- Email: [email protected]
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel
Available online at www.sciencedirect.com
-"
.:;, ScienceDirect JOURNAL
OF IRON
AND STEEL RESEARCH, INTERNATIONAL. 2009, 16(4): 49-54
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel C S Ramachandran,
V Balasubramanian ,
R Varahamoorthy
[Centre for Materials joining and Research (CEMAjOR), Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608002, India] Abstract: The effects of different experimental conditions on the dry sliding wear behavior of stainless steel surface produced by plasma transferred arc (PTA) hardfacing process were studied. The wear test was conducted in a pinon- roller wear testing machine, at constant sliding distance of 1 km, Mathematical models were developed to estimate -wear rate incorporating with rotational speed, applied load and roller hardness using statistical tools such as design of experiments, regression analysis and analysis of variance. It is found that the wear resistance of the PTA hardfaced stainless steel surface is better than that of the carbon steel substrate. Key words: dry sliding wear; plasma transferred arc hardfacing; carbon steel; stainless steel; variance analysis; experimental design
Dry sliding wear can be seen in gears, cams, bearings, clutches, brakes and other applications involving sliding contact or rolling contact-". The contact surfaces are rough and possess hills and valleys, so the applied normal stress is very high in the contact regions and may exceed the yield point of the solids. This could result in localized yielding of the material, improved bearing area and more interaction, and localized weld formation. The welds could be disturbed during the sliding process, resulting in loss of materialsl". For similar metals, the junction formed between asperities was stronger than that of parent metals because of work hardening during the sliding process. Material was lost through removal of lumps from the mating faces. For dissimilar metals, when the welded asperity junction was shared, part of the weaker metal was 10st[3J. Hardfacing is primarily done to enhance the surface properties of the base metal, and hardfaced materials generally exhibit better wear, corrosion and oxidation resistance than the base metal[4 J. Conventional weld hardfacing is done by oxyfuel welding, gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), shielded metal arc welding (SMAW), flux cored arc welding (FCAW), and Blography:C S Ramachandranr 1983-). Male. Doctor. Research Scholar;
submerged arc welding (SAW). Plasma transferred arc (PTA) hardfacing and laser beam hardfacing are relative newcomers to this arena. At present, many of the fabrication industries are adopting submerged arc surfacing using wire electrodes. With conventional submerged arc surfacing, percentage dilution levels are higher. To attain low dilution, the surfacing technique used should enable spreading the arc energy uniformly over the area to be surfaced'r". Eventhough PTA hard facing technique offers many advantages over other processes, the published information on dry sliding wear behavior of PTA hardfaced surface is very limited. Hence, the present investigation was carried out to study the dry sliding wear behaviour of PTA hardfaced stainless steel surface, and the results are reported in this paper.
1
Experimental
From Ref. [6J and Ref. [7J, the predominant factors, which have greater influence on dry sliding wear behaviour, were identified. They are: (1) rotational speed of the roller, (2) applied load, and (3) roller hardness. Trial experiments were conducted to determine the working range of the above factors. During the trial experiments, the following E-mail: [email protected];
Revised Date: October 26. 2008
• 50 •
Journal of Iron and Steel Research, International
observations were made: (1) if the rotational speed was greater than 500 r /rnin , the wear test machine produced a lot of noise and vibration under the ac. tion of lower loads. If the rotational speed was lower than 100 r/min , the wear test machine was not able to rotate under the action of higher loads. ( 2) The minimum load that can be applied to the specimen was 50 N (a limitation of the test setup). If the applied load was greater than 90 N. the machine could experience overload effect and not run smoothly at higher speeds. (3) Rollers of different hardness were fabricated using PTA hardfacing. By considering all conditions mentioned above. the feasible limits of the parameters were chosen in such a way that the dry sliding wear test could be conducted without any difficulty. The important factors that will influence the dry sliding wear behaviour and their working range Table 1
Vol. 16
are presented in Table 1. Due to a wide range of factors. it was decided to use three factors. five levels central composite design matrix to optimise the experimental conditions. Table 2 shows the set of 20 coded conditions used to form the design matrix. The method of designing such a matrix was dealt with elsewhere[B-lO]. For the convenience of recording and processing experimental data. the upper and the lower levels of the factors were coded as 1. 682 and -1. 682. respectively. The coded values of the intermediate values can be calculated using the following relationship'P", Xi = [1. 682X - (X max X min ) J/[ (X max X min ) / 1. 682J (1) where. Xi is the required coded value of a variable X; X is any value of the variable from X min to X max ; X min is the lowest level of the variable; X max is the highest level of the variable.
+
+
Important parameters and their working range Level
Notations
Unit
Rotational speed
N
r/min
Applied load
P
N
Roller hardness (HRC)
H
Factors
Experimental No.
