Effect of different carbides on the wear resistance of Fe-based hardfacing alloys

Effect of different carbides on the wear resistance of Fe-based hardfacing alloys

International Journal of Refractory Metals & Hard Materials 78 (2019) 288–295 Contents lists available at ScienceDirect International Journal of Ref...

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International Journal of Refractory Metals & Hard Materials 78 (2019) 288–295

Contents lists available at ScienceDirect

International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM

Effect of different carbides on the wear resistance of Fe-based hardfacing alloys

T

Sachin Pawara, , Aman Kumar Jhab, Goutam Mukhopadhyaya ⁎

a b

R&D and Scientific Services, Tata Steel, Jamshedpur 831001, India National Institute of Technology, Rourkela, India

ARTICLE INFO

ABSTRACT

Keywords: Hard facing Wear Microstructure Carbides SEM-EDS

Hardfacing plates are being used in raw material conveying system of an integrated steel plants to mitigate the wear of chutes and hoppers. Four Fe-based commercial hardfacing alloys were studied in this work. To prepare test samples, mild steel base plates was used. In hardfaced plates, mild steel backing provides the weldability, formability, and ductility whereas the hard weld deposit provides the required wear resistance. This investigation aims to correlate microstructural, tribological and hardness properties of hardfacing plate samples with varying chemical composition. Microstructural characterization involved the morphological study and elemental analysis of different types of carbides through EDS, hardness evaluation mainly involved measurement of bulk hardness and micro-hardness, whereas tribological studies involved pin-on-disc wear test. Higher hardness doesn't always mean higher wear resistance. Presence of alloying elements resists the material removal by abrasive action and increases the wear resistance.

1. Introduction 1.1. Losses due to wear A component is said to be failed when it does not perform its intended function. Failure of engineering components are mainly of four types fracture, corrosion, wear and deformation. Wear accounts for Σ55% of the total failures [1]. Abrasion accounts for Σ20% of wear failures [1]. This signifies the importance of studying for abrasive wear solutions. Wear can be defined as damage to a solid surface due to removal of material by the mechanical action of a contacting solid, liquid or gas [2]. Different machinery components in raw material handling processes of an integrated steel plant are subjected to different types of wear as shown in Fig. 1 [3]. These components include liner plates, jaws, chutes, hoppers etc. Severity of wear varies according to the properties of the material being handled and on the material, being used as wear plates. This plays an important role in the selection of solution for wear problems. Out of various protective measures, use of hardfaced components is very common (Fig. 2). 1.2. Hardfacing – process Hardfacing technique involves deposition of wear and/or corrosion ⁎

resistant material on the surface of a less wear and/or corrosion resistant material called as base metal. Hardfacing can be applied to restore the worn-out surfaces or to improve the wear resistance of a new component. Most common welding processes for deposition of hardfacing alloy are gas metal arc welding, submerged arc welding, oxyacetylene welding and shielded metal arc welding [4]. 1.3. Hardfacing- material The most cost effective hardfacing alloys are Fe-Cr-C or Fe-C-B. In addition to this for applications involving more severe environmental conditions, addition of Mo, Ti, W, V, Nb along with B and C is done. Addition of these elements increases wear resistance due to precipitation of abrasion resistant hard phases and optimized base matrix properties [6]. In this work such alloys containing strong carbide forming elements have been evaluated. Change in microstructure leads to change in mechanical properties of the material and consequent modification in wear properties [7–9]. Basis of decision making on the most effective wear solution involves in-situ tests, practical experiences and conceptual understanding of wear behaviour. This work aims to evaluate the wear properties of Fe-based hardfacing alloys containing different carbide forming elements under pure abrasion.

Corresponding author. E-mail address: [email protected] (S. Pawar).

https://doi.org/10.1016/j.ijrmhm.2018.10.014 Received 28 August 2018; Received in revised form 17 October 2018; Accepted 22 October 2018 Available online 23 October 2018 0263-4368/ © 2018 Published by Elsevier Ltd.

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Fig 1. Types of wear mechanism [5].

2. Experimental procedures 2.1. Materials

Layer 2

Four commercial hardfacing alloys deposited by arc welding method on mild steel plates were used for this study which had different chemical compositions as shown in Table 1. Selection of alloys was done from readily available components in the plant. Due to confidentiality of manufacturing process, details are not shared. To prepare test samples, plain carbon steel base plate was used. Images of these test samples are given in Fig. 3.

