Cast iron MN
Designation
| Name |
The value |
| Designation GOST Cyrillic |
МН |
| Designation GOST Latin |
MH |
| Transliteration |
MN |
| The chemical elements |
MoН |
Description
Cast iron MN is used: for the production of castings for aircraft.
Note
High-strength cast iron with spherical graphite pearlitic class.
Standards
| Name |
Code |
Standards |
| Castings with special properties (cast iron and steel) |
В83 |
OST 1 90077-72 |
Chemical composition
| Standard |
C |
S |
P |
Mn |
Si |
Ni |
Fe |
Mg |
| OST 1 90077-72 |
3-3.6 |
≤0.03 |
≤0.15 |
0.6-1.5 |
2-3.4 |
≤2 |
The rest |
0.03-0.08 |
Fe is the basis.
According to OST 1 90077-72, with the following mechanical properties and microstructure satisfactory, the following deviations in chemical composition are acceptable: for carbon ± 0.10%, for chromium, silicon, molybdenum, nickel and copper + 0.2% for each.
Mechanical characteristics
| σB, MPa |
d5, % |
Brinell hardness number, MPa |
| Castings on OST 1 90077-72 |
| ≥490 |
≥2 |
170-320 |
Description mechanical marks
| Name |
Description |
| σB |
Limit short-term strength |
| d5 |
Elongation after rupture |
Technological properties
| Name |
The value |
| Macrostructure and contamination |
The appearance of the fracture of castings on OST 1 90077-72 should be dense, fine-grained, light-gray, with no signs of chill. Surface of castings shall be cleaned of sand and metal penetration. Sprues, heaving, bays, growths and veining must be cut or polished by abrasive material in the tolerances on the drawing. Nikitina, crack and end-to-end sinks are not allowed. |
| Microstructure |
According to OST 1 90077-72 microstructure of castings shall consist of spherical graphite of various sizes. Allowed the presence of lamellar graphite in a small quantity, providing the required mechanical properties. The bulk of the cast should consist of sarbatoarea and lamellar pearlite. Presence of ferrite in the field of cone up to 40%. |
| Features of heat treatment |
According to OST 1 90077-72 heat treatment of castings of high-strength cast iron with spherical graphite is made depending on the specific purpose of casting. Casting antifriction purposes, as a rule, the heat treatment is not exposed, and to reduce the hardness of the castings are subjected to heat treatment regime: aging at a temperature of 650°C for 3.0 and 5.0 hours with subsequent cooling in air. Casting for structural purpose are heat-treated to improve mechanical properties (mainly ductility) in the following regime: the iron brand MN pearlitic structure of the casting is subjected to normalization (heating to 850-960°C, exposure to 2.5 and 5.0 hours, air cooling). If the results of testing of mechanical properties does not satisfy the requirements of the standard, it is allowed to re-heat treatment. |
