Diffusion in Fe-base Thick Coatings Produced by Hot Extrusion S. Weber, P. Silva Max-Planck-Institut für Eisenforschung GmbH Materials Diagnostics and Steel Technology Prof. Dr.-Ing. A.R. Pyzalla Düsseldorf (Germany)
Definition of Wear Resistant Composite Materials Hot Extrusion Resulting Microstructures Thermo-Calc and Dictra Calculations Comparison with Experimental Results Conclusions & Outlook (1) Outline
steel powder PM hard composite materials - Mixture of steel powders and hard particles hard particles - Hard particles for increasing wear resistance - Compaction by hot isostatic pressing (HIP) => Materials with highest resistance against abrasive wear => Possibility of HIP-cladding => Application: Extruder coatings MMC after HIP (2) Introduction
substrate material (steel bar of 1.2714) large capsule and surrounding space filled with a cold work tool steel powder (1.2380) extruded bar with: core of high fracture toughness wear resistant layer of several milimeters inductive one billet furnace heating up system closed, evacuated, heat-treated treated (1150 C, 2h) and hot extruded (3) Hot Extrusion Process insertion of the billet into the container powder mixture is consolidated and bonded substrate deformed during process
coating substrate core Coating steel: cold work tool steel [1.2380] C Cr Mo V Mn Si Fe 2.39 12.56 1.10 3.69 0.37 0.55 Bal. 8mm 8mm Interface region Substrate core bar: hot work tool steel [1.2714] Ø = ~30mm C Cr Mo V Mn Si Cu Ni Fe 0.56 1.15 0.46 0.08 0.75 0.29 0.11 1.74 Bal. (4) Cross Section
1.2714 1.2380 extrusion direction 1.2714 1.2380 20 µm Defect free interface region, no pores Full densification and bonding of tool steel powder 1.2714 substrate fully martensitic 1.2380 coating: martensitic matrix + embedded carbides (5) Microstructure
1.2714 hot work tool steel - Fully austenitic at T=1150 C 1.2380 cold work tool steel - At 1150 C equilibrium of austenite with two different carbides (M 7 C 3 and MC) - Volume fraction M 7 C 3 : 0.128 = 12.8 vol.-% - Volume Fraction MC: 0.046 = 4.6 vol.-% Calculation Details Thermo-Calc => Thermo-Calc version R => TCFe4 database => T=1150 C, p=1e5pa => Basis for Dictra calculation Phases and element levels of 1.2714 and 1.2380 at 1150 C [wt%] C Cr Mo V Mn Si Ni Fe 1.2714 Austenite 0.56 1.15 0.46 0.08 0.75 0.29 1.74 Bal. 1.2380 Austenite 0.88 7.61 0.74 0.67 0.39 0.65 0.23 Bal. 1.2380 M 7 C 3 8.74 46.45 1.55 7.74 0.32-0.01 Bal. 1.2380 MC 15.82 14.44 7.15 60.1 0.01 2e-6 0.001 Bal. (6) Thermo-Calc
Calculation Details Dictra Dictra version 2.4 / TCFe4 and Mob2 databases Isothermal calculation T=1150 C, p=1e5pa, 7200s and 36000s Phases: FCC_A1 (Matrix), M 7 C 3 (spheroid), MC (spheroid) Element levels and volume fraction of carbides according to TC calculation 1.2380 coating 1.2714 substrate FCC FCC MC + M 7 C 3 (spheroid) 16 mm (7) Dictra T = 1150 C, p=1e5 Pa
Cr [wt.%] Ni [wt.%] 14 12 10 8 6 4 K DICTRA K EPMA 1.2380 coating 1.2714 substrate 2 2h / 1150 C 0-100 -50 0 50 100 1,8 K DICTRA K EPMA 1,5 1,2 0,9 0,6 0,3 Distance [µm] 1.2380 coating 1.2714 substrate -100-50 0 50 100 Distance [µm] 2h / 1150 C V [wt.%] (8) Concentration Profiles 5 4 3 2 1 0-100 -50 0 50 100 Good agreement of measured and calculated profiles Deviation in vanadium profile K DICTRA K EPMA 1.2380 coating 1.2714 substrate 2h / 1150 C Distance [µm] Calculated width of interface region comparable to experimental results
1.2380 coating 1.2714 substrate 1.2380 coating 1.2714 substrate Dissolution of M 7 C 3 leads to shift of interface with respect to the presence of this type of carbide Enrichment of MC carbides predicted to appear close to the initial interface, towards the coating Uphill diffusion and enrichment of carbon towards coating (9) Carbide Profiles
1.2714 substrate 1.2380 coating 1.2714 substrate 1.2380 coating vanadium signal chromium signal Enrichment of V-rich carbides at interface Shift of M 7 C 3 due to dissolution Increased microhardness at interface towards coating due to carbide enrichment and higher local carbon content (10) EPMA / Microhardness
Diffusion between a coating of a cold work tool steel and a hot work tool steel was simulated with Dictra Calculated and measured element profiles are in good agreement Simulation predicts increase of MC carbide content and hardness at interface towards the substrate Microhardness and EPMA measurements are in agreement with this prediction Ongoing work on coatings with hard particle addition Thank you for your attention! (11) Conclusions / Outlook