Abstract: Microstructure, hardness and fracture toughness of low and high chromium high speed steel used in hot strip mills and subjected to conventional heat treatment have been examined. The influence of tempering temperatures on the mechanical properties of these products, determined using tensile and fracture toughness tests, was studied in this research work. The developed microstructures have been characterized by XRD, optical microscopy and SEM examinations. Macrohardness and microhardness of the specimens have been evaluated by Vickers indentation technique. The fracture toughness of these products was investigated using the rupture weight on 3 points bending specimens. The plane strain fracture toughness KIc and the fracture strength were measured for each alloy. The shell is high harness high speed steels, and the core is nodular cast iron. It was found that most fracture occurred in the eutectic carbides formed by the high content alloy element, such as Mo,V,Cr, but that for the alloys with a reduced volume fraction of eutectic carbides, a small amount of crack propagation occurred in the austenitic dendrites.
Abstract: It was found that a large number of aluminum alloy strain clamps cracked. Cracking mainly occurred in the drainage plate of strain clamps. Nondestructive testing technologies and physicochemical analysis devices such as optical microscope, spectrograph, SEM and EDS were adopted to analyze the reasons of cracking. The results tell that there are numerous shrinkage cavities and cracks inside the drainage plate of strain clamps. The maximum area fraction of shrinkage cavities is 10.7%, and the maximum size is over 1mm2. A lot of shrinkage cavities and cracks gather together to form big flaws, which seriously reduce the mechanical properties of the drainage plates. After a long period of vibration, cracks gradually develop to the surrounding cavities and connect adjacent cavities. Eventually, cracks develop to the surface of drainage plates.
Abstract: The investigations of ultrasound Rayleigh wave parameters changing depending on localized plastic strain in AlCu4MgSi alloy and austenitic stainless steel AISI 304 are presented in this paper. Measurements of the ultrasound parameters and localized strain bands motion were carried out in-situ during the tensile tests of the specimens at the constant rate and room temperature. It has been found that the measurement of ultrasound velocity allows detecting the initiation of a localized strain band and its location relative to the acoustic measurement area independently of the deformation mechanism.
Abstract: Continuous cooling transformation (CCT) diagram of a high strength weathering prefabricated building steel was determined using a DIL805L thermal dilatometer by means of the expansion method combined with metallography hardness method. Effect of cooling rate on microstructure and hardness of the steel was also studied. The results show that the austenite transformation products of the steel are ferrite and pearlite when cooling rate is lower than 3°C/s. In the cooling rate range of 3 to 20°C/s, the mixed microstructure of ferrite, pearlite and bainite can be obtained. When cooling rate is higher than 20°C/s but lower than 100°C/s, the microstructure is composed of ferrite, bainite and martensite. When cooling rate is above 100°C/s, ferrite disappeared completely, and transformation products are bainite and martensite.
Abstract: The effect of enter rolling temperatures on the grain size and toughness was investigated in Q345E H-beam steels. The experimental results shown that the grain size exhibited a complicated phenomenon with rolling temperature instead of refining as the temperature decreased as expected. It would be interpreted by the behaviors of deformation and recrystallization in austenite during rolling. The toughness is not only depended on the average grain size but also on the distribution of grain size as well as morphology of pearlite. The toughness would be decreased by the mixed grain size.
Abstract: The high temperature relaxation in cold-rolled Ti (CR-Ti) and commercial pure Ti (CP-Ti) has been investigated using internal friction apparatus operating in forced oscillations from room temperature to 650°C. It is shown that there is an internal friction peak at around 510°C for the CR-Ti and there is no 510°C internal friction peak in the CP-Ti. The internal friction peak shows typical features of phase transformation in the CR-Ti. It is tentatively suggested that this peak is due to the ordering of disordered lattices resulted from cold-rolling. The high temperature background damping (HTBD) in the CP-Ti is much lower than that in the CR-Ti. It is concluded that the HTBD is related to the microstructure observed inside the grains and does not dependent on grain size.
Abstract: Preparation of Mn-Cu based damping alloy ingots coupled with strong magnetic fields shows many interesting phenomena on the solidification microstructure and the crystal lattice. In this study, modified M2052 ingots were prepared under different magnetic fields to investigate the bulk solidification behavior by using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Metallographic analysis reveals that the deflection angle of the primary dendrite arm increases with the increase of magnetic field strength. The distribution of chemical composition characterized by X-ray Fluorescence discloses that Mn is enriched while Cu is depleted along the circumferential surface side, and the variation tendency changes from almost a level to a sloping line under applied magnetic field. High magnetic field have altered the orientation of the γ-Mn dendrites from (200) to (111), and the coupling mechanism of alloy solidification with strong magnetic field is discussed based on the experimental results.
Abstract: The microstructure of commercial pure copper TP2 tube by three roll planetary mill processing was investigated. Due to work hardening and subsequent softing by dynamic recrystallization during milling process,the coarse grain structure of the copper transformed to fine grain structure. The grain refinement is achieved along the axial moving in general; in the reducing zone, the sample has a gradient structure along the radial direction; uniform equiaxed grain with size of ~2 μm could be obtained at the outlet. The initiation of dynamic recrystallization occurred in the three roll planetary mill the reduction engineering strain reach ~30%, where some equiaxed grains replaced the elongated grains because of recrystallization.
Abstract: The effect of C addition on the microstructure of a Cu-Fe alloy was investigated by combining the calculation of phase diagram (calphad) and the experimental research. The calphad results indicated that the addition of C substantially enlarged the zone of liquid immiscibility gap in the metastable phase diagram of Cu-Fe alloy. In addition, the larger the addition content of C was, the more obvious the phenomenon was. As a result, the presence of trace amounts of C in the Cu-Fe alloy containing 5~20% (wt.) Fe would cause the liquid phase separation of Cu-rich and Fe-rich liquid phases during the solidification process of the alloy. The experimental results showed that the dendritic secondary phase in the as-cast microstructure of the Cu-14Fe alloy tended to be spheroidized after the addition of C due to the separation of Cu-rich and Fe-rich liquid phases. With the increasing content of C, the volume fraction and the average diameter of the spherical Fe-rich particles both increased. The calphad conclusions are in agreement with the experimental results.