General:

904L may considered as a high performance austenitic stainless steel when compared with the general purpose austenitics such as 304 and 316. It has the characteristic high ductility and formability and good weldability of the austenitic grades, but its use is primarily a consequence of its corrosion resistance rather than its mechanical properties. Applications for the alloy range from the chemical and mineral processing industries to pollution control and water treatment. For many years it has been a useful upgrade to 316L but in more recent times the cost effectiveness of duplex grades has limited its use.

Corrosion Resistance:

A primary feature of 904L is its very good corrosion resistance in dilute sulphuric acid across the full range of concentrations up to 35° C. It also has useful resistance to a number of other inorganic acids, but its performance may be limited when halide ions are present.

Whilst the nickel content of conventional stainless steels (eg 316L) is such that they are very susceptible to chloride stress corrosion cracking, the higher level of this element in 904L imparts good resistance to this form of corrosion. The nitrogen, molybdenum and chromium contents in stainless steels have a direct bearing on their resistance to pitting and crevice corrosion and in the case of 904L this parameter is good. However, the 6% molybdenum austenitic grades or super- duplex grades do display superior resistance to these forms of localised corrosion.

Mechanical properties:

The strength characteristics of 904L are in line with that of the common austenitic grades viz 40% elongation and 220MPa Proof and 520MPa UTS (Minima at room temperature.)

Commercial Consideration:

As a consequence of the high alloy content of 904L, which gives rise to its useful corrosion resistance, the grade is subject to moderate price fluctuations in line with commodities. Nonetheless 904L is produced and stocked in a range of product forms and sizes. Available from local stock are:

• Plate: 2 to 25mm Thick – generally 3000mm x 1500mm but a range of PreCuts are also available
• Pipe: ½” to 6”nb Sched 40 – 6 mtr random lengths but also supplied cut to length
• Round Bar: 12mm to 250mm Dia
• Welding Consumables: TIG and MMA

Items outside this range are also supplied to customers specific requirements.