JPH034618B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a nitride-containing sintered material that has excellent heat resistance, wear resistance, and hardness, and has free machinability as a cutting tool (elimination of heat generation, discontinuity of cutting layer, beautiful finished surface, and shortening of working time). The present invention relates to a V-shaped tool steel and its manufacturing method. High-speed steel, which is a typical tool steel, is W + 2Mo (W
Equivalent weight) 10.0 to 24 wt% (hereinafter wt% is simply abbreviated as %), Cr3.0 to 6.0%, V1 to 5%, Co18% or less,
It has a composition consisting of 0.3 to 1.5% C, 1% or less of Mn and Si as other metals, and the balance Fe and unavoidable impurities, and the structure is M ₆ in an austenitic matrix (turned into martensite by heat treatment). C, _{M23C6 ,}
It is a product in which carbides such as MC and M ₂ C (M is one or more metal elements) are dispersed, and by increasing V (almost present in steel as carbide VC or V ₄ C ₃ ) Although it has been pointed out for a long time that hardness, wear resistance, and heat resistance are improved, the V content has been limited to about 5% due to manufacturing constraints.
That is, the reason for this is that while an increase in V makes melting difficult, hot forging for the purpose of crushing feather-like carbides generated during solidification becomes difficult. In addition, atomized high-speed steel is known, in which a molten alloy having the above composition is rapidly cooled by spraying to prevent agglomeration of carbides, and the resulting powder is hot-formed into a material. According to this method, Although it is possible to increase the V content, the V content is still limited to about 7% due to hot working for the purpose of plastic deformation and other constraints. In view of this, as a result of various research conducted by the present inventors, we developed a sintered high-V high-speed steel with excellent heat resistance, wear resistance, and hardness, and a manufacturing method for the same.
Suggested by 52709. The basic idea is to create an alloy powder by reducing a mixed powder of metal oxide powder and carbon powder in a hydrogen atmosphere, sintering it in vacuum, and then subjecting it to high density by hot isostatic pressure treatment if necessary. According to this, the V content is 8.5 to 38
% of sintered high V high speed steel is obtained. The feature of this method is that a high V alloy powder can be obtained by simultaneously reducing the oxide powder of the component metal element of the alloy with carbon and hydrogen.
During this period, the solid-phase reaction occurs from start to finish, so that coarsening of the carbide does not occur. The sintered high-V alloy steel obtained in this way takes advantage of the advantages of conventional high-speed steel while adding carbide (VC)
As a result of this increase, various properties such as heat resistance, abrasion resistance, and hardness become superior. As a result of further studies on this sintered high-V alloy steel, the present inventors found that the above-mentioned properties could be further improved by adding nitrides and/or carbonitrides (hereinafter simply referred to as nitrides) to this alloy. The present invention was achieved based on the finding that it is possible to improve the machinability and provide free machinability. That is, one of the present inventions is W+2Mo (W equivalent) 10.0
~24%, Cr3.0~6.0%, V6.0~25%, Co18% or less, C1.0~7.0%, Mn+Si<1.0%, balance Fe and unavoidable impurities. Alloy equivalent to high V high speed steel. The present invention relates to a nitride-containing sintered high-V tool steel characterized by having 1.0 to 25.0% TiC _1-x N _x (1≧x≧0.5) dispersed in the steel. Another aspect of the present invention is W+2Mo (W equivalent)
10.0~24%, Cr3.0~6.0%, V6.0~25%, Co18%
Below, oxide powder of each metal component element equivalent to high V high speed steel consisting of C1.0~7.0%, Mn+Si<1.0%, balance Fe and unavoidable impurities is mixed with carbon powder, and this is heated in a hydrogen atmosphere. Add 1.0 to 25.0% TiC _1-x N _x (1≧x≧0.5) powder to the powder heated and alloyed in
The present invention relates to a method for manufacturing a nitride-containing sintered high-V tool steel, which is characterized in that the mixture is mixed and molded, vacuum sintered, and then densified by hot isostatic pressure treatment. The composition of high-V high-speed steel that is mixed with nitrides is the same as that of conventional high-speed steel, except for a large amount of V, and is merely a successor of this (Reference: 'Masao Kondo', Bulletin of the Japan Institute of Metals) , vol.5, No.7 (1966),
(p. 445-449) Next, the reason why the composition of the high V tool steel of the present invention is limited as described above will be described below. W and Mo are elements that stabilize the austenite phase of steel, and also contribute to the formation of M ₆ C carbides,
The content of W+2Mo was limited to 10.0 to 24% because
If these are less than 10%, sufficient hardness and wear resistance cannot be obtained, and if they exceed 24%, toughness is impaired. The total amount of W + 2Mo is specified as 1.
