JPS5826430B2 - Manufacturing method of mild carburizing drill - Google Patents

Description

Detailed Description of the Invention Nitriding is mainly used as a surface hardening method for high-speed steel drills, but the surface hardening layer created by nitriding has a very high hardness, Hv (0,2) 1000 or more. Because of this, there is a risk of the cutting edge becoming brittle, and it is difficult to determine the optimum processing time.

Another disadvantage is that the cost of nitriding is relatively high, making it unsuitable for mass production.

Increasing the C content of high-speed steel increases the tempering hardness and improves the wear resistance, but on the other hand, the toughness decreases, so increasing the C content of only the surface layer through carburizing can provide both wear resistance and appropriate toughness. be able to.

Carburizing is usually thought to involve heating to a high temperature above the transformation point to infiltrate carbon, but when high speed steel is carburized above the transformation point, the surface C becomes 2 or more, and the carburization depth becomes over 1M. , which results in so-called excessive carburization, so it cannot be applied to drills.

Therefore, as a result of extensive research, the present inventors found that steel containing large amounts of alloying elements such as Cr, W, Mo, and V, such as high-speed steel, It was discovered that the amount of surface C and the depth of carburization can be appropriately adjusted by controlling the heating temperature, heating time, and gas carburizing atmosphere composition.

In other words, when carburizing below the transformation point, the carburizing rate is lower than when above the transformation point, so the surface C is reduced by 1.1%.
It has become clear that relaxation carburizing can be easily performed by controlling the back and forth and reducing the carburizing depth to around 0.5 mm.

In this way, the present inventors produced a drill semi-finished product with a groove formed by grinding or cutting at a temperature below the transformation point of high-speed steel, that is, 750 to 700°C, with a surface C of 0.
Manufacture of a mild carburizing drill characterized by performing mild carburizing such that the carburization depth is 95 to 1.2% and carburizing depth to 0.2 to 0.6 mm, followed by heat treatment of quenching and tempering. They established a new method and succeeded in significantly improving the cutting performance of drills.

When carburizing is used as a surface hardening method for high-speed steel cutting tools such as drills, if the surface C becomes higher than 1.2, a large amount of retained austenite will be produced in the quenched state. The number of times of tempering must be significantly increased, which is not a good thing, and the toughness of the old cutting edge deteriorates.

Furthermore, if the surface C is less than 0.95%, the effect of surface hardening is small, so the surface C of the mild carburizing drill should be 0.95 to 1.2%.
It is necessary to limit it to those in charge.

Furthermore, if the carburizing depth exceeds 0.6 ms, the toughness of the blade part will decrease, and if the carburizing depth is less than 0.2 ms, the effect of surface hardening will be small. 6 yn
, m.

Hereinafter, the performance of the mild carburizing drill of the present invention will be explained based on test results.

Table 1 shows the chemical composition of the steel that makes up the drill sample.

Gas carburizing is performed using a continuous atmosphere annealing furnace for 5UJ2 wire annealing (
Using RX+NX gas (750~7oooC), the relaxed carburizing method was carried out by placing the sample in an iron pipe with 3φ and 5φ holes in the side, closing both ends, and charging this into an atmospheric furnace. .

The carbon, potential of relaxation carburization changes the size and number of holes drilled on the side of the iron pipe, and the CO in the pipe is reduced.
It was adjusted by changing the gas concentration.

In addition, the atmosphere gas of the continuous atmosphere annealing furnace is C012~1
4%, CO20.95-1.02% and heating is 7.
The temperature curve was maintained at 50° C. for 2 hours and then slowly cooled at 700'Ctf/*2 hours.

Table 2 shows the mild carburizing method used in the test and the carburized layer C% of SKH9.

That is, the bottom welded inner diameter 50, length 300vt, v
SK in the pipe with 3, 5, and 8 3φ holes drilled on the side of the iron pipe of t, and the pipe with 5 5φ holes drilled in the side.
This is the result of inserting an H9 round bar sample, closing the other end, inserting it into a continuous atmosphere annealing furnace, heating it, turning it in steps of 0.1 m from the surface, and analyzing the C of the chips.

