Dynamic Flowform Corporation of Billerica, Massachusetts, USA, has been successfully flowforming Inconel 718 for many years. Flowforming is a cold forming process for the production of seamless, dimensionally precise tubular components. Beside offering lower cost alternatives to machining from solid bar, due to the cold working of the material, the microstructure of flowformed products are superior to that of bar or sheet.

After flowforming, shafts with a wall-thickness of 0.098” were given a standard solution heat treatment (at a temperature of 1750° F) and a two-step precipitation or aging heat treatment. Flat-type tensile specimens having the curvature of the tube were prepared from a representative piece. The results from these tests are as follows.

PROPERTIES OF FLOWFORMED INCO 718 AFTER SOLUTION & AGING HEAT TREATMENT

MICROSTRUCTURES BEFORE AND AFTER FLOWFORMING
Figure 1: Preform 100X etched	Figure 2: Flowformed 100X etched	Figure 3: Flowformed 700X etched

A typical microstructure of Inconel 718 AMS 5662 is shown in Figure 1. The specimen was etched in Kallings’ (non-water containing) etching solution by immersion for 5 minutes. The grain sizes range from ASTM 5.5 – 6.

The microstructure of flowformed Inconel 718 after a full heat treatment is shown in Figures 2 and 3. The specimen was electrolytically etched in a solution of 50% hydrochloric acid, 50% water plus a few drops of hydrogen peroxide for 30 seconds at 6 volts. The grain sizes range from ASTM 11 - 12.

It is noteworthy that micro structural examination of specimens from this and other parts reveals no evidence of internal cracking, galling or tearing of the metal from the flowforming process. Typical surface finishes are 8 micro inch on the ID and 16 on the OD.