Application of ultrasonic testing method for determining defects of hot-deformed powder materials

The article is devoted to the analysis of elastic and plastic characteristics of composite materials during hot stamping. The purpose of this work is to offer optimal conditions for hot plasticity of composite porous material with determination of temperature conditions of hot stamping excluding the appearance of defects in the structure. Production of details of the difficult form by method of hot stamping from preparations of the cylindrical form is followed by development of barrel on a peripheral surface. Sludge sintered porous blanks, and sediment compact material, accompanied by a nonuniform height lateral deformation. In connection with the action of friction forces on the contact surfaces, this leads to the formation of a “barrel”. The heterogeneity of the deformed state is associated with the appearance of tangential tensile stresses on the free surface of the workpiece. If they exceed some critical degree of transverse deformation, cracks appear on the side surface, which leads to gas saturation (oxidation) of the inner layers of the forging, to the ingress of grease into them and its pressing into the volume of the part during hot stamping. In the end, this significantly reduces the properties of hot-stamped parts. Conclusion: the methods of determining the elastic characteristics depending on the geometric parameters of the workpieces, the applied strain energy, body density and temperature dependence of the plasticity characteristics of the hot deformation of the powder material are сonsidered.

The Role of Martensitic Transformation in Thermomechanical Development of Microstructure and Plasticity of Two-Phase Ti-6Al-4V Titanium Alloy

Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.

Effect of Sulfur on the Hot Plasticity of GH625 Superalloy

The influences of sulfur on the hot plasticity of superalloy GH625 were studied. The results indicate that the area reduction rate were 70% between 950°C to 1250°C with the S content below 0.0020%. When the S content is higher than 0.0025%, the area reduction rate was below 50%. The fractography was examined and analyzed by scanning electric microscope (SEM). The SEM results showed that the tensile fracture was cleavage fracture with the S content above 0.0030%. There were dimples in the tensile fracture when the S content was 0.0020% and below. It is indicated that the content of sulfur has great effect on the mechanical properties of GH625. In order to improve the hot plasticity of superalloy GH625, the content of sulfur should be controlled below 20ppm.

The influence of the residual copper on the pipes steel hot plasticity according to environmental requirements

Considering the importance of gaseous and/or liquid fuels impact on the environment, the resistance of pipelines at hot plastic deformation is important. Therefore, in order to avoid or reduce any adverse impact on the environment, the influence of residual copper on hot deformability of steel pipes was investigated in this paper. The negative copper influence was experimentally proved using torsion deformation at temperatures above 1000o, under the air and argon atmosphere. The samples were heated and then deformed at different temperatures with constant deformation rate. Also, structural analysis of investigated materials was done, using metallographic and SEM analysis.

Deformability of Eutectic Al-Si Alloys Produced by Semi-Continuously DC Casting during Hot-Rolling

The deformability and the microstructures of Al-12.2Si-0.6Mg alloy during hot-rolling were investigated by means of rolling the specimens of wedge bars with length of 180mm and width of 30mm, which had front thickness of 5mm and back thickness of 44mm.The wedge bars were cut from the ingots of the Al-12.2Si-0.6Mg alloy by the semi-continuously direct chill (DC in short) casting. The specimens of wedge bars were hot-rolled following holding between 410°Cand 480°C for different time. The results show that the size, morphology, distribution characters of eutectic Si particles in the Al-12.2Si-0.6Mg alloy can be remarkably modified by semi-continuously DC casting, which consists of coarse ribbon-like Si-particles with less than 5μm in length and 1μm in width and quite a lot eutectic phases of less than 0.4μm in size and space. The results also show that the ingots of the Al-12.2Si-0.6Mg alloy by the semi-continuously DC casting can possess excellent deformability during hot-rolling if the extent of heating is provided over 440°C for 60min and 410°C for 120min, and they cannot emerge cracked edges with the compression ratio of 85% by single-pass rolling. Their hot-plasticity depends on the size and space between eutectic phases in the ingots. Hot-rolling deformation makes ribbon-like Si phases in them crack and spheroidize, and then results in the sizes of coarse Si particles tending to be consistent.

Microstructural Evolution of Eutectic Al-Si Alloys Produced by Semi-Continuously DC Casting during Heating and Hot-Rolling

Semi-continuously direct chill (DC in short) casting was carried out to modify the size and morphology of eutectic Si particles in eutectic Al-Si alloy. Successively, the size, morphology, distribution characters of eutectic Si particles and the hot plasticity ability of the alloy during heating and hot-rolling were investigated by the observation of optical microstructure characterization and the rolling of wedge bar. The results show that the eutectics in the eutectic Al-Si alloy can be remarkably fined by semi-continuously DC cast. The eutectic Si phase particles will coarsen and spheroidize after holding at 480°C for 2h, which enables eutectic Al-Si alloy to possess excellent hot plasticity free of cracked edge with compression ratio of rolling up to 85% by single pass. Though little difference on the size of spheroidized Si particles during hot rolling can be observed, uniform distribution of the Si particles can be obtained by hot rolling with compression ratio of 85%.