UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

1068 IMMC 2018 | 19th International Metallurgy & Materials Congress

Investigation on the Eff ect of Titanium Addition on Structural Properties of Iron Boride Based Surface Alloyed Steel

Mustafa Durmaz¹, Bülent Kılınç², Eray Abakay¹, Uğur Şen¹, Şaduman Şen¹

¹Sakarya University, Faculty of Engineering, Department of Metallurgical and Materials Engineering, Esentepe Campus, TR-54187, Sakarya, Turkey

²Arifi ye Vocational School, Sakarya University, Turkey

Abstract

This study covers the structural properties of surface alloyed SAE 1320 steel with Fe3B2 and the effect of titanium addition on the properties. Ferrous-boron and ferrous-titanium powders and Armco iron were used as raw materials. Powders were mixed into the compositions of Fe12-xTixB8 (x=0 and x=3). Mixed powders were pressed on the steel substrate and melted by TIG welding technique for surface alloying. Structural properties of the surface alloyed layer formed on the steel substrate were investigated by means of optical and scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. X-ray diffraction analysis revealed that the surface alloyed

-Fe, FeB, Fe2B and TiB2 phases. Microstructural analysis showed that the alloyed layers have composite structure including steel matrix and homogenously distributed boride phases. Ti addition on the iron boride based surface alloyed layer lead to the formation of titanium boride phase. Micro-hardness values were determi -Fe

0.025, Fe2 0.01 and TiB2HV0.01.

1. Introduction

The harsh working conditions of cutting tools and machine parts make it necessary to increase the wear resistance of these materials. Hardfacing, a surface modification technique, involves deposition of a wear-resistant alloy on either a worn out or new component to improve its service life. In this process, an alloy is homogeneously deposited onto the surface of a soft material (usually plain carbon steels) by welding with the purpose of increasing hardness, wear resistance without significant loss in ductility and toughness of the base metal [1]. Hardfacing is a method that enables to obtain coatings against wear against the surface without altering the properties of the used substrate material. In this method, the powder mixtures of the desired alloy are melted on the surface of the substrate using various welding methods [2-3]. High energy sources such as submerged arc welding (SAW), electron beam, laser and plasma arc (PA)

can be used to obtain a hardfacing coatings. Tungsten inert gas (TIG) welding, one of the widely used welding methods for welding metals such as titanium, steel and aluminum, is mainly used for high quality welded parts [4-7].

The boron produced by transition metals is attracting attention with their high hardness, high abrasion resistance and high corrosion resistance. Titanium diboride (TiB2) is notable for its high hardness (25-35 GPa) and high melting

C). In addition, it has high elastic modulus (>570 GPa), low density (~4.52 g/cm3), low electrical conductivity (10-30 10-6 cm), and good thermal conductivity (60-120 W/mK) are also important features. Titanium diboride is added to iron matrix materials to provide high abrasion resistance [8-10].

In this study, the effect of titanium on the hardfacing alloy consisting of iron and boron was investigated. Mixed powders composed of Fe, Ti and B were melted at the surface of SAE 1320 steel and hard filling process was carried out. The microstructural and chemical analyzes of the obtained samples were carried out through cross-sectional views. The phases formed by X-ray diffraction analysis were determined. Hardness of the resulting phases was measured by micro hardness measurements.

2. Experimental Procedure

SAE 1320 steel with the dimensions of 50 mm x 100mm x10 mm were used as a substrate material. Nominal composition of the substrate material is 0.183 C, 1.37 Mn, 0.2 Si, 0.021 Cr, 0.0177 P, 0.0018 S, 0.062 Ni, 0.0056 Mo and Fe in balance (wt.%). Specimens were ground, cleaned, and then dried with compressed air before the surface alloying process. Commercial ferrous-titanium, ferrous-boron and Armco iron powders were used for the surface alloying treatment. Powders with the compositions of Fe12-xTixB8(x=0 and 3; at.%) were well mixed. Mixed powders were placed on the substrate material and pressed. Alloying powders were melted to form surface alloyed layer by TIG welding process. Table 1 shows the welding parameters,

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which are used for hardfacing by tungsten inert gas (TIG) method.

Table 1. Welding parameters of the Fe-based hardfacing alloys.

