Martensitic Stainless Steels

These are alloys that can be heat treated to give high proof stresses and tensile strengths and they are widely used in industry where high strength and some corrosion resistance is required.  Such alloys include UNS S41000, S42000 and precipitation hardening grades such as J91540 and S17400.  These alloys have chromium contents from about 12 to 17% plus small additions of nickel and other elements.

However, the corrosion resistance of these alloys is not very good in oxidizing media, and is inferior to that of the 300 series austenitics ,e.g. 304L and 316L, because of their lower chromium content.  While they have some resistance to atmospheric corrosion, they have little resistance to corrosion in oxidizing, aqueous media, e.g. fresh water. 

Where high strength is required and corrosion resistance in an oxidizing medium, then it is safer to use a duplex stainless steel or a heat treatable nickel alloy, with good corrosion resistance in the medium of interest.

Where the martensitic stainless steels have good corrosion resistance is in reducing media, such as sweet and sour oil and gas fluids.  Even in these media, there can be a risk of sulphide SCC and adherence to correct heat treatment and hardness requirements is essential, as specified in ISO15156/ NACE MR01075 (upstream) and NACE MR0103 (downstream).

Posted on: 7th Feb 2017

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Image (top left) by Agnieszka