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Experimental investigation of hardfaced martensitic steel under slurry abrasion conditions
Materials and Design 31 (2010) 4001–4006
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Technical Report
Experimental investigation of hardfaced martensitic steel under slurry abrasion conditions S.G. Sapate a,*, A. Selokar a, N. Garg b a b
Department of Metallurgical and Materials Engineering, V.N.I.T Nagpur 440011, India Diffusion Engineers Limited, MIDC, Hingana, Nagpur 440022, India
a r t i c l e
i n f o
Article history: Received 18 November 2009 Accepted 6 March 2010 Available online 11 March 2010
a b s t r a c t Wear by slurry abrasion is a potential problem in engineering components subjected to particulate flow. The life of the components under slurry abrasive wear situations is primarily decided by operating conditions and the materials properties. Martensitic steels are widely used for abrasion resistant applications. The present work reports slurry abrasion response of hardfacing martensitic steel under a wide range of experimental conditions. The response data is generated using systematic and simultaneous variation of test parameters. The experiments were performed using silica sand slurry with different slurry concentration, particle size, sliding distance and load. The results of the investigation suggest that slurry concentration had relatively stronger effect than normal load. The wear volume loss exhibited an increasing trend with increasing severity of test parameters. An empirical equation is proposed to describe the interactive effect of the test parameters, abrasive particle properties and material property. SEM (Scanning Electron Microscope) studies revealed different morphology of the worn surfaces which was attributed to mild to severe slurry abrasion test conditions. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Martensitic steels are being used as cost effective materials for wear and abrasion resistant application chiefly because of their greater hardness and relatively higher toughness as compared to high chromium cats irons, which exhibit excellent abrasion resistance [1–2]. The high chromium irons are widely used for hardfacing of industrial components in mining, cement plants, thermal power plants and iron and steel industries. Due to their higher hardness, they are however, relatively difficult to machine. The abrasive wear properties of carbon steels by way of change in hardness and microstructure by heat treatment have been investigated in the past by many researchers. The quenched and tempered carbon steel with martensitic microstructure showed 1.5–2.0 times better slurry abrasion resistance as compared to pearlitic microstructure [3–5]. The abrasion resistance of steels increased with increasing volume fraction of martnesite [6–9] whereas Tekeli [10] reported that martensite hardness had greater influence than its volume fraction in deciding wear rate of heat treated carbon steels. Lu Zhenlin [1] noted an increase in slurry abrasion resistance of martensitic steel with carbon content. The wear properties of steels reinforced with second phase particles has been investigated in the past. In general it was observed that the wear resistance of steels is influenced by morphology of * Corresponding author. Tel.: +91 712 2222828; fax: +91 712 2223230. E-mail address: [email protected] (S.G. Sapate). 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.03.009
carbides inter lamellar spacing and properties of abrasive particles, test conditions and mechanical properties of steels and material properties [4,5,7,11–14,15–17]. Wear by slurry abrasion occurs in extruders, slurry pumps, coal water slurry nozzles and pipes carrying slurry of minerals and ores in mineral processing industries. The wear resistance of components used under slurry abrasion conditions is governed by the severity of the operational parameters, and properties of the abrasive particles in the slurry medium. The interactive effect of these parameters decides wear life of the components under actual service conditions. The weld hardfacing is one of the economic methods to improve wear life of industrial components. The wear behaviour of steels with martensitic microstructure, obtained either by heat treatment or casting has been investigated in the past under two body or three body dry abrasive wear situations. A little data is available on slurry abrasion response of weld deposited (hardfaced) martensitic steel. The interactive effect of test conditions and abrasive particle properties on wear rate of hardfaced martenstic steel has not been investigated. There was no attempt made by previous researchers to obtain quantitative correlation between wear properties of hardfaced martensitic steels as a combined function of test parameters and abrasive particle properties. The objective of present work is to investigate slurry abrasion response of weld deposited martensitic steel. The slurry abrasion response data generated by a suitably designed experimental plan consisting of systematic as well as simultaneous variation of test parameters and particle properties was used to
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formulate quantitative relationship between wear loss and severity parameter. 2. Experimental 2.1. Materials The material selected for the present investigation was iron– carbon–chromium alloy steel deposited on mild steel plate (0.19 carbon) with dimensions of 200 mm (length) 200 mm (width) 10 mm (thickness), by manual metal arc welding method. The consumable used for deposition was in the form of electrode with diameter of 3.15 mm. The welding parameters were; voltage – 22 V and current – 120 A (direct current). The thickness of the weld deposit was typically 4 mm. The specimens for chemical analysis, hardness, metallography and slurry abrasion testing were derived from the top surface of the weld deposited plate. The chemical composition of the weld deposited steel surface was analyzed by spectrometer (Spectrolab make). The chemical composition of the deposited surface was carbon – 0.46%, silicon – 0.710%, manganese – 0.37%, phosphorous – 0.025%, sulfur – 0.008%, chromium – 8.45% and vanadium – 0.48%. Energy Dispersive X-ray (EDX) analysis of the surface was also carried out. Fig. 2 shows EDX spectrum indicating elemental analysis. The pres-
Fig. 1. Microstructure of weld deposited specimen showing martensite and carbides.
