Magnetoelastic properties of heat treated steels
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Lämpökäsiteltyjen terästen magneettiset ominaisuudet
Mechanical and magnetic properties of materials are closely coupled, because both properties arise from the structure of the material. Magnetoelasticity describes the inter-action between the elastic and magnetic properties of the material. The influence of stress on the magnetic properties of steels is of interest because magnetoelasticity can be exploited in the condition monitoring of structural components. The most important phenomena related to magnetoelasticity are magnetostriction and magnetomechanical effect. Magnetostriction is a fractional change in length due to the applied magnetic field. Magnetomechanical effect describes the stress-induced change in the magnetization of ferromagnetic materials. Both phenomena occur simul-taneously. The aim of this work was to examine the magnetic and magnetoelastic properties of steel bars. The literature survey revealed that the interaction between stress and magnet-ic properties of steel is complicated because it is non-linear and exhibits hysteresis. It was found that the microstructural features influence the basic magnetic and magneto-mechanical properties of steels. The experimental part of this work consisted of two parts. In the first part the hyste-resis curves of different steel grades were measured in order to investigate the basic magnetic properties of the samples. It was found that gas carburizing and prior cold working decrease the permeability of the material. No simple relationship was revealed between steel composition and magnetic properties. The purpose of the second part of the experimental work was to build a test device in order to study the magnetoelastic properties and behaviour of the steel bars under impact loading. The main goal of this work was to find out the scatter of the measure-ment results between the samples. The impact tests revealed that there are differences in the results obtained on samples of the same material. The factors of uncertainty were identified and discussed. The main challenge in the magnetic measurements is the inter-pretation of the results because there are several factors influencing the results. Future work requires more detailed study of the microstructure of the samples in order to inter-pret the results with more accuracy.