No abstract

The effect of different loads on the high-temperature wear behavior of 5Cr5Mo2V steel at 700 °C was investigated. Wear morphologies, oxide compositions and matrix evolution were studied. The results showed that the wear rate increased with an increased test load, and the wear mechanism transformed from abrasive-oxidative wear to adhesive-oxidative wear. The relation between a delaminated oxide layer and cracks in the matrix were investigated. The exfoliation of carbides and displacement difference between the matrix and carbides caused a crack initiation. The wear rate strongly related to carbides, and coarse M6C carbides with poor holding power led to a high wear rate. Besides, a diagram of wear characteristics under different loads was suggested in this work.

The wear under high-temperature condition is one of the die failure patterns. Therefore, the wear resistance at high temperature is an important parameter for selecting die materials. In this work, the wear resistance of SDHA steel and 4Cr5Mo2V steel at 400 - 700°C were evaluated by a friction and wear tester. The wear behaviors and oxide types were investigated through a scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the oxides on the worn surface are Fe2O3 and Fe3O4 at the test temperatures. The wear volume of two steels first decreases and then increases, reached the minimum value at 500 ℃. Besides, SDHA steel has better wear resistance compared with 4Cr5Mo2V steel, which is attributed to the excellent hardness stability at high temperature. The coarse M7C3 carbides in 4Cr5Mo2V steel cause the peeling and delamination of oxide layer to damage wear resistance at 700 ℃.

Die corrosion has been a concern during aluminum alloy die casting. The casting parameters play a significant role in causing corrosion, such as the temperature of the aluminum alloy melt and working time. In order to study the effect of temperature and working time on dynamic corrosion behaviors, SDHA steel was stirred in molten ADC12 aluminum alloy at 650–800 °C. The corrosion morphology and corrosion product were investigated through X-ray diffraction (XRD) and scanning electron microscope (SEM) observations. The results show that the matrix reacts with aluminum alloy to form an Al8Fe2Si phase at experimental temperatures. The growth activation energy of the Al8Fe2Si phase is 89 kJ/mol. The dynamic corrosion rate rises with increasing temperature and holding time. The most serious corrosion was found when the experimental temperature reached 800 °C, which is closely related to the peeling of matrix and the formation of Al8Fe2Si at the grain boundary. Besides, the vanadium carbides in the matrix act as barriers to hinder the diffusion of Al and Si atoms effectively.

Due to the washout of aluminum alloy melt, the erosion failure of steel is a complex problem in die casting. To explain the erosion mechanism in flowing aluminum alloy melt, 6Mn14Cr3Mo2Si1V2 steel, and 4Cr5Mo2V steel were stirred at 700°C in ADC12 melt. The erosion characteristics were studied via the scanning electron microscope. At the test time increased from 600 to 1800 s, the weight loss rate of 6Mn14Cr3Mo2Si1V2 steel increased from 5.0% to 14.1%, and the weight loss rate of 4Cr5Mo2V steel increased from 5.4% to 12.8%. If the corrosion time reaches more than 1200 s, 6Mn14Cr3Mo2Si1V2 steel has lower erosion resistance because intergranular corrosion causes the matrix to peel off. Besides, the lump-like Vanadium carbides with a low erosion rate act as obstacles to prevent the invasion of aluminum alloy melt. The reaction product of steel and aluminum alloy melt is identified as