Temperature and Processing Guidelines for Hastelloy Alloys C22, C276, and Others

In the Hastelloy corrosion-resistant alloy series, most alloys can be hot worked to form various product shapes. However, compared to stainless steel, these alloys are more sensitive to changes in strain and strain rates and have a relatively narrow temperature range for hot working.

To achieve the best performance from these alloys, careful processing is required. Certain characteristics of Hastelloy alloys must be considered during hot working, including their relatively low melting point, high high-temperature strength, sensitivity to strain rates, low thermal conductivity, and relatively high work-hardening coefficient. Additionally, within the hot working temperature range, the strength of the alloy increases rapidly as the temperature decreases. Due to these characteristics, ASTM alloy guidelines suggest using relatively moderate degrees of deformation in each processing step and frequent reheating. Moreover, relatively slow hot deformation helps achieve higher quality products by requiring less force and keeping heat accumulation within reasonable limits.

Here are the basic guidelines for forging Hastelloy corrosion-resistant alloys:

1. Hold the entire forging at the forging temperature for 0.5 hours per inch of thickness.

2. Rotate the billet frequently to expose the cooler sections to the furnace air. Avoid direct contact between the alloy and open flames.

3. Begin forging immediately after removing the alloy from the furnace, as the temperature can drop by 38°C-93°C in a short time. It is not recommended to increase the forging temperature to compensate for heat loss, as this can lead to melting.

4. Larger reduction rates (25%-40%) can retain heat as much as possible, thereby minimizing grain size and reducing the number of heating cycles. The reduction rate per operation should not exceed 40%.

5. Avoid sudden changes in cross-sectional shape during the initial forming stage, such as transitioning directly from square to round. It is better to transition from square to rounded square or polygon before achieving a round shape.

6. Remove all cracks or fissures produced during the forging process.