JPH0297647A - Steel for valve stem having excellent torsional strength and its manufacture - Google Patents

Abstract

PURPOSE:To improve the torsional strength, low temp./ toughness, high temp. strength, etc., of the title steel by subjecting a steel contg. specified C, Si, Mn, Ni, Cr, N and Nb to two-stage controlled rolling and forming its structure into the recrystallization treated double constitutional one. CONSTITUTION:A steel constituted of, by weight, <=0.03% C, <=20% Si, <=10% Mn, 6 to 20% Ni, 16 to 30% Cr, 0.1 to 0.3% N, 0.02 to 0.25% Nb and the balance Fe is melted. The steel is rolled at 1000 to 1200 deg.C rough rolling temp. at >=50% working ratio and is thereafter cooled for 16sec to 5min. The steel is then rolled at 800 to 1000 deg.C finish rolling temp. at >=30% working ratio and is thereafter cooled at >=4 deg.C/min cooling speed to form its structure into the recrystallization treated double constitutional one.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is applicable to various plans 1 to LP such as chemical, seawater, and nuclear power.
t; This invention relates to a valve stethoscope for butterfly valves used in tankers, materials for the same, and methods for manufacturing the same.

[Technology from 2007] A valve stem is a member that becomes a rotation axis of a butterfly valve when the butterfly valve is opened and closed. Since butterfly valves are used in various types of chemical blunts and L F' G tankers, the characteristics required of valve stems include torsional strength, low temperature toughness, high temperature strength, corrosion resistance, and weldability, especially torsional strength. is an important characteristic. Note that weldability is required because it is used with stellite mounding at high temperatures, and it is difficult to secure 7g contact unless it is Ni-based.

As the conventional valve stem material f1, when used only at room temperature, martinsite stainless steel substituted by 5US431 is used.

However, when using 5US431, the torsional strength is sufficient at 35 kgf/am', but the low temperature toughness (
-196℃) is equal to 0, high temperature strength (600℃103
It has a low corrosion resistance and weldability of 7 kgf/export 2, and its applications are limited.

Therefore, 5US304 is the material for the valve stem for low temperatures.
．． 5US304N! Austenitic stainless steels, typically represented by , are used. However, 5US304 and 5US304Nz have a torsional strength of 10 to 20 k
Since gf/a+s+2 is low, the diameter of the shaft must be increased, which poses problems in that the weight increases and the valve becomes larger.

Furthermore, high-Ni alloys such as Incoloy 800 are available as valve stem materials for high temperatures.

However, this Incoloy 800 has drawbacks in that it does not have sufficient torsional strength and is expensive.

[Problems to be solved by the invention] - Unlike ferritic stainless steel, austenitic stainless steel has low torsional strength in the proportional limit (elastic limit), but it has low torsional strength in terms of low temperature toughness, high temperature strength, corrosion resistance, and weldability. Therefore, austenitic stainless steel is most suitable.The present invention was made in view of the above-mentioned problems with materials for valve stems. The purpose is to provide materials and methods for their production.

[Means for Solving the Problems] The steel for valve stems of the present invention having excellent torsional strength contains as essential components C; 0, O 3% or less, and S
i: 2.0% or less, Mn: 10.0% or less, Ni: 6-
20%, Cr; 16-30%, N, 0.1-0.3%,
Contains Nr: 0.02 to 0.25%, the remainder consists of Fe and impurity elements, and its structure is a recrystallized double structure structure, and Mo is added as necessary to improve corrosion resistance. 4.0% or less, Cu; 4.0% or less, S, 0.002% or less, and further contains Se; 0.0% or less if necessary to improve machinability. 080% or less, Te; 0.080% or less, S
Contains one or more of o, o 80% or less, P, 0.100% or less, and further contains B i as necessary to improve machinability without deteriorating hot workability. 0.300% or less, Pb, 0.300% or less, B, 0.0100% or less, and further contains V, T as necessary to improve strength.
0.30% each of i, W, Ta, Hf, Zr, and Al
lf below! Contains i or more, and B as necessary to further improve hot workability; 0.0005 to 0.0100%
, Ca; 0.0005% to 0.0100%, Mg; 0.
0005~0.0100%, rare earth elements 0.0005~
The gist is to contain one or more of 0.0100%.