Layer 1 Base metal Fig. 2. Schematic of hardfacing layers. Table 1 Hardfacing deposits chemical composition.

2.2. Macro-etching

Chemical composition (wt%) Sample id

C

Cr

Mo

Ti

W

V

Nb

Fe

Alloy Alloy Alloy Alloy

1.87 1.03 3.32 2.88

6.34 6.07 15.76 17.39

0.90 2.63 5.00 3.26

7.03 2.65 0.03 0.05

0.03 – 1.16 1.75

– – – 1.61

– – – 3.01

Bal. Bal. Bal. Bal.

A B C D

To determine the soundness of hardfacing layers, macro-etching of cross sections of all four alloy were done with 50% HCl + 50% water. After macro-etching, cross section and surface of the samples were visually observed to identify presence of any weld defects or occurrence of cracks. Images of macro-etched cross sections are given in Fig. 3. Thickness of hardfacing layer and base metal was also measured.

Fig. 3. Macro etched cross section of test samples (a) Alloy A hardfacing (b) Alloy B hardfacing (c) Alloy C hardfacing and (d) Alloy D hardfacing.

Fig. 4. Cross section samples for microstructural analysis (a) alloy A (b) alloy B (c) alloy C (d) alloy D. 289

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Fig. 5. 10 mm × 10 mm cross section samples for rotary disc wear test (a) Alloy A (b) Alloy B (c) Alloy C (d) alloy D.

2.3. Hardness testing

Table 2 Pin-on-disc wear test parameters. Parameter

Load (N)

Velocity (rpm)

Wear track diameter (mm)

Test duration (min.)

Value

50

300

70

30

Vickers hardness tester (Make: EMCO TEST, Model: DuraScan) with 10 kg load was used to measure the bulk hardness of base metal and Rockwell hardness tester was used to measure the bulk hardfacing layer. of hardness. To study the hardness variation of cross section, Vickers microhardness machine with 100 g load was used. Hardness profile starting from hardfacing layer to interface to base metal was plotted.

Table 3 Measurement of thickness of different layers from top surface to bottom. Alloy A

Alloy B

Alloy C

Alloy D

Visual inspection

Two porous layers

Single layer

Single layer

Two layers

Total Weld Layer (mm) Base Metal(mm) Total(mm)

15–16

9–12

5–7

9–10.5

10–11 25–26

10–11.5 20–21

6–8 13–13.5

7.5–9 18–19

2.4. Microstructural study Cross section of all test samples was mounted in phenolic resin as shown in Fig. 4. To observe the microstructure, samples were polished by polishing machine (Make: MECAPOL, Model: P 320) and etched by freshly prepared aqua regia (HNO3: HCl:: 1: 3). Samples were cleaned with distilled water before conducting a microstructural survey. Optical (Make: LEICA, Model: DMRX) as well as scanning electron microscope (SEM) and wavelength dispersive spectroscopy(WDS) were used to study the microstructures and understand the distribution and morphologies of various types of carbide particles.

Table 4 Rockwell hardness measurement results. Sample

Weld (HRC)

Sample

Weld (HRC)

Alloy A Alloy B

Inner and outer layer: 45 57.5

Alloy C Alloy D

62 Inner layer: 53 Outer layer: 60.5

2.5. Pin-on-disc abrasion test A rotary disc tribometer (Make: DUCOM, Model: TR200) was used to

Fig. 6. Cross sectional micro-hardness profile of all four alloys from top(hardfaced) surface to base metal. 290

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Fig. 7. Microstructure of alloys from weld top surface to base metal (a) Alloy A - top (b) Alloy A - middle (c) Alloy A - interface (d) Alloy B- top (e) Alloy B- middle (f) Alloy B- interface (g) Alloy C - top (h) Alloy C– middle (i) Alloy C – interface (j) Alloy D –top (k) Alloy D – middle (l) Alloy D-Interface.

conduct 2-body sliding wear test as per ASTM G99. Samples of 10 mm × 10 mm cross section were prepared for the test. All samples were polished by 220 grit paper and ultrasonically cleaned before the test to get uniform surface finish as shown in Fig. 5. Counter body(disc) used in the test was of 42CrMo4 steel coated with Tungsten carbide coating (thickness Σ300 μm, Ra < 2.5 μm, hardness of 70–75 HRC). Test parameters were same for all samples and are shown in the Table 2.

propagated through hardfacing layer till the hardfacing-base metal interface. These cracks perpendicular to the cross section of hardfacing of all alloys as observed in Fig. 3 were believed to be present because of thermomechanical loads during and after solidification process of hardfacing deposit [10]. Cracks in hardfacing can limit its application in corrosive environment. It can allow the corrosive environment to reach to the hardfacing-base metal interface which can adversely affects the performance. Absence of cracks in base metal of all alloys were due to its lower hardness and better toughness. Hardfacing layer thickness in all four alloys were measured and reported in Table 3. Highest hardfacing layer thickness was found in alloy A and lowest was found in alloy C. Hardfacing layer thickness decides performance of the liner. Alloy A and D had two layers of hardfacing as compare to one in alloy B and C as shown in Fig. 4.

