2-296. SURFACE TREATMENTS FOR CORROSION AND HEAT-RESISTING STEELS AND ALLOYS . Normally the corrosion-
resisting and heat resisting alloys are unplated unless a coating is necessary to minimize the effect of dissimilar metal contacts.
When a plating is required it shall be in accordance with specification MIL-S-5002A or other approved technical engineering data.
Where a plating is required, steel parts plated with hard coating, such as nickel and chromium or combinations thereof, shall be
processed as follows in accordance with MIL-S-5002A):
a. Plated parts below Rockwell C40 hardness and subject to static loads or designed for limited life under dynamic loads, or
combinations thereof, need not be shot peened prior to plating or baked after plating.
b. Plated parts below Rockwell C40 hardness which are designed for unlimited life under dynamic loads shall be shot
peened in accordance with specification MIL-S-13165 prior to plating. Unless otherwise specified, the shot peening shall be
accomplished on all surfaces for which the coating is required and on all immediately adjacent surfaces when they contain notches,
fillets or other abrupt changes of section size where stresses will be concentrated.
c. Plated parts which have a hardness of Rockwell C40, or above, and are subject to static loads or designed for limited life
under dynamic loads or combination thereof, shall be baked at 375° 25°F for not less than three (3) hours after plating.
d. Plated parts which have a hardness of Rockwell C40, or above, and are designed for unlimited life under dynamic loads,
shall be shot peened in accordance with specification MIL-S-13165 prior to plating. Unless otherwise specified, the shot peening
shall be accomplished on all surfaces for which the coating is required and all immediately adjacent surfaces when they contain
notches, fillets, or other abrupt changes of section size where stresses will be concentrated. After plating, the parts shall be baked it
375° 25°F for not less than three (3) hours.
2-297. PASSIVATION OF STAINLESS STEELS . The stainless steels are usually passivated after fabricating into parts to remove
surface contaminates, which may cause discoloration or corrosive attack after the parts are placed in use. The process is primarily a
cleaning operation which removes the contamination and speeds up the formation of the protective (invisible) oxide film which would
occur naturally but slower in the presence of oxygen in abnormal atmosphere. The protective film formation is inherent with the
stainless steels in normal air when they are clean.
2-298. The foreign materials are removed from stainless to provide for uniform surface contact with oxidizing agents (Air or Acid)
which forms the protective film or passive surface. In this case after the film has formed the material is placed in a condition
approaching that of maximum corrosion resistance. Any areas to which oxygen contact is prevented by contaminants or other means
tends to remain activated and subject to corrosion attack.
2-299. Prior to accomplishing the passivation treatments the parts shall be cleaned, all grease, oil, wax, which might contaminate the
passivation solution and be a detriment to the passivation treatment shall be removed. Surfaces will be considered sufficiently clean
when a wetted surface is free of water breaks. After cleaning the parts will be passivated by immersing in a solution of 20-25%
(Volume) nitric acid (Sp.gr 1.4A2) plus 1.5-2.5% (Weight) sodiumdichromate with process times and temperatures as follows:
CAUTION Excessive time shall not be used, as damage to parts may occur. In addition the times and temperatures shall be
selected according to the alloy involved.
TYPES OF PROCESS
For parts made of ferritic or austenitic stainless use process Type I, II or III. For parts made of martensitic stainless steel, use
process Type II or III. Within 15 minutes after above treatment, thoroughly rinse in hot water (140°F-160°F). Within 1 hour after hot
water rinse, immerse in an agueous solution containing 4-6% sodium dichromate (by weight) at 140-160°F for 30 minutes, and rinse
thoroughly with water and dry.
After the parts are passivated they shall be handled the minimum necessary consistent with packaging,
assembly/installation. Parts for installations in high temperature areas shall not be handled with bare
hands because finger prints will cause carburization and pitting of surface when heated.