JPH0121845B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing high-strength non-magnetic steel that can be strengthened by hot working. Austenitic stainless steel and high Mn steel are non-magnetic, so they are generally used as non-magnetic steels, but these have low yield strength in the solution-treated state, and when high strength is required, they are generally solution-treated. It is used after being subjected to cooling processing or aging treatment after treatment. According to JP-A-53-117617 and JP-A-53-117618, high-strength austonitic stainless steels having a 0.2% yield strength of 60 Kg/mm ² class are disclosed, and these steels are solution-treated. This is steel that has been subjected to a treatment to obtain the above characteristics. The present invention addresses the drawback that conventional solution-treated steel has low yield strength, or the cost of steel that is subjected to cold working or aging treatment after solution treatment to eliminate the drawback. It is an object of the present invention to provide a method for producing high-strength nonmagnetic steel that eliminates the disadvantage of That is, in the present invention, C: 0.15% or less, Si: 0.1 to 2.0%, Mn: 7.0 to
25.0%, Ni: 0.5~10.0%, Cr: 15.0~26.0%,
Contains Mo: 4.0% or less, N: 0.2 to 0.8%, and Cu: 0.1 to 2.0% or Nb, Zr, V, Ta,
Contains 0.5% or less of one or more selected from Ti and Al, and the remainder is substantially Fe.
A: First, the steel is heated to a temperature range of 1100°C to 1300°C and processed, and this processing is finished at 800°C or above. B: Then, the steel is heated to a temperature range of 1050°C to 1250°C. , firstly processed by 10% or more at a temperature of 1000°C or higher, and then processed by 10% or more at a temperature of 600°C to 1000°C.
% or more, and then cooled to room temperature at a cooling rate higher than the air cooling rate, or following steps A and B, C: further heat-treated within a temperature range of less than 700°C.
The present invention proposes a method for manufacturing high-strength nonmagnetic steel characterized by the following. Next, details of the manufacturing method of the present invention will be explained. The present inventors investigated the properties of the conventional steel without the solution treatment, that is, after only hot working, and found that the steel had excellent mechanical properties. The present invention was completed by newly discovering that Hot treatment A performed on the steel ingot in the present invention,
Items B and C will be explained respectively. Section A is a section related to normal casting operations, and is intended for forging and forming. In other words, the coarse dendrites in the steel ingot are destroyed at a temperature higher than the recrystallization temperature.
In addition to miniaturization, bubbles, cracks, etc. are crimped to form a predetermined shape.
It is necessary to make it possible to increase the ratio to 20% or more. If the steel ingot is heated to a temperature higher than 1300℃, the grain boundary ductility will decrease and cracks will occur during forging, while if it is lower than 1100℃, the workability of forging will deteriorate.
It is necessary to heat within the temperature range of °C. At temperatures lower than 800°C, the material has high deformation resistance and is inefficient for the purpose of forging and forming, so the processing temperature was set at 800°C or higher. Item B is the most important processing part performed in the present invention. Heating at a temperature higher than 1250℃ will cause significant coarsening of crystal grains, while heating at a temperature lower than 1050℃ will not dissolve carbonitrides sufficiently and have a negative effect on mechanical properties after processing. 1250
It is necessary to heat to a temperature range of °C. Processing at temperatures above 100°C is intended to refine the grains. If the processing rate within this temperature range is less than 10%, there is almost no effect of grain refinement, so the processing rate is reduced to 10%. % or more. If the following processing is performed within the temperature range of 600°C to 1000°C without performing this processing, coarse grains will remain and have a negative effect on mechanical properties. Processing within the temperature range of 600°C to 1000°C aims at grain refinement and fine precipitation of carbonitrides, making the steel extremely tough. Processing at a temperature higher than 1000°C does not precipitate carbonitrides during processing and has a small strengthening effect. Processing at a temperature lower than 600°C is effective for strengthening steel, but it only deteriorates toughness and ductility. This is not a good idea because the deformation resistance is large and a large amount of force is required for processing. Therefore, it was decided to give the final processing within the temperature range of 600°C to 1000°C. If the final processing rate is less than 10%, the contribution to strengthening the steel is small, so we decided to perform processing at a processing rate of 10% or more. When slowly cooled after the above-mentioned processing, carbonitrides precipitate at the grain boundaries, resulting in significant deterioration of toughness and ductility. Therefore, after processing, it was decided to cool to room temperature at a cooling rate higher than the cooling rate by air cooling. For item C, heat treatment is performed within a temperature