JP3775371B2 - Low alloy steel - Google Patents

Description

【００５０】
【表２】

【００５１】
【表３】

【００５２】
【表４】

【００５３】
得られた鋼塊は、熱間鍛造を行って厚さ50mm、幅150 mmの板状とした。また、得られた板材には、950 ℃に１時間加熱保持してから空冷した後、鋼の硬さがビッカース硬さHvで180〜200程度となるように、720〜760℃に１時間加熱保持した後に空冷する焼戻し処理を施した。
【００５４】
熱処理後の板材は、組織を調べる一方、板材から、直径10mm、標点距離(GL)50mmのクリープ試験片およびJIS Z 2202に規定されるＶノッチ試験片を採取し、それぞれ下記条件のクリープ試験とシャルピー衝撃試験に供した。
【００５５】
1.クリープ試験
クリープ試験は、試験温度550℃、負荷応力200MPaで行い、破断時間(ｈ)を調べ、5000時間以上のものを良好と評価した。
【００５６】
2.シャルピー衝撃試験
シャルピー衝撃試験は、試験温度−60〜60℃で行って破面遷移温度vTrs(℃)を調べ、vTrsが−40℃以下のものを靭性が優良「◎」、−40℃を超え−20℃以下のものを良好「○」、−20℃を超え−０℃以下のものをやや不良「△」、−０℃を超えるものを不良「×」と評価した。
【００５７】
以上の結果を、焼戻し温度、表面硬さおよび調査した組織と合わせて表５に示した。
【００５８】
【表５】