Parameter Value Electrode : Type W-2 pct ThO Electrode diameter : 2.4 mm Angle : 70 degrees Voltage : 20 V Current : 110 A Heat input : 2.2 MJ/m Shielding gas : Argon (99.9% Ar) Gas flow rate : 12 l/min Welding speed : 60 mm/min Heat input Q=60xIxV/S; I:current, V:voltage, and S: travel speed [11].

Metallographically prepared surface alloyed samples from cross-section were used to evaluate structural properties. Microstructural examinations were realized by using NICKON ECLIPSE L150 optical microscopy and JEOL 6060 LV scanning electron microscopy equipped with energy dispersive x-ray spectroscopy (EDS). X-ray diffraction analyses were performed on the surface of the samples by using RIGAKU XRD D/MAX/2200/PC X-ray diffractometer with a CuK radiation. Micro-hardness measurements were carried out on metalographically prepared cross-sections of the samples by using FUTURE TECH FM 700 micro-hardness tester.

3. Results and Discussion

Investigation on the microstructural analysis of the Fe12-

xTixB8 (x=0 and 3) based hard-faced alloy coating on SAE 1320 steel reveals that the thickness of the coating layer is about 2-3 mm. (Figure 1) Besides, it can be inferred that the layer compose of three distinct layers as the surface alloyed layer, transition zone and steel matrix.

X-ray diffraction analysis showed that Fe3B2 and Fe9Ti3B8

hard faced coating layers comprise of -Fe, FeB, Fe2B and -Fe, TiB2, Fe2B, FeB phases respectively (Figure 2).

(a) Fe12-xTixB8 (x=0)

(b) Fe12-xTixB8 (x=3) Figure 1. Optical micrographs of the iron boride based surface alloyed steel.

10 20 30 40 50 60 70 80 90

x=3

14

2222333432 12

4

12

Inte

nsity

(a.

u.)

2 (°)

x=0

1 - Fe2 - TiB

2

3 - Fe2B

4 - FeB

3

Figure 2. X-ray diffraction pattern of Fe12-xTixB8 surface alloying layer.

Figure 3 and 4 shows SEM micrographs and EDS analysis of the Fe9Ti3B8 based hard-faced alloys. Light gray matrix

UCTEA Chamber of Metallurgical & Materials Engineers’s Training Center Proceedings Book

1070 IMMC 2018 | 19th International Metallurgy & Materials Congress

phases include Fe element beside small Ti peaks, which indicate that the matrix Fe-Ti solute solutions, see Figure 4 (b1). Dark gray phase took place in the eutectic morphology includes Fe and B peaks which indicate that Fe2B phases as determined in the XRD analysis, see Figur 4 (b3, b4). Blaack phases took place in the microstructure well distributed includes strong Ti and B peaks as shown in Figure 4 (b2) which indicate that the phases are TiB2 which was confirmed by XRD analysis. However, it is possible to deviate from the initial stoichiometry of the hard-faces alloy powders due to the melting of substrate during TIG welding. With the further analysis on the EDS results and considering the phase diagram it can be inferred that black colored regions compose of TiB2 phase as the analysis shows Ti and B elements. Similarly, white colored and eutectic regions compose of Fe2B and - Fe+Fe2B phases respectively. . Ternary phase diagram of Fe-Ti-B reveals that the promising phases to be -Fe+Fe2B+TiB2 at room temperature [12].

Micro-hardness measurements were carried out under the loads of 10 gf and 25 gf for 10 sec. Distinct phases of each specimen sampled and the results given as HV. On the Fe9Ti3B8 -Fe, Fe2B and TiB2 0.025 0.01

0.01 respectively.

Figure 3. SEM micrograph of the Fe9Ti3B8 based surface alloyed layer.

(a)

(b) Figure 4. (a) SEM micrograph and (b) EDS analysis of the Fe9Ti3B8 based surface alloyed layer.

4. Conclusion

The surface alloying treatment was successfully realized by tungsten inert gas processing on the steel with Fe12-xTixB8alloy composition powders. The results as follows:

1. Surface alloying process was realized on SAE 1320 steel substrates by TIG welding, successfully.

2. The alloyed layer was porosity free and moderately smooth rippled surface topography.

3. The alloyed steel includes three different regions which are surface alloyed layer which includes Fe, B, Nb and V, separating line and steel matrix.

4. The surface a -Fe, TiB2 and Fe2B in the eutectic structure together with primer -

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Fe phase.

5. The hardness of the Fe, Fe2B and TiB2 phases are 0.025 0.01 0.01

respectively.

References

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