New energy saving technology of fastener heat treatment

01Research on fastener Technology: new technology of heat treatment and energy saving

1) If the carburizing temperature is increased from 930 ℃ to 1050 ℃, the process cycle can be reduced by 40%. For example, in the low-pressure carburizing process of vacuum furnace, carburizing can be carried out at 1050 ℃.

2) The process temperature can be reduced from 850-930 ℃ to 550-580 ℃, and the nitriding time can be reduced from 30-70h to 2-3H instead of general gas nitriding.

3) The thin layer carburizing is replaced by carbonitriding. The treatment temperature can be reduced from 930 ℃ to 850 ℃; when the depth of carburizing layer is less than 1mm, the carburizing time can be shortened by 30% compared with carburizing time; and the deformation of workpiece after quenching is small due to the low heating temperature and short time.

4) Acetylene low pressure carburizing technology has the advantages of high carburizing speed and energy saving, low consumption of feed gas and small emission, which can realize high temperature carburizing, shorten process cycle and save energy.

02 process of shortening heating time

1) According to the traditional heat treatment process, the heat preservation time is no less than 1 / 2 or 1 / 3 of the total heating time. For carbon steel and low alloy structural steel reaching the size of thin parts, zero heat preservation quenching process can be used when the heating temperature is above AC1 or AC3. The practice shows that the quenched and tempered steels such as 35Cr, 45Cr and 42CrMo can all meet the service conditions of the unit. Compared with the traditional heat preservation and quenching process, it can save the time needed for the through burning of workpieces and the homogenization of austenite, and reduce the energy consumption by 20% - 30%.

For example, a transmission shaft made of 45 steel, the traditional heat treatment process is 840 ℃× 60min quenching, 600 ℃× 120min tempering, and the hardness is 215-245hbw. On the basis of the test, the "zero heat preservation" tempering process of (870 ± 10) ℃× 0min quenching and (680 ± 10) ℃× 0min tempering is adopted for the transmission shaft. The results show that the microstructure is fine tempered sorbite, the hardness is 215-235hbw, which can meet the technical requirements completely and the effect is good.

2) Heating and quenching of non-uniform austenite. It will take a long time for the steel to be heated to austenite state so that the carbide can be fully dissolved and the austenite can be homogenized. However, if the austenite is not homogenized, the quenching will not affect its properties after quenching and tempering.

03 use surface and local heating instead of integral heating

The method of surface heating and quenching is to heat the surface of workpiece by induction, flame, laser and so on, and then harden the steel workpiece by spraying, soaking and self cooling. These methods can also be used to quench the local surface of the workpiece. It can save 33% ~ 50% energy by using induction heating instead of whole heating quenching, and 90% energy by using induction heating instead of carburizing quenching. For example, low hardenability structural steel 55ti, 60ti and 70ti are used to manufacture automobile and tractor gears instead of carburizing and quenching gears.

04 adopt accelerated chemical heat treatment process technology

In the accelerated chemical heat treatment process, the carburizing speed can be increased by about 20% or the temperature can be reduced by about 40 ℃ by using the direct atmosphere, ion bombardment (ion carburizing, ion nitriding and ion carbonitriding), chemical acceleration (rare earth acceleration and BH acceleration).

05 method of reducing heating temperature

The steel is heated in two-phase zone (sub temperature). It is proved by production practice that the steel can often get excellent properties when it is heated and quenched in a + F two-phase zone lower than AC3, especially the F + m mixed structure obtained by sub temperature quenching of low carbon alloy steel, which can make the strengthening and toughening achieve good coordination.

06 simplify or cancel heat treatment process

For example, the method of high pressure air quenching after carburizing, the high pressure (6 × 105 ~ 2 × 106pa) air cooling quenching of H2, he and N2 for steel parts after vacuum carburizing or general gas carburizing can achieve the cooling speed of static oil, with uniform cooling and small workpiece deformation; the air cooling quenching instead of oil can avoid oil fume pollution; the elimination of intermediate cleaning process can save electricity and energy.

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