Further, the method for producing the steel for valve stems having excellent torsional strength according to the present invention has a cHo. 03% or less, Si
; 2.0% or less, Mn; 10.0% or less, Ni; 6-2
0%, Cr; 16-30%, N, 0.1-0.3%, N
r; Contains 0.02 to 0.25%, or M
o; 4.0% or less, Cu; 4.0% or less, S, 0.00
Contains one or more of 2% or less, the balance being Fe
and steel consisting of impurity elements, 1100 to 1300
℃, then rolled at a rough rolling temperature of 1000-1200℃ with a processing amount of 50% or more, cooled for 10 seconds to 5 minutes after rough rolling, and then processed at a finish rolling temperature of 800-1000℃! 13
The gist is that by performing rolling of 0% or more and cooling at a cooling rate of 4° C./min or more after rolling, the structure becomes a knee-heavy structure before recrystallization.

The present invention is based on the new finding that the recrystallized double structure improves the torsional strength of austenitic stainless steel while maintaining its low-temperature toughness, high-temperature strength, corrosion resistance, and weldability. The recrystallized double structure is obtained when an alloy having the composition of the present invention is processed by the manufacturing method of the present invention. Generally, the structure of austenitic stainless steel is 100% as observed with an optical microscope.
It is composed of a microstructure of approximately μ size and a substructure of approximately 1 layer, which is observed with an electron microscope. Austenitic stainless steel is usually used after being solution heat treated, and Figure 2 (A) shows a structure 200 times larger than the structure after solution heat treatment, and Figure 2 shows a structure 20,000 times larger than the structure after solution heat treatment. As shown in (b),
The conventionally known controlled rolling structure is shown in Figure 3 (A), where the microstructure in (A) is a processed structure of mixed grains, and the substructure in (A) is also a processed structure. It is.

FIG. 1 is a diagram showing the relationship between temperature and time for obtaining the recrystallized I2-fold N4 structure of the present invention. First, Nb precipitates are completely dissolved at a heating temperature of 1,100 to 1,300°C. Then, 150% processing is performed at 1,000 to 1,200°C.
The above rough rolling is performed, and the cooling time after rough rolling is 10 seconds to 5 seconds.
The material is quickly cooled to a predetermined temperature from the final roll of rough rolling to the start of finish rolling, and recrystallized to obtain a fine recrystallized structure. Finish rolling is performed at 800-1000℃ with a processing amount of 30% or more, and the cooling rate after finish rolling is 4"C/w
In or more.

Photographs of m-microstructures manufactured by the manufacturing methods of the present invention and comparative examples are shown in FIGS. 4 to 8.

Finish rolling start temperature is 1050℃, 980℃, 900℃1
(A) in each photo is 200 at 850℃ and 700℃
Multiply (b) is 20,000 times 0 Recrystallization processing according to the present invention 2
As is clear from the photographs in FIGS. 5 to 7, the heavy JR4 microstructure consists of a recrystallized structure of several tens of microns, which in turn consists of a sub-recrystallized structure of several microns.

The subgrains of this substructure are a processed structure having a high density of dislocations.

Here, if the finish rolling start temperature is made higher than 1000°C,
As shown in FIG. 4, almost no dislocations are observed in the sub-crystal grains, and the torsional strength amplifier is almost eliminated. On the other hand, 800℃
If it is lower, as is clear from FIG. 8, no sub-recrystallized structure is formed, and no improvement in torsional strength can be obtained.

