Application of the hottest vacuum heat treatment i

2022-08-24
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Application of vacuum heat treatment in cemented carbide cutting tools and dies

Abstract: the effect of vacuum heat treatment on the properties of cemented carbide was studied. Cemented carbide inserts and dies were strengthened and toughened as a whole after heat treatment, especially the bending strength σ BB increased significantly. Through the production test, the service life can be doubled

key words: cemented carbide; Vacuum heat treatment; Strengthening and toughening; Bending strength

1 preface

cemented carbide, as a tool and die material in machinery, mining, electronics, standard parts and other industries, although it has excellent properties such as high hardness, wear resistance, corrosion resistance and so on, in the use of mining drilling and metal cutting tools, there are two common problems: severe edge collapse and brittle fracture and early wear failure due to poor toughness, which limit its scope of use, especially in the occasion of impact load, For example, in tool and die materials such as mine rock drilling, geological drilling, cold punching and cold forging, rough milling, it is not only required to have high hardness and wear resistance, but also required to have good overall strength and toughness. In recent ten years, we have made a systematic study on the heat treatment of cemented carbide. In the late 1980s, a new generation of cemented carbide for mining was developed, which has been widely used [1], and remarkable economic and social benefits have been achieved. In order to further expand and develop the application field of heat-treated cemented carbide and form the serialization of heat-treated cemented carbide, it is the direction of future research. This paper focuses on the vacuum heat treatment of cemented carbide for milling and stamping die, and obtains obvious results

2 test method

2.1 heat treatment method

previously, the heat treatment method of cemented carbide was to imitate the heat treatment of steel, that is, after the cemented carbide products were sintered, they were heated and quenched twice, and then tempered. Now we use a new heat treatment method to replace it. This method is sintering quenching, that is, after sintering, the product is not cooled to room temperature with the furnace, but directly quenched at the sintering temperature or cooled to a certain temperature, eliminating the secondary heating process, so as to save time, labor, reduce energy consumption and improve efficiency

2.2 raw materials and alloy grades

two series of cemented carbide are prepared in this test:

① mold series: yg15c, YG20C

② milling series: YG6, YG8, ys30, YT14, YT5, yw2

yg6c, yg8c and YG15 alloys were also prepared for some condition comparison tests

WC, (TiW) C and co powders used to prepare the above alloys are all from Zhuzhou Cemented Carbide plant

2.3 test equipment

conventional production equipment is used for cemented carbide batching, mixing, pressing and dewaxing. Sintering and quenching are carried out in wzs-20 and WZS-45 vacuum sintering and quenching dual-purpose furnaces

process test is carried out in wzs-20 furnace and industrial production application is carried out in WZS-45 furnace. Two vacuum furnaces can complete vacuum sintering, vacuum quenching, air cooling quenching and other processes. The whole process of quenching process can be carried out automatically according to the preset program, and it can also be operated manually

3 test content

the standard sample used for routine test items is 5mm × 5mm × 30mm bending strength specimen, use a116 blade to test the alloy density, hardness and coercivity. After dewaxing the pressed sample, do the following tests

3.1 comparison of two heat treatment methods

the secondary heating and oil quenching after sintering and the direct oil quenching after sintering were carried out on yg15c and YT14 alloys respectively, and the comparative tests of the two heat treatment methods were carried out

in the two heat treatment methods, take one process with the best effect to treat YG6, YG8, yg11c, yg15c, YG20C, ys30, YT14, YT5, yw2 alloys. The test results are the final test results after tempering, as shown in Figure 1 (the increment of bending strength is the relative increment compared with the sintered state, and the following figures are the same)

it can be seen from Figure 1 that direct heat treatment is feasible, and the treatment of wc- (TiW) c-co alloy by this method is better than the secondary temperature rise heat treatment

Figure 1 comparison test results of two heat treatment methods for each alloy brand

1 Direct oil quenching after sintering 2 Second heating after sintering oil quenching

3.2 test of different quenching media

vacuum quenching of cemented carbide adopts oil quenching and gas quenching. Nitrogen is selected for gas quenching, which is more economical. Figure 2 and figure 3 show the effect of YG8 and yw2 alloys quenched in different media

Fig. 2 bending strength of YG8 alloy after different medium quenching increments

1 Oil quenching 2 Gas quenching

Figure 3 bending strength of yw2 alloy after different medium quenching increments

1 Oil quenching 2 Gas quenching

it can be seen from Fig. 2 that the bending strength of YG8 alloy is increased significantly by direct oil quenching than by direct gas quenching, while it can be seen from Fig. 3 that the bending strength of yw2 alloy is increased significantly by direct gas quenching than by direct oil quenching. Therefore, different grades of alloys should use different quenching media, that is, different alloys, and require different quenching and cooling rates, so as to achieve the best combination of the dissolution of W and C in the cobalt phase, the martensitic transformation of the cobalt phase, and the thermal stress caused by the different thermal expansion coefficients of each component of the alloy

3.3 comparison of alloys with different cobalt contents

Figure 4 shows the comparison of bending strength of alloys with different cobalt contents after heat treatment. Figure 4 shows that the maximum bending strength of the alloy after heat treatment increases with the increase of cobalt content in the alloy, which is consistent with the mechanism of strengthening and toughening the cobalt phase by heat treatment. With the increase of cobalt content, the peak bending strength of the alloy corresponds to a higher optimal quenching temperature (TQ). The increasing trend of TQ is due to the increase of cobalt content and the enhancement of strain relaxation ability of the alloy, which increases the dissolution of W and C in cobalt phase, the optimal combination temperature of martensitic transformation in cobalt phase and thermal stress

