Sintering of PM Tool Steels supported by Computational Thermodynamics

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1 Sintering of PM Tool Steels supported by Computational Thermodynamics S. Weber a,b, W. Theisen a a Ruhr-Universitaet Bochum, Werkstofftechnik D Bochum, Germany b Helmholtz-Zentrum Berlin fuer Materialien und Energie D Berlin, Germany 10. & , Aachen

2 Introduction Motivation Super solidus liquid phase sintering Thermo-Calc calculations - solidus temperature - influence of nitrogen - equilibrium compositions Dilatometry t Microstructure Outlook 10. & , Aachen Outline

3 steel powder Lehrstuhl Werkstofftechnik PM hard composite materials - Mixture of steel powders and hard particles - High hardness & toughness: WC/W 2 C - Compaction by hot isostatic pressing (HIP) WC/W 2 C hard particles => Materials with highest resistance against abrasive wear => Possibility of HIP-cladding => Application: Extruder coatings MMC after HIP Introduction 10. & , Aachen

4 PM cold work tool steel + 30% WC/W 2 C HIP: 1150 C, 4h, 100MPa Sintered: 1150 C, 4h, 0,1MPa Liquid phase necessary to obtain full density => Super solidus sintering (SLPS) Restriction: WC/W 2 C particles dissolve in steel matrix forming eta carbides (M 6 C) => Objectives: Investigation of fusion behaviour Reduction of sintering temperature to minimize dissolution 10. & , Aachen Motivation

5 spheroidization spheroidization of eutectic carbides during heating to sintering temperature melting occurs along the eutectic parts of the powder microstructure if T>T sol separation to smaller particulates and fast densification (within seconds) Designation carbide types optimal sintering temperature in vacuum reduction by N 2 X220CrVMo13-4 M 7 C 3, MC 1260 C 15 K X190CrVMo M 7 C C n.b. X240VCrMoCoW MC 1280 C 80 K X250CrNiMoV M 7 C C 20 K X340VMoCrNi MC 1260 C ~ 100 K 10. & , Aachen Powders

6 Designation Cr Mo V Mn Si Co W C Fe Carbides Steel A bal. MC, M 7 C 3 Steel B bal. MC Steel A T sol,calc. l =1213 C Steel B T sol,calc. l =1265 C Influence of nitrogen? In 10. & , Aachen Calculations

7 Steel A (high-cr) Steel B (high-v) pressure (MPa) pressure (MPa) Slightly increasing T sol for steel A with nitrogen partial pressure Strong decrease of T sol predicted for steel B => Sintering in nitrogen beneficial for steel B for reducing sintering temperature? 10. & , Aachen Calculations

8 dl / L 0 0,01 - dilatometry of green compacts 0,00-0,01-0,02-0,03-0,04-0,05-0,06-0, heating rate of 10K/min - argon or nitrogen as purge gases after evacuation to 5*10-1 Pa - evaluation of DIL curve by tangent method - shift from 1235 C To 1220 C (Δ=-20K) to lower temperature by N 2-0,08-0,09 Steel A (Ar) Steel A (N 2 ) -0, Temp. [ C] 10. & , Aachen Dilatometry: Steel A

9 0,01 - shift from 1230 C to 1150 C (Δ=-80K) to lower temperature by N 2 0,00-0,01-0,02-0,03 - Results of dilatometry verified by thermal analyses L 0 dl / -0,04-0,05-0,06-0,07-0,08-0, Steel B (Ar) Steel B (N 2 ) -0, Temperature in C 10. & , Aachen Dilatometry: Steel B

10 Steel B without N Steel B with N Stabilization of the M 7 C 3 carbide at T=T sol by nitrogen Carbon is exchanged by nitrogen: MC => M(N,C) Purity of M(N,C) regarding vanadium content is increased => verified by EDX Phase equilibria 10. & , Aachen

11 MC 7 3 M(C,N) Microstructure: Steel A 10. & , Aachen

12 MC 7 3 M(C,N) 10. & , Aachen Microstructure: Steel B

13 Sintering of corrosion resistant tool steels and MMCs Simulation of carburization and nitridation of the system Fe-Cr-Nb using Dictra Interdiffusion between TiC and cold work steels during liquid id phase sintering i Interdiffusion in tool steels coatings prepared by high volocity oxy fuel (HVOF) Precipitation kinetics in Fe-Cr-Mn-C-N steels (=> next talk) 10. & , Aachen Outlook

14 ThermoCalc S, TCFE 4 ThermoCalc S, TCFE 6 Steel A, Thermo-Calc version S, TCFe4 or TCFe6 database 10. & , Aachen Problems with TCFe6

15 T sol DIL = 1235 C sol,dil T sol,dta = 1229 C Consistent results using TCFe2,3,4 and 5 Strong deviations using TCFe6 in different alloy systems Where do these differences result from? 10. & , Aachen Problems with TCFe6

16 Thank you for your attention! 10. & , Aachen