OPTIMIZATION OF PROPERTIES AND STRUCTURE WITH ADDITION OF TITANIUM IN HADFIELD STEELS Mohammad Bagher Limooei (1), Shabnam Hosseini (1)

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1 Abstract OPTIMIZATION OF PROPERTIES AND STRUCTURE WITH ADDITION OF TITANIUM IN HADFIELD STEELS Mohammad Bagher Limooei (1), Shabnam Hosseini (1) 1- Islamic Azad University, Ayatollah Amoli Branch Manganese steel (Hadfield), is a non-magnetic alloy composed from Fe, carbon (1-1.4 %), and manganese (10-14%) which the carbon to manganese ratio equal 10 is high significance. These alloys have extensively application in industries due to good resistance to wear, high work hardening ability with high toughness and ductility. There is a limitation in production of Hadfield steel through casting parts under high tension, which is referring to its low thermal conductivity and coarse grain structure while solidification. Decreasing of grain size and structure modification have been performed on mentioned steel to improve its mechanical properties, wearing resistance, machining and welding properties, in recent decades. At this research, improvement of its properties and wearing resistance as an effect of alloy elements addition has been investigated. Addition of titanium to Hadfield Steel, making its grains as fine as possible and as well cause for increasing its wearing resistance up to 40 percent. Key word: Manganese steel (Hadfield), Titanium addition, Grain size, Wear resistance, Mechanical properties 1- INTRODUCTION Manganese steels are one of the most important engineering alloys due to their unique properties. High work hardening and proper toughness are within its particular properties which caused to place this steel in high tension conditions. Hardness of these alloys has a direct relativity to its wearing resistance, it means that, increasing in hardness, wearing resistance also enhance. Moreover, Hardness increasing through different mechanism in alloys mostly resulting in toughness or impact strength decrease [1]. It has showed that, there is a relation between Mn and C content in alloys and strength and toughness. Addition of alloy element such as Cr and Al will cause increasing in yielding strength while impact test value will be decreased [2]. Addition of Mo to Hadfield steels resulting austenite stabilizing and decrease critical cooling rate to obtain austenite structure [3]. Also, Molybdenum will cause change in carbide shape and transfer grain boundary continues carbides to unbounded spherical carbides. This ability use as basis for diffusion hardening in manganese steels. Increasing Mo up to 2%, resulted in yield strength, elongation and toughness enhancement in thicker sections [1]. Increasing of 1% Mo, increases impact strength within casting of thicker sections even up to twice [4]. Endeavors to utilizing major and micro alloy elements, has illustrated that, some elements such as B, V, Al, Ti cause to makes grain austenite finer by which heavy parts application will be improved. Vanadium will intensively produce carbide which is stable up to high temperature and will dissolve in 1100 C. Addition of 5.5% Vanadium to Hadfield steels has more influences on its yield strength and wearing resistance [5,6]. Also, Vanadium addition less than 0.2% concluded to increase Hadfield strength significantly [7]. In Hadfield steels resulting to aging hardening ability [8]. Titanium as well considered as a carbide generation element as TiC which add to Manganese steel in extent of micro alloy. The result of studies performed on Ti addition is partially inconsistent but in most cases, nucleation ability, reduce destroying effect of nitride impurities and phosphide low temperature melting phases [9,10]. Due to modification of solidification structure by titanium, it will protect the parts against brittleness or cracking during heat treatment [11]. 1

2 One of the major purposes of present research is effect of titanium on Hadfield steels properties. Titanium will cause to making fine grains and consequently improvement in wearing resistance of Hadfield steels. 2- METHODS AND MATERIALS According to fig. 2-1 molds are created through Sodium Silicate / CO2 procedure. To prevent burn on and obtain surface desire quality, proper coating material called Moldcoat 31 was used. Arc furnace was used to melting steel. Through steel melting continuously lime stone was charged in furnace to forming slag and increasing efficiency and decrease heating lost. Table 1-1 illustrates chemical composition of final samples which analyzed by Hilgor quantometer. 3 different chemical compositions were utilized that is showed in table 1-1. Alloy no.1 shows standard manganese steel chemical composition. Properties assessment of this alloy has been performed to compare with modified group by titanium. Titanium and Vanadium have been added to alloys no.2 and 3 within micro alloy limitations. Fig (2-1) Mold schematic Table (1-1) weight percent of chemical composition No. C Si Mn P S Cr Mo Ti V Standard Hadfield % Ti % Ti Slagging has been performed while melting temperature has been reached to 1500±10 and poured to preheated ladle which has aluminum layer at the bottom inside and then casting through transferring melted steel to mold has performed. Hadfield steel samples heat treated in electrical furnace. Heat treatment cycle is showed in fig

