Study on the influence of the two hottest quenchin

Research on the influence of two kinds of quenching oil on the heat treatment quality of leaf springs

Abstract: This paper studies the influence of two kinds of oil on the heat treatment quality of leaf springs by comparing the cooling characteristics of N32 engine oil and Jinyu y15-ii rapid bright quenching oil, and analyzing the microstructure and properties of 60Si2Mn and 50CrVA steel samples quenched and cooled with two kinds of oil. The experimental results show that the insufficient high temperature cooling rate of N32 engine oil is the reason why it is not suitable for the quenching of 60Si2Mn leaf springs with an effective thickness greater than 12mm. Today, Yu y15-ii fast bright quenching oil has short steam film stage, fast high-temperature cooling rate, and sufficient low-temperature cooling rate, which can meet 60Si2Mn and 20 with a thickness of less than 14mm. According to the actual needs, it can refresh the data and quench 50CrVA leaf springs with a thickness of about mm

key words: 60Si2Mn leaf spring cooling characteristics effective thickness

1. Preface

for a long time, there has been a widespread phenomenon in the heat treatment industry that "heavy heat and light cold" - paying attention to the heating control of workpiece and ignoring quenching and cooling technology. Various available modern technologies are constantly applied to the heating of workpieces, but the cooling is still carried out in the customary water and ordinary engine oil. It is possible to harden the 12mm thick 60Si2Mn leaf spring with good oil quality and good swing by quenching with engine oil, but it is difficult to achieve satisfactory results under the premise of mass production and many influencing factors. Although the effect of using water-soluble quenchant is also good, due to many management links, an independent circulation system is required, which lacks flexibility for the production of products of different materials and specifications, and is difficult to cope with the rapid and changing market demand. In order to solve the above contradiction, tap the potential of the traditional 60Si2Mn spring steel. This paper attempts to quench and cool the thicker 60Si2Mn leaf spring with a new type of Jinyu y15-ii fast bright quenching oil, and compares the cooling characteristics with N32 engine oil. "In the past, we are familiar with plastics, metals, ceramics and other materials to explore new oil products suitable for the quenching of 60Si2Mn leaf springs with thicker sections.

2. test conditions and methods

the cooling characteristics of N32 engine oil with different proportions of old and new and today's Yu y15-ii rapid bright quenching oil are tested under the condition of oil temperature of 50 ℃ and volume of 1200ml, using is09950 international standard, and using khr-01 cooling characteristics tester to determine the cooling characteristics of oil Sex

leaf springs of two kinds of steel and 14 × 100 60Si2Mn spring steel and 18 × 100 standard tensile samples of 50CrVA spring steel are heated with Bll type walking beam furnace, Quenched and cooled with N32 engine oil and Jinyu y15-ii fast bright quenching oil respectively, and the oil temperature is ℃. Check the metallographic structure with axiotech metallographic microscope; We-30t universal material testing machine is used for tensile test; Check the hardness with hb-3000 cloth hardness tester

3. Test results

3.1 cooling characteristics of N32 engine oils with different proportions of new and old

the cooling characteristics of N32 engine oils with different proportions of new and old are listed in Table 1. According to the data in Table 1, although the Tvmax of old oil is significantly lower than that of new oil, the Vmax of old oil is close to that of new oil. However, with the increase of new oil, the quenching oil V300 ℃ is increased, and the chance of non martensitic transformation (a → b) is reduced. Therefore, for the quenching of 60Si2Mn steel, the new oil has better comprehensive cooling characteristics. Table 1 cooling characteristics of new and used oils with different components of N32 engine oil

note: t650 ℃ in Table 1 is the time to cool to 650 ℃ (i.e. the nose tip temperature of 60Si2Mn a → P)

