JPH03294448A - High chromium-nickel stock and its manufacture - Google Patents

Abstract

PURPOSE:To obtain high chronium-nickel stock free from internal defects by subjecting an ingot formed by chromium powder and carbonyl nickel powder to hot working into the dual phase structure of a hard phase and a soft phase and regulating its grain size. CONSTITUTION:Chromium powder having >=99% purity and carbonyl nickel powder are used to manufacture an ingot having >=7g/cm<3> packing density. This ingot is packed into a capsule and is subjected to hot working treatment to obtain high chromium-nickel stock contg, by weight, <=0.5% components other than chromium and nickel, 50 to 90% chromium and the balance substantial nickel. The structure of this stock is formed of the dual phases of a hard phase and a soft phase. Furthermore, the grain size and working temp. of the raw material are controlled to regulate the grain size of the stock to <=50mum. In this way, the stock having a dense structure, excellent in workability and free from the generation of cracks or the like by the subsequent treatment can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high chromium nickel material and a method for producing the same. More specifically, the present invention relates to a high chromium nickel material containing 0.5% by weight or less of components other than chromium and nickel, and a method for producing the same.

[Prior art and its problems] High chromium nickel materials are widely used in the fields of various target materials, wear-resistant protective materials, switching materials, various electrode materials, and thermal spray coating materials.

Conventionally, methods for manufacturing high chromium nickel materials are roughly divided into melting/casting methods and powder metallurgy methods. Among these, melting/casting methods include high frequency induction heating and arc melting methods. For example, the arc melting method is a method of producing an ingot by arc melting in an inert gas using a water-cooled mold.
As shown in a (47Cr-N1 material), the dendrite structure has developed and the crystal grains are large. In addition, since ferrochrome or low-purity chromium powder is used as the chromium raw material, there are phases other than the hard and soft phases that reduce deformability, and the resulting product is extremely brittle and has poor workability, so care must be taken when handling it. However, this makes forging and rolling difficult.
Voids such as casting defects existing within the ingot deteriorated the properties of the product. There was also the problem of cracking during the cooling process after melting, making it difficult to manufacture large ingots.

On the other hand, even in the powder metallurgy method, it is difficult to obtain a dense and crack-free sintered body by normal molding and sintering because chromium has a high melting point and high vapor pressure, and hot pressing method Even if chromium is used, there are restrictions on the size of the product and productivity is poor, and this tendency becomes stronger as the chromium content increases. In this way, manufactured by conventional manufacturing methods,
In particular, high chromium nickel materials have internal defects.
It is very brittle and has problems such as being easily broken by cutting or other handling, and when processing is to be carried out, it is impossible to process it by normal hot working or the like.

For example, the main method for processing these high chromium nickel materials into wire rods is the melting method for materials with a low melting point and a chromium content of less than 50% by weight. However, those with a chromium content of 50% by weight or more have a high melting point and are difficult to melt, and even if they are processed into a wire, cracks and internal defects remain, and the crystal structure becomes coarser and the deformability of the wire decreases. You can only get something inferior. In addition, when processing wire rods using the powder metallurgy method, as mentioned above, chromium has a high melting point and high vapor pressure. It is difficult to obtain wire connection material, and ingots obtained by hot pressing or hot isostatic pressing are often used for hot swaging, forging, and rolling. However, in the hot isostatic pressing method etc., excessive solid phase diffusion occurs between the chromium powder and the nickel powder.
As shown in Material), grain growth occurs and a homogeneous microstructure cannot be formed, and the amount of chromium in the soft phase increases, making it easy to become brittle and difficult to process into wire rods. This tendency becomes stronger as the chromium content increases.

In this way, particularly in high-chromium nickel materials manufactured by conventional manufacturing methods, the crystals are coarsened structurally, there are phases that reduce the deformability of the material, and the material is extremely brittle due to the presence of internal defects. The deformability etc. were inferior.

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a high chromium nickel material that satisfies certain conditions has no internal defects and has a dense structure. The present invention has been completed based on the discovery that this is an unprecedented high-chromium nickel material that has excellent workability and can be used industrially without cracking during subsequent handling.

That is, in the present invention, components other than chromium and nickel are 0.5
% by weight or less, and chromium is 50 to 90% by weight,
A high chromium nickel material with a composition in which the remainder essentially consists of nickel, and its structure consists of two phases: a hard phase and a soft phase.
The present invention relates to a high chromium nickel material having a crystal grain size of 50 μm or less, and a method for manufacturing the same.

Next, the manufacturing method of the present invention will be explained in more detail.