3000
FeKa MnKb
FeKb
VKb CrKa
FeKesc
CrKb MnKa
6000
TiKb VKa
9000
TiKa
12000
PKa
15000
SiKa
Counts
18000
CKa
21000
CrLa
24000
OKa TiLl TiLa VLl VLa CrLl FeLl
27000 001
0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV Fig. 2. EDX spectrum showing the elemental analysis of the weld deposited surface.
ence of titanium (Ti) in the EDX analysis is attributed to the flux coating on the electrode used for the deposition. The specimen for metallography was prepared using standard metallographic technique. The polished specimens were etched with 2% Nital for observations of microstructure. The microstructure consisted of martensite and carbides and is shown in Fig. 1. The bulk hardness was measured using Vickers Indentation Hardness tester at a load of 30 kg. An average of five readings is reported in the results. The bulk hardness of the sample was 496 HV30. 2.2. Slurry abrasion testing The slurry abrasion wear tests were performed using slurry abrasion test apparatus (Ducom make, India) using silica sand abrasive (hardness = 1000–1100 HV) particles with different particle size as shown in Fig. 3(a–d). The silica sand particles were having sub rounded to angular shape. Finer particles were relatively more angular as compared to coarser particles. The slurry abrasion wear tests were performed using slurry abrasion test apparatus (Ducom make, India). The apparatus consisted of a slurry abrasive chamber enclosing the rubber lined steel wheel, test specimen and slurry. The wheel is made of steel disc with an outer layer of neoprene rubber (durometer hardness of 60 ± 2) molded to its periphery. Diameter of wheel is 178 mm and thickness is 12.7 mm. The maximum speed of the rubber lined wheel is 250 ± 5 rpm (revolutions per minute). The double walled jacket enables to maintain the slurry temperature by circulating coolant. The load was monitored by a load cell (450 N capacity) which was pre-calibrated to measure the force applied by the specimen over the rubber wheel. A photograph of the slurry abrasion test apparatus is shown in Fig. 4. The method of slurry abrasion testing is reported elsewhere [5]. The specimens for slurry abrasion testing were rectangular blocks measuring 57.2 mm (length) 25.4 mm (width) 9 mm (thickness). The specimens for abrasion testing were polished with successive silicon carbide paper followed by polishing with alumina slurry to obtain average surface roughness, Ra = 0.60 lm and cleaned with ethyl alcohol and then weighed using a digital electronic balance to the accuracy of 0.1 mg. After the test, specimens were cleaned with dry compressed air followed by cleaning with ethyl alcohol and then weighed. The loss in mass (g) was calculated as the difference of initial and final weight of the specimen. In addition, wear volume loss was also determined. In the present work slurry abrasion tests were carried out to study the effect of load, slurry concentration and sliding distance on wear loss. In addition slurry abrasion tests were also performed by simultaneous variation of load, slurry concentration and total revolutions. The range of test parameters used was load (35, 70, 95 and 125 N), slurry concentration (40%, 80%,120%,150%) and total revolutions (500, 1000, 1500 and 2000) and abrasive particle size (53–64, 125–150, 212–250, 250–300 lm). The test conditions involving simultaneous variation of test parameters were designated as A (35 N load, 40% slurry concentration, 500 revolutions, 53–64 lm abrasive particle size) B (70 N load, 80% slurry concentration, 1000 revolutions, 125–150 lm abrasive particle size) C (95 N load, 120% slurry concentration, 1500 revolutions, 212–250 lm abrasive particle size and D (125 N load, 150% slurry concentration, 2000 revolutions, 250–300 lm abrasive particle size). A summary of slurry abrasion tests performed in the present investigation and test designations is given in Table 1. 3. Results The effect of slurry concentration and normal load on slurry abrasion volume loss of hardfaced martensitic steel is shown in
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Fig. 4. Photograph of the slurry abrasion test apparatus.
Table 1 Summary of slurry abrasion tests performed in the present work. Load (N)
No. of revolutions
Particle size of silica sand (lm)
Slurry concentration (%)
35, 70, 95, 125 125 125 35 (A) 70 (B) 95 (C) 125 (D)
1000 500, 1000, 1500, 2000 1000 500 1000 1500 2000
250–300 250–300 250–300 53–64 125–150 212–250 250–300
150 150 40, 80, 120, 150 40 80 120 150
sulted in increase in volume wear loss from 19.4864 to 29.100 mm3 as shown in Fig. 5a. When the normal load was increased from 35 N to 125 N, volume loss increased nearly two times from 20.5229 mm3 to 40.30 mm3 as shown in Fig. 5b. The volume loss increased from 19.175 mm3 to 72.2059 mm3 when the sliding distance was increased from 18.838 m to 77.486 m under given slurry abrasion conditions. The simultaneous variation of test parameters from test conditions A–D resulted in significant increase in volume loss which was observed to be 0.259 mm3, 0.816, 14.316 and 77.5 mm3, respectively. 4. Discussion Fig. 3. (a–d) SEM photographs of silica sand particles used for slurry abrasion testing: (a) 53–64 lm, (b) 125–150 lm, (c) 212–250 lm and (d) 250–300 lm.
