Sintering temperature, too high temperature will accelerate the growth of titanium carbide grains. The final sintering temperature of titanium carbide high manganese steel cemented carbide is generally 1420 ℃. The sintering temperature should not be too high. Even making the binder phase into liquid phase metal loss, so that the hard phase adjacent, aggregate and grow, forming a source of fragmentation. This is why the bonding phase between the hard phase grains analyzed earlier becomes less. Of course, the sintering temperature should not be too low, otherwise the alloy will be under-fired. In addition to the aforementioned control of the sintering temperature and speed, the degree of vacuum in the furnace enters the liquid phase sintering stage. It is also necessary to control the degree of vacuum in the furnace during sintering, because an excessively high degree of vacuum will evaporate a large amount of liquid metal, causing segregation of the components. Especially in the three stages of degumming, reduction and liquid phase sintering, the rate of temperature increase during sintering is not suitable for such alloys.
Strictly control the heating rate and holding time. Because in the process of low temperature degumming, the green compact releases the pressing stress and the volatilization process of the forming agent. If the heating rate is fast, the forming agent will not evaporate and become liquefied and become steam, which causes the green compact to burst or microcrack; In the reduction stage, the compact should be given enough time to remove the volatiles and oxygen in the raw material powder (such as Mn2Fe master alloy); when entering the liquid phase sintering stage, the heating rate should be slowed down to fully alloy the compact. The sintering principle of steel-bonded cemented carbide is the principle of wetting. Let the liquid phase fully wet the solid phase (hard phase). Otherwise, the liquid metal FeMn will be precipitated on the surface of the green compact, or even be lost.
Under the same conditions, industrial titanium plates with different compositions will show different decarburization behaviors. For example, Si can increase the elastic limit, strength, tempering stability and elasticity resistance, because different alloy elements have different effects on the activity and diffusion of carbon. However, we must pay attention to the serious decarburization of the surface caused by Si increasing the activity of carbon in austenite and the chemical potential gradient. The low-carbon industrial titanium plate 28MnSiB trial-produced by Stone Titanium Co., Ltd. reduces the content of carbon and silicon in titanium and effectively reduces the surface decarburization tendency. The inspection results show that the actual carbon content is 0.10% -0.16% and the average is 0.12% The carbon content is less than 0.23%.
Part surface strength is an important factor affecting fatigue strength. Surface heat treatment and surface cold plastic deformation processing are very effective for improving fatigue strength. Reduce fatigue crack formation. Grinding away the surface decarburization layer produced by heat treatment can significantly improve the fatigue limit; direct shot peening without removing the surface decarburization layer produced after heat treatment has a greater increase in the working limit than after decarburization removal, such as surface quenching and carburization , Carbonitriding, Nitriding, Shot Peening and Rolling. Increasing the surface strength of the part can reduce the effective tensile stress and local uneven deformation on the part surface. The former is 30% -50%, the latter is only 3% -6%. In order to reduce the effect of surface decarburization, the surface of hot rolled spring round titanium is stripped. To avoid surface decarburization, the carbonation degree gradient between the two should be eliminated or reduced. Taking protective atmosphere heating is an effective measure to avoid or reduce surface decarburization. To shorten the heating time and reduce the depth of decarburization, rapid induction heating should be used.
