Monel 400 alloy is a nickel-copper solid solution alloy that can
be hardened only by cold working. It has high resistance to various types of
corrosion. This alloy is strong over a wide range of temperatures. Monel 400
alloy can be readily joined and fabricated. Finished fabrications can be
produced to a wide range of mechanical properties by proper control of the
amount of hot or cold work and by the selection of appropriate thermal
treatments.
The material remains bright and free from discoloration when heated
and cooled in a reducing atmosphere or quenched in an alcohol-water solution.
Rate of cooling will not have any significant effect and this alloy will form
an adherent oxide film if allowed to cool in air after heating. Both
cold-worked and hot-worked Monel 400 alloy needs thermal treatment to develop
the optimum combination of strength and ductility and to minimize distortion
during subsequent machining. Stress equalizing of cold-worked material causes
an increase in the yield strength of 0.00% offset without marked effects on
other properties. Stress equalizing is performed by holding for about 3 hour at
a temperature of 575°F. Stress relieving can reduce stresses without producing
a recrystallized grain structure. This treatment is recommended to achieve
minimum “walking” or distortion after metal removal. Heating for 1 to 2 hour at
1000°F to 1050°F relieves strains in either hot or cold-worked products. Stress
relief that is holding at 1000°F-1200°F for 1 hour followed by slow cooling is
strongly recommended as a precaution against stress-corrosion cracking in
certain environments. Stress relieving slightly decreases tensile strength,
hardness, yield strength and it slightly increases elongation.
Annealing can completely soften work-hardened material. Time and
temperature needed depend on the amount of previous cold work. Monel 400 alloy
is generally annealed by the open heating method by holding at 1600°F to 1800°F
for 2-10 min, whereas box annealing is performed suitably at 1400°F to 1500°F
for 1-3 hour at temperature. The effects of heating on properties of cold-drawn
and hot-rolled material are compared. In three tests, the cold-drawn rod
developed an annealed temper after 3 hours at temperature of 1300°F, and the
hot-rolled plate, after 3 hours at about 1470°F. Grain growth occurs when
material is heated in the upper portion of the annealing temperature range.
Pickling produces bright and clean surfaces on this alloy and this
alloy is readily fabricated by standard processes. Monel 400 alloy is softer than many steels with respect to its
resistance to hot deformation therefore it can be hot-formed into almost any
shape. It is essential to use proper temperature during hot forming and that
range is 1200°F to 2150°F. Suitable metal temperature for heavy reductions is
1700°F to 2150°F and light reductions can be taken down to 1200°F. Highermechanical properties of Monel 400 wire and smaller grain size are produced by working at lower
temperatures.
Prolonged soaking at hot-working temperatures is detrimental and
if a delay occurs during processing, the furnace should be cut back to 1900°F
and not brought to temperature until operations are resumed. This alloy should
not be heated above 2150°F otherwise permanent damage can occur. Heavy forging
should not be carried out so quickly that the metal becomes overheated from
working. An optical pyrometer is recommended for use.
No comments:
Post a Comment