Stainless Steel Grades

Stainless steel grades are selected on the basis of required properties (e.g. corrosion resistance), design criteria and fabrication requirements. Thi

Stainless steel grades are selected on the basis of required properties (e.g. corrosion resistance), design criteria and fabrication requirements. However, there are many different iron-carbon-chromium alloys that are collectively referred to as stainless steels. A steels corrosion resistance, weld ability, mechanical properties, etc. are largely determined by its micro-structure (see figure above). This, in turn, is determined by the steel’s chemical composition. As per EN 10088, stainless steels can be divided into the following, basic, microstructure-dependent groups: 

• Martensitic.
• Ferritic.
• Austenitic.
• Austenitic-ferritic (duplex).

As they are normally added to increase corrosion resistance, the various alloying elements have a large impact on the ease with which a stainless steel can be pickled (pickleability). It is the proportions of the different alloys that have a great effect on the pickleability of a stainless steel. As regards steel grades, the rule of thumb is: The higher the alloy content (i.e. the corrosion resistance), the more difficult it is to pickle the steel. The most basic grades are the iron-carbon-chromium alloys. These fall into two groups – martensitic and ferritic.

Martensitic

stainless steels generally contain only 11 to 17% chromium and have a higher carbon content than the ferritic grades. The steels in this group are characterised by high strength and limited corrosion resistance. They are mainly used where hardness, strength and good wear resistance are required (e.g. turbine blades, razor blades and cutlery).

Ferritic

stainless steels are more corrosion resistant than the martensitic grades, but less resistant than the austenitic grades. Like martensitic grades, these are straight chromium steels with no nickel. The most common of these steels contain either 12% or 17% chromium – 12% steels are used mostly in structural applications and automotive applications (exhaust systems) while 17% steels are used for catalytic converters, housewares, boilers, washing machines and internal building structures.

Austenitic

is the most widely used type of stainless steel. It has a nickel content of at least 7%. This makes the steel structure fully austenitic and gives it non-magnetic properties, good ductility and good weldability. Austenitic steels can also be used throughout a wide range of service temperatures. Applications for which austenitic stainless steels are used include: housewares; containers; industrial piping; tanks; architectural facades; and, building structures. This type of stainless steel dominates the market.

Austenitic-ferritic (duplex)

stainless steels have a ferritic and austenitic lattice structure (hence duplex). To give a partly austenitic lattice structure, this steel has some nickel content. The duplex structure delivers both strength and ductility. Duplex steels are mostly used in the petrochemical, paper, pulp and shipbuilding industries. Modern duplex steels span the same wide range of corrosion resistance as the austenitic steels. For more detailed information about the stainless steel grades, see the Avesta Welding Manual (Practice and products for stainless steel welding) and the Outokumpu Corrosion Handbook.

• [accordion]
• 1. Guide to Understanding Steel
• 
• 2. Stainless Steel Grades Explained
• 
• 3. BS EN 10088-1-2014 SS List of stainless steels
• 4. BS EN 10088-2-2014 SS Tech Sheet Plate And Strip of Corrosion Resisting steels
• 5. BS EN 10088-3-2014 SS products of corrosion resisting steels
• 6. BS EN 10088-4-2009 SS Technical Sheet Plate And Strip of Corrosion Resisting steels
• 7. BS EN 10088-5-2009 SS Technical Corrosion Resisting Steels
• 8. ISO 3506-1-2020 Coating Reference Book
• 9. A959-19 1.03 Standard Guide for Spec Harmonized Standard Grade Compositions for Wrought SS