High Temperature Resistant Eddy Current Sensor for “in situ” Monitoring the Material Microstructure Development of Steel Alloys during Heat Treatment : Bainite Sensor

Production of tools and component for automotive and energy production includes in most application the adjustment in hardness, toughness, fatigue and wear properties. This is done by heat treatment [4]. Depending on material and Target course different treatment processes are applied like martensitic hardening, bainitic hardening [3], nitriding, nitrocarburizing, carburizing and annealing. Up to now these heat treatment processes are done by recipe.Temperature and time of treatment are measured. No information about the change in material microstructure is available during treatment. So scattering results are the consequence and high security time factors have to be Included to get the necessary process capability. To overcome this difficulty, eddy current sensors, measuring and analysis systems have been developed and are implemented in the hot furnace to measure in-situ the progress of thedeveloping material microstructure during heat treatment of the components

Energy and media efficient nitriding and nitrocarburising

To reduce energy consumption and also CO2 emission in industrial production a new and more general attempt is aspired by the project “ETA-Factory” 4. The first step is to improve the efficiency of every single machine in a production chain. This should already be done with the background in mind, whether waste energy and heat can be used in another step of the production. By this way also the building with its facilities itself is implemented and all heat and energy flows are cross-linked and controlled. The nitriding and nitrocarburising process is a very high energy consuming part in many production chains. Many aspects of energy saving with high potential are identified for this production step like heating with primary energy, better furnace isolation, heat recuperation, reuse of exhaust gas, light weight constructions, efficiency improvement of electrical components and also the reduction of process gas consumption. All these aspects are evaluated and experimentally verified at an industrial box type furnace in order to demonstrate the key benefits and also the risks. Finally the whole process chain including nitrocarburising is build up in the model factory and all heat and energy flows are controlled and interconnected even with the new production adapted building with all its new facilities and components. Depending on plant and treatment conditions at least up to 50% of energy consumption can be saved, if all aspects are implemented

Residual stress-affected diffusion during plasma nitriding of tool steels

Plasma nitriding of tool materials is common practice to improve the wear resistance and lifetime of tools. Machining-induced compressive residual stresses in shallow layers of some tenths of microns are observed accompanied by other characteristic properties of machined surfaces in these high-strength materials. After plasma nitriding of M2 high-speed steel, previously induced compressive residual stresses remain stable and the depth of diffusion layers decreases with increasing compressive residual stresses. This article reports investigations of plasma nitrided samples with different levels of residual stresses induced prior to the nitriding process. For comparison, experiments with bending load stresses during plasma nitriding have also been carried out. The plasma nitriding treatment was performed at constant temperature of 500 °C with a gas mixture of 5 vol pct N2 in hydrogen. Nitriding time was varied from 30 to 120 minutes. All samples were characterized before and after plasma nitriding concerning microstructure, roughness, microhardness, chemical composition, and residual stress states. Experimental results are compared with analytical calculations on (residual) stress effects in diffusion and show a clear effect of residual and load stresses in the diffusion of nitrogen in a high-strength M2 tool steel