4J32(Super-Invar)

1. Introduction to 4J32 materials

4J32 alloy is also called Super-Invar alloy. In the temperature range of -60-80℃, its expansion coefficient is lower than that of 4J36 alloy, but its low-temperature structure stability is worse than that of 4J36 alloy. This alloy is mainly used to manufacture highly precise instrument parts required to size within ambient temperature variation range.

2. Technical standards for 4J32 materials
YB/T 5241-1993 “Technical Conditions for Low-Expansion Alloys 4J32, 4J36, 4J38 and 4J40”.

The performance test samples for the expansion coefficient and low-temperature tissue stability specified in the 4J32 heat treatment system standard are processed and heat treated according to the following methods: Heat the semi-finished sample to 840℃±10℃, insulated for 1 h, water quenched, and then process the sample into a finished sample, insulated at 315℃±10℃ for 1 h, and cooled with the furnace or air.
4J32 varieties specifications and supply conditions include rods, tubes, plates, silk and belts.
4J32 smelting and casting process uses non-vacuum induction furnaces, vacuum induction furnaces and arc furnaces.
4J32 Application Overview and Special Requirements This alloy is a typical low-expansion alloy, and has been used for a long time in aviation factories and has stable performance. It is mainly used to manufacture precision components with highly accurate dimensions within the ambient temperature range. During use, the heat treatment process and processing process should be strictly controlled, and the tissue stability should be strictly checked according to the use temperature.

3. 4J32 physical properties

4J32 melting temperature range is 1430~1450℃[1,2].
4J32 thermal conductivity λ=13.9W/(m•℃)[1,2].
The standard for linear expansion coefficient of 4J32 stipulates that α1 (20~100℃) is ≤1.0×10-6℃-1[5].
Like 4J36 alloy, the 4J32 alloy has the highest linear expansion coefficient value when annealed above 850 ℃. Fast cooling speed can reduce the linear expansion coefficient. For α1 (room temperature ~ 100°C), quenching (fast cooling rate) can be reduced by nearly half compared to annealing.

4. 4J32 special handling system

The performance test samples for the expansion coefficient and low-temperature tissue stability specified by the standard are processed and heated according to the following methods: Heat the semi-finished sample to 840℃±10℃, insulated for 1 h, water quenched, and then process the sample into a finished sample, insulated at 315℃±10℃ for 1 h, and cooled with the furnace or air.

4J32 application profile and special requirements

This alloy is a typical low-expansion alloy, and has been used for a long time in aviation factories and has stable performance. It is mainly used to manufacture precision components with highly accurate dimensions within the ambient temperature range. During use, the heat treatment process and processing process should be strictly controlled, and the tissue stability should be strictly checked according to the use temperature.

4J32 alloy structure:

After the 4J32 inwa alloy is treated according to the heat treatment system specified in 1.5, and then the cooling speed is 2h at -60℃, martensite structure should not appear. However, when the alloy composition is not right, different degrees of austenite (γ) will undergo a transformation to acicular martensite (α) at ​​room temperature or low temperature, and the phase change will be accompanied by a volume expansion effect. The expansion coefficient of the alloy increases accordingly. The main factor affecting the stability of the alloy’s low-temperature structure 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 gamma phase. A high nickel content is conducive to the stability of the gamma phase. Copper is also an important element in stabilizing alloy structure. As the total deformation rate of the alloy increases, its structure tends to be more stable. Alloy composition segregation may also cause γ→α phase change in local areas. In addition, coarse grains will also promote the phase transition of γ→α.

4J32 welding performance alloys can be welded by brazing, fusion welding, resistance welding and other methods. Since the expansion coefficient is related to the chemical composition, changes in the alloy composition should be avoided as much as possible, so it is best to use argon arc welding.
4J32 parts heat treatment process heat treatment can be divided into: stress removal annealing, intermediate annealing and stabilization treatment.
(1) Stress elimination annealing To eliminate the residual stress after mechanical processing of parts, stress elimination annealing must be performed: 530~550 ℃, insulation for 1~2h, and furnace cooling.
(2) Intermediate annealing is to eliminate the process hardening of the alloy during cold rolling, cold drawing and cold stamping to facilitate continued processing. Heat the workpiece to 830-880 ℃, keep the heat for 30 minutes, and the furnace is cooled or air-cooled.
(3) The stabilization treatment can achieve a lower expansion coefficient and stabilize its performance. Generally, three-stage treatment is used.
a) Homogenization: During heating, the impurities in the alloy are sufficiently dissolved and the alloying elements tend to be uniform. The workpiece is heated to 830 °C in a protective atmosphere, kept in heat for 20 minutes to 1 h, and quenched.
b) Tempering: During the tempering process, the stress generated by quenching can be partially eliminated. Heat the workpiece to 315 ℃, keep it in heat for 1 to 4 hours, and the furnace is cooled.
c) Stabilization aging: stabilize the dimensions of the alloy. The workpiece is heated to 95 ℃ and kept in heat for 48 hours.
When high-temperature treatment is not suitable for high-temperature treatment, the following stress-removing and stabilization treatment can be used: the workpiece is heated to 315-370 ℃, 1-4h.
The alloy cannot be hardened by heat treatment.
4J32 surface treatment process The surface treatment can be sandblasted, polished or pickled. The alloy can be pickled at 70°C with 25% hydrochloric acid solution to remove the scale.
4J32 cutting and grinding properties The cutting and processing characteristics of this alloy are similar to those of austenitic stainless steel. High-speed steel or carbide cutting tools are used for processing, and low-speed cutting and processing. Coolant can be used when cutting. The alloy has good grinding performance.

5. 4J32 application fields

4J32 is a typical low-expansion alloy, and has been used for a long time in aviation factories and has stable performance. It is mainly used to manufacture precision components with highly accurate dimensions within the ambient temperature range. During use, the heat treatment process and processing process should be strictly controlled, and the tissue stability should be strictly checked according to the use temperature.