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  1. 1. S.N.Chaudhari, Dr. G.J. Vikhe Patil / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1163-1166 An Investigation of Optimum Heat Treatment Strategy for M2 Tool Steel. S.N.Chaudhari1, Dr. G.J. Vikhe patil2 1 Amrutvahini College of Engineering, sangamner,Ahmednagar, Maharastra. 2 Amrutvahini College of Engineering, sangamner,Ahmednagar,Maharastra.Abstract M2 tool steel is categorised as carbon and alloying elements. The carbon andmolybendum tool steel. Due to high hardness and alloying elements from the carbides are dissolved inwear resistance it is well suited for drill bits, the matrix.milling cutters and hobs. The current work If the steel is quenched sufficiently rapid inreports and analyzes results of mechanical testing the hardening process, the carbon atoms do not haveperformed on various heat treated samples of M2 time to reposition themselves to allow the reformingtool steel (Twist Drill size 16mm dia.). It was of ferrite from austenite, i.e. as in annealing. Instead,found that maximum tool life obtained when M2 they are fixed in positions where they really do nottool steel hardened at 12000C and tempered at have enough room, and the result is high5600C temperature. microstresses that can be defined as increased hardness. This hard structure is called martensite.I. INTRODUCTION Thus, martensite can be seen as a forced solution of One of the higher-grade tool steels that can carbon in ferrite. When steel is hardened, the matrixbe used in various hot and cold-work manufacturing is not completely converted into martensite. Someprocesses is M2 tool steel. It has relatively high- austenite is always left and is called “retainedcarbon and high-chromium contents compared to austenite.”The amount increases with increasingother tool steels, and are therefore categorized as a alloying content, higher hardening temperature andMolybdenum based tool steel. It possesses high longer soaking times. After quenching, the steel hasstrength, and good wear resistance. It is therefore a microstructure consisting of martensite, retainedsuited for the manufacturing of some tools including austenite and carbides. This structure containsmilling cutters, drill bits and hobs. During these inherent stresses that can easily cause cracking. Butmanufacturing operations, various damage this can be prevented by reheating the steel to amechanisms act simultaneously to produce certain temperature, reducing the stresses andcumulative damage to the tool and because transforming the retained austenite to an extent thatincreasing deviations from the original tool depends upon the reheating temperature. Thisgeometry due to wear, micro-chipping, heat- reheating after hardening is called tempering.checking, or breaking of the tool or a part of the tool Hardening of a tool steel should always be followed.For better tool performance, material of the tool immediately by tempering. It should be noted thatmust be improved by changing its properties. The tempering at low temperatures only affects thetwo most relevant properties are toughness and martensite, while tempering at high temperature alsohardness; toughness prevents instantaneous fracture affects the retained austenite. In case of tool steelof the tool or tool edges, and hardness must be toughness and hardness can be inter-dependent, andsufficiently high to avoid local plastic deformation a good combination can be achieved by optimumso that tool geometry remains unchanged. heat treatment. In soft annealed tool steel, most of thealloying elements are bound up with carbon in II. EXPERIMENTAL WORKcarbides. In addition to these there are the alloying Samples of M2 tool steel were subjected toelements cobalt and nickel, which do not form different heat treatment sequences: annealing,pre-carbides but are instead dissolved in the matrix. heating,high heating hardening, salt bathWhen the steel is heated for hardening, the basic quenching, and three tempering at four differentidea is to dissolve the carbides to such a degree that temperatures: 5400C,5500C,5600C,5700C.Heatthe matrix acquires an alloying content that gives the treated specimens were mechanically tested forhardening effect without becoming coarse grained impact toughness, and hardness.and brittle. When the steel is heated to the hardening TABLE I CHEMICAL COMPOSITIONS OF M2temperature (austenitizing temperature), the carbides TOOL STEELare partially dissolved, and the matrix is also altered. Steel C Mn Si Cr W Mo VIt is transformed from ferrite to austenite. This Typemeans that the iron atoms change their position in M2 0.85 0.3 0.3 4.15 6.4 5.0 1.9the atomic lattice and make room for atoms of 1163 | P a g e
