Structural Features of Fatigue Crack Propagation of a Forging Die Made of Chromium–Molybdenum–Vanadium Tool Steel on Its Durability

Abstract

The paper presents the results of tests on a die insert made of non-standardised chrome-molybdenum–vanadium tool steel used during pre-forging, the life of which was 6000 forgings, while the average life for such tools is 8000 forgings. It was withdrawn from production due to intensive wear and premature breakage. In order to determine the causes of increased tool wear, a comprehensive analysis was carried out, including 3D scanning of the working surface; numerical simulations, with particular emphasis on cracking (according to the C-L criterion); and fractographic and microstructural tests. The results of numerical modelling in conjunction with the obtained results of structural tests allowed us to determine the causes of cracks in the working area of the die, which were caused by high cyclical thermal and mechanical loads and abrasive wear due to intensive flow of the forging material. It was found that the resulting fracture initiated as a multi-centric fatigue fracture continued to develop as a multifaceted brittle fracture with numerous secondary faults. Microscopic examinations allowed us to evaluate the wear mechanisms of the insert, which included plastic deformation and abrasive wear, as well as thermo-mechanical fatigue. As part of the work carried out, directions for further research were also proposed to improve the durability of the tested tool. In addition, the observed high tendency to cracking of the tool material used, based on impact tests and determination of the K1C fracture toughness factor, led to the proposal of an alternative material characterised by higher impact strength.

Effect of Metallic Coatings on the Wear Performance and Mechanism of 30CrMnSiNi2A Steel

“…The element analysis at a normal load of 150 N and a wear time of 20 min is shown in Figure 11 b. The microanalysis indicated that the wear was more severe, and intense plastic deformation occurred in the wear scars [ 38 , 39 ]. Fractures and deep furrows were visible in the wear scars.…”

The Role of the Distance between Fine Non-Metallic Oxide Inclusions on the Fatigue Strength of Low-Carbon Steel

“…The vast majority of works describing the impact of inclusions on steel durability analyze hard steels, most often bearing and tool steels (this is the same group of steels) [27][28][29][30][31][32]. In these steels, almost every brittle inclusion is a structural micro-notch, which is the focus of the crack.…”