In this diploma thesis, precipitation-hardened stainless steel 17-4 PH (AISI 630) was investigated, as it combines high strength, good corrosion resistance, and stability of mechanical properties at elevated temperatures. These properties result from the precipitation of copper-rich phases during the aging process, which leads to microstructural changes that significantly affect the mechanical and physical properties of the material.
The study focused on the influence of aging temperature and time on microstructural evolution, as well as on changes in the electrical and thermal properties of 17-4 PH stainless steel, together with the achieved hardness. The kinetics of precipitation were monitored by in-situ electrical resistivity measurements using high-precision measurement equipment, namely a Keithley 6220 current source and a Keithley 2182A nanovoltmeter, enabling the detection of microstructural changes in real time.
Thermal conductivity, thermal diffusivity, and specific volumetric heat capacity were determined using a Hot Disk TPS 2200 device based on the Transient Plane Source (TPS) method, in accordance with the ISO 22007-2 standard. The degree of hardening was evaluated through hardness measurements using the Vickers (HV) and Rockwell (HRc) methods under different aging conditions.
Based on the obtained results, correlations between microstructural changes and variations in electrical resistivity, thermal conductivity, and hardness were established. The results contribute to a better understanding of precipitation processes in 17-4 PH stainless steel and support the optimization of heat treatment procedures to achieve the desired combination of properties.
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