This is because % Mo has the same effect as 2% W. Next, the addition of Cr is to stabilize the austenite phase and improve the high-temperature hardness of the material, and the reason why the content is 3.0 to 6.0% is that if it is less than 3%, it will stabilize the austenite phase and improve the high-temperature hardness. This is because the improvement is insufficient, and if it exceeds 6%, the effects of stabilizing the austenite phase and improving high-temperature hardness are saturated and the cost increases. In addition, Co has the effect of increasing heat resistance and improving high temperature hardness, and the reason why the content is 18% or less is that
This is because if it exceeds 18%, the material becomes brittle. Furthermore, C forms carbides such as M ₆ C and hardness.
It contributes to improving wear resistance, but its content is reduced to 1.0
The reason why it is limited to ~7.0% is that if it is less than 1%, sufficient hardness and wear resistance cannot be obtained, and if it exceeds 7%, toughness will be impaired. Note that C is usually added based on the following formula. C (%) = 0.19 + 0.17 (W + Mo) (%) + 0.22 V (%) Furthermore, Mn + Si are mixed as impurities, but if their total content exceeds 1.0%, workability will be impaired. This causes an adverse effect. Further, in the present invention, the addition of V and nitrides and the critical significance of their contents are as follows. That is, there are two direct reasons why nitrides are made to coexist in high V alloys. One of these is that the high V alloy is sticky in the annealed state and has poor machinability, resulting in large cutting resistance and heating of both the cutting tool and the workpiece, resulting in a poor finished surface. When nitride is added to this,
Machinability is significantly improved. This effect appears when 1% or more of nitride is added. Another reason is the trade-off with toughness. Although V carbide and nitride both improve hardness, wear resistance, etc., nitride makes a stronger contribution. Furthermore, nitrides have the unique effect of improving seizure resistance and heat resistance. The decrease in toughness due to high V is slight. On the other hand, if nitrides are added to low V alloy steel, the toughness will drop sharply. On the other hand, when added to high V alloy steel with a V content of 6% or more, the degree of decrease is reduced;
When the amount exceeds 25%, the effect of high V addition becomes saturated.
Therefore, in order to improve a specific property under the condition that toughness is not reduced, it is possible to achieve the objective by simply increasing V, but the degree of improvement may be insufficient or the nitride may When you want to impart unique properties to an alloy, increase the V and add nitrides to make both coexist.
You will be able to reach your goal. For this purpose, use V
Keep nitrides at levels above 6.0 and below 25%
% or less. However, nitride is 1
If it is less than 25%, the effect of nitride addition is insufficient, and if it exceeds 25%, the material becomes brittle and its resistive strength decreases. The nitride-containing sintered high-V tool steel of the present invention is manufactured as follows. That is, an alloy powder excluding nitrides is made, nitride powder is added to this, mixed and pulverized to adjust the particle size, and then molded, and the molded body is vacuum sintered to have a theoretical density ratio of 95.
