JPH0118987B2 - - Google Patents

Description

[Detailed description of the invention]

Technical Field This invention aims to achieve a significant improvement in room temperature strength, especially yield strength, as well as workability, by adjusting the composition of high-Mn non-magnetic steel. It is particularly suitable for use in applications such as the outer rotor of a generator, where rotational centrifugal force is applied in addition to large electromagnetic induction force. Technical background The development of generators that utilize superconducting phenomena belongs to the field of cutting-edge technology, and there has been no actual production results to date. Prototypes are currently being produced in various countries including Japan, as it is expected to have significant economic benefits such as the effect of occupying land. By the way, the outer rotor of such a superconducting generator needs to withstand both electromagnetic force and centrifugal force, so it is not only non-magnetic.
Yield strength at room temperature is 70Kg/ ^mm2 or more, preferably 80
It is required to have a high strength of Kg/mm ² or more. And even if it is manufactured by rolling,
Even if manufactured by forging, hot workability must be good as a manufacturing condition, and good machinability and weldability are required from the perspective of actual machine assembly. Therefore, in addition to strength, high ductility is required. In addition, it is assumed that the price will be low considering the practical stage. However, to date, no material has been found that meets all of the above conditions. For example, austenitic stainless steel has a yield strength at room temperature of at most 40 kg/ ^mm2 , and
Even in the case of the high manganese steel disclosed in Publication No.-110757, the room temperature strength is only about 45 kg/mm ² . In this regard, high Ni steel (such as A286) and Ti alloys may be able to address this issue in terms of material properties, but such alloys are inherently expensive materials and also have problems in terms of manufacturability. The disadvantage is that the yield is poor and the cost is even higher. Purpose of the Invention The present invention advantageously solves the above-mentioned problems, and proposes a high-Mn nonmagnetic steel that has high strength at room temperature, excellent hot workability, machinability, and weldability, and is inexpensive. The purpose is to Summary of the Invention The present invention discloses that in high Mn nonmagnetic steel, Cr, Al, and
Alternatively, it is extremely important to utilize the precipitation hardening effect of V along with the solid solution hardening effect of Cr and N, or to reduce P and S and add REM and Ca in combination to improve workability. Based on new findings that are effective. Background to the elucidation of the solution Although various materials can be considered for the outer rotor of a superconducting generator, high Mn steel is particularly promising from various viewpoints such as magnetic stability, ease of improving proof strength, and economic efficiency. Therefore, the inventors conducted various studies on high-Mn steel, and as a result, established a technology for producing an alloy based on the strengthening mechanism described below, and completed the present invention. Now, the methods to increase the room temperature strength of high Mn steel are: (1) Utilizing solid solution hardening of components (2) Utilizing precipitation hardening of carbides, nitrides, intermetallic compounds, etc. (3) Utilizing working strain There are many things that can be considered. Among these methods, method (3) is extremely difficult in practice because the product is shaped like a fairly large hollow rod. Therefore, as a result of various studies on the possibilities of methods (1) and (2), we decided to use both methods together, specifically (1), which also includes solid solution hardening of Cr, Al, or Cr, and N. As for (2), we have found that the combined use of precipitation hardening of V carbide is extremely effective in achieving the intended purpose. Furthermore, we investigated improvements in machinability, machinability, etc., and found that in order to improve these properties at the same time, we should reduce P and S and then REM.
They also discovered that it is best to add Ca and Ca simultaneously. In other words, the strength improvement of high Mn steel can be achieved simply by adding Cr and Al.
(In this case, if AlN is generated, the toughness will be impaired, so N should be kept at a low value), or only by the solid solution strengthening effect of Cr and N (also in this case, Al should be kept low for the same reason). For example, Cr, Al
Cr and N systems have an advantage in toughness but are disadvantageous in hot workability, while Cr and N systems have the opposite tendency.
In any case, the problem still remained, but if the solid solution strengthening effect is combined with the strengthening effect due to the intragranular precipitation of VC, the above problem is solved and the room temperature strength is significantly increased. By reducing S, ductility, hot workability and weldability are improved, and by adding REM and Ca in combination, hot workability and machinability are further improved. It was discovered that this can be achieved. Structure of the Invention The present invention is derived from the above knowledge. That is, in this invention, C: 0.30 to 1.00% by weight
(hereinafter simply expressed in %), contains Mn: 24.0 to 31.0%, V: 0.2 to 1.5%, and Cr: 2.0 to 10.0%.
Al: 3.0% or less, N: 0.02 to 0.40%, and together with the amounts of Al and N shown in the coordinates within the range shown in the attached Figure 1, and REM: 0.002 to 0.002.
Contains at least one selected from 0.010% and Ca: 0.002 to 0.010%, and the remainder is
P suppressed to 0.015% or less, S suppressed to 0.010% or less, and other unavoidable impurities and Fe.