3 Fig. 2-2 Heat treatment cycle Metallographic examination has been done in accordance with ASTM E3-01(metallographic samples preparation), ASTM E (metal micro etch) and ASTM (optical microscopic images). Micro structures of specimens have been investigated by optical microscope (Olympus, PMG3 model). Tensile test has been done according to ASTM-E8 by a universal INSTRON machine in ambient temperature. Impact test has been done according to ASTM E by impact machine of 300J capacity and charpy method. To perform wearing examination, first was prepared a cubic specimen of each sample approximately 40 grams by weight. These specimens will be charged to a laboratory ball mill with diameter of 70 cm along with 20 kg steel balls and 5 kg silica sand. Examination took 150 hours and fresh sand has been substitute with crushed ones each 20 hours. At the end of examination, specimen weight reduction measured and wearing coefficient has been resulted through dividing secondary to primary weight. Hardness test has been done on all heat treated specimens by Brinel machine. 3- RESULTS & DISCUSSION Fig. 3-1 illustrates Hadfield steel microstructure. In this figure rough structure and coarse grain modification to fine grain (alloying by titanium) could be observed. Structural thinning in said steels could reduce significantly existing major defects such as hot tearing and segregation. Considering fig. 3-2 it would specify that grain sizes within steel sample no.3, have been more fined up to 50% than sample no.1. The micro structure of these steels was austenitic and there is no carbide precipitation in grain boundaries. In samples including titanium which aiming to micro structure thinning, carbide generation and grain sizes reduction have been occurred. Fig. 3-1 microstructure of heat treated specimens, Etched in 2% natal, 100 Fig.3-3 illustrates the tensile test results. As it could be observed titanium addition caused to enhance yield strength and a few change in tensile strength reduction of these steels. This phenomenon could be easily justified based on strengthening effect of these elements. In manganese steel, the cross section of fractured 3

4 sample is an exceptional case. Samples of these Steels represent high flexibility in tensile test and will be broken without indication of necking at the end. Fig.3-2 effect of Ti addition on grain size Fig.3-3 Ultimate and yield strength vs. Ti addition Fig.3-4 illustrates impact testing results. Addition of alloy elements such as Vanadium and Titanium will cause reduction in impact strength about 10% in relation to standard steels (no.1). Melting preparation and casting process have a significant influence on impact strength. Generally, impurities in melt from Arc furnaces are more obvious than induction furnaces, which resulting to impact strength reduction. Wearing test results performed on said steels illustrated in fig.3-5. One of most important purpose of Manganese steels structural modification is to enhance wearing resistance. Alloy and micro alloy elements existence, results to structural modification (Carbides presence, Increasing in grain sizes) and mechanical properties. Wearing coefficients in laboratory conditions show wearing resistance increasing in all modified structures rather than standard steels (no.1). Through titanium addition, high wearing properties would be observed in samples. 4

5 Fig.3-4 Impact Energy vs. Ti addition Fig.3-5 wearing coefficient vs. Ti addition Hardness test results have been shown in fig.3-6. Hardness testing after heat treatment represents treatment effect on structural modification and in same way hardness test after wearing test performing determines alloy ability in hard working. Generally, hardness reduces after heat treatment because carbides dissolving in heat treatment process, but it would increase after wearing test since hard working performed. As a conclusion, the samples which their hardness value are higher rather than prior to wearing test, represent low wearing coefficient. 5

6 Fig.3-6 Hardness vs. Ti addition REFERENCE: [1] D.K. Subramanya, A.E. Swansiger, H.S. Avery, Austenitic Manganese Steels, 10 th Edition, ASM Metals Handbook, Vol.1, [2] I.Elmahallawi, R.Abdolkarim, and A.Naguib, Evaluation of Effect of Chromium on Wear Performance of High Manganese Steel, Mater Science and Technol, 2001, Vol. 17, pp [3] N.Tsujimoto, Casting Practice of Abrasion Resistant Austenitic Manganese Steel, [4] H.L.Amson, F.Borik, J.Hoit, Optimizing the toughness and abrasion resistance of as-cast Austenitic 6Mn- 1Mo, 8 Mn-1Mo and 12 Mn-1Mo Steels, Nov [5] A.K. Srivastava, K.Das, Microstructural Characterization of Hadfield Austenitic Manganese Steel, Materials Sciences, 2008, Vol. 43, pp [6] D.K. Subramanyam, G.W. Grube, H.J. Chapin, Austenitic Manganese Steel Castings, 9 th Edition, ASM Metals Handbook, Vol. 9, 1985, pp [7] B.B.Vinokur, Cold Brittleness of Alloyed High Manganese Steel,1990. [8] M.S.Mikhaler, High-Mn Steel for casting Exposed in subzero conditions [9] M.Mohtarami,S.Javadpoor,et all, Effect of Ti And Al Addition on MnS Impurities in Steels,2005 Steel conference,yazd,iran,pp [10] A.A. Astafev, Effect of Grain Size on the Properties of Manganese Austenitic Steel 110G13L, Metal Science and Heat Treat, 1997, Vol. 39, pp [11] R.W. Smith, A.Demonte and W.B.F. Mackay, Development of High Manganese Steels for Heavy Duty Cast-to-Shape Applications, Materials Processing Technology, 2004, Vol , pp