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Analysis of cavitation erosion resistance of cast iron and nonferrous metals based on database and comparison with carbon steel data
Wear 269 (2010) 443–448
Contents lists available at ScienceDirect
Wear journal homepage: www.elsevier.com/locate/wear
Analysis of cavitation erosion resistance of cast iron and nonferrous metals based on database and comparison with carbon steel data Shuji Hattori ∗ , Tetsuo Kitagawa Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui-shi, Fukui 910-8507, Japan
a r t i c l e
i n f o
Article history: Received 5 December 2007 Received in revised form 28 April 2010 Accepted 30 April 2010 Available online 7 May 2010 Keywords: Cavitation erosion Iron and steel Nonferrous metals Hardness
a b s t r a c t Cavitation erosion is a form of damage which occurs in many types of fluid machinery such as water turbines, pumps and torque converters, as well as in industrial machines such as cylinder liners of diesel engines, ship propellers and valves. We have constructed a database of cavitation erosion and analyzed carbon steel data. In this study, erosion resistance was analyzed for cast iron, aluminum alloys, copper alloys, and titanium alloys, in comparison with regular carbon steels. The cavitation erosion resistance can be separately evaluated in terms of hardness for these alloys. The resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron compared with carbon steel of the same hardness, and it is 1/3 to 1/5 lower for aluminum alloys compared with carbon steel. The resistance of copper alloys and titanium alloys is almost the same as that of carbon steel. © 2010 Elsevier B.V. All rights reserved.
1. Introduction A small number of studies [1,2] have been performed on the statistical evaluation of cavitation erosion. Heymann [1] summarized that the erosion resistance (the reciprocal value of the maximum instantaneous erosion rate) is strongly correlated with hardness for nine kinds of materials (the total number is 119) such as carbon steels, cast irons, stainless steels and many nonferrous alloys, and the erosion resistance increases roughly with the 5/2 power of the hardness excluding stellite (and similar cobalt alloys). However, the analyzed erosion test data included not only cavitation tests but also impingement tests, so that the scattering of the erosion resistance for materials of the same hardness was broad (upper limit/lower limit ∼30 times, correlation coefficient: 0.77), and therefore it was still very difficult to evaluate erosion resistance from hardness. Hammitt [2] collected many data of cavitation erosion and obtained the base-fit curve in terms of ultimate resilience. Hattori and Ishikura [3] constructed a database on cavitation erosion from 1970 to 2002. We concluded that the erosion resistance of carbon steel increases proportionally with 2.4th power of the Vickers hardness with a correlation coefficient of 0.92. Cavitation erosion data obtained from 2003 to 2005 was added to the existing database [4]. Stainless steels have excellent corrosion resistance, and are used for many types of fluid machinery. We found [4] that a very good correlation coefficient of 0.98 for stainless steels was obtained as. Like as for carbon steel, the erosion resistance is in
∗ Corresponding author. Tel.: +81 776 27 8546; fax: +81 776 27 8546. E-mail address: [email protected] (S. Hattori). 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.04.031
proportion to the 2.4th power of the hardness, when it is evaluated in terms of the Vickers hardness after erosion tests, by introducing an increase ratio of hardness as a material constant Fmat . However, the analysis was not made for cast iron and various nonferrous metals that are used for various kinds of fluid machinery components. In this study, we discuss the erosion resistance of various kinds of cast iron, aluminum alloys, copper alloys, and titanium alloys compared with the results for carbon steels based on the database constructed in our laboratory. 2. Conversion of test data Since many data under the same condition are required to statistically analyze a database, the method to convert data into the values under standard test conditions specified by the American Society for Testing and Materials, ASTM [5] (amplitude: 50 m, frequency: 19.5 kHz) was examined. First, data other than 50 m amplitude (peak to peak) were converted into data values equivalent to 50 m amplitudes. For the relation between amplitude and erosion rate, Thiruvengadam and Hobbs found that erosion rates increased proportionally to the approximate powers of 1.8 and 1.5 of the amplitude (peak to peak), respectively [6,7]. In this study, the exponent of the amplitude was simply assumed to be 2, in order to convert data with other amplitudes (not 50 m) into data values equivalent to 50 m amplitude data. Incidentally, the error between exponent 1.5 and 2 is only 12%, when data of 40 m amplitude are converted into equivalent 50 m amplitude data. In this way, all data were converted to a condition equivalent to 50 m amplitude, and were rearranged into 4 types of 14.7 kHz and 19.5 kHz of both vibratory and stationary specimen methods.
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S. Hattori, T. Kitagawa / Wear 269 (2010) 443–448
Fig. 1. MDER curve of S15C. Fig. 2. Relation between hardness and erosion resistance of carbon steel.