Fig. 5a and b respectively. The data points in each case were fitted by best fit line and the slope of the line gives volume wear rate with respect to slurry concentration (Sc) and normal load (L). In each case a linear relationship was noted with regression coefficients of 0.9846 and 0.9459. The volume wear loss increased from 2.4487 mm3 to 13.3192 mm3 when slurry concentration was increased from 40% to 80%. A further increase from 80% to 150% re-
The present investigation reports wear behaviour of hardfaced martensitic steel under different experimental conditions. The volume wear loss exhibited increasing trend with slurry concentration, normal load and the sliding distance. The magnitude of increase in volume loss was, however different in each case. It can be concluded from Fig. 5a and b. that nearly four fold increase in slurry concentration resulted in more than eleven times increase in wear volume loss. The significant increase in volume loss of more than five times for two times increase in slurry concentration, initially, can also be noted. The increase in volume loss, further with slurry concentration was more or less linear. The
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35
25 20 15 10 5 0
0
50
100
150
200
Slurry concentration(%) Fig. 5a. Effect of slurry concentration on wear volume loss of hardfaced martensitic steel.
Q ¼ k½ðS L=Ac ÞðSc =DÞðHa =Ht Þm
32.5
Volume loss (mm3)
30 27.5 25 22.5 20 17.5 15
0
50
100
150
Normal Load (N) Fig. 5b. The effect of normal load on slurry abrasive wear volume loss of hardfaced martensitic steel.
relationship between volume loss and sliding distance was linear. The slope of the best fit line indicated volume loss for per unit% of slurry concentration, per unit normal load and sliding distance. The respective values were 0.2316, 0.1019 and 0.9382 for slurry concentration, normal load and sliding distance indicating that volume loss exhibited relatively greater dependence on slurry concentration than normal load. Similar observations were reported in an earlier investigation [18]. Simultaneous variation of test parameters from test conditions A–D resulted in nearly three times increase in volume loss. Under actual service conditions, the engineering components are subjected to slurry abrasion situations with different severity, which is influenced by operational parameters (load, velocity), properties of abrasives particles (hardness, size, shape, fraction of abrasives in slurry). The severity of slurry abrasion condition is generally represented by wear constant K in Archard’s wear equation; V = K(SL/H) where V is volume wear loss, S is the sliding distance (S), L is normal load, H is bulk hardness of the surface [5]. Cozza and coworkers [19] used product of contact pressure and velocity as measure of ‘test severity’ in micro-abrasion test whereas Adachi and Hutchings [20,21] used ‘severity of contact’ to indicate severity of test conditions, which incorporated applied load, wear scar area, slurry faction and hardness of surface and abrasive.
ð1Þ
where k is constant and m is the exponent. The value of the exponent m was observed to be 2.4236 and the regression coefficient was 0.8858. The Test Severity Parameter [(S L/Ac) (Sc/D) (Ha/ Ht)], not only takes into account the operating variables like sliding distance, normal load and slurry concentration but also the properties of the abrasive particle in slurry and the material property. Thus slurry abrasion volume loss can be more meaningfully represented by this parameter under a range of given slurry abrasion conditions. SEM (Scanning Electron Microscope) investigations on abraded surface revealed significant differences in morphology of the surfaces. Under benign experimental conditions, the abraded surface was relatively smooth and shallow grooves were observed on the worn out surface and material was predominantly removed by ploughing mechanism. The lip of work hardened material still attached to the groove edges can be observed in Fig. 7a. In Fig. 7b, relatively deeper grooves can be seen indicating greater depth of penetration by relatively coarser abrasive particles at higher loads as compared to test condition A. The material removal in the form of flakes can also be observed at the centre and top side of the photographs and material is primarily removed by cutting indicating micro cutting mechanism of material removal as seen in
1.00E-06
Wear volume loss ( m3)
Volume loss (mm 3)
30
In the present work the two different approached were used. The first approach was to evaluate the effect of individual test parameters like load, slurry concentration and sliding distance on slurry abrasion volume loss. The second approach was aimed at studying the effect of simultaneous variation of applied load, slurry concentration, sliding distance and abrasive particle size on slurry abrasion behaviour of hardfaced martensitic steel. In the present work the size of the abrasive particles is also incorporated in the ‘Test Severity Parameter’ (TSP). To assess the simultaneous variation of test parameters, and properties of abrasive particle and material hardness, the volume loss Q was plotted vs. Test Severity Parameter expressed as TSP = [(S L/Ac) (Sc/D) (Ha/Ht)], where S is sliding distance (m), L is normal load (N), Ac is area of worn out crater (m2), Sc is fraction of abrasive particles in slurry, D is average particle size of abrasive (m), Ha/Ht is the ratio of hardness of abrasive particle (Ha) to hardness of the target material (Ht) as shown in Fig. 6. The data points on log–log plot were fitted by the best fit line and slope of the line indicated the exponent of the combined parameters. The dependence of the wear volume loss (Q) on Test Severity Parameter, TSP, was expressed as,
1.00E-07
1.00E-08
1.00E-09
1.00E-10 1.00E+10
1.00E+11
1.00E+12
(SxL/Ac) (Sc/D) (Ha/Ht) Fig. 6. Slurry abrasion wear volume loss plotted vs. Test Severity Parameter TSP, [(S L/Ac) (Sc/D) (Ha/Ht)].
