Martensitic stainless steel and precipitation hardening (PH) grades

Martensitic stainless steel and precipitation hardening (PH) grades

Martensitic steel grades and precipitation hardening (PH) stainless steels are heat treatable and can therefore provide hardness and strength in a wide range of applications. Allowing to workability they are supplied in solution annealed condition. The downstream manufacturer performs final heat treatment to meet the mechanical properties required.

Martensitic stainless steel grades are basically Fe-Cr alloys with a higher carbon content than ferritics which enables them to harden on cooling in air, oil or water. Depending on grade and intended use, ductility is improved by tempering.

What is martensitic stainless steel?

High strength and hardness distinguish martensitic stainless steels from the other stainless steel families. After austenitizing cooling is performed in air, water or oil, depending on steel grade. If the intended application requires a high level of hardness (e.g. knives, HRC55), only stress relief annealing will be performed. Normally martensitic stainless steels are tempered in order to acquire useful mechanical properties, i.e. a certain level of toughness (A5 ≥ 15 %).

Typical applications for martensitic stainless steel grades:

•    cutting utensils
•    surgical and dental Instruments
•    fasteners, springs and ball bearings
•    press plates
•    steam and gas turbines

Limited weldability

Traditional martensitic steels with a carbon content > 0.20 % are difficult to weld; assistance is advised. The hardenable high-carbon grades are not suitable for welding. Low-carbon nickel-martensitic steel grades have relatively good weldability. Welding of precipitation hardened stainless steel grades is possible, but depending on grade some limitations might have to be regarded.

Varying corrosion resistance

Corrosion resistance of martensitic stainless steels may vary considerably depending on chemical composition (C, Cr, Mo), surface finish and especially heat treatment. Smooth polished surfaces experience higher resistance than rougher finishes. In terms of heat treatment the hardened condition is more favourable, since the elements promoting corrosion resistance are in solution and therewith effective. Tempering may lead to carbide precipitation which impairs corrosion resistance. This is always the case for traditional martensitic grades, whereas nickel-martensitic grades with max 0.06 % carbon and 3-6 % nickel (e.g. EN 1.4313 and EN 1.4418) do not sacrifice corrosion resistance by tempering.

Corrosion resistance of precipitation hardening steels is higher compared with heat treatable martensitic stainless steels ranking between ferritic Cr and austenitic CrNi steels.

What is precipitation hardening stainless steel?

Precipitation hardening stainless steels provide remarkable levels of high strength and hardness in a very wide range. With the exception of the martensitic alloys (e.g. Dura 17-4PH / EN 1.4542) cold formability is satisfactory.

Precipitation hardening grades have higher alloying contents than martensitic steel grades. They contain nickel, and in order to achieve hardening by aging additions of copper, aluminium, titanium, niobium and molybdenum. Depending on chemical composition their microstructure after final heat treatment is austenitic, semi-austenitic or martensitic.

Typical applications for precipitation hardening grades:

•    retaining rings, spring holders, springs
•    chains, valves and gears
•    aircraft parts
•    pressure vessels and seals

Stainless Steel Finder

Check Stainless Steel Finder to compare the properties of our different martensitic and PH stainless steel products.

Outokumpu product ranges with martensitic and precipitation hardening (PH) steel grades

Dura

Our martensitic and precipitation hardening grades can be found in our Dura range. Head over to the Dura range site to learn more.

Prodec

The Prodec range comprises stainless steel grades that are optimized for consistently superior machinability, enabling faster machining speed, longer tool life, and enhanced quality. Head over to the Prodec range site to learn more.

 

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May 24, 2019