MARAGING STEEL

SANDEEP NAIRCB.EN.P2.MFG15018

INTRODUCTION

• Developed in 1959• Extra-low-carbon, high nickel, iron base alloy• Extra ordinary combination of structural

strength and fracture toughness, at the same time , readily weldable and easy to heat treat

• Martensitic microstructure when annealed and ultra high strength on being aged

IRON-NICKEL ALLOY SYSTEM

IRON-NICKEL TRANSFORMATION DIAGRAM

IRON-NICKEL TRANSFORMATION

• At 1100⁰f and above, equilibrium structure is gamma (austenite)

• Below 1100⁰f, duplex structure-mixture of alpha(ferrite) and gamma

• Single phase accelerated transformation at comparatively low temperature(Ms = 5000f)

• Single phased alloy display significantly more toughness and ductility

• Higher nickel alloy tend to transform by shearing or diffusionless type and lower nickel alloy by diffusion

• Hardenability which dominates in quenched and tempered steel is inapplicable

• Tempering does not takes place• Martensite is the only transformation in 18%

or more Nickel alloy and reversible• Cold working prior to heat treatment is

required for grain refining

CRYSTAL STRUCTURE COMPARISONFEATURE IRON-NICKEL MARTENSITE IRON-CARBON

MARTENSITESTRUCTURE BCC BCT

STRENGTH FACTOR DISLOCATION DENSITY AND FINE TWIN BOUNDARY

CARBON CONTENT

AGE HARDENING PRECIPITATE

AGING REACTION

• Rapid response in age hardening for a narrow temperature band (750-950⁰F)

• Limited altering in heat treatment scheduled for compensating undesired composition variation

IDENTITY OF PRECIPITATES

• Zones based on an Ni₃Mo grouping containing iron((Ni,Fe)₃Mo)

• The equilibrium phase is Fe₂Mo • Rate of hardening depends entirely on

precipitate growth rate and aging temperature• Overaging occur earlier at higher aging

temperature

PROPERTIES

APPLICATIONS

AEROSPACELARGE ROCKET-MOTOR CASES• High strength to weight ratio with good fracture

toughness,ready weldablity and simple heat treatment

HYDROSPACEPRESSURE HULL (Deep Quest)• High strength to density ratio,good fracture

toughness,resistance to corrosion

TOOLING APPLICATION• High strength, simple heat treatment, good

toughness,• Good machinability and fabricability• Excellent resistance to heat checking and erosion by

the aluminum• Used in die-casting operations,core pins core dies

and extrusion ram

LARGE ROCKET-MOTOR CASE

LARGE ROCKET-MOTOR CASES

NOZZLE SHELL

ALUMINUM DIE CASTING DIE

ALUMINUM DIE CASTING CORE PIN

EXTRUSION RAM