The present invention is based on the knowledge that in order to obtain excellent properties through the above-mentioned controlled rolling in austenitic stainless steel, it is important to lower the amount of C and add N and Nb. According to the composition of the present invention, the recrystallization temperature is significantly raised to facilitate controlled rolling, and it becomes easier to obtain a fine crystal structure after 1 inch of rolling. Also, during finish rolling (
Cr, Nb)N is strain-induced to precipitate on dislocations or lower recrystallization grain boundaries in an ultrafine manner, and as well as dispersion strengthening, solid solution Nr;N and <Cr, Nb)N suppress dislocation recovery. By increasing the dislocation density in the crystal structure, a significant increase in strength is achieved. C promotes Nb(C,N) precipitation, impairs hot workability, and at the same time detracts from the precipitation strengthening ability of (Cr, Nh)H. Furthermore, it also promotes the precipitation of Cr2°C, which lowers the corrosion resistance, so it is most important to lower the C content.

The effects of the microalloy elements of C, N and Nb contained in the steel of the present invention will be described in more detail below.

First, regarding strength, in a solution heat treated structure, N contributes to solid solution strengthening. In addition, Nb (C, N) precipitates and makes the crystal grains V& finer, thereby contributing to improving the strength. In the steel of the present invention composition having the recrystallized double structure fibers of the present invention, the effect of N and Nb is approximately twice as large as the normally known effect of N and Nb in a solution heat treated structure. According to research conducted by the present inventors, this two-difficult effect is caused by ultrafine strain-induced precipitation of (CrNb)N and the dislocation structure and subgrain boundaries introduced during finish rolling.
It has been clarified that this is to fix them, delay recovery of dislocations, and increase dislocation density.

Next, regarding the corrosion resistance, the corrosion resistance of the control-rolled steel of the present invention containing 0.03% or less of C and 31 Jt of N and Nb is as follows: Cr2. The 18Cr-
It was found that the corrosion resistance of 8Ni steel was higher than that of Ni steel.
Grain boundary C: The reason why r 23 Cs is not formed is that in stainless steel with low C and high N content, Cr2j (C,N)6 precipitates in place of CrBCs, but the precipitation rate of this precipitate is extremely slow. This is also because due to Nb, C, which is small in the first place, becomes NbC, and there is almost no solid i8C.

As mentioned above, microalloy elements with low C, N, and Nb are essential for improving the strength and corrosion resistance of controlled rolled materials, and only by combining these elements with controlled rolling can excellent torsional strength be achieved. It was discovered that austenitic stainless steel could be obtained, and this was used as a material for valve stems.

The reasons for limiting the composition of the steel of the present invention will be explained below.

C; O, o 3% or less C is an important element in the present invention, as it significantly impairs corrosion resistance after controlled rolling and hot workability during controlled rolling, and must be at least 0.03% or less. Also, the more C there is, the more Nb(C,N) grows, and (Cr,Nb)N
The upper limit was set at 0.03% because it interferes with the fine precipitation of carbon and causes a decrease in strength.

Si: 2.0% or less Si is an element that is added as a deoxidizing agent and also improves strength, but on the other hand, it is also an element that reduces hot cracking during welding and the amount of N solid solution during solidification. To obtain a good steel ingot 2.
It is necessary to keep the amount below 0%, and the upper limit is set at 2.0%.

Mn: 10.0% or less Mn is an element that is added as a deoxidizing agent and increases the solubility of N, but on the other hand, as the content increases, corrosion resistance and hot workability are impaired, so the upper limit is set at 10.0%. did.

Ni; 6-20% Ni is a basic element of austenitic stainless steel, and must be contained in an amount of 6% or more in order to obtain excellent corrosion resistance, low-temperature toughness, and an austenitic structure. However, N
If the amount of i increases too much, weld cracking properties during welding, hot workability, etc. will be reduced, so the upper limit was set at 20%.

Cr: 16-30% Cr is a basic element of stainless steel, and in order to obtain excellent corrosion resistance, it must be contained at least 16% or more. However, if the Cr content increases too much, the balance of the δ/γ structure at high temperatures will be impaired, so the upper limit was set at 30%.

N, 0.10-0.30% N has interstitial solid solution strengthening, grain refinement due to (CrNb)N precipitation, and improved torsional strength and high-temperature strength due to precipitation strengthening. is the most important strengthening element and is also an element that contributes to improving corrosion resistance after controlled rolling, and to obtain these effects, 0.
It is necessary to contain 10% or more, and the lower limit is set to 0.10%. However, as the N content increases, hot workability decreases and blowholes are more likely to occur during solidification and welding, so the upper limit was set at 0.30%.

