1. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide  High Thermal Conductivity= K Molybdenum High, Martensitic Fair, Austenitic Poor  High Yield Strength/Softening resistance = K Molyddenum High, Chromium, Low vanadium Good Molyddenum High, Chromium, Low vanadium Good  Thermal Expansion Rate= K Molybdenum High, Martensitic Fair, Austenitic Poor  Low Modulus of Elasticity= K Inherit steel property - difficult to do much about this  High Thermal Conductivity= K Molybdenum High, Martensitic Fair, Austenitic Poor  High Yield Strength/Softening resistance = K Molyddenum High, Chromium, Low vanadium Good Molyddenum High, Chromium, Low vanadium Good  Thermal Expansion Rate= K Molybdenum High, Martensitic Fair, Austenitic Poor  Low Modulus of Elasticity= K Inherit steel property - difficult to do much about this K = Thermal Conductivity x Yield Strength at High Temperature Thermal Expansion x Modulus of Elasticity Thermal Expansion x Modulus of Elasticity Click here to continuehereClick here to return to first slidehere A higher K steel value resists Thermal Fatigue

2. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide  The strength of untreated H13 at 1200F is half of the yield strength at room temperature  Thermal cracking and breakout are the MOST COMMON modes of failure.  Localized softening at elevated temperature, surface strain, and deformation result in fatigue cracking.  High repetitive collapsing of trapped void bubbles contributes to lowering yield strength and subsequent cracking.  The strength of untreated H13 at 1200F is half of the yield strength at room temperature  Thermal cracking and breakout are the MOST COMMON modes of failure.  Localized softening at elevated temperature, surface strain, and deformation result in fatigue cracking.  High repetitive collapsing of trapped void bubbles contributes to lowering yield strength and subsequent cracking. Thermal Fatigue Failure (die temperature lowers yield strength)

3. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide  Continuous heating and cooling of the die causes the thin surface where the die contacts molten metal to expand at a faster rate than internally.  This rapid and constant heating/cooling with die lubricants creates increasing surface tensile stresses that eventually exceed the inherent fatigue strength of the material leading to cracks.  Cracks are prone to develop first in high stress areas such as sharp corners, or sharp edges and then eventually spread over the entire surface or start at inside waterlines.  Continuous heating and cooling of the die causes the thin surface where the die contacts molten metal to expand at a faster rate than internally.  This rapid and constant heating/cooling with die lubricants creates increasing surface tensile stresses that eventually exceed the inherent fatigue strength of the material leading to cracks.  Cracks are prone to develop first in high stress areas such as sharp corners, or sharp edges and then eventually spread over the entire surface or start at inside waterlines. Thermal Fatigue Failure (a frequent cause of die degradation)

4. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide Molten metal contacts die surface where temperature increases more than the core. Die face expands, however cooler underlying core resists. Die sub-surface in compression. Die surface reverts to tensile when die cools. Lubricant cools die even faster. Die surface in cycled tension yields and crack. Data supports this phenomena. Mechanism of Die Heat Checking Die surface face Water Cooling Line Die Surface Temperature Increases Die Casting Water Cooling Line Die Resulting sub-surface Compression Water Cooling Line Die Resulting tension Spraying Cools Die Surface Core Stabile Core resists temp changes

5. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide Die Cycling Surface Effects Water Cooling Line Die Thermal Cycling places die surface in residual tension Thermal Cycling places die surface in residual tension This reduces the yield strength of the steel making the die easier to upset. This reduces the yield strength of the steel making the die easier to upset. Continued high stress lowers strength and thin surface cracking results Continued high stress lowers strength and thin surface cracking results Water Cooling Line Die Die Surface Water Cooling Line Die

6. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide Sharp Edges Sharp Corners Sharp Edges Sharp Corners Radii are preferred Sharp Edges and Corners High Stress Locations

7. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide Over time this cycling causes surface micro stress cracks to develop H-13 As die cools, opposite occurs H-13 - Side View Die at normal temperature Cycle effect of rapid heating and cooling of the die surface (emphasized surface deformation for demonstration) Heated surface expands more rapidly than the interior creating surface tensile stress

8. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide Ideal Steel Attributes  Resistance to thermal fatigue cracking – low coefficient of thermal expansion, high thermal conductivity, high hot yield strength, temper softening resistance, high creep strength, and adequate ductility Breakout and pitting are influenced by improvements in die filling conditions. Lubrication and intrinsic barriers are necessary to prevent soldering due to aluminum and iron interaction. Professor Wallace’s “K” Factor Formula

9. Copyright © 1996-2009 Badger Metal Tech, Inc – Rev 03-2009 Return to HomeFirst Slide  Remove Residual Tensile Stress Buildup to prevent heat checking  Minimize Softening Effect to the Surface to prevent heat checking  Reduce Negative EDM Effect to prevent premature surface cracking  Remove Residual Tensile Stress Buildup to prevent heat checking  Minimize Softening Effect to the Surface to prevent heat checking  Reduce Negative EDM Effect to prevent premature surface cracking a world apart Reducing Thermal Fatigue Cracking a world apart Reducing Thermal Fatigue Cracking Jump to section