The raw material used in the production method of the present invention is a mixed powder of metal chromium, carbonyl nickel, or a chromium-nickel alloy powder. The metallic chromium powder used here has a purity of 99% or more.

If chromium with a purity of less than 99% is used as a chromium raw material, the resulting material will contain 0.0% of components other than chromium and nickel.
When the amount exceeds 5% by weight, a precipitated phase containing impurities as a main component is formed in addition to two phases, a hard phase and a soft phase. Also,
If a metal nickel powder other than carbonyl nickel (excluding the chromium-nickel alloy described below) is used as a nickel raw material, there is a limit to the fineness of the powder used, so the sintering reaction will be insufficient, resulting in defective material or bonding between two phases. A decrease in strength occurs.

In addition, in the method of using high chromium nickel alloy powder as a raw material, the structure of the chromium nickel alloy powder consists of two phases: a soft phase and a finely dispersed lamellar hard phase. If an alloy powder of 10μ or more is used, the workability of the ingot filled in the capsule will be poor, sufficient ductility will not be obtained during hot working, and cracks will occur during material processing. Therefore, if an alloy powder with a lamellar hard phase spacing of 10 μm or less is used, the above-mentioned cracks will not occur and the material deformability will be further improved.

Inert gas atomization is the most suitable method for obtaining alloy powder with such a structure.

Further, it is desirable to use a particle size of these raw material powders of 50 μm or less. If a powder with a particle size exceeding 50μ■ is used, a material with sufficient tissue deformability cannot be obtained.
This causes problems such as cracks during hot processing of the material.

Furthermore, it is desirable that the particle size of the raw material powder is 20 microns or less, and when such a raw material powder is used, the uniform dispersibility of the hard phase increases in the hot working process, improving the processing characteristics,
The wear resistance becomes even better.

Next, the raw material powder described above is thoroughly mixed and stirred using a binder such as alcohol, ethyl ether, or ethylene glycol as necessary, and then molded into an ingot with a density of 7 g/cm3 or more by cold isostatic pressing or the like. The ingot is heat treated in vacuum or inert gas. If the density of the ingot is less than 7g1c113, a gap will occur between the capsule and the ingot during hot processing in the post-process,
The reduction ratio between the capsule and the ingot is different, and cracks may occur from the surface. Furthermore, if the heat treatment is omitted, internal defects or areas where diffusion between the two phases is insufficient will exist inside the ingot, which may lead to breakage during hot processing, for example, during the hot swaging step.

Next, the ingot is filled into a capsule. The material of the capsule is not limited, but it is preferable to select a material that has a coefficient of thermal expansion close to that of the ingot material and can withstand subsequent hot working. For example, when metal is used as the capsule material, stainless steel, mild steel, etc. are generally used. Furthermore, if there is a gap between the capsule and the ingot, when pressure is applied to the outside of the capsule by squirting or forging, the processing elongation and deformability of the capsule and the ingot will not be the same, resulting in damage to the capsule and damage to the ingot. The bonding strength between the hard phase and the soft phase necessary for ingot deformation decreases, eventually causing cracks and internal defects. Further, after filling the capsule, it is preferable to seal it in a vacuum or inert gas to prevent surface oxidation of the Cr-NI ingot material and improve workability. After that, hot processing is performed, and generally hot swaging, hot forging, or hot rolling is used, and the processing temperature range is 300 to 300°C.
It is desirable to heat it at 800° C., preferably around 600° C., and process it to predetermined dimensions. The processing temperature is 30
If the temperature is lower than 0°C, the ingot will break, and if the temperature exceeds 800°C, the components of the capsule will be thermally diffused into the ingot.
Impurities other than the components of the present invention increase, and cracks occur between the hard phase and the soft phase due to the difference in coefficient of thermal expansion. It is clear from FIG. 2 that the processing temperature range of 300 to 800° C. provides the best workability. No, 1-No in Figure 2
, 5 each contain chromium 150.60.70.80.90
Weight Ik%, components other than chromium and nickel 0.5% by weight
The following shows the temperature dependence of the maximum tensile strain at break and the maximum tensile elongation during a tensile test of a high chromium nickel material in which the remainder is essentially nickel. 300-80 from the same figure
It shows maximum strain and maximum elongation in the temperature range of 0°C, indicating high plastic deformability.

In addition, these materials can be used to form plates, pipes, Wire rods can be processed into complex shapes.

Next, the composition and structure of the high chromium nickel material of the present invention produced in this manner will be explained below. First, the chromium and nickel compositions of the present invention will be explained.

Chromium is an element with excellent corrosion resistance and wear resistance under various environments, but it has poor workability when used alone. on the other hand,
Nickel is an effective element for improving processing characteristics.