Nr: 0.02-0.25% Nb fixes residual C as NbC, improves corrosion resistance after controlled rolling, and improves torsional strength and high-temperature strength due to grain refinement due to (CrNb)N precipitation. In the present invention, which improves the strength and strength after controlled rolling, it is a major element and must be contained in an amount of at least 0.02%. However, Nb is also an expensive element, and if it is included more than necessary, it impairs hot workability, so the upper limit was set at 0.25%.

Mo: 4.0% or less, Cu: 4.0% or less MO--Cu are all elements that further improve the corrosion resistance of the steel of the present invention. However, Mo and Cu are also expensive elements, and
If the content exceeds 4%, hot workability will be impaired, so the upper limit was set at 4%.

S, 0.002% or less S is an element that improves corrosion resistance by significantly reducing its content, and also improves ductility and low-temperature toughness after controlled rolling, and the lower its content is, the more desirable it is. , at least 0.002% or less, preferably 0.0
It is preferable to make it 0.01% or less.

5eH0,080% or less, s;0, Os o% or lessS, Se are elements that improve the stiffness of the steel of the present invention;
must exceed 0.020%, and Se must be contained at 0.005% or more. However, both S and Se are o and oso.
If the content exceeds 0.0%, the hot workability and corrosion resistance will decrease, so the upper limit should be set to o, os.

%.

Te: 0.080% or less Te is an element necessary to spheroidize MnS inclusions, improve toughness in the direction perpendicular to the rolling direction, and prevent a decrease in anisotropy, and it should be contained at least 0.0050% or more. It is desirable that this is done. If more than 0% is added, hot workability will be inhibited, so the upper limit was set at 0.080%.

P, 0.100% or less P is an element added to improve machinability, and is preferably contained at least 0.04% or more.

But 0.100? If the content exceeds 10%, hot workability will be impaired, so the upper limit should be set at 0.100%.

Bi: 0.300%, Pb: 0.300% or less Bi and Pb are elements necessary to improve machinability, and it is desirable to contain at least 0.3% or more. If it exceeds .300%, hot workability will be inhibited, so the upper limit was set at .0300%.

B, O, 0100% or less B is added to prevent hot workability from deteriorating when B1 and Pb are added, but in order to obtain the above effect, at least 0.00050% or more is added. It is desirable that it be added. However, even if it is added in excess of 100%, no improvement in the effect is expected.
It was set as too%.

V, Ti, W, Ta, lit, Zr, Al; 0.30%
Below, V, Ti, W, Ta, Hf, Zr, A, and l are elements added to improve torsional strength and high-temperature strength, but even if the content exceeds 0.630%, the effect will not be improved. Since this is not possible, the upper limit was set at 0.3096.

B, 0.0005 No. 0100%, Ca; 0.00
05-0.0100%, Mg: 0.0005-0.01
00%, rare earth elements; 0.0005 to 0.0100% B, Ca, M8, and rare earth elements are elements necessary to improve hot workability, and in order to improve hot workability, at least It is necessary to add 0.0005% or more. However, if more than 0.0100% is added, no improvement in the effect can be expected, so the upper limit is set at 0.0100! ! It turned into stone.

In addition, in controlled rolling, the heating temperature is set to 1100 to 130.
The temperature was set at 0°C in order to reduce the deformation resistance during rolling and to sufficiently dissolve Nb precipitates in the steel! ). This is because the deformation resistance is large below 1100°C and it is difficult to form a complete solid solution with Nb precipitates.
This is because, if heated above 300° C., part of the grain boundaries will become L8 fused or the crystal grains will become coarse, making rolling difficult.

The reason why the rough rolling temperature was set to 1000 to 1200°C is to obtain a fine recrystallized structure, and it is not possible to obtain a fine recrystallized structure below 1000°C.
This is because the crystal grains become coarser due to recrystallization.

The reason why the amount of processing is set to 50% or more in rough rolling is that when the amount of processing is less than 50%, the energy of lattice defects is small, la, t.
This is because lllt41m cannot be obtained.