>
-1
2 3 4 5 6 7 8 9
1 -1
10 11
12 13 14 15 16 17 18 19 20
1 -1 1 -1 1 -1. 682 1. 682 0 0 0 0 0 0 0 0 0 0
Highest
-1.0
0
+1.0
+ 1. 682
200 60 50
300 70 55
400 80 60
500 90 65
-1. 682 100 50 45
Experimental design matrix and measured wear rates
Coded val ues
Original values
min-I)
1
High
Low
Table 2 N/ (r
Middle
Lowest
PIN
H
-1 -1
-1 -1 -1 -1 1 1 1 1 0 0 0 0 -1. 682 1. 682 0 0 0 0 0 0
1 1 -1 -1 1 1 0 0 -1. 682 1. 682 0 0 0 0 0 0 0 0
N/ (r
>
Wear rate/j mg
PIN
H
200 400 200 400 200 400 200 400 100 500 300 300 300 300 300 300 300 300 300
60 60 80 80 60 60 80 80 70 70 50 90 70 70 70 70 70 70 70
50 50 50 50 60 60 60
300
70
55
min-I)
60 55 55 55 55 45 65 55 55 55 55 55
>
(N· km)-IJ
Substrate (carbon steel)
Hardfaced (stainless steel) surface
4.45 6.25 6.74 8.68 8.36 10.36 11. 68 13.46 5. 54 9.42 5.82 10. 12 6.42 11. 05 8.75 8. 72 8.76 8.78 8.74 8. 71
2.45 4. 32 4. 86 6. 76 6. 42 8.46 9.75 11. 62 3.46 7.46 3. 72 8. 12 4.46 9.12 6.85 6.82 6.88 6.83 6.85 6.86
Issue 4
• 51 •
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel
The dry sliding wear test was conducted as per the ASTM G 190-06 guidelines using pin-on-roller wear testing machine (Make: CAMERON PLINT. UK. Model: GOI-I0/DK 64-163 L). Here. the specimens were used as pins (12 mm in diameter and 12 mm in height). and different levels of hardened rollers (60 mm in diameter and 15 mm in width)
were used as rollers. The specimen dimensions and roller dimensions are shown in Fig. 1. As prescribed by the design matrix. twenty experiments were conducted and the wear rate was measured using mass loss concept. All the specimens were tested for 1 km distance of travel and the measured values of wear rate are presented in Table 2.
(b)
eso
Unit: mm Fig. 1
2
Dimensions of specimen (pin) (a) and rollers (b)
Developing Mathematical Models
The response function representing dry sliding wear rate (DSW) is a function of rotational speed of roller (N). applied load (P) and roller hardness (H) and it can be expressed as DSW= !(N.P.H) (2) The second order polynomial (regression) equation used to represent the response surface 'Y' Y = b., + b, (N) + b z (P) + b 3 ( H) + b ll (N Z ) +
O. 2ICp· H)} (5) The adequacy of the developed models was tested using the analysis of variance technique (ANOVA). As per this technique. if the calculated value of the F"t;o of the developed model is less than the standard F,a"o (from F-table) value at a desired level of confidence (say 95 %). the model is said to be adequate within the confidence limit. ANOVA test results are presented in Table 3 for both the models. From the table.
bZZ(P2)+b:J3(HZ)+blz(N· P)+ b I 3 ( N · H)+b z3 ( P ' H)
Table 3 (3)
where. b., is the average of responses. and b l • bz • •••• b 33 are the coefficients that depend on the respective main and interaction effects of the parameters. The values of the coefficients were calculated using SPSS statistical software. All the coefficients were tested for their significance at 90 % confidence level by applying Student's t-test using SPSS statistical software package. After determining the significant coefficients. the final models were developed and they are given below: For substrate (carbon steeD: DSW s ={8. 72+1. 03(N)+1. 35(P)+1. 87(H) O. 3(N Z) -0. 2(P Z ) +0. 15( HZ) + O. 2ICP • H)} (4) For hard faced surface (stainless steel ) , DSW H ={6. 82+1. 06(N)+1. 37(P)+1. 88(H)0.32(N Z ) - 0 . 15(P Z)+0. 15(H 2)+
Terms First order terms Sum of squares Degrees of freedom Mean square Second order terms Sum of squares Degrees of freedom Mean square Error terms Sum of squares Degrees of freedom Mean square Lack of fit Sum of squares Degrees of freedom Mean square F,,,,o(calculated) F,,,'o(5. 5. O. 05) R"t;o (calculated) R,at;o(9. 5. O. 05) Whether the model is adequate?