The erosion rate can be obtained by converting these data to conditions equivalent to 19.5 kHz and the stationary specimen method (standoff distance: 1 mm). We multiplied the data of vibratory specimen method by 0.28 and the data of 14.7 kHz by 1.2. The erosion resistance of cast iron, aluminum alloys, copper alloys and titanium alloys was evaluated in terms of hardness and compared with the results of carbon steel obtained by Hattori and Ishikura [3]. The results of an erosion test are often expressed by the “mean depth of erosion” (MDE) [5], which is mass loss divided by the material density and the eroded surface area. Another expression is the instantaneous “mean depth of erosion rate” (MDER), that is, the slope of the tangent to the cumulative erosion–time curve at a given point. For example, the MDER–time curve under the condition of 19.5 kHz and the stationary specimen method for S15C (carbon steel) is shown in Fig. 1 The MDER increases gradually and reaches a peak, followed by a gradual decrease. MDERmax is the “maximum of the mean depth of the erosion rate”, that is, the slope of the straight line that best approximates the steepest linear (or nearly linear) portion of the cumulative MDE–time curve, and it is expressed in m/h. We define the reciprocal value of MDERmax as erosion resistance (ER).
which was constructed in our laboratory. The relation between hardness and erosion resistance of carbon steel can be expressed as ER = 5.8 × 10−7 × HV2.4
(1)
with a coefficient of correlation of 0.92. The erosion resistance has a very high correlation with the hardness. We similarly analyze the data for cast iron, aluminum alloys, copper alloys and titanium alloys in the following chapter. 4. Analysis of cast iron and nonferrous metals 4.1. Cast iron We analyzed seven types of cast iron, i.e. gray cast iron FC100 and FC200, ductile cast iron FCD400 and FCD700, ferrite phase ductile cast iron FDI, perlite phase ductile cast iron PDI, and austempered ductile cast iron ADI. Table 1 shows the chemical composition and mechanical properties of cast iron. The tensile strength is the value written on the inspection certificate sheet of the test material which we used in the experiments. The Vickers hardness HV is a value measured in our laboratory. HV ranges from 150 to 400 for both gray cast iron and ductile cast iron. Fig. 3 shows the relation between the Vickers hardness of cast iron and the erosion resistance which has been tested in our laboratory. A solid line in this figure shows the base line of carbon steel given in the previous sec-
3. Relation between hardness and erosion resistance of carbon steels Fig. 2 shows the relation between the hardness and the erosion resistance of carbon steels for machine structural use, and carbon tool steels including various heat-treated steels in the database, Table 1 Chemical composition and mechanical properties of cast iron (mass%). Material
C
(a) Chemical composition FC100 3.38 FC200 3.38 FCD400 3.47 FCD700 3.25 FDI 3.76 PDI 3.76 ADI 3.76
Si
Mn
P
S
Cu
Cr
Mo
Mg
Zn
2.19 2.19 2.71 2.68 2.15 2.15 2.15
0.58 0.58 0.31 0.24 0.32 0.32 0.32
0.021 0.021 0.033 0.03 0.019 0.019 0.019
0.016 0.016 0.013 0.01 0.042 0.04 0.009
– – – – – – 0.62
0.038 0.038 – – 0.04 – 0.04
– – – – – – 0.02
– – 0.035 0.033 – – 0.042
– – – – 0.04 0.04 –
Material
Density (g/cm3 )
E (GPa)
B (MPa)
HV
(b) Mechanical properties FC100 FC200 FCD400 FCD700 FDI PDI ADI
7.1 7.1 7.1 7.1 7.1 7.1 7.1
71.5 97 167 167 167 167 173
110 230 414 861 414 861 902
155 350 201 385 190 247 370
S. Hattori, T. Kitagawa / Wear 269 (2010) 443–448
Fig. 3. Relation between hardness and erosion resistance of cast iron.
tion. The erosion resistance of gray cast iron was compared with carbon steel. The resistance is about 1/3 at HV 150, and about 1/5 at HV 350. The erosion resistance of ductile cast iron is the same as that of carbon steel at HV 150, and about 1/3 at HV 350. Thus, the erosion resistance of cast iron is different between gray cast iron and ductile cast iron. Therefore, cast iron was divided into these two categories for analysis. The erosion resistance ER of cast iron is given by the following equation in terms of the Vickers hardness HV.
ER =
1.3 × 10−5 × HV1.58 −5
2.1 × 10
1.61
× HV
(gray cast iron)
(2)
(ductile cast iron)
The coefficient of correlation is 0.92 and 0.98 for gray cast iron and ductile cast iron, respectively. The exponent of hardness for the erosion resistance of cast iron is about a half of that of carbon steel.
445
Fig. 4 shows SEM photographs of eroded surfaces of cast iron [8]. (a) and (b) are for gray cast iron FC250, and (c) and (d) are for ductile cast iron FCD700. Linear graphites of 30–200 m in length are distributed uniformly on the virgin surface of gray cast iron. The removal of graphite occurred when the specimen was exposed to cavitation. Spheroidal graphites of 10–40 m in diameter are distributed uniformly on the virgin surface of ductile cast iron. The graphites were removed similarly to gray cast iron. Therefore, the portion remaining after the graphite removal has the form of a notch with high stress concentration, resulting in a site favorable for cavitation erosion. Cavitation erosion is considered to be a fatigue phenomenon of the material surface [2], because material removal occurs after the repeated action of bubble collapse impact forces. Therefore, the cavitation erosion resistance of cast iron should be compared with the fatigue strength of a notched specimen. Fig. 5 shows the relation between the Vickers hardness of carbon steel and the rotary bending fatigue strength of smooth specimen and notched specimen with a circumferential V shaped groove of radius 0.1 mm. Since the original experimental data [9] showed the relation between fatigue strength and tensile strength, we converted the strength into hardness by multiplying with 0.3 [10]. Open square symbols show data points of smooth specimen, and the solid line is an approximation line. Solid square symbols show data points of notch specimen, and the broken line is an approximation line. At about HV 100, the difference of the fatigue strength between notched and smooth specimens diminishes. At about HV 550, the fatigue strength of notched specimen is remarkably lower than that of smooth specimen. When the carbon steel data in Fig. 3 is assumed to correspond to the smooth specimen data in Fig. 5 and the gray cast iron data in Fig. 3 correspond to the notched specimen data in Fig. 5, the trend of Fig. 3 is similar to that of Fig. 5.
