Utility Ferritics - Fabrication

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Thermal processing and fabrication

 

ANNEALING

Annealing is achieved by heating to between 700°C and 750°C for 90 minutes per 25mm thickness (3.5min/mm) followed by air cooling. Controlled atmospheres are recommended in order to avoid excessive oxidation of the surface.


STRESS RELIEVING

The utility ferritics can be stress relieved at 600°C to 650°C for 60 minutes per 25mm thickness (2.5min/mm). Stress relieving after welding is not normally required. Should this be necessary, temperatures between 200°C and 300°C are recommended.


HOT WORKING

The utility ferritics can be readily forged, upset and hot headed. Uniform heating of the steel in the range of 1 100°C to 1 200°C is required. The finishing temperature should not be below 800°C. Upsetting operations require a finishing temperature between 900°C and 950°C. Forgings should be air cooled.
All hot working operations should be followed by annealing and then pickling and passivating to restore the mechanical properties and corrosion resistance.

COLD WORKING

The utility ferritics have good formability, but severe draws may require intermediate annealing. Roll forming, press braking, bending and pressing can be readily applied, but loadings will be about 30% higher than for mild steel. The minimum inner bend radius is twice the plate thickness. The utility ferritics exhibit greater spring back than mild steel and this should be compensated for by slight over bending.


MACHINING

The utility ferritics have machining characteristics similar to U-430 (i.e. a machinability rating of 60 compared to mild steel of 100). The reduced extent of work hardening compared to austenitic stainless steels eliminates the need for special cutting tools and lubricants. Slow speeds and heavy feed rates with sufficient emulsion lubricant will help prevent machining problems.


WELDING

The utility ferritics have good weldability and are suited to most standard welding methods (MMA/SMAW, MIG/GMAW, TIG/GTAW, FCAW and PAW). They can be welded to other ferrous metals, for example mild and stainless steels, quite satisfactorily. The recommended grade of electrode is the AWS 309L type. It is important that this type of overalloyed consumable is used, rather than one which matches either of the base metals, in order to avoid martensite formation in the weld. When welding a utility ferritic to itself, E308L or E316L can also be used. The heat input should be controlled to between 0.5kJ/mm and 1.5kJ/mm per pass. The weld discolouration should be removed by pickling and passivating to restore maximum corrosion resistance.