  2. 2. S.N.Chaudhari, Dr. G.J. Vikhe Patil / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1163-1166 Heat treatment was carried out in line with D.Quenchingthe standard procedure. Three sets of specimens In quenching process samples werewere prepared in this way: quenched in salt bath furnace at 5700C temperature(a) Hardening temperature 11800C and tempering for 5 minute. Then samples were reload from at 5400C,5500C,5600C and 5700C temperature. furnace and air cooled at room temperature. During(b) Hardening temperature 12000C and tempering at quenching carbon atom not get enough time to 5400 C,5500C,5600C and 5700C temperature. reposition and they fix in the position where they(c) Hardening temperature 12200C and tempering at really do not enough room. As a result of this high 5400C,5500C,5600C and 5700C temperature. microstresses developed i.e martensite which (All samples were three tempered for two hour) responsible for hardness due to quenching.TABLE II HEAT TREATMET SEQUENCE E.Tempering Quench-hardened samples are brittle and 1.Normalising 2.Annealing 3.Warmimg 4.High heating hardening stresses are present. In such a condition it is of little practical use and it has to be reheated, or 770-8200C 870-9000C 4000C 8500C tempered, to relieve the stresses and reduce the brittleness. 5.Austanising 6.Quenching 7.Tempering In this process, furnace is set to the desired tempering temperature. Samples were load inside the 1180-12200C 7600C 540-5600C furnace immediately after they reach room temperature after quenching for two hours. Then samples were removed from the furnace and allowA. Normalising them to cool to room temperature in still air. In In this process tool steel specimen is heated multiple tempering (Generally two or three)6500C for 24 hour and then cooled in air. As shank samples cool for at least two hour and again place inand flute part of twist drill is butt welded it become furnace at the same tempering temperature and airnecessary to relive the stresses due to welding. cool to room temperature. Tempering causes the transformation ofB.Annealing martensite into less brittle structures. Unfortunately, This is the softening process in which tool any increase in toughness is accompanied by somesteel specimen were heated to 8200C for eight hour decrease in hardness. Tempering always tends toand cooled at room temperature. transform the unstable martensite back into the stable pearlite of the equilibrium transformations. After tempering as quenched martensite precipitate to fine carbide. Nucleation of this carbide relieves microstresses in martensite matrix and prevent cracking. Tempering is done in following steps. 1. Hardening at 11800C and then tempering at four different temperatures 5400C, 5500C, and 5600C resp. 2. Hardening at 12000C and then tempering at four different temperatures 5400C, 5500C, 5600C and 5700C resp. 3. Hardening at 12200C and Temping at four different then temper temperatures 5400C, 5500CFig.1 Time versus temperature plot illustrating and 5600 C 5700 C resp.sequences required to properly heat treat high-speedtool steels IV. MECHANICAL TESTING Heat-treated samples (with different heatC.Austenitizing (Hardening) treatment sequences) were tested for various Before austenitizing, warming and mechanical properties. For hardness testing, oxidepreheating of tool steel specimen was carried at layers etc formed during heat treatment were8500C in salt bath furnace. The purpose of this removed by stage-wise grinding. Average VPNprocess is to reduce thermal shock, reduce danger of readings were determined by taking three hardnessexcessive distortion or cracking and to reduce time readings at different positions on the samples, usingrequired in high heat furnace. a vicker hardness tester. Impact energy (CVN) was Tool specimens were hardened at recorded using the Charpy impact tester. All testing11800C,12000C and 12200C for 5 minutes soaking was done in accordance with ASTM standard testtime. This soaking time is depend upon type of tool procedures.and size. In hardening process ferrite is convertedinto austenite. 1164 | P a g e
