Structural Stability of Sandvik 3R60™ After 240 131 Hours Ageing and Creep Test at 700 °C

Sandvik 3R60™ is an AISI 316/316L type of stainless steel. In this paper, the structural stability of the material under long-term ageing or creep test has been studied. The material had been creep tested with a stress of 45 MPa at 700 °C. The predicted rupture time for the creep specimen was about 100,000 h; however, the specimen broke first after 240,131 h. The oxidation behavior and structural stability in both aged and creep-tested samples were studied using SEM/EDS, EBSD and ECCI techniques. Thin oxide layers near the sample surface are mainly spinel oxides and eskolaite (Cr2O3). Sigma phase, χ-phase, Eta phase, M23C6 and Cr2N have been observed in the matrix of the samples. In the crept sample, the amount of sigma phase has increased, so has Eta phase and χ-phase as well. Thermo-Calc evaluation can reasonably predict precipitation of sigma phase, Eta phase and M23C6, but not χ-phase and Cr2N phases. Creep crack initiation behavior has been studied. It is mainly noticed to start at surface oxide layer or coarse sigma particles at grain boundary or triple point. Additionally, it is also observed that the presence of a thin Cr2O3 layer between the oxide and matrix along with discontinuous sigma phase distribution at grain boundary that will reduce the risk for creep crack initiation. Further, the crack propagation behavior has also been discussed.

The Microstructural Peculiarities of Beryllium Bronze after Heat Treatment

In this article, the microstructural peculiarities and properties of dispersion-hardened beryllium bronze with Ni and Ti are studied after quenching (780 °C) in a supersaturated solid solution and aging (320 °C, 3h). Decomposition of the α-solid solution matrix is implemented by means of an intermittent reaction with a primary allocation intermetallic χ-phase (type Be12Ti) with a VCT-lattice. It is shown that the strength properties (yield strength, micro-hardness) of the alloy more than double after aging.

Microstructural and Mechanical Characterization of As-Cast Co-Cr-Mo Alloys with Various Content of Carbon and Nitrogen

Co-Cr-Mo alloys is the material used as a biomedical implant in human body. This material is widely used because they have excellent in corrosion and wear resistance. In this study, microstructure and results of tensile test that were affected by carbon and nitrogen were investigated. The specimens of Co-Cr-Mo alloy were made by investment casting. The compositions of the alloys are Co-28Cr-6Mo-0.8(Si, Mn, Fe)-0,2Ni-(0.08-0.25)C-(0-0.2)N. After that process, microstructure of the alloys is characterized by, SEM/EDX and XRD testing using bulk and electrolytic extracted specimens. The mechanical properties were determined by tensile test. The precipitate content in as-cast alloys was higher when carbon and nitrogen was added. The main precipitate formed in the specimens with variations in carbon and nitrogen is M23X6 type, π-phase, χ-phase, and σ-phase. Carbon and nitrogen promoted M23X6 type and π-phase precipitation, respectively, meanwhile χ-phase was formed in the alloys with low carbon content. The addition of carbon and nitrogen shows an increased in yield strength, tensile strength and elongation of as-cast Co-28Cr-6Mo-0.8(Si, Mn, Fe)-0,2Ni-(0.08-0.25)C-(0-0.2)N alloys.

Structure Formation in High-Nitrogen Steel during Heat Treatment

Steel 06Cr18Mn19Mo2N (P900N + Mo) was chosen to study the phase composition and structural transformations occurring in high-nitrogen nickel-free austenitic steels as a result of heat treatments to which they are exposed during production or operation. The methods of light and electron microscopy, X-ray diffraction and dilatometric analysis were used in the work. The heat treatment scheme included hot plastic deformation, quenching and aging over a wide temperature range. It is shown that after the hot plastic deformation and quenching from 1050-1150 °С, and also after quenching with subsequent aging at 300 and 500 °С, the structure consists of austenite and isostructural matrix of nanoscale nitrides CrN. Thermal aging of steel at 700-750 °C causes the formation of Mo2N nitrides along the grain boundaries, and at 800 °C the decomposition of austenite is accompanied by a discontinuous reaction γγdepleted + σ with the formation of the χ-phase at prolonged exposures.