurred during the cavitation test. Before exposure, the microstructure of the surface of specimen was g, as shown in Fig. 3Ža.. The chromium and nickel equivalent of the steel in this work was calculated to be 18 and 14, respectively, corresponded to the range of metastable w7x. The metastable g phase is subjected to deformation and transformation into a phase under the external impact. The results of SEM, optical microscopy and the g a phase transformation demonstrate that the mechanism of cavitation damage for the material was mechanical failure. Damage is caused by the impacting of microjets emanating from the collapse of cavities near or adhering to the surface of the material. A typical cavity has a maximum radius of the order of 100 mm and a corresponding collapse time of the order of a few microseconds. When the cavity collapse, pressure can be achieved by impact of the microjet up to 10 5 atmosphere, with momentary temperature of the order of thousands of degrees Kelvin w8x. Under the impact of such microjets, the impacted region of the surface would deformed instantly, which would account for the g a phase transformation but not for hNi 3Ti precipitation. hNi 3Ti, a hexagonal phase, is often found in FeNi alloys. Its precipitation occurs during the aging of steel at high temperature w9x. Therefore, it is certain that the temperature of the cavitated area had increased during the
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™
233
cavitation test. The temperature rise in the cavitated area may be attributed to the following sources. The first is the heat produced by the rapid deformation in the deformation region. The second is the heat released from the collapsing cavities. It is thought that at ordinary temperatures, the thermal diffusion length of entrained gas in cavities corresponding to the collapse time is of the same order of magnitude as the maximum radius of the cavities, indicating that there is plenty of time for heat conduction from the gas into the surrounding including the metal matrix w8x. The exact mechanism of temperature rise in the damaged area could not be certain because there are many factors such as the cooling of the surroundings. But the phenomenon of hNi 3Ti precipitation has revealed that the temperature of cavitated material had been high during the impacting of collapsing cavities. Because of the temperature rise in the damaged area, the material in this area was exposed to a combined thermal–mechanical fatigue field, accompanied with the repeating impact of collapsing cavities and the temperature difference between the impacted area and the surroundings. Thermal effects could play an important role in the cavitation damage of the material. They might increase the cavitation resistance of a material by annealing the hardened microstructure to recover the material’s ability to absorb external energy. However, the cavitation resistance of a material might also be reduced because it is thermally softened. In such a combined thermal–mechanical fatigue field, the cavitated material would be expected to exhibit entirely different behavior from that at room temperature. To evaluate the cavitation resistance of material, the high-temperature behavior and properties should be taken into account.
4. Conclusion
™
From the observation of g a phase transformation and hNi 3Ti precipitation in a metastable Cr–Mn–Ni steel, it is concluded that the cavitated area had undergone a temperature rise during cavitation damage, perhaps caused by the impact of collapsing cavities. The cavitated material was exposed to a combined thermal–mechanical fatigue field. It is suggested that high-temperature and thermal properties may therefore play an important role in the cavitation damage of materials. Research into the cavitation behavior of metastable materials may thus help in understanding the cavitation mechanisms.
References w1x A. Thiruvengadam, A unified theory of cavitation damage, J. Basic Eng., Trans. ASME Ž1963. 365–376, September. w2x F.G. Hammitt, L.L. Barinka, M.J. Robinson, R.D. Pehlke, C.A. Siebert, Initial phases of damage to test specimens in a cavitating venturi, J. Basic Eng., Trans. ASME Ž1965. 453–464, June.
234
Y. Zhang et al.r Wear 240 (2000) 231–234
w3x R. Garcia, F.G. Hammitt, Cavitation damage and correlations with material and fluid properties, J. Basic Eng., Trans. ASME Ž1967. 753–761, December. w4x B.G. Syamala Rao, N.S. Lakshmana Rao, K. Seethramiah, Cavitation erosion studies with venturi and rotating disk in water, J. Basic Eng., Trans. ASME Ž1970. 563–579, September. w5x H.G. Feller, Y. Kharrazi, Cavitation erosion of metal and alloys, Wear 93 Ž1984. , 249–260. w6x T. Okada, Y. Iwai, S. Hattori, N. Tanimura, Relation between impact
load and the damage produced by cavitation bubble collapse, Wear 184 Ž1995. 231–239. w7x W.H. Cubberly, Metals Handbook vol. 6 American Society for Metals, Metals Park, 1983, 322 pp. w8x R. Hickling, Some physical effects of cavity collapse in liquids, J. Basic Eng., Trans. ASME Ž1966. 229–235, March. w9x T.B. Massalski, Binary Alloy Phase Diagrams vol. 3 ASM International, 1996, 2784 pp.
