JPH08158017A - Production of cutting tool for gear cutting - Google Patents

Abstract

PURPOSE: To produce a cutting tool for gear cutting, having toughness equal to that of a forged material and having excellent tool life, from a cast product. CONSTITUTION: The cutting tool for gear cutting is produced by casting a molten steel in a lost wax mold above a temp. higher than the melting point of this molten steel by 20-60 deg.C. As to the contents of alloying elements, this cutting tool for gear cutting has a composition consisting of, by mass, 0.70-2.00% C, <=3.00% Si, <=1.50% Mn, 3.0-6.0% Cr, <=13.5% Mo, <=27.0% W, <=6.0% V, >=0.025% N, and the balance Fe with inevitable impurities and satisfying W+2Mo=14.0 to 27.0%. Further, <=13.0% Co, <=1.0% Al, <=1.0% Nb, <=1.0% Ti, <=0.30% S, <=0.40% Pb, <=0.15% Te, <=0.01% Ca, and <=0.60% rare earth elements can be incorporated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tooth cutting blade such as a hob cutter and a spiral bevel gear cutter of integral type and assembled type.

[0002]

2. Description of the Related Art Tooth cutting tools for gears are required to have high hardness and wear resistance as well as toughness. Therefore, as a material for a tooth-cutting tool, a high-speed steel wrought material has been mainly used conventionally. That is, molten steel of high-speed steel adjusted to the required chemical composition is cast in a mold to form a steel ingot, which is subjected to hot working such as hot forging and hot rolling to obtain a bar. By this, the steel is wrought and the structure is refined to improve the toughness of the steel.
The shape of the tooth cutting blade is cut out from this bar material by quenching, quenching and tempering, and cutting edge processing is performed. In the case of an assembly type hob cutter, the tooth cutting blade is manufactured through an assembly process.

[0003]

If a large steel ingot is used in the above-described steel ingot forming process, there is a possibility that composition segregation may occur or crystallized carbide may grow large and impair the toughness of the steel. There is. Therefore, high speed steel powder is produced from molten steel by a gas atomization method or the like, and the high speed steel powder is sintered and solidified by using a high temperature isostatic press (HIP) to form a steel ingot. ing. This is hot worked into a bar.

As described above, since the tooth-cutting blade is manufactured by cutting from a wrought material, the material yield is poor even though an expensive steel material is used, the cutting cost is high, and it takes a long time to manufacture the cutter. There was a big financial problem. If you cast molten steel of high-speed steel into a shape close to the shape of a cutting gear and use this as a material, the amount of cutting can be reduced, so the above-mentioned material yield, cutting cost, manufacturing period, etc. It is effective in solving problems. However, since the cast product has a problem that the metal structure is rough and the toughness of steel is low, the conventional cast product has not been used as a material for a tool requiring toughness such as a cutting tool.

The present invention has been made against the background of the above-mentioned state of the art. The object of the present invention is to cast a tooth cutting blade having a toughness comparable to that of a forged material and an excellent tool life. It is to provide a method of manufacturing by.

[0006]

According to the method for manufacturing a cutting tool for gear cutting of the present invention, the molten steel is kept at a temperature not lower than the melting point of the molten steel of 20 to 60 ° C.
A tooth cutting blade manufactured by casting in a lost wax mold at a temperature of (1), wherein the content of alloying elements in the tooth cutting blade is C: 0.70 to 2.00% in mass%, Si: 3.00% or less,
Mn: 1.50% or less, Cr: 3.0 to 6.0%, M
o: 13.5% or less, W: 27.0% or less, V:
6.0% or less, N: 0.025% or more, but W + 2
Mo is 14.0 to 27.0%, and is characterized by the balance Fe and unavoidable impurities.

(2) It is characterized in that, in addition to the alloy element of (1), it contains Co: 13.0% or less by mass% and the balance is Fe and unavoidable impurities. (3) In addition to the alloy element described in any one of (1) and (2) above, Al: 1.0% or less by mass%, Nb:
It is characterized by containing any one or more of 1.0% or less and Ti: 1.0% or less, and the balance Fe and unavoidable impurities.

(4) In addition to the alloy element described in any one of (1), (2) and (3), S in mass%:
0.30% or less, Pb: 0.40% or less, Te: 0.1
It is characterized by containing any one kind or two kinds or more of 5% or less and Ca: 0.01% or less, and the balance Fe and unavoidable impurities.

(5) In addition to the alloying element described in any one of (1), (2), (3) and (4) above, mass%
And a rare earth element: 0.60% or less, and the balance Fe and inevitable impurities.

