MICROSTRUCTURE AND TEXTURE WELDS OF 15-7Mo STEEL AFTER HEAT TREATMENT

This paper presents the results of determining the effect of heat treatment after welding X8CrNiMoAl15-7-2 steel (commercial name: PH 15-7Mo steel) on the microstructure and texture of the welds. XRD studies showed the presence of the two phases in the welds of 15-7Mo steel; i.e., δ ferrite and austenite. Annealing at a temperature of 400°C/1 h and 550°C/1 h results in changes of the intensities for individual peaks derived from austenite and ferrite. Microstructure investigations carried out by LM and TEM indicated that the austenite and δ ferrite coexist in themicrostructure of 15-7Mo steel in as-welded condition. Annealing at a temperature range of between 400–620°C after welding causes small changes in the microstructure. The hardness of the welds after annealing in that temperature range increases

Fatigue Resistance of GX12CrMoVNbN9-1 Cast Steel after Ageing Process

In the present paper, low cycle fatigue behaviour of GX12CrMoVNbN9-1 (GP91) cast steel is presented. Fatigue tests were performed under isothermal conditions at room temperature and at 550 and 600oC, on five levels of total strain amplitude value ɛac = 0.25÷0.60%. The cast steel subject to investigation was in the as-received condition (after heat treatment) and after 8000 hours of ageing at the temperature of 600oC. Performed research has shown an insignificant influence of the ageing process on mechanical properties of GP91 cast steel, determined with the static test of tension. Analysis of the performed tests has proved that GP91 cast steel in the as-received condition and after ageing process was characterized by strong cyclic softening without a clear period of stabilization of the hysteresis loop parameters. The fatigue lifetime curves at each temperature were obtained based on Basquin and Coffin – Manson equations. The process of ageing of GP91 cast steel contributed to a decrease in its fatigue life Nf from a few to a few dozen percent, and the level of fatigue life was dependent on the value of strain amplitude ɛac. It has also been stated that the fatigue life Nf of GP91 cast steel is determined by its plastic properties, and the degree of changes in fatigue life Nf was dependent not only on the temperature of testing, but also on the value of strain amplitude ɛac. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6077</p

ESTIMATION OF THE COOLING RATE IN 3 mm SUCTION-CAST RODS BASED ON THE MICROSTRUCTURAL FEATURES

One of the factors influencing possibly of bulk metallic glass fomation is cooling rate attainable in the casting process. The evaluation of the cooling rate of the suction-cast 3 mm rods is presented based on the measurements of the cellular spacing in the Fe-25Ni and lamellar spacing in the Cu-33 Al alloys. The estimated cooling rates are higher close to the rod surface than in the rod axis, which indicates the dominant radial heat flow. In contrast, for the Al-33Cu alloy higher cooling rates were evaluated in the rod axis than close to the surface due to the concave perturbation of the solidification front during eutectic transformation. Based on the results obtained for the Fe-25Ni alloy, it is concluded, that the cooling rate for the suction-cast 3 mm rod is not lower than 228 Ks-1

Analysis of γ′ Precipitates, Carbides and Nano-Borides in Heat-Treated Ni-Based Superalloy Using SEM, STEM-EDX, and HRSTEM

The microstructure of a Ren&eacute; 108 Ni-based superalloy was systematically investigated by X-ray diffraction, light microscopy, energy-dispersive X-ray spectroscopy, and electron microscopy techniques. The material was investment cast in a vacuum and then solution treated (1200 &deg;C-2h) and aged (900 &deg;C-8h). The &gamma; matrix is mainly strengthened by the ordered L12 &gamma;&prime; phase, with the mean &gamma;/&gamma;&prime; misfit, &delta;, +0.6%. The typical dendritic microstructure with considerable microsegregation of the alloying elements is revealed. Dendritic regions consist of secondary and tertiary &gamma;&prime; precipitates. At the interface of the matrix with secondary &gamma;&prime; precipitates, nano M5B3 borides are present. In the interdendritic spaces additionally primary &gamma;&prime; precipitates, MC and nano M23C6 carbides were detected. The &gamma;&prime; precipitates are enriched in Al, Ta, Ti, and Hf, while channels of the matrix in Cr and Co. The highest summary concentration of &gamma;&prime;-formers occurs in coarse &gamma;&prime; surrounding MC carbides. Borides M5B3 contain mostly W, Cr and Mo. All of MC carbides are enriched strongly in Hf and Ta, with the concentration relationship between these and other strong carbide formers depending on the precipitate&rsquo;s morphology. The nano M23C6 carbides enriched in Cr have been formed as a consequence of phase transformation MC + &gamma; &rarr; M23C6 + &gamma;&prime; during the ageing treatment