It is a high Mn nonmagnetic steel characterized by a composition of The reason why the composition range of each component is limited as described above in this invention will be explained below. C: 0.30-1.00% C is a useful element that contributes to solid solution hardening as an interstitial solid solution element and also combines with V to cause precipitation hardening. At least 0.30% is required, but
If the content exceeds 1.00%, machinability deteriorates, so the content was limited to a range of 0.30 to 1.00%. Mn: 24.0 to 31.0% Mn is required to be at least 24.0% in order to stabilize the austenite phase, that is, to stabilize the magnetic properties and ensure workability, but if it exceeds 31.0%, toughness and weldability deteriorate. Therefore, the Mn content is 24.0
The range was 31.0%. V: 0.2-1.5% V effectively contributes to improving room temperature strength through the precipitation hardening action of V carbides, but the content
If it is less than 0.2%, the effect of the addition is poor, while if it is 1.5%
If the content exceeds this amount, the deterioration of ductility becomes so severe that it cannot be avoided by other means, so it is limited to a range of 0.2 to 1.5%. Cr: 2.0 to 10.0% Cr is an element that not only improves strength through solid solution hardening action together with Al and N, which will be described later, but is also useful for improving toughness, but if the content is less than 2.0%, The addition effect is poor, and if it exceeds 10.0%, it inhibits the stability of the austenite phase and has a negative effect on toughness and stress corrosion cracking susceptibility.
It was limited to a range of 10.0%. Al: 3.0% or less, N: 0.02-0.40%, and attached No. 1
The areas Al and N indicated by diagonal lines in the figure are substitutional and interstitial solid solution elements, respectively, and although their solid solution forms are different, they are equivalent solid solution hardening components. However, if large amounts of both are contained, AlN will be generated and cause a significant deterioration of toughness, so the amount of N, for example, needs to be controlled within an appropriate range depending on the content of the other (Al in this case). There is. If the Al content exceeds 3.0%, it will have a negative effect not only on toughness but also on hot workability.
Must be 3.0% or less. Here, when the Al amount is 3.0 to 0.1%: the N content is
If it exceeds 0.10%, as mentioned above, AlN precipitation will become severe and the toughness will be impaired, while if it is less than 0.02%, the solid solution strengthening effect of N cannot be expected at all. For %, N is 0.02
Must be in the range of ~0.10%. Also, if the Al content is less than 0.1%: the N content is 0.40
%, the solid solution strengthening effect reaches saturation, and
Toughness and weldability also tend to deteriorate;
If Al is less than %, solid solution strengthening cannot be expected.
If it is less than 0.1%, N needs to be in the range of 0.10 to 0.40%. That is, when the relationship between the above-mentioned Al content and N content is illustrated, the area is indicated by diagonal lines in the attached FIG. 1. REM: 0.002 to 0.010%, Ca: 0.002 to 0.010% As described later, hot workability is improved to some extent by simultaneously reducing P and S, but problems arise when the rolling rate and forging ratio are high. Therefore, further improvement is attempted by adding REM and Ca. Furthermore, the steel of this invention is a high-strength material, and although there remains a problem in that the product has poor machinability, these elements can effectively contribute to solving this problem. However, whether REM and Ca are used alone or in combination, if the content is less than 0.002%, the addition effect is poor;
If added in excess of
It is necessary to add it in the range of 0.002 to 0.010%. P: 0.015% or less, S: 0.010% or less Since this invention steel aims to improve room temperature strength through solid solution hardening and precipitation hardening, it naturally has ductility, hot workability, and weldability. This leads to deterioration in properties (especially high-temperature ductility reduction cracking). In order to avoid such damage, simultaneous reduction of P and S is effective, and from this point of view, the upper limits of P and S are limited to 0.015% and 0.010%. Next, a method for manufacturing this invented steel will be described. After melting in a conventional converter or electric furnace, a degassing process is performed to purify the molten steel, and then a slab is produced by continuous casting or by an ingot casting and blooming process. Then 1100-1200
After heating the slab at a relatively low temperature of 0.degree. C., it is rolled into a thick plate product, or hot rolled to make a hot rolled product. In some cases, after annealing the mother plate of the hot-rolled coil (also heated at 1100 to 1200°C), grinding and pickling are performed, followed by cold rolling to produce a cold-rolled product. In either case, a final precipitation aging treatment is performed at 650°C. Examples Examples of the present invention will be described below together with conventional examples and comparative examples. After melting the various steels whose compositions are shown in Table 1 in a converter, they are refined in an outside-furnace vacuum refining furnace, and then ingot-formed, bloomed, hot-rolled, and, as the case may be, in accordance with conventional methods. After that, it is further cold rolled and then rolled at 650℃.
A 4.0 mm thick plate product was obtained by precipitation hardening treatment for 4 hours. Table 1 also shows the results of examining various tensile properties, magnetic permeability, Charpy impact value, hot workability, machinability, and weldability for each of the obtained steel plates (steel Nos. 1 to 28). Note that hot workability is the hot rolling property of the wedge-shaped specimen, and machinability is the machinability and drilling property.
Furthermore, weldability was determined by TIG tanning and fillet weldability.

