JPH06336651A - High manganese nonmagnetic cast body - Google Patents

Abstract

PURPOSE:To low suppress the thermal expansion coefficient and magnetic permeability of a high manganese nonmagnetic casting free from the need of heat treatment and to improve its using performance by specifying the content of C, Mn and Cr as essential components. CONSTITUTION:This casting has a compsn. contg., by weight, <=0.2% C, <=1.0% Si, 15 to 35% Mn, <=0.1% P, <=0.05% S and 3.0 to 9.0% Cr, and the balance iron with inevitable impurities, and in which an epsilon martensitic phase is precipitated at least by 10%, the average thermal expansion coefficient alpha in the temp. range of 25 to 100 deg.C is regulated to 12X10<-6>/ deg.C and its permeability is low suppressed as well. In this way, the high manganese casting within 120mm free from the need of heat treatment and used as cast can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-magnetic material having a small average coefficient of thermal expansion .alpha.

[0002]

2. Description of the Related Art In recent years, many members used under the environment of a strong magnetic field have been developed, and particularly nonmagnetic materials which are not affected by the magnetic field have been actively developed. For example, the fields used for various facilities of fusion reactors, various parts for magnetic levitation railways, motors, parts for transformers, etc. have expanded, and metallurgical research and development of components and heat treatment have been widely conducted, and many You can see the announcement. Looking at these conventional technologies,
Austenitic stainless steel, which has been universally used as the most non-magnetic material, requires a large amount of expensive Ni and induces transformation by cold working to precipitate martensite, thereby making it non-magnetic. The high risk of deterioration is taken up as a difficulty, and in place of this, high-manganese non-magnetic materials have attracted new attention, and it is understood that a considerable weight of development is related to this material.

The high manganese non-magnetic material is not only economically advantageous because an austenite phase similar to that of stainless steel can be obtained by blending a large amount of inexpensive manganese, but it is also associated with cold working as in stainless steel. A stable austenite phase in which no transformation induction is observed and the possibility of non-magnetic deterioration is small is receiving great attention as a great advantage. However, high manganese non-magnetic material has a larger average coefficient of thermal expansion α than ordinary carbon steel, similar to stainless steel,
The high manganese non-magnetic material is at a level of 14-18 × 10 ^-6 / ° C, whereas that of ordinary steel is about 12 × 10 ^-6 / ° C. However, in the case where a small amount of eddy current is generated by magnetism and heat is generated, a problem due to expansion during use is expected, so there is no choice but to place a large restriction. To solve this, many of the prior art provide improvements to improve adaptability in various applications.

The purpose of improving the high-manganese non-magnetic material is to lower the high average coefficient of thermal expansion α, which is a drawback, and to improve the strength of the material at low temperatures. This is because the point at which the material is used is diverted to a structural material such as the linear motor car or the fusion reactor, so that the material strength at low temperature is inevitably one of the major problems. For example, in JP-B-59-31569, C: 0.5% or less, S
i: 2% or less, Mn: 20 to 30%, N: 0.05 to
0.04%, the balance consisting of unavoidable impurities, a specific inequality holds between C and Mn, and the steel of this component is heated to 1220 ° C. or lower to perform hot rolling,
Disclosed is a method for producing a low magnetic expansion high yield point non-magnetic steel, which is characterized in that the finishing temperature is 800 ° C. + 400 ° C. × C (%) or less. That is, in order to enhance the stabilization of the austenite phase, a certain amount of N must be contained, and by specifying the rolling conditions (temperature), a manufacturing method is proposed in which the magnetic permeability does not deteriorate due to plastic deformation of the material. It was done.

