Maraging steel

Maraging is a 18% nickel, cobalt reinforced steel (C-type) with excellent machinability and heat treatment properties. Maraging steel is double vacuum melted by VIM (Vaccum Induction Melt) followed by VAR (Vaccum Arc Remelt). The material is delivered in annealed and descaled condition. The alloy is very tough and relatively soft (HRC 30/35) and is relatively easy to machine and shape. Maraging steel is used for critical parts in aerospace, structural, component and tooling applications.

Maraging

  • MARtensitic - a very hard form of steel crystal structure
  • Subsequent AGING (age hardening - approx. 3-6 hours at 900°F (~482°C) gives optimal material properties).

Specifications:

  • AMS 6512 = C250 maraging
  • AMS 6514 = C300 maraging
  • AMS 6515 = C350 maraging
  • Mil-S-46850 (applies to all grades) -breakability applies

Processing

The machinability of annealed maraging steel is comparable to steel such as AISI 4340 at the same hardness level (HRC 30/35). However, once the material is aged (heat treated), the choice of cutting tools and machining parameters become very important. Robust equipment such as very sharp tools and an abundance of coolant are essential.

Heat treatment

Maraging alloys are essentially carbon-free, a protective atmosphere is not required during annealing or ageing. The material is supplied in a solution annealed condition with a hardness of 30/35 HRC. Typical heat treatment time/temperature is listed below. Large cross sections should be aged for longer periods.

Composition

C If Mn Ni Co Mo Ti Al Fairy
C250 .03 max .10 max .10 max 18,50 7,50 4,80 ,40 ,10 Ball.
C300 .03 max .10 max .10 max 18,50 9,0 4,80 ,60 ,10 Ball.
C350 .03 max .10 max .10 max 18,50 12,0 4,80 1,40 ,10 Ball.

 

Characteristics

C250 C300 C350
Density .289 lbs./cu. in. .289 lbs./cu. in. .292 lbs./cu. in.
Average coefficient of thermal expansion 5.6×10-6 in./in./ °F 5.6×10-6 in./in./ °F 6.3×10-6 in./in./ °F
Modulus of elasticity 27.0×10-6 psi 27.5×10-6 psi 29.0×10-6 psi

 

Ageing (heat treatment)

  Temp Time Hardness
Maraging 250 900/925 °F 6 hours 48/52 Rc
Maraging 300 900/925 °F 6 hours 50/55 Rc
Maraging 350 900/925 °F 6 hours 55/60 Rc
Or 950 °F 3 hours 55/60 Rc

NOTE: A modified ageing cycle is proposed for die casting for increased service life. The following thermal treatments have been used to obtain desirable properties for moulding machines. After roughing the mould, annealing at 1500-1525°F for 1 hour per inch of thickness is typical. After upon completion of processing, an ageing heat treatment of 980-1000°F for 6 hours is typical.

Typical - round bar. Min. characteristics

Post-ageing (longitudinal) Rc Offence threshold ,02% KSI Extension strength 4,5 a% Reduction of area
250 50 254 248 11,0 53
300 54 293 286 10,0 46
350 57 342 336 6,2 28

 

Advantages of maraging steel

Excellent mechanical properties

  • high yield and maximum tensile strength
  • high toughness, ductility and impact resistance
  • high fatigue strength
  • high compressive strength
  • hardness and wear resistance sufficient for many tool applications

Excellent working capacity

  • high resistance to crack propagation
  • easily moulded - cold, warm, hot (without process annealing)
  • good weldability without hardening
  • excellent polishability

Excellent heat treatment characteristics

  • low oven temperatures are required
  • precipitation hardening, ageing heat treatment
  • uniform, predictable shrinkage during heat treatment
  • freedom for carbonisation or decarbonisation
  • by hardening without hardening
  • minimal distortion during heat treatment (0.0009 in/in C250 //.001 in/in C300)

Advantages in application

  • low coefficient of expansion minimises heat control
  • pitting and corrosion resistance superior to ordinary tool steel
  • good repair weldability
  • excellent mechanical properties have led to longer tool life
  • slightly re-engineered and retired for secondary tool life

The technical information presented in this section is only representative and is not guaranteed values.