range of less than 700°C as necessary so as not to destroy the structure formed in item B. Heating to 700°C to 100°C causes carbonitrides to precipitate at the grain boundaries, leading to deterioration of toughness and ductility, and solution treatment at temperatures higher than 1000°C significantly reduces strength. As described above, the steel of the present invention is a steel obtained by processing as described in Sections A and B, or by further subjecting it to strain relief annealing at less than 700° C. after the processing described in Sections A and B. Next, the reason for limiting the composition of the steel material in the present invention will be explained. Carbon is a strong austenite-forming element and at the same time is very effective in strengthening the austenite matrix.However, if the amount exceeds 0.15%, a large amount of carbides will precipitate at grain boundaries during hot working, significantly impairing toughness. must be below 0.15%. Silicon is an effective deoxidizing agent and an essential component in steelmaking operations, and about 1% is usually required. Furthermore, silicon is a ferrite-forming element and is effective in strengthening the austenite matrix. 2.0% silicon
If the amount is too large, scratches and cracks are likely to occur during manufacturing, and δ ferrite is generated, which increases magnetic permeability and deteriorates non-magnetic properties. Furthermore, it is difficult to reduce the silicon content to less than 0.1% in terms of manufacturing. Therefore, silicon is 0.1~
Must be within the range of 2.0%. Manganese is an austenite-forming element;
and significantly increases the solubility of nitrogen. In order to achieve a single austenite phase in balance with the Ni content, 7.0% or more is required, so the lower limit of manganese is set.
On the other hand, if the content exceeds 25.0%, hot and cold workability will be significantly impaired, so the manganese content must be within the range of 7.0 to 25.0%. Nickel is an element that stabilizes austenite together with C, N, and Mn, and at least 0.5% is required to obtain a stable austenite phase. If the nickel content exceeds 10.0%, the price will be high and it is economically disadvantageous, and furthermore, the strength will decrease, which is undesirable. Therefore, the nickel content must be within the range of 0.5 to 10.0%. Chromium is a basic component for maintaining corrosion resistance and at the same time is an element that acts as a ferrite element. Also, like manganese, it significantly increases nitrogen solubility. If the chromium content is less than 15.0%, corrosion resistance will significantly deteriorate. In order to increase nitrogen solubility, the higher the amount of chromium, the better; however, if the content exceeds 26.0%, the structure will not be a single-phase austenite structure but a mixed structure with ferrite, leading to an increase in magnetic permeability and deterioration of hot workability. Therefore, chrome is 15.0 ~
Must be within the range of 26.0%. Molybdenum acts as a ferrite-forming element and is an element harmful to obtaining a single austenite phase. If molybdenum is within the range of solid solution in the matrix, it is effective for strengthening the matrix, improving toughness, and especially corrosion resistance. If the content exceeds 4.0%, ferrite is produced, making it difficult to obtain a single austenite phase, and the price becomes high, which is economically disadvantageous. Therefore, the molybdenum content is
Must be 4.0% or less. Nitrogen, like carbon, is a strong austenite-forming element and has a remarkable strengthening effect, but unlike carbon, the amount of nitrogen that precipitates as nitrides at grain boundaries during hot working is small, and it can be used to improve toughness without sacrificing toughness. It is an element that enables strengthening. If it is less than 0.2%, no improvement in material strength can be expected, so the lower limit is set at 0.2%.
Further, if the nitrogen content exceeds 0.8%, blowholes often occur and a sound steel ingot cannot be obtained, so the nitrogen content needs to be within the range of 0.2 to 0.8%. Copper acts as an austenite-forming element and is an effective element for obtaining austenite single phase.
It is also an element that strengthens the austenite matrix. It also has the effect of contributing to increasing nitrogen solubility in austenite and improving corrosion resistance.
If it is less than 0.1%, the effect will be small, so if it is contained more than 0.1%, on the other hand, if it is more than 2.0%, grain boundary embrittlement will be promoted at high temperatures and hot workability will be significantly deteriorated.
Therefore, the copper content must be within the range of 0.1 to 2.0%. Niobium, zirconium, vanadium, titanium,
Tantalum and aluminum have fine grains,
It is an element that greatly contributes to improving material strength.
If the content exceeds 0.5%, the contribution to material strength will be reduced and the price will increase, so one or more selected from niobium, zirconium, vanadium, titanium, tantalum, and aluminum.
Must be 0.5% or less. Next, the present invention will be explained using experimental data. Table 1 shows the chemical components of sample materials No. 1 to 10. Table 3 shows the mechanical properties and magnetic permeability at room temperature of the test materials manufactured under the manufacturing conditions shown in Table 2.