[0010]

In the following, the reasons for limiting the content of alloying elements contained in the tooth-cutting tool of the present invention will be described. C: 0.70 to 2.00% C is for increasing the hardness of steel by forming carbides with Cr, W, Mo, and V that are contained at the same time to crystallize, precipitate, and form a solid solution in the matrix. Is an essential element for. In order to obtain the high hardness required for a tooth cutting blade, 0.
C of 7% or more is required. However, if C is contained excessively, the toughness of the steel is impaired, so the upper limit of the C content is made 2.00%.

Si: 3.00% or less Si is added to deoxidize steel. Further, Si has the effect of forming a solid solution in the steel matrix to increase its hardness. However, if added excessively, the toughness of the steel will be impaired, so the upper limit of the Si content is made 3.00%. Mn: 1.50% or less Mn is added to deoxidize steel. Further, Mn increases the hardenability of steel and wear resistance. However, if added excessively, quench cracking occurs during heat treatment or a large amount of retained austenite is generated to embrittle the steel, so the upper limit of the Mn content is set to 1.50%.

Cr: 3.0 to 6.0% Cr is added in order to increase the hardness of the steel by precipitating as a carbide during tempering of the steel. Cr also contributes to improving the hardenability of steel and increasing the hardness of steel. In order to obtain the high hardness required for a tooth cutting blade, the Cr content must be 3.0% or more. However, if added excessively, the amount of precipitation of M ₂₃ C ₆ carbide mainly composed of Cr increases and the toughness of the steel decreases, so the upper limit of the Cr content is made 6.0%.

Mo: 13.5% or less, W: 27.0% or less, but W + 2Mo: 14.0 to 27.0% Mo and W both precipitate as M ₆ C type carbides during tempering of steel. , To increase the hardness of steel.
During casting of steel, M ₂ C type carbides are crystallized in a net form to increase the hardness of the steel and improve wear resistance. To obtain the high hardness required for a gear cutting tool, 1 as (W + 2Mo)
It is necessary to contain 4.0% or more. However, if added excessively, the amount of coarse M ₂ C carbides produced increases and the toughness of the steel decreases, so the W and Mo contents alone are W: 27.0% and Mo: 13.5%, respectively. % Is the upper limit. The upper limit of the content of (W + 2Mo) is 27.0%.

V: 6.0% or less V precipitates as MC type carbide in the steel and increases the hardness of the steel. However, if added excessively, the amount of MC type carbides increases and the toughness of the steel decreases, so the upper limit of the V content is made 6.0%. N: 0.025% or more N has the effect of reducing the crystallization interval of net-like carbides that crystallize during the casting of steel and improving the toughness of the steel.

In the wrought material, the carbides crystallized in a net shape during the casting of steel are dispersed and refined by wrought. This improves the toughness of the steel. However, when a cast material is used as in the present invention, the crystallization state of the net-like carbide is not modified, so the toughness of the steel is greatly affected by the crystallization state of the net-like carbide during casting. .

Due to the above N effect, in order to obtain the toughness equivalent to that of the forged material in the cast material, the N content is 0.025.
% Or more is required. If the amount of N added is excessive, casting defects such as blow holes may occur in the cast product, so the N content is preferably 0.1% or less. Co: 13.0% or less Co has the effect of increasing the hardness of steel by forming a solid solution in the steel matrix and increasing the solubility of C in the matrix. Further, Co increases the temper softening resistance of steel. It is added when a highly hard cutting tool is needed or when the temperature of the cutting edge becomes abnormally high. However, even if added excessively, the effect is saturated and the cost is only increased, so the upper limit of Co content is 13.0%.

Al: 1.0% or less, Nb: 1.0% or less, Ti: 1.0% or less Al precipitates as a nitride in the steel matrix, and N:
b and Ti are finely precipitated in the steel matrix as carbides or carbonitrides, and both have the effect of preventing coarsening of crystal grains during quenching of the steel. This prevents deterioration of the toughness of the steel, so that it may be added especially when toughness is required. However, even if it is added excessively, the effect is saturated, and it only increases the cost, so Al, N
The upper limit of the content of both b and Ti is 1.0%.

S: 0.30% or less, Pb: 0.40% or less, Te: 0.15% or less, Ca: 0.01% or less S, Pb, Te and Ca all have the machinability of steel. Effective to improve. If the cutting amount after casting is large, it may be added. If S, Pb, Te and Ca are all excessively added, the toughness of the steel is impaired. Therefore, the upper limits of the contents are S: 0.30%, Pb: 0.40%, Te:
0.15% and Ca: 0.01%.

Rare earth element: 0.60% or less The rare earth element has the effect of narrowing the crystallization temperature range of MC type carbides, thereby refining the net carbides that crystallize during casting and improving the transverse rupture strength of steel. Have. However, even if it is added excessively, the effect is saturated and the cost is only increased, so the upper limit of the content rate is made 0.60%.