% or more, and further increase the density ratio to 100% or more by hot isostatic processing. The alloy powder excluding nitrides is obtained by reducing a mixed powder consisting of oxides of the constituent elements (however, carbon is mixed alone) in a hydrogen stream at a relatively low temperature. In this method, co-reduction by carbon and hydrogen and alloying proceed simultaneously, and high temperatures are not required, so that the resulting alloy powder does not substantially undergo secondary growth. Therefore, it can be easily crushed. Note that a part of the oxide powder of the constituent elements may be replaced with metal powder or carbide powder. As a guideline, the amount of carbon that is ultimately incorporated into the alloy (the amount that forms carbides and forms a solid solution) should be approximately half of the amount required to reduce the oxide to CO. The remaining half required for reduction is taken over by hydrogen reduction. The above conditions are just a guideline, and the details vary somewhat depending on the amount of reduction, furnace dimensions, hydrogen supply conditions, etc. The particle size of the alloy powder due to reduction should be 10μ or less, preferably 3μ or less, and the reduction temperature should be set high to speed up the reduction, and low to avoid secondary growth of the alloy powder, at 950 to 1200℃. It can be carried out within a temperature range of Nitride powder is added to the alloy powder thus obtained, and the mixture is mixed and ground to form a powder of micron order. At this time, carbon powder may be added to adjust the carbon content as necessary, or metal carbide, particularly V carbide, may be newly added. Nitrides include IVa or Va group metal nitrides, such as TiN, ZrN, HfN, TaN, NbN, VN,
TiCN, ZrCN, HfCN, TaCN, NbCN, VCN
One or more of the following may be considered,
All nitrides other than TiN are heavy and expensive;
TiN or TiCN in terms of heat resistance, hardness and nitrogen content
is the most desirable. Non-stoichiometric TiCN is correctly TiC _1-x N _x , but if x≧0.5) then TiN
It is equal to It will be used in this meaning below. It is the same as the normal powder metallurgy method to mold and sinter the mixed powder that has been pulverized with the addition of nitrides, with or without the addition of a binder, but vacuum sintering is required to ensure complete degassing. In order to perform sintering and reduce denitrification, it is desirable to sinter in a nitrogen atmosphere. In addition, sintering is performed in a solid phase region where the structure is not rough.
The theoretical density ratio shall be 95% or more. It is difficult to achieve a density ratio of 100% through such solid phase sintering,
As a result, the toughness remains at a low value. Of course, high V alloys have good sinterability, so depending on the application, they can be used as they are sintered. Hot forging can be considered to increase the density, but there are restrictions on the shape of the workpiece, and there is a risk of forging cracks in the alloy of the present invention, which contains many carbides and nitrides. Densification by hot isostatic pressing without undergoing heat is most desirable. Hereinafter, the present invention will be explained with reference to examples. Example 1 WO ₃ 1.261Kg, MoO ₃ 0.525Kg, Cr ₂ O ₃ 0.585Kg,
2.321Kg of V ₂ O ₅ , 1.271Kg of CoO, 8.049Kg of Fe ₂ O ₃ and 1.90Kg of carbon powder were mixed and pulverized in a ball mill to give an average particle size of 2μ or less, which was lightly formed into pellets and then pulverized for 1120 minutes under a hydrogen stream. After heating for 4 hours at a temperature of
W-3.5%Mo-4%Cr-3.5%V-10%Co-1.25
%C-67-75%Fe (including 1% or less of Mn and Si in total)], 10kg of high V alloy powder with V increased to 13.0%, C increased to 3.2%, and Fe reduced to 56.3%. I built it. Carbon 0.48 to remove residual oxygen from this alloy powder
Kg and 1.11Kg (10%) of TiN with an average particle size of 1.2μ or less
were added and mixed and ground in alcohol. The alloy powder did not undergo secondary growth and was easily pulverized.
Add 2% paraffin binder to this, dry it, then mold the test piece in a vacuum (0.01 mmHg or less).
(deparaffinization at 300°C, degassing at 900-1000°C, main sintering at 1200°C for 1 hour) to obtain a sintered body with a theoretical density ratio of 96%. This was subjected to hot isostatic compression (1100°C, 1500 atm, 30 minutes) to reduce the density ratio to 100.
% post-heat treatment (1200℃, air-cooled air quenching, 560
Tempering was performed 3 times for 1 hour). Similarly, with a composition equivalent to SKH57, increase the V amount to 3.5%, 8
%, 13%, and 25%.
TiC _1-x N _x (1≧X≧0.5) 0%, 5%, 10%,
High V alloy steels with various compositions shown in Table 1 were manufactured by adding 15% and 20%. These high V alloy steels were tested for hardness, transverse rupture strength, and machinability after annealing at 850 x 1 hour. The results are also listed in Table 1. Also, in Table 1, comparative alloy No. 14 (18%V-0%
Throwaway inserts (shape TNPR332) were made from alloys No. 6 (8% V - 10% TiN) and No. 10 (13% V - 5% TiN) of the present invention, with a diameter of 43 mm.
