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J.V. Skoff Badger Metal Tech, Inc

Combining induced compression and ferritic nitrocarburizing for an effective proactive and reactive surface engineering treatment for die casting tools. J.V. Skoff Badger Metal Tech, Inc. Introduction. Mechanical Ambient Compressive Stress FPP or MPCMP & Thermal Diffusion

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J.V. Skoff Badger Metal Tech, Inc

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  1. Combining induced compression and ferritic nitrocarburizing for an effective proactive and reactive surface engineering treatment for die casting tools • J.V. Skoff • Badger Metal Tech, Inc

  2. Introduction • Mechanical Ambient • Compressive Stress • FPP or MPCMP • & • Thermal Diffusion • Compressive Stress • Solder Protection

  3. History of Peening and FNC • Peening • 11th Century – Toledo Blades • Automotive Leaf Springs – 20th CenturyToday – Aerospace, Automotive, Military, Nuclear, Industry • FNC or Nitriding • Over 100 years old – Adolph Frye – Affinity Fe & N • Evolution to today’s many types • Gas, Heat, Time • Today – Automotive, Military, Industry

  4. Physics of shot peening just below the surface is a cold work compressive zone when media hits the surface there is a kinetic transfer of energy and a plastic deformation flow at the surface the plastic flow at impact can also close minor cracks in softer metals such as hot work steels

  5. Compressive Curve - Typical Example of non MPCMP compressive curve showing the high compression just below the surface which allows for polishing for cosmetic casting applications

  6. MPCMP (FPP) Curves formulated curves of compression developed for the MPCMP

  7. Shot Peening controls (not blasting) • Media shape and size • Classification monitoring • Intensity – Almen StripN(.031”), A(.051”), C(.094”) • Saturation (no more compression) • Coverage (area)

  8. Benefits of MPCMP • INCREASE FATIGUE STRENGTH • CLOSE MINOR CRACKS (plastic flow) • RETARDS THE PROPAGATION OF EXISTING CRACKS • FURTHER INCREASE FATIGUE STRENGTH OF FNC(when done before or after) • VERIFY SURFACE HARDNESS INTEGRITY • INCREASE EFFECTIVENESS OF WELDED AREAS • COUNTER EDM EFFECT • POSSIBLE BUFFERING OF CAVITATION EFFECT (texturing) • REDUCE TENDENCY TO SOLDER (texturing) • REDUCE LAMINAR FILL (texturing) • ENHANCE FLOW (texturing) • BETTER POWDER COAT PAINT ADHESION (texturing)

  9. Chemistry of FNC • Gases – Nitrogen, Carbon source • NH3, N, CO, or CO2 • Heat – Atmosphere, Vacuum, Fluidized Bed • Time – Below last temper temperature • Compound layer and diffusion zone Micro hardness readings

  10. FNC Curve - Typical FNC alone provides some shallow compressive values

  11. FNC - Controls • Correct recipe for the steel • Cleanliness – prevent contamination • Gases – type and % • Temperature – control • Time – enough but not too much • Pressure volume changes of gas micro hardness, diffusion zone, and compound layer Too thick of diffusion zone leads to chipping, flaking, and cracking of the FNC

  12. Same Recipe different Results This will not happen with

  13. Benefits of FNC • Reduce soldering - barrier • Increase fatigue strength(nitrogen and carbon) • Wear resistance (not caused by cavitation) • Corrosion and oxidation resistance

  14. Characteristics of Each • MPCMP • Line of sight • Can weld or polish • Cannot repair existing cavitation breakout • FNC • No line of sight • Compound layer – should not be polished/stoned • Welding similar to nitrided surface

  15. Combining MPCMP (F) & FNC (N) • MPCMP then FNC • Compressive value present after heat • Proto X-ray diffraction coupons • Keio U in Japan – AISI 4135 steel Electron probe micro analysis Nitrogen concentration near surface

  16. Compression Curves both sequences • First MPCMP then FNC (heat) compressive value and depth characteristics: • crystalline structure • dense compound layer • dislocation density • stratification pattern First FNC then MPCMP – offers higher compressive characteristics: porous component highest fatigue strength FPP removes porous compound layer component the compound layer is brittle and will chip off if too thick H-13 specimen 46-48Rc Oil

  17. 2008 Study at Keio University Japan • AISI 4135 Steel • Round Notch Charpy • Rotational Bending Fatigue Test • Fine Particle Peening (FPP) • Nitriding (N) • Various Combinations • FPP prior to N ref (FN) • FN - Higher fatigue strength than N alone • Highest fatigue strength with N prior to FPP (NF)

  18. Keio Specimens 7 specimens – FN, NF, F, N, FNP, NP, Untreated Peening – F Nitriding - N Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008

  19. Chemical Composition Comparison Similar chemical compositions With exception of Ni, Cu, Al Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008 Die steels have higher amts Cr, Mo, V

  20. 2008 Study Keio – The Why N FN N FN FE-SEM view of surface shows stratification pattern and higher dislocation densities at the surface of the FN specimen enabling more nitrogen diffusion near the surface of (b) a) compound layer N shows cracks and pores b) compound layer FN without cracks and pores (2% Nital etch)

  21. Higher concentration of NitrogenHigher fatigue strength than N alone Electron probe micro analysis hardness value of FN at surface higher than N. Depth of hardened layer .4mm (.016”) more diffused N at the surface of FN. Higher dislocation densities and altered grain structure Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008

  22. Residual stress distribution both N and FN generate residual compressive stress for increased fatigue strengththe stress value for FN an N and were similar (heat relaxes stress) Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008

  23. Fatigue test results Rotational bending fatigue test FN was higher than N – implies porous compound layer effect on N NP (polished removal of compound layer) Was higher than N FN similar to FNP Removal of porous compound layer after Nitriding by FPP (NF) shows the highest fatigue strength. Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008

  24. Distribution comparison FN and NF FN NF AISI 4135 compressive residual stress H-13 compressive residual stress Steels with greater hardness are able to generate higher compressive stress levels since yield stress is higher Courtesy Journal of Solid Mechanics and Materials Engineering – Keio University Japan – Vol 2 No. 2008

  25. Profile Comparisons Dievar Diffusion density compound layer 400x 400x 400x POLISHED STONED 1000x 1000x FNC to a stoned surface FNC to MPCMP Dievar coupon – 47-49 Rc denser diffusion zone indicates higher concentration of nitrogen

  26. MPCMP + FNC - Example Tooling initially treated with MPCMP (ML) and then FNC (TL) – BMT recipe

  27. Summary & Conclusions • Combining MPCMP and FNC have benefits over FNC or N alone • MPCMP followed by FNC removes porosity and cracks in compound layer, increases fatigue strength and hardness, and increases N diffusion compared to N or FNC alone without disturbing the compound layer (preferred) (NEW or USED) • FNC followed by MPCMP offers the greatest increase in fatigue strength, however, removes some of the compound layer which provides solder protection (alternate) • MPCMP has advantages over FPP for HPDC

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