Influence of the grade of hot work tool steels and its microstructural features on the durability of punches used in the closed die precision forging of valve forgings made of nickel-chrome steel

• Published in: Wear 2023-09, Vol.528-529, p.204963, Article 204963
• Main Authors: Hawryluk, Marek, Lachowicz, Marzena, Zwierzchowski, Maciej, Janik, Marta, Gronostajski, Zbigniew, Filipiak, Jarosław
• Format: Article
• Language: English
• Subjects: Carbide banding; Durability of forging tools; Plastic deformation and triboxidation; Precision forging of valve; Scratch and ball on disc tests; Wear
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2023.204963

The work concerns research related to the assessment of the influence of the impact of the steel grade used for forging punches in terms of the durability of tools used in the precision forging process in closed dies of a chrome-nickel steel valve forging. The tests were carried out on post-service punches, showed microstructural differences in the intensity of carbide precipitations banging. Two of them were made of a materials showing carbide banding (W360 after ESR; 1.2365), which achieved average durability at the level of: 2400 and 1200 forgings. The other two were without clear carbide banding (Unimax after ESR; 1.2344). They also had much lower durability at the level of: 700 and 200 forgings. Tests of post-service punches were carried out in order to assess the mechanism of their destruction. They were supplemented with hardness measurements. The dominating mechanism of their wear was the loss of properties of the surface layer. The decrease in hardness and plastic deformation of the material resulted in increase of the punches wear rate. As part of laboratory tests, scratch-tests and abrasion wear tests on a “ball on disc” tribotester at elevated temperatures (above 400 °C, i.e. contact temperature: tool-forging) were carried out. The obtained test results showed that punches made of materials with distinct banding, compared to materials with evenly spaced carbide clusters, are characterized by better resistance to the destructive mechanisms prevailing in hot forging processes. [Display omitted] •The surface plastic deformation and triboxidation affect the wear of the tool material.•Finely dispersed carbide bands parallel to the punch axis can have a positive effect on tool life.•The formation of an oxide film on the wear surface can increase the material wear resistance.•The tribo-oxide layer on the surface of the tool preventstempering of its surface.