JPS5817250B2 - High speed tool steel for cold working - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a high-speed tool steel that can be used for thick cold working tools with a large mass and has sufficient hardness down to the core even when air quenched.
This invention relates to a high-speed tool steel that can obtain high heat treatment hardness even if the quenching cooling rate is slow, such as by vacuum heat treatment.

High-speed tool steel used for cold tools is hardened at a high temperature of approximately 1100° C. or higher, and then undergoes secondary hardening through tempering to obtain a tough, durable state with excellent strength and wear resistance.

However, if the cooling during quenching is slow, the temperature
Carbides have already precipitated in the high temperature range of °C, so even if tempering is done, secondary hardening is insufficient and high hardness cannot be obtained. Unable to exhibit excellent characteristics.

The above problem does not occur in normal hot bath quenching or oil quenching.

However, recently, bright heat treatment by heating and cooling in a vacuum or an inert atmosphere has become popular, but in this case, the cooling rate in the high temperature range is faster than that of the normally performed hot bath quenching or oil quenching. Because of its slowness, conventional high-speed cold working tool steels are currently only applicable to relatively small diameter tools of 20 mmφ or less.

In addition, cold working tools are often formed into the tool shape by cold plastic working (usually called cold hobbing), and therefore high speed tool steel for cold working has excellent cold hobbing properties. The present invention was implemented to solve these problems, and it has the high mechanical strength and wear resistance necessary for cold working tools, and at the same time has two
The object of the present invention is to provide a high-speed tool steel that allows atmosphere hardening even for tools with a diameter of 0 mrnφ or more and has excellent cold hobbing properties.

In order to achieve this objective, the present invention has developed CO,5 to
0.9%, Si0.2-1.5%, Cr6.1-8.0
, W 6% or less, Mo 5.9% or less (however, 5 (W
+2Mo(,12),V O,5~1. Si%, Co1
．． 0 to 8.0%, NiO, 3 to 1.0%, the balance consisting of Fe and impurities, and in some cases NO, 03 to o,
, to% and one or more of Ti, Nb, Zr, AI, and H in a total of 0.01 to 0.2%.

The effects and reasons for limitations of the constituent elements in the steel of the present invention will be explained below based on Examples.

The characteristics that high-speed tool steel should have in order to be used with good performance as a cold work tool were determined as follows based on a number of conventional usage examples, and research and development for the steel of the present invention was conducted.

1. High tempering hardness of HR, C60 or higher can be obtained.

2. Has excellent mechanical breaking strength (Charpy impact value of 5 kg-m/a or more).

3. Good cold hobbing properties (annealing hardness of H8217 or less).

4. Furthermore, even large diameter tools of 20 mm or more can be hardened in an atmosphere.

Table 1 shows the chemical composition of the inventive steel, comparative steel, and conventional steel.
A round bar sample of 0 mm φ x 20 m++i was quenched by air cooling, 56
The hardness when tempered at 0°C, 10R, C-notch Charpy impact value, and annealed hardness are shown.

Conventional steel H is a low-alloy high-speed tool steel with an improved matrix composition of 5KH9, ■ is a steel with a lower C content than 5KH9, and J is 5KH9, all of which are manufactured industrially and traditionally used as cold work tools. It is a type of steel that is

Invention steel A has the highest quenching-tempering hardness of HRC65.0 among the invention steels, but its Charpy impact value and annealing hardness are close to the lower limits of the required properties. , the annealing hardness is extremely good, but the quenching -
Tempering hardness is relatively low at approximately HRC62.

B and C have properties intermediate between these, but B has a higher Becharpy impact value than C, whereas C tends to have lower annealing hardness.

When the present invention was carried out, better performance was obtained when a high-speed tool steel having a chemical composition corresponding to A was used for a tool whose workpiece was a difficult-to-work material such as stainless steel.

On the other hand, in cases where the tool was prone to chipping or breakage and needed to have toughness, a high-speed tool steel with a chemical composition corresponding to D or E was used and good performance was obtained.

Comparative steel F has low quenching-tempering hardness and poor hardenability.

For G, the Charpy impact value does not meet the required properties.

Conventional steels H, I, and J all have oI, which has poor hardenability.
Since J has a low Charpy impact value and high annealing hardness, cold hobbing properties are also poor.

A more detailed study was conducted on the relationship between hardenability and chemical composition of high-speed tool steel.