The reason why the finish rolling temperature was set to 800 to 1000°C is to obtain a recrystallized double structure structure. This is because if it is below 800°C, it becomes a processed structure and it is not possible to obtain a recrystallized double structure structure, and if it exceeds 1000°C, it becomes a recrystallized structure due to recrystallization.
and the upper limit.

In finish rolling, the processing amount was 30% or more.
% or less, the processing strain is small and a recrystallized double structure cannot be obtained.

The reason why cooling is performed for 10 seconds to 5 minutes after rough rolling is because it is the time required to cause recrystallization after rough rolling. In addition, the reason why the cooling rate after rolling was set at 4°C/min or more was because slow cooling at 4°C/min or less was Cr23C or Cr23C.
This is because 2N precipitates at grain boundaries and reduces corrosion resistance.

[Example] Next, the characteristics of the steel of the present invention and its manufacturing method will be clarified by comparing it with conventional steel and comparative steel through examples.

Table 1 shows the chemical composition (weight j!l %) of these test steels.The test steels in Table 1 were subjected to controlled rolling by the method of the present invention and controlled rolling by other methods for comparison.
The structure, torsional strength, pitting potential, machinability, hot workability, low temperature toughness, and high temperature strength were measured, and the results are shown in Table 2.

Regarding the structure, the optical E microstructure was subjected to 10% oxidized acid electrolytic etching and then observed using an optical microscope. Further, the electron microscopic structure was observed using a transmission electron microscope after forming the thin film.

Regarding torsional strength, twisting speed is 10”/wi at room temperature.
A torsion test was conducted to the proportional limit under the condition of n, and the strength at that time was measured.

Regarding hot workability, 110
A high-speed high-temperature tensile test was conducted at 0° C. and a tensile rate of 501/sec, and the aperture value was measured.

Corrosion resistance was measured by measuring pitting potential in a 3.5% NaCl aqueous solution at 30°C.

Regarding machinability, a 20-wheel test piece was used, and a 5KH9 5+
A drill life test was conducted using a mmφ drill at a rotational speed of 725 rps, a feed rate of 0, and 16 aml rev, and the results are shown.

Regarding low-temperature toughness, the Charpy impact value at -196°C (77K) was measured using a 5mm thick JIS No. 3 U-notch (2m-) test piece.

Regarding high temperature strength, the breaking stress at 103 hours in a creep-Labuture test at 600°C was measured.

(Margin below) As is known from Tables 1 and 2, no.

Nos. 1 to 3 and Nos. 11 to 12 are steels with the composition of the first invention steel, which were subjected to controlled rolling according to the method of the present invention, but the torsional strength, low temperature toughness, high temperature strength, pitting potential, machinability, hot workability were Satisfactory results were obtained for each gender. On the other hand, No. 4 to No. 10 are steels having the composition of the first invention steel that have been processed using methods other than the method of the present invention, and No. 4, which has a high finish rolling temperature of 1050°C, only obtains a recrystallized structure. low torsional strength, low finish rolling temperature 70
No. 5, which has a temperature of 0° C., provides only a processed structure and has extremely large anisotropy. No. 6, which is subjected to solution heat treatment after rolling, is inferior in torsional strength. No. 7 was subjected to one-step controlled rolling at 900°C, and has a processed structure with extremely high anisotropy. No. 8 was subjected to one-step controlled rolling at 700°C, and has a processed structure with extremely large anisotropy. No. 9, which has extremely high orientation, has a cooling rate of 3° C./min after finish rolling, and is inferior in pitting corrosion potential. No. 10 has a low processing rate of 10% in finish rolling, but sufficient torsional strength is not obtained.

Nos. 13 to 16 are comparative examples having components outside the composition range of the steel of the present invention, and were subjected to controlled rolling according to the method of the present invention. ,
No. 14 has less Cr than the composition range, but its pitting potential is inferior. No. 15 contains N within the composition range, but is inferior in torsion strength and pitting corrosion potential. No. 16 is Nb
However, the torsional strength and pitting potential are inferior.

