چكيده به لاتين
In this research, the effect of different conditions of heat treatment on microstructure and mechanical properties of a type of precipitation hardening martensitic stainless steel, called GTD450 was investigated. To do so, first this alloy was solution treated at 1040 °C for 1 hour and then it was quenched in 3 different media, including: air, water and oil. Then, the effect of different conditions of aging treatment including time and temperature on micro-structure and mechanical properties of this alloy was investigated. The micro-structure of different samples was observed by Optical Microscopy (OM) and Scanning Electron Mi-croscopy (SEM). To detect different phases which were present in the samples and also to recognize the micro strains arising from coherency between precipitates and the matrix with Williamson-Hall method, the X-Ray Diffraction (XRD) analysis was used. The mechanical properties of samples were tested in terms of Vickers hardness test (At least 3 repetitions) and tensile test. JMatPro software pack was used to study the micro-structure changes and probability of different precipitates, thermodynamically. The results of hardness test and microstructure evaluations have revealed that quenching the samples in air and oil result more hardness than water. The main effective factor in strength in-crease during precipita-tion hardening is precipitation of very fine Cu precipitates (less than 1μm) within the sam-ple’s microstructure. In the early stages of precipitation, these precipitates are coherent with the matrix and consequently they yield the best properties. In comparison with variation in the time of aging, variation in the temperature of aging had more influence on sample’s properties. The Ultimate Tensile Strength (UTS) in solu-tion treated sample was 986 MPa and its elongation was 13.3%, these values changed to 1207.73 MPa and 11.6 % respec-tively, After aging at 500 °C for 6 hours. The sample which was aged at this circumstance has shown the best toughness among other samples, too.
