Superalloy forging temperature and heating specification

Superalloy heating is carried out in two stages: preheating and heating.

In order to shorten the insulation time of superalloy at forging heating temperature and avoid excessive coarsening of grains and dilution of the alloy element, in order to reduce the thermal stress caused by poor thermal conductivity and large thermal expansion coefficient of superalloy, the blank should be preheated before forging.

The preheating temperature is 750~800℃, and the insulation time is calculated as 0.6~0.8min/ mm; the heating temperature is generally 1100~1180℃, and the insulation time is calculated at 0.4~0.8min/ mm.

Heating equipment can choose resistance furnace, with temperature measuring instrument and automatic adjustment temperature control device, for accurate control. When using the flame furnace, the sulfur content in the fuel should be strictly controlled: the sulfur content in diesel oil or heavy oil should be less than 0.5%, and the sulfur content in coal gas should be less than 0.7g / m ^ 3. When the sulfur content in the fuel is too much, when it penetrates into the blank surface, the Ni-Ni3S3 low melting point (650℃) co-crystal will form, making the alloy hot brittle.

In the heating of superalloy fine forging, little and no oxidation heating measures must be taken to avoid the dilution of chromium, aluminum, titanium and other elements produced on the surface of the blank, and reduce the fatigue strength and high temperature lasting strength of the alloy. Local induction heating can be used during pre-forging. Before heating, the blank shall be cleaned to remove dirt and avoid the formation of surface defects due to corrosion.

1. Forging temperature of iron-based and nickel-based superalloy

The forging temperature and heating specifications for iron-based and nickel-based superalloy are shown in the following below.

2. Example of the influence of deformation temperature on superalloy properties

The influence of forging temperature on tensile properties and stress fracture properties of GH 738 alloy as shown in the following below.

As can be seen from the figure, at the heat treatment temperature (solid solution: 996℃, 4h, oil quenching: stabilization: 843℃, 4h, air cooling; aging: 760℃, 16h, air cooling), the tensile strength index (room temperature and the forging temperature and the plasticity index increases; the stress fracture life at 732℃ and 517MPa can be greatly extended when the forging temperature increases to more than 1093℃, and maintain a stable level. Therefore, in order to make the GH738 alloy with good comprehensive mechanical properties, the forging temperature must be controlled accordingly.