JPS61221327A - Production of steel plate for pressure vessel having excellent low-temperature toughness - Google Patents

Abstract

PURPOSE:To improve the strength, weldability and low-temp. toughness of a steel plate for a pressure vessel in the stage of producing said steel plate by adjusting the value of PCM to a suitable range and subjecting the steel to hot rolling then to a heat treatment under specific conditions. CONSTITUTION:The steel material contg. 0.12-0.195 C, 0.10-0.30% Si, 0.80-1.50% Mn, <0.015% P, 0.15-0.75% Cr, 0.10-0.30% Mo, 0.02-0.08% sol, Al and 0.0002-0.0010% B is subjected to a component adjustment so that the value of PCM as an index to indicate the sensitivity with low-temp. cracking during welding of the steel plate as expressed by the equation (1) is maintained in a 0.22-0.30% range. Such billet is heated to a 950-1,175 deg.C range and is hot-rolled to the thick plate. The plate is normalized at the temp. from 750 deg.C up to A3-10 deg.C{A3 is the value expressed by the equation (2)} and is then air- cooled. The thick steel plate having the characteristics suitable for the pressure vessel is produced.

Description

【発明の詳細な説明】 産業上の利用分野 本発明は圧力容器用鋼板の製造方法に関し、更には、高
い強度と優れた溶接性を有すると同時に低温靭性の優れ
た圧力容器用の鋼板の製造方法に関する。DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a steel plate for pressure vessels, and more particularly to a method for producing a steel plate for pressure vessels that has high strength and excellent weldability as well as excellent low-temperature toughness. Regarding the method.

従来の技術 圧力容器等に使用される厚鋼板は、熱間でのプレス加工
等の後、放冷されて常温で溶接され、その残留応力を除
去するための規準（ＳＲ処理）が施される。そのため放
冷＋ＳＲＳＲ処理で十分な引張り強さおよび降伏強さを
確保するために、多量のＣおよび焼入性向上の合金成分
を含有させねばならず、溶接時の予熱を充分に行っても
頻繁に溶接ワレが生じ、そのワレ補修溶接とその後のＳ
Ｒ処理に膨大な時間を労力を要している。Conventional technology Thick steel plates used for pressure vessels, etc. are subjected to hot press processing, etc., then allowed to cool, welded at room temperature, and subjected to a standard (SR treatment) to remove residual stress. . Therefore, in order to ensure sufficient tensile strength and yield strength in the cooling + SRSR process, it is necessary to contain a large amount of C and alloy components that improve hardenability. Welding cracks occurred, and welding to repair the cracks and subsequent S
The R processing requires a huge amount of time and effort.

上記のような難点を解決するには、放冷、即ち焼準状態
、または規準後、焼きもどしした状態で高い強度をもち
、しかも溶接性のすぐれた厚鋼板が要求される。鋼の溶
接性を改善するには、Ｃおよび合金成分のