Specialty Stainless Steel Processes (S³P)

Specialty stainless steel processes (S³P) featuring Kolsterising^®  technology offer unique surface hardening solutions for austenitic stainless steel, nickel-based alloys and cobalt-chromium alloys producing increased mechanical and wear properties without adversely affecting corrosion resistance.

Benefits

Austenitic stainless steel parts improve their mechanical properties by applying the S³P processes, resulting in hardened austenitic stainless steel surfaces. In all S³P processes, the corrosion of the base material is not altered, while exhibiting superior wear resistance, strength and ductility, as well as resistance to galling. As surface diffusion processes, the surfaces do not crack or chip, offering significant advantages over coating technologies. S³P A^® and Kolsterising^® are the state of the art processes for austenitic stainless steel, duplex stainless and nickel-based materials. S³P M is used for the treatment of martensitic and precipitation hardened stainless steel materials.

Benefits include

• Increased surface hardness to 900-1300 HV0.05 (depending on base material and surface conditions)
• Properly selected and designed materials and parts maintain corrosion resistance
• Treated parts offer colour and dimensional stability
• No post treatment is necessary
• No risk of delamination
• The paramagnetic properties of austenitic materials remain unchanged after treatment
• Eliminates fretting and galling
• Highly resistant to surface wear environments such as sliding in combination with abrasive wear and cavitation erosion.

What is Galling?

Galling is a type of mechanical wear caused by a combination of friction and adhesion between sliding surfaces typically under a compressive load. It is the result of tearing and slipping of the crystal structure at the surface once the protective chromium oxide layer has worn away. Further mechanical forces cause the material to become stuck or welded to the mating surface, and ultimately results in the seizing of interfacing components. In the case of fasteners, this is problematic since a galled fastener assembly has to be drilled or cut to be removed.

Galling resistance in stainless steel metal–on–metal applications can be achieved through Bodycote’s Specialty Stainless Steel Processes (S³P) while preserving the corrosion resistance properties of the base material.

Photographs of AISI 316 buttons after G98 galling test.
Left: S³P treated condition at 122.2 KSI (842.5 MPa);
Right: untreated condition at 14.3 KSI (98.6 MPa)

Learn more about the galling resistance of S³P treated stainless steel

Application & materials

S³P processes are used for products across a wide range of markets from precision medical tools to automotive components.

• Food and other manufacturing equipment parts on production lines benefit from S³P processes to decrease downtime and achieve cost savings
• Non-galling wear resistant demands of industrial fluid handling pumps, valves and fittings
• Fasteners that need to maintain their corrosion resistance, to be non galling and wear resistant, and may need to be disassembled easily
• New fuel efficiency challenges in today’s automotive applications require corrosion resistant, hardened components that resist wear and provide longer part life
• Medical devices that require improved wear resistance, fatigue resistance, and maintain a hard, sharp edge
• Wear and scratch resistant parts and fasteners that maintain corrosion resistance used in marine applications
• Many of today’s stainless steel consumer goods that demand a tough, scratch and wear resistant surface

All stainless steel as well as nickel-based and cobalt-chromium alloys can be treated by various S³P processes. Some typical examples are:

• Austenitic stainless steel
  – AISI 304, 304L, 316, 316L, 904L
• Martensitic stainless steel
  – AISI 430, 440
• Duplex stainless steel
  – UNS S32205, S32750
• Precipitation hardened stainless steel
  – PH 17-4, PH 13-8 Mo
• Nickel Based Alloys
  – Hastelloy® and Inconel®
• Cobalt-chromium alloys
  – BioDur® CCM Plus® alloy
• Stellite®

Process details

S³P treatments involve low temperature diffusion of large quantities of carbon and/or nitrogen into the surface without the formation of chromium precipitations. No additional chemical elements that were not already present prior to the treatment are introduced during the process. There is no risk of delamination because S³P processes neither add a coating nor introduce brittle phases in the material.