表５からわかるように、鋼No. １〜20の本発明の鋼は、温度550 ℃、負荷応力200MPaでのクリープ破断時間がいずれも10000 時間を超えており、鋼No. 21〜24の従来鋼の約10倍強と極めて長い。また、伸びが25％以上、絞りが51％以上で、長時間のクリープ延性も良好であり、vTrsがいずれも−20℃以下で靱性も良好である。
【００５９】
これに対し、鋼No. 25〜38の比較鋼は、成分のいずれかが本発明で規定する範囲を外れているか、成分範囲に加えて、(1) 式で表されるBeff値が0.0001〜0.0060を外れているため、破断時間、伸びおよび絞りのうちのいずれか不良であり、靱性も悪い。また、鋼No. 39と40の比較鋼は、いずれの成分の含有量も本発明で規定する範囲内ではあるが、(1) 式で表されるBeff値が0.0001〜0.0060を外れているため、破断時間、伸びおよび絞りのうちのいずれか不良であり、靱性も悪い。
【００６０】
【発明の効果】
本発明の低合金鋼は、クリープ強度およびクリープ延性ともに優れており、しかも靭性も良好である。従って、発電プラントなどで、550℃程度までの温度域において使用される耐熱構造部材用の材料として極めて有効である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low alloy steel excellent in high temperature creep strength, creep ductility and toughness suitable for use as heat resistant structural members such as power generation boilers, turbines, nuclear power generation facilities, and chemical industrial equipment.
[0002]
[Prior art]
Power generation boilers, turbines, nuclear power generation equipment, chemical industrial equipment, and the like are used for a long time under high temperature and high pressure. Therefore, the heat-resistant materials used in these devices are required to have good strength at high temperatures, corrosion resistance, oxidation resistance, and toughness at room temperature. Conventionally, these applications include austenitic stainless steel (eg JIS SUS321H and SUS347H steel), low alloy steel (eg JIS STBA24 (2 / 4Cr-1Mo steel)), 9-12Cr high Cr ferrite. Steels such as JIS STBA26 (9Cr-1Mo steel) and STBA28 (modified 9Cr-1Mo steel) have been used.
[0003]
In recent years, thermal power plants need to improve thermal efficiency to reduce CO ₂ emissions from the viewpoint of preventing global warming, and boiler steam conditions have been increased to high temperatures and pressures (eg, over 600 ° C, 300 atm). New plants are being built one after another. On the other hand, whether a number of existing plants built during the high growth period will reach their planned lives and be replaced with new plants or extend their lives by partial repairs, etc. It is becoming a big social problem.
[0004]
On the other hand, in response to requests for deregulation from inside and outside Japan, the liberalization of the electric power business has progressed, allowing companies and trading companies other than electric power companies to enter, and as a result of intensifying price competition, As a result, economics are becoming more important.
[0005]
Under such a social background, as one method of reducing the cost of power plants, it is aimed to increase the strength of heat-resistant structural members used in the plant to reduce the amount of steel used and to reduce costs. The development of high-strength materials that can meet such requirements is underway.
[0006]
In particular, in the relatively low temperature range up to about 550 ℃, conventional Cr-Mo series such as JIS STBA22 (1Cr-0.5Mo), STBA23 (1.25Cr-0.5Mo), or STBA24 (2.25Cr-1Mo) Although alloy steel was used, steel with some Mo replaced with W (for example, steel disclosed in Patent Document 1) for the purpose of further increasing high-temperature strength, and hardenability is dramatically increased by adding Co. Steel (for example, steel disclosed in Patent Document 2) has been developed.
[0007]
In these new steels, softening resistance at high temperatures has been improved by W and Co. Especially, the creep strength at 500 ° C or higher is higher than that of conventional general-purpose steel. In particular, it is clear that the deterioration of toughness and the decrease in long-term creep ductility (elongation and squeezing) become remarkable.
[0008]
In order to prevent such deterioration of toughness and improve reheat cracking resistance, steels with a very small amount of Ti added to Cr-Mo steel or a N amount limited to a very small amount have been proposed (patents). References 3, 4 and 5). Although these steels certainly have improved toughness, they are not steels that achieve both creep strength and creep ductility.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 8-134584 [Patent Document 2]
JP-A-9-268343 [Patent Document 3]
Japanese Patent Laid-Open No. 8-144010 [Patent Document 4]
JP 2001-164332 A [Patent Document 5]
JP 2001-234276 A [0010]
[Problems to be solved by the invention]
The present invention is a low alloy steel for heat-resistant structural members used in a temperature range up to about 550 ° C. in a power plant etc., and has higher high-temperature strength and toughness than conventional steel, and excellent long-term creep ductility. Another object is to provide a low alloy steel.
[0011]
[Means for Solving the Problems]
In order to achieve the above-mentioned problems, the inventors have studied the long-term creep deformation characteristics (strength and ductility) and toughness of various heat-resistant low-alloy steels by the chemical composition and microstructure of the steel (microstructure). The impact was examined in detail. As a result, the following new findings were obtained.
[0012]
(a) When V, Nb, and Ti are added to Cr-Mo steel, MC carbides (M is mainly composed of V, Nb, Ti, and partly dissolves Mo) are finely dispersed and precipitated, and Mo is added alone. As compared with, a remarkable precipitation strengthening action is obtained, and the high temperature creep strength is improved. However, the creep embrittlement sensitivity is greatly increased and the creep ductility is lowered.
[0013]
(b) Decrease in creep ductility due to V, Nb, and Ti can be prevented by adding a small amount of rare earth element Nd to improve creep embrittlement susceptibility. In particular, the Nd content of B, Ti, and N The effect is remarkable when the Beff value expressed by the following formula (1) is within the range of 0.0001 to 0.0060 in relation to the content, and the creep ductility is greatly improved.
[0014]
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel.
[0015]
(c) Addition of B to Cr-Mo steel improves hardenability and is effective in improving strength and toughness. However, excessive B reduces the toughness, so its content is 0.0060%. It is necessary to restrict to the following.
[0016]
(d) In Cr-Mo steel, when a part of Mo is replaced by W, carbides (for example, (1) M ₃ C, (2) M ₇ C ₃ and (3) M ₂₃ C ₆ where M is Fe and Cr are mainly dissolved in Mo, W, etc., but changes from (1) → (2) → (3) with increasing Cr amount) for a longer time and creep strength is improved. improves. However, since toughness and creep ductility are lowered, addition of W should be avoided, but when adding with emphasis on strength, there is no particular problem if it is up to 0.20%.