S.G. Sapate et al. / Materials and Design 31 (2010) 4001–4006
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Fig. 7c and d which show the SEM photographs of worn surfaces under relatively severe test conditions (test conditions C and D). With increasing severity of experimental conditions, the depth and width of the wear groove increased significantly resulting in increased material removal, since with increasing severity of test parameter, increased load and particle size leads to greater depth of penetration into the surface. With increasing particle size decrease in abrasive wear resistance has been reported earlier [17,22]. The relatively harder silica sand particles can indent the surface, as ratio of hardness of silica sand particle and hardfaced martensitic steel was more than 1.2 required to cause plastic indentation of the surface [23]. Thus significant increase in volume loss with increasing severity parameter can be attributed to increasing number of abrasive particle in slurry causing grooving abrasion, increased normal pressure and particle size effect [22]. The ratio of hardness of abrasive particles to that of the surface has been included in the Eq. (1) for the sake of brevity realizing that the slurry abrasion tests were conducted with silica sands abrasive particles on hardfaced martensitic steel. The response data generated by simultaneous variation of test parameters shall be useful in selecting wear resistant steel under particular set of slurry abrasion situations. It is realized that the experimental model presented in this work can be made more comprehensive by incorporating a range of relative hardness of the target material. Further experimentation is in progress in this direction to extend the validity the experimental model over a wide range of experimental conditions, material and particle properties.
Fig. 7. (c and d) SEM micrograph of worn surface of hardfaced martensitic steel after slurry abrasion test under test conditions C and D respectively.
5. Conclusion (1) The slurry abrasion response of hardfaced martensitic steel was investigated by systematic and simultaneous variation of test parameters. (2) The volume wear loss of hardfaced martensitic steel increased with slurry concentration, normal load and the sliding distance. The magnitude of increase in volume loss was, however different in each case. (3) The volume loss exhibited relatively greater dependence on slurry concentration than normal load. Increasing severity parameter resulted in significant increase in wear volume loss under the given test conditions. (4) The dependence of wear volume loss on Test Severity Parameter was expressed by the equation, m Q ¼ k½ðS L=Ac Þ ðSc =DÞ ðHa =Ht Þ . (5) The difference in morphology of the abraded surface was attributed to the differential severity of the test conditions. (6) The important mechanisms of material removal were ploughing, micro cutting and indentation. With increasing severity of test conditions, material removal occurred predominantly by micro cutting mechanism.
Acknowledgement Fig. 7. (a and b) SEM micrograph of worn surface of hardfaced martensitic steel after slurry abrasion test under test conditions A and B respectively.
The authors are grateful to Director, VNIT for providing necessary facilities in carrying out this investigation. The authors are
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grateful to Diffusion Engineers Limited for providing samples for the present investigation. The thanks are due to Mr. K.M. Manapure and Mr. Kapil for their assistance during experimentation and SEM work. References [1] Zhenlin Lu, Qichang R, Zhihao Jin. An investigation of the corrosion abrasion behaviour 6% chromium cats steel. J Mater Process Technol 1999;95:180–4. [2] Sapate SG, RamaRao AV. Erosive wear behaviour of weld hardfacing high chromium cast irons: effect of erodent particles. Tribol Int 2006;39(3):206–12. [3] Shu Sun J. The abrasion characteristics of some carbide containing alloys. In: Ludema KC, editor. Proc of the int conf on wear of materials, ASME; 1983. p. 79–86. [4] He Lin, Zhang CJ. An investigation of the role of secondary carbides in martensitic steel during three body abrasion wear. Wear 1994;16:103–9. [5] Sapate SG, Chopde AD, Nimbalkar PM, Chandrakar DK. Effect of microstructure on slurry abrasion response of En-31 steel. Mater Des 2008;29(3):613–21. [6] ZumGahr KH. Abrasive wear of two phase metallic materials with a coarse microstructure. In: Ludema KC, editor. Proc of int conf on wear of materials, Vancouver, ASME; April 1985. p. 45–57. [7] Modi OP, Pandit P, Mondal DP, Prasad BK, Yegneswaran AH, Chrysanthou A. High-stress abrasive wear response of 0.2% carbon dual phase steel: effects of microstructural features and experimental conditions. Mater Sci Eng 2007;A 458:303–11. [8] Saghafian H, Kheirandish S. Correlating microstructural features with wear resistance of dual phase steel. Mater Lett 2007;61:3059–63. [9] Jha AK, Prasad BK, Modi OP, Das S, Yegneswaran AH. Correlating microstructural features and mechanical properties with abrasion resistance of a high strength low alloy steel. Wear 2003;254:120–8. [10] Tekeli S, Gural A. Dry sliding behaviour of heat treated iron based powder metallurgy steels with 0.3 Graphite + 2% Ni additions. Mater Des 2006.