Fig. 4. Erosion surface of cast iron [8].
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Fig. 6. Relation between hardness and erosion resistance of Al alloy. Fig. 5. Relation between hardness and bending fatigue strength of carbon steel.
Thus, the erosion resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron, compared with carbon steel, because graphite removal occurs which produces high stress concentrations for cast iron. 4.2. Pure aluminum and aluminum alloys We discuss 9 types of aluminum alloys including 4 types of pure aluminum: Al, A1050, A1070, and A1070BD-F for pure aluminum and A2017, A5052, A5083, A5454 and A7075 for aluminum alloys. Table 2 shows the chemical composition and the mechanical properties of the aluminum alloys. The HV ranges from 30 to 50 for pure aluminum, and from 60 to 170 for aluminum alloys. The hardness is about half the hardness of cast iron. Fig. 6 shows the relation between the Vickers hardness of aluminum alloy and the erosion resistance, which has been obtained in our laboratory. The solid line shows the base line of carbon steel. The erosion resistance of pure aluminum at HV 100 or less cannot be compared with that of carbon steel, because the Vickers hardness HV of carbon steel is 100 or more. The erosion resistance of aluminum alloy at HV 100 or more was compared with that of carbon steel. The resistance is about 1/3 lower at HV 100, and about 1/5 lower at HV 150. The erosion resistance ER of aluminum alloy is given by the following
equation in terms of the Vickers hardness HV similarly to the ER of cast iron. ER = 0.75 × 10−5 × HV1.6
(3)
The coefficient of correlation is 0.87. It reported that cavitation erosion proceed by fatigue phenomenon [2]. Fig. 7 shows the relation between the rotary bending fatigue strength [11] of aluminum alloy and carbon steel and the Vickers hardness on a log–log scale. The hardness was converted from the tensile strength. The area surrounded by the solid lines shows a scattering of the fatigue strength for carbon steels. The broken line area is the scattering for aluminum alloys. The rotary bending fatigue strength of carbon steel is from 180 MPa to 300 MPa at Vickers hardness HV 150. The fatigue strength of aluminum alloy is from 90 MPa to 180 MPa at HV 150. The fatigue strength of aluminum alloy is much lower than the fatigue strength of carbon steel of the same hardness. This is because local overaging occurs in aluminum alloy caused by repeated stress at room temperature [9]. We can assume that a similar phenomenon occurs for cavitation erosion. Therefore, the erosion resistance of aluminum alloy is much lower than that of carbon steel at the same hardness. Thus, the erosion resistance is 1/3 to 1/5 lower for aluminum alloy compared with carbon steel, because strength reduction occurs due to local overaging by the repeated stress of cavitation bubble collapses.
Table 2 Chemical composition and mechanical properties of Al alloys (mass%). Material
Si
(a) Chemical composition Al 0.09 A1050 0.06 A1070 0.09 A1070BD-F 0.09 A2017 0.61 A5052 0.09 A5083 0.1 A5454 0.07 A7075 0.1
Mn
Cu
Cr
Fe
V
Ms
Zn
Ti
Al
0.01 0.01 – 0.01 0.7 0.07 0.6 0.57 0.02
0.01 0.01 0.01 0.01 4.18 0.03 – 0.04 1.3
– – 0.01 – 0.034 0.21 0.05 0.08 0.13
0.14 0.12 0.11 0.15 0.32 0.24 0.2 0.16 0.21
– – 0.01 0.01 – – – – –
0.01 – 0.01 0.035 0.54 2.6 4.7 2.7 2.4
0.01 0.01 – – 0.194 0.01 – – 5.8
0.01 0.01 0.01 0.01 – – 0.02 – 0.03
Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal.
Material
Density (g/cm3 )
E (GPa)
B (MPa)
HV
(b) Mechanical properties Al A1050 A1070 A1070BD-F A2017 A5052 A5454 A5083 A7075
2.71 2.71 2.71 2.71 2.7 2.7 2.7 2.7 2.7
125 71 71 49 71 70 70 70 71
125 178 95 99 454 205 224 308 540
33 40 38 32 136 65 69 88 166
S. Hattori, T. Kitagawa / Wear 269 (2010) 443–448
447
Fig. 8. Relation between hardness and erosion resistance of Cu alloy.
the mechanical properties of copper alloys. Fig. 8 shows the relation between Vickers hardness and erosion resistance of copper alloys. The data of erosion resistance of pure copper are concentrated at HV 90. When the erosion resistance of pure copper was compared with carbon steel, the resistance was about 1/2 lower at HV 90. The resistance of copper alloy is the same as that of carbon steel. Therefore, copper was divided into these two categories for analysis. The relation between Vickers hardness and erosion resistance of copper alloy is
Fig. 7. Relation between tensile strength and rotary bending fatigue strength of carbon steel and Al alloy.
4.3. Copper alloys and titanium alloys We discuss four types of copper alloys, i.e. pure coppers C1020 (purity 99.96%) and C1100 (purity 99.90%), alloy equivalent to aluminum bronze C6280, and alloy in which Mn and Fe was added to improve the strength. Table 3 shows the chemical composition and
ER = 2.8 × 10−6 × HV2.19
(4)
Table 3 Chemical composition and mechanical properties of Cu alloys (mass%). Material (a) Chemical composition Pure Cu
Cu alloy
Al
Mn
Fe
Ni
Co
Cu
C1020 C1100
– –
– –
– –
– –
– –
99.96 99.90
Al bronze Al–Mn bronze
9.0 9.0
– 9.0
1.0 3.0
– 2.0
– 1.0
Bal. Bal.