The molten steel is cast in a lost wax mold to obtain a cast product having a shape close to the finished shape of the cutting blade. Assembled products such as assembly hobs shall be cast products that are close to the shape of the assembled parts.
As a result, it is possible to reduce the processing cost of cutting or grinding to finish the finished shape. The upper limit of the casting temperature is 60 ° C or higher, which is higher than the melting point of the molten steel. This reduces the crystallization interval of carbide and improves the toughness of steel. However, if the casting temperature is too low, the flow of the molten metal may be deteriorated, which may cause shape defects and internal defects.

[0021]

EXAMPLE Molten steel was cast in a lost wax mold by a vacuum suction casting method to obtain a hob casting product for gear cutting having the chemical composition shown in Table 1. Table 1 shows the difference between the casting temperature and the melting point of steel as the superheating temperature. The cast product at 870 ° C for 1 h
After heating at r, it was gradually cooled at a cooling rate of 15 ° C./hr and annealed. The edge of the annealed cast product was cut to produce a hob for gear cutting of module 0.5. This is heat-treated under the quenching and tempering conditions shown in Table 2 and the cutting edge is ground to obtain a tool life test specimen.

From the heat-treated test piece, a structure observation test piece and a bending test piece were cut out.

[0023]

[Table 1]

[0024]

[Table 2]

According to the tool life test specimen, S45
The C normalizing material round bar was subjected to gear cutting, and the tool life was measured by the number of round bars processed until it became impossible to cut. Further, as a comparative material, a gear cutting hob having the same shape as the tool life test specimen was cut out from a wrought material to measure the tool life.
The tool life index of each test body was determined with the tool life of the forged material being 100.

With respect to the test piece for observing the structure, net-like primary carbides at the cutting edge portion of the test body were detected, and the carbide crystallization interval was measured by the cutting method. Width 5 mm x height 3 mm x length 30
3 mm with folding test piece of 20 mm between fulcrums
A point bending test was performed to measure the transverse rupture strength. The hardness of the bending test piece was measured.

Table 2 shows the measurement results of the carbide crystallization interval, hardness, transverse rupture strength and tool life. As is clear from Table 2, all of the examples of the present invention have high transverse rupture strength, and the tool life index shows a high value comparable to that of the wrought material.

[0028]

As described above, according to the method for manufacturing a tooth cutting blade of the present invention, a tooth cutting blade having a tool life equivalent to that of a wrought material can be obtained from a cast product. Since it is molded into a shape close to the finished product for gear cutting, it eliminates the work of finishing the material into a finished product for gear cutting and has a great economic effect such as an improvement in material yield. it can. Further, according to this manufacturing method, high performance is exhibited even in cutting applications such as end mills.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication C22C 38/60

Claims (5)

[Claims] 1. A molten steel, the melting point of which is equal to or higher than 20 to 6
A tooth-cutting blade manufactured by casting in a lost wax mold at a temperature of 0 ° C., in which the content of alloying elements in the tooth-cutting blade is C: 0.70 to 2.00% by mass%, Si : 3.00% or less, Mn: 1.50% or less, Cr: 3.0 to 6.0%, Mo: 13.5% or less, W: 27.0% or less, V: 6.0% or less, N: 0.025% or more, provided that W + 2Mo: 14.0 to 27.0%, and the balance Fe and unavoidable impurities. 2. The gear cutting according to claim 1, characterized in that, in addition to the alloying element according to claim 1, it contains Co: 13.0% or less by mass% and the balance is Fe and unavoidable impurities. Method of manufacturing cutting tools. 3. In addition to the alloy element according to claim 1 or 2, in mass% Al: 1.0% or less, Nb: 1.0% or less, Ti: 1.0% The method for producing a tooth-cutting blade according to any one of claims 1 and 2, characterized in that it contains any one or more of the following, and the balance is Fe and inevitable impurities. 4. In addition to the alloying element according to any one of claims 1, 2 and 3, in mass% S: 0.30% or less, Pb: 0.40% or less Te: 0 0.1% or less, Ca: 0.01% or less, and any one kind or two or more kinds is contained, and the balance Fe and unavoidable impurities are included.
The method for manufacturing a tooth-cutting blade according to claim 2. 5. In addition to the alloy element according to claim 1, claim 2, claim 3 or claim 4, mass%
The rare earth element: 0.60% or less is contained, and the balance Fe and unavoidable impurities are contained, and the gear cutting according to any one of claims 1, 2, 3 and 4. Method of manufacturing cutting tools.