In Japanese Examined Patent Publication No. 57-55784, Mn: 20 to 35% and Cr: 1.0 to 8.0% are used as basic components, and V: 0.1 to 1.0% and N: 0.2
〜0.4% including the average coefficient of thermal expansion α 0 ~ 100 ℃ 1
A high-manganese non-magnetic material having a yield strength of 2.5 × 10 ⁻⁶ / ° C. or less and a 0.2% proof stress of 35 Kgf / mm ² in a solution heat treatment state is proposed. That is, the high manganese non-magnetic material of the present invention utilizes the special addition components of V and N and the special behavior of the components in the heat treatment so that the magnetic permeability μ is 1.1 or less and the average thermal expansion coefficient α is 12.5. × 10 ^-6 / ° C or less, proof stress 35 kg
It is said that all of f / mm ^{2 and} above are satisfied. Other Al,
A high-manganese non-magnetic material containing Ca and subjected to solution toughening treatment after solution treatment, which has improved strength at -196 ° C. Japanese Patent Publication No. 59-11661, Ni, N, and at least one reinforcing component. There are a wide variety of compounds such as Japanese Examined Patent Publication No. Sho 49-10892 in which the toughness at -196 ° C. is improved by blending the above.

[0006]

All of the high manganese non-magnetic materials described here are intended to improve strength, particularly toughness and ductility at low temperatures, and their application is that of a magnetic levitation system driven by a linear motor. Guideways for railways,
As described above, it is applied as a reinforced concrete building that houses a fusion reactor or as a facility member for storing cryogenic substances such as liquid nitrogen. In this case, it is expected that an opportunity to encounter extremely low temperatures will be unavoidable, and since it is a condition that it must withstand a large load as a structural material when installed in equipment,
It is understandable that the issues are naturally limited to this point. Moreover, as long as it is used as a structural material, forming by plastic deformation is a normal condition, and there are many conditions such as how to prevent induced transformation at that time, thermal conditions for that, constituent restrictions, etc. It is difficult to solve a complicated relationship that combines

However, the region where the non-magnetic material is used is not limited to the extremely low temperature as exemplified here. On the contrary, the temperature used is at or around room temperature, but depending on the mode of use, other issues may be important, and it is often necessary to solve new problems as technological innovation progresses in the future. Is expected.

That is, when it is incorporated as a member under a strong magnetic field environment, it is of course a non-magnetic material in order to suppress the heat generation due to the generation of eddy current, that is, the magnetic permeability μ is at least 1.05. Even if it is necessary to be below, in addition to this, when the volume and thickness of the member are large, the absolute total thermal expansion reaches a non-negligible amount even if a small amount of heat is generated. Therefore, it is not acceptable that the average coefficient of thermal expansion α is higher than that of any ordinary iron system.
^{X10 -6} / ° C or less, the above properties are maintained equal in any part even if the member becomes large or complicated, and the shape of the member is considerably complicated and molding It cannot be denied that the problem to be solved will appear as a considerably different point from the prior art when the usage conditions such as the subsequent maintenance and the difficult processing finish are included are added.

For example, the transformer insulator has conventionally been made of a non-magnetic metal such as an aluminum casting or a bronze casting in order to prevent heat generation of the metal fitting due to an eddy current in a magnetic field. Since the size of the bushing also increases, the heat generated in the bushing of conventional non-ferrous metal materials
The difference in the absolute value of the thermal expansion amount between the metal fittings and the porcelain due to direct sunlight becomes large, and it becomes a factor that can no longer be ignored. Since the average coefficient of thermal expansion α of the porcelain (ceramic) itself is 8 to 9 × 10 ⁻⁶ / ° C., it is desirable that the average coefficient of thermal expansion α of the fitting holding the same be as low as possible. As a matter of course, the metal fitting is required to be a non-magnetic material and have an average coefficient of thermal expansion α equal to or lower than that of a normal steel material. Especially when the shape is large, even if the temperature is raised to the same temperature, the absolute value of the amount of expansion becomes larger than expected, so the importance of the average coefficient of thermal expansion increases. The situation is the same for metal fittings that attach precision-ground ceramic materials to equipment. Furthermore, if the shapes of these members are large and fairly complicated, a decarburized layer is always generated on the surface when the solution treatment and water toughness treatment peculiar to high-manganese non-magnetic materials are added, and as a result, it should be avoided. Impossible deterioration of magnetic permeability occurs. Usually, this decarburized layer is removed after heat treatment, but there is a problem that depending on the shape of the member, the decarburized layer may not be ground or removed by machining.

