Duplex stainless steels comprise a mixture of ferrite and austenite, producing a material with many of the advantages offered by both structures. They generally have comparable or better corrosion resistance to austenitic steels, with more than twice the yield strength, and are especially resistant to pitting corrosion and stress corrosion cracking in chloride environments.

Duplex stainless steels have for years been providing excellent service in seawater on offshore platforms and in a wide variety of other chloride containing environments.

The pitting resistance equivalent number (PREN) is an empirical guide to the grading of materials for resistance to seawater. Duplex stainless steel has been designed to exceed the commonly specified PREN of 40 and provide, for example, castings suitable for pumps and valves on offshore oil and gas platforms.

Austenitic stainless steels are very tough and essentially non-magnetic materials that are alloyed to produce resistance to corrosion in a variety of environments.

The basic 18% chromium/10% nickel grade (R31) has a very good corrosion resistance in many applications. This alloy can be refined (R31LC) or alloyed with molybdenum (R33,R34) for enhanced corrosion resistance or modified for improved welding (R30) and machining (R32) characteristics. Increasing nickel content and alloying with molybdenum and copper results in greatly improved corrosion resistance in more aggressive environments such as hot sulphuric acid (R36,R37).

Strength and corrosion resistance superior to many martensitic stainless steel alloys is achieved by precipitation hardening a low carbon martensitic or semi-martensitic stainless steel. This is accomplished by accurate alloying and a low temperature heat treatment, allowing machined parts to be age hardened with only minimal distortion and scaling. Depending upon the particular material composition and heat treatment programme, precipitation hardening stainless steels can be supplied with appropriate hardness differentials to avoid galling and seizing during metal to metal contact

A protective passive oxide film can develop on steels with chromium contents above 12%, imparting to these steels “stainless” characteristics. By maintaining a suitable composition balance between carbon and chromium, a series of high strength stainless steels are produced (R23-R23XHC).

Components cast in these alloys meet specific hardness and wear resistance criteria through closely controlled heat treatment practices. Material toughness and versatility are enhanced by additions of nickel and molybdenum (R24).

Alloys of iron, carbon and silicon where carbon is present in excess of the amount which can be retained in solid solution are termed cast irons The common engineering grades contain Carbon in the form of flake graphite, but this can be modified with additions to a spheroidal shape. This imparts major improvements in strength and ductility and the alloys are then called SG, Nodular or Ductile irons (N1-N5).. Additions of nickel and chromium change the structure to produce the wear resisting alloy Ni Hard (Q51-Q52), while higher amounts of these elements yield the excellent corrosion resistance of the Ni Resist Family (R10-R13).

From a low carbon iron for electro-magnetic applications (S1), our range of low carbon steels (S3, S4) can be produced to meet specific strength and hardness requirements. Higher hardenability, wear resistance and sub-zero impact criteria are achieved through minor alloying additions and precise heat treatment control (R60-R67).

An additional series of steels resistant to high temperature creep is developed by alloying low and medium carbon steels with chromium, molybdenum, vanadium and tungsten (R68-R72). Nickel is added to many of these grades to improve sub-zero impact properties (R66).