Density (g/cm3 )
E (GPa)
B (MPa)
C1020 C1100
8.96 8.96
115 129
326 328
Al bronze Al–Mn bronze
7.8 7.5
118 118
– 809
Material (b) Mechanical properties Pure Cu
Cu alloy
HV 90 92.2 227 275
Table 4 Chemical composition and mechanical properties of Ti alloys (mass%). Material
Type
N
O
Fe
H
Al
C
V
Cr
Sn
Mo
Zn
Ti
(a) Chemical composition Pure Ti Ti–15V–3Cr–3Sn–3Al Ti–3Al–8V–3Cr–4Mo–4Zn Ti–6A1–4V
␣   ␣+
0.01 0.01 0.17 0.01
0.13 0.12 0.18 0.017
0.06 0.15 – 0.14
0.01 0.001 0.0033 0.0009
– 3.5 3.06 6.29
– 0.005 0.01 0.01
– 14.8 7.4 4.17
– 3.4 4.23 –
– 3.0 – –
– – 4.2 –
– – 5.1 –
Bal. Bal. Bal. Bal.
Material
Density (g/cm3 )
Young’s modulus E (GPa)
Tensile strength B (MPa)
Vickers hardness HV
Micro-hardness Ht
(b) Mechanical properties Pure Ti Ti–15V–3Cr–3Sn–3Al Ti–3Al–8V–3Cr–4Mo–4Zn Ti–6A1–4V
4.49 4.76 4.74 4.32
116 113 113 116
490 1297 1330 971
206 329 334 270
␣: 161 : 276 : 282 ␣: 187, : 82
Material
B (MPa)
HV
Ti–6A1–4V (700 ◦ C AC) Ti–6A1–4V (850 ◦ C AC) Ti–6A1–4V (900 ◦ C AC) Ti–6Al–4V (1100 ◦ C AC)
971 969
270 256 328 327
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Fig. 9. Relation between hardness and erosion resistance of Ti alloy.
and the coefficient of correlation is 0.92. The erosion resistance is almost the same as the erosion resistance of carbon steel at the same hardness, because the fatigue strength of copper alloy is the same as that of carbon steel [11]. We discuss 8 types of titanium alloys, i.e. ␣ type pure titanium,  type alloys of Ti–15V–3Cr–3Sn–3Al and Ti–3Al–8V–3Cr–4Mo–4Zr, ␣ +  type Ti–6Al–4V and 4 types of Ti–6Al–4V with different heattreatment temperatures. Table 4 shows the chemical composition and the mechanical properties of titanium alloys. Ht in the table is the micro-hardness at a force of 0.5 g. Fig. 9 shows the relation between the Vickers hardness and the erosion resistance of titanium alloys. The resistance of titanium alloy is almost the same as that of carbon steel, because notch effect is extremely small compared to cast iron, although titanium alloys have a microscopic dual phase [12]. 5. Conclusions In this study, we analyzed the cavitation erosion resistance of cast iron, aluminum alloy, copper alloy and titanium alloy. The following conclusions can be drawn:
1. The cavitation erosion resistance can be separately evaluated for cast iron, aluminum alloys, copper alloys and titanium alloys in terms of the hardness. 2. The erosion resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron compared with that of carbon steel with the same hardness, because graphite removal occurs to produce high stress concentrations for cast iron. 3. The erosion resistance of aluminum alloy is 1/3 to 1/5 lower than that of carbon steel with the same hardness, because strength reduction occurs due to local overaging by the repeated stress of cavitation bubble collapses. 4. The erosion resistances of copper alloy and titanium alloy are almost the same as that of carbon steel at the same hardness, because the fatigue strength of these alloys is similar as the strength of carbon steel, provided that the hardness is the same. References [1] F.J. Heymann, Characterization and Determination of Erosion Resistance, ASTM STP474, 1970, pp. 212–222. [2] F.G. Hammitt, Cavitation and Multiphase Flow Phenomena, McGraw-Hill, New York, 1980. [3] S. Hattori, R. Ishikura, Construction of database on cavitation erosion and analysis of carbon steel data, Wear 257 (2004) 1022–1029. [4] S. Hattori, R. Ishikura, Revision of cavitation erosion database and analysis of stainless steel data, Wear 268 (2010) 109–116. [5] ASTM Designation, Annual Book of ASTM Standards, G32-03, 2003. [6] H. Kato, Cavitation, Maki Shoten Publisher, 1979, pp. 175–188. [7] T. Okada, S. Hattori, Cavitation erosion (2), Sci. Mach. 49 (10) (1997) 1078–1081. [8] T. Okada, Y. Iwai, A. Yamamoto, A study of cavitation erosion of cast iron, Wear 84 (1983) 297–312. [9] The Society of Materials Science, Japan, Fatigue of Metal, Maruzen Publisher, 1964, pp. 170–191. [10] The Society of Materials Science, Japan, Engineering Materials for Machine Use, Taiyodo Publisher, 2002, p. 91. [11] The Society of Materials Science, Japan, Handbook of Fatigue Design for Metals, Yokendo Publisher, 1981, pp. 4–5. [12] S. Hattori, et al., Cavitation erosion of titanium alloys, Trans. Jpn. Soc. Mech. Eng. 66 (2000) 187–193.
