Common sense of the hottest quenching heating and

2022-08-19
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Common sense of quenching heating and quenching oil selection

I Quenching heating:

the quenching heating temperature is determined according to the composition, structure and different performance requirements of the steel. Hypoeutectoid steel is ac3+ (30 ~ 50 ℃); Eutectoid steel and hypereutectoid steel are ac1+ (30 ~ 50 ℃)

the quenching heating temperature of hypereutectoid steel is generally recommended as ac1+ (30 ~ 50 ℃). In actual production, it is also increased by about 20 ℃ according to the situation. When heated within this temperature range, the microstructure is fine grained austenite and some fine and uniformly distributed undissolved carbides. After quenching, except for a few residual austenite, its structure is fine carbonized material points evenly distributed on the sheet martensite matrix. Such a structure has high hardness, wear resistance and relatively less brittleness

if the quenching heating temperature of hypoeutectoid steel is lower than AC3 to the special device degree that each tool needs to be made separately, then the steel is not fully austenitized at this time, and there are some unconverted ferrite. Domestically speaking, ferrite remains in the quenching structure after quenching. The hardness of ferrite is low, so that the hardness after quenching can not meet the requirements, but also affect other mechanical properties. If the hypoeutectoid steel is heated to a temperature much higher than AC3 for quenching, the austenite grains will be significantly coarser, and the properties after quenching will be destroyed. Therefore, the quenching heating temperature of hypoeutectoid steel is ac3+ (30 ~ 50 ℃), which not only ensures full austenitization, but also maintains the fine austenite grains

when selecting the quenching and heating temperature of the workpiece in production practice, in addition to the above general principles, the chemical composition, technical requirements, size and shape, original structure, heating equipment, cooling medium and other factors of the workpiece should be considered, and the heating temperature should be adjusted appropriately. For example, for alloy steel parts, the upper limit is usually taken, and for parts with complex shapes, the lower limit is taken

the quenching heating temperature selected for the new strengthening and toughening process is different from the common quenching temperature. For example, sub temperature quenching is the quenching of hypoeutectoid steel after austenitizing at a temperature slightly lower than AC3, which can improve toughness, reduce brittleness transition temperature, and eliminate tempering brittleness. For example, the heating temperature of workpiece made of 45, 40Cr, 60Si2 and other materials is AC3 - (5 ~ 10 ℃)

the quenching heating temperature of hypereutectoid steel should not be lower than AC1, because the steel has not been austenitized at this time. If heated to a temperature slightly higher than AC1, pearlite must also discharge the capacitor and completely transform into austenite, and a small amount of cementite will dissolve into austenite. At this time, the austenite grain is fine, and its carbon mass fraction has been slightly higher and eutectoid composition. If the temperature continues to rise, the secondary cementite will continue to dissolve into austenite, resulting in the continuous growth of austenite grains and the continuous increase of its carbon concentration, which will lead to the increase of quenching deformation tendency, the increase of quenching microstructure microcracks and brittleness. At the same time, due to the high carbon content in austenite, the amount of residual austenite after quenching increases, reducing the hardness and wear resistance of the workpiece. Therefore, it is inappropriate for hypereutectoid steel to be quenched at a heating temperature higher than AC1, especially when it is heated to ACM or above which is fully austenitized

high temperature quenching can obtain more lath martensite or improve the strength and toughness of all lath martensite. For example, 16Mn steel is quenched at 940 ℃, 5crmnm and O steel is quenched at 890 ℃, and 20CrMnMo steel is quenched at 920 ℃

II: selection of quenching oil:

1. Bright quenching oil (quenching at oil temperature of 70 ℃)

bright quenching oil is a cooling medium for heating and quenching parts in a controllable atmosphere. Its main feature is that the surface of parts is bright after quenching. It mainly deals with small parts that will not be processed again after quenching, such as precision instrument parts, watches and small cutting tool parts. In addition to meeting the cooling performance requirements, bright quenching oil can prevent oxidized products from forming large micelles to adhere to the surface of parts, and replace the insoluble products that have been attached to the surface of parts to ensure the bright surface of quenched parts

bright quenching oil is mainly suitable for quenching in protective atmosphere furnace as cooling medium. It can be used for quenching of small and medium section bearing steel, tool and die steel, measuring and cutting tool steel, instruments and meters and other parts. It can also be used for non protective atmosphere quenching furnace to deal with steel with good hardenability. The operating temperature of the oil is 60 ℃ ~ 80 ℃. The moisture content must be controlled during use. When the moisture content is greater than 200 g/g, the brightness will drop sharply, and the quenching oil must be treated, otherwise the quenching quality of parts will be seriously affected

2. ordinary quenching oil (quenching at oil temperature of 60 ℃)

ordinary quenching oil is mainly applicable to the quenching of ferroalloys with good hardenability, such as small-size bearing steel and tool and die steel parts. In the past, only different brands of machine oil were used as quenching oil in China. In the early 1980s, in order to improve the cooling performance, thermal oxidation stability and rust prevention performance of oil products, cryogens, antioxidants and rust inhibitors were added to machine oil, and ordinary quenching oils of different brands were developed, which have better performance than machine oil

ordinary quenching oil can be mainly used for general process quenching of salt bath furnace, box furnace and well furnace, and should not be mixed with other oil products. When changing oil, thoroughly clean the oil groove. The best service temperature of the oil is 50 ℃ ~ 80 ℃, and the maximum service temperature is not more than 80 ℃, so as not to affect the service life. A mixing or oil circulating device should be installed in the oil tank to further improve the cooling capacity of the oil, so that the surface of the workpiece can be evenly cooled, and new oil should be added to the oil tank regularly

3. Vacuum quenching oil (quenching at oil temperature of 80 ℃)

in some special industrial departments, the general heat treatment technology can not meet the use requirements, so the vacuum heat treatment technology is developed. Vacuum quenching oil is suitable for quenching large and medium aviation structural steel, bearing steel, tool and die steel and other alloy steel

during initial use, pre pump for 10min ~ 20min under 66 103 PA to remove the air mixed in the oil, so as to prevent the air mixed in the oil from carrying the oil into the pipeline and vacuum unit due to too low vacuum

4. fast bright quenching oil (quenching at oil temperature of 80 ℃)

fast bright quenching oil is also used for quenching in protective atmosphere as cooling medium. The difference between this oil and bright quenching oil is its fast cooling speed. It is mainly used for quenching materials with poor hardenability and large-size parts in protective atmosphere

fast bright quenching oil is mainly suitable for protective atmosphere quenching in automobile, tractor, bearing and textile machinery industries. It can be used for carburizing and carbonitriding quenching of automobile gears, and can also be used as cooling medium for quenching other steels in protective atmosphere or in non protective atmosphere furnaces

the maximum oil temperature in use shall not exceed 100 ℃, ensuring that the oil has long-term stable cooling capacity and good quenching brightness. It is strictly forbidden to mix water with other oil products. A small amount of water may seriously affect the surface state of quenched parts. The content of carbon black and sulfur should be strictly controlled in the protective atmosphere, which also affects the quality of parts after quenching

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