Materials Testing for Cold Forging

Abstract

The article describes a series of experiments, and some associated theoretical work, which should assist in assessing the suitability of certain steels designated for cold forging operations. The compression of a circular cylinder is often used to assess the cold forgeability, but with ductile materials the test can result in excessively high loads before surface cracking occurs. Some alternative upsetting procedures are described and the so-called collar test is recommended when studying the upsetting of ductile materials. Information is presented herein which indicates that a single fracture line, in the manner of Kuhn, is not applicable for a variety of steels when different upsetting tests are compared. The hoop, εθ, and axial, εz, strain history at the free surface of an upset specimen is employed to obtain the associated stress history using simple plasticity theory. Three distinct upsetting tests are analyzed using a finite element method and the predictions of the surface strains compare well with experimental data. The behavior of AISI 1045 and 1144 steels in the collar test is also examined. The steels were subjected to three different heat treatments, and the effect of composition and thermal processing on the fracture behavior is discussed.