Dura-Bar® Ni-Resist irons contain an austenitic matrix of approximately 10% alloy carbides. The austenitic structure is suitable for corrosive environments in sour well oils, salts, salt water acids and alkalis. The iron is relatively soft and chrome is added to produce carbides that help improve wear resistance. Ni-Resist is denser than gray or ductile irons and has a higher coefficient of thermal expansion. Dura-Bar® Type 1 Ni-Resist is manufactured to produce a material conforming to ASTM A436.
As-cast round bars are made to clean up at the nominal size. Additional stock is added to allow for out-of-round and normal imperfections in the as-cast surface. Stock allowance is a function of the bar diameter - see Stock Allowances for details. Other finishes available are Centerless Grinding and Centerless Turning, for demanding tolerance applications.
The microstructure will consist of Type VII, A, size 4-6 graphite as defined in ASTM A247. The matrix will be austenite with 5-10% alloy carbide. The edge or rim will contain Type D graphite, size 6-8. Chill carbides are less than 5% in any field at 100x and will be well dispersed.
Austenitic alloys cannot be hardened by heat treatment. They may be softened and homogenized by heating to 1800-1900° F (980-1040° C) for three to five hours and air-cooling. This breaks down some of the carbides and most of those remaining will be spheroidized. Anneal softens the material without detrimental effect on the strength properties. Type 1 Ni-Resist should not be used in applications involving service above 1300° F (430° C).
|Silicon||1.00 - 2.80%|
|Manganese||0.50 - 1.50%|
|Nickel||13.50 -17.50% Max|
|Copper||5.50 - 7.50%|
|Chromium||1.50 - 2.50%|
|Tensile Strength (PSI)*||20,000|
|Brinell Hardness (BHN) **||131 Min/183 Max|
* The tensile strength will be approximately 25,000 psi for bars up to 3.00" diameter and 20,000 psi for bars larger than 3.00". Tensile strength tests in bars 1.750" and smaller may not be accurate because of thermal center micro shrinkage.
** Brinell hardness values for nominal as-cast diameters are shown in the table. Hardness properties listed are minimum, maximum across the bar. Hardness values for rectangles and squares are a function of the height and width ratios and will be supplied on request. BHN in the center of bars 1.750" and smaller may be lower than the values shown because of thermal center micro shrinkage.