3. Result and discussion 3.1. Observations after macro-etching Porosity in alloy A is an indication of poor weld quality as shown in Fig. 3. All other alloys revealed few cracks which were thoroughly

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Table 6 EDS point analysis in alloy C. Chemical composition (Wt%) Point

Si

Ti

Cr

Mn

Fe

Nb

Mo

Tb

W

1 2 3 4 5 6 7 8

– 1.94 1.63 – 0.33 – – 1.74

– – – – 13.86 19.86 – –

11.12 7.56 8.37 32.79 2.52 7.22 32.66 7.74

1.79 0.98 1.58 1.27 – – 1.65 1.37

71.63 89.07 88.43 62.3 10.79 26.13 62.25 86.88

– – – – 68.61 38.13 – –

6.6 – – – – – – –

– – – – – – – 2.26

8.88 – – 3.24 3.89 8.66 3.43 –

Table 7 EDS point analysis in alloy D. Chemical composition (Wt%) Point

C

Si

Ti

V

Cr

Fe

Nb

Mo

W

1 2 3 4 5

23.2 9.78 2.88 10.4 10.5

– 0.84 1.63 0.72 –

1.22 – – – –

5.19 1.26 0.51 2.31 3.69

3.88 15.59 9.98 23.53 36.12

4.29 67.4 84.6 59.9 42.9

58.4 – – – –

– 1.9 – 1.6 3.6

3.84 1.62 – 1.6 2.65

wear rate with hardness, bulk hardness of all alloys was measured and reported in Table 4. Alloy A had lowest hardness because of presence of porosities. Hardness of alloy C was highest which could be because of highest ‘C’ content. This also explains the higher hardness of alloy D than that of alloy B. Hardness variation across the cross section of hardfacing layer was studied by conducting the micro hardness measurement. Hardness profile was plotted with distance from the top surface as shown in Fig. 6. There are two different regions of hardness. Higher hardness region indicates the hardfacing whereas lower corresponds to the base material. Trend of microhardness measurement result was in line with the bulk hardness measurement. Microhardness values of hardfacing deposition layer of all the alloys were in the range of 450–1050 HV1. Four verticles lines in the plot represent hardfacing-base metal interface of respective alloys. 3.3. Characterization of microstructure 3.3.1. Optical microscopic observations Amount, distribution and morphology of the carbides are important parameters which decides the wear properties of the hardfacing alloys. In case of alloy A, Ti and Cr containing hardfacing alloy was deposited on the base metal as confirmed by chemical composition analysis in 2.1. Microstructure revealed presence of large amount of porosity as shown in Fig. 7. Porosity is expected to give inferior wear resistance. When observed under high magnification, unifrom distribution of polygonal carbides was present. Higher quantity of martensite was present in the layers close to interface. This could be because of faster heat dissipation into the base metal and lower Cr in the deposition due to dilution [12]. Martensite with some amount of retained austenite was observed in middle and top beads which could be due to insufficient undercooling and dilution during weld deposition [13]. For Alloy B, Cr, Mo and Ti containing hardfacing alloy electrode was used. The microstructure of hardfacing deposit revealed uniform distribution of polygonal carbides within the martensitic matrix as shown in Fig. 7. When observed at higher magnification, partial networking of carbides and uniform distribution of polygonal carbides were observed. Same as Alloy A, higher amount of martensite was observed near weld layer-base metal interface. For Alloy C, Cr, Mo and W containing hardfacing alloy electrode

Fig. 8. EDS Point Analysis for (a)Alloy B, (b)Alloy C, and (c)Alloy D.