ANOV A tested results Substrate (carbon steel)
Hardfaced surface (stainless steel)
86.881 3 28.96
89. 275 3 29.758
2. 175 6 O. 363
2. 537 6 0.423
4. 298 5 O. 859
4. 782 5 O. 956
0.003 5 O. 000 7 O. 000 8 5.05 11.51 4.77
O. 002 3 5 O. 000 5 O. 000 5 5.05 10.667 4.77
Yes
Yes
Journal of Iron and Steel Research, International
• 52 •
it is understood that both the developed mathematical models were found to be adequate at 95 % confidence level. The coefficient of determination 'r' was used to find how close the predicted and experiTable 4
Substrate (carbon steel)
Hardfaced surface (stainless steel)
3
Parameter
Experimental value
Estimated value
Variation/
N=400; P=60; HRC=50
6.25
5. 95
+4.80 -1. 65
6.05
6. 15
N=200; P=60; HRC=60
8.36
8.30
+0.72
N=100; P=60; HRC=50
3.25
3.45
-6.15
N=300; P=70; HRC=55
8.75
8. 45
+3.43
N=200; P=60; HRC=50
2.45
2. 65
-9.20
N=300; P=60; HRC=50
3.45
3. 75
-8.60
N=300; P=70; HRC=55
6.85
6.45
+5.84
N=400; P=80; HRC=60
10.25
10. 15
+0.98
N=500; P=90; HRC=65
14. 10
14.45
-2.48
3. 1
Effect of roller rotational speed on wear rate Fig. 2 reveals the effect of rotational speed of roller on dry sliding wear behaviour of substrate (carbon steel ) and hardfaced (stainless steel ) surface. From Fig. 2, the following inferences can be obtained: dry sliding wear rate has a directly propor-
Carbon steel
0
L - _ " ' - -........_~_.....J
~
~
8
8
4
4Lo.--~_........._~---'-'
100 200 300 400 500 100 200 300 400 500 NI(r.min- l ) P=60 N, H=50; (c) P=80 N. H=60;
Fig. 2
(c)
~12~ ~
12
(a)
Carbon steel
j
~ 16 (c) ~ 00 o
0.91
12 (a) 8
.~:.;
j:
0.94
tional relationship with rotational speed irrespective of the applied load and roller hardness, i. e. , if the rotational speed increases, the wear rate increases, and vice versa. Dry sliding wear rate is rapid in the rotational speed of 100 to 400 rlmin, but beyond 400 rlmin, the wear rate attains a steady state. Here, the roller acts as a rotating body and the hardfaced surface (specimen) acts as a stationary body. The roller slides over the specimen (pin) surface under the action of the applied load, which leads to the generation of a frictional force between the roller and the specimen. The magnitude of the frictional force depends mainly on the rotational speed. Frictional force has a directly proportional relationship with rotational speed, i. e. , if the rotational speed increases, the frictional force at the mating
(b)
8
%
N=300; P=60; HRC=50
Using the above-developed mathematical models, the dry sliding wear rate was estimated for different combinations of rotational speed, applied load and roller hardness. The estimated values of dry sliding wear rate for substrate (carbon steel ) . and hardfaced (stainless steel) surface are presented In graphical form as shown in Fig. 2 to Fig. 4.
z
mental values lie. The values of 'r 2 ' for the abovedeveloped models are presented in Table 4, which indicates that a high correlation exists between experimental values and predicted values.
Comparison between experimental wear rate and estimated one
Results and Discussion
12 (a)
Vol. 16
(b) P=70 N. H=55; (d) P=90 N, H=65
Effect of rotational speed of roller on wear rate
Stainless steel ,,-_~_,,--_~-....J
50
60
70
80
(a) N=200 r' min-I. H=50; (c) N=400 r' min-I. H=60;
Fig. 3
90 50 PIN
60
70
80
90
(b) N=300 r' min-I. H=55; (d) N=500 r' min-I, H=65
Effect of applied load on wear rate
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel
Issue 4
12 (a)
:~ :&o~
iz
16 (c)
~ 12
rJ:J
Cl
8 4
(d)
~
~ Stainless steel L..-~_~_~........J
45
50
(a) N=200 r > min-I. (b) N=300 r ' min-I. (c) N=400 r > min-I, (d) N=300 r > min-I.
Fig. 4
55
60
65
P=60 N; P=70 N; P=80 N; P=70 N
Effect of roller hardness on wear rate
surface will increase. At higher rotational speed, the velocity of periphery of the rotating roller is higher, so the frictional force generated subsequently between the roller and the specimen is higher. Moreover, at higher speed, the number of times that the specimen comes under the rotation of the roller is greater at specified time intervals. These may be the reasons for high wear rates at higher rotational speed.