A chromium-nickel material composed of these two components forms a two-phase structure of a hard phase mainly composed of chromium and a soft phase mainly composed of nickel. If the total chromium content in the chromium-nickel material is less than 50% by weight, corrosion resistance and wear resistance will deteriorate, and the object of the present invention will not be achieved.

In addition, if the total chromium content exceeds 90% by weight, the plastic deformability of the material will decrease, making it difficult to process into other materials and causing internal defects and surface cracks. The amount needs to be in the range of 50 to 90% by weight.

The material of the present invention needs to have a crystal grain size of 50 microns or less. The grain size of high chromium nickel material is 50
If the particle size exceeds μ, sufficient compositional deformability of the material will not be obtained and problems such as cracks will occur during hot working, so the grain size must be 50 μ or less, more preferably 20 μ. - less than or equal to When the crystal grain size is less than 20μ, the uniform dispersion of the hard phase increases during the material manufacturing process.
Improved machining characteristics and even better wear resistance.

Such adjustment of the crystal grain size can be achieved by using raw materials with a grain size of 50 μm or less, or by adjusting the processing temperature described above, that is, 300 to 300 μm.
This can be done by heating in the range of 800°C.

In addition, Cs and Mn are components other than chromium nickel.

If the total amount of Fes N, etc. exceeds 0.5% by weight, a precipitated phase mainly composed of impurities is generated in addition to the hard phase and the soft phase, reducing the deformability of the material and causing localized areas with poor corrosion resistance. appear. Therefore, it is necessary to suppress the total amount of components other than chromium nickel to 0.5% by weight or less, and to form a two-phase structure of a hard phase and a soft phase.

This is controlled by using highly pure raw materials during the production of the material. Figure 1-〇 (50Cr-Ni material) shows the structure of the material according to the present invention, and it can be seen that it satisfies all of the characteristics described above.

[Effects of the Invention] The material of the present invention has excellent plastic deformability. or,
This can be produced by a relatively simple method [Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

Examples 1 to 6 Table 1 shows the raw material powder composition of each material used in Examples 1 to 6. The raw material powder was adjusted to the composition shown in the table, and the powder (mixed powder: mixed powder of metal chromium powder and carbonyl nickel powder, alloy powder: high chromium nickel alloy powder) in the state shown in the notes in the table was added to the entire powder. The mixture was mixed with double ffi% ethyl alcohol, and an ingot was produced by cold isostatic pressing to a density of 7.5 g/cm3. This ingot was sintered at 1250°C for 2 hours in a vacuum heat treatment furnace, and then the ingot was sintered with a length of 125), a diameter of 33), and a thickness of 5ff11.
It was filled in the steel tube of No. 1 so that there were no gaps. Thereafter, it was kept in an argon gas atmosphere for about 15 minutes, then evacuated to 10'mtnHg at room temperature, and the exhaust hole was welded to form a capsule.

Next, the capsule was heated to 750°C from the outside, and the area reduction rate was 50.
%, hot rolling (11 passes) was carried out to obtain a slowly cooled material. This material was further held at 800"C for 2 hours and rolled at 600"C with the rolling direction changed by 90°, resulting in an area reduction of 93%.
Processed to. Table 1 shows the results of the structure, deformability, wear resistance, and corrosion resistance of each material obtained. The evaluation measurement method was determined as follows.

Structure measurement: After the material was puff-polished and electrolytically etched with oxalic acid, the structure was observed using an optical microscope.

Deformability measurement: Both ends of the material were fixed, a load of 50 kgf was applied to the center, and the bending angle of the material was measured.

Wear resistance measurement: The hardness of the hard phase and soft phase was measured using a hardness meter, and it was determined that the harder the hardness, the better the wear resistance.

Corrosion resistance measurement: To measure the corrosion rate, each material is polished and weighed before testing. Thereafter, it was immersed in a solution of 10% nitric hydrofluoric acid at 50° C. and 30% caustic soda at 150"C, and the corrosion rate was determined from the change in weight. The immersion test for the caustic soda solution was conducted in an autoclave.

As is clear from Table 1, the material of the present invention showed no cracks or defects in appearance, and exhibited excellent deformability in the 45° bending test. Also, in terms of organization, Fig. 3-b (Example 1
It can be seen that the two phases, a hard phase and a soft phase, are uniformly dispersed from the material), and the crystal grain size is also 50 μm or less. Furthermore, the results of hardness measurements show that it has excellent wear resistance and excellent corrosion resistance against strong acid solutions and strong alkaline solutions.