In order to solve the above-mentioned problems, the present invention has an average coefficient of thermal expansion at a level lower than that of ordinary steel while having a level of low magnetic permeability superior to the standard.
Providing high manganese non-magnetic materials that can be easily applied to large and complex members without depending on special additive components and heat treatments, which tend to cause large changes in physical properties of products due to melting and heat treatment conditions. To aim.

[0011]

The high manganese non-magnetic casting according to the present invention has a C: 0.2% or less, Si: 1.0% or less, Mn: 15-35%, P: 0.1%. Hereinafter, S: 0.
05% or less, Cr: 3.0 to 9.0%, with the balance being iron and unavoidable impurities, and having an average thermal expansion coefficient α in the temperature range of 25 to 100 ° C. of 12 × 10 ⁻⁶ / ° C. or less. Therefore, the above-mentioned problems have been solved by making it as-cast. Further, in this case, the as-cast microstructure is characterized in that at least 10% of ε-martensite phase is precipitated, and the cast wall thickness is at least 120 mm.
It is the most preferable embodiment that the above conditions are satisfied.

[0012]

The high manganese non-magnetic material according to the present invention uses a casting method as its forming means. Therefore, unlike other forming means, for example, a method for forcing plastic deformation such as drawing, rolling, extrusion, or forging, it has a considerably complicated shape. But it can be easily molded.
Further, since plastic deformation is not involved, work hardening peculiar to the high-manganese non-magnetic material does not occur, so that good machinability thereafter can be maintained. Next, since this high-manganese non-magnetic cast body is not accompanied by heat treatment, a decarburized layer is less likely to occur on the surface casting surface, and the steps for scraping off the decarburized layer are also reduced. When the member becomes large, it is usual that the solution treatment time in the conventional high manganese non-magnetic material becomes long and the thickness of the decarburized layer also increases, but in the present invention which is used as an as-cast material, this may occur. In addition, even if the shape is complicated, it is free from the occurrence of cracks due to uneven quenching during water toughness. Needless to say, the solution-hydrous toughness treatment aims to systematically complete the austenite phase, but this is a thought that emphasizes magnetic permeability and toughness, and from the standpoint of the average coefficient of thermal expansion. On the contrary, the paradox that the average coefficient of thermal expansion α increases, which is a bad thing, also holds.

From the point of view of components, no specific additive components other than Mn and Cr are required, so that the dissolution conditions are simple and there are few mistakes in component adjustment. For example, N mentioned in the prior art cited at the beginning is contained in a considerable amount in steel alloys such as steel scraps, ferromanganese, and ferrosilicon which are raw materials in the melting of ordinary high-manganese cast steel products. However, the rate at which they remain after solidification is greatly affected by the furnace conditions during refining, and intentionally keeping this within a narrow range is premised on a considerably advanced refining technology. . That is, it must be said that it is quite delicate to judge that the invention material has an action and an effect capable of significantly differentiating from other known materials at least near this lower limit. On the contrary, the present invention is characterized by the effect that the desired numerical values can be sufficiently maintained without depending on a special additive component as in the prior art.

