Design of a small-scale hot forging test

Abstract

Small scale material testing offers many advantages compared to large or full scale testing. Small scale tests are usually simpler and quicker to perform than full scale tests, and as a consequence they are cost-effective - the concomitant speed of screening has implications for product commercialization (notably the time to market and the time in market). However, in order to make sure that small scale tests produce relevant information for the full scale process, it should always be demonstrated that the material is exposed to thermo-mechanical and environmental conditions similar to those of the full scale process. The objective of the work described in this article has been to demonstrate the feasibility of miniaturizing a hot forging process. In the original full scale process, a medium carbon steel pipe with Outer Diameter (OD) of 200 mm and wall thickness of 12 mm is heated locally by high-frequency induction heating coil before being forged to a plastic strain of approximately 1 and subsequently cooled in air. In the small scale test, specimens with OD 12 mm and wall thickness 3 mm are heated in a similar way by induction heating coil and forged. The heating and cooling rates (as well as gaseous environment) are controlled in order to carefully recreate the temperature history of the full scale test. Finite element simulations of heating, forging and cooling phases clearly demonstrate how to design the small scale test. If the specimen is heated by an induction coil during the cooling phase, it is possible to compensate the greater heat losses to the surroundings experienced by the small scale specimen.