The cavitation behavior of a metastable Cr–Mn–Ni Steel Yi Zhang ) , Zhechang Wang, Yan Cui Ceramic and Composite Department, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shengyang 110015, People’s Republic of China Received 28 November 1999; received in revised form 8 March 2000; accepted 24 March 2000
Abstract The cavitation behavior of metastable Cr–Mn–Ni steel was investigated in a rotating disk machine. The microstructure of the cavitated area was investigated by X-ray diffraction ŽXRD., scanning electron microscopy ŽSEM. and optical microscopy. The results of XRD showed that the g a phase transformation and hNi 3Ti precipitation had occurred during cavitation testing. Cavitation damage of the material occurred by combined thermal–mechanical fatigue failure. It was deduced that the high-temperature behavior and properties should be taken into account in evaluating the cavitation resistance of such materials. q 2000 Elsevier Science S.A. All rights reserved.
™
Keywords: Cavitation; Erosion; Thermal effects
1. Introduction
2. Experiment details
Though cavitation damage of materials is probably the oldest known effect of cavitation, its mechanism has been a matter of controversy. The consensus opinion nowadays is that it is largely mechanical in nature. Many efforts have been applied to correlate cavitation resistance with the mechanical properties of materials, for example, strain energy w1,2x, and ultimate resilience w3x. Syamala Rao et al. w4x studied the cavitation erosion behind blunt bodies with varying hydrodynamic factors of flow and geometrical parameters of the system. They found that there was no general correlation between the cavitation damage and mechanical properties of a material, including the density, yield strength, tensile strength, engineering strain energy, hardness, percentage elongation, elastic modulus and so on. Recently, more material properties were taken into account to investigate the mechanism of cavitation damage, such as bonding energy w5x and dynamic hardness w6x. In fact, most research works has been focussed on correlating the cavitation resistance of a material with its roomtemperature properties. A material in a cavitation environment would be expected to exhibit different behavior from that at room temperature. In this work, the cavitation behavior of metastable austenite steel was studied.
2.1. Apparatus
)
Corresponding author. Tel.: q86-24-23843531-55287. E-mail address: [email protected] ŽY. Zhang..
The cavitation experiments were conducted with a rotating disk machine as shown in Fig. 1. The test disk was 360 mm in diameter; 12 mm thick and contained six 15 mm diameter through holes on both sides of disk to induce cavitation as shown in Fig. 2Ža.. There were two fixed grids consisting of spokes on both sides of disk. The test disk was powered by a 30-kW d.c. electric motor and its rotating rate could vary up to 3000 rpm. In order to make the fluid flow symmetrically in the chamber, the fluid was supplied through the hole in the center and drained from four holes at the rear edge. The pressure in the chamber was measured with a standard pressure gauge and regulated by a pump and valve. In this work, the speed of the test disk was 2900 rpm and the temperature of the water was kept at 12 " 18C. 2.2. Experimental procedure The steel used in this study was supplied in the form of rolled plate. Its nominal chemical composition was 0.15 wt.% C; 13 wt.% Mn; 18 wt.% Cr; 3 wt.% Ni; 0.5 wt.% Ti; Fe balance. After solution heat treatment at 10508C, the material was machined into specimens as shown in Fig. 2Žb.. The specimens were polished with 800-emery paper. XRD method and SEM were used to investigate the mi-
0043-1648r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 0 4 3 - 1 6 4 8 Ž 0 0 . 0 0 3 8 8 - 4
232
Y. Zhang et al.r Wear 240 (2000) 231–234
Fig. 1. Schematic diagram of rotating disk unit. Dimensions are shown in mm.
crostructural changes on the surfaces of the specimens both before and after the cavitation tests. The duration of the cavitation test was 18 h. Fig. 3. SEM micrograph of specimen surface after exposure to cavitation field.
3. Results and discussion Fig. 3 shows SEM micrographs of the cavitated surface with typical fatigue characters such as steps and striations.
Fig. 4 shows that many slip bands had appeared in and around the grains. This indicates that the deformation had occurred in the surface and subsurface. Fig. 5 shows the XRD patterns from the surface for specimens before and after the cavitation test, and shows that the g a phase
™
Fig. 2. Schematic diagram of Ža. rotating test disk and Žb. specimen. Dimensions are shown in mm.
Fig. 4. Optical micrographs of cross sections of specimens Ža. before and Žb. after the cavitation test.