【table】

【table】

【table】

[Table] In Section A of Table 2, a 15Kg steel ingot was heated to 1200℃ and forged, and the above processing was completed at 1000℃.
A billet with a size of mm×lmm was obtained, and the forging described above was performed once before obtaining the billet of the above shape. Such treatments are listed in Table 2 as one heat. In addition, in Section B, processing was performed in Section A.
After heating a billet with a size of 40mm x 40mm x lmm to 1150℃, forging was started, and when the temperature reached 1000℃, the shape of the semi-finished product was 25mm x 25mm x lmm, and as a result of further forging, it became 25mmφ x lmm. The finishing temperature when the final product was obtained was 900°C. According to Table 3, the 0.2% yield strength is 85.5 to 94.0Kg/mm ²
The impact value is within the range of 21.8 to 28.1Kgm/
cm ² range, it can be seen that the steel of the present invention has excellent high strength and high toughness, and the magnetic permeability measured at 100 Oe is low at less than 1.01. Next, Table 5 shows the mechanical properties and magnetic permeability of sample No. 5 among the above samples at room temperature when the test was carried out under each manufacturing condition shown in Table 4.

[Table] Note: All dimensions of steel ingots and billets are in mm.

[Table] In Table 4, for example, under manufacturing condition d, 500
A Kg steel ingot was heated to 1230℃ and forged, and the processing was completed at 900℃ to obtain a billet with a size of 140mm x 140mm x lmm. was repeated three times. The repetition of such treatment is shown in Table 4 as 3 heats. For example, in the B section of the manufacturing condition a, the billet with a size of 40 mm x 40 mm x lmm treated in the A section is
After heating to 1150℃, forging was started, and when the temperature reached 1000℃, the shape of the semi-finished product was 25mm x 25mm x lmm, and as a result of further forging, a final product of 25mmφ x lmm was obtained. The finishing temperature was 900°C. According to Table 5, for the series of the present invention, the 0.2% yield strength is within the range of 89.8 to 120.5 Kg/mm ² and the impact value is within the range of 12.0 to 26.8 Kgm/cm ² . On the other hand, for comparative examples f and i, the impact value was 31.9Kgm/cm ² ,
Although it is high at 35.1Kgm/cm ² , the 0.2% yield strength is 60.5Kg/mm ² ,
It is extremely low at 70.5Kg/ ^mm2 . Also, comparative examples g and h are
Although the 0.2% yield strength is high at 100.0Kg/mm ² and 102.1Kg/mm ² ,
The impact values of both were extremely low at 2.0Kg/cm ² . As is clear from the above, the examples of the present invention have both strength and toughness, but the comparative examples are found to be significantly inferior in either strength or toughness.
For sample No. 5 shown in Table 1, a round bar with a size of 85 mmφ x lmm was made under the manufacturing conditions d shown in Table 4, and from this, a sleeve with a size of 75 mmφ/55 mmφ x 180 mm was made, and the core was When used as a joint member for coaxial cables used in experimental fusion reactor equipment, it was able to withstand compression processing used to make joints due to its high strength and toughness. Furthermore, due to the low magnetic permeability, which is a characteristic of this steel, it did not generate heat during use. As explained above, the non-magnetic steel manufactured by the manufacturing method of the present invention has excellent strength and toughness, and is particularly suitable as a member for a fusion reactor experimental device. It can also be advantageously used as a structural material for the tracks of linear motor cars, a retaining ring for generators, and structural materials for superconducting magnetic storage equipment, MHD power generation equipment, superconducting generators, and the like.

