Die Steel Improvements for AHSS Applications

HITACHI Intro

− Steel Production Methods for Die & Tooling Steels

− Typical Failure modes of Die Steels for AHSS

− Solutions to improve Tooling Performances

−Steel Types, Coatings

− Hot Stamping Die Steels

− Pre Hardened Die Steels

− Grain Oriented Die Steel Study

Ask Your Tool Steel supplier……

• Test Certifications (actuals from Mill Source )

• Method of Manufacturing

• Forged, Rolled , etc.

• Recommended Heat Treat

Surface Coating advancements have greatly improved steel performances.

Part material

• Aluminum or Steel: What type & thickness?

• Press Size (Servo or Mechanical) & Strokes per minute cycle

• Current Die Construction

• Progressive or Transfer?

• Castings? Inserts?

• Tooling steels used ?

• What coating?

• Die Clearance

• Heat Treating Recipe

• Welding (In House? Outsource? Consumable used?)

• Failure Observations: What Happened?

• What's been tried so far?

Coarse & directional carbide

• Large & anisotropic deformation after heat treatment

• Medium galling & wear resistance

• Characteristics will be affected by grain direction Small, dense & homogeneous carbide

• Small & isotropic deformation after heat treatment

• Same HT & Chem as D2

• Good galling & wear resistance

• Achieve higher hardness than

Machining of Pre-Hard Tool Steels @ 60 HRC

• 1) Machine Tool

• Rigid Construction:

• High Spindle Speed:20,000+

• 2) Cutting Tool

• Solid Carbide with ductile properties for interrupted cut

• 3) Consistent substrate of Die Steel

• Demands on Die Materials

−Wear

−Conductivity

−Watch for industry developments on 3D Additive Mfg. inserts w/ conformal cooling lines

• Use of higher alloyed Die Steel

•  Upgrade to a NADCA Class C Hot Work Steel in place of AISI H13

1. Conductivity

− Class B H13 is 32.6 @ 600C  Class C is 35.8 @ 600C

− Better for heat conductivity than H13 means better cycle times .

2. Toughness:

− Why? Higher Impact Values (charpy) prevent cracking on the surface of Hot Stamping Dies close to the cooling channel .

3. Wear:

− Why? NADCA Class C ( HITACHI DAC-MAGIC ) is higher strength under high temperature. Diesurfaces can reach ~ 400C & higher alloyed steels are needed to extend wear.

4. Coatablity

− Coatable and Wear resistance at room temperature, almost same as H13.

• Review Die Standards & allow for areas requiring better tooling steels in trouble-spots

• Compare results with other steels in side by side like- environments

• Insist on controlled HT path & Welding steps

• Ask for grain orientation on larger cross sections

• “If you can’t use a better tool steel, use your tool steel better”