【table】

[Table] As is clear from the formation shown in Table 1, conventional austenitic stainless steel (Steel No. 22) and
Each Al alloy (Steel No. 25) has a room temperature yield strength of 50Kg/
It is low at less than mm ² , and high Mn steel (Steel No. 26 to 28) is also 45
This is about Kg/mm ² , which is far below the target value of this invention of 80 Kg/mm ² . In this regard, in the case of high Ni steel (Steel No. 23) and Ti alloy (Steel No. 24) such as A286, almost the desired tensile properties were obtained, but both materials are used in large quantities as structural materials. Ti alloys are too expensive to use, have poor hot workability and weldability, and, especially for Ti alloys, have poor ductility and toughness. Among the comparative examples, steel No. 13 has poor toughness due to an excessive amount of Al, and steel No. 14 has poor hot workability and weldability due to excessive amounts of both P and S. No. 15 has poor hot workability, machinability, and weldability because it does not contain REM and Ca, No. 16 has poor toughness due to too much V, No. 17 lacks strength due to too little C, and No. 18 has poor Mn If the amount is too low, the permeability is large, and the same
No. 19 had too little Cr and lacked strength, No. 20 had too much Cr and poor toughness, and No. 21 had too much N and poor toughness, all of which still have problems. On the other hand, all of the steels of this invention (Steel Nos. 1 to 12) have a yield strength at room temperature of 80 kg/mm ² or more, and have good ductility, hot workability, machinability, and weldability. Moreover, the magnetic permeability also shows a low value. Effects of the Invention Thus, according to the present invention, it is possible to achieve a significant improvement in the room temperature strength of high-Mn nonmagnetic steel compared to conventional steels, as well as improvements in ductility, hot workability, machinability, and weldability. Therefore, it is particularly effective when used in applications where strong electromagnetic force and large centrifugal force act, such as the outer rotor of a superconducting generator, and where ease of manufacture is required.

[Brief explanation of drawings]

FIG. 1 is a chart showing appropriate ranges for the amount of Al and the amount of N in this invention.

Claims (1)

[Claims] 1 Contains C: 0.30 to 1.00% by weight, Mn: 24.0 to 31.0% by weight, and V: 0.2 to 1.5% by weight, and Cr: 2.0 to 10.0% by weight, and Al: 3.0% by weight or less. , N: 0.02-0.40% by weight, and further contains Al and N in the amounts shown in the coordinates within the range shown in the attached Figure 1, and further contains REM: 0.002-0.010% by weight and Ca: 0.002-0.010% by weight. Room-temperature strength characterized by containing at least one selected from the following, with the remainder being P suppressed to 0.015% by weight or less, S suppressed to 0.010% by weight or less, other unavoidable impurities, and Fe. Excellent for high
Mn non-magnetic steel.