Fig. 4 Comparison of heat treatment effects of alloys with different cobalt contents

15C 11C 6C 8

3.4 quenching temperature

the allowance is very small. The vacuum sintering quenching process of cemented carbide is very important after the heat treatment method and quenching medium are determined. From the above tests, it can be seen that the best quenching temperature (TQ) is also different with different alloy grades. TQ mainly depends on the composition of the alloy (as shown in Figure 4). With the increase of cobalt content, TQ tends to increase. TQ is finally determined through repeated tests

3.5 selection of tempering temperature

because the expansion coefficient of hard phase (WC) and bonding phase CO is about 3 times different, there is stress in the alloy after quenching, which may lead to the selective tempering temperature (TT) of the alloy. Two points are mainly considered: one is to eliminate the stress of the alloy as much as possible, and the other is to minimize the precipitation of cobalt phase. Therefore, the tempering temperature should be the best temperature for both. When tempered at low temperature, the bending strength increases with the increase of TT. At this time, tempering is mainly a stress relief process, and there are few precipitates of CO phase. According to the principle of CO phase precipitation strengthening, a small amount of CO precipitates lead to dispersion strengthening. However, with the continuous increase of TT, the precipitates of CO phase increase, and the coercivity of the alloy increases rapidly. The precipitated products such as co3w3c, co7w6, co3w, co7w2 are brittle phases, which seriously worsens the microstructure of the alloy, so the bending strength decreases sharply. Therefore, for low and medium cobalt alloys, TT should be higher, and for high cobalt alloys, TT should be lower. As shown in Figure 5, the tempering time of YG15 alloy is between 4 ~ 30h, and the bending strength, hardness and coercivity change little. Therefore, it is of little significance to extend the tempering time

Fig. 5 Effect of tempering time on the properties of YG15 alloy

(based on the sintered state)

4 production test

4.1 cutting tool

production test shows that the properties of all grades of cemented carbide blades after heat treatment are significantly better than those in the sintered state, and their service life is doubled, as shown in table 1. For example, the wear resistance, toughness and service life of the heat treatment blade tested by Beijing internal combustion engine factory have been significantly improved. The field operators of all test units reported that the carbide heat-treated blade has higher finish, better durability and longer service life than the untreated blade. Table 1 field milling test results of cemented carbide blades

manufacturer alloy

brand alloy

state specification

model processing

material workpiece

name cutting neoprene composite products, if not, will account for more than 90% of the purchase volume of Funeng technology aluminum plastic film roughness/

μ M processing amount/

parts or

time * service life

increase

(Times) speed n/tool walking amount AR/cutting depth AP/N - 1mm R-1mm ys30 sintered state

heat treatment

heat treatment

steel

quenching and tempering parts gasoline engine

camshaft 350

350

3501.2

1.23-4

3-4

3-45

5

5296 pieces

808 pieces

946 pieces -

1.7

2.2 YT14 sintered state of Taiyuan mining machinery plant

heat treatment 313108

313108zg25

cast steel right traction

box Body 226

2261.3

1.32.5

2.54

520min

32min -

1.6 YT14 sintered

heat treated steel

quenched and tempered parts reverse shaft

rough 350

3500.4

0.43

3 250 pieces

550 parts -

1.2 YT14 sintered state of Yunnan machine bed plant

1 # heat treatment

2 # heat treatment 416108

416108

steel

forged steel 590

590

5900.2

0.2

0.23

3

<3 100 in the summary, it is necessary to explain the inspection, problem discovery and treatment of enterprises one by one

200

400

1

3

* the processing time of each edge is 1 # 2 for different heat treatment systems

4.2 die

Shanghai steel ball factory is a large professional steel ball production factory in China. The 19/32 "steel ball die was tested and after heat treatment, the service life of the die is more than twice that of the untreated die, The service life of cr12mo steel mold is increased by 10 times. At present, the steel mold used has short service life and low work efficiency. Therefore, three sets of 11/16 "mold have been trial produced. The service life of heat-treated mold is 4.2 times higher than that of untreated mold, and more than ten times higher than that of Cr12 Steel mold. The field test results are shown in Table 2. The service life of cemented carbide dies after heat treatment is generally improved. Table 2 field test results of cemented carbide steel ball stamping die

manufacturer alloy

brand alloy

State specification

model upsetting

material specification/

mm stamping times/

times Min-1 service life

life/ten thousand grain life

high (Times) remarks Luoyang Bearing Factory tg20c

cr12 heat treatment

bearing steel 19/32 ″

19/32 ″ GCr15

gcr15 < 10.7

< 10.7106

10630

310

- cracking

size out of tolerance on the sea

steel ball

YG20C sintered 19/32 "GCR - contact circle worn, scratch extended heat treatment 19/32" GCr15 ㎜ 1. The contact circle is slightly worn, the core is depressed, and the sintered state is 11/16 "GCr15 ﹤ 18.06837.5 - crack propagation, core damage heat treatment 11/16" GCr15 ﹤ 18.068338.84.2 the contact circle is worn, and the scratch is slightly extended

5 conclusion

(1) using wzs-20 and WZS-45 vacuum sintering quenching furnaces can realize direct quenching of cemented carbide after sintering, saving time, labor, energy and consumption

(2) the performance of cemented carbides for various purposes can be improved to varying degrees after appropriate process heat treatment. The service life of cemented carbides for milling and stamping dies can be doubled after heat treatment. (end)

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