Volume 77, Issue 3

The medical device industry demands unique device identification (UDI) tags on metallic components applied via laser marking. A common issue is that the visual appearance of the marking becomes poorly legible over time due to loss of contrast. Nanosecond pulsed laser irradiation was used to grow an oxide layer on two different martensitic stainless steels AISI 420F mod and 420B to compare the influences of the chemical composition of the steel (with and without S), power density, and energy input. The corrosion behavior was found to depend strongly on laser energy input. The presence of sulfur negatively affected the corrosion resistance and narrowed the applicable window for the laser processing parameters significantly. For the sulfur-containing AISI 420F steel, 3‒5 μm wide craters formed on the surface after laser marking, which is interpreted as thermal degradation of protruding MnS inclusions resulting from the laser marking process. Also, substantial cracking in the oxide layer was observed. The marked specimens suffered from corrosion in a thin zone below the formed oxide layer. This behavior is attributed to Cr-depletion in the zone adjacent to the oxide layer, resulting from providing Cr to the growing oxide layer.

This article reports the microstructural development of a molybdenum and copper alloyed steel by different thermochemical heat treatments for gears and shafts in automotive applications. The case hardening is compared to a duplex heat treatment consisting of carburising, ageing and plasma nitriding. This study evaluates the microstructure, the surface hardness and hardness profiles. For all applied heat treatment routes, the ageing conditions have a minor influence on the case and core hardness compared to the influence of the carbon concentration. Retained austenite fractions decreased to < 5 % in all duplex heat-treated samples without cryogenic treatment. Material characterisation with optical light microscopy and scanning electron microscopy indicate unwanted phases of nitrogen and carbon-rich precipitates at the grain boundaries after duplex heat treatment. Therefore, the sequence of duplex heat treatment is changed to carburising followed by solely plasma nitriding where the unwanted precipitates are detected only up to a depth of 15‒20 μm from the compound layer.

In order to enhance the load capacity, gears can be nitrided. The diffusion zone, measurable by the nitriding hardness depth, is considered to be the parameter governing for the high load-bearing capacity of nitrided gears. The wear behavior of gears is mainly determined by the characteristics (phase, porosity and chemical composition) of the compound layer but the influence of the compound layer on the load carrying capacity is not known yet. In this work, nitriding treatments for gears were developed with the aim to create compound layers with varying thickness, composition and properties in order to ensure a maximum load carrying capacity for nitrided gears.

The steadily increasing demands on the crash safety of automobiles with simultaneous weight reduction also mean higher requirements for crash simulation. In addition to manufacturability, the focus in component dimensioning is increasingly on crash properties. In order to improve the predictive accuracy of crash simulation, the individual process steps must be coupled in the simulations. To increase the quality of the predictions, thermal treatments such as curing of the paint, which normally takes place at 170 °C for around 20 minutes, should also be taken into account. In many steels, the so-called bake-hardening effect occurs. This leads to an increase in the yield stress. In this publication, different transformation approaches for the hardening curves will be investigated in order to increase the prediction accuracy in the process chain. An example is used to demonstrate their easy applicability in the simulation of the process chain.

Corrigendum to T. Wegener, A. Liehr, A. Bolender, S. Degener, F. Wittich, A. Kroll, T. Niendorf: Calibration and Validation of Micromagnetic Data for Non-Destructive Analysis of Near-Surface Properties after Hard Turning. HTM J. Heat Treatm. Mat. 77 (2022) 2, pp. 156-172, DOI:10.1515/htm-2021-0023.