The figure shows the results. After heating the sample to the quenching temperature and cooling it at various cooling rates, the sample was repeatedly tempered twice at 560° C. for 1 hour, and the hardness was measured.

Steels C, D, and E of the present invention containing 6.1% or more of Cr show little decrease in hardness even when the cooling rate is slow, and the hardness is approximately 100 mm.
Tempering hardness of HRC 60 or higher can be obtained even if the round bar is cooled at a rate equal to the cooling rate of the center when air-cooled.

Conventional steels H and I can obtain high tempering hardness under conditions where the cooling rate is extremely fast at 200°C/rn 1 n or more, but
As the cooling rate becomes slower, the hardness decreases rapidly, and at a cooling rate comparable to the cooling rate when air-cooling a 20 mm diameter round bar, a hardness of only about HRC58 is obtained.

Comparative steel F has a high Cr content of 7.8%, but its hardenability is poor.

It was found that this was because the content of ■ was as high as 2.0%.

In other words, the hardenability of high-speed tool steel is greatly influenced by the content of Cr and ■, and in order for a round bar of 20 mm or more in diameter to be sufficiently hardened even when air-cooled, it must contain more than a certain amount of Cr. and ■It is necessary to suppress the content below a certain amount.

From numerous experiments related to the present invention, it has been found that the lower limit for Cr is 6.1%, and the upper limit for ■ is 1.8%.

Furthermore, as shown in Comparative Steel G, even if Cr is contained in excess of 8%, the effect of improving hardenability is saturated, and on the contrary, the Charpy impact value is reduced.

This is the reason why the Cr content in the present invention is limited to 6.1 to s, o%.If the OV is less than 0.5%, the austenite crystal grains will become coarser and the wear resistance will deteriorate significantly. Therefore, the content (1) of the present invention was limited to 0.5 to 1.8.

C forms a carbide with W, Mo, and V contained at the same time to provide wear resistance, and a part of it is formed by quenching and heating to form a carbide.
It has the effect of solid solution in J Lux and gives secondary hardening by tempering. Therefore, the C content is W, 'Mo (Actually W + 2M0)
, ■Must be considered in parallel with content.

The tempering hardness of the invention steel E shown in Table 1 is HRC62,
0, which is close to the lower limit of the required characteristics (HRC 60 or higher).

This means that the C content of E is 0.52%, and the W and Mo content is W.
This is because secondary hardening due to tempering is low since + 2 Mo = 6.5%.

According to this research, in order to obtain secondary tempering with HRC of 60 or higher, the C content must be 0.5% or more, and the W and Mo contents must be W
Since it was found that 5% or more is required for +2Mo, C
And the lower limit of W and Mo content is C0.5%, respectively.

W+2Mo was limited to 5 people.

Furthermore, the Charpy impact value and annealing hardness of the steel A of the present invention shown in the table are close to the lower limits of the required properties.

This is the C content of A and W. This is because the Mo content is high. Conventional steels I and J have even higher W and Mo contents than A (16.5 in W+2Mo), so the Charpy impact annealing hardness no longer satisfies the required properties.

That is, it can be seen that the C content and W+2Mo amount of A are almost the upper limit of the present invention. Therefore, the C content of the present invention,
The upper limit of W, Mo content is C0.9+%, W6%, Mo
5.9% (W + 2M.

12).

The reason why W was limited to a coefficient of 6 or less is that W is an expensive alloying element.
This is because it is not economical to contain more than 6 parts.

Si is usually added as a deoxidizing agent and is contained in an amount of 0.2% or more.

Furthermore, Si content of 1 to 1.5% has the effect of increasing the annealing hardness, but as can be seen from the comparison of the invention steels B and C in Table 1, the higher the Si content, the lower the annealing hardness. The upper limit of the Si content was limited to 1.5 parts.

It is not necessary to add Co to general-purpose high-speed tool steel, but when using difficult-to-process materials as work materials, it is necessary to add 1.0 Co.
A longer life can be obtained by containing Co of ~8.0.

However, if it is less than 1.0%, there is no effect of improving life, and if it is contained in a Co content exceeding a coefficient of 8, the annealing hardness will not decrease and the Charpy impact value will also decrease, so the Co content was limited to a coefficient of 8 or less.

Generally, sufficiently good performance can be obtained without adding Ni, but the addition of Ni in an amount of 1 or less improves toughness.

However, if the content is less than 0.3%, there is no effect of improving toughness, and if the content exceeds 1%, there is little effect, and conversely, the annealing hardness becomes difficult to reduce, so the content was limited to 1% or less.