Contents lists available at ScienceDirect
Wear journal homepage: www.elsevier.com/locate/wear
Analysis of cavitation erosion resistance of cast iron and nonferrous metals based on database and comparison with carbon steel data Shuji Hattori ∗ , Tetsuo Kitagawa Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui-shi, Fukui 910-8507, Japan
a r t i c l e
i n f o
Article history: Received 5 December 2007 Received in revised form 28 April 2010 Accepted 30 April 2010 Available online 7 May 2010 Keywords: Cavitation erosion Iron and steel Nonferrous metals Hardness
a b s t r a c t Cavitation erosion is a form of damage which occurs in many types of fluid machinery such as water turbines, pumps and torque converters, as well as in industrial machines such as cylinder liners of diesel engines, ship propellers and valves. We have constructed a database of cavitation erosion and analyzed carbon steel data. In this study, erosion resistance was analyzed for cast iron, aluminum alloys, copper alloys, and titanium alloys, in comparison with regular carbon steels. The cavitation erosion resistance can be separately evaluated in terms of hardness for these alloys. The resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron compared with carbon steel of the same hardness, and it is 1/3 to 1/5 lower for aluminum alloys compared with carbon steel. The resistance of copper alloys and titanium alloys is almost the same as that of carbon steel. © 2010 Elsevier B.V. All rights reserved.
1. Introduction A small number of studies [1,2] have been performed on the statistical evaluation of cavitation erosion. Heymann [1] summarized that the erosion resistance (the reciprocal value of the maximum instantaneous erosion rate) is strongly correlated with hardness for nine kinds of materials (the total number is 119) such as carbon steels, cast irons, stainless steels and many nonferrous alloys, and the erosion resistance increases roughly with the 5/2 power of the hardness excluding stellite (and similar cobalt alloys). However, the analyzed erosion test data included not only cavitation tests but also impingement tests, so that the scattering of the erosion resistance for materials of the same hardness was broad (upper limit/lower limit ∼30 times, correlation coefficient: 0.77), and therefore it was still very difficult to evaluate erosion resistance from hardness. Hammitt [2] collected many data of cavitation erosion and obtained the base-fit curve in terms of ultimate resilience. Hattori and Ishikura [3] constructed a database on cavitation erosion from 1970 to 2002. We concluded that the erosion resistance of carbon steel increases proportionally with 2.4th power of the Vickers hardness with a correlation coefficient of 0.92. Cavitation erosion data obtained from 2003 to 2005 was added to the existing database [4]. Stainless steels have excellent corrosion resistance, and are used for many types of fluid machinery. We found [4] that a very good correlation coefficient of 0.98 for stainless steels was obtained as. Like as for carbon steel, the erosion resistance is in
∗ Corresponding author. Tel.: +81 776 27 8546; fax: +81 776 27 8546. E-mail address: [email protected] (S. Hattori). 0043-1648/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2010.04.031
proportion to the 2.4th power of the hardness, when it is evaluated in terms of the Vickers hardness after erosion tests, by introducing an increase ratio of hardness as a material constant Fmat . However, the analysis was not made for cast iron and various nonferrous metals that are used for various kinds of fluid machinery components. In this study, we discuss the erosion resistance of various kinds of cast iron, aluminum alloys, copper alloys, and titanium alloys compared with the results for carbon steels based on the database constructed in our laboratory. 2. Conversion of test data Since many data under the same condition are required to statistically analyze a database, the method to convert data into the values under standard test conditions specified by the American Society for Testing and Materials, ASTM [5] (amplitude: 50 m, frequency: 19.5 kHz) was examined. First, data other than 50 m amplitude (peak to peak) were converted into data values equivalent to 50 m amplitudes. For the relation between amplitude and erosion rate, Thiruvengadam and Hobbs found that erosion rates increased proportionally to the approximate powers of 1.8 and 1.5 of the amplitude (peak to peak), respectively [6,7]. In this study, the exponent of the amplitude was simply assumed to be 2, in order to convert data with other amplitudes (not 50 m) into data values equivalent to 50 m amplitude data. Incidentally, the error between exponent 1.5 and 2 is only 12%, when data of 40 m amplitude are converted into equivalent 50 m amplitude data. In this way, all data were converted to a condition equivalent to 50 m amplitude, and were rearranged into 4 types of 14.7 kHz and 19.5 kHz of both vibratory and stationary specimen methods.
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S. Hattori, T. Kitagawa / Wear 269 (2010) 443–448
Fig. 1. MDER curve of S15C. Fig. 2. Relation between hardness and erosion resistance of carbon steel.
The erosion rate can be obtained by converting these data to conditions equivalent to 19.5 kHz and the stationary specimen method (standoff distance: 1 mm). We multiplied the data of vibratory specimen method by 0.28 and the data of 14.7 kHz by 1.2. The erosion resistance of cast iron, aluminum alloys, copper alloys and titanium alloys was evaluated in terms of hardness and compared with the results of carbon steel obtained by Hattori and Ishikura [3]. The results of an erosion test are often expressed by the “mean depth of erosion” (MDE) [5], which is mass loss divided by the material density and the eroded surface area. Another expression is the instantaneous “mean depth of erosion rate” (MDER), that is, the slope of the tangent to the cumulative erosion–time curve at a given point. For example, the MDER–time curve under the condition of 19.5 kHz and the stationary specimen method for S15C (carbon steel) is shown in Fig. 1 The MDER increases gradually and reaches a peak, followed by a gradual decrease. MDERmax is the “maximum of the mean depth of the erosion rate”, that is, the slope of the straight line that best approximates the steepest linear (or nearly linear) portion of the cumulative MDE–time curve, and it is expressed in m/h. We define the reciprocal value of MDERmax as erosion resistance (ER).
