This Project has an aim to study and evaluate the effect of reheat treatment
conditions on microstructural refurbishment in cast nickel base superalloy, Grade MGA 1400. This cast nickel base superalloy is used as turbine blade material in Japanese gas turbine engines. The evaluated reheat treatment programs consist of solution treatment at 1125◦C, 1150◦C and 1175◦C for 2 , 4 and 6 hours, respectively. Then the solutioning treated specimens were followed with primary aging at 925◦C for 2 hours and secondary aging at 845◦C for 25 hours, respectively. All reheat treated microstructures were investigated and analyzed by SEM and image analysis program, namely, “ImageJ”. From all obtained results, it was found that the most proper solution treatment is at temperature of 1125◦C for 2 hours to provide the most uniform microstructural characteristics, which consist of the uniform distribution of very dense gamma prime particles precipitating in the gamma matrix. This microstructure also provides the highest area fraction of gamma prime phase and the proper average size of the gamma prime particles.
The company Linseis which is located in Selb/Germany, produces analytical instruments since 1957. The product portfolio includes Thermal Analysis (e.g. TGA, DSC, STA), Thermophysical Instrument (e.g. Laser Flash Analyzers) and Dilatometers.
With the Linseis instruments many material properties can be measured in a temperature range between -260 to 2800 °C.
For metals the Linseis Laser Flash Analyzer is commonly used to measure the thermal conductivity and the Linseis Quenching and Deformation Dilatometers are the standard tools to generate ZTU- diagrams and to simulate forming processes.
New trends and developments for these measurement methods are presented, e.g. the newly developed Thin Film Laser Flash Analyzer which enables measurement of the thermal conductivity of very thin layers down to 80 nm and and opto-acustical extension of the Quenching and Deformation Dilatometer with which it is possible to analyze the metal structer in-situ.
This paper deals with the problem of quenching distortions that usually occur during the heat treatment of steel components. This is an important problem in the industrial production of precision steel components such, as for example gears, because the quenching distortion can lead to dimensional changes, the removal of which require expensive machining. In extreme cases, machining may be insufficient and the heat treated components cannot be used. Therefore, methods of reducing quenching distortion are the subject of intense research. One of the directions of work is the design of heat treatment with the aim to reduce the quenching distortion. Traditionally used heat treatment of steels, which consists of rapid martensitic quenching and tempering, usually leads to significant distortions. In our previous work we have revealed, that by use of isothermal quenching in the lower range of bainitic transformation temperatures it is possible to produce in some commercial steels a nanocrystalline bainitic microstructure. We have also shown, that steels with nanocrystalline microstructure have high strength parameters, similar to parameters of steels after martensitic quenching and tempering. Moreover, nanostructured steels have other advantageous properties, such as high fracture toughness, and high resistance to abrasive wear, which are highly desirable in gears. Thus, in the first stage of the investigation we have compared the distortions generated by both kinds of heat treatment in previously studied steel grades: 35CrSiMn5-5-4 structural steel, X37CrMoV5-1 tool steel, 60Si7 spring steel and 100CrMnSi6-4 bearing steel. It was shown, that the nanostructuring process causes less quenching distortions than conventional martensitic quenching and tempering treatment. In the second stage of the work, a study of quenching distortions in gears made of X37CrMoV5-1 tool steel and subjected to the nanostructuring process, was carried out. The distortions were compared with those in conventionally manufactured gears made of 42CrMo4 steel after surface hardening and low tempering. Our research revealed greater dimensional stability of the gears subjected to the nanostructuring process than gears after surface hardening and low tempering. The factors that may explain the obtained results were analyzed.
The aim of this study was to investigate the possibility of applying a quenching and partitioning process (Q&P) of X46Cr13 (4H13) stainless steel. This steel is characterized by very good corrosion resistance; however, it has limited strength and ductility. Therefore, due to the limited mechanical properties, X46Cr13 stainless steel was subjected to Q&P heat treatment. It allowed the microstructure consisting of tempered martensite and stable retained austenite to be obtained and high strength to be achieved. During the research, simulation of phase transformation, dilatometric measurements, light and electron microscopy and Vickers hardness tests were used. Retained austenite was calculated with the use of Koistinen-Marburger (K-M) equation and dilatometric measurements.
