JPS58213677A - Silicon nitride composite sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon nitride composite sintered body having particularly corrosion resistance for casting molten metal, particularly high alloy steel, and a method for producing the same.

° Refractories such as high alumina, zirconia, and alumina-graphite are used as casting materials for general high-alloy steel such as stainless steel, but dimensional accuracy of 0.1 m or less is required and thermal shock resistance etc. There are limits to these refractories in places where the usage conditions are severe, and special ceramics such as hot-pressed boron nitride (HPBN) are used.

HPBN is a material that has particularly excellent thermal shock resistance, can be cut after forming, and has good surface precision, but it cannot be said to be a material with high corrosion resistance compared to high alloy steels higher than stainless steel and steel containing TiK.

Therefore, we investigated the corrosion resistance of various ceramic materials such as oxides, carbides, and nitrides, which account for 1/3 of the stainless steel. As a result, it was found that the materials with excellent corrosion resistance are dense A40s #zrOt, Sialon (z=J), HPBli, and dense &810, 81sN, which are not necessarily highly corrosion resistant materials.

Table 1 Wettability of various ceramics to stainless steel*
Density characteristics: 9gA-100% B: 0% or more 0: 70~De0chi conditions) Temperature: /! Hold DO℃/1 hour (temperature increase 1oo
o~/00℃J, j℃/min) Atmosphere HAr Stainless steel: SUS, ? O$φ/0. tX/,
Therefore, in order to develop a material with characteristics of dimensional accuracy and corrosion resistance, reaction sintering 81. We investigated the creation of composite materials based on N and oxides.

As a result of intensive study on the above points, Si by reaction sintering,
It has been found that a composite sintered body with a structure consisting of a dispersed phase of ZrO uniformly distributed in an N4 skeleton has significantly improved side-effect corrosion against stainless steel. ZrO as this dispersed phase,
There was no difference in corrosion resistance between unstabilized and stabilized ZrO, but silicon nitride composite sintered bodies containing unstabilized ZrO had an exponential coefficient of thermal expansion with the addition of ZrO. It was found that it could not withstand use as a heat-resistant component that is particularly susceptible to thermal shock.

The silicon nitride composite sintered body using the zirconia reaction sintered 81. N exists as a dispersed phase in the pores and grain boundaries of the skeleton, and is caused by volume expansion of zirconia particles due to equiaxed and monoclinic phase transitions due to thermal changes.81. By applying N and compressive stress to the skeleton, the strength characteristics and thermal shock resistance of the composite sintered body are improved, and the coefficient of thermal expansion is 81. It turned out to be almost identical to N.

Next, we will discuss the reaction mechanism between the silicon nitride sintered body and stainless steel. Stainless steel is Or
, Ni, Ti, Mn, and Mo components, and also has low viscosity and melting point in a molten state.

Therefore, N! near 1 soo℃! When we calculated the formation energy of 1 mole of silicon nitride and the formation free energy of 1 mole of stainless steel component N, we found that the energy levels were reversed.81. Erosion will occur due to the reaction between the N in N4 and the stainless steel components.

It is also believed that the high-temperature properties of stainless steel itself, such as its low viscosity, and the formation of low-melting compounds such as Mn, work effectively against corrosion. The reason why the silicon nitride composite sintered body has excellent corrosion resistance is that zirconia exists as a uniformly dispersed phase within the silicon nitride skeleton, and it is mixed with molten iron by 81%. This is thought to be because it acts as a protective film for the silicon nitride skeleton at the interface between N and N.

Next, the manufacturing method aK of the present invention will be explained.

First, the starting materials will be explained. The sintered body of the present invention is formed by reaction sintering of metallic silicon and metallic silicon, such as stabilized zirconia, with nitrogen. The metal silicon powder as starting material has a purity of qq
A powder containing 81 tlb or more and a particle size of taμ or less is used. Ikunoshotouta H-in [di-stabilized zirconia has a purity of 9t% or more, a particle size of 741μ or less, and a neck-shaking mechanism 4!
It is possible to use raw materials with a stabilizer of less than μ and using any stabilizer such as OaO, MgO, Y2O, etc. The silicon nitride-based composite sintered body contains the above-mentioned B1 powder and stabilized zirconia as essential components, which are mixed in a certain ratio, and then mixed with a non-oxidizing solvent such as alcohol (water may be used in some cases), PVA, etc. After adding an appropriate amount of a binder and uniformly mixing and kneading, the mixture is granulated and dried to obtain a raw material for molding. After molding this raw material with a mechanical press using a rubber press or a mold, place it in an Ar, H, non-oxidizing atmosphere.
The molded body is fired at around 00°C to remove alcohol, water and binder, and to impart strength to the molded body and make it machinable.

After machining this molded body with dimensional accuracy according to the purpose,
The final sintering temperature is 4t00 to 1azO<0>C in a nitrogen gas atmosphere, and the siltation reaction of sl is completed, yielding a silicon nitride composite sintered body by reactive sintering.

Next, the present invention will be explained in more detail based on Examples.