[0017]
(e) Addition of Co to Cr-Mo steel improves hardenability and improves creep strength. However, the addition of Co increases the creep embrittlement susceptibility and decreases the creep ductility as in the case of W described above. Therefore, it is better not to add Co, but when adding with emphasis on strength, 0.50% or less is acceptable.
[0018]
The low alloy steel of the present invention completed based on the above knowledge is the following steels (1) and (2).
[0019]
(1) By mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, sol.Al: 0.010 % Or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, the balance being Fe and impurities, and the content of Ti, B, N and Nd represented by the following formula (1) A low alloy steel characterized by having a value in the range of 0.0001 to 0.0060.
[0020]
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel.
[0021]
(2) In addition to the component described in (1) above, it further includes at least one component selected from at least one of the following first to third groups, with the balance being Fe and impurities A low alloy steel characterized in that the contents of Ti, B, N and Nd satisfy the above formula (1).
[0022]
First group: 0.01% to 0.20% W by mass%.
Second group: 0.01% to 0.20% Cu and 0.01% to 0.50% Co by mass%.
Third group: by mass, 0.0001-0.0050% Mg, 0.0001-0.0050% Ca, 0.0001-0.020% La, 0.0001-0.020% Ce, 0.0001-0.040% Y, 0.0001-0.040% Sm and 0.0001-0.040% Pr.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason for determining the chemical composition of the low alloy steel of the present invention as described above will be described in detail. In the following, “%” represents “% by mass” unless otherwise specified.
[0024]
C: 0.03-0.10%
C is an austenite stabilizing element, which stabilizes the bainite structure or martensite structure, which is the basic matrix structure of Cr-Mo steel, and forms various carbides to contribute to high strength. For this purpose, a content of at least 0.03% is necessary. On the other hand, if it exceeds 0.10%, the steel is markedly hardened, and the weldability and workability are drastically reduced. For this reason, C content was made into 0.03-0.10%. Preferable is 0.04 to 0.08%, and more preferable is 0.05 to 0.07%.
[0025]
Si: 0.10% or less
Conventionally, Si has been commonly added to low alloy steels for heat-resistant structural members as an important element for ensuring oxidation resistance. It has also been considered essential as a deoxidizer in the steelmaking stage. However, according to the research results of the present inventors, when the content is suppressed to 0.10% or less, not only creep embrittlement but also reheat embrittlement and cracking susceptibility can be effectively suppressed, and the oxidation resistance is improved. It became clear that there was no adverse effect. For this reason, content of Si shall be 0.10% or less. A preferable upper limit is 0.08%, and a more preferable upper limit is 0.05%.
[0026]
Mn: 0.001 to 0.30%
Mn, like C, is an austenite stabilizing element and is important for stabilizing the bainite or martensite matrix structure, and a content of at least 0.001% is required. On the other hand, excessive Mn not only lowers the _AC1 transformation point of the steel, but also adversely affects creep ductility, so it was made 0.30% or less. Preferable is 0.001 to 0.25%, and more preferable is 0.001 to 0.20%.
[0027]
P: 0.020% or less P is an impurity element, and excessive P adversely affects toughness and the like. However, in the steel of the present invention, if it is 0.020%, there is no particular problem, so the allowable upper limit is set to 0.020%. The smaller the P content, the better.
[0028]
S: 0.0080% or less S is an impurity element like P described above, and excessive S adversely affects toughness and the like. However, with the steel of the present invention, if it is up to 0.0080%, there is no particular problem, so the allowable upper limit was made 0.0080%. The smaller the S content, the better.
[0029]
Cr: 0.40 to 1.50%
Cr is an element indispensable for stabilizing a low C bainite or martensite matrix structure by precipitating stable carbides at a high temperature, and a content of at least 0.40% is required. On the other hand, if it exceeds 1.50%, precipitation of M ₇ C ₃ type carbides becomes remarkable, and the creep strength decreases. Therefore, the Cr content is set to 0.40 to 1.50%. A preferred range is 0.80 to 1.30%, and a more preferred range is 1.00 to 1.30%.
[0030]
Mo: 0.25 to 1.00%
Mo is a solid solution strengthening element and contributes to the stabilization of M ₃ C, M ₇ C ₃ and M ₂₃ C ₆ type carbides, and further to the stabilization of Mo ₂ C and MC type carbides. It contributes to the improvement. For that purpose, a content of 0.25% or more is necessary, but excessive Mo destabilizes the bainite or martensite matrix structure, so the upper limit was made 1.00%. Preferable is 0.30 to 0.80%, and more preferable is 0.30 to 0.70%.
[0031]
V: 0.03-0.15%
V forms MC-type carbide together with Nb described below and contributes to high strength, but for that purpose, a content of 0.03% or more is necessary. On the other hand, if it exceeds 0.15%, the creep ductility is lowered for a long time, so the upper limit was made 0.15%. A preferable range is 0.04 to 0.12%, and a more preferable range is 0.05 to 0.10%.
[0032]
Nb: 0.001 to 0.070%
Nb contributes to high strength by forming fine carbides as in the case of V described above, but for that purpose a content of 0.001% or more is required. On the other hand, if it exceeds 0.070%, excessive carbonitride is formed and the toughness is impaired. Therefore, the Nb content is set to 0.001 to 0.070%. Preferable is 0.020 to 0.050%, and more preferable is 0.025 to 0.040%.
[0033]
Ni: 0.001 to 0.30%
Ni is an austenite stabilizing element similar to C and Mn described above, and is important for stabilizing the bainite or martensite matrix structure. A content of at least 0.001% is necessary, but excess Ni is a steel. _{Lowering the} AC1 transformation point. Therefore, the Ni content is set to 0.001 to 0.30%. A preferable range is 0.001 to 0.20%, and a more preferable range is 0.001 to 0.18%.
[0034]
Ti: 0.001 to 0.020%