[11] Reponen PK, Liimatainen J, Ala-Kleme S, Hellman J, Hannula SP. The correlation of material characteristics and wear in a laboratory scale cone crusher. Wear 2009;267:568–75. [12] Badisch E, Mitterer. Abrasive wear of high speed steels influence of abrasive particles and primary carbides on wear resistance. Tribol Int 2003;36:765–70. [13] Katsuki F, Watari K, Tahira H, Umino M. Abrasive wear behavior of a pearlitic (0.4% C) steel microalloyed with vanadium. Wear 2008;264:331–6. [14] Modi OP, Mondal DP, Prasad BK, Singh M, Khaira HK. Abrasive wear behaviour of a high carbon steel: effects of microstructure and experimental parameters and correlation with mechanical properties. Mater Sci Eng 2003;A343:235–42. [15] Bourithisa L, Papadimitrioua GD, Sideris J. Comparison of wear properties of tool steels AISI D2 and O1 with the same hardness. Tribol Int 2006;39:479–89. [16] Larsen Basse J, Premaratne B. Effect of relative hardness on transitions in abrasive wear mechanisms. In: Ludema KC, editor. Proc of int conf on wear of materials, ASME; 1983. p. 161–6. [17] Sevim I, Eryurek IB. Effect of abrasive particle size on wear resistance in steels. Mater Des 2006;27:173–81. [18] Balasubramanian V, Varahamoorthy R, Ramachandran CS, Babu S. Abrasive slurry wear behavior of stainless steel surface produced by plasma transferred arc hardfacing process. Surf Coat Technol 2008;202:3903–12. [19] Cozza RC, DeMello JDB, Tanaka DK, Souza RM. Relationship between test severity and wear mode transition in micro-abrasive wear test. Wear 2007;263:111–6. [20] Adachi K, Hutchings IM. Wear mode mapping for the micro-scale abrasion test. Wear 2003;255:23–9. [21] Adachi K, Hutchings IM. Sensitivity of wear rates in the micro-scale abrasion test to test conditions and material hardness. Wear 2005;258:318–21. [22] Misra A, Finnie I. On the size effect in abrasive and erosive wear. Wear 1981;65:359–73. [23] Hutchings IM. Tribology, friction and wear of engineering materials. Edward Arnold; 1992.
Contents lists available at ScienceDirect
Materials and Design journal homepage: www.elsevier.com/locate/matdes
Technical Report
Experimental investigation of hardfaced martensitic steel under slurry abrasion conditions S.G. Sapate a,*, A. Selokar a, N. Garg b a b
Department of Metallurgical and Materials Engineering, V.N.I.T Nagpur 440011, India Diffusion Engineers Limited, MIDC, Hingana, Nagpur 440022, India
a r t i c l e
i n f o
Article history: Received 18 November 2009 Accepted 6 March 2010 Available online 11 March 2010
a b s t r a c t Wear by slurry abrasion is a potential problem in engineering components subjected to particulate flow. The life of the components under slurry abrasive wear situations is primarily decided by operating conditions and the materials properties. Martensitic steels are widely used for abrasion resistant applications. The present work reports slurry abrasion response of hardfacing martensitic steel under a wide range of experimental conditions. The response data is generated using systematic and simultaneous variation of test parameters. The experiments were performed using silica sand slurry with different slurry concentration, particle size, sliding distance and load. The results of the investigation suggest that slurry concentration had relatively stronger effect than normal load. The wear volume loss exhibited an increasing trend with increasing severity of test parameters. An empirical equation is proposed to describe the interactive effect of the test parameters, abrasive particle properties and material property. SEM (Scanning Electron Microscope) studies revealed different morphology of the worn surfaces which was attributed to mild to severe slurry abrasion test conditions. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Martensitic steels are being used as cost effective materials for wear and abrasion resistant application chiefly because of their greater hardness and relatively higher toughness as compared to high chromium cats irons, which exhibit excellent abrasion resistance [1–2]. The high chromium irons are widely used for hardfacing of industrial components in mining, cement plants, thermal power plants and iron and steel industries. Due to their higher hardness, they are however, relatively difficult to machine. The abrasive wear properties of carbon steels by way of change in hardness and microstructure by heat treatment have been investigated in the past by many researchers. The quenched and tempered carbon steel with martensitic microstructure showed 1.5–2.0 times better slurry abrasion resistance as compared to pearlitic microstructure [3–5]. The abrasion resistance of steels increased with increasing volume fraction of martnesite [6–9] whereas Tekeli [10] reported that martensite hardness had greater influence than its volume fraction in deciding wear rate of heat treated carbon steels. Lu Zhenlin [1] noted an increase in slurry abrasion resistance of martensitic steel with carbon content. The wear properties of steels reinforced with second phase particles has been investigated in the past. In general it was observed that the wear resistance of steels is influenced by morphology of * Corresponding author. Tel.: +91 712 2222828; fax: +91 712 2223230. E-mail address: [email protected] (S.G. Sapate). 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.03.009
carbides inter lamellar spacing and properties of abrasive particles, test conditions and mechanical properties of steels and material properties [4,5,7,11–14,15–17]. Wear by slurry abrasion occurs in extruders, slurry pumps, coal water slurry nozzles and pipes carrying slurry of minerals and ores in mineral processing industries. The wear resistance of components used under slurry abrasion conditions is governed by the severity of the operational parameters, and properties of the abrasive particles in the slurry medium. The interactive effect of these parameters decides wear life of the components under actual service conditions. The weld hardfacing is one of the economic methods to improve wear life of industrial components. The wear behaviour of steels with martensitic microstructure, obtained either by heat treatment or casting has been investigated in the past under two body or three body dry abrasive wear situations. A little data is available on slurry abrasion response of weld deposited (hardfaced) martensitic steel. The interactive effect of test conditions and abrasive particle properties on wear rate of hardfaced martenstic steel has not been investigated. There was no attempt made by previous researchers to obtain quantitative correlation between wear properties of hardfaced martensitic steels as a combined function of test parameters and abrasive particle properties. The objective of present work is to investigate slurry abrasion response of weld deposited martensitic steel. The slurry abrasion response data generated by a suitably designed experimental plan consisting of systematic as well as simultaneous variation of test parameters and particle properties was used to
