Cold treatment and cryogenic treatment of steel

Cold Treatment and Deep Cold Treatment of Steel:The Secret to Enhancing Material Performance in Metalworking

One,Cold Treatment:Fine-tuning After Quenching

Cold treatment,also known as low-temperature treatment,refers to a heat treatment operation in which the steel after quenching is further cooled below room temperature,allowing the remaining austenite at room temperature to continue transforming into martensite.The purpose of this process is to minimize the remaining austenite in quenched steel as much as possible,thereby improving the steel's hardness,stability,and wear resistance.

1.Temperature and holding time for cold treatment

The temperature range for cold treatment is usually around the Mf point(the temperature at which the transformation of martensite ends),which is generally between-30°C and-

2.The Effect of Cold Treatment

(1)Increasing the Hardness of Quenched Steel:By undergoing cold treatment,residual austenite can be further eliminated,making the transformation of martensite more complete,thus increasing the hardness of the steel.This is particularly important for various tool steel and carburized steel parts,as it can significantly improve their wear resistance and service life.

(2)Stabilize workpiece dimensions:Cold treatment can basically eliminate various factors that cause dimensional changes(such as residual austenite),so that the workpiece's dimensions remain stable during use.This is particularly important for precision parts,which can ensure their dimensional accuracy and stability in performance.

(3)Increase steel's ferromagnetic properties:Cold treatment can also increase steel's ferromagnetic properties,which is of great significance for certain parts that require specific magnetic properties.

(4)Improving the fatigue performance of carburized parts:Cold treatment can optimize the microstructure of carburized parts,thereby improving their fatigue performance.This is particularly important for parts subjected to alternating loads,as it can extend their service life.

3.Key points of cold treatment process:

(1)Timely cooling:Cold treatment should be carried out immediately after quenching to avoid prolonged stay at room temperature,which leads to stabilization of residual austenite.The longer the stay at room temperature,the more serious the stabilization of austenite,and the worse the cold treatment effect.

(2)Even cooling:To ensure that the internal temperature of the workpiece is evenly consistent,appropriate insulation measures can be taken.For batch-loaded workpieces,insulation may be required for 1 to 3 hours depending on the situation.

(3)Slow heating up:After the cold treatment is over,the workpiece should be slowly raised to room temperature in the air.It cannot be heat-treated before it reaches room temperature,and it should be heat-treated promptly after it reaches room temperature to prevent the parts from cracking.

Two,Deep Cryogenic Treatment:An Advanced Strengthening Technique Beyond Conventional Methods

Deep cryogenic treatment is a method developed on the basis of conventional cryogenic treatment,in which liquid nitrogen is used as the refrigerant to treat workpieces at temperatures below-130°C.This technology can significantly improve the workpiece's toughness,wear resistance,and corrosion resistance without reducing its strength and hardness.

The principle and process of deep cryogenic treatment:

The principle of deep cryogenic treatment is to utilize the extremely low temperature environment of liquid nitrogen,which causes further changes in the microstructure of steel,such as suppressing dynamic recrystallization and grain growth,promoting the precipitation of carbides,etc.These changes can significantly improve the comprehensive performance of steel.

The deep cryogenic treatment method consists of liquid and gas methods.The liquid method is to directly immerse the workpiece in liquid nitrogen,with a treatment temperature of around-150℃.However,this method has a large thermal shock and sometimes even causes the workpiece to crack.The gas method,on the other hand,is to cool the workpiece by the latent heat of liquefaction of liquid nitrogen and the heat absorption of low-temperature nitrogen gas,with a treatment temperature of as low as-196℃,resulting in better treatment effects.

2.The function of cryogenic treatment:

(1)Increasing the hardness and strength of the workpiece:Cryogenic treatment can further promote the transformation of martensite,resulting in a significant increase in the hardness and strength of the steel.

(2)Ensure dimensional accuracy of workpieces:By deep cryogenic treatment,residual austenite can be further eliminated,thereby improving the dimensional stability of the workpieces.

(3)Improve the wear resistance of workpieces:deep cryogenic treatment can optimize the microstructure of steel,promote the precipitation of carbides,and thus improve the wear resistance of workpieces.

(4)Improve the impact toughness of the workpiece:Although deep cryogenic treatment results in a reduction of residual austenite,the increase of martensite and the precipitation of carbides can compensate for this loss,and even improve the impact toughness of the workpiece in some cases.

(5)Improve the distribution of internal stress in the workpiece:deep cryogenic treatment can improve the distribution of internal stress in the workpiece and enhance its fatigue strength.

(6)Improve the corrosion resistance of workpieces:deep cryogenic treatment can optimize the microstructure of steel,reduce corrosion sensitive points,and thus improve the corrosion resistance of workpieces.

3.Key points of deep cryogenic treatment:

(1)Choose the appropriate deep cryogenic treatment method:According to the material,shape,and size of the workpiece,choose the appropriate deep cryogenic treatment method(liquid method or gas method).

(2)Control the rate of temperature rise and fall:The rate of temperature rise and fall has a significant impact on the treatment effect in deep cryogenic treatment.A too fast rate of temperature rise and fall may cause internal stress in the workpiece to increase,leading to deformation or cracking.Therefore,the appropriate rate of temperature rise and fall should be selected based on specific circumstances.

(3)Holding Time:The holding time for deep cryogenic treatment should be determined based on factors such as the workpiece's thermal conductivity,volume,and the time required for it to cool down completely.Generally speaking,the longer the holding time,the better the treatment effect.However,excessively long holding times will also increase costs and time.Therefore,the appropriate holding time should be selected based on actual conditions.

(4)Tempering treatment:After deep cryogenic treatment,it is necessary to carry out tempering treatment in time to eliminate the residual stress in the workpiece and improve its stability and service life.

III.Application and Prospects of Cold Treatment and Deep Cold Treatment

Cold treatment and deep cold treatment have broad application prospects in the field of metal processing.They not only can improve the hardness and strength of steel,but also can optimize its microstructure,improve wear resistance,corrosion resistance and dimensional stability.Therefore,in the fields of aerospace,automobile manufacturing,electronic and electrical,mechanical manufacturing,etc.,cold treatment and deep cold treatment have become an important means of improving the performance of parts.

With the continuous advancement of technology and the constant changes in market demand,cold treatment and deep cold treatment technologies are also constantly innovating and developing.For example,by adopting advanced pulse and microwave deep cold treatment methods,the processing efficiency and quality can be further improved.By utilizing emerging technologies such as artificial intelligence and big data,the process parameters can be optimized and predicted,thereby improving the comprehensive performance of materials.

In the future,cold treatment and cryogenic treatment technologies will continue to play an important role in the metal materials industry.By continuously optimizing and innovating,they will provide more efficient,environmentally friendly,and sustainable solutions for related industries,driving the continuous development of the metal materials industry.

Conclusion

Cold treatment and deep cold treatment,as important branches of heat treatment,have significant advantages in enhancing the performance of steel.By understanding their principles,processes,and applications,we can better utilize these technologies to optimize material performance and meet the ever-changing market demands.At the same time,we should also pay attention to the innovation and development trends of these technologies to drive the sustainable development of the metal materials industry.