Effect of casting technology on microstructure and phases of high carbon high speed steel

The as-cast microstructures of high carbon high speed steels (HC-HSS) made by sand casting, centrifugal casting and electromagnetic centrifugal casting, respectively, were studied by using of optical microscopy (OM) and D/max2200pc X-ray diffraction. The results show that the microstructure of as-cast HC-HSS is dominated by alloy carbides (W2C, VC, Cr7C3), martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting apparently improve the solidification structure of HC-HSS. With the increase of magnetic intensity (B), the volume fraction of austenite in the HC-HSS solidification structure increases significantly while the eutectic ledeburite decreases. Moreover, the secondary carbides precipitated from the austenite are finer with more homogeneous distribution in the electromagnetic centrifugal castings. It has also been found that the lath of eutectic carbide in ledeburite becomes finer and carbide phase spacing in eutectic ledeburite increases along with the higher magnetic field strength

STRUCTURAL STRENGTH ANALYSIS AND EXPERIMENTAL RESEARCH FOR WORKING DEVICE OF LOADER

In order to obtain the positions of load spectrum measuring points of the loader working device,the structural strength and fatigue strength of the working device were evaluated. The bucket force model was set up and the working device finite element model was builted. The method with typical operating conditions was used in simulation and experimental research on the structure strength analysis. The results showed that the simulation results agree well with the measured values,and the error of them between the 1. 6% 7. 3%,so as to effectively determine the load measuring point location area. Goodman fatigue limit diagram method was used to evaluate the fatigue strength of the measuring point. The results showed that the structure satisfied the requirements of fatigue strength. The static strength and fatigue strength evaluation were combined to obtain a more complete structural strength analysis method. Structural strength analysis and test results provide bases for the load spectrum test and fatigue life analysis of the loader working device

Study on Determination Method of Load Measurement Sample Length of the Loader Working Device

In order to determine the sample size in the load spectrum measure of the loader working device, the methods of the sample length determining were studied. The load test system of the loader working device was constructed and the original load time history data were collected. Considering the load characteristics and the confidence level of the population and the sample data, a new method was proposed and the minimum sample size required for the load test of the loader working device on ZL50 loader was 70 based on the measured load. The results of sample length of different methods were compared and analyzed. The new method presented in this paper was more reliable and credible than other methods. Methods and results to determine the test data is obtained, which provides a reference for the load test and life cycle spectrum compiling

STUDY ON LOAD MEASURING METHOD AND TEST OF THE PIN-SHAFT IN LOADER WORKING DEVICE

Based on the mechanical force model of the bucket on the working device of loader,the problem of the dynamic loading test was analyzed. The testing method considering pin-shaft lateral dynamic force was put forward,and the 3D forces in horizontal,vertical and lateral direction of the loader working device were accurately measured. Without changing the loading characteristics of the working device,the pin-shaft dynamic force test system was established with the pin-shaft sensor design and the bucket structure modification. Primary soil containing granular iron ore was chosen as the shovel loading operation case,and the dynamic forces in three directions of the pin-shaft linking the arm and the bucket were acquired through the shovel loading test. The results show that: the dynamic testing method and the system could accurately obtain the dynamic loads of three directions of the pin-shaft; the dynamic loads of the three directions measured by the pin-shaft sensors are closely related to the loading process; the dynamic loads of the lateral force of the loader working device with the change of loading process were obtained firstly. It has important guiding roles for the study on the mechanical characteristics of the loader working device,the acquisition of the load spectrum and the prediction of fatigue life

STUDY ON LOAD EQUIVALENT METHOD AND LOAD SPECTRUM OF THE BOOM OF LOADER

Based on the measured load of the 5 t loader working device,the method of solving the load with the attitude change to the local coordinate system of the boom has been studied and the MATLAB software to write the corresponding data processing program has been sued to obtain the loader arm under the fixed attitude of the load time course. The dangerous position of the boom is determined by the static analysis,and the equivalent external load of the boom is obtained by the stress equivalent principle of dangerous cross section position. On this basis,the boom load spectrum is compiled. The results provide a reference for the fatigue test and anti-fatigue design of the boom

Unexpected dynamic recrystallization behavior of Ti-7Cu alloy in semi-solid state

Titanium alloy obtained from semi-solid processing has received increasing attentions recently for its excellent formability and mechanical properties. This work intends to unveil the puzzling deformation process of the alloy during semi-solid processing. Through the compressive tests of semi-solid Ti-7Cu under various conditions (temperatures or strain rates), the deformation is found to be dominated by the plastic deformation of solid particles. Strikingly, the dynamic recrystallization (DRX), as commonly occur during hot deformation, is also observed. Based on the Poliak's theory and Avrami equation, the critical strain that triggers the DRX and the DRX kinetics are analyzed. It is found that the kinetics of DRX during semi-solid deformation is highly sensitive to temperature and strain rate. More specifically, higher percentages of DRX grains present at lower temperatures or higher strain rates, which is in contrary with that in solid state. Such phenomenon is considered as originated from the lubricating effect caused by the flow of the liquid phase during semi-solid deformation. Further, a modified DRX kinetic model is developed based on the Zener–Hollomon parameter Z, the predicted grain size agrees well with the experimental measurements

Tailorable burning behavior of Ti14 alloy by controlling semi-solid forging temperature

Semi-solid processing (SSP) is a popular near-net-shape forming technology for metals, while its application is still limited in titanium alloy mainly due to its low formability. Recent works showed that SSP could effectively enhance the formability and mechanical properties of titanium alloys. The processing parameters such as temperature and forging rate/ratio, are directly correlated with the microstructure, which endow the alloy with different chemical and physical properties. Specifically, as a key structural material for the advanced aero-engine, the burn resistant performance is a crucial requirement for the burn resistant titanium alloy. Thus, this work aims to assess the burning behavior of Ti14, a kind of burn resistant alloy, as forged at different semi-solid forging temperatures. The burning characteristics of the alloy are analyzed by a series of burning tests with different burning durations, velocities, and microstructures of burned sample. The results showed that the burning process is highly dependent on the forging temperature, due to the fact that higher temperatures would result in more Ti2Cu precipitate within grain and along grain boundaries. Such a microstructure hinders the transport of oxygen in the stable burning stage through the formation of a kind of oxygen isolation Cu-enriched layer under the burn product zone. This work suggests that the burning resistance of the alloy can be effectively tuned by controlling the temperature during the semi-solid forging process