Product Description

Introduction
 
***5 is the most widely used duplex (ferritic/austenitic) stainless steel grade. It finds applications due to both excellent corrosion resistance and high strength.
 
The standard S****3 composition has over the years been refined by many steel suppliers, and the resulting restricted composition range was endorsed as UNS S****5 in ***6. S****5 gives better guaranteed corrosion resistance, but much of the S****3 currently produced also complies with S****5.
 
***5 is not generally suitable for use at temperatures above **0°C as it suffers from precipitation of brittle micro-constituents, nor below **0°C because of its ductile-to-brittle-transition.
Corrosion Resistance
 
***5 possesses excellent general corrosion resistance; superior to Grade **6 in most environments. Excellent resistance to localised corrosion including intergranular, pitting and crevice corrosion; the CPT of ***5 is generally at least *5°C. The grade is also resistant to chloride stress corrosion cracking (SCC) at temperatures of up to about **0°C. Grade ***5 will often perform well in environments which cause premature failure of austenitic grades. It has better resistance to sea water than grade **6. Consult our Technical Assistance for specific environmental recommendations.
 
Heat Resistance
 
Although ***5 has good high temperature oxidation resistance this grade, like other duplex stainless steels, suffers from embrittlement if held for even short times at temperatures above **0°C. If embrittled this can only be rectified by a full solution annealing treatment. Duplex stainless steels are almost never used above **0°C.
 
Conditions of Supply Finish, Dimensions and Tolerances
Surface Finish
 
Round bar up to *5.4mm diameter is all cold drawn. Round bars over *5.4 and up to **7.*0mm diameter are smooth-turned and polished. Round bars over **7.*0mm diameter are all peeled.
 
All hexagon bar and all square bar is cold drawn.
 
Diameter and A/F tolerances
 
Round Bar: Cold drawn h9; Smooth-turned and Polished h*0; Peeled up to **0mm k*2; Peeled over **0mm *1.5mm/*0; Centreless ground h9 or h8
Square Bar: h*1; Hex Bar: h*1.
 
Straightness Maximum deviation from a straight line
 
Round Bar: 1.5mm in ***0mm and may not exceed: 1.5mm x length in mm / ***0mm
 
Squares and Hexagon: 1.5mm in ***0mm and may not exceed: 1.5mm x length in mm / ***0mm
Other tolerances may be supplied for more critical applications upon enquiry.
 
Processing
 
The high strength that makes ***5 useful in many applications also reduces its machinability. The high work-hardening rate further decreases the machinability of ***5. Cutting speeds are approximately *0% slower than for a standard grade **4.
 
The high strength of ***5 also makes bending and forming more difficult; these operations will require larger capacity equipment than would be required for austenitic stainless steels. The ductility of ***5 is less than that of an austenitic grade (but is not low when compared to most other structural materials), so severe forming operations, such as cold heading, are not generally possible. If severe cold working is required it is recommended that intermediate annealing be carried out.
 
Welding
 
Weldable by all standard methods, but should not generally be welded without filler metal as this may result in excessive ferrite. AS ***4.6 pre-qualifies welding of ***5 with ***9 rods or electrodes to ensure that deposited metal has the correctly balanced duplex structure. Nitrogen added to the shielding gas will also assist in ensuring adequate austenite in the structure. Heat must be kept low and no pre- or post-heat should be used. The lower co-efficient of thermal expansion of all duplex stainless steels compared with austenitic grades reduces distortion and associated stresses.
 
Applications of ***5
 
Chemical processing, transport and storage. Oil and gas exploration and processing equipment. Marine and other high chloride environments. Pulp & Paper digesters, liquor tanks and paper machines.

Duplex ***5 Stainless Steel is a nitrogen-enhanced duplex used in applications requiring high strength and excellent corrosion resistance. It is designed to combine improved resistance to stress corrosion cracking, pitting and crevice corrosion. Duplex ***5 provides nearly double the corrosion resistance typical in other austenitic stainless steels.