Table 5 EDS point analysis in alloy B. Chemical composition (Wt%) Point

C

Al

Ti

Cr

Mn

Fe

Ni

Mo

1 2 3 4

21.82 15.75 5.68 4.43

– 0.27 – 0.54

51.52 9.77 0.54 –

1.74 4.72 6.91 5.67

– – 0.52 –

8.13 63.91 82.13 86.99

– – 0.55 0.58

16.78 5.58 3.23 1.49

3.2. Study of hardness profile One of the important properties in deciding the wear rate of material is its hardness. Generally, wear occurs when hardness of base material is lower than that of abrasives [11]. To correlate the variation of 292

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Fig. 9. WDS compositional map of alloy B.

was used. Mo is generally used to improve abrasion resistance and fracture toughness [14]. The hot-hardness of the Mo and W containing alloys was generally found to be higher than that of the other alloys [14]. The microstructure of hardfacing deposit revealed presence of fine needles which could be because of considerably higher Cr content than that of alloy A and alloy B. The percentage of needles, polygonal and fine carbides was in the range of 5–10%, 10–15%, and 40–50% respectively as shown in Fig. 7. Microstructural analysis revealed randomly oriented and uniformly distributed needle shape primary carbides at weld surface (top) [15]. In Alloy D, Cr, Mo, W, Mo and V containing alloy electrode was used. In microstructural analysis, weld layer revealed well-distributed fine needle shape carbides as shown in Fig. 7. Percentage of needles was highest at the top surface and lowest near the interface. Same was the case with polygonal carbides. Mixture of needles and irregular shape carbides was observed under high magnification. Base metal microstructure revealed ferrite-pearlite. Microstructure also indicated austenite dendrites with inter-dendritic carbides. The presence of WC, VC, NbC and TiC have been reported to be more effective in increasing abrasive wear resistance than either raising the eutectic M7C3 content or increasing the width of the M7C3 eutectic carbide particles [16].

concluded that alloy A have significant porosity which will result in poor wear resistance. Considering this, further microstructural analysis of alloy A was not done. To find out the carbides distribution and composition of carbides, point analysis by Energy dispersive spectroscopy (EDS) technique and elemental mapping by wavelength dispersive spectroscopy (WDS) were done. From Fig. 8(a) and Table 5 prominent presence of primary TiC (point 1-blackish gray particles) in Alloy B can be confirmed. Presence Mo, along with Ti suggest formation of complex carbide. These particles had non-uniform shape and were separated from each other within the matrix [13]. EDS analysis of an Alloy C (Fig. 8(b) and Table 6) suggest the presence spheroidal Nb-Ti-W complex carbides. These carbides were present in groups. Alloy D (Fig. 8(c) and Table 7) revealed presence of polygonal Nb-V-W-Ti complex carbides and needle shape Cr-VW-Mo complex carbide. 3.3.3. WDS Analysis (Elemental mapping) Carbides are known to increase the wear properties of materials. Identifying the type of carbide is crucial in tailoring structure to properties. In Alloy B carbides of Ti and Mo were detected in the cubic/ granular form as shown in Fig. 9. No presence of Nb and V was observed. In alloy C (Fig. 10) confirmed the presence of large Cr carbides having plate/needle shape. Additionally, Nb, Mo and Ti carbides of

3.3.2. EDS point analysis From macrostructural and microstructural observation, it was

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Fig. 10. WDS compositional map of alloy C.

small sizes were also observed. It was clear from the mapping that the carbide volume fraction was > 70%. Presence of primary carbides provide more abrasive wear resistance. Fig. 11 revealed the presence of coarse Cr carbides. in alloy C. Second to the Cr, considerable amount of NbeTi complex carbides were also present. Addition of Mo2C and VC could improve the wetting between the matrix and carbides.

during testing. Also, all alloys had different slopes in work hardening region due to different extent of work hardening. This behavior is in line with the results reported in the literature. 4. Conclusions Different alloying elements can be introduced into the base metal in the form of weld consumables to achieve desired properties such as hardness, wear resistance etc. The detailed analysis and thus results led to the following inferences:

3.3.4. Pin-on-disc tribometer wear test results As evident from Fig. 12, wear resistance of an Alloy D was higher than that of other three alloys. Results of Alloy A can't be considered reliable for evaluation as it was too porous. Considering remaining three alloys, wear resistance of an alloy C was lowest though its bulk hardness was highest. This could be because of higher brittleness owing to high carbon content. Brittle material is prone to allow easy removal of material by chipping. Presence of carbide forming elements is one of the reasons for better wear resistance of alloy D. In addition to this, wide size variation and uniform distribution of carbides could be a contributing factor. One interesting observation from the plot is that wear rate of alloy A and alloy B increased drastically at start and then remained constant. Whereas, wear rate of alloy C and alloy D were increasing gradually till the end of the test. This indicates that presence of alloying elements resists the material removal by abrasive action and increases the wear resistance. For all 4 alloys, initial high wear followed by comparatively stabilized wear is because of work hardening of alloys