3.2 comparison of cooling characteristics between y15-ii rapid bright quenching oil and N32 engine oil

the cooling characteristic parameters of the two oils obtained from the experiment are listed in Table 2. Through the comparison in Table 2, it can be seen that y15-ii rapid bright quenching oil has a shorter vapor film stage, and the temperature at which the maximum cooling rate occurs is higher, which avoids the possibility of precipitation of proeutectoid ferrite from supercooled austenite first; At the same time, y15-ii fast bright quenching oil has a sufficiently high low-temperature cooling rate to reduce the transformation amount of bainite (b), so that martensite (m) transformation is sufficient and sufficient quenching depth is obtained. Table 2 Comparison of cooling characteristics between y15-ii fast bright quenching oil and N32 engine oil

in addition, viscosity and flash point are the acceptance criteria of oil products. Y15-ii fast bright quenching oil has the characteristics of low viscosity, good fluidity, less consumption in use and higher flash point than ordinary engine oil

3.3 comparison of quenching and cooling test results of 60Si2Mn and 50CrVA spring steel in two media

specification is 14 × 60si2nn and 18 of 100 × Under the chemical composition and heat treatment process conditions listed in Table 3, the test results of 100 50CrVA leaf spring steel and samples quenched and cooled in y15-ii rapid bright quenching oil and N32 engine oil are listed in Table 4. Table 3 chemical composition and heat treatment process of the sample

Table 4 tensile test results of two kinds of spring steels quenched by different quenching media

it can be seen from table 4 that the strength of the same material after heat treatment with y15-ii rapid bright quenching oil is slightly higher than that of N32 engine oil, and the plasticity index is higher than that of N32 engine oil quenching

the metallographic structure of l#, 4# samples before and after heat treatment is shown in Figure 1. It can be seen from Figure 1 that the raw material structure of 60Si2Mn steel is pearlite + Ferrite: the raw material structure of 50CrVA spring steel is pearlite + a small amount of ferrite; The quenching and tempering structure of 60Si2Mn steel with N32 engine oil is troostite + a small amount of bainite; the quenching and tempering structure of 50CrVA spring steel with N32 engine oil is tempered troostite; The microstructure of 60Si2Mn steel quenched and tempered by y15-ii rapid oil is tempered troostite; 50CrVA spring steel is quenched and tempered with y15-ii rapid oil, and the microstructure is uniform and fine tempered troostite. Obviously, the cooling of y15-ii fast oil is better than N32 oil

the tensile fracture of different samples is shown in Figure 2. Compared with the fracture morphology in the figure, it can be seen that the radiation area of the sample quenched with yl5-ii rapid oil is smaller than that quenched with N32 engine oil. The reduction of area of the former is higher than that of the latter, while the strength of the former is slightly higher. Such mechanical properties are more ideal for leaf springs

3.4 comparison results and analysis of quenching hardness of products at the production site

in actual production, the heating temperature is ℃, the heating time is minutes, three pieces are taken every half an hour, and N32 engine oil is used to 12 × 100 60Si2Mn leaf spring and use yl5-ii fast bright quenching oil to pair 14 × When 60Si2Mn leaf spring of 76 is quenched, the two oil temperatures are ℃, and the hardness value after quenching is shown in Table 5. Table 5 quenching hardness of 60Si2Mn leaf springs produced on site with different quenching oils of the same material

the data in Table 5 shows that the quenching hardness of 12mm 60Si2Mn leaf springs in N32 engine oil is 485hb at the highest and 321hb at the lowest. The hardness is uneven, and only a few values meet the requirements. It shows that the oil is not enough for the high temperature cooling rate and maximum cooling rate of 60mm 60Si2Mn leaf spring with an effective thickness of 12mm. In today's Yu y15-ii fast bright quenching oil, the quenching hardness of 14mm 60Si2Mn leaf spring is 550hb at the highest and 463hb at the lowest, with an average of 505hb. The hardness is relatively uniform, and its cooling performance can meet the quenching requirements of 14mm thick 60Si2Mn leaf spring

after a year of use and exploration, today Yu in fact y15-ii fast bright quenching oil can meet the quenching of 60Si2Mn leaf springs with a thickness of less than 14mm, and on the quenching treatment of 50CrVA leaf springs with a thickness of about 20mm, it can harden thoroughly on the whole section, obtain good mechanical properties, and maintain the workpiece with good brightness

