How to modify the surface of titanium plate and improve the toughness

Sintering temperature, high temperature will accelerate the growth rate of titanium carbide grain. The final sintering temperature of titanium carbide high manganese steel cemented carbide is generally 1420℃. The sintering temperature should not be too high. Even the bonding phase becomes a liquid phase of metal loss, so that the hard phase occurs adjacent, aggregate and grow, forming a fragmentation source. This is the reason why the adhesive phase transition between the hard phase grains analyzed above is less. Of course, the sintering temperature can not be too low, otherwise the alloy will underburn. In addition to the above mentioned to control the sintering temperature and speed, the vacuum degree in the furnace, when entering the liquid phase sintering stage. It is also necessary to control the vacuum degree in the furnace during sintering, because too high a vacuum degree will cause a large amount of liquid metal volatilization, resulting in component segregation. Especially in the three stages of degumming, reduction and liquid phase sintering, the heating rate during sintering, and the heating rate during sintering of such alloys should not be fast.

It is necessary to strictly control the heating rate and holding time. Because in the low temperature degumming stage, the compact releases the pressing stress and the process of forming agent volatilization, if the heating rate is fast, the forming agent can not volatilize and liquefied into steam, causing the compact to burst or micro-crack. At the reduction stage above 900℃, the compact should have enough time to remove the volatiles and oxygen in the raw material powder (such as Mn2Fe intermediate alloy); When entering the liquid phase sintering stage, it is also necessary to slow down the heating rate to make the compact fully alloyed. The sintering principle of steel-bonded cemented carbide is the wetting principle, so that the liquid phase fully wets the solid phase (hard phase), otherwise the liquid phase metal FeMn will precipitate on the surface of the compact, and even lose.

Under the same conditions, different components of industrial titanium plates will show different decarbonization behavior. For example, Si can improve the elastic limit, strength, tempering stability and elastic decline resistance, because different alloying elements have different effects on the activity and diffusion of carbon. However, the serious decarburization of the surface caused by Si increasing the activity of carbon in austenite and chemical potential gradient must also be paid attention to.

The surface strength of parts is an important factor affecting the fatigue strength. Surface heat treatment and surface cold plastic deformation are very effective for improving fatigue strength. Reduce fatigue crack formation. The fatigue limit can be significantly increased by removing the surface decarburization layer caused by heat treatment. Direct shot peening without removing the surface decarburization layer produced after heat treatment has a larger amplitude than that after removing the decarburization and then shot peening, such as surface quenching, carburizing, carbonitriding, nitriding, shot peening and rolling. Increasing the surface strength of parts can reduce the effective tensile stress and local non-uniform deformation on the surface of parts. The former is 30%-50%, the latter is only 3%-6%. In order to reduce the impact of surface decarbonization, the surface of hot rolled spring round titanium is stripped, and the carbonization degree gradient between the two should be eliminated or reduced to avoid surface decarbonization. Protective atmosphere heating is an effective measure to avoid or reduce surface decarbonization. Shorten the heating time to reduce the depth of decarbonization, and rapid induction heating should be used.