• Microstructures of hardfacing plates confirmed the presence of needle, polygonal and hexagonal shaped carbides in the matrix. • Wear resistance of an Alloy D was higher than that of other three • •

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alloys. Presence of carbide forming elements is one of the reasons for better wear resistance of alloy D. Highest hardness of alloy C did not give higher wear resistance. This could be because of higher carbon content leading to the brittleness which is expected to facilitate easy material removal by abrasive action. Wear rate of alloy A and alloy B increased drastically at start and then remained constant. Whereas, wear rate of alloy C and alloy D were increasing gradually till the end of the test. This indicates that presence of alloying elements resists the material removal by abrasive action and increases the wear resistance.

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Fig. 11. WDS compositional map of alloy D. [2] R. Tucker, Failure Analysis and Prevention, ASM International, 1986. [3] C. Okechukwu, O.A. Dahunsi, P.K. Oke, I.O. Oladele, M. Dauda, Review on hardfacing as method of improving the service life of critical components subjected to wear in service, Niger. J. Technol. 36 (4) (2017) 1095–1103. [4] M. Kirchgabner, E. Badisch, F. Franek, Behaviour of iron-based hardfacing alloys under abrasion and impact, Wear 265 (2008) 772–779. [5] K.H. Zum Gahr, Wear by hard particles, Tribol. Int. 31 (1998) 587–596. [6] M. Buchely, J. Gutierrez, L. Leon, A. Toro, The effect of microstructure on abrasive wear of hardfacing alloys, Wear 259 (2005) 52–61. [7] R. Colaco, R. Vilar, A model for the abrasive wear of metallic matrix particle-reinforced materials, Wear 254 (2003) 625–634. [8] K.V. Acker, D. Vanhoyweghen, R. Persoons, J. Vangrunderbeek, Influence of tungsten carbide particle size and distribution on the wear resistance of laser clad WC/Ni coatings, Wear 258 (2005) 194–202. [9] R. Colaco, R. Vilar, On the influence of retained austenite in the abrasive wear behaviour of a laser surface melted tool steel, Wear 258 (2005) 225–231. [10] M. Carvalho, Y. Wangb, J. Souza, E. Braga, L. Li, Characterization of phases and defects in chromium carbide overlays deposited by SAW process, Eng. Fail. Anal. 60 (2016) 374–382. [11] J. Gates, Wear plate and materials selection for sliding abrasion, Aust. J. Min. August (2003) 26–32. [12] J. Hornung, Z. A, K. Pichelbauer, M. Kalin, M. Kirchgabner, Influence of cooling speed on the microstructure and wear behaviour of hypereutectic Fe–Cr–C hardfacings, Mater. Sci. Eng. 576 (2013) 243–251. [13] X. Wang, F. Hanb, X. Liu, S. Qu, Z. Zou, Microstructure and wear properties of the Fe–Ti–V–Mo–C hardfacing Alloy, Wear 265 (2008) 583–589. [14] M.R. Khanzadeh GharahShiran, H. Bakhtiari, A. Dadvar, Investigation on microstructure and wear resistance of the plain carbon steel hardfaced by the Fe-Cr-C electrodes containing Mo, W, V elements, J. Environ. Friendly Mater. 1 (2017) 32–39. [15] M. I.S, Morphology and identification of carbides in aged W-alloyed austenitic stainless steel, Mater. Lett. 51 (2001) 375–384. [16] Weibin Qiu, Ying Liu, Jinwen Yea, Hanjie Fan, Yuchong Qiu, Effects of (Ti,Ta,Nb,W)(C,N) on the microstructure, mechanical properties and corrosion behaviors of WC-Co cemented carbides, Ceram. Int. 43 (2017) 2918–2926.

120 110 100

Wear (Micron)

90 80 Alloy A 70

Alloy B

60

Alloy C Better wear resistance

50

Alloy D

40 30 20 -100.1

399.9

899.9 Time(Sec)

1399.9

1899.9

Fig. 12. Abrasive wear of the hardfacing alloys.

References [1] A. Jeffrey, D. Hawk, R. Wilson, R.D. Daniel, M.T. Kiser, Abrasive wear failures, Failure Analysis and Prevention, ASM Handbook, vol. 11, 2002, p. 16.

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