Ti forms fine carbides and contributes to high strength, but for that purpose a content of 0.001% or more is required. In particular, when the content is 0.005% or more, the effect of improving creep ductility and suppressing embrittlement and cracking during reheating is great. On the other hand, if it exceeds 0.020%, the toughness is adversely affected. For this reason, Ti content shall be 0.001 to 0.020%. A preferred range is 0.005 to 0.020%, and a more preferred range is 0.008 to 0.018%. However, the Ti content must be such that the Beff value represented by the formula (1) described later falls within the range of 0.0001 to 0.0060.
[0035]
B: 0.0001-0.0060%
B is an element effective for improving hardenability, and a content of 0.0001% or more is necessary to obtain this effect. On the other hand, excess B adversely affects toughness. For this reason, B content was made into 0.0001 to 0.0060%. A preferable range is 0.0010 to 0.0050%, and a more preferable range is 0.0010 to 0.0040%. However, the B content must also be an amount such that the Beff value represented by the formula (1) described later falls within the range of 0.0001 to 0.0060.
[0036]
Nd: 0.0001 to 0.030%
Nd is one of the most important elements indispensable for improving long-term creep ductility for the steel of the present invention, and a content of at least 0.0001% is necessary. However, excess Nd forms coarse inclusions that are undesirable for toughness, which in turn reduces toughness. Therefore, the Nd content is set to 0.0001 to 0.030%. However, the content of Nd must be such that the Beff value represented by the formula (1) described later falls within the range of 0.0001 to 0.0060, similarly to the above Ti and B.
[0037]
sol.Al: 0.010% or less
Al is an important element as a deoxidizer, but in order to achieve both strength and toughness, it is necessary to suppress it to 0.010% or less with sol.Al. A preferable upper limit is 0.008%, and a more preferable upper limit is 0.005%.
[0038]
N: Less than 0.0060% N is a solid solution strengthening element and may form carbonitride to contribute to high strength. However, in the present invention, in order to improve both creep strength and toughness and improve creep ductility. Since it is a harmful impurity element, the content was made less than 0.0060%. Preferable is 0.0030% or less. However, the content of N must be an amount such that the Beff value represented by the formula (1) described later falls within the range of 0.0001 to 0.0060.
[0039]
O (oxygen): 0.0050% or less O is an impurity element, and excessive O adversely affects toughness and the like. However, in the steel of the present invention, if it is 0.0050%, there is no particular problem, so it was made 0.0050% or less. The smaller the O content, the better.
[0040]
B, N, Ti and Nd content relationships:
The content of these elements needs to be an amount within which the Beff value expressed by the following formula (1) falls within the range of 0.0001 to 0.0060.
[0041]
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
That is, when the Beff value is less than 0.0001, the effect of improving the creep strength cannot be obtained. Conversely, when the Beff value exceeds 0.0060, the effect of improving the creep ductility cannot be obtained. This is clear from the examples described later.
[0042]
The above formula (1) indicates the hardenability of the steel, and in addition to the conventionally known effective B amount, the effect of Nd is clarified based on the experimental results. This is the first relational formula.
[0043]
W:
W may not be added. If added, it has the effect of stabilizing the carbide for a long time and improving the creep strength. Therefore, when the strength is emphasized and the high temperature long time creep strength is desired to be further increased, it may be added positively, and the effect becomes remarkable when the content is 0.01% or more. However, as described above, when the content exceeds 0.20%, not only the creep ductility is lowered, but also reheat embrittlement and cracking sensitivity are increased. For this reason, when W is added, the W content is preferably 0.01 to 0.20%. More preferred is 0.05 to 0.20%.
[0044]
Cu, Co:
These elements may not be added. If added, each is an austenite-forming element, contributing to stabilization of the bainite structure or martensite structure of the parent phase and improving the creep strength. Co also enhances the hardenability of the steel and improves the creep strength. Therefore, when emphasizing strength and wanting to further increase the high-temperature long-term creep strength, either one or both may be added positively, and the effect is remarkable when the content of each element is 0.01% or more. become. However, when Cu exceeds 0.20% and Co exceeds 0.50%, creep ductility decreases. For this reason, when added, the Cu content is preferably 0.01 to 0.20%, and the Co content is preferably 0.01 to 0.50%. More preferable are Cu: 0.05 to 0.15% and Co: 0.05 to 0.50%.
[0045]
Mg, Ca, La, Ce, Y, Sm, Pr:
These elements may not be added. If added, they all have the effect of preventing solidification cracking during steel casting, particularly during continuous casting. Therefore, when it is desired to obtain the effect, one or more kinds may be positively added. In this case, the above effect becomes remarkable when the content of each element is 0.0001% or more. However, when Mg and Ca are over 0.0050%, La and Ce are over 0.020%, and Y, Sm, and Pr are over 0.040%, the toughness is lowered. Therefore, the content of these elements when added is 0.0001 to 0.0050% for Mg and Ca, 0.0001 to 0.020% for La and Ce, and 0.0001 to 0.040% for Y, Sm, and Pr. It is good.
[0046]
The low alloy steel of the present invention is steel in which the balance of the above components is substantially Fe, in other words, Fe and impurities other than those described above.
[0047]
Note that the bainite structure or martensite structure of the parent phase structure is obtained by rapidly cooling or air-cooling the steel after being formed into a predetermined product shape from a temperature range above the Ar3 or Ac3 transformation point (about 860 to 920 ° C). can get. However, since the low alloy steel of the present invention is too hard if it is quenched or air-cooled as described above, the surface hardness is usually about 180 to 200 in terms of Vickers hardness Hv as appropriate according to its chemical composition. It is used after tempering at a proper temperature and time (for example, the temperature and time shown in the examples described later).
[0048]
【Example】
Forty kinds of steel having chemical compositions shown in Table 1 to Table 4 were melted using a vacuum induction melting furnace to obtain a 150 kg steel ingot.
[0049]
[Table 1]