which was constructed in our laboratory. The relation between hardness and erosion resistance of carbon steel can be expressed as ER = 5.8 × 10−7 × HV2.4
(1)
with a coefficient of correlation of 0.92. The erosion resistance has a very high correlation with the hardness. We similarly analyze the data for cast iron, aluminum alloys, copper alloys and titanium alloys in the following chapter. 4. Analysis of cast iron and nonferrous metals 4.1. Cast iron We analyzed seven types of cast iron, i.e. gray cast iron FC100 and FC200, ductile cast iron FCD400 and FCD700, ferrite phase ductile cast iron FDI, perlite phase ductile cast iron PDI, and austempered ductile cast iron ADI. Table 1 shows the chemical composition and mechanical properties of cast iron. The tensile strength is the value written on the inspection certificate sheet of the test material which we used in the experiments. The Vickers hardness HV is a value measured in our laboratory. HV ranges from 150 to 400 for both gray cast iron and ductile cast iron. Fig. 3 shows the relation between the Vickers hardness of cast iron and the erosion resistance which has been tested in our laboratory. A solid line in this figure shows the base line of carbon steel given in the previous sec-
3. Relation between hardness and erosion resistance of carbon steels Fig. 2 shows the relation between the hardness and the erosion resistance of carbon steels for machine structural use, and carbon tool steels including various heat-treated steels in the database, Table 1 Chemical composition and mechanical properties of cast iron (mass%). Material
C
(a) Chemical composition FC100 3.38 FC200 3.38 FCD400 3.47 FCD700 3.25 FDI 3.76 PDI 3.76 ADI 3.76
Si
Mn
P
S
Cu
Cr
Mo
Mg
Zn
2.19 2.19 2.71 2.68 2.15 2.15 2.15
0.58 0.58 0.31 0.24 0.32 0.32 0.32
0.021 0.021 0.033 0.03 0.019 0.019 0.019
0.016 0.016 0.013 0.01 0.042 0.04 0.009
– – – – – – 0.62
0.038 0.038 – – 0.04 – 0.04
– – – – – – 0.02
– – 0.035 0.033 – – 0.042
– – – – 0.04 0.04 –
Material
Density (g/cm3 )
E (GPa)
B (MPa)
HV
(b) Mechanical properties FC100 FC200 FCD400 FCD700 FDI PDI ADI
7.1 7.1 7.1 7.1 7.1 7.1 7.1
71.5 97 167 167 167 167 173
110 230 414 861 414 861 902
155 350 201 385 190 247 370
S. Hattori, T. Kitagawa / Wear 269 (2010) 443–448
Fig. 3. Relation between hardness and erosion resistance of cast iron.
tion. The erosion resistance of gray cast iron was compared with carbon steel. The resistance is about 1/3 at HV 150, and about 1/5 at HV 350. The erosion resistance of ductile cast iron is the same as that of carbon steel at HV 150, and about 1/3 at HV 350. Thus, the erosion resistance of cast iron is different between gray cast iron and ductile cast iron. Therefore, cast iron was divided into these two categories for analysis. The erosion resistance ER of cast iron is given by the following equation in terms of the Vickers hardness HV.
ER =
1.3 × 10−5 × HV1.58 −5
2.1 × 10
1.61
× HV
(gray cast iron)
(2)
(ductile cast iron)
The coefficient of correlation is 0.92 and 0.98 for gray cast iron and ductile cast iron, respectively. The exponent of hardness for the erosion resistance of cast iron is about a half of that of carbon steel.
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Fig. 4 shows SEM photographs of eroded surfaces of cast iron [8]. (a) and (b) are for gray cast iron FC250, and (c) and (d) are for ductile cast iron FCD700. Linear graphites of 30–200 m in length are distributed uniformly on the virgin surface of gray cast iron. The removal of graphite occurred when the specimen was exposed to cavitation. Spheroidal graphites of 10–40 m in diameter are distributed uniformly on the virgin surface of ductile cast iron. The graphites were removed similarly to gray cast iron. Therefore, the portion remaining after the graphite removal has the form of a notch with high stress concentration, resulting in a site favorable for cavitation erosion. Cavitation erosion is considered to be a fatigue phenomenon of the material surface [2], because material removal occurs after the repeated action of bubble collapse impact forces. Therefore, the cavitation erosion resistance of cast iron should be compared with the fatigue strength of a notched specimen. Fig. 5 shows the relation between the Vickers hardness of carbon steel and the rotary bending fatigue strength of smooth specimen and notched specimen with a circumferential V shaped groove of radius 0.1 mm. Since the original experimental data [9] showed the relation between fatigue strength and tensile strength, we converted the strength into hardness by multiplying with 0.3 [10]. Open square symbols show data points of smooth specimen, and the solid line is an approximation line. Solid square symbols show data points of notch specimen, and the broken line is an approximation line. At about HV 100, the difference of the fatigue strength between notched and smooth specimens diminishes. At about HV 550, the fatigue strength of notched specimen is remarkably lower than that of smooth specimen. When the carbon steel data in Fig. 3 is assumed to correspond to the smooth specimen data in Fig. 5 and the gray cast iron data in Fig. 3 correspond to the notched specimen data in Fig. 5, the trend of Fig. 3 is similar to that of Fig. 5.