When using method A, the surface C is 1.02% and the carburization depth is 0.4.
For method B, surface C1.09, carburizing depth 0.4
5m, in case of C method, surface C1,171:ib, carburization depth 0.45m, and in case of B method, surface C1,26%.

The carburization depth was 0245 mm.

Next, semi-finished drills with a diameter of 11.65 mm that have been grooved by grinding are placed in these pipes, sealed, and then placed in an atmospheric furnace for mild carburization, followed by quenching and quenching. A test drill was manufactured by performing a restoring heat treatment, electrolytic polishing, centerless grinding (grinding allowance, diameter: 0.1571.), second recess, and button and homo treatment for the blade.

Table 3 shows the cutting test results when using this test drill and using 5K7 (HB223) as the work material.

The cutting conditions are: rotation speed 780r, plrrk cutting speed 28.2m/min, feed 0.3rn, yty
'rev1, hole depth was 40 m, yn blind hole, and Johnson Wax JR570 water-soluble cutting oil was used.

The machine used is Iwata automatic drilling machine YUD 680.

The normally processed drill without mild carburizing showed cutting performance of 50 holes.

On the other hand, in the case of mild carburizing method A, the drill surface C
is 1.02%.

The carburizing depth was 0.35 m, but the number of holes drilled increased to 63.

In addition, in the case of mild carburizing method B, the surface C of the drill is 1.0
7%, the carburizing depth is 0.40m, and the number of holes drilled is 73.
This showed a marked improvement in cutting performance.

Next, in the case of mild carburizing method C, the drill surface C is **1
．． The carburizing depth was 12% x 0.40T1712, and the number of holes drilled was 70.

As is clear from the above, the work material is 5K7 (HB223
), the mild carburizing drill drills 1.26 to 1.46 times as many holes as the normal process drill (homo process drill), and the cutting performance is significantly improved.

Next, Table 4 shows the cutting test results of a mild carburizing drill when SKD 61 tempered to HRC41 was used as the work material.

The cutting conditions are rotation speed 42 Or, pom, cutting speed 15.2m/min, feed 0, 123pun/re.
A 30 ma blind hole was used, and Johnson Wax JR570 water-soluble was used as the cutting oil.

While the normal treatment drill showed cutting performance with 20 holes drilled, the mild carburizing drill of method A had a surface C of 1.02%.
, carburizing depth 0.35. However, the number of holes drilled increased to 27.

In addition, the mild carburizing drill of Method B had a surface C of 1.07%, a carburizing depth of 0.40772 J, and the number of holes drilled was 32, showing a marked improvement in cutting performance.

Next, the mild carburizing drill of method C had a surface C of 1.12%, a carburizing depth of 0.40 van, and the number of holes drilled increased to 30.

As is clear from the above, when the work material is hard as HRC41, the improvement in cutting performance of the relaxation carburizing drill is greater than when the work material is soft SK7.

As explained above, the manufacturing method of the mild carburizing drill of the present invention involves forming grooves on the drill by grinding or cutting, and then cutting the drill at a temperature below the transformation point of high-speed steel, e.g.
Mild carburization is performed at 700°C so that the surface C is around 1.1 mm and the carburizing depth is around 0.40 m5, followed by heat treatment of quenching and tempering, followed by electrolytic polishing, centerless polishing, and No. 2 polishing. The mild carburizing drill manufactured by this method, which is characterized by performing drilling, cutting, and homo-processing, can significantly improve the drilling and cutting performance of soft materials and high-hardness tempered materials.

Claims (1)

[Claims] 1. After machining the drill groove by grinding or cutting, maintain the temperature below the transformation point of high-speed steel so that the surface C is 0.95 to 1.2 mm and the carburization depth is 0.2 to 0.6 mm. 1. A method for producing a high-speed steel relaxed carburizing drill, which is characterized by performing relaxing carburizing so that the drill becomes quenched, followed by heat treatment of quenching and tempering.