Silicon plays an important role in the manufacture and processing of steel. It is involved in metallurgical processes in the melt, improves castability, and, together with aluminium, belongs to the elements which suppress cementite formation during heat treatment of steels. The last-named aspect offers a great potential for developing high-strength steels with excellent ductility. The amount of bainite in the microstructure has a substantial impact in this respect. Bainite fraction depends mainly on temperature and on the isothermal holding time in the bainitic transformation region. In steels with low silicon levels, isothermal bainitic transformation continues until all austenite has transformed to bainite. At higher silicon levels, approximately 2 weight percent, the bainitic transformation is expected to be incomplete. The resulting bainite fraction would then be dictated by the thermodynamic equilibrium in the austenite-bainite system. As a result, one could control microstructural evolution, and thus the mechanical properties in high-strength bainitic-martensitic steels.
The aim of the study was to investigate the effect of initial microstructure of 100CrMnSi6-4 steel on the bainitic transformation’s kinetic as well as on the microstructure obtained after the bainitic transformation. The steel samples with two different initial microstructures were prepared by use of the appropriate heat treatments. As a result, one sample contained lamellar pearlite, whereas the other one contained the spheroidal cementite. Both steel samples were then subjected to the same heat treatment consisting on austenitization followed by isothermal quenching at two different temperatures lying in the bainitic transformation range. The heat treatments were performed in a quenching dilatometer in order to determine the bainitic transformation incubation time and the time at which the transformation was completed. It has been shown that the bainitic transformation strongly depends on the initial microstructure of steel. In both tested temperatures, the time to end of the bainitic transformation was significantly shorter and the rate of transformation was higher for steel sample with a spheroidal cementite microstructure than for steel with lamellar cementite. Moreover, it was shown, that the final bainitic microstructure depends on the initial one: the austempering of steel with spheroidal cementite microstructure led to finer bainite than in the case of steel with initial lamellar pearlite. The kinetics of bainitic transformation and the microstructure of austempered spheroidal pearlitic steel were compared to steel after accelerated carbide spheroidisation and refinement (ASR) subjected to austempering process.
In the paper, nitrided layers on unalloyed and alloyed steels and their corrosion properties are presented. Nitrided layers in the controlled gas nitriding process on C10, C45 and 42CrMo4 steels were produced.
Two types of nitrided layers with nitride iron layers (white layers) above and below 15 µm are presented. Nitrided layer with nitride layer above 15 µm has good corrosion resistance, but after nitriding of machine parts were subsequently oxidised and impregnated. In the second type of nitrided layer, the surface layers of iron nitrides had a thickness of 3.0 to 11.0 µm. Nitrided layers with a surface layer of iron nitrides with the gamma’ (Fe4N) structure were formed on unalloyed steel and investigated.
The so-produced layers were subject to basic metallographic, X-ray crystallography and corrosion resistance studies carried out by electrochemical methods and in a neutral salt spray chamber. It was found that the layers consisting only of gamma’ phase had a good corrosion resistance. Necessary requirements for achieving an enhanced resistance comprise their complete tightness and thickness not lower than 9.0 µm. Thinner layers had good electrochemical properties but did not exhibit corrosion resistance in the salt spray chamber.
ACKNOWLEDGEMENTS: The research and its dissemination is an ongoing program design TANGO NITROCOR "Innovative nitrided layers of new generation with increased corrosion resistance produced on machine elements", funded by the National Centre for Research and Development in the years 2015-2018.
The paper presents the technology consisting in combination of the nitriding process with subsequent austenitizing at temperature above eutectoid temperature of the Fe-C system and further rapid cooling. Such treatment will cause formation of the martensite in the area of the primarily nitrided layer and the additional precipitation hardening by tempering of heat treated steel.
The article shows that the heat treatment process of nitrided layer formed on X37CrMoV5-1 steel leads to strengthening of surface layer, substrate and the core of nitrided part. Very important from the point of view of the effects of strengthening of nitrided layers by heat treatment is the structure and thickness of the primarily thermo-chemically treated layer formed on steel. Heat treatment in the active atmosphere of nitrided steel can increase the thickness of the layer formed by short-term nitriding process. After the nitriding process of X37CrMoV5-1 steel the nitrided layer had a thickness of about 160 μm, while a subsurface layer of iron nitrides had a thickness of 7 μm. After subsequent quenching and tempering processes the nitrided layer undergoes further diffusion and its thickness is increased to about 220 μm, while the layer of iron nitrides disappears. Basic properties of nitrided layers formed in such way, like hardness and wear resistance, are presented.
Introduction of dispersed particles in the molten metal during casting is one of the effective methods of hardening metal. Solid dispersed particles introduced into the steel, partly dissolved in the melt, forming a supersaturated solid solution. By heat treatment may create the conditions for the loss of particles from a supersaturated solution. The article describes an experiment for obtaining of dispersed-reinforced metal, the study of metal micro-structures before and after heat treatment, as well as the estimated effect of heat treatment on the quantity of particles.