Fig. 4. Erosion surface of cast iron [8].
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Fig. 6. Relation between hardness and erosion resistance of Al alloy. Fig. 5. Relation between hardness and bending fatigue strength of carbon steel.
Thus, the erosion resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron, compared with carbon steel, because graphite removal occurs which produces high stress concentrations for cast iron. 4.2. Pure aluminum and aluminum alloys We discuss 9 types of aluminum alloys including 4 types of pure aluminum: Al, A1050, A1070, and A1070BD-F for pure aluminum and A2017, A5052, A5083, A5454 and A7075 for aluminum alloys. Table 2 shows the chemical composition and the mechanical properties of the aluminum alloys. The HV ranges from 30 to 50 for pure aluminum, and from 60 to 170 for aluminum alloys. The hardness is about half the hardness of cast iron. Fig. 6 shows the relation between the Vickers hardness of aluminum alloy and the erosion resistance, which has been obtained in our laboratory. The solid line shows the base line of carbon steel. The erosion resistance of pure aluminum at HV 100 or less cannot be compared with that of carbon steel, because the Vickers hardness HV of carbon steel is 100 or more. The erosion resistance of aluminum alloy at HV 100 or more was compared with that of carbon steel. The resistance is about 1/3 lower at HV 100, and about 1/5 lower at HV 150. The erosion resistance ER of aluminum alloy is given by the following
equation in terms of the Vickers hardness HV similarly to the ER of cast iron. ER = 0.75 × 10−5 × HV1.6
(3)
The coefficient of correlation is 0.87. It reported that cavitation erosion proceed by fatigue phenomenon [2]. Fig. 7 shows the relation between the rotary bending fatigue strength [11] of aluminum alloy and carbon steel and the Vickers hardness on a log–log scale. The hardness was converted from the tensile strength. The area surrounded by the solid lines shows a scattering of the fatigue strength for carbon steels. The broken line area is the scattering for aluminum alloys. The rotary bending fatigue strength of carbon steel is from 180 MPa to 300 MPa at Vickers hardness HV 150. The fatigue strength of aluminum alloy is from 90 MPa to 180 MPa at HV 150. The fatigue strength of aluminum alloy is much lower than the fatigue strength of carbon steel of the same hardness. This is because local overaging occurs in aluminum alloy caused by repeated stress at room temperature [9]. We can assume that a similar phenomenon occurs for cavitation erosion. Therefore, the erosion resistance of aluminum alloy is much lower than that of carbon steel at the same hardness. Thus, the erosion resistance is 1/3 to 1/5 lower for aluminum alloy compared with carbon steel, because strength reduction occurs due to local overaging by the repeated stress of cavitation bubble collapses.
Table 2 Chemical composition and mechanical properties of Al alloys (mass%). Material
Si
(a) Chemical composition Al 0.09 A1050 0.06 A1070 0.09 A1070BD-F 0.09 A2017 0.61 A5052 0.09 A5083 0.1 A5454 0.07 A7075 0.1
Mn
Cu
Cr
Fe
V
Ms
Zn
Ti
Al
0.01 0.01 – 0.01 0.7 0.07 0.6 0.57 0.02
0.01 0.01 0.01 0.01 4.18 0.03 – 0.04 1.3
– – 0.01 – 0.034 0.21 0.05 0.08 0.13
0.14 0.12 0.11 0.15 0.32 0.24 0.2 0.16 0.21
– – 0.01 0.01 – – – – –
0.01 – 0.01 0.035 0.54 2.6 4.7 2.7 2.4
0.01 0.01 – – 0.194 0.01 – – 5.8
0.01 0.01 0.01 0.01 – – 0.02 – 0.03
Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal.
Material
Density (g/cm3 )
E (GPa)
B (MPa)
HV
(b) Mechanical properties Al A1050 A1070 A1070BD-F A2017 A5052 A5454 A5083 A7075
2.71 2.71 2.71 2.71 2.7 2.7 2.7 2.7 2.7
125 71 71 49 71 70 70 70 71
125 178 95 99 454 205 224 308 540
33 40 38 32 136 65 69 88 166
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Fig. 8. Relation between hardness and erosion resistance of Cu alloy.
the mechanical properties of copper alloys. Fig. 8 shows the relation between Vickers hardness and erosion resistance of copper alloys. The data of erosion resistance of pure copper are concentrated at HV 90. When the erosion resistance of pure copper was compared with carbon steel, the resistance was about 1/2 lower at HV 90. The resistance of copper alloy is the same as that of carbon steel. Therefore, copper was divided into these two categories for analysis. The relation between Vickers hardness and erosion resistance of copper alloy is
Fig. 7. Relation between tensile strength and rotary bending fatigue strength of carbon steel and Al alloy.
4.3. Copper alloys and titanium alloys We discuss four types of copper alloys, i.e. pure coppers C1020 (purity 99.96%) and C1100 (purity 99.90%), alloy equivalent to aluminum bronze C6280, and alloy in which Mn and Fe was added to improve the strength. Table 3 shows the chemical composition and
ER = 2.8 × 10−6 × HV2.19
(4)
Table 3 Chemical composition and mechanical properties of Cu alloys (mass%). Material (a) Chemical composition Pure Cu
Cu alloy
Al
Mn
Fe
Ni
Co
Cu
C1020 C1100
– –
– –
– –
– –
– –
99.96 99.90
Al bronze Al–Mn bronze
9.0 9.0
– 9.0
1.0 3.0
– 2.0
– 1.0
Bal. Bal.
