High-Temperature Oxidation Behaviour of AISI H11 Tool Steel

Abstract

The high-temperature oxidation of hot-work tool steel AISI H11 was studied. The high-temperature oxidation was investigated in two conditions, the soft annealed condition, and the hardened and tempered condition. First, calculations of the compositions of the oxide layers formed were carried out using the CALPHAD method. The samples were oxidised in a chamber furnace and in a simultaneous thermal analysis instrument, for 100 h in the temperature range between 400 °C and 700 °C. The first samples were used for metallographic (optical microscopy and scanning electron microscopy) and X-ray diffraction analysis of the formed oxide layers, and the second ones for the analysis of the oxidation kinetics by thermogravimetric analysis. Equations describing the high-temperature oxidation kinetics were derived. The kinetics can be described by three mathematical functions, namely: exponential, parabolic, and cubic. However, which function best describes the kinetics depends on the oxidation temperature and the thermal condition of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. The oxide layers consist of three sublayers, the inner one being spinel-like oxide (Fe, Cr)3O4, the middle one a mixture of magnetite and hematite and the outer one of hematite. At 700 °C there is also some wüstite in the inner oxide sublayer of the soft annealed sample.

High-Temperature Behavior of Metals

“…A first contribution dealing with microstructure evolution at high temperature was that by Balaško et al [2]. The tool steel AISI H11 initially soft annealed or hardened and tempered was exposed for up to 100 h in air in a temperature in the range 400-700 • C, in order to investigate the effect of oxide formation by combining experimental analysis and thermodynamic predictions.…”

Early Spalling Analysis of Large Particles in High-Cr Steel during Thermal Fatigue: Relevant Mechanisms

“…The literature indicates that the oxidation rate of hot work tool steels becomes noticeable at 500 °C and increases rapidly at 700 °C [ 1 ]. However, there are differences in the oxidation of chromium hot work tool steels.…”

“…The choice of a an appropriate heat treatment and the addition of molybdenum slow down the oxidation process [ 2 ]. In addition, molybdenum-rich carbides are resistant to oxidation and remain intact, whereas the surrounding matrix is completely oxidized [ 1 , 3 ]. The occurrence of spalling in the surface layer is considered critical, as both the surface quality of the rolled product and the ability of the rolls to resist fractures (critical crack size) are called into question.…”