JPH01139741A - Warm forging mold - Google Patents

Abstract

PURPOSE:To develop the title warm forging mold having extremely high hardness and excellent wear resistance by mixing the powder of the high-speed tool steel having a specified composition and the powder of the nitride, carbide, and carbonitride of a specified metal in a specified ratio, press-forming, and then sintering the mixture. CONSTITUTION:From 88 to 90% atomized powder of the high-speed tool steel wherein the equilibrium carbon amt. (Ceq) expressed by (0.06Cr+0.033W+0.063 Mo+0.2V) is controlled to 0.1<=C-Ceq<=0.6 at 2.0-3.5% C, contg., by weight, 3-10% Cr, 1-20% W, 1-11% Mo, 5.6-15% V, <15% Co, <2% Si, <1% Mn, <2% Ni, <0.1% N, and the balance Fe where (W+2Mo) is controlled to 18-24% and 2-12% powder of one or >=2 kinds among the nitride, carbide, and carbonitride of Ti, Zr, V, Nb, Hf, and Ta are uniformly mixed. The mixture is formed into a mold, and then the surface is nitrided. Consequently, a warm forging mold having >72 HRC hardening and tempering hardness and >=63 HRC high-temp. hardness after tempering and having excellent wear resistance and seizing resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a warm forging die made of high speed tool steel manufactured by powder metallurgy.

[Traditional nuclear technique]

Generally, cold forming or hot forging is often used for plastic working of carbon steel/alloy steel for machine structures, rolled steel for general manufacturing, etc., but these plastic working methods are mutually exclusive. In recent years, a warm forging method in which the workpiece is heated to about 60° C. to 800° C. has begun to attract attention as a processing method that takes advantage of the advantages of each of the above-mentioned plastic working methods and compensates for their shortcomings. However, the warm forging method imposes harsh usage conditions on the mold, so the mold material must have high hardness even in warm conditions, high thermal shock resistance, and seizure resistance. Good quality is required.

For this reason, in modern times, warm forging dies are often made of ingot high-speed tool steel, powdered high-speed tool steel, cemented carbide, and the like.

[Problems that the invention attempts to address]

Conventional warm forging molds made from melted lumber or powdered high-speed tool steel can cause friction between the workpiece and the mold when the load during use reaches a high load of approximately 500 tons. The life of the mold was short because it caused galling and seizure on the mold and caused scratches on the surface of the workpiece.

Cemented carbide has a carbide content of about 80%, which causes seizure, and also has high high temperature hardness and little wear.
It is also widely used in warm forging dies.

However, since cemented carbide has lower toughness than high-speed tool steel, it is susceptible to thermal shock, and some heat cracks can develop into large cracks, and the service life of each product varies widely.

In view of this, the present invention has developed a mold that has a higher normal hardness and better corrosion resistance than conventional molds made of high-speed tool steel, and has a higher content of carbides and nitrides to improve seizure resistance. The purpose of the present invention is to provide a warm-working mold that has higher toughness and is more resistant to thermal shock than alloy molds. is Ceq=0-06C
r10-033W+0.063Mo+0.2V
When C2, 0.1≦C−C in the range of 0 to 3.5%
satisfies eq≦0.6, furthermore Cr: 3 to 10%, W:
1~20%+Mo: 1~11chi (however, 18≦W
+2Mo≦24), V: 5.6-15%
.

Co: 15% or less* Si: 2% or less, Mn
: Less than 1%.

Ni: 2% or less, N: 0.1% or less, remainder F
The atomized powder of high speed tool steel consisting of e and inevitable impurities is 88-98%, Ti, Zr, V, Nb, H
f, one or two of Ta nitrides, carbides, and carbohydrides
After uniformly mixing 2 to 12% of the seeds and above, molding and
A mold for warm forging made by sintering, which has a hardness of HRC 72 or higher after quenching and tempering, and then 600℃
It is characterized by having a high-temperature hardness of HRC 63 or higher even when heated to a temperature of 72, and by having a hardness of HRC 72 and an absorption rate of 130 kqf, and depending on the situation, it has been subjected to surface treatment. This is a mold for warm forging.

