JP2698815B2 - Silicon nitride sintered body with excellent wear resistance for cutting tools - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool member requiring abrasion resistance, particularly to a cutting tool member suitable for cutting cast iron.

[Prior Art] Sintered silicon nitride is a ceramic having high hardness, excellent wear resistance, and excellent strength and toughness, and thus has been actively applied to cutting tools.

On the other hand, a sintered body to which an auxiliary component such as MgO, ZrO ₂ , CeO ₂ , and Al ₂ O ₃ is added to improve the sinterability and mechanical properties of silicon nitride has been proposed. (For example, JP-A-1-157466, JP-A-2-74564) [Problems to be Solved by the Invention] In cutting tools at present, it is necessary to further reduce the amount of wear which is the cutting life. With respect to fracture resistance, an improved sintered body can be obtained by improving the strength and toughness of silicon nitride. However, the relationship between wear resistance and mechanical properties is not clear, and the means of improving wear resistance is clear. Was not.

[Means for Achieving the Object] Accordingly, an object of the present invention is to develop a cutting tool member having excellent wear resistance, and it is effective to reduce the amount of an auxiliary agent to improve the wear resistance. Was found. In other words, focusing on the amount of auxiliaries added to improve sinterability and conducting various studies, it was found that Mg, Zr, and Ce were 0.5 wt.
%, The total of which is 5% by weight or less, the balance consisting of Si ₃ N ₄ and the relative density of 99% or more. I got it.

[Action] The cutting edge temperature of a tool during cutting varies depending on the mating material and cutting conditions, but is generally said to be as high as 800 ° C. or higher. For this reason, it is important that heat resistance and chemical stability are excellent in order to improve wear resistance.

The grain boundary phase in the silicon nitride sintered body exists as an amorphous glass phase or a crystalline phase composed of auxiliary components and Si, N, O.
Heat resistance and corrosion resistance are inferior to silicon nitride, and the amount and composition of the grain boundary phase affect the heat resistance and chemical stability of the sintered body.

From the above viewpoint, first of all, the amount of the grain boundary phase, which is inferior in heat resistance, corrosion resistance, and chemical stability, is reduced, that is, the amount of the sintering agent is reduced, and an auxiliary agent that can be densified even with a small amount. The system was examined. As a result, in order to have excellent wear resistance, the total amount of auxiliaries needs to be 5 wt% or less in terms of oxide, and in order to achieve densification, Mg, Zr,
It was found that the three components of Ce were optimal as sintering aids.

In the silicon nitride sintered body of the present invention, Mg, Zr and Ce synergistically promote the densification action, and even in a small amount of 5 wt% or less, the densification can be sufficiently achieved by the combination of these three components. However, any component of Mg, Zr, and Ce in oxide conversion was 0.5 wt.
%, The effect of densification cannot be exhibited effectively.

When the sum of the three components exceeds 5 wt% in terms of oxide,
The amount of the crystal phase and the glass phase at the grain boundaries increases, and the wear resistance decreases. In particular, when it is used as a cutting tool member for cutting a work material such as cast iron (FC), the content is more preferably 3 wt% or less.

Further, if the relative density is less than 99%, 1
% Or more of the pores remain, and the presence of the pores causes the deterioration of not only the fracture resistance but also the wear resistance.

The auxiliary components Mg, Zr, and Ce are contained in the amorphous glass phase or crystalline phase such as Mg ₂ SiO ₄ (forsterite) or complex solid solution ZrO _x N _y C at the Si ₃ N ₄ grain boundary in the sintered body. Exists as _z .

The manufacturing conditions of the silicon nitride sintered body of the present invention are as follows. The raw material powder of Si ₃ N ₄ and Mg, Zr and Ce components has a specific surface area of 4 m ²
Use / g or more. As raw material powders of Mg, Zr, and Ce components, oxides or those that can be converted to oxides during the firing process,
For example, salts (such as carbonates) and hydroxides are used. In order to raise the relative density to 99% or more after sintering after molding these compounded powders, normal pressure sintering is performed, and then atmospheric pressure sintering is performed as secondary sintering. The firing temperature is normal pressure and atmospheric pressure sintering.
The secondary sintering is performed in a pressurized atmosphere having a nitrogen partial pressure of 10 atm or more at 1500 to 1900 ° C. Atmospheric pressure sintering includes hot isostatic press sintering (HIP) and gas pressure sintering (GPS).

