JPH0643622B2 - Method for producing nitrogen-containing cermet - Google Patents

Description

Description: TECHNICAL FIELD The present invention provides a method for producing a high-quality nitrogen-containing cermet which is extremely rich in strength.

[Prior art and its problems]

Nitrogen-containing cermets in which double carbonitrides of Ti, Ta, W, Mo are bonded by a metal composed of Ni and Co have extremely hard dispersed phase fine particles compared to conventional cermets that do not contain nitrogen. The characteristics are greatly improved. For this reason, it has already been put to practical use as a cutting tool along with a so-called cemented carbide containing WC as a main component.

However, this nitrogen-containing cermet, particularly an alloy having a high nitrogen content, has extremely poor sinterability as compared with the cemented carbide.
This is because the double carbonitride contained in vacuum sintering decomposes, a so-called denitrification phenomenon occurs, the effect of nitrogen addition decreases, and the nitrogen gas generated at that time does not sufficiently escape from the sintered body. , Because it remains as pores after sintering.

These significantly reduce the reliability of the nitrogen-containing cermet as a tool. Therefore, attempts have been made to suppress the decomposition of carbonitrides by sintering the cermet in a nitrogen atmosphere instead of in a vacuum (Japanese Patent Publication No. 49-1364), but N / C + N in a hard dispersed phase has been tried. When the (atomic ratio) is 0.6 or more, the atmospheric nitrogen pressure is required to be 80 Torr or more, so that the degassing from the cermet during sintering becomes insufficient, and the pores remain in the obtained cermet.

Therefore, in order to eliminate the pores remaining after this sintering, hot isostatic pressing (hereinafter referred to as HIP) is performed after normal sintering.
Have been attempted. As a result, the pores inherent in the alloy are changed to a pool of the binding metal, so that the electro-deposition force, the fracture toughness value and the hardness are improved, and the cutting performance is also improved in the wear resistance. However, the toughness decreases unexpectedly.

The present invention aims to present HIP conditions for improving the toughness described above.

[Disclosure of Invention]

As a result of detailed examination of the sintering phenomenon of the nitrogen-containing cermet, the inventors have obtained the following findings.

Despite the increase in the anti-segregation force and fracture toughness value due to HIP, the improvement in cutting toughness commensurate with the increase was not observed, but the value decreased. Since HIP is performed in an inert gas such as Ar, the cermet sintered in a nitrogen atmosphere causes a denitrification phenomenon at this time in order to prevent denitrification. Therefore, the following two events are considered to occur. First, the hardness of the surface portion is extremely increased, and the wear resistance is improved as described above.
The other is that the surface properties are rough due to denitrification, and the surface has a high hardness, so good results cannot be obtained in the cutting toughness test.

Then, the inventors arrived at the present invention as a result of various studies to solve this problem.

That is, by mixing an appropriate amount of nitrogen gas in addition to Ar to the filling gas at the time of HIP, denitrification at the time of HIP is suppressed, and peculiar phenomena such as hardening and skin roughening that occur on the surface part are lost, and abrasion resistance is significantly improved. It is to significantly improve the cutting toughness without damaging it.

The reasons for limitation will be described below.

(1) Components of hard dispersed phase The present invention relates to a nitrogen-containing cermet. Therefore, a complex carbonitride of Ti, Ta, Mo, W is indispensable as the hard dispersed phase, and as the composition of this complex carbonitride, if the ratio of Ti in the metal atoms is 0.5 or less in atomic ratio. The cermet has insufficient wear resistance, and if it is 0.95 or more, the toughness is insufficient, which is not preferable. Further, when the ratio of N in the non-metal atoms is 0.1 or less in atomic ratio, the effect of N addition, that is, the effect of suppressing grain growth of the hard dispersed phase during sintering is poor.
The above results are not preferable because the sinterability is poor.

(2) Amount of bonded metal phase in the alloy If the amount is 3% by weight or less, the strength is insufficient, and if it is 50% by weight or more, the hardness is insufficient, which is not preferable.

(3) Sintering conditions As for the sintering temperature, if the temperature is 1350 ° C. or lower, the sintering is insufficient and pores remain, and if it is 1600 ° C. or higher, the evaporation of the binder metal and the grain growth of the hard dispersed phase become remarkable, which is not preferable.

(4) HIP condition When the nitrogen partial pressure is 5 Torr or less, denitrification of the cermet occurs, and when it is 700 Torr or more, nitriding of the cermet causes conversely softening of the surface portion, which is not preferable. The control of the nitrogen partial pressure can also be performed by filling the periphery of the body to be HIP with powders having different nitrogen contents.

Hereinafter, detailed description will be made with reference to examples.

[Example 1] Ti (CN), TaC, and WC powders were measured and mixed, then extruded and granulated, charged into a carbon board, and charged at 1600 ° C for 1 hour in a nitrogen stream (nitrogen partial pressure 100 Torr). It was processed (hereinafter, this powder is referred to as raw material powder). In the obtained double carbonitride
Ni, Co, Mo ₂ C, C powders were added, wet-mixed, the powders were pressed and molded, and the green compacts were heated to 1200 ° C in vacuum, and the nitrogen partial pressure was 5 Torr at 1450 ° C for 1 hour. Sintered.