[0050]
[Table 2]

[0051]
[Table 3]

[0052]
[Table 4]

[0053]
The obtained steel ingot was hot forged into a plate having a thickness of 50 mm and a width of 150 mm. The obtained plate is heated and held at 950 ° C. for 1 hour and then air-cooled, and then heated to 720 to 760 ° C. for 1 hour so that the steel has a Vickers hardness Hv of about 180 to 200 After holding, a tempering treatment for air cooling was performed.
[0054]
The plate after heat treatment was examined for the structure, and from the plate, a creep test piece having a diameter of 10 mm and a gauge distance (GL) of 50 mm and a V-notch test piece specified in JIS Z 2202 were collected and subjected to a creep test under the following conditions. And subjected to Charpy impact test.
[0055]
1. Creep test The creep test was performed at a test temperature of 550 ° C and a load stress of 200 MPa, and the fracture time (h) was examined.
[0056]
2. Charpy impact test The Charpy impact test is conducted at a test temperature of -60 to 60 ° C, and the fracture surface transition temperature vTrs (° C) is examined. If the vTrs is -40 ° C or less, the toughness is excellent "◎", -40 ° C More than −20 ° C. and less than −20 ° C. were evaluated as good “◯”, more than −20 ° C. and −0 ° C. or less were evaluated as slightly poor “Δ”, and those exceeding −0 ° C. were evaluated as defective “x”.
[0057]
The above results are shown in Table 5 together with the tempering temperature, the surface hardness, and the investigated structure.
[0058]
[Table 5]

As can be seen from Table 5, the steel Nos. 1 to 20 of the present invention have a creep rupture time exceeding 10000 hours at a temperature of 550 ° C. and a load stress of 200 MPa. It is about 10 times as long as steel. Further, the elongation is 25% or more, the drawing is 51% or more, the long-term creep ductility is good, and the vTrs is -20 ° C. or less and the toughness is good.
[0059]
On the other hand, the comparative steel of Steel Nos. 25 to 38 has either a component outside the range defined in the present invention, or in addition to the component range, the Beff value represented by the formula (1) is 0.0001 to Since it is out of the range of 0.0060, any one of the breaking time, elongation and drawing is inferior, and the toughness is also poor. Further, the comparative steels of Steel No. 39 and 40 have a content of any component within the range specified in the present invention, but the Beff value expressed by the formula (1) is out of the range of 0.0001 to 0.0060. , Any one of breaking time, elongation and drawing, and toughness is also poor.
[0060]
【The invention's effect】
The low alloy steel of the present invention has excellent creep strength and creep ductility, and also has good toughness. Therefore, it is extremely effective as a material for a heat-resistant structural member used in a temperature range up to about 550 ° C. in a power plant or the like.