[Example] The average particle diameter of 0.7 [mu] m, alpha 98%, the Si ₃ N ₄ powder having a specific surface area of 10 m ² / g, MgO having a specific surface area of 4m ² / g, the 14m _² / g ZrO ² of, the 8m ² / g C
Each powder of eO ₂ was blended in the ratio shown in Table 1. The dried compounded powder was pressed with a mold at a pressure of ² ton / cm2, 1550-1750
After primary firing at ₂ ° C. (holding in N ₂ normal pressure for 2 hours), secondary firing was performed to produce a sintered body.

Table 1 shows the results of measuring wear resistance and fracture resistance as cutting characteristics of the obtained sintered body.

 The sintering conditions and measuring methods of each characteristic are shown below.

Firing conditions primary firing: N ₂ latm-1500~1750 ℃ -2h secondary _{firing: HIP - N 2 2000atm-1600} ℃ -2h GPS - N 2 100atm-1800 ℃ -2h measuring method (1) Relative Density: Archimedes The sintered body density is measured by the method. Relative density = Sintered body density / Dense sintered body density of the same composition (porosity = 0) (2) Abrasion resistance: Machining using SNGN432, chamfer-0.15 tip Select FC23 240mmφ × 100mmL as material, cutting speed 300m / min,
Cut 1.5 mm, feed rate 0.30 mm / rev, measured flank wear width V _B under the conditions of the cutting length 400 mm (3) breakage resistance: SNGN432, using the chip of the chamfer -0.07, select FC23 as workpiece, Under the conditions of cutting speed 150m / min, depth of cut 2.0mm, feed speed 0.8mm / rev, the outer surface of a disk 200mm in outer diameter and 11mm in thickness is cut in the axial direction, and the number of disks until a defect is generated is measured. Those sintered body according Ordinance from the results in Table 1, the V _B 0.3 mm or less for wear resistance, the chipping resistance is the disc number to defect occurs and excellent cutting properties than seven It is. On the other hand, No. 9 does not perform secondary firing, has a low relative density of 97%, and is inferior in both wear resistance and fracture resistance. Also
Nos. 10 to 13 have sufficient densities (relative density = 100%) because the sum of auxiliary components exceeds 5 wt%.
Poor wear resistance. Further, No. 14 using a component other than Mg, Zr, and Ce as a sintering aid does not provide sufficient wear resistance.

In addition, as a reference diagram showing the relationship between the amount of auxiliaries and wear resistance, MgO
The change in flank wear width V _B against auxiliary component total amount of -ZrO ₂ -CeO ₂ aid system shown in Figure 1. As shown in FIG. 1, as the aid amount is small wear width V _B decreases, has a very good wear resistance is V _B becomes 0.3mm or less in total amount 5 wt% or less.

In the examples of the present application, the comparative example may show better results with respect to the fracture resistance. However, the biggest practical problem of the current silicon nitride tool is the improvement of the wear resistance. Performance is not so much a problem, so it is only necessary to ensure a certain level of performance.

[Effects of the Invention] By using Mg, Zr, and Ce as sintering aids, the total amount of the aids is reduced to 5 wt% or less in terms of oxide, and the relative density is increased to 99% or more. Thus, a silicon nitride sintered body for a cutting tool was manufactured.

[Brief description of the drawings]

Figure 1 represents a graph showing changes in wear width V _B by auxiliary component total amount.

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Claims (1)

(57) [Claims] [1] Mg, Zr, Ce converted to MgO, ZrO ₂ , CeO ₂ respectively
0.5 wt% or more, the total of which is 5 wt% or less, with the balance Si ₃ N
_{4. A} silicon nitride sintered body for a cutting tool, comprising ₄ and having a relative density of 99% or more.