Papers by Keyword: Austenite Grain

Abstract: In view of the special requirements of rails to ensure the safe and stable operation of Railways in China, the formation characteristics of austenite grains in high carbon rail are revealed through industrial exploration, the process of industrial rail heating and rolling is simulated, innovative experimental research methods such as different heating and heat treatment are carried out on the actual rails in the laboratory. Transfer characteristics of austenite grain size, microstructures and key properties of high carbon rail during the process are also revealed. The results show that the austenite grain size of industrial produced U75V rail is about 9.0 grade. When the holding temperature is increased from 800 C to 1300 C, the austenite grain size of high carbon rail steel decreases, the austenite grain are gradually coarsened, and the tensile strength increases slightly. The tensile strength is affected by the heating temperature. With the increase of heating temperature, the elongation and impact toughness of high carbon rail decrease. The heating temperature of high carbon rail combined with austenite grain size shows that the heating temperature has a great influence on austenite grain size, and has the most obvious influence on the toughness of high carbon rail.

Abstract: The effect of austenitizing temperature on the quenching microstructure and properties of 51CrV4 steel was studied. The results show that with the increase of austenitizing temperature, the austenite grains grow gradually. After quenching, the hardness increased first and then decreased, and the strength increased first and then decreased after tempering at 460°C. When the austenitizing temperature was 880°C, the austenite grains were fine and uniform, about 16μm, the martensite structure was dense, the strength and hardness reached maximum. When the austenitizing temperature was 910°C, the decarburization phenomenon was obvious, and the strength, hardness and plasticity of the test steel decreased obviously. When the austenitizing temperature exceeded 910°C, the austenite grains grow sharply and some grains were abnormally coarse. The austenite grain size reached 20μm and the microstructure was coarser at austenitizing temperature of 950°C. Therefore, in order to ensure uniform grain size and no decarburization under the premise of complete austenitization, the best austenitizing temperature of 51CrV4 steel for good properties is 880°C.

Abstract: The simulation experiments of heating process for X80 pipeline steel were carried out to investigate the influence of austenite grain size and micro alloy element solution. The results showed that a reasonable industrial production process of slab heating control system was developed, and the guidance of good industrial test could be provided for the acquisition of reasonable microstructure of 22mm thickness X80 pipeline steel hot rolled steel strip.

Abstract: The microstructure evolution during rapid induction heating process of 22MnB5 steel after double cold rolling was investigated, and the effects of deformation, heating temperature and heating rate on austenitic grain size and micro-hardness of quenched samples were discussed. The results show that the austenite begins to when heated to 850 °C and the austenite grains grow significantly when heated to 950 °C during rapid induction heating process. With the deformation increasing, the austenite grain size decreases, and the austenite grain refinement weakened when the deformation increases to a certain extent; but the influence of cold rolling on micro-hardness after quenching is not significant. In addition, there is little effect of heating rate on the 22MnB5 steel austenite with large cold deformation and a certain effect on the micro-hardness after quenching.

Abstract: The characteristic of structural inheritance for 300M steel was explored and the eliminating effect of normalization was investigated. Then, both the first and secondary normalization process was optimized by comparing eliminate effect. It is known that obvious characteristic of structural inheritance can be shown with the condition of 810°C-840°C×30min/OC after over-heated treatment. The first normalization process whose condition is 950°C~1100°C×2.5h/air cooling has the good effect on eliminating structural inheritance. While, the secondary normalization process whose condition is 960°C~1060°C×2h/air cooling+925°C×2.5h/air cooling owns the better effect on eliminating structural inheritance.

Abstract: The GX12CrMoVNbN9-1 (GP91) cast steel belongs to a new group of high-temperature creep resistant cast steels being introduced to the power industry. The cast steel is characterized by higher mechanical properties in comparison with the low alloy Cr – Mo or Cr – Mo – V cast steels used so far. The mechanical properties of martensitic cast steels depend on the parameters of heat treatment, such as the temperature of austenitizing. The paper is to present the results of research on the influence of austenitizing temperature ranging from 980 to 1100oC and hold time of 12 hours on the growth of austenite grain. The tests were carried out on test samples taken from a test coupon. Description of the influence of austenitizing temperature on the austenite grain size was made using the mean diameter of grain. Performed tests have shown that the distributions of mean diameters are of normal character, on the significance levels α = 0.05 and α = 0.04. For the investigated temperature range, the ν coefficient of non-homogeneity of the mean diameter of prior austenite grain was determined. The achieved results have proved that in the temperature range of 1010 to 1070°C the mean diameters stay within the same grade of grain size and the considerable grain growth is visible at the temperature of 1100°C.

Abstract: In the course of our experiments we have developed an etching process by means of which the austenite grains formed subsequent to roughing can be made visible in the case of Grade X80Mo0 and X80Mo2 microalloyed steels. The definition of the size and elongation of the grains enables the production process to be optimized and the microstructure features associated with the desired mechanical properties attained thereby.

Abstract: The low carbon steels were smelted with special oxide introduction technique and the HAZ properties has been studied with thermal simulation. The optical microscope, SEM and TEM were used to analyze the composition, size and distribution of the inclusions, and the mechanical properties after thermal simulation were also investigated. The influence of oxide inclusions on the austenite grain size was also studied. The results show that after the smelting the inclusion is complex, in the core is Ti oxides about 1-3 micron and around it is MnS. When the reheat temperature is below 1000, the size of austenite grain is the same for experimental steel and base steel. However, when the reheat temperature is over than 1100, the size of austenite grains in experimental steel is one third of that in base steels. After thermal simulation, with the t_8/5 increasing the toughness of HAZ decreased. The austnite grain size also increased. The microstructure is composed of intergranular ferrite and intragranular acicular ferrite. Therefore by introducing the fine oxide inclusion to the steel the austenite grain was refined and during the phase transformation the acicular ferrite formed at inclusions at first. These two factors are the main causes to improve the toughness of heat affected zone for steels produced by oxide metallurgy technique.