Next, the reasons for limiting each component will be described for each component. C is a stabilizing element of the austenite phase and is an essential component in the high manganese non-magnetic material. However, even in the case of a thick cast product, which is one of the objects of the present invention, in order to maintain a predetermined average thermal expansion coefficient α, it must be 0.2% or less. The reason is that if C exceeds 0.2%, the ε-martensite phase decreases, which is disadvantageous in terms of average thermal expansion coefficient. Conventionally, as will be specifically described later in Examples,
Part of the austenite phase is
The change to the martensite phase has the advantage of decreasing the average coefficient of thermal expansion α, but has the disadvantage of increasing the magnetic permeability μ. However, it has been proved by experiments that the precipitation of the ε-martensite phase has the advantage of lowering the average thermal expansion coefficient α and that it does not adversely affect the magnetic permeability μ. That is, the normal α
The martensite phase is a body-centered cubic lattice and is a magnetic substance, whereas the ε-martensite phase is a non-magnetic hexagonal close-packed lattice, which is considered to cause a large difference in the effect on magnetic permeability. A structure containing at least 10% of ε-martensite phase is a requirement for maintaining the lower limit of the average thermal expansion coefficient α, and this structure is limited only when C: 0.20% or less. Mn is an element that stabilizes the austenite phase and is an indispensable element for making it a nonmagnetic material and having a low average thermal expansion coefficient, but excessive distribution lowers castability and is accompanied by an increase in the addition amount. Therefore, the lower limit is 15% and the upper limit is 35% for the above reason. Si is necessary as a deoxidizing material and for maintaining the fluidity of the molten metal to enhance the castability, but since it has the property of lowering the toughness when it is excessively distributed, it is limited to 1.0% or less. Cr is an effective element that improves strength and corrosion resistance, but if it is distributed excessively, it forms a ferrite phase to increase the magnetic permeability, so the upper limit is 9.0%.
Limited to. However, the content of at least 3.0% is essential in order to suppress the average thermal expansion coefficient α to be equal to or less than the limit value by the synergistic action with C and Mn. If the P content exceeds 0.1%, the toughness of the welded portion will be significantly lowered, so this value is the upper limit. Sn becomes MnS when Mn acts as a desulfurizing material, but if it is contained in an excessively large amount, this MnS becomes too much as inclusions, leading to a decrease in ductility and deterioration of the material. And

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a so-called Schaeff.
FIG. 3 is a structural state diagram of a welded stainless steel according to FIG.
The horizontal axis shows the Cr equivalent and the vertical axis shows the Ni equivalent. The limitation of the component range in the present invention does not start from the maintenance of a stable austenite phase, but on the contrary, a part of the austenite phase having a large average thermal expansion coefficient is replaced with another structure to increase the average thermal expansion coefficient. The idea is to lower it. That is, the test was repeated from the state diagram of the existing stainless steel, and the point B in the diagram was found as champion data. Based on the best point B, Cr equivalent and Ni equivalent are increased or decreased as shown in FIG. 2 to conduct an experiment on the magnetic permeability μ, the average thermal expansion coefficient α, and various mechanical properties. 3 and FIG. 4 were obtained respectively.

[0016]

[Table 1]

[0017]

[Table 2]

In this case, of course, the Ni equivalent is N
i itself is not included and C% has the greatest effect as a variable of the equivalent. Since the average thermal expansion coefficient α and the magnetic permeability μ both increase with the increase of Cr, the Cr amount is set to the optimum 5.5.
%, And then the Ni equivalent, that is, C% was changed, and the average thermal expansion coefficient α and the magnetic permeability μ were measured, and the obtained values are summarized in the tables and figures. The average coefficient of thermal expansion α rises with the increase of C%, and point B (C: 0.14%)
Has an average coefficient of thermal expansion α of 10.71 × 10 ⁻⁶ / ° C.,
The average thermal expansion coefficient α at the K point (C: 0.26%) is 1
A recording of 1.12 x 10 ^-6 / ° C was recorded. Even if there is a correlation with other components, the amount of C still satisfies the target average thermal expansion coefficient α of 12 × 10 ^-6 / ° C or less at the point K, but observation of the microscopic structure To C: 0.2%
Limited to: That is, FIG. 5 shows point B, FIG. 6 shows point K,
FIG. 7 is a micrograph of each of M points. All magnifications were taken at 100 times, and the corrosive liquid was a mixed solution of saturated sodium thiosulfate solution and potassium bisulfite isomer. Precipitation of ε-martensite phase was observed only in FIG. 5 (point B) with a white austenite phase, and the area ratio was about 15
It has risen to about 20%. However, at the point K, this ε-martensite phase has completely disappeared from the visual field. Therefore, since the other components are almost aligned, it can be interpreted that this difference is apparently caused only by the difference in C%. It is reasonable. Therefore, it became a strong basis for C% limitation.

