Effect of heat treatment of preform on the mechanical properties of flow formed AISI 4130 Steel Tubes - a theoretical and experimental assessment

Flow forming is an advanced eco-friendly chipless metal forming process, which employs an incremental rotary point deformation technique. Flow forming offers a remarkable increase in tensile properties due to strain hardening and provides excellent dimensional accuracy and surface finish for the formed part. This paper presents the results of a study on the effect of heat treatment of preform material on the mechanical properties of the flow formed part and the validity of using empirical relations in predicting the properties of the flow formed components. The strength coefficient K and strain hardening exponent n of equation sigma = Kepsilon(n) are determined from stress-strain curves under different heat treatment conditions for AISI 4130 steel. The effect of cold work on mechanical properties of flow formed part for a given reduction in area (RA) is predicted using empirical relations published in literature. In order to validate the hypothesis of prediction of cold worked material properties after flow forming, a few flow forming experiments are carried out. The preform dimensions are worked out based on constant volume principle. A three pass flow forming sequence was followed and the properties are measured for about 88-90% thickness reduction. Comparison of the experimental results and the properties of the flow formed tubes predicted using empirical relations shows that empirical relations can be used for predicting the properties of flow formed tubes with reasonable accuracy. Preforms processed through hardening and tempering route give better performance. These results are used for design of performs for manufacturing of large number of high strength pressure vessels successfully. (C) 2002 Elsevier Science B.V. All rights reserved.