3. 2
Effect of applied load on wear rate
Fig. 3 shows the effect of applied load on dry sliding wear behaviour of substrate (carbon steel) and hardfaced (stainless steel) surface. From Fig. 3, the following inferences can be obtained: dry sliding wear rate has a directly proportional relationship with applied load, irrespective of rotational speed, and roller hardness, i. e. , if the applied load increases, the wear rate increases, and vice versa. Wear characteristics of substrate (carbon steel) and hardfaced (stainless steel ) surface can be divided into two stages: (a) under the action of 50 to 80 N applied load, the change of wear rate is very rapid; (b) beyond the applied load of 80 N, the wear rate seems to be approaching a steady state. Under low load condition, there is only a scratching action, i. e. , a small-sized roller region is in elastic contact with the test specimen and thus supports the applied load without contributing to material removal. Thus, the wear rate is less as compared to high load condition. Again at higher loads and longer sliding distances, due to continuous and simultaneous ac-
• 53 •
tion , material removal occurs in micro ploughing. This mechanism is referred to as an important mechanism of material removal in wear of materials. For both substrate (carbon steel) and hardfaced (stainless steel) surface, wear rate increases linearly when applied load up to 80 N, but beyond 80 N the wear rate attains a steady state. The common feature of all specimens is that the mass loss increases with the increase of wear distance. However, a rapid increase in mass loss during the initial wear period was observed in all specimens. Increase of wear resistance after the initial wear period is thought to be the result of work hardening. Work hardening during cold deformation leads to an increase in hardness, and this in turn results in the increase of wear resistance'Y'
3. 3
Effect of roller hardness on wear rate
Fig. 4 shows the effect of roller (counter face) hardness on dry sliding wear behaviour of substrate (carbon steel) and hardfaced (stainless steel) surface. From Fig. 4, the following inferences can be obtained: dry sliding wear rate has a directly proportional relationship with roller hardness irrespective of rotational speed and applied load, i. e. , if the roller hardness is higher, the wear rate is also higher, and vice versa. Dry sliding wear characteristics of substrate (carbon steel) and hardfaced (stainless steel) surface can be divided into three stages based on the slope of the curve: (a) in the roller hardness region of HRC 45 to 50, the wear rate is low as it is evident from the small slope of the curve; (b) in the roller hardness region of HRC 50 to 60, the wear rate is rapid as it is shown by the very steep slope of the curve; (c) beyond the roller hardness level of HRC 60, wear rate marginally decreases compared to the previous region. It is well known that the initial contact between two mating surfaces is only point contact, and there is no area contact. This is because that it is very difficult to produce an optical flat surface using any of the machining processes, and hence all the surfaces invariably contain peaks and valleys (undulations). For this reason, the mating surfaces will initially establish contact only at a few points (peak to peak contact). The contact regions will undergo localized plastic deformation when there is an applied load and a possibility of solid state bonding between mating surfaces. Under the action of sliding speeds, the bonds will be ruptured, and based on the hardness of the mating surfaces, the material will be removed gradually. The
• 54 •
Journal of Iron and Steel Research. International
material loss will mainly depend on the hardness of the mating surfaces. Usually. from the lower hardness surface. the material loss will be more compared to higher hardness surface. The substrate (carbon steel) and the hardfaced (stainless steel) surface show similar wear characteristics. In the lower roller hardness region (region I). the material loss is low. and this may be due to the minimum difference in hardness between the roller and the surface. In the higher roller hardness region (region II). the material loss is marginally lower compared to the previous region (region I) and this may be due to work hardening effect.
4
nsored R&D project No. 2003/20/36/1-BRNS. References : [lJ
[2J [3J
[4J
Conclusions
( 1) Mathematical models were developed to estimate the dry sliding wear behaviour of carbon steel and stainless steel surface including the main and interaction effects of rotational speed. applied load and roller hardness. (2) The influence of rotational speed. applied load and roller hardness on dry sliding wear characteristics of PTA hardfaced stainless steel surface were analysed in detail. It was found that the roller hardness had a predominant effect on the wear rate compared to the rotational speed and the applied load. ( 3) The wear resistance of stainless steel hardfaced surface was one and half times higher than that of the carbon steel substrate.
[5J [6J
[7J
[8J [9J
Do]
[llJ
The authors wish to express their SIncere thanks to the Board of Research in Nuclear Sciences (BRNS). Department of Atomic Energy (DAE). Government of India. Mumbai for granting financial support to carry out this investigation through the spo-
Vol. 16
[12J
Ocken H. The Galling Wear Resistance of New Iron Base Hardfacing Alloys: A Comparison With Established Cobalt and Nickel Base Alloys [JJ. Surface Coatings and Technology. 1995. 76-77: 456. Deisburg L. Source Book of Wear Control Technology [MJ. New York: ASME. 1978. Tadeusz Hejwowski, Sliding Wear Resistance of Fe-, Ni- and Co-Based Alloys for Plasma Deposition [JJ. Vacuum. 2006. 80: 1326. http://www.springerlink.com/content/ju406034hk6t6833/. V Balasubramanian , R Varaharnoorthy , C S Ramachandran. et al. Selection of Welding Process for Hardfacing on Carbon Steels Based on Quantitative and Qualitative Factors [JJ. International Journal of Advanced Manufacturing Technolology , Published Online: February 14. 2008. DOl: 10.1007 /s00170008-1406-8. Gourd L M. Principles of Welding Technology [MJ. New Delhi: Viva Books PVT Ltd. 1998. Bourithis L. Papadimitriou G D. Synthesizing a Class "M" High Speed Steel on the Surface of a Plain Steel Using the Plasma Transferred Arc (PTA) Alloying Technique: Microstructure and Wear Properties [JJ. Materials Science and Engineering. 2003. 361 A: 165. Kumar S. Balasubramanian V. Developing a Mathematical Model to Evaluate Wear Rate of AA7075/SiC p Powder Metallurgy Composites [J]. Wear. 2008. 26401-12): 1026. Box G E P. Hunter W H. Hunter J S. Statistics for Experiments [MJ. New York: John Wiley and Sons. 1978. Montgomery DC. Design and Analysis of Experiments [MJ. New York: John Wiley and Sons. 1991. Miller I. Freund J E. Johnson. Probability and Statistics for Engineers [M]. New Delhi: Prentice of Hall of India PVT Ltd. 1999. Johnson. Leona F C. Statistics and Experimental Design in Engineering and Physical Sciences [M]. New York: John Wiley and Sons. 1964. Behcet Gulenc , Nizamettin Kahraman. Wear Behaviour of Bulldozer Rollers Welded Using a Submerged Arc Welding Process [J]. Journal for Materials and Design. 2003. 24: 537.
