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17-4 PH Stainless Steel Fasteners

17-4 PH stainless steel is one of the most common martensitic stainless steel. 17-4 PH stainless steel is precipitation hardening of martensite stainless steel. Precipitation hardening is a special type of heat treatment technique used to improve the yield strength of the material; it is also called age hardening (or) particle hardening.

 

Precipitation hardening stainless steels are characterized into one of three groups based on their final microstructures after heat treatment. The three types are:

  1. Martensitic (e.g., 17-4 PH)
  2. Semi-austenitic (e.g., 17-7 PH)
  3. Austenitic (e.g., A-286)

Martensite stainless steel is one of the types of PH stainless steels. In this they are already martensitic in solution and annealed condition and only requires precipitation hardening. Martensite stainless steels are similar to iron carbon alloys that are austenitized. They are hardened by quenching and tempered for increased ductility and toughness. Their heat-treated structure is BCT (Body Centered Tetragonal). These alloys are magnetic.

PRECIPITATION HARDENED HEAT TREATMENT consists of three stages:

  1. Solution Heat treatment
  2. Quenching
  3. Precipitation or Aging

Solution Heat treatment: Consists of high temperature heat treatment that allows any precipitates and alloying element to dissolve or go in to super saturated state. Temperature is around 980 – 1065°C.

Quenching (or) Cooling: After the alloys are brought to solution the metal is cooled to room temperature. Cooling can be done in air, water or oil but must be accomplished fast enough to obtain a super saturated solution.

Precipitation (or) Aging: The super saturated solid solution decomposes with time or temperature as the alloying elements forms small clusters.

Precipitation Treatment for 17-4 PH: 17-4 PH stainless steel is a martensitic stainless steel containing approximately 3% copper and is strengthened by precipitation of copper in the martensite matrix. Addition of copper is made to promote its precipitation hardening capability. Precipitation hardened by only holding the steel at 480°C for 1 hour. Thereby minimizing scaling and distortion and allowing the parts to be machined to close tolerances, prior to heat treatment. These coherent particles are transformed to incoherent FCC – cu after long term aging at temperature about 400°C.

Properties of 17-4 PH Stainless Steel Fasteners

  • High strength
  • High hardness
  • Good corrosion resistance
  • Resistance to atmospheric corrosion
  • Good machinability
  • Resistance to stress corrosion cracking
  • Magnetic
  • Coherency

Limitations: Dimensional inaccuracy occurs due to heat treatment and should be careful. Stress cracking occurs. Scaling and distortion may occur.

Common Applications for 17-4 PH Fasteners

  • Pump Shafts
  • Pulp and Paper Industry
  • Aerospace (turbine blades)
  • Food Industry
  • Off-shore (foils, helicopter deck platforms)
  • Oil and Petroleum Refining Equipment
  • Gears
  • Paper Mill Equipment

Precipitation Hardening 17-4 PH Fasteners (UNS S17400)

Common Trade Name: 17-4PH

UNS: S17400

Specifications: ASTM A564 type 630

Approx. Room Temp. Mechanicals: Solution & Aged (up to) UTS = 190 ksi

Typical % Compositions Summary: Cr 15.0 – 17.5, Cu 3.0 – 5.0, Fe 75.5, Ni 3.0 – 5.0, Si 1.0

Corrosion Resistance:

A martensitic precipitation/age-hardening stainless alloy with high strength and corrosion resistance.