  3. 3. S.N.Chaudhari, Dr. G.J. Vikhe Patil / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1163-1166V. RESULTS AND DISCUSSION As described above, samples weresubjected to three types of heat treatment sequences.All mechanical testing was performed at roomtemperature. (a) Hardening temperature 18000C, (b)Hardening temperature 12000C and (c) Hardeningtemperature 12200C and all double tempered.Variation of mechanical properties of M2 tool steelafter these heat treatments is presented below in agraphic format. Fig 8. Variation of hardness against tempering temperature for different heat treatments at 12200C hardening temperature. Fig.8 shows as tempering temperature increases, hardness first increases and remains constant to a maximum at 12200Chardening temperature.Fig.6 Variation of hardness against temperingtemperature for different heat treatments at11800Chardnenig temperature. Fig.6 shows that as tempering temperatureincreases, hardness first increases to a maximum andthen gradually decreases. For all three heattreatments, maximum hardness is obtained forsamples tempered at 5500C at 18000C hardeningTemperature. Fig. 9 Variation of impact energy against tempering temperature for different heat treatments at 11800C hardening temperature Fig.9 presents the variation of impact strength against tempering temperature for heat treatment sequence at 11800C hardening temperature. With an increase in tempering temperature, impact strength decreases.Fig. 7 Variation of hardness against temperingtemperature for different heat treatments at 12000Chardening temperature.Fig.7 shows as tempering temperature increases,hardness first increases to a maximum and thengradually decreases at 12000C hardeningtemperature. Fig. 10 Variation of impact energy against tempering temperature for different heat treatments at 12000C hardening temperature. 1165 | P a g e
  4. 4. S.N.Chaudhari, Dr. G.J. Vikhe Patil / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 1, January -February 2013, pp.1163-1166 REFERENCESFig.10 presents the variation of impact energy [1] S.Z. Qamar Effect of heat treatment onagainst tempering temperature for heat treatment mechanical properties of H11 tool steelsequence at 12000C hardening temperature. With an Journal of Achievement in material andincrease in tempering temperature, impact energy manufacturing Engineering Vol 35 Pp 115-increases. Maximum impact energy occurs for 120, 2009.samples tempered at 5600C. [2] J. Kaszynski, R. Breitler, How the Steelmaking Process Influences theVII. TOOL LIFE Properties of Hot Work Die Steels, The tool life of hardened and tempered drill Technical Paper - Society of Manufacturingtool is calculated based on number of hole drilled. Engineers, Pp 1-12,2002. [4] ASM International, ASM HandbookTABLE III DRILL MATERIAL AND Volume 1: Properties and Selection -WORKPIECE MATERIAL DETAILS Nonferrous Alloys and Special PurposeDrill Tool Material M2 (Dia.16 mm) Materials, 10th edition, American SocietyWorkpiece Material EN8 (Hardened ) for Metals, Metals Park, Ohio,1990. [5] J.R. Davis ASM Specialty Handbook: ToolSr. No. Hardening Tempering No. of Materials, ASM International, Materials Temperature Temperature Hole Park, Ohio, 1995. (0C) (0C) Drilled [4] G.A. Roberts, G. Krauss, Kennedy, Tool befor Steels, 5th edition, American Society for failure Metals, Metals Park, Ohio, 1998.01 1180 540 5 [6] Material Science and metallurgy by V.K02 1180 550 6 kodgire & S.V. kodgire Everest Publishing House.03 1180 560 13 [7] Alam M. Bayer ,Bruce A, Becere R and05 1200 540 4 Teledyne vasco “High Speed Tool Steel” ASM Handbook, Volume16,1989 ,Pp 51-06 1200 550 12 59.07 1200 560 18 [8] A.Kokosza and J.Pacyna “Effect of retained08 1200 570 7 austenied on fracture impact energy of tool09 1220 540 7 steel’ studied about heat treatment on10 1220 550 8 70MnCrMoVn 2-42 tool steel. Journal of11 1220 560 13 Archive of materials Science and Engineering,, Vol 31,(2008) Pp,87-90.VIII. CONCLUSION1) Heat treatment result shows that secondaryhardness of M2 tool observed at 5500C.2) The experimental results show that maximum toollife is achieves when tool specimen hardened at12000C and tempered at 5600 C. This might due toless impact energy at 5500C tempering temperature.ACKNOWLEDGMENT I am very thankful to Indian Tool Companyfor allowing me to do project. I earnestly express mysincere thanks to my guide Prof. Dr.G.J.Vikhe Patil .for his valuable help and guidance also I expresssincere thanks, to Prof. A. K. Mishra, Prof.V.S. Aherand Prof.V.D. Wakchuare for their kind co-operation. . I highly obliged to entire staff ofMechanical Engineering and my friends for theirkind co-operation, help & encouragement me forpresent this paper in International Conference. 1166 | P a g e