Technology Trends in Vacuum Heat Treating

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Titanium alloy has many characteristics such as strong corrosion resistance, good heat resistance, low elastic modulus, and non-magnetic. After solution treatment and aging strengthening, its specific strength is much higher than that of high-strength aluminum alloy, magnesium alloy and high-temperature alloy, and even comparable to ultra-high-strength steel. It is widely used in aerospace, shipbuilding, biomedicine, chemical industry, automobile and other fields. Vacuum oil quenching and vacuum gas quenching are one of the main methods of vacuum heat treating.

Research status of vacuum heat treating technology of titanium alloys

Vacuum heat treating technology is to select suitable cooling medium according to the requirements of organizational performance and the phase change law of component materials, so that the vacuum-heated materials and components are cooled to the furnace temperature at the required cooling rate under vacuum environment. Common cooling media for vacuum heat treating include: vacuum quenching oil, non-oxygen-containing gas and water. Different cooling media have different cooling rates.

Vacuum oil quenching cooling technology

The cooling medium used in vacuum oil quenching cooling is vacuum quenching oil. This technology can replace salt bath and atmosphere protection heat treatment. While obtaining ideal core organization and mechanical properties, it ensures the smoothness of the surface. It is particularly suitable for quenching medium and high alloy steel. At present, vacuum oil quenching technology is widely used in vacuum heat treating industry. Through long-term improvement of equipment, process and quenching oil quality, vacuum oil quenching technology is relatively mature. However, due to its slow cooling rate (lower than water quenching), if it is not properly controlled during the heat treatment of titanium alloy, it is easy to form brittle ω phase; on the other hand, after the titanium alloy workpiece is heated at high temperature and put into oil, the surface of the workpiece contacts with oil vapor and reacts to form carbon increase instantly, which is not conducive to the improvement of the performance of titanium alloy. Therefore, it is not suitable for vacuum heat treating of titanium alloy.

Vacuum gas quenching cooling technology

Vacuum gas quenching cooling uses non-oxygen-containing gas as the cooling medium. Its characteristic is that within a certain range, as the gas pressure in the furnace increases, the cooling rate can be increased accordingly. The commonly used cooling gases for vacuum gas quenching are: N2, H2, He and Ar. Their thermal conductivity varies greatly. H2 has the strongest cooling capacity, followed by He, N2 third, and Ar the worst. Using 40bar H2 ultra-high pressure gas quenching, its cooling rate can be close to the water quenching rate, but H2 is more dangerous to use, and titanium alloys are prone to absorb H at high temperatures, causing hydrogen embrittlement, so it cannot be used as a cooling medium for vacuum heat treatment of titanium alloys; using 20bar He ultra-high pressure gas quenching, its cooling rate is between oil and water, which can replace vacuum oil quenching, but He and Ar are too expensive, and recycling needs to be considered after quenching. The heat treatment cost is too high and cannot be used as the main cooling medium for vacuum heat treating of titanium alloys; N2 is cheap and safe, but has poor cooling capacity, and reacts strongly with Ti at high temperatures, reducing the performance of titanium alloy materials. This technology is also not suitable for solid solution strengthening treatment of titanium alloys.

SIMUWU Two Chamber Vacuum Oil Gas Quenching Furnace

Model	Temperature Uniform Size	MAX.Temperature	Ultimate Pressure	Heating Power	TemperatureUniformity	Loading Capacity
VOGQ-446-2	400*400*600mm(W*H*L)	1350℃	4*10-1Pa	100kW	±5℃	200Kg
VOGQ-669-2	600*600*900mm(W*H*L)	1350℃	4*10-1Pa	120Kw	±5℃	500Kg
VOGQ-7710-2	700*700*1000mm(W*H*L)	1350℃	4*10-1Pa	260Kw	±5℃	700Kg