The new alloy of FeMnAlC was design, melted and cast into ingots in Lab, these ingots were hot rolled into plates with different thickness reduction with plate thickness larger than 12mm or into rods with diameter of about 20mm. The microstructures of the plates and rods were examined by the optical microscopy, the electron back scattered diffraction, the scanning electron microscopy and the transmitted electron microscopy. It was found that the micro-laminated microstructure with alternative ferritic phase and matensitic phase was developed in the hot rolled steel plates, but the microstructure with the ferritic micro-fiber embedded in the martensitic matrix was formed in the hot rolled steel rods. The mechanical properties including tensile test and impact toughness test were carried out in these hot rolled steel plates and steel rods. It was found that an ultrahigh toughness of about 300-450J was obtained in the steel plates, ultrahigh toughness of about 150-300J was obtained in the hot rolled steel rods, and the tensile strength varied from 1000-1800MPa was obtained both in the hot rolled plates and rods. Based on the analysis of the microstructure evolution during hot deformation process and the relationship between the microstructure and the impact toughness, it was proposed that the development of the hot hot rolled laminated structure was mainly controlled by the geometric thinning of the ferrite phase/austenite phase and the retarded recrystallization due to the sluggish diffusion of Mn and Al during intercritical rolling process, and the ultrahigh impact toughness was attributed to the micro-laminated microstructure. This research was believed to provide a promising way to develop advanced steel with both ultrahigh strength and ultrahigh toughness by simple alloy design and conventional hot rolling techniques.
The purpose of the work was to test a new heat treatment designated as B-Q&P on an experimental steel (95SiAlCrMnMoV 6-4-4-3-2-2), which was designed for nanostructurization by bainitic transformation. The B-Q&P heat treatment consists of partial nanobainitic transformation (B) followed by partial martensitic quenching (Q) and partitioning (P) process. During the partitioning which is performed at elevated temperature, the carbon atoms diffuse from supersaturated bainitic ferrite plates to the surrounding austenite without any phase transformation. The parameters of the heat treatment were selected on the basis of TTT diagram, which was determined by means of dilatometric studies of phase transformations. The influence of the heat treatment parameters on the microstructure, phase composition and hardness of steel was investigated. The microscopic observations revealed a multiphase microstructure that was composed of nanobainite (ferrite plates separated by thin layers of residual austenite), blocky austenite and martensite. It was shown that novel B-Q&P heat treatment increases hardness of treated steel as compared to conventional nanostructurization process. It was revealed, that the hardness of steel depends on the phase composition but also on the time and temperature of partitioning process.
Reduction of processing time is the goal of every business. In some cases, acceleration of manufacturing processes is impossible or takes place at the expense of quality. The purpose of soft annealing is to obtain globular carbides in the microstructure. However, it is one of the most time-consuming heat treatment operations. Even its optimised versions require several hours of time. „Accelerated Carbide Spheroidisation and Refinement” (ASR) is an alternative process which can be performed using induction heating or thermomechanical treatment. It only takes several minutes to complete and has a beneficial effect on resultant mechanical properties.
In this experiment, the impact of various microstructures in 54SiCr6 spring steel on hardening behaviour was explored. For this purpose, specimens with two different microstructures containing spheroidised carbides were produced by ASR accelerated annealing and by conventional soft annealing. Another initial microstructure, with lamellar pearlite, was obtained by hot rolling. It was found to have a certain effect as well. Quenched and tempered microstructures were observed using electron microscopy (SEM). Their mechanical properties were measured. The effects of various initial microstructures on resultant mechanical properties after cryogenic treatment were studied as well.
The article presents the influence of multistage cryogenic treatment (MCT) on the microstructure and properties of X153CrMoV12 cold work steel. Basic mechanical properties of steel, such as hardness and wear resistance (3 rolls-cone system) were tested. The microstructure of steel was observed by means of scanning microscopy. Test results were compared with the properties of steel subjected to conventional heat treatment and deep cryogenic treatment (DCT). The cryogenic processes of X153CrMoV12 steel influenced on the percentage of strengthening phases in the material matrix microstructure. In the case of MCT and DCT, similar changes in the microstructure were observed, consisting in increasing of the amount, more uniform distribution and refinement of carbide phases. Changes in the microstructure of steel affected the mechanical properties of the material. As compared to conventional heat treatment, the MCT processes reduced the hardness of X153CrMoV12 steel. Despite of smaller share of the retained austenite, the hardness of cryogenically treated and tempered steel decreased by 6.4 ÷ 7.3 HRC. The above changes result from shifting of nucleation and carbide growth stages to lower temperatures, and thus faster proceeding of their coagulation and coalescence processes. The processes of MCT caused an increase of the wear resistance of samples.
