With the development of science, we have invented many quenching methods of quenching furnace. So, what are the details of it? At the same time, what are the advantages? Next, let's have a look!
1. High pressure gas quenching method
The rapid uniform cooling of workpiece in strong inert gas flow can prevent surface oxidation, avoid cracking, reduce deformation ensure the required hardness. It is mainly used for quenching tool steel. In recent years, this technology has made rapid development, its application scope has been greatly expanded. At present, the vacuum high-pressure air-cooled quenching technology has developed rapidly. There are new technologies such as negative pressure (< 1 × 105 PA), large flow air-cooled pressurized (1 × 105 ~ 4 × 105 PA), high pressure (5 × 105 ~ 10 × 105 PA) air-cooled, ultra-high pressure (10 × 105 ~ 20 × 105 PA) air-cooled, which only greatly improve the vacuum air-cooled quenching It has the advantages of high efficiency, energy saving no pollution. The purpose of vacuum high pressure gas cooling quenching is quenching tempering of materials, solid solution aging of stainless steel special alloys, ion carburizing carbonitriding, vacuum sintering, cooling quenching after brazing.
When 6 × 105 PA high pressure nitrogen is used for cooling quenching, the cooling load can only be loose type. High speed steel (W6Mo5Cr4V2) can be hardened to 70-100 mm, high alloy hot working die steel can reach 25-100 mm, gold cold working die steel (such as Cr12) can reach 80-100 mm. When using 10 × 105 PA high pressure nitrogen cooling for quenching, the cooling load will be large, which is about 30% to 40% higher than the cooling load density of 6 × 105 PA. When 20 × 105 PA ultra-high pressure nitrogen mixture of helium nitrogen is used for cooling quenching, the cooling load is very dense can be tied together.
Compared with 6 × 105 PA nitrogen cooling, its density increases by 80% to 150%. It can cool all high speed steel, high alloy steel, hot work tool steel, Cr13% chromium steel more alloy oil quenched steel. Large size 9mn2v steel. The cooling capacity of double chamber gas quenching furnace with independent cooling chamber is better than that of single chamber gas quenching furnace of the same type. The cooling effect of 2 × 105 PA nitrogen cooling double chamber furnace is comparable to that of 4 × 105 PA single chamber furnace. But the operation cost maintenance cost are low.
2. Strong quenching method
Conventional quenching usually uses oil, water polymer solution cooling, while strong quenching method uses water low concentration brine. The characteristic of strong quenching is that the cooling rate is very fast, there is no need to worry about excessive deformation cracking of steel parts. When conventional quenching is cooled to the temperature of quenchant, tensile stress low stress state will be formed on the surface of steel parts, while strong quenching is in the cooling process, when the workpiece core is still in a static state, the cooling heat will be stopped to form compressive stress on the surface. Under the condition of strong quenching, when the cooling rate of martensitic transformation zone is more than 30 ℃ / s, the supercooled austenite on the steel surface is subjected to a compressive stress of 1200 MPa, which increases the yield strength of the quenched steel by at least 25%. ％。
Principle: when quenching austenitizing temperature, the temperature difference between surface core will cause internal stress. The change of specific volume plasticity of phase transformation structure also cause additional phase transformation stress.
If the thermal stress phase change stress are superposed together, that is to say, the combined stress exceeds the yield strength of the material, plastic deformation will occur; otherwise, it will . If the combined stress exceeds the tensile strength of hot steel, quenching crack will be formed. In the process of strong quenching, the residual stress caused by the change of transformation plasticity austenite martensite transformation specific volume will increase the residual stress.
During intense cooling, the surface of the workpiece is immediately cooled to the bath temperature, the core temperature is almost constant. Rapid cooling will produce high tensile stress, which will contract the surface layer be balanced by the core stress.
The increase of temperature gradient will increase the tensile stress caused by initial martensitic transformation, while the increase of MS at the beginning of martensitic transformation will cause the surface expansion caused by transformation plasticity, the surface tensile stress will increase significantly. Reduced converted to compressive stress. The surface compressive stress is proportional to the amount of surface martensite.
The surface compressive stress determines whether the core undergoes martensitic transformation under compression reverses the surface tensile stress during further cooling.
If the martensitic transformation expands the volume of the heart sufficiently the surface martensite is very hard brittle, it will lead to the fracture of the surface layer due to stress reversal. Therefore, compressive stress should be produced on the surface of steel parts martensitic transformation should occur in the core as late as possible.
3. Cooling method of water air mixture
By adjusting the pressure of water air the distance between the atomizer the workpiece surface, the cooling capacity of the water air mixture can be changed the cooling can be uniform. The production practice shows that this method can effectively prevent the occurrence of quenching cracks for carbon steel alloy steel parts with complex shape.
4. Hot oil quenching
Using hot quenching oil, the temperature of workpiece before further cooling is equal to close to the temperature of MS point, can effectively prevent the deformation cracking of quenching workpiece. The small alloy tool steel is cooled quenched in 160-200 ° C hot oil, which can effectively reduce deformation avoid cracking.
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