Regulación emocional y competencia social en la infancia

The formation of liquation cracking in a simulated heat affected zone of René108 is reported. The stress controlled thermo-mechanical experiments were carried out on a Gleeble®3800 testing system. The base alloy was lost-wax cast and then solution treated and aged. Light and scanning electron microscopy of this material revealed high volume fraction of γ' precipitates in the dendrite arms and residual eutectic γ/γ' islands in the interdendritic areas. As a result of short-term exposure to high homologous temperature, the volume fraction of γ' phase was significantly decreased due to the dissolution of precipitates in the surrounding matrix. The thin non-equilibrium liquid film, formed locally along grain boundaries, was a key-factor favoring initiation of cracks and their spreading during the Gleeble testing. The liquid appeared as a result of constitutional liquation, mainly of the γ' precipitates

Characterization of γ′ Precipitates in Cast Ni-Based Superalloy and Their Behaviour at High-Homologous Temperatures Studied by TEM and in Situ XRD

In situ X-ray diffraction and transmission electron microscopy has been used to investigate Ren&eacute; 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of &gamma;&prime; precipitates, their volume fraction, evolution of the lattice parameter of &gamma; and &gamma;&prime; phases and misfit parameter of &gamma;&prime; in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of &gamma;&prime; precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100&ndash;1250 &deg;C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both &gamma; and &gamma;&prime; phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient

The role of the strengthening phases on the HAZ liquation cracking in a cast Ni-based superalloy used in industrial gas turbines

This work presents the influence of microstructural constituents on liquation crack formation in the cast Ni-based superalloy, René 108. The investigation was divided into three parts: characterisation of the material's microstructure in pre-weld condition, hot ductility studies and analysis of liquation cracking induced by the gas tungsten arc welding process. Using advanced electron microscopy techniques it is shown that the base material in pre-weld condition is characterised by a complex microstructure. The phases identified in René 108 include γ matrix, γ' precipitates, MC and M23C6 carbides, and M5B3 borides. Based on Gleeble testing, it was found that René 108 is characterised by high strength at elevated temperatures with a maximum of 1107 MPa at 975 °C. As a result of constitutional liquation, the superalloy’s strength and ductility were significantly reduced. The nil strength temperature was equal to 1292 °C, while the nil ductility temperature was 1225 °C. The low ductility recovery rate (32.1), ratio of ductility recovery (36.2) and hot cracking factor (Rf = 0.05) values confirmed the low weldability of Renѐ 108. In the heat-affected zone (HAZ) induced by welding, constitutional liquation of mainly γ' precipitates, with a contribution of M23C6 carbides and M5B3 borides, was observed. The thin non-equilibrium liquid film, which formed along high-angle grain boundaries, led to crack initiation and their further propagation during cooling. The eutectic γ–γ' re-solidification products are visible on the crack edges.Acknowledgements This work was supported by the Polish National Science Centre (Preludium 13) under grant 2017/25/N/ST8/02368. The authors acknowledge the contribution of DAAD (Research Grants-Short-Term Grants 2021) in supporting the collaboration between AGH-UST and the Technical University of Munich. Also, Łukasz Rakoczy has been partly supported by the Foundation for Polish Science (FNP) with scholarship START 2022 (no. START 066.2022). MGR thanks to the National Center for Research and Development for the support in project LIDER 0147/L-13/2022.CC BY-4.0</p