Nos. 17 to 21 are steels with the composition of the second invention steel of the present invention that were subjected to controlled rolling according to the method of the present invention, and a recrystallized double structure structure was obtained, and the torsional strength, pitting corrosion potential, and low-temperature toughness were improved. Excellent results were obtained in both high-temperature strength and high-temperature strength. In particular, it was confirmed that the material was excellent in terms of pitting potential and corrosion resistance. N
No. 22 to 23 are steels with the composition of the second invention that have been subjected to a treatment other than the method of the present invention. No. 22 is inferior in pitting potential, low-temperature toughness, and high-temperature strength, and No. 23 is 95.
One-step controlled rolling was performed at 0°C, and although the torsional strength was excellent, it was confirmed that the anisotropy was extremely large.

No. 24 to 28 contain Se, Te, and Te to improve machinability.
The third invention steel added S and P, but by controlled rolling according to the method of the invention, it became a recrystallized double-structure structure and obtained excellent results in terms of torsional strength, pitting potential, low temperature toughness, and high temperature strength. . Furthermore, as a result of measuring the machinability, it was confirmed that excellent results were obtained.

No. 29 to 31 contain Bi, Pb, and
The fourth invention steel added B had a recrystallized double-structure structure by controlled rolling according to the method of the invention, and excellent results were obtained in both torsional strength, pitting potential, low-temperature toughness, and high-temperature strength. Furthermore, as a result of measuring machinability and hot workability, it was confirmed that machinability was improved without reducing hot workability.

No. 32 to 40 contain V, Ti, W,
This is the fifth invention steel to which Ts, Hr, Zr, and A1 are added, but by controlled rolling according to the method of the present invention, it becomes a re-solidified, highly processed double structure structure, and the torsional strength, pitting potential, low temperature toughness, and high temperature strength are improved. Excellent results were obtained.

No. 41 to 45 contain B and Ca to improve hot workability.
, Mg, and rare earth elements are added to the sixth invention steel, but by controlled rolling according to the method of the present invention, it becomes a recrystallized double-structured structure, resulting in excellent results in terms of torsional strength, pitting potential, low-temperature toughness, and high-temperature strength. Obtained. Furthermore, as a result of measuring hot workability, it was confirmed that the product had excellent hot workability.

Nos. 46 to 48 are the seventh invention steels to which all the above-mentioned elements are added to improve strength, corrosion resistance, rigidity, and hot workability. Torsional strength, pitting potential, low temperature toughness,
Excellent results were obtained in both high-temperature strength and strength. It was also confirmed that excellent results were obtained in terms of stiffness and hot workability.

[Effects of the Invention] As explained above, the valve stem steel of the present invention and its manufacturing method reduce the C content of austenitic stainless steel, add appropriate amounts of N and Nb, and improve the structure by two-step controlled rolling. The recrystallized double structure structure is
We have discovered that the torsional strength of austenitic stainless steel can be significantly improved, and we have successfully developed a new use for this as a valve stem steel.

The steel for pulp stems of the present invention satisfies all the required properties of torsional strength, low temperature toughness, high temperature strength, corrosion resistance and weldability, and is suitable for bell stems of butterfly valves used in various plants such as chemical, seawater, and nuclear power plants. It is extremely useful as a material.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between temperature and time in the controlled rolling process according to the method of the present invention, and Figures 2 (a) and (b) are reproductions of micrographs showing the recrystallized structure after solution heat treatment. , Figures 3 (a) and (b) do not show the worked structure after final rolling at 900°C. A copy of the micrograph showing the crystal structure, Figure 5 (A) is at the finish rolling start temperature 9
A copy of a microscopic photograph showing the double structure structure after recrystallization at 80°C, Figure 6)
A replica of a micrograph showing the double structure structure of the recrystallized process,
Figures 7 (a) and (b) are reproductions of micrographs showing the double structure structure after recrystallization at a finish rolling start temperature of 850°C, and Figures 8 (a) and (b) are reproductions of micrographs showing a recrystallized double structure structure at a finish rolling start temperature of 700°C. It is a replica of a micrograph showing a processed structure.