Example 1 Using 81 powder with a purity of 11 cm and a particle size of less than Kuda μ and various ZrO powders with a purity of 11 cm and a particle size of less than Dada μ as raw materials,
They were blended in the predetermined proportions as shown in Table 1. This formulation is 0.1
% PTA in an alcohol solvent, granulated into O, CO to A'll, dried, and then placed in a mold and molded using a rubber press at a molding pressure of 77 cm. This molded body was placed in a non-oxidizing atmosphere of Ar/:
It was fired at a temperature of 100°C for 1 hour) to form a temporary sintered body, and this temporary sintered body was used as a sample for strength measurement with rxsxzoB and as a crucible for erosion test φ30×30t (inner diameter φXJ7t).
) (After processing into an i-shaped shape, it is heated to a maximum temperature of 1 qoo to 1 a
A silicon nitride composite sintered body was produced by nitriding and firing lθ at ro°Ct for a time.

Table 1 lists the corrosion resistance, thermal shock resistance and density characteristics of the silicon nitride composite sintered bodies produced as described above, together with comparative examples. Corrosion resistance is determined by using 0-Bteel and stainless steel 5USJO41 in the above crucible (approximately 36)
using the block of iss;.

The amount of erosion was measured after being held in an ArAr atmosphere for a certain period of time.

As a result, ZrO! It can be seen that the corrosion resistance against stainless steel is low when the amount of powder is 3 or more.

For excellent thermal shock properties, use JXQX test pieces for strength measurement!
0＠＠ was finished by grinding with goo diamond, rapidly heated to 1ooo℃ in air and held for 30 minutes, and then
After quenching in water at a temperature of °C, the strength was measured at a span of 308 m and a crosshead speed of o, s; As a result, unstabilized ZrO! rO! It was found that the material used had a significant deterioration in strength and was unusable. On the other hand, PF
-8Z exhibits good strength properties, but if the additive content exceeds 60% by weight, there is a limit in terms of density properties and strength properties. As a result of the above, the essential condition for satisfying both characteristics is a sintered body containing 3-60% by weight of stabilized zirconia.

Example 31BN4- ZrO system uses unstabilized ZrO as ZrO, and OaO stabilized Zr stand, ZrO content is 3°10, /! A sintered body with a weight composition of , KO 0, JO, 10 is prepared and kept at room temperature ~/! Thermal expansion in oxidizing and non-oxidizing atmospheres was measured at DO°C, and the relationship with thermal shock properties was investigated. The manufacturing method was the same as in Example 1, using a reaction sintering method using 81 as a starting material. As a result, oxidation
A clear difference in thermal expansion depending on the type of ZrO was found regardless of the non-oxidizing atmosphere. Unstabilized ZrO exhibited abnormal expansion near 600-100°C, which is thought to be the cause of the decrease in thermal shock resistance, while OaO-stabilized ZrO
, reaction sintering with a sintered body containing 81. It was found that it exhibited almost the same thermal expansion as N4 and also had excellent thermal shock resistance.

Figures 1 and 1 show unstabilized ZrO and Oa, respectively.
1 shows a thermal expansion curve of an O-stabilized Zr-based silicon nitride composite sintered body.

Example 3 Wettability and corrosion resistance at 1300°C were investigated for a silicon nitride composite sintered body (OaO stabilized Zr stand, reaction sintered body 813N4, and hot pressed BN manufactured by the same method as in Example 3). Sex measurement is 1oxio
xsH ceramic test piece φ/,,tX/
Jm stainless steel was placed on it, heated at a rate of 3°C/min in an Ar atmosphere, and the contact angle at 1zoo°C and /! TOO″C/
The contact angle after holding for a time was measured, and the amount of erosion after cooling was examined using a microscope. As a result, the product of the present invention had a contact angle of ii6° with no change observed over time, and exhibited good corrosion resistance with almost no amount of corrosion. N and hot-pressed BN have a small contact angle of yo~60°, and erosion is also observed in the structure. Table 3 shows the results.

/ ~ 7/ Table 3 Corrosion resistance of silicon nitride composite sintered body As stated above, the silicon nitride composite sintered body of the present invention is
The corrosion resistance of molten metals, especially high-alloy steel, which is a disadvantage of Li and N, is significantly improved, and since it is a reactive joint process, it is easy to process with high dimensional accuracy and is an economically superior sintered body.

[Brief explanation of drawings]

Figure 1 shows the thermal expansion curve of a silicon nitride composite sintered body containing 9 unstabilized zirconia, and Figure 2 shows the thermal expansion curve of a silicon nitride composite sintered body containing OaO-stabilized zirconia. be. Patent applicant: Shinagawa White Brick Co., Ltd.

Claims (1)

[Claims] The stabilized zirconia is uniformly present as a dispersed phase in the continuous skeleton of the silicon nitride, and the stabilized zirconia is uniformly present as a dispersed phase in the continuous skeleton of the silicon nitride. A silicon nitride composite sintered body produced by the reaction sintering method, which is characterized by corrosion resistance against alloy steel.