-"
.:;, ScienceDirect JOURNAL
OF IRON
AND STEEL RESEARCH, INTERNATIONAL. 2009, 16(4): 49-54
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel C S Ramachandran,
V Balasubramanian ,
R Varahamoorthy
[Centre for Materials joining and Research (CEMAjOR), Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar 608002, India] Abstract: The effects of different experimental conditions on the dry sliding wear behavior of stainless steel surface produced by plasma transferred arc (PTA) hardfacing process were studied. The wear test was conducted in a pinon- roller wear testing machine, at constant sliding distance of 1 km, Mathematical models were developed to estimate -wear rate incorporating with rotational speed, applied load and roller hardness using statistical tools such as design of experiments, regression analysis and analysis of variance. It is found that the wear resistance of the PTA hardfaced stainless steel surface is better than that of the carbon steel substrate. Key words: dry sliding wear; plasma transferred arc hardfacing; carbon steel; stainless steel; variance analysis; experimental design
Dry sliding wear can be seen in gears, cams, bearings, clutches, brakes and other applications involving sliding contact or rolling contact-". The contact surfaces are rough and possess hills and valleys, so the applied normal stress is very high in the contact regions and may exceed the yield point of the solids. This could result in localized yielding of the material, improved bearing area and more interaction, and localized weld formation. The welds could be disturbed during the sliding process, resulting in loss of materialsl". For similar metals, the junction formed between asperities was stronger than that of parent metals because of work hardening during the sliding process. Material was lost through removal of lumps from the mating faces. For dissimilar metals, when the welded asperity junction was shared, part of the weaker metal was 10st[3J. Hardfacing is primarily done to enhance the surface properties of the base metal, and hardfaced materials generally exhibit better wear, corrosion and oxidation resistance than the base metal[4 J. Conventional weld hardfacing is done by oxyfuel welding, gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), shielded metal arc welding (SMAW), flux cored arc welding (FCAW), and Blography:C S Ramachandranr 1983-). Male. Doctor. Research Scholar;
submerged arc welding (SAW). Plasma transferred arc (PTA) hardfacing and laser beam hardfacing are relative newcomers to this arena. At present, many of the fabrication industries are adopting submerged arc surfacing using wire electrodes. With conventional submerged arc surfacing, percentage dilution levels are higher. To attain low dilution, the surfacing technique used should enable spreading the arc energy uniformly over the area to be surfaced'r". Eventhough PTA hard facing technique offers many advantages over other processes, the published information on dry sliding wear behavior of PTA hardfaced surface is very limited. Hence, the present investigation was carried out to study the dry sliding wear behaviour of PTA hardfaced stainless steel surface, and the results are reported in this paper.
1
Experimental
From Ref. [6J and Ref. [7J, the predominant factors, which have greater influence on dry sliding wear behaviour, were identified. They are: (1) rotational speed of the roller, (2) applied load, and (3) roller hardness. Trial experiments were conducted to determine the working range of the above factors. During the trial experiments, the following E-mail: [email protected];
Revised Date: October 26. 2008
• 50 •
Journal of Iron and Steel Research, International
observations were made: (1) if the rotational speed was greater than 500 r /rnin , the wear test machine produced a lot of noise and vibration under the ac. tion of lower loads. If the rotational speed was lower than 100 r/min , the wear test machine was not able to rotate under the action of higher loads. ( 2) The minimum load that can be applied to the specimen was 50 N (a limitation of the test setup). If the applied load was greater than 90 N. the machine could experience overload effect and not run smoothly at higher speeds. (3) Rollers of different hardness were fabricated using PTA hardfacing. By considering all conditions mentioned above. the feasible limits of the parameters were chosen in such a way that the dry sliding wear test could be conducted without any difficulty. The important factors that will influence the dry sliding wear behaviour and their working range Table 1
Vol. 16
are presented in Table 1. Due to a wide range of factors. it was decided to use three factors. five levels central composite design matrix to optimise the experimental conditions. Table 2 shows the set of 20 coded conditions used to form the design matrix. The method of designing such a matrix was dealt with elsewhere[B-lO]. For the convenience of recording and processing experimental data. the upper and the lower levels of the factors were coded as 1. 682 and -1. 682. respectively. The coded values of the intermediate values can be calculated using the following relationship'P", Xi = [1. 682X - (X max X min ) J/[ (X max X min ) / 1. 682J (1) where. Xi is the required coded value of a variable X; X is any value of the variable from X min to X max ; X min is the lowest level of the variable; X max is the highest level of the variable.
+
+
Important parameters and their working range Level
Notations
Unit
Rotational speed
N
r/min
Applied load
P
N
Roller hardness (HRC)
H
Factors
Experimental No.