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S.G. Sapate et al. / Materials and Design 31 (2010) 4001–4006
formulate quantitative relationship between wear loss and severity parameter. 2. Experimental 2.1. Materials The material selected for the present investigation was iron– carbon–chromium alloy steel deposited on mild steel plate (0.19 carbon) with dimensions of 200 mm (length) 200 mm (width) 10 mm (thickness), by manual metal arc welding method. The consumable used for deposition was in the form of electrode with diameter of 3.15 mm. The welding parameters were; voltage – 22 V and current – 120 A (direct current). The thickness of the weld deposit was typically 4 mm. The specimens for chemical analysis, hardness, metallography and slurry abrasion testing were derived from the top surface of the weld deposited plate. The chemical composition of the weld deposited steel surface was analyzed by spectrometer (Spectrolab make). The chemical composition of the deposited surface was carbon – 0.46%, silicon – 0.710%, manganese – 0.37%, phosphorous – 0.025%, sulfur – 0.008%, chromium – 8.45% and vanadium – 0.48%. Energy Dispersive X-ray (EDX) analysis of the surface was also carried out. Fig. 2 shows EDX spectrum indicating elemental analysis. The pres-
Fig. 1. Microstructure of weld deposited specimen showing martensite and carbides.
3000
FeKa MnKb
FeKb
VKb CrKa
FeKesc
CrKb MnKa
6000
TiKb VKa
9000
TiKa
12000
PKa
15000
SiKa
Counts
18000
CKa
21000
CrLa
24000
OKa TiLl TiLa VLl VLa CrLl FeLl
27000 001
0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV Fig. 2. EDX spectrum showing the elemental analysis of the weld deposited surface.
ence of titanium (Ti) in the EDX analysis is attributed to the flux coating on the electrode used for the deposition. The specimen for metallography was prepared using standard metallographic technique. The polished specimens were etched with 2% Nital for observations of microstructure. The microstructure consisted of martensite and carbides and is shown in Fig. 1. The bulk hardness was measured using Vickers Indentation Hardness tester at a load of 30 kg. An average of five readings is reported in the results. The bulk hardness of the sample was 496 HV30. 2.2. Slurry abrasion testing The slurry abrasion wear tests were performed using slurry abrasion test apparatus (Ducom make, India) using silica sand abrasive (hardness = 1000–1100 HV) particles with different particle size as shown in Fig. 3(a–d). The silica sand particles were having sub rounded to angular shape. Finer particles were relatively more angular as compared to coarser particles. The slurry abrasion wear tests were performed using slurry abrasion test apparatus (Ducom make, India). The apparatus consisted of a slurry abrasive chamber enclosing the rubber lined steel wheel, test specimen and slurry. The wheel is made of steel disc with an outer layer of neoprene rubber (durometer hardness of 60 ± 2) molded to its periphery. Diameter of wheel is 178 mm and thickness is 12.7 mm. The maximum speed of the rubber lined wheel is 250 ± 5 rpm (revolutions per minute). The double walled jacket enables to maintain the slurry temperature by circulating coolant. The load was monitored by a load cell (450 N capacity) which was pre-calibrated to measure the force applied by the specimen over the rubber wheel. A photograph of the slurry abrasion test apparatus is shown in Fig. 4. The method of slurry abrasion testing is reported elsewhere [5]. The specimens for slurry abrasion testing were rectangular blocks measuring 57.2 mm (length) 25.4 mm (width) 9 mm (thickness). The specimens for abrasion testing were polished with successive silicon carbide paper followed by polishing with alumina slurry to obtain average surface roughness, Ra = 0.60 lm and cleaned with ethyl alcohol and then weighed using a digital electronic balance to the accuracy of 0.1 mg. After the test, specimens were cleaned with dry compressed air followed by cleaning with ethyl alcohol and then weighed. The loss in mass (g) was calculated as the difference of initial and final weight of the specimen. In addition, wear volume loss was also determined. In the present work slurry abrasion tests were carried out to study the effect of load, slurry concentration and sliding distance on wear loss. In addition slurry abrasion tests were also performed by simultaneous variation of load, slurry concentration and total revolutions. The range of test parameters used was load (35, 70, 95 and 125 N), slurry concentration (40%, 80%,120%,150%) and total revolutions (500, 1000, 1500 and 2000) and abrasive particle size (53–64, 125–150, 212–250, 250–300 lm). The test conditions involving simultaneous variation of test parameters were designated as A (35 N load, 40% slurry concentration, 500 revolutions, 53–64 lm abrasive particle size) B (70 N load, 80% slurry concentration, 1000 revolutions, 125–150 lm abrasive particle size) C (95 N load, 120% slurry concentration, 1500 revolutions, 212–250 lm abrasive particle size and D (125 N load, 150% slurry concentration, 2000 revolutions, 250–300 lm abrasive particle size). A summary of slurry abrasion tests performed in the present investigation and test designations is given in Table 1. 3. Results The effect of slurry concentration and normal load on slurry abrasion volume loss of hardfaced martensitic steel is shown in
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Fig. 4. Photograph of the slurry abrasion test apparatus.