Claims (8)

In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, sol.Al: 0.010% or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, the balance is made of Fe and impurities, and the content of Ti, B, N and Nd is 0.0001 as a Beff value expressed by the following formula (1) Low alloy steel characterized by being in the range of ~ 0.0060.
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, W: 0.01-0.20%, sol .Al: not more than 0.010%, N: less than 0.0060%, O (oxygen): not more than 0.0050%, the balance consists of Fe and impurities, and the content of Ti, B, N and Nd is expressed by the following formula (1) A low alloy steel having a Beff value in the range of 0.0001 to 0.0060.
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, sol.Al: 0.010% or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, Cu: 0.01 to 0.20% and Co: 0.01 to 0.50%, and the balance is Fe and impurities, Ti, B, A low alloy steel characterized in that the contents of N and Nd are in the range of 0.0001 to 0.0060 as Beff values represented by the following formula (1).
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, sol.Al: 0.010% or less, N: Less than 0.0060%, O (oxygen): 0.0050% or less, Mg: 0.0001-0.0050%, Ca: 0.0001-0.0050%, La: 0.0001-0.020%, Ce: 0.0001-0.020%, Y: 0.0001-0.040% , Sm: 0.0001 to 0.040% and Pr: 0.0001 to 0.040%, the balance is Fe and impurities, and the contents of Ti, B, N and Nd are expressed by the following formula (1) Low alloy steel characterized by having a Beff value in the range of 0.0001 to 0.0060.
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, sol.Al: 0.010% or less, N: Less than 0.0060%, O (oxygen): 0.0050% or less, Cu: 0.01 to 0.20% and Co: 0.01 to 0.50% or more, and Mg: 0.0001 to 0.0050%, Ca: 0.0001 to 0.0050% , La: 0.0001-0.020%, Ce: 0.0001-0.020%, Y: 0.0001-0.040%, Sm: 0.0001-0.040% and Pr: 0.0001-0.040%, and the balance is Fe and impurities A low alloy steel characterized in that the content of Ti, B, N and Nd is within the range of 0.0001 to 0.0060 as a Beff value represented by the following formula (1).
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, W: 0.01-0.20%, sol .Al: 0.010% or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, and Cu: 0.01 to 0.20% and Co: 0.01 to 0.50%, with the balance being Fe and impurities A low alloy steel characterized in that the content of Ti, B, N, and Nd is in the range of 0.0001 to 0.0060 as a Beff value represented by the following formula (1).
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, W: 0.01-0.20%, sol .Al: 0.010% or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, Mg: 0.0001-0.0050%, Ca: 0.0001-0.0050%, La: 0.0001-0.020%, Ce: 0.0001-0.020% , Y: 0.0001-0.040%, Sm: 0.0001-0.040% and Pr: 0.0001-0.040%, and the balance is composed of Fe and impurities, and the contents of Ti, B, N and Nd are as follows: A low alloy steel having a Beff value represented by the formula (1) of 0.0001 to 0.0060.
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel. In mass%, C: 0.03 to 0.10%, Si: 0.10% or less, Mn: 0.001 to 0.30%, P: 0.020% or less, S: 0.0080% or less, Cr: 0.40 to 1.50%, Mo: 0.25 to 1.00%, V: 0.03-0.15%, Nb: 0.001-0.070%, Ni: 0.001-0.30%, Ti: 0.001-0.020%, B: 0.0001-0.0060%, Nd: 0.0001-0.030%, W: 0.01-0.20%, sol .Al: 0.010% or less, N: less than 0.0060%, O (oxygen): 0.0050% or less, Cu: 0.01 to 0.20% and Co: 0.01 to 0.50% or more, and Mg: 0.0001 to 0.0050% , Ca: 0.0001-0.0050%, La: 0.0001-0.020%, Ce: 0.0001-0.020%, Y: 0.0001-0.040%, Sm: 0.0001-0.040% and Pr: 0.0001-0.040% The balance is made of Fe and impurities, and the content of Ti, B, N and Nd is within the range of 0.0001 to 0.0060 as a Beff value expressed by the following formula (1).
Beff = B- (11/14) N + (11/48) Ti + (11/144) Nd (1)
Here, the element symbol in a formula means content (mass%) of each element contained in steel.