>
-1
2 3 4 5 6 7 8 9
1 -1
10 11
12 13 14 15 16 17 18 19 20
1 -1 1 -1 1 -1. 682 1. 682 0 0 0 0 0 0 0 0 0 0
Highest
-1.0
0
+1.0
+ 1. 682
200 60 50
300 70 55
400 80 60
500 90 65
-1. 682 100 50 45
Experimental design matrix and measured wear rates
Coded val ues
Original values
min-I)
1
High
Low
Table 2 N/ (r
Middle
Lowest
PIN
H
-1 -1
-1 -1 -1 -1 1 1 1 1 0 0 0 0 -1. 682 1. 682 0 0 0 0 0 0
1 1 -1 -1 1 1 0 0 -1. 682 1. 682 0 0 0 0 0 0 0 0
N/ (r
>
Wear rate/j mg
PIN
H
200 400 200 400 200 400 200 400 100 500 300 300 300 300 300 300 300 300 300
60 60 80 80 60 60 80 80 70 70 50 90 70 70 70 70 70 70 70
50 50 50 50 60 60 60
300
70
55
min-I)
60 55 55 55 55 45 65 55 55 55 55 55
>
(N· km)-IJ
Substrate (carbon steel)
Hardfaced (stainless steel) surface
4.45 6.25 6.74 8.68 8.36 10.36 11. 68 13.46 5. 54 9.42 5.82 10. 12 6.42 11. 05 8.75 8. 72 8.76 8.78 8.74 8. 71
2.45 4. 32 4. 86 6. 76 6. 42 8.46 9.75 11. 62 3.46 7.46 3. 72 8. 12 4.46 9.12 6.85 6.82 6.88 6.83 6.85 6.86
Issue 4
• 51 •
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel
The dry sliding wear test was conducted as per the ASTM G 190-06 guidelines using pin-on-roller wear testing machine (Make: CAMERON PLINT. UK. Model: GOI-I0/DK 64-163 L). Here. the specimens were used as pins (12 mm in diameter and 12 mm in height). and different levels of hardened rollers (60 mm in diameter and 15 mm in width)
were used as rollers. The specimen dimensions and roller dimensions are shown in Fig. 1. As prescribed by the design matrix. twenty experiments were conducted and the wear rate was measured using mass loss concept. All the specimens were tested for 1 km distance of travel and the measured values of wear rate are presented in Table 2.
(b)
eso
Unit: mm Fig. 1
2
Dimensions of specimen (pin) (a) and rollers (b)
Developing Mathematical Models
The response function representing dry sliding wear rate (DSW) is a function of rotational speed of roller (N). applied load (P) and roller hardness (H) and it can be expressed as DSW= !(N.P.H) (2) The second order polynomial (regression) equation used to represent the response surface 'Y' Y = b., + b, (N) + b z (P) + b 3 ( H) + b ll (N Z ) +
O. 2ICp· H)} (5) The adequacy of the developed models was tested using the analysis of variance technique (ANOVA). As per this technique. if the calculated value of the F"t;o of the developed model is less than the standard F,a"o (from F-table) value at a desired level of confidence (say 95 %). the model is said to be adequate within the confidence limit. ANOVA test results are presented in Table 3 for both the models. From the table.
bZZ(P2)+b:J3(HZ)+blz(N· P)+ b I 3 ( N · H)+b z3 ( P ' H)
Table 3 (3)
where. b., is the average of responses. and b l • bz • •••• b 33 are the coefficients that depend on the respective main and interaction effects of the parameters. The values of the coefficients were calculated using SPSS statistical software. All the coefficients were tested for their significance at 90 % confidence level by applying Student's t-test using SPSS statistical software package. After determining the significant coefficients. the final models were developed and they are given below: For substrate (carbon steeD: DSW s ={8. 72+1. 03(N)+1. 35(P)+1. 87(H) O. 3(N Z) -0. 2(P Z ) +0. 15( HZ) + O. 2ICP • H)} (4) For hard faced surface (stainless steel ) , DSW H ={6. 82+1. 06(N)+1. 37(P)+1. 88(H)0.32(N Z ) - 0 . 15(P Z)+0. 15(H 2)+
Terms First order terms Sum of squares Degrees of freedom Mean square Second order terms Sum of squares Degrees of freedom Mean square Error terms Sum of squares Degrees of freedom Mean square Lack of fit Sum of squares Degrees of freedom Mean square F,,,,o(calculated) F,,,'o(5. 5. O. 05) R"t;o (calculated) R,at;o(9. 5. O. 05) Whether the model is adequate?