Comparative Examples 1 to 11 Each material was manufactured in the same manner as in the example except that the raw materials shown in Table 3 were used. Differences from the present invention are shown in the notes in the same table. Comparative Example 11 is an example in which an alloy powder manufactured using a water atomization method was used, and the powder particle size was 50 μm or less, but the powder was not spherical but had an acute-angled shape.

These materials were measured in the same manner as in the examples, and the results of structure, deformability, corrosion resistance, and abrasion resistance are shown in Table 3.

As is clear from Table 3, among Comparative Examples 1-11, Comparative Examples 1 to 3.7.10 have a chromium content of 50 to 90% by weight,
For example, Comparative Example 2 because the total amount of impurities is 065% by weight or less, which deviates from the chemical composition in which the remainder is substantially nickel.
As shown in FIG. 3-a, the cross-sectional structure of the material consists of three phases: a black precipitated phase is observed in addition to the two phases, a hard phase and a soft phase. Moreover, microcracks were observed on the surface, and cracks were generated during hot working. In Comparative Examples 4 to 6.9, the particle size of the raw material powder exceeds 50 μm, and in Comparative Example 11, the grain size is not spherical because the method for producing the alloy powder is different, so the crystal grain size is 50 μm or less. In addition, the deformability was poor, and cracks and microcracks occurred on the surface of the material. Furthermore, there are variations in hardness in terms of wear resistance, suggesting that wear tends to occur locally. In terms of corrosion resistance, it is also found that if the structure is non-uniform, a potential difference occurs between two or three phases in a corrosive solution, resulting in poor corrosion resistance.

Comparative Examples 12 to 15 Using the raw materials shown in Table 3, materials were manufactured according to the method and conditions shown in the notes of the same table. Comparative Example 12 is a material produced by melting and casting. In Comparative Example 13, raw material powder was subjected to cold isostatic pressing to form an ingot with a packing density of 7.5 g/cIIl', and instead of heat treatment, hot isostatic pressing (1200°C 1.2 ton-f* (in Ar) for 30 minutes, and then hot worked.

In Comparative Example 14, the ingot packing density was 7.5 g/cI.
Although it is I+3, it is a hot-processed material that was not subjected to subsequent heat treatment. In Comparative Example 15, the ingot has a packing density of 8.5 g/cm', and is a material obtained by hot processing the ingot which has been subjected to subsequent heat treatment.

Table 3 shows the results of surface condition, deformability, structure, and crystal grain size as material properties. Measurements were carried out in the same manner as in the examples. The material obtained in Comparative Example 12 had a structure in which the hard phase had developed into a dendrite shape, similar to that shown in FIG. The material obtained in Comparative Example 13 has an ingot packing density of 7.5 g/cIIl', but the material was subjected to hot isostatic pressing instead of subsequent heat treatment,
Although there were few cracks and internal defects on the surface of the material, the crystal grains grew because it was pressed at high temperatures, and its deformability was poor. In Comparative Examples 14 and 15, microcracks were generated on the material surface due to insufficient bonding strength between the two phases and insufficient packing density, and internal defects were also observed.

[Brief explanation of drawings]

Figure 1-a shows 47Cr- obtained by conventional arc melting method.
The ingot composition of the Ni material is shown in Figure 1. Figure 1 shows the structure of the 55Cr-Ni material also produced by the powder metallurgy method, and Figure 1-0 shows the cross-sectional structure of the chromium-nickel material of the present invention. Optical micrograph (1,000x), 2nd
The figure shows the maximum tensile strength at various temperatures for a material with a chromium content of 50.60.70.80.90% by weight, a total impurity of 0.5% by weight or less, and the remainder essentially nickel. The tensile fracture strain and maximum tensile elongation are shown in Figure 3 (
a) (b) shows SEX photographs (1,000x magnification) of the materials of Comparative Example 2 and Example 1.

Claims (1)

[Scope of Claims] 1) A high chromium nickel material having a composition in which components other than chromium and nickel are 0.5% by weight or less, chromium is 50 to 90% by weight, and the balance is substantially nickel. The structure consists of two phases, a hard phase and a soft phase,
A high chromium nickel material with a crystal grain size of 50 μm or less. 2) Use chromium powder and carbonyl nickel powder with a purity of 99% or more to form an ingot with a packing density of 7 g/cm^3 or more, heat the ingot in a vacuum or inert gas, and then perform hot processing, A high chromium nickel material having a composition in which components other than chromium and nickel are 0.5% by weight or less, chromium is 50 to 90% by weight, and the remainder is substantially nickel, and its structure is a hard phase. The crystal grain size of the material is 50μ.
A method for manufacturing a high chromium nickel material having a chromium-nickel content of less than m. 3) The manufacturing method according to claim 2), which uses high chromium nickel alloy powder as the raw material powder.