Claims (1)

[Claims] 1 C: 0.15% or less, Si: 0.1 to 2.0%, Mn: 7.0
~25.0%, Ni: 0.5~10.0%, Cr: 15.0~26.0%,
A steel containing Mo: 4.0% or less, N: 0.2 to 0.8%, and the remainder substantially Fe is processed by heating to a temperature range of 1100℃ to 1300℃, and this processing is carried out to 800℃. B Next, heat within the temperature range of 1050°C to 1250°C, first process 10% or more at a temperature of 1000°C or higher, and then process 10% or more within the temperature range of 600°C to 1000°C.
A method for manufacturing high-strength non-magnetic steel, which is characterized by subjecting it to a final processing of % or more, and then cooling it to room temperature at a cooling rate equal to or higher than the air-cooling rate. 2 C: 0.15% or less, Si: 0.1-2.0%, Mn: 7.0
~25.0%, Ni: 0.5~10.0%, Cr: 15.0~26.0%,
A steel containing Mo: 4.0% or less, N: 0.2 to 0.8%, and the remainder substantially Fe is processed by heating to a temperature range of 1100℃ to 1300℃, and this processing is carried out to 800℃. B Next, heat within the temperature range of 1050°C to 1250°C, first process 10% or more at a temperature of 1000°C or higher, and then process 10% or more within the temperature range of 600°C to 1000°C.
A method for producing high-strength nonmagnetic steel, characterized by subjecting it to a final processing of % or more, then cooling it to room temperature at a cooling rate equal to or higher than an air cooling rate, and further heat-treating within a temperature range of less than 700°C. 3 C: 0.15% or less, Si: 0.1-2.0%, Mn: 7.0
~25.0%, Ni: 0.5~10.0%, Cr: 15.0~26.0%,
Contains Mo: 4.0% or less, N: 0.2 to 0.8%, and one or two selected from the following (a) and (b).
The steel containing seeds and the remainder being essentially Fe is processed by heating it to a temperature range of 1100°C to 1300°C, and finishing the processing at 800°C or above, and then processing it at 1050°C to 1050°C. Heating within the temperature range of 1250℃, first applying 10% or more processing at a temperature of 1000℃ or higher, then 10% processing within the temperature range of 600℃ to 1000℃
A method for manufacturing high-strength non-magnetic steel, which is characterized by subjecting it to a final processing of % or more, and then cooling it to room temperature at a cooling rate equal to or higher than the air-cooling rate. (a) Cu: 0.1-2.0%. (b) One or more selected from Nb, Zr, V, Ta, Ti, and Al, 0.5% or less. 4 C: 0.15% or less, Si: 0.1-2.0%, Mn: 7.0
~25.0%, Ni: 0.5~10.0%, Cr: 15.0~26.0%,
Contains Mo: 4.0% or less, N: 0.2 to 0.8%, and one or two selected from the following (a) and (b).
The steel containing seeds and the remainder being essentially Fe is processed by heating it to a temperature range of 1100°C to 1300°C, and finishing the processing at 800°C or above, and then processing it at 1050°C to 1050°C. Heating within the temperature range of 1250℃, first applying 10% or more processing at a temperature of 1000℃ or higher, then 10% processing within the temperature range of 600℃ to 1000℃
A method for producing high-strength nonmagnetic steel, characterized by subjecting it to a final processing of % or more, then cooling it to room temperature at a cooling rate equal to or higher than an air cooling rate, and further heat-treating within a temperature range of less than 700°C. (a) Cu: 0.1-2.0%. (b) One or more selected from Nb, Zr, V, Ta, Ti, and Al, 0.5% or less.