Tribological Behavior of Tool Steel Under Press Hardening Conditions Using Simulative Tests

Abstract

Press hardening is employed in the automotive industry to produce advanced high-strength steel components for safety and structural applications. This hot forming process depends on friction as it controls the deformation of the sheet. However, friction is also associated with wear of the forming tools. Tool wear is a critical issue when it comes to the dimensional accuracy of the produced components and it reduces the service life of the tool. It is therefore desirable to enhance the durability of the tools by studying the influence of high contact pressures, cyclic thermal loading, and repetitive mechanical loading on tool wear. This is difficult to achieve in conventional tribological testing devices. Therefore, the tribological behavior of tool–workpiece material pairs at elevated temperatures was studied in a newly developed experimental setup simulating the conditions prevalent during interaction of the hot sheet with the tool surface. Uncoated 22MnB5 steel and aluminum–silicon (Al–Si)-coated 22MnB5 steel were tested at 750 °C and 920 °C, respectively. It was found that higher loads led to lower and more stable friction coefficients independent of sliding velocity or surface material. The influence of sliding velocity on the coefficient of friction was only marginal. In the case of Al–Si-coated 22MnB5, the friction coefficient was generally higher and unstable due to transfer of Al–Si coating material to the tool. Adhesion was the main wear mechanism in the case of uncoated 22MnB5.

High Temperature Friction and Wear Performance of PVD Coatings under Press Hardening Contact Conditions

“…In this work, we followed the experimental methods described in detail by Mozgovoy et al (2017) in [6]. This section gives an overview of the used materials and specimen geometries as well as the employed experimental equipment and followed test procedure.…”

“…In this study, the base materials and specimen geometries were the same as employed by Mozgovoy et al (2017) [6]. The chemical compositions of the different materials used in the current work are summarised in Table 1.…”

“…For high-temperature friction and wear studies, the hot strip tribometer described in more detail by Mozgovoy et al (2017) in [6] was used to investigate the tribological characteristics of hard coated tool-22MnB5 work piece strip material pairs. The custom-built hot strip tribometer consists of hydraulically actuated clamping jaws that secure the work piece strip.…”

“…Procedure. The experimental method described in [6] by Mozgovoy et al (2017) was followed in this work. First, the tool pin specimens were cleaned in an ultrasonic cleaner is the normal force, is the friction force, is the pretension force, is the temperature of the work piece, V is the velocity and is the sliding distance per work piece strip.…”

“…The motivation for conducting the present study is mainly in view of evaluating hard PVD coatings under contact conditions prevalent in the press hardening process regarding their tribological performance. In a previous work, we investigated the influence of sliding velocity, normal load, and work piece surface material (uncoated or Al-Si coated 22MnB5 steel) on the tribological behaviour of plain quenched and tempered tool steel [6]. The mechanisms behind material transfer occurring at elevated temperatures need to be fully understood in order to develop strategies to prevent material transfer from the work piece to the forming tool.…”