11 measures of energy saving in heat treatment process

Heat treatment has great energy saving potential. How to take measures to strengthen energy saving is an important topic for every heat treatment worker. The following is only a simple discussion on heat treatment process energy saving.

Reduce heating temperature

Generally, the quenching temperature of subeutectoid carbon steel is above 30 ~ 50℃, while that of eutectoid and hypereutectoid carbon steel is above 30 ~ 50℃.In recent years, however, it has been proved that the heating quenching (i.e., subeutectoid quenching) in a + two-phase region slightly lower than Ac3 can improve the toughness of the steel, reduce the brittle transition temperature, and eliminate the temper brittleness. The quenching temperature can be reduced by 40℃.

The high carbon steel can be quenched quickly and quickly at low temperature, which can reduce the carbon content of austenite, and is beneficial to obtain the lat martensite with the good strong and tough fit, which can not only improve its toughness but also shorten the heating time.

For some transmission gear, with carbonitriding instead of carburizing, wear resistance increased by 40% ~ 60%, fatigue strength increased by 50% ~ 80%, the total penetration time is the same, but the total penetration temperature (850℃) than carburizing temperature (920℃) low 70℃, but also can reduce heat treatment deformation.

Shorten heating time

The production practice has shown that the traditional heating time determined based on the effective thickness of the workpiece is mostly conservative, so the heating coefficient in the heating duration formula.According to the traditional process parameters, when heating to 800 ~ 900℃ in an air furnace, the value is recommended to be 1.0 ~ 1.8min/mm, which is obviously conservative.If the alpha value can be reduced, the heating time can be greatly reduced. The heating time should be determined by experiments according to the size of the steel workpiece and the amount of furnace loading, etc. The optimized process parameters should be carefully executed once they are determined to achieve significant economic benefits.

Cancel tempering or reduce tempering times

To cancel the tempering of carburized carbon steel, for example, the fatigue limit of 20Cr steel loader to cancel the tempering with double-sided carburized piston pin can be increased by 16% compared with the tempering; The tempering of low-carbon Martensite steel is canceled, and the bulldozer pin sleeve is simplified to 20 steel quenched (low-carbon Martensite). The hardness is stable at about 45HRC, and the strength and wear resistance of the product is significantly improved, and the quality is stable. For example, the W18Cr4V steel saw blade adopts one tempering (560 ° C ×1h) instead of the traditional 560 ° C ×1h three temperings, and its service life is increased by 40%.

Use low to medium tempering instead of high tempering

Medium carbon or medium carbon alloy structural steel can obtain higher multi-punch resistance by tempering at medium and low temperature instead of high temperature.W6Mo5Cr4V2 steel Φ 8 mm drill bit, after quenching + 560 ℃ to 350 ℃ by 1 h x 1 h secondary tempering, a 560 ℃ by 1 h three tempering the bit cutting life of 40.

Reasonable reduction of seepage depth

The chemical heat treatment has a long cycle and high power consumption. It is an important means of energy saving to reduce the penetration depth and shorten the time. The necessary depth of the hardening layer is obtained by stress measurement. It shows that the current hardening layer is too deep and only 70% of the traditional hardening depth is enough. The results show that carburizing can reduce the depth of the layer by 30% ~ 40%. At the same time, if the depth of seepage layer is controlled at the lower limit of the technical requirements in actual production, it can also save 20% energy, shorten the time and reduce the deformation.

High temperature and vacuum chemical heat treatment are used

The high temperature chemical heat treatment is in the equipment use temperature permit and the condition that the osmotic steel austenite grain does not grow narrow, raises the chemical heat treatment temperature, thus greatly accelerates the rate of carburizing. The carburizing temperature from 930℃ to 1000℃ can make the carburizing speed increased more than 2 times. However, due to many problems, future development is limited.

Vacuum chemical heat treatment is carried out in a gas phase medium under negative pressure. Because the surface of the workpiece is cleaned in the vacuum state, and the higher temperature is used, the seepage velocity is greatly increased. Such as vacuum carburizing can improve productivity 1 ~ 2 times; At 133.3× (10-1 ~ 10-2) Pa, the penetration rate of aluminum and chromium can be increased by more than 10 times.

Ionic chemical heat treatment

It is a chemical heat treatment process that USES a glow discharge between the workpiece (cathode) and the anode to infiltrate the permeable element in a gas phase medium containing permeable elements at a pressure lower than one atmosphere. Such as ion nitriding, ion carburizing, ion sulfur carburizing, with the advantages of fast permeability, good quality, energy saving, etc.

Self – tempering by induction

Use induction tempering themselves instead of tempering furnace because is the use of induction heating heat into the hardening layer, heat quenching when not all take away the remnant of the tempering and implementation for short periods of time, thus has high efficiency and energy saving, and in many cases, such as the high carbon steel and high carbon high alloy steel) can avoid quenching cracking, and the advantages of various process parameters can be mass production after confirmation, the economic benefit is remarkable.

Use pre-heat quenching after forging

Preheating quenching after forging can not only reduce heat treatment energy consumption and simplify the production process but also improve the product performance.

The remaining heat quenching and high temperature tempering after forging as pretreatment, can eliminate hardening in final heat treatment after forging the coarse grains, poor impact toughness of faults, than spheroidizing annealing or general annealing time is short, high productivity, plus high temperature tempering temperature lower than that of annealing and administration work, so can greatly reduce the energy consumption, and simple equipment, easy operation.

Compared with the general normalcy, the residual heat normalcy after forging can not only improve the strength of the steel but also improve the plasticity and reduce the cold and brittle transition temperature and notch sensitivity. For example, 20CrMnTi steel is cooled at 730 ~ 630℃ at 20℃/h after forging, and good results have been achieved.

Surface quenching instead of carburizing quenching

The systematic study on the performance (such as static strength, fatigue strength, multiple impact resistance, and residual internal stress) of medium and high carbon steel with a carbon content of 0.6% ~ 0.8% after high-frequency quenching shows that it is completely possible to replace carburizing quenching with induction hardening part. We use 40Cr steel high frequency quenching to manufacture gearbox gear, instead of the original 20CrMnTi steel carburized quenching gear has been successful.

Use partial heating instead of integral heating

For some local and technical requirements of parts (such as wear-resisting tooth trunnion, roll diameter, etc.), can use bath heating furnace, induction heating, local heating mode pulse heating, flame heating instead of overall heating, such as box-type furnace can make the appropriate coordination between the friction parts occlusion parts, improve the service life of the parts, and because it is local heating, so can significantly reduce the quenching distortion and reduce energy consumption.

We deeply realize that an enterprise can make rational use of energy and achieve maximum economic benefits with limited energy, which involves the efficiency of energy-using equipment, whether the process and technology route is reasonable, whether the management is scientific and other factors. This requires us to consider comprehensively from a systematic point of view, and each link cannot be ignored. At the same time, it requires that we should also have a global idea when making the process, which should be closely combined with the economic benefits of the enterprise, and not make the process for the sake of making the process. This is particularly important in today’s rapid development of the market economy.

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