Super-Invar Super-Invar superalloy applications
Super-Invar Super-Invar/ Super-Nilvar/ Superieur/Inva
Alloys are also known as Super-Invar alloys. In the temperature range of -60~80 °C, its expansion coefficient is lower than that of 4J36 alloy, but the low temperature microstructure stability is worse than that of 4J36 alloy. This alloy is mainly used in the manufacture of instrument parts that require high dimensional precision within the ambient temperature variation range.
full name
Super-Invar alloy
overview
Similar grades
Russia United States Japan France
32HКД Super-Invar - Invar
32HК-BИ Super-Nilvar SI Superior
Technical standard for materials YB/T 5241-1993 "Technical conditions for low expansion alloys 4J32, 4J36, 4J38 and 4J40".
chemical composition
C≤0.05% P≤0.02% S≤0.02% Si≤0.2%
Mn=0.20~0.60% Cu=0.40~0.80% Co=3.2~4.2% Ni=31.5~33.0%
Fe = margin
Under the condition that the average expansion coefficient reaches the standard specification, the nickel content is allowed to deviate from the specified range in the above table.
Heat treatment system
The performance test specimen specified in the standard expansion coefficient and low temperature microstructure stability is processed and heat treated according to the following method: the semi-finished product specimen is heated to 840 °C± 10 °C, insulation is 1h, water quenching, and then the specimen is processed as a finished sample, in 315 °C± 10 °C insulation for 1h, with the furnace cold or air cooling.
Application overview and special requirements
The alloy is a typical low-expansion alloy that has been used for a long time by aviation plants and has stable performance. It is mainly used to manufacture precision parts with highly accurate dimensions within the range of ambient temperature variations. In use, the heat treatment process and processing technology should be strictly controlled, and its tissue stability should be strictly checked according to the use temperature.
Alloy microstructure
After the alloy is treated according to the heat treatment system specified in 1.5, and then the cold speed of -60 °C is 2h, martensitic structure should not appear. However, when the alloy composition is not appropriate, at room temperature or low temperature, different degrees of austenite (γ) to needle-like martensitic (α) will occur, and the phase change is accompanied by the volume expansion effect. The coefficient of expansion of the alloy is correspondingly increased. The main factor affecting the low temperature microstructure stability of the alloy is the chemical composition of the alloy. As can be seen from the Fe-Ni-Co ternary phase diagram, nickel is the main element of the stable γ phase. The high nickel content is conducive to the stability of the γ phase. Copper is also an important element in stabilizing the structure of the alloy. As the total deformation rate of the alloy increases, its structure becomes more stable. Segregation of alloy composition may also cause γ→α phase transitions in local areas. In addition, coarse grain size will also promote γ→α phase transition.