We conducted a cutting test on SUS304. Cutting tests were conducted at a depth of cut of 1.0 mm and a feed of 0.21 mm, using cutting fluid and varying the rotational speed. The results are also listed in Table 1.

【table】

[Table] Comparing Comparative Alloys No. 1 and No. 2 in Table 1, it is clear that in the alloy with a V content of 3.5%, the transverse rupture strength is reduced by 280 Kg/mm ² due to the addition of 5% TiN. For,
Comparing Comparative Alloy No. 4 and Invention Alloy No. 5, it is clear that in an alloy with a V content of 8%, the decrease in transverse rupture strength is as small as 31 Kg/mm ² with the addition of the same amount of TiN. The same thing happened with comparison alloy No. 9 and invention alloy No. 10.
It is also observed in Comparative Alloy No. 14 and Invention Alloy No. 15. In addition, in comparison alloy No. 1 with a V content of 3.5%, the rotation speed
It is known that the cutting length at 290 rpm (cutting speed 42 m/min) is about several mm, and comparative alloy No.
Although machinability improves when V is increased as in No. 14, the effect becomes more pronounced when a high V content and nitride coexist as in the alloy of the present invention, and moreover, the machinability improves with more nitride. It turns out that it is effective. Example 2 Alloy No. 1 shown in Table 1 of Example 1 (comparative alloy,
SKH57 composition equivalent), No. 3 (comparison alloy), No. 7 (invention alloy), and No. 14 (comparison alloy) were each made into standard-sized end mills with two flutes, a diameter of 10 mm, and short length. The cutting ability was compared. The conditions are rotation speed 580 rpm,
Feed rate: 51 mm/min, depth of cut: 9 mm, dry method for mating material
It is SKD-11 with HRC20-25. As a result, the end mill diameter wear of No. 1 reached 0.08 mm at a cutting length of 800 mm and was almost at the end of its life, whereas No. 3 had wear of 0.075 mm at 1600 mm, and No. 7 had wear of 0.025 mm.
mm, No. 4 remained at 0.040 mm. No.3, No.7,
No. 14 has V+TiN of almost 18%, so
At the same amount of V + TiN, VC is more TiN than TiN.
It can be seen that the coexistence of VC and VC increases the wear resistance in this order. When the rotational speed is doubled, the end mill becomes red hot, but it still maintains its cutting ability. Heat resistance was also ranked high. The finished surface was good in all cases. Conventionally, surface treatments using TiC, TiN, etc. have become commonplace for the purpose of extending the life of cutting tool steel.However, with this method, there is a risk of the surface layer peeling off, but with the present invention, Since the nitrides are incorporated into the alloy, there is no need to worry about the surface layer peeling off, and the nitrides are always exposed even when worn, ensuring excellent cutting performance and significantly increasing service life. This has the following effects.

Claims (1)

[Claims] 1 W+2Mo (W equivalent) 10.0 to 24 wt%, Cr3.0 to
6.0wt%, V6.0~25wt%, Co18wt% or less, C1.0
~7.0wt%, Mn + Si 1.0wt% or less, balance Fe and unavoidable impurities, making it an alloy steel equivalent to high-V high-speed steel.
A nitride-containing sintered high-V tool steel, characterized in that TiC _1-x N _x (1≧x≧0.5) is dispersed in an amount of 1.0 to 25.0 wt%. 2 W+2Mo (W equivalent) 10.0~24wt%, Cr3.0~
6.0wt%, V6.0~25wt%, Co18wt% or less, C1.0
Oxide powder of each metal component element equivalent to high V high speed steel consisting of ~7.0wt%, Mn+Si1.0wt% or less, balance Fe and unavoidable impurities is mixed with carbon powder, and this is heated in a hydrogen atmosphere. into an alloyed powder
TiC ₁ -x _N A method for manufacturing nitride sintered high V tool steel.