ANOV A tested results Substrate (carbon steel)
Hardfaced surface (stainless steel)
86.881 3 28.96
89. 275 3 29.758
2. 175 6 O. 363
2. 537 6 0.423
4. 298 5 O. 859
4. 782 5 O. 956
0.003 5 O. 000 7 O. 000 8 5.05 11.51 4.77
O. 002 3 5 O. 000 5 O. 000 5 5.05 10.667 4.77
Yes
Yes
Journal of Iron and Steel Research, International
• 52 •
it is understood that both the developed mathematical models were found to be adequate at 95 % confidence level. The coefficient of determination 'r' was used to find how close the predicted and experiTable 4
Substrate (carbon steel)
Hardfaced surface (stainless steel)
3
Parameter
Experimental value
Estimated value
Variation/
N=400; P=60; HRC=50
6.25
5. 95
+4.80 -1. 65
6.05
6. 15
N=200; P=60; HRC=60
8.36
8.30
+0.72
N=100; P=60; HRC=50
3.25
3.45
-6.15
N=300; P=70; HRC=55
8.75
8. 45
+3.43
N=200; P=60; HRC=50
2.45
2. 65
-9.20
N=300; P=60; HRC=50
3.45
3. 75
-8.60
N=300; P=70; HRC=55
6.85
6.45
+5.84
N=400; P=80; HRC=60
10.25
10. 15
+0.98
N=500; P=90; HRC=65
14. 10
14.45
-2.48
3. 1
Effect of roller rotational speed on wear rate Fig. 2 reveals the effect of rotational speed of roller on dry sliding wear behaviour of substrate (carbon steel ) and hardfaced (stainless steel ) surface. From Fig. 2, the following inferences can be obtained: dry sliding wear rate has a directly propor-
Carbon steel
0
L - _ " ' - -........_~_.....J
~
~
8
8
4
4Lo.--~_........._~---'-'
100 200 300 400 500 100 200 300 400 500 NI(r.min- l ) P=60 N, H=50; (c) P=80 N. H=60;
Fig. 2
(c)
~12~ ~
12
(a)
Carbon steel
j
~ 16 (c) ~ 00 o
0.91
12 (a) 8
.~:.;
j:
0.94
tional relationship with rotational speed irrespective of the applied load and roller hardness, i. e. , if the rotational speed increases, the wear rate increases, and vice versa. Dry sliding wear rate is rapid in the rotational speed of 100 to 400 rlmin, but beyond 400 rlmin, the wear rate attains a steady state. Here, the roller acts as a rotating body and the hardfaced surface (specimen) acts as a stationary body. The roller slides over the specimen (pin) surface under the action of the applied load, which leads to the generation of a frictional force between the roller and the specimen. The magnitude of the frictional force depends mainly on the rotational speed. Frictional force has a directly proportional relationship with rotational speed, i. e. , if the rotational speed increases, the frictional force at the mating
(b)
8
%
N=300; P=60; HRC=50
Using the above-developed mathematical models, the dry sliding wear rate was estimated for different combinations of rotational speed, applied load and roller hardness. The estimated values of dry sliding wear rate for substrate (carbon steel ) . and hardfaced (stainless steel) surface are presented In graphical form as shown in Fig. 2 to Fig. 4.
z
mental values lie. The values of 'r 2 ' for the abovedeveloped models are presented in Table 4, which indicates that a high correlation exists between experimental values and predicted values.
Comparison between experimental wear rate and estimated one
Results and Discussion
12 (a)
Vol. 16
(b) P=70 N. H=55; (d) P=90 N, H=65
Effect of rotational speed of roller on wear rate
Stainless steel ,,-_~_,,--_~-....J
50
60
70
80
(a) N=200 r' min-I. H=50; (c) N=400 r' min-I. H=60;
Fig. 3
90 50 PIN
60
70
80
90
(b) N=300 r' min-I. H=55; (d) N=500 r' min-I, H=65
Effect of applied load on wear rate
Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel
Issue 4
12 (a)
:~ :&o~
iz
16 (c)
~ 12
rJ:J
Cl
8 4
(d)
~
~ Stainless steel L..-~_~_~........J
45
50
(a) N=200 r > min-I. (b) N=300 r ' min-I. (c) N=400 r > min-I, (d) N=300 r > min-I.
Fig. 4
55
60
65
P=60 N; P=70 N; P=80 N; P=70 N
Effect of roller hardness on wear rate
surface will increase. At higher rotational speed, the velocity of periphery of the rotating roller is higher, so the frictional force generated subsequently between the roller and the specimen is higher. Moreover, at higher speed, the number of times that the specimen comes under the rotation of the roller is greater at specified time intervals. These may be the reasons for high wear rates at higher rotational speed.
