AerMet 100 Machining: Ultra-High-Strength Steel Tooling

AerMet 100 Machining: Tooling Strategies for Ultra-High-Strength Steel

AerMet 100 (Carpenter Technology) is a secondary-hardening, cobalt-nickel steel delivering 1930 MPa (280 ksi) ultimate tensile strength with exceptional fracture toughness (KIC of 110 MPa-m^0.5). Used in aircraft landing gear, arrestor hooks, and armor-piercing penetrator bodies, AerMet 100 represents one of the most challenging ferrous alloys for CNC machining. Its combination of high cobalt (13.4%), nickel (11.1%), chromium (3.1%), and molybdenum (1.2%) produces a fine lath martensite matrix with M2C carbide precipitates that aggressively abrade cutting tools.

Material Conditions and Machinability

Normalized and tempered (pre-hard): 35-40 HRC, 1200-1400 MPa UTS. Machinability approximately 25-35% of B1112 free-cutting steel.

Fully hardened and aged (H900 condition): 50-54 HRC, 1930-2100 MPa UTS. Machinability drops to 5-8% of B1112.

Ausformed condition: Some landing gear components are ausformed (thermomechanically processed) to achieve even higher strength (2200+ MPa). Machinability in this condition is 3-5% of B1112, comparable to hardened tool steels.

Insert Grade Recommendations

Roughing – Pre-Hardened (35-40 HRC):

• Sandvik GC4330 or GC4340 (tough substrate, CVD TiCN/Al2O3 coating). CNMG 160616 with wiper geometry for heavy cuts.
• Kennametal KCP30B or KCP40B (tough grade for interrupted cuts)
• Iscar SUMO TEC IC907 (PVD TiAlN, medium-tough substrate)
• Nose radius: 1.2-1.6mm for heavy roughing, 0.8mm for semi-finishing

Finishing – Pre-Hardened:

• Sandvik GC4315 (hard, wear-resistant grade) or Tungaloy T9125
• DNMG 150408 with 0.8mm nose radius and sharp edge prep (0.01mm hone)
• Vc: 100-150 m/min, fn: 0.10-0.18 mm/rev

Roughing – Fully Hardened (50-54 HRC):

• PCBN: Sandvik CB7015 or Kennametal KD050 with 50-65% CBN content
• Ceramic: Sandvik CC6050 (SiAlON) for continuous cuts only
• CNMX 120408 geometry with 25 deg x 0.03mm T-land
• Vc: 80-140 m/min (PCBN), 150-300 m/min (ceramic, light cuts only)

Finishing – Fully Hardened:

• PCBN: Sumitomo Secomax BN250 (fine-grain, low CBN content for superior surface finish)
• Kyocera KBN500 (nano-CBN for Ra below 0.4 micrometers)
• DNMX 150404 with polished rake face and 0.015mm edge hone
• Vc: 100-180 m/min, fn: 0.05-0.12 mm/rev, ap: 0.1-0.5mm

Cutting Parameters – Detailed Tables

Turning – Pre-Hardened AerMet 100 (38 HRC):

Turning – Hardened AerMet 100 (52 HRC):

Milling AerMet 100

Milling ultra-high-strength steels requires rigid tool holders and adaptive toolpaths to manage cutting forces:

• Roughing end mills: 4-flute solid carbide, 16-25mm diameter, AlCrN or nACRo coating (3000+ HV hardness). Brands: OSG A-Brand AE-HXS, Harvey Tool, or Mitsubishi 4XBR.
• Vc: 40-70 m/min (pre-hardened), 25-45 m/min (hardened)
• fz: 0.04-0.08 mm/tooth (roughing), 0.02-0.05 mm/tooth (finishing)
• Radial engagement: 5-10% of diameter (trochoidal slotting), 40-60% (peripheral)
• Axial depth: 0.5-1.0 x diameter

Use shrink-fit or hydraulic chucks exclusively. ER collet holders introduce runout that causes uneven flute loading and premature fracture in the hardened condition.

Drilling and Tapping

Drilling (pre-hardened):

• Solid carbide drills with 130-140 deg point, internal coolant
• Vc: 30-50 m/min, fn: 0.05-0.12 mm/rev
• Peck cycle: 1.5-2.0 x diameter, full retract
• Expected life: 30-80 holes per drill (10mm diameter, 30mm deep)

Drilling (hardened):

• Reduce parameters by 40-50% across all axes
• Consider pre-drilling in the soft condition and reaming to final size after hardening
• For holes below 5mm in hardened material, EDM is often more economical

Tapping: Thread forming (roll tapping) is preferred over thread cutting in AerMet 100. Form taps produce stronger threads with no chip evacuation issues. Use TiN or TiCN-coated HSS-E taps at 5-12 m/min with peck tapping cycles. For hardened material, thread milling with a solid carbide cutter is the only practical option.

Coolant and Chip Management

• Use high-pressure flood coolant (minimum 70 bar) with synthetic or semi-synthetic emulsion at 10% concentration. EP additives are essential.
• Through-tool coolant is mandatory for drilling and deep boring operations.
• AerMet 100 produces tough, work-hardened chips in the pre-hard condition. Use inserts with aggressive chipbreaker geometries (Sandvik -MR or Kennametal -RP) to control chip curl.
• Chip volume ratio is approximately 1:3 (chip to workpiece). Plan chip conveyors and collection bins accordingly.

Economic Considerations

AerMet 100 machining costs typically run 4-8x higher than standard alloy steel (4340, 300M). Key cost drivers include:

1. Raw material cost: $25-40/kg for bar stock, compared to $3-5/kg for 4340
2. Tool consumption: 3-5x higher insert usage per part due to abrasive M2C carbides
3. Machine time: 2-3x longer cycle times due to reduced cutting speeds
4. Quality assurance: 100% NDT (magnetic particle or ultrasonic) inspection is standard for flight-critical components

Shops quoting AerMet 100 work should build these multipliers into pricing and allow 15-20% scrap allowance during process development.