This research was supported by CORNET Programme ("COOLBEND" Project).
Co-based alloys are used over a wide range of application because of their excellent corrosion and wear properties. Especially the Stellites (Co-Cr-W) are well known and quite well researched. The CoCrTaAlCSiY is a new material on the field of thermal spray coatings and due to its composition was chosen for studding of tribological behavior. In this paper the HVOF sprayed and post heat treated coatings of CoCrTaAlCSiY are presented. Specimens were remelted by a laser with two different laser parameters in order to reach different thickness of laser remelted coatings. Erosion test and linearly oscillating ball on flat test were applied to evaluate the wear behavior of CoCrTaAlCSiY coating. Microstructure of as-sprayed and heat treated coatings were also studied. The evaluation revealed a positive effect on wear coefficient for both laser remelted coatings. A significant improvement of volume loss during erosion test was also observed for both laser remelted coatings.
The problem of nanostructuring cast iron is hardly ever reported in scientific reports. Most of the research is undertaken in terms of steel nanostructurization. Bhadeshia states that to obtain a fragmented matrix of steel, the carbon content in the matrix must be at the level of 0.6% C. It should be noted that the carbon in the ferrite-pearlite matrix meets this condition because the content of this element in the matrix is within the range of 0.7-0.9%.
The authors of this work have attempted to evaluate the ability to shape the properties and microstructure of ductile cast iron as a result of not fully completed bainitic transformation, compared to the standard process of obtaining ADI cast iron. The tested material was characterized by a higher degree of alloying elements compared to the basic chemical composition of ADI cast iron.
The aim of the work was to maximize the fragmentation of the cast iron microstructure by selecting a low temperature of isothermal transformation, i.e. 40 degrees C above Ms temperature in the lower bainite range. The JMatPro program was used to determine the isothermal transformation temperature. Heat-treated cast iron was subjected to dilatometer tests to compare the results obtained from the computer program, microstructure research and hardness tests. Heat-treated cast iron was subjected to dilatometer tests to compare the results obtained from the computer program, microstructure research and hardness tests.
An increase in surface absorptivity can be helpful with a number of laser heat treatment processes. This study examines the relation between surface condition and its influence on interaction with a laser beam. The aim of this paper is to examine the effect of the oxide layer pattern size on the absorption of IR radiation and the influence of ambient atmosphere. Process carried in air was compared to processing with inert gas shielding. The oxide layers are created by the controlled heating method. The controlled heating method uses a scanning laser system to create oxide layers of different thickness on steel EN 10083-2: C45. Subsequently, the absorbency of the formed oxide layer were measured, depending on the irradiation energy emitted into the surface. According recent experiments has been found that higher the thickness of the oxide layer increases absorption, but the growth is not linear. These results have shown that the use of surface oxidation increases the coupling of laser energy to material surface in the order of tens of percent. The thickness and hardness of laser hardened layer were considered. That paper describes possibilities of precious laser hardening of the oxidized C45 material surface.
The various application of shape memory alloys requires shape setting of NiTi ribbon in particular form. Shape setting is accomplished by constraining the NiTi ribbon on a mandrel that undergoes heat treatment. Surface annealing of NiTi ribbon was performed on bent shape inside the furnace. The duration of furnace temperature was kept fixed for 2h. The sample was held in bend position for annealing the martensite phase created on the surface of NiTi ribbon. The aim is to anneal the martensite phase on the upper surface region and introduce the compressive stress on the edge of the alloy. The induced surface strain and the annealed temperature determine the volume fraction of martensite formed on the sample in the flat position at room temperature. The shifting of peak and evolution of new peaks as the function of temperature on the annealed NiTi ribbon at the flat position was observed. X-ray diffraction was carried out on the shape set bended sample at room temperature and constrained flat position (both outer and inner surface). The bended NiTi ribbon annealed at 350 °C shows a mixture of austenitic phase and plastic deformation region that confirms from the broadening of some peaks. The residual stress arises from the plastically induced periphery region and the elastic core region that allows the NiTi ribbon returns partially to original flat shape. However, fully shape set achieved on NiTi ribbon annealed at 400 and 450 °C.