3. 2
Effect of applied load on wear rate
Fig. 3 shows the effect of applied load on dry sliding wear behaviour of substrate (carbon steel) and hardfaced (stainless steel) surface. From Fig. 3, the following inferences can be obtained: dry sliding wear rate has a directly proportional relationship with applied load, irrespective of rotational speed, and roller hardness, i. e. , if the applied load increases, the wear rate increases, and vice versa. Wear characteristics of substrate (carbon steel) and hardfaced (stainless steel ) surface can be divided into two stages: (a) under the action of 50 to 80 N applied load, the change of wear rate is very rapid; (b) beyond the applied load of 80 N, the wear rate seems to be approaching a steady state. Under low load condition, there is only a scratching action, i. e. , a small-sized roller region is in elastic contact with the test specimen and thus supports the applied load without contributing to material removal. Thus, the wear rate is less as compared to high load condition. Again at higher loads and longer sliding distances, due to continuous and simultaneous ac-
• 53 •
tion , material removal occurs in micro ploughing. This mechanism is referred to as an important mechanism of material removal in wear of materials. For both substrate (carbon steel) and hardfaced (stainless steel) surface, wear rate increases linearly when applied load up to 80 N, but beyond 80 N the wear rate attains a steady state. The common feature of all specimens is that the mass loss increases with the increase of wear distance. However, a rapid increase in mass loss during the initial wear period was observed in all specimens. Increase of wear resistance after the initial wear period is thought to be the result of work hardening. Work hardening during cold deformation leads to an increase in hardness, and this in turn results in the increase of wear resistance'Y'
3. 3
Effect of roller hardness on wear rate
Fig. 4 shows the effect of roller (counter face) hardness on dry sliding wear behaviour of substrate (carbon steel) and hardfaced (stainless steel) surface. From Fig. 4, the following inferences can be obtained: dry sliding wear rate has a directly proportional relationship with roller hardness irrespective of rotational speed and applied load, i. e. , if the roller hardness is higher, the wear rate is also higher, and vice versa. Dry sliding wear characteristics of substrate (carbon steel) and hardfaced (stainless steel) surface can be divided into three stages based on the slope of the curve: (a) in the roller hardness region of HRC 45 to 50, the wear rate is low as it is evident from the small slope of the curve; (b) in the roller hardness region of HRC 50 to 60, the wear rate is rapid as it is shown by the very steep slope of the curve; (c) beyond the roller hardness level of HRC 60, wear rate marginally decreases compared to the previous region. It is well known that the initial contact between two mating surfaces is only point contact, and there is no area contact. This is because that it is very difficult to produce an optical flat surface using any of the machining processes, and hence all the surfaces invariably contain peaks and valleys (undulations). For this reason, the mating surfaces will initially establish contact only at a few points (peak to peak contact). The contact regions will undergo localized plastic deformation when there is an applied load and a possibility of solid state bonding between mating surfaces. Under the action of sliding speeds, the bonds will be ruptured, and based on the hardness of the mating surfaces, the material will be removed gradually. The
• 54 •
Journal of Iron and Steel Research. International
material loss will mainly depend on the hardness of the mating surfaces. Usually. from the lower hardness surface. the material loss will be more compared to higher hardness surface. The substrate (carbon steel) and the hardfaced (stainless steel) surface show similar wear characteristics. In the lower roller hardness region (region I). the material loss is low. and this may be due to the minimum difference in hardness between the roller and the surface. In the higher roller hardness region (region II). the material loss is marginally lower compared to the previous region (region I) and this may be due to work hardening effect.
4
nsored R&D project No. 2003/20/36/1-BRNS. References : [lJ
[2J [3J
[4J
Conclusions
( 1) Mathematical models were developed to estimate the dry sliding wear behaviour of carbon steel and stainless steel surface including the main and interaction effects of rotational speed. applied load and roller hardness. (2) The influence of rotational speed. applied load and roller hardness on dry sliding wear characteristics of PTA hardfaced stainless steel surface were analysed in detail. It was found that the roller hardness had a predominant effect on the wear rate compared to the rotational speed and the applied load. ( 3) The wear resistance of stainless steel hardfaced surface was one and half times higher than that of the carbon steel substrate.
[5J [6J
[7J
[8J [9J
Do]
[llJ
The authors wish to express their SIncere thanks to the Board of Research in Nuclear Sciences (BRNS). Department of Atomic Energy (DAE). Government of India. Mumbai for granting financial support to carry out this investigation through the spo-
Vol. 16
[12J
Ocken H. The Galling Wear Resistance of New Iron Base Hardfacing Alloys: A Comparison With Established Cobalt and Nickel Base Alloys [JJ. Surface Coatings and Technology. 1995. 76-77: 456. Deisburg L. Source Book of Wear Control Technology [MJ. New York: ASME. 1978. Tadeusz Hejwowski, Sliding Wear Resistance of Fe-, Ni- and Co-Based Alloys for Plasma Deposition [JJ. Vacuum. 2006. 80: 1326. http://www.springerlink.com/content/ju406034hk6t6833/. V Balasubramanian , R Varaharnoorthy , C S Ramachandran. et al. Selection of Welding Process for Hardfacing on Carbon Steels Based on Quantitative and Qualitative Factors [JJ. International Journal of Advanced Manufacturing Technolology , Published Online: February 14. 2008. DOl: 10.1007 /s00170008-1406-8. Gourd L M. Principles of Welding Technology [MJ. New Delhi: Viva Books PVT Ltd. 1998. Bourithis L. Papadimitriou G D. Synthesizing a Class "M" High Speed Steel on the Surface of a Plain Steel Using the Plasma Transferred Arc (PTA) Alloying Technique: Microstructure and Wear Properties [JJ. Materials Science and Engineering. 2003. 361 A: 165. Kumar S. Balasubramanian V. Developing a Mathematical Model to Evaluate Wear Rate of AA7075/SiC p Powder Metallurgy Composites [J]. Wear. 2008. 26401-12): 1026. Box G E P. Hunter W H. Hunter J S. Statistics for Experiments [MJ. New York: John Wiley and Sons. 1978. Montgomery DC. Design and Analysis of Experiments [MJ. New York: John Wiley and Sons. 1991. Miller I. Freund J E. Johnson. Probability and Statistics for Engineers [M]. New Delhi: Prentice of Hall of India PVT Ltd. 1999. Johnson. Leona F C. Statistics and Experimental Design in Engineering and Physical Sciences [M]. New York: John Wiley and Sons. 1964. Behcet Gulenc , Nizamettin Kahraman. Wear Behaviour of Bulldozer Rollers Welded Using a Submerged Arc Welding Process [J]. Journal for Materials and Design. 2003. 24: 537.