In addition, NO, 03% or more and Ti, N within the above limited range of components.
0.2 of one or two or more of b, Zr, AI, and B
By jointly adding % or less, crystal grains become finer and toughness is improved.

However, if the content exceeds 0.2, many non-metallic inclusions will occur underground, and the quality of the product will deteriorate significantly.
~0.10%.

The total content of one or more of Ti, Nb, Zr, AI, and B was limited to 0.01 to 0.2.

Table 2 shows the basic components of the invention steel C (see Table 1), including Co, Ni, N, Ti, Nb, Zr, Al, B.
The tempering hardness, Charpy impact value, and annealing hardness of the invented steel containing an appropriate amount of

The test method was conducted according to the method shown in Table 1.

This table shows the advantages and disadvantages of containing each alloying element.

That is, Co increases the tempering hardness, but lowers the Charpy impact value and annealing hardness.

Although Ni improves the Charpy impact value, the annealing hardness does not easily decrease.It is clear that the joint addition of ON and one or more of Ti, Nb, Zr, AI, and H has the effect of improving the Charpy impact value. It became.

Furthermore, Co of sections 1 to 8 is 0. :3-1.0% N
i and 0.03-0.10% N and Ti, Nb, Zr
tAl, one or more of B in total 0.01
When contained at the same time in the range of ~0.2%, properties such as increased tempering hardness and improved Charpy impact value can be obtained, which has great industrial effects.

[Brief explanation of drawings]

The figure shows inventive steel C, D, E1 comparative steel F, and conventional steel H2■
This is a graph showing the relationship between hardness and cooling rate when heated to the quenching temperature shown in Table 1, cooled to room temperature at various cooling rates, and repeatedly tempered twice at 560°C for 1 hour. be.

Claims (1)

[Claims] 1 Weight ratio: C0.5 to 0.9, Si 0.2 to 1.5
Cr6.1-8.0%, W61% or less, Mo5.9
% or less (however, 5 < W + 2 Mo (12), Vo
, 5 to 1.8%, balance Fe and impurities, high speed cold working tool steel 02, in claim 1, C0.8 to 0.9%, Si 0.2 to 0.4% , Mo 5.9% or less (however, 8<W+2 Mo<12), Vl, 3~
High speed cold working tool steel consisting of 1.8'%. 3 In claim 1, C0.7 to 0.8, MO 5.9% or less (however, 8 < w + 2 Mo
<12) ■High speed tool steel for cold working consisting of a steel of 0.5 to 1.3. 4 In claim 1, C0, 6 to 0.7, W3 or less, Mo 4% or less (5 W + 2 Mo
<8) Cold work high speed tool steel having a V ratio of 1.3 to 1.8. 5 In claim 1, C095 to 0.6, W3 and below, Mo4 and below (5 W+2 Mo
<8) High-speed tool steel for cold working consisting of a V ratio of 0.5 to 1.3. 6 Weight ratio of C0.5 to 0.9, SiO, 2 to 1.5
Cr6.1-8.0%, W6% or less, Mo5.9%
Below (5≦W+ 2 Mo (12), Vo, 5
A high-speed tool steel for cold working consisting of Co: 1.8 to 1.8, Co: 1.0 to 8.0, the balance being Fe and impurities. 7 Weight ratio C015~0.9, Si0.2~1.5
%, Cr6.1-8.0%, W6% or less, Mo5.9%
Below (5≦W+2 Mo (12), VO15
A high-speed tool steel for cold working consisting of NiO, 3 to 1.0, the remainder being Fe and impurities. 8 Weight ratio of C015 to 0.9, SiO, 2 to 1.5
Section, Or6.1-8.0%, W6% or less, Mo5.9%
Below (5≦W+ 2 Mo (12), Vo, 5
〜1.8 section further NO, 03~0.10% and Ti, N
b, Zr. One or more of Al and B in total from 0.01 to
A high-speed tool steel for cold working consisting of 0.2 residual Fe and impurities. 9 Weight ratio: C065~0.9, Si0.2~1.5
Cr6.1-8.0%, W61% or less, Mo5.9
% or less (however, 5≦W+ 2 Mo (12), Vo,
5-1.8, Co1.0-8.0%, NiO, 3-1
．． 0% and further NO, 03~0.10%, Ti, Nb
, Zr, AA, B, one or more types in total 0
．． High speed tool steel for cold working consisting of 01~0.2% balance Fe and impurities 0