Page 3 - SH 253

Due to its thin compact adhesive superficial protective film, SH 253 grade
reduces pick up of carbon when oxygen level in the gases is sufficient to form a
protective film.

 Nitriding atmospheres - Nitrogen pick-up at high temperature in furnaces using
cracked amonia or N 2 /H 2 mixtures as protective gases, may result in severe
embrittlement problems particularly in reducing atmospheres. For such
applications, nickel based alloys containing chromium and silicon additions
(Sirius 800 or 600 grades) are prefered.

In mixed gases containing enough oxygen to form a protective oxide superficial
layer on SH 253, the pick-up of nitrogen is delayed. In that case, Alloy SH 253 has
improved properties compared to other stainless steels due to the specific
properties of its oxIde superficial layer.

PROCESSING Hot forming
Hot forming should be carried out in a temperature range of 1150°C-900°C (2102-
1652°F) after the piece has been uniformely heated. Final full annealing heat

treatment at 1020-1090°C (1868-1994°F) may be performed. Quenched annealing
heat treatment is nevertheless not generally required since the material is
designed for high temperature applications.

Cold forming

SH 253 grade can be cold formed without any problem. Its austenitic
microstructure makes the alloy very ductile. The high nitrogen additions increase
the mechanical properties. This explains why more strength is generally needed
compared to standard austenitic grade. Long term high temperature service may

reduce the ductility of the steel. Cold worked and aged structures may require a
preliminary solution annealing heat treatment to restore the ductility of the steel.

Pickling

Residual high temperature oxides improve the resistance of the steel to scaling. If
the oxides must be removed, use sand blasting or controlled pickling solutions.
Don't use strong pickling paste or solution even to clean up the welds due to
possible intergranular corrosion.

WELDING SH 253 grade is easily welded by following processes

 GTA (TIG) welding - both normal and automatic
 GMA (MIG) welding  Plasma welding or SMAW

Use SH 253 type products or as an alternative 309 type products. Nickel based
filler materials containing Nb additions are not recommended since intermetallic
intergranular precipitations may occur at fusion line.

The SH 253 alloy is less sensitive to hot cracking phenomena than high nickel heat
resistant steels. No pre or post welding heat treatments are required. Limit
interpass temperature to 150°C (302°F). If necessary, stress relieve in the 900-
1000°C (1652-1832°F) temperature range.

Usual precautions for stainless steels welds including cleaning and degreasing of
weld areas, protection against weld spatters must be taken. Grind the start and
finish of each filler pass before to start with the next filler pass. Mechanical
methods, including fine grinding and polishing, will be prefered to pickling to
remove oxide, slag, incrustations, heat tints or other surface contaminations.
Strong pickling pastes should be avoided since the alloy is susceptible to
intergranular corrosion in the as welded condition.