Table 1 Summary of slurry abrasion tests performed in the present work. Load (N)
No. of revolutions
Particle size of silica sand (lm)
Slurry concentration (%)
35, 70, 95, 125 125 125 35 (A) 70 (B) 95 (C) 125 (D)
1000 500, 1000, 1500, 2000 1000 500 1000 1500 2000
250–300 250–300 250–300 53–64 125–150 212–250 250–300
150 150 40, 80, 120, 150 40 80 120 150
sulted in increase in volume wear loss from 19.4864 to 29.100 mm3 as shown in Fig. 5a. When the normal load was increased from 35 N to 125 N, volume loss increased nearly two times from 20.5229 mm3 to 40.30 mm3 as shown in Fig. 5b. The volume loss increased from 19.175 mm3 to 72.2059 mm3 when the sliding distance was increased from 18.838 m to 77.486 m under given slurry abrasion conditions. The simultaneous variation of test parameters from test conditions A–D resulted in significant increase in volume loss which was observed to be 0.259 mm3, 0.816, 14.316 and 77.5 mm3, respectively. 4. Discussion Fig. 3. (a–d) SEM photographs of silica sand particles used for slurry abrasion testing: (a) 53–64 lm, (b) 125–150 lm, (c) 212–250 lm and (d) 250–300 lm.
Fig. 5a and b respectively. The data points in each case were fitted by best fit line and the slope of the line gives volume wear rate with respect to slurry concentration (Sc) and normal load (L). In each case a linear relationship was noted with regression coefficients of 0.9846 and 0.9459. The volume wear loss increased from 2.4487 mm3 to 13.3192 mm3 when slurry concentration was increased from 40% to 80%. A further increase from 80% to 150% re-
The present investigation reports wear behaviour of hardfaced martensitic steel under different experimental conditions. The volume wear loss exhibited increasing trend with slurry concentration, normal load and the sliding distance. The magnitude of increase in volume loss was, however different in each case. It can be concluded from Fig. 5a and b. that nearly four fold increase in slurry concentration resulted in more than eleven times increase in wear volume loss. The significant increase in volume loss of more than five times for two times increase in slurry concentration, initially, can also be noted. The increase in volume loss, further with slurry concentration was more or less linear. The
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35
25 20 15 10 5 0
0
50
100
150
200
Slurry concentration(%) Fig. 5a. Effect of slurry concentration on wear volume loss of hardfaced martensitic steel.
Q ¼ k½ðS L=Ac ÞðSc =DÞðHa =Ht Þm
32.5
Volume loss (mm3)
30 27.5 25 22.5 20 17.5 15
0
50
100
150
Normal Load (N) Fig. 5b. The effect of normal load on slurry abrasive wear volume loss of hardfaced martensitic steel.
relationship between volume loss and sliding distance was linear. The slope of the best fit line indicated volume loss for per unit% of slurry concentration, per unit normal load and sliding distance. The respective values were 0.2316, 0.1019 and 0.9382 for slurry concentration, normal load and sliding distance indicating that volume loss exhibited relatively greater dependence on slurry concentration than normal load. Similar observations were reported in an earlier investigation [18]. Simultaneous variation of test parameters from test conditions A–D resulted in nearly three times increase in volume loss. Under actual service conditions, the engineering components are subjected to slurry abrasion situations with different severity, which is influenced by operational parameters (load, velocity), properties of abrasives particles (hardness, size, shape, fraction of abrasives in slurry). The severity of slurry abrasion condition is generally represented by wear constant K in Archard’s wear equation; V = K(SL/H) where V is volume wear loss, S is the sliding distance (S), L is normal load, H is bulk hardness of the surface [5]. Cozza and coworkers [19] used product of contact pressure and velocity as measure of ‘test severity’ in micro-abrasion test whereas Adachi and Hutchings [20,21] used ‘severity of contact’ to indicate severity of test conditions, which incorporated applied load, wear scar area, slurry faction and hardness of surface and abrasive.