Density (g/cm3 )
E (GPa)
B (MPa)
C1020 C1100
8.96 8.96
115 129
326 328
Al bronze Al–Mn bronze
7.8 7.5
118 118
– 809
Material (b) Mechanical properties Pure Cu
Cu alloy
HV 90 92.2 227 275
Table 4 Chemical composition and mechanical properties of Ti alloys (mass%). Material
Type
N
O
Fe
H
Al
C
V
Cr
Sn
Mo
Zn
Ti
(a) Chemical composition Pure Ti Ti–15V–3Cr–3Sn–3Al Ti–3Al–8V–3Cr–4Mo–4Zn Ti–6A1–4V
␣   ␣+
0.01 0.01 0.17 0.01
0.13 0.12 0.18 0.017
0.06 0.15 – 0.14
0.01 0.001 0.0033 0.0009
– 3.5 3.06 6.29
– 0.005 0.01 0.01
– 14.8 7.4 4.17
– 3.4 4.23 –
– 3.0 – –
– – 4.2 –
– – 5.1 –
Bal. Bal. Bal. Bal.
Material
Density (g/cm3 )
Young’s modulus E (GPa)
Tensile strength B (MPa)
Vickers hardness HV
Micro-hardness Ht
(b) Mechanical properties Pure Ti Ti–15V–3Cr–3Sn–3Al Ti–3Al–8V–3Cr–4Mo–4Zn Ti–6A1–4V
4.49 4.76 4.74 4.32
116 113 113 116
490 1297 1330 971
206 329 334 270
␣: 161 : 276 : 282 ␣: 187, : 82
Material
B (MPa)
HV
Ti–6A1–4V (700 ◦ C AC) Ti–6A1–4V (850 ◦ C AC) Ti–6A1–4V (900 ◦ C AC) Ti–6Al–4V (1100 ◦ C AC)
971 969
270 256 328 327
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Fig. 9. Relation between hardness and erosion resistance of Ti alloy.
and the coefficient of correlation is 0.92. The erosion resistance is almost the same as the erosion resistance of carbon steel at the same hardness, because the fatigue strength of copper alloy is the same as that of carbon steel [11]. We discuss 8 types of titanium alloys, i.e. ␣ type pure titanium,  type alloys of Ti–15V–3Cr–3Sn–3Al and Ti–3Al–8V–3Cr–4Mo–4Zr, ␣ +  type Ti–6Al–4V and 4 types of Ti–6Al–4V with different heattreatment temperatures. Table 4 shows the chemical composition and the mechanical properties of titanium alloys. Ht in the table is the micro-hardness at a force of 0.5 g. Fig. 9 shows the relation between the Vickers hardness and the erosion resistance of titanium alloys. The resistance of titanium alloy is almost the same as that of carbon steel, because notch effect is extremely small compared to cast iron, although titanium alloys have a microscopic dual phase [12]. 5. Conclusions In this study, we analyzed the cavitation erosion resistance of cast iron, aluminum alloy, copper alloy and titanium alloy. The following conclusions can be drawn:
1. The cavitation erosion resistance can be separately evaluated for cast iron, aluminum alloys, copper alloys and titanium alloys in terms of the hardness. 2. The erosion resistance is 1/3 to 1/5 lower for gray cast iron and 2/3 to 1/3 lower for ductile cast iron compared with that of carbon steel with the same hardness, because graphite removal occurs to produce high stress concentrations for cast iron. 3. The erosion resistance of aluminum alloy is 1/3 to 1/5 lower than that of carbon steel with the same hardness, because strength reduction occurs due to local overaging by the repeated stress of cavitation bubble collapses. 4. The erosion resistances of copper alloy and titanium alloy are almost the same as that of carbon steel at the same hardness, because the fatigue strength of these alloys is similar as the strength of carbon steel, provided that the hardness is the same. References [1] F.J. Heymann, Characterization and Determination of Erosion Resistance, ASTM STP474, 1970, pp. 212–222. [2] F.G. Hammitt, Cavitation and Multiphase Flow Phenomena, McGraw-Hill, New York, 1980. [3] S. Hattori, R. Ishikura, Construction of database on cavitation erosion and analysis of carbon steel data, Wear 257 (2004) 1022–1029. [4] S. Hattori, R. Ishikura, Revision of cavitation erosion database and analysis of stainless steel data, Wear 268 (2010) 109–116. [5] ASTM Designation, Annual Book of ASTM Standards, G32-03, 2003. [6] H. Kato, Cavitation, Maki Shoten Publisher, 1979, pp. 175–188. [7] T. Okada, S. Hattori, Cavitation erosion (2), Sci. Mach. 49 (10) (1997) 1078–1081. [8] T. Okada, Y. Iwai, A. Yamamoto, A study of cavitation erosion of cast iron, Wear 84 (1983) 297–312. [9] The Society of Materials Science, Japan, Fatigue of Metal, Maruzen Publisher, 1964, pp. 170–191. [10] The Society of Materials Science, Japan, Engineering Materials for Machine Use, Taiyodo Publisher, 2002, p. 91. [11] The Society of Materials Science, Japan, Handbook of Fatigue Design for Metals, Yokendo Publisher, 1981, pp. 4–5. [12] S. Hattori, et al., Cavitation erosion of titanium alloys, Trans. Jpn. Soc. Mech. Eng. 66 (2000) 187–193.