[Effect]

Next, the effect of each additive element in the present invention and the reason for limiting the abrasion range will be described.

Among the compositions of the mold material of the present invention, the C content is the most important component. C is Cr contained at the same time,
It combines with W + Mor V to form carbides such as Ms C and MC, and has the effect of imparting wear resistance, as well as the repair and strength of the martensite base through quench hardening heat treatment, and further secondary tempering. It has the effect of increasing the amount of hardening. Cr and W are the carbide-forming elements mentioned above.

It is theoretically known that Mo, V and C combine in just the right amount to form a carbide, with an equilibrium carbon content Ceq Vi expressed by the following formula.

Ceq-0.06 (%Cr) + 0.033 (%W)
+ 0.063 (% Mo ) + 0.2 (% V) In conventional high-speed tool steel, the difference between C content and equilibrium coal For example, JIS 5KH59 is Habo-0,
3, -0,05 for AISIM42).

In the present invention, even if the amount of W, Mo, V and the amount of dispersed particles such as TiN are relatively small, a super hardness of HRC 72 or more can be obtained, and the purpose is to obtain a highly practical mold for gastric speed tool 1. After experimenting and examining many alloy systems, Ceq=0-06Cr+0.033W+0.
When 063Mo+0.2V, 18≦W + 2
It has been newly discovered that in the range of Mo≦24, instead of making C-Ceq negative as in the past, it is sufficient to contain C so that 0.1≦C-Ceq≦0.6 is satisfied. C-C
When eq is less than 0.1, a large amount of W as mentioned above,
If JVfo, V, and TiN are not included, H
A superhardness of RC72 or higher cannot be obtained. On the other hand, when C-Ceq exceeds 0.6, stable retained austenite increases significantly during quench hardening heat treatment, and the decomposition temperature of retained austenite shifts to a high temperature side, so secondary hardening is performed by tempering. Even if the hardness is higher than HRC72, it will not be possible to obtain a superhardness of HRC72 or higher. That is, in the range of 18≦W+2Mo≦24,
The object of the present application can be achieved only under the condition of 0.1≦C-Ceq≦0.6.

As mentioned above, C should be appropriately changed depending on the amount of Cr*W e Mo and V that are simultaneously enriched. At least 2.0% of C is required in order to satisfy 0.1≦C-Ceq≦0.6 within a range of the content of Cr, W, Mo, and V of the present invention, which will be described later.

On the other hand, even if the above conditions are met, the at content is 3.5%.
If the C content exceeds 2.0, the decrease in toughness will be significant, so the C content should be 2.
In the range of 0 to 3.5 kou, and 0.1≦C-Ceq≦0.
It was limited to 6.

CrFi has the effect of increasing sintering hardenability, but if it is less than 6%, this effect is small, and on the other hand, if it exceeds 10%, the residual austenite (t) increases and the phosphorization φ restoration hardness is lowered, so the inclusion of Or. The amount was limited to 3-10%. In particular, even if heat treated in a quenching furnace with a slow cooling rate such as vacuum quenching, the
In order to obtain a superhardness of C72 or higher, the Cr content must be 6%.
It is desirable to exceed 10 inches or less.

W and Mo combine with the aforementioned Totoku C to form MgC type carbide, which has the effect of increasing wear resistance and solid solution in the matrix during quenching and hardening heat treatment, which precipitates as fine carbide during tempering heat treatment. It has the effect of increasing the degree of secondary hardening. In order to achieve the purpose of stably obtaining superhardness of HRC72 or higher according to the present invention, W1-20%, Mo1-1
It is necessary to contain W+2Mofi of 18 or more in the range of 1'%.

However, if W+2Mo'f exceeds 24%, the material not only becomes expensive but also has poor toughness, so the content of W + Mo was limited to 18 to 24% in terms of W+2Mo. In addition,
In the present invention, etc.! W and Mo (in atomic percent) have approximately equivalent effects.

Like W and Mo, V also combines with C to form MC type carbide. The hardness of this MC type carbide is HV 2500~3
000 and MaC type carbide carbide HV1500-1800
Its hardness is significantly higher than that of For this reason, in tools where wear resistance is particularly important, use of high speed tool steel with a high V content will improve tool life.

However, even if the content of
The upper limit of i was 15 inches. On the other hand, if the V content is less than 5.6%, the wear resistance effect will be insufficient, so the V content should be 5.6 to 15%.
limited to.

Co dissolves in the matrix and has the effect of reducing tempering hardness and high temperature hardness. However, if it is contained in a large amount, the toughness will be significantly reduced, so the content of Co is limited to 15% or less.

St is contained in an amount of 2% or less for the purpose of deoxidation, but especially in the range of 5iO08 to 2%, it not only has a deoxidizing effect but also has the effect of increasing the hardness of the base, oxidation resistance, corrosion resistance, and even atomization. It has the effect of improving work efficiency. If it exceeds 2%, the toughness will be significantly reduced.

Mn also has a deoxidizing effect and also has the effect of improving bankability, so it is contained in an amount of 1% or less. In particular, the above S i
When the amount of Ta is moderate, it is preferable to contain 0.25 to 1.0% of Mn, since the arrangement of Si, which stabilizes ferrite and raises the A transformation point, can be relaxed by seeds.

Ni has the effect of increasing the toughness of the matrix, but if it exceeds 2%, the amount of retained austenite increases extremely and the tempering hardness decreases, so the present invention allows the content to be 2% or less. In addition, a trace amount of Ni is contained in the normal side speed tool steel, and the range of Ni O, 25 or less is JIS
It is treated as an amount of impurities.

N has the effect of increasing the hardness of the matrix and the Kf in the MC type carbide.
i! It also has the effect of increasing welding resistance by melting and forming MCN-type carbonitrides. However, since the upper limit of the amount that can be contained industrially is 0.1%, it is limited to 0.1% or less. In addition, in high-speed tool steel, usually NO, 05%
Anything below this level is contained as an impurity.

Dispersing Ti, Zr, V, Nb, ) (f + Ta nitrides, carbides, and carbonitrides has the effect of increasing hardness.On the other hand, as in the present invention, the C content is equal to the equilibrium carbon amount (Ceq) It was conventional wisdom that if the value was higher than 0.1 to 0.6, the austenite crystal grains would become coarse during the quench hardening process, the martensite structure would become rough, and the toughness would be extremely reduced. .

However, according to the present invention, 'ri + Zr, V, Nb,
This drawback can be overcome by uniformly dispersing one or more of Hf + Ta nitrides, carbides, and carbonitrides in a total amount of 2 to 12%. It was discovered that even if phosphorescence hardening treatment was performed at the curing temperature ψ, a significantly finer structure was obtained.

That is, by dispersing the above nitrides, carbides, and carbonitrides, the disadvantages caused by the C content being higher than that of Ceq il can be successfully overcome, and the object of the present invention can be achieved. However, if it is less than 2%, the above effect will be small;
On the other hand, the effect is not saturated when it exceeds 12%;
The above nitrides, as they significantly reduce grindability and toughness,
The amount of dispersion of carbides and carbonitrides was limited to 2 to 12% in total.

A method for uniformly dispersing nitrides, carbides, and carbonitrides in a matrix is to produce high-speed tool steel powder with the above chemical composition by atomizing water, scum, oil, etc. matter, carbide.

After mixing with carbonitride powder, molding and sintering are performed.
most suitable.

When mixing, carbon powder such as graphite powder or black carbon may be added and mixed at the same time for the purpose of controlling the final carbon content after sintering and improving sinterability. Furthermore, Cr, Ni.

When one or more of Mo t W, Cu + Co, and Fe powder are simultaneously mixed in a total amount of 5% or less,
It has the effect of improving sinterability.

〔Example〕

Next, the present invention will be explained in more detail based on an actual flow example.

In order to manufacture a warm forging die having the shape shown in FIG. 6, first, a die material having the composition shown in Table 1 was prepared.

A mold was made from this material, and samples for high-temperature hardness and bending tests were also made. Regarding this sample and mold, three materials other than the cemented carbide were subjected to Vi predetermined standard heat treatment to obtain the hardness shown in the table.

High temperature hardness of 4 materials including cemented carbide after heat treatment.

The absorbed energy was measured and the results are shown in Figure 1.

Shown in Figure 2.

As shown in Figure 1, the high-temperature hardness of the mold material of the present invention is lower than that of the cemented carbide mold material at each temperature, but it is higher than that of the ingot material 5KH51 or powdered high-speed oil mold material. It shows the value. Furthermore, as shown in Fig. 2, the absorbed energy in the bending test of the material for molds of the present invention is 5KH51.
Although the toughness value is lower than that of powdered high-speed tool steel mold materials, it has a higher toughness value than cemented carbide mold materials, and shows good toughness values commensurate with the hardness level. There is.

In addition, the mold material of the present invention has a high temperature hardness of HRC63 (HV772) or higher at 600°C, which is the target value, and HRC7
It was found that the absorbed energy in the case of No. 2 was 130 hf-wm or more.

Next, as shown in FIG. The warm forging mold was completed by assembling it into the inner case 2. Are some of them included in the mold of the present invention? A chemical treatment was applied.

Outer case 6 and inner case 2 are HRCed using heat mold tools.
After heat treatment to a temperature of 48°C, finishing by grinding was performed.

After this, the inner case 2 was fired using gold t1!1 with a margin of 0.5. Then, the outer case 6 was fired with the same shrink fitting allowance, and the end face was finished with a grinding finish.

JIS 555C heated to 700-750℃ was forged according to the forging method shown in Figure 4, and the point at which seizing occurred on the inner diameter of the mold and the φ began to be transferred to the workpiece as scratches was determined. The lifespan is also listed in Table 1 as an index with the lifespan number of the cemented carbide as 100.

According to the results of the forging test, it was found that the mold of the present invention exhibited a life index almost equivalent to that of cemented carbide, and that the mold of the present invention subjected to nitriding treatment showed an additional 20% improvement in life. In this embodiment, the mold was made into a 6-layer cylinder based on the results of shrink-fitting allowance and stress calculation, but it goes without saying that the inner case and the outer case can be integrated into a 2N cylinder depending on the case.

〔Effect of the invention〕

As described above, the warm forging mold according to the present invention has superior toughness and the same lifespan as cemented carbide molds, and the lifespan can be further improved by nitriding. This invention is extremely effective industrially.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the high-temperature hardness of the present invention mold and the conventional mold according to the present invention, and Fig. 2 shows the relationship between absorbed energy and hardness in the bending test of the present invention mold and the conventional mold. 6 is a diagram showing an embodiment of a warm forging die, and FIG. 4 is a diagram showing an embodiment of a warm forging method.

Claims (1)

[Claims] 1. Equilibrium carbon content (Ceq) is Ceq=0.06 in weight ratio
When Cr+0.033W+0.063Mo+0.2V, C: 0.1≦C-Ce in the range of 2.0 to 3.5%
Satisfies q≦0.6, further Cr: 3 to 10%, W: 1
~20%, Mo: 1~11% (however, 18≦W+2M
o≦24), V: 5.6 to 15%, Co: 15% or less,
Si: 2% or less, Mn: 1% or less, Ni: 2% or less, N:
Atomized powder of high speed tool steel consisting of 0.1% or less, the balance Fe and unavoidable impurities, 88 to 90% Ti,
High hardness made by uniformly mixing 2 to 12% of one or more of nitrides, carbides, and carbonitrides of Zr, V, Nb, Hf, and Ta, then molding and sintering. A mold for warm forging characterized by using speed tool steel. 2. HRC of superhard high speed tool steel is achieved by quenching and tempering.
Hardness of 72 or higher and 600℃ after quenching and tempering
The warm forging mold according to claim 1, wherein the hot forging mold has a high temperature hardness of HRC63 or higher when heated to . 3. Bending test of superhard high-speed tool steel with hardness HRC72 (test piece: 5 mmφ x 70 mml, distance between fulcrums: 5
Absorbed energy at 0 mm (center single point loading method) is 13
The mold for warm forging according to claim 1 or 2, characterized in that it has a diameter of 0 kgf·mm or more. 4. The mold for warm forging according to any one of claims 1 to 3, characterized in that the mold is made of superhard high-speed tool steel and then subjected to surface treatment.