4. Discussion

the purpose of spring quenching is to quench austenitized steel in a reasonable way to form martensite, and then temper to achieve the required microstructure and properties. The key to ensure quenching is that the cooling rate of the quenching medium at the nose tip of the C curve of the spring steel should be large enough to prevent the supercooled austenite from forming pearlite or bainite structure. According to the supercooled austenite transformation curve and end quenching curve of 60Si2Mn steel and 50CrVA steel, the martensite formation temperature is about 300 ℃, so the appropriate cooling medium should reach the maximum cooling rate at the nose tip and have an appropriate cooling rate below 300 ℃, In order to achieve the purpose of both hardening and reducing deformation

according to the data in Table 1, N32 engine oil (whether old or new), t650 ℃ (which is the time for a → p to cool to 650~c) is ≥ 4.8 seconds, while the shortest time for 60Si2Mn steel "C" curve to change from a → p to the tip of the nose is about 4 seconds, resulting in medium temperature transformation during the quenching process of the workpiece and the appearance of undue bainite structure (b), as shown in Figure 1 (c). The hardness analysis of the production site (Table 5) shows that the quenching hardness with N32 engine oil is uneven and low, because its Tvmax is lower than the nose tip temperature of 60Si2Mn steel "C" curve and Vmax (see Table 2) is slow, which is obviously not suitable for mass production of 60Si2Mn steel leaf springs with an effective thickness greater than 12mm. N32 engine oil is suitable for quenching 50CrVA steel, but the effect is worse than that of y15-ii, which strives to be the leader in implementing the new development concept. See Fig. 1 (d) for rapid bright quenching oil

the data in Table 2 shows that the steam film stage of y15-ii rapid bright quenching oil is shorter, and the temperature at which the maximum cooling rate occurs is higher. This avoids the precipitation of pre eutectoid ferrite and bainite from supercooled austenite, and has a sufficiently high low-temperature cooling rate (usually 300 ℃ cooling rate represents the low-temperature cooling rate of quenching medium), so as to obtain an ideal structure. According to the metallographic examination standard, the microstructure level of the sample quenched with y15-ii for 60Si2Mn steel is higher than that quenched with N32 engine oil; After heat treatment of 50CrVA spring steel with two quenching media, y15-ii fast bright quenching oil has finer and more uniform tempered troostite structure than N32 engine oil in terms of microstructure, as shown in Figure 1 (E) and (f). Although there is not much difference from the fracture morphology photos in Figure 21, it can be seen from the tensile data that after heat treatment, the material strength of y15-ii oil is slightly higher than that of N32 engine oil, and the plasticity index is higher than that of N32 engine oil quenching. This is mainly because the characteristic temperature and maximum cooling rate of y15-ii oil are better than that of N32 engine oil

therefore, the use of y15-ii fast bright quenching oil, on the one hand, ensures 14 × 60Si2Mn of 100 (18 × 100 50CrVA) leaf spring is hardened on all sections; On the other hand, it also ensures the mechanical properties after heat treatment

5. conclusion

1. adding new oil to the old N32 engine oil can not significantly improve the cooling characteristics, and N32 engine oil is not suitable for mass production with an effective thickness greater than 12mm

2. Y15-ii fast bright quenching oil has good cooling characteristics. After 60Si2Mn material is heat treated with y15-ii fast bright quenching oil, the plasticity and metallographic structure level of the material after stretching are better than N32 engine oil

3. for large section (about 12mm) 60Si2Mn leaf spring, y15-ii rapid bright quenching oil heat treatment can improve the comprehensive mechanical properties of the material and better meet the performance requirements of the product. (end)