Claims (9)

[Claims] (1) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
A steel for valve stems containing 02 to 0.25%, the balance consisting of Fe and impurity elements, and having an excellent torsional strength consisting of a recrystallized double structure structure. (2) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
02 to 0.25%, and further contains 1 of Mo: 4.0% or less, Cu: 4.0% or less, and S: 0.002% or less.
A steel for valve stems having excellent torsional strength, containing one or more seeds, the remainder being Fe and impurity elements, and having a recrystallized double structure structure. (3) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
02 to 0.25%, and further Se; 0.080%
Contains one or more of Te: 0.080% or less, S: 0.080% or less, P: 0.100% or less, and the remainder consists of Fe and impurity elements, and the structure is regenerated. Steel for valve stems with excellent torsional strength consisting of a crystal-processed double-structure structure. (4) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
02 to 0.25%, and further Bi; 0.300%
Contains one or two of the following, Pb: 0.300% or less, and B: 0.0100% or less, with the balance consisting of Fe and impurity elements, and whose structure is a recrystallized double structure structure. Steel for valve stems with excellent torsional strength. (5) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
02 to 0.25%, and further contains V, Ti, W, Ta
, Hf, Zr, and Al in an amount of 0.30% or less each, and the balance is Fe and impurity elements, and the structure is a recrystallized double structure structure, and has excellent torsional strength. . (6) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
Contains 02-0.25%, B; 0.0005-0.0
100%, Ca; 0.0005% to 0.0100%, M
g; 0.0005-0.0100%, rare earth element 0.0
A steel for valve stems having excellent torsional strength, containing one or more of 0.005 to 0.0100%, the remainder consisting of Fe and impurity elements, and having a recrystallized double structure structure. (7) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
02 to 0.25%, and further contains 1 of Mo: 4.0% or less, Cu: 4.0% or less, and S: 0.002% or less.
A species or two or more species, Se; 0.080% or less, Te;
0.080% or less, S; 0.080% or less, P; 0.1
00% or less and one or more of them and Bi: 0.3
00% or less, Pb; one or two of 0.300% or less and B; 0.0100% or less, V, Ti, W,
0.30% or less of each of Ta, Hf, Zr, and Al is 1
More than species, B; 0.0005 to 0.0100%, Ca;
0.0005% to 0.0100%, Mg; 0.0005
~0.0100%, rare earth elements 0.0005~0.01
A steel for valve stems having excellent torsional strength, containing one or more of 0.00%, the remainder consisting of Fe and impurity elements, and having a recrystallized double structure structure. (8) C: 0.03% or less, Si: 2.0 in terms of weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nb: 0.
A steel containing 02 to 0.25% and the balance consisting of Fe and impurity elements is heated to 1100 to 1300°C and rolled with a working amount of 50% or more at a rough rolling temperature of 1000 to 1200°C. After cooling for 5 seconds to 5 minutes, rolling is performed at a finish rolling temperature of 800 to 1000°C with a processing amount of 30% or more, and the cooling rate after rolling is 4°C/min or more, so that the structure is recrystallized double structure. A method for manufacturing valve stem steel with excellent torsional strength. (9) C: 0.03% or less, Si: 2.0 in weight ratio
% or less, Mn; 10.0% or less, Ni; 6 to 20%, C
r: 16-30%, N: 0.1-0.3%, Nr: 0.
02 to 0.25%, and further contains 1 of Mo: 4.0% or less, Cu: 4.0% or less, and S: 0.002% or less.
A steel containing one or more seeds and the remainder consisting of Fe and impurity elements is heated to 1100 to 1300°C, and rolled at a rough rolling temperature of 1000 to 1200°C with a working amount of 50% or more, and for 10 seconds after rough rolling. After cooling for ~5 minutes, rolling is performed at a finish rolling temperature of 800 to 1000°C with a processing amount of 30% or more, and the cooling rate after rolling is 4°C/min or more, so that the structure becomes a recrystallized double structure structure. A method for producing valve stem steel with excellent torsional strength.