FIG. 8 is a table in which changes in the product thickness at the point B, which is the champion data, are measured and summarized. According to the figure, as the casting surface of the as-cast product progresses from the surface to the inside of the product, coarsening of the grain size is unavoidable, so a reduction in mechanical strength such as tensile strength and elongation cannot be denied, but the yield strength is almost Since it can hold a constant value and the average coefficient of thermal expansion α is located at almost the same level, at least as confirmed in this experiment, it is sufficiently reliable even when applied to large-sized products with a wall thickness of 120 mm or less. It indicates that it can be used. By the way, general high-manganese non-magnetic materials are always subjected to water toughness treatment, but as the wall thickness increases, the water toughness effect does not reach completely to the inside, and it is easy to cause unevenness, distortion, and cracking of the structure. It is desirable that the wall thickness be 50 mm or less.

[0020]

As described above, the present invention is a high-manganese non-magnetic material, but there is no special additive component other than Mn and Cr, and it is technically difficult to adjust a low content component delicately. Is unnecessary and the influence of dissolution conditions is small.
Since the molding is performed by a casting method, it is possible to economically manufacture a defect-free member having an accurate dimension even if the member has a considerably complicated shape or a member having a considerably large size as long as a casting method is suitable. Since the forming is not accompanied by plastic deformation, the directionality of the crystal grains is small and no large deviation due to the direction of the material force appears. It is also free from the problem of reduced magnetic permeability during plastic deformation, and is accordingly free from fine component adjustments. Further, since the heat treatment is unnecessary, the formation of the decarburized layer is small, and the troublesome finishing and machining for removing the decarburized layer are minimized. From a systematic perspective, there is a clear advantage in maintaining a low level of average coefficient of thermal expansion. On the other hand, the magnetic permeability is superior to the conventional non-magnetic material. For example, since the point B is 1.005, the conventional standard is 1.1 to 1.05. It records low figures that are orders of magnitude lower. On the other hand, since it is a cast body and heat treatment is not required, the product thickness is less restricted than other non-magnetic materials, and even if a product thickness of at least 120 mm is applied, a reliable average thermal expansion coefficient, magnetic permeability, It has the strength. Such a property exceeds the limit that cannot be reached by the conventional high manganese non-magnetic material.

[Brief description of drawings]

FIG. 1 is a chart in which an embodiment of the present invention is plotted on a Schaeffler tissue phase diagram.

FIG. 2 is a flowchart illustrating the progress of the experiment.

FIG. 3 is a chart showing changes in C% and various properties.

FIG. 4 is a chart showing changes in Cr% and various properties.

FIG. 5 is a micrograph of a metal structure at point B.

FIG. 6 is a micrograph of a metal structure at point K.

FIG. 7 is a micrograph of a metal structure at point M.

FIG. 8 is a chart showing the relationship between the depth of the large-walled thick product that has progressed from the surface of the casting to the inside and changes in various properties.

Front page continued (72) Inventor Hiroto Matsuo 4-9 Kawasumi-cho, Mizuho-ku, Nagoya, Aichi (72) Inventor Iwaji Kawamoto 2-1-1 Shinkawa-cho, Minato-ku, Aichi (72) Invention Person Yamamori Gou 15 Wakabayashi Higashi-cho Miyama 15-4 Toyota City, Aichi Prefecture

Claims (3)

[Claims] 1. C: 0.2% or less, Si: 1.0% or less, Mn: 15 to 35%, P: 0.1% or less, S: 0.
05% or less, Cr: 3.0 to 9.0%, with the balance being iron and unavoidable impurities, and having an average thermal expansion coefficient α in the temperature range of 25 to 100 ° C. of 12 × 10 ⁻⁶ / ° C. or less. A high-manganese non-magnetic cast body characterized by being used as cast. 2. The high-manganese nonmagnetic cast body according to claim 1, wherein the as-cast microstructure has at least 10% of ε-martensite phase precipitated. 3. The high manganese non-magnetic cast body according to claim 1, wherein the above conditions are satisfied up to a casting thickness of at least 120 mm.