Y. Zhang et al.r Wear 240 (2000) 231–234
Fig. 5. XRD patterns from surfaces of specimens Ža. before and Žb. after the cavitation test.
transformation and hNi 3Ti precipitation had occurred during the cavitation test. Before exposure, the microstructure of the surface of specimen was g, as shown in Fig. 3Ža.. The chromium and nickel equivalent of the steel in this work was calculated to be 18 and 14, respectively, corresponded to the range of metastable w7x. The metastable g phase is subjected to deformation and transformation into a phase under the external impact. The results of SEM, optical microscopy and the g a phase transformation demonstrate that the mechanism of cavitation damage for the material was mechanical failure. Damage is caused by the impacting of microjets emanating from the collapse of cavities near or adhering to the surface of the material. A typical cavity has a maximum radius of the order of 100 mm and a corresponding collapse time of the order of a few microseconds. When the cavity collapse, pressure can be achieved by impact of the microjet up to 10 5 atmosphere, with momentary temperature of the order of thousands of degrees Kelvin w8x. Under the impact of such microjets, the impacted region of the surface would deformed instantly, which would account for the g a phase transformation but not for hNi 3Ti precipitation. hNi 3Ti, a hexagonal phase, is often found in FeNi alloys. Its precipitation occurs during the aging of steel at high temperature w9x. Therefore, it is certain that the temperature of the cavitated area had increased during the
™
™
233
cavitation test. The temperature rise in the cavitated area may be attributed to the following sources. The first is the heat produced by the rapid deformation in the deformation region. The second is the heat released from the collapsing cavities. It is thought that at ordinary temperatures, the thermal diffusion length of entrained gas in cavities corresponding to the collapse time is of the same order of magnitude as the maximum radius of the cavities, indicating that there is plenty of time for heat conduction from the gas into the surrounding including the metal matrix w8x. The exact mechanism of temperature rise in the damaged area could not be certain because there are many factors such as the cooling of the surroundings. But the phenomenon of hNi 3Ti precipitation has revealed that the temperature of cavitated material had been high during the impacting of collapsing cavities. Because of the temperature rise in the damaged area, the material in this area was exposed to a combined thermal–mechanical fatigue field, accompanied with the repeating impact of collapsing cavities and the temperature difference between the impacted area and the surroundings. Thermal effects could play an important role in the cavitation damage of the material. They might increase the cavitation resistance of a material by annealing the hardened microstructure to recover the material’s ability to absorb external energy. However, the cavitation resistance of a material might also be reduced because it is thermally softened. In such a combined thermal–mechanical fatigue field, the cavitated material would be expected to exhibit entirely different behavior from that at room temperature. To evaluate the cavitation resistance of material, the high-temperature behavior and properties should be taken into account.
4. Conclusion
™
From the observation of g a phase transformation and hNi 3Ti precipitation in a metastable Cr–Mn–Ni steel, it is concluded that the cavitated area had undergone a temperature rise during cavitation damage, perhaps caused by the impact of collapsing cavities. The cavitated material was exposed to a combined thermal–mechanical fatigue field. It is suggested that high-temperature and thermal properties may therefore play an important role in the cavitation damage of materials. Research into the cavitation behavior of metastable materials may thus help in understanding the cavitation mechanisms.
References w1x A. Thiruvengadam, A unified theory of cavitation damage, J. Basic Eng., Trans. ASME Ž1963. 365–376, September. w2x F.G. Hammitt, L.L. Barinka, M.J. Robinson, R.D. Pehlke, C.A. Siebert, Initial phases of damage to test specimens in a cavitating venturi, J. Basic Eng., Trans. ASME Ž1965. 453–464, June.
234
Y. Zhang et al.r Wear 240 (2000) 231–234
w3x R. Garcia, F.G. Hammitt, Cavitation damage and correlations with material and fluid properties, J. Basic Eng., Trans. ASME Ž1967. 753–761, December. w4x B.G. Syamala Rao, N.S. Lakshmana Rao, K. Seethramiah, Cavitation erosion studies with venturi and rotating disk in water, J. Basic Eng., Trans. ASME Ž1970. 563–579, September. w5x H.G. Feller, Y. Kharrazi, Cavitation erosion of metal and alloys, Wear 93 Ž1984. , 249–260. w6x T. Okada, Y. Iwai, S. Hattori, N. Tanimura, Relation between impact
load and the damage produced by cavitation bubble collapse, Wear 184 Ž1995. 231–239. w7x W.H. Cubberly, Metals Handbook vol. 6 American Society for Metals, Metals Park, 1983, 322 pp. w8x R. Hickling, Some physical effects of cavity collapse in liquids, J. Basic Eng., Trans. ASME Ž1966. 229–235, March. w9x T.B. Massalski, Binary Alloy Phase Diagrams vol. 3 ASM International, 1996, 2784 pp.