ð1Þ
where k is constant and m is the exponent. The value of the exponent m was observed to be 2.4236 and the regression coefficient was 0.8858. The Test Severity Parameter [(S L/Ac) (Sc/D) (Ha/ Ht)], not only takes into account the operating variables like sliding distance, normal load and slurry concentration but also the properties of the abrasive particle in slurry and the material property. Thus slurry abrasion volume loss can be more meaningfully represented by this parameter under a range of given slurry abrasion conditions. SEM (Scanning Electron Microscope) investigations on abraded surface revealed significant differences in morphology of the surfaces. Under benign experimental conditions, the abraded surface was relatively smooth and shallow grooves were observed on the worn out surface and material was predominantly removed by ploughing mechanism. The lip of work hardened material still attached to the groove edges can be observed in Fig. 7a. In Fig. 7b, relatively deeper grooves can be seen indicating greater depth of penetration by relatively coarser abrasive particles at higher loads as compared to test condition A. The material removal in the form of flakes can also be observed at the centre and top side of the photographs and material is primarily removed by cutting indicating micro cutting mechanism of material removal as seen in
1.00E-06
Wear volume loss ( m3)
Volume loss (mm 3)
30
In the present work the two different approached were used. The first approach was to evaluate the effect of individual test parameters like load, slurry concentration and sliding distance on slurry abrasion volume loss. The second approach was aimed at studying the effect of simultaneous variation of applied load, slurry concentration, sliding distance and abrasive particle size on slurry abrasion behaviour of hardfaced martensitic steel. In the present work the size of the abrasive particles is also incorporated in the ‘Test Severity Parameter’ (TSP). To assess the simultaneous variation of test parameters, and properties of abrasive particle and material hardness, the volume loss Q was plotted vs. Test Severity Parameter expressed as TSP = [(S L/Ac) (Sc/D) (Ha/Ht)], where S is sliding distance (m), L is normal load (N), Ac is area of worn out crater (m2), Sc is fraction of abrasive particles in slurry, D is average particle size of abrasive (m), Ha/Ht is the ratio of hardness of abrasive particle (Ha) to hardness of the target material (Ht) as shown in Fig. 6. The data points on log–log plot were fitted by the best fit line and slope of the line indicated the exponent of the combined parameters. The dependence of the wear volume loss (Q) on Test Severity Parameter, TSP, was expressed as,
1.00E-07
1.00E-08
1.00E-09
1.00E-10 1.00E+10
1.00E+11
1.00E+12
(SxL/Ac) (Sc/D) (Ha/Ht) Fig. 6. Slurry abrasion wear volume loss plotted vs. Test Severity Parameter TSP, [(S L/Ac) (Sc/D) (Ha/Ht)].
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Fig. 7c and d which show the SEM photographs of worn surfaces under relatively severe test conditions (test conditions C and D). With increasing severity of experimental conditions, the depth and width of the wear groove increased significantly resulting in increased material removal, since with increasing severity of test parameter, increased load and particle size leads to greater depth of penetration into the surface. With increasing particle size decrease in abrasive wear resistance has been reported earlier [17,22]. The relatively harder silica sand particles can indent the surface, as ratio of hardness of silica sand particle and hardfaced martensitic steel was more than 1.2 required to cause plastic indentation of the surface [23]. Thus significant increase in volume loss with increasing severity parameter can be attributed to increasing number of abrasive particle in slurry causing grooving abrasion, increased normal pressure and particle size effect [22]. The ratio of hardness of abrasive particles to that of the surface has been included in the Eq. (1) for the sake of brevity realizing that the slurry abrasion tests were conducted with silica sands abrasive particles on hardfaced martensitic steel. The response data generated by simultaneous variation of test parameters shall be useful in selecting wear resistant steel under particular set of slurry abrasion situations. It is realized that the experimental model presented in this work can be made more comprehensive by incorporating a range of relative hardness of the target material. Further experimentation is in progress in this direction to extend the validity the experimental model over a wide range of experimental conditions, material and particle properties.
Fig. 7. (c and d) SEM micrograph of worn surface of hardfaced martensitic steel after slurry abrasion test under test conditions C and D respectively.
5. Conclusion (1) The slurry abrasion response of hardfaced martensitic steel was investigated by systematic and simultaneous variation of test parameters. (2) The volume wear loss of hardfaced martensitic steel increased with slurry concentration, normal load and the sliding distance. The magnitude of increase in volume loss was, however different in each case. (3) The volume loss exhibited relatively greater dependence on slurry concentration than normal load. Increasing severity parameter resulted in significant increase in wear volume loss under the given test conditions. (4) The dependence of wear volume loss on Test Severity Parameter was expressed by the equation, m Q ¼ k½ðS L=Ac Þ ðSc =DÞ ðHa =Ht Þ . (5) The difference in morphology of the abraded surface was attributed to the differential severity of the test conditions. (6) The important mechanisms of material removal were ploughing, micro cutting and indentation. With increasing severity of test conditions, material removal occurred predominantly by micro cutting mechanism.
Acknowledgement Fig. 7. (a and b) SEM micrograph of worn surface of hardfaced martensitic steel after slurry abrasion test under test conditions A and B respectively.
The authors are grateful to Director, VNIT for providing necessary facilities in carrying out this investigation. The authors are
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