The composition of the obtained cermet, the hard dispersed phase in atomic ratio (T
i _0.87 , W _0.06 , Ta _0.04 , Mo _0.03 ) (C _0.54 , N _0.46 ) _0.95 , and the bonding metals were Co 12 wt% and Ni 4 wt%.
Embedding this cermet in raw material powder, 1450 ℃, Ar + N
₂ (Nitrogen partial pressure 200 Torr) H at 1 atmosphere for 1 hour
I made an IP. This cermet is designated as A, the same sintered cermet is embedded in TiN powder, and the cermet subjected to the same HIP (but nitrogen partial pressure of 760 Torr) is B, Al ₂ O ₃
The cermet embedded in the powder (without nitrogen partial pressure) is designated as C. The hardness distribution near the surface of these three cermets is
Shown in the figure. Compared with A, the surface of C is abnormally harder and the surface of B is softer, and only A maintains the hardness inside the cermet up to the surface portion. The transverse rupture strength and fracture toughness of the samples obtained by grinding 0.3 mm surface layer of these three types of cermets are A: 255 Kgf / mm ² , 5.61 MN / m ^3/2 and B: 24, respectively.
2Kgf / mm ² , 5.68MN / m ^3/2 , C: 264Kgf / mm ² , 5.51MN / m
^{On March 2} , it showed almost the same value. For comparison, if the sintered cermet is D, the hardness is about 100 lower than C, and the transverse rupture strength and fracture toughness are 164 Kgf / mm ² and 3.74, respectively.
It became MN / m ^3/2 , and HIP clearly improved the internal characteristics. These A, B, C and D were further subjected to a cutting test under the following conditions.

Cutting condition 1 Work material SCM435 (H _B = 250) Cutting speed 200m / min Feed 0.25mm / rev Depth of cut 1.5mm Chip shape TNMG 332ENZ Holder MTJNR2525-33 Cutting time 3 minutes As a result, A has flank wear of 0.24mm. On the other hand, B reached 1 mm in 1 minute, and the composition deformation amount of the cutting edge increased in 2 minutes, so that cutting could not be continued. The flank wear of C was 0.18 mm and D was 0.22 mm.

Next, a test was conducted under the following cutting conditions 2.

Cutting condition 2 Work material SCM435 (H _B = 250) 4-groove material Cutting speed 100m / min Feed 0.34mm / rev Depth of cut 2.0mm Chip shape TNMG 332ENZ Holder MTJNR2525-33 Cutting time 2 minutes 6 times when cutting was repeated, 36 In the cutting blade A, only 5 small cutting edges were formed, but in C, 31 cutting edges were formed. In D, 11 cutting edges were defective. From the above, it was confirmed that the effect of the present invention is to bring out the internal characteristics and significantly improve the cutting toughness without significantly impairing the wear resistance.

[Example 2] The composition of the alloy was such that the hard dispersed phase had an atomic ratio of (Ti _0.72 , W _0.12 Ta
_0.11 , Mo _0.05 ) (C _0.63 , N _0.37 ) _0.90 , and the bonding metal is
Ti (CN), Ta so that Co 10% by weight and Ni 5% by weight
C, WC, Mo ₂ C, Co, Ni and C were mixed, embossed, sintered under the same conditions as in Example 1, and subjected to HIP under the conditions shown in Table 1.
Flank wear amount when cutting test under cutting condition 1,
The data on the number of missing edges in 36 cutting edges when tested under cutting condition 2 is also shown.

[Example 3] The composition of the hard dispersed phase was (Ti _0.82 , W _0.06 , Ta _0.06 , Mo _0.06 ).
After mixing and embossing so that (C _0.55 , N _0.45 ),
Cermet A of Example 1 sintered under the same conditions as Example 1
HIP was performed under the same conditions as described above. At this time, the weight% of Co and Ni
Was changed as shown in Table 2. The bending strength and hardness of the obtained alloy are also shown in Table 2.

[Brief description of drawings]

FIG. 1 is a diagram showing the hardness distribution in the depth direction due to the difference in nitrogen partial pressure during HIP in Example 1.

Continuation of front page (56) Reference JP-A-60-165305 (JP, A) JP-A-59-118852 (JP, A) JP-B-49-1364 (JP, B2)

Claims (1)

[Claims] 1. In a nitrogen-containing cermet having a hard carbon-nitride complex of Ti, Ta, W, Mo as a hard dispersed phase and a metal composed of Ni and Co as a bonded metal phase, the amount of Ti in the metal atoms of the hard dispersed phase. Is 0.5 or more and 0.95 or less in atomic ratio, the amount of N in the non-metal atoms is 0.1 or more and 0.9 or less in atomic ratio, and the balance of the binding metal phase
In producing a nitrogen-containing cermet in which the amount of Co is 0.1 or more and 0.9 or less in atomic ratio and the binder metal phase accounts for 3 to 50% by weight in the alloy, after sintering at 1350 ° C or more and 1600 ° C or less, heat treatment is performed. A method for producing a nitrogen-containing cermet, which comprises controlling the nitrogen partial pressure in the total applied pressure during the isostatic pressing process to 5 Torr or more and 700 Torr or less.