Microstructural evolution and microhardness response of H11 hot forging dies

Abstract

Purpose The prime task of research in hot forging industry is to improve the service life of forging dies. The in-service microstructural changes that may occur in a die during hot forging is expected to significantly affect the service life. The purpose of this work is to analyse the microstructural evolution of double tempered hot forging dies in a real industrial environment, and the correlation of microstructural and microhardness evolution to the in-service wear and plastic deformation. Design/methodology/approach Specific hot forging tests were carried out on double tempered AISI H11 chromium tool steel for 100, 500 and 1,000 forging strokes. Macro analysis was conducted on die cross section to analyse the wear and plastic deformation at different stages of forging cycles. Microhardness and microstructural analyses were performed on the die surface after these forging tests. Findings The macro analysis on the transverse section of dies shows that wear is predominant during initial forging strokes, whereas plastic deformation is observed in later stages. Microstructural analyses demonstrate that during first 500 forging cycles, carbide population decreases at 63 per cent higher rate as compared to corresponding drop during 501 to 1,000 forging cycles. Additionally, the carbide size increases at all stages of forging cycle. Further, microstructural images from dies after 1,000 forging strokes show clustering and spherodisation of carbides by which the “blocky”-shaped carbides in pre-forging samples had spherodised to form “elongated spherical” structures. Practical implications The findings of this work can be used in hot forging industries to predict amount of wear and plastic deformation at different stages of service. From the results of this work, the service life of double tempered H11 hot forging dies used in forging without lubrication is within 501 to 1,000 forgings. Originality/value Most of the literatures are focussed on the cyclic softening of material at constant temperature. This work analyses the microstructural evolution of double tempered hot forging dies in a real industrial environment and correlates the microstructural and microhardness evolution to the in-service wear and plastic deformation.

Sensitivity analysis of the artificial neural networks in a system for durability prediction of forging tools to forgings made of C45 steel

“…Hence, thoroughly analysing the wear of forging tools and predicting their life is a very important issue and a huge challenge for technologists, tool designers, process engineers and forging companies, as well as many research centres [9,10]. Numerous studies described in the technical literature are devoted, on the one hand, to research works which make it possible to increase the tool life by various techniques of surface engineering [11][12][13][14][15][16] and, on the other, to improvements of the technical and technological process parameters [17], optimization of the tool shape [18], conversion of the tool material to a material more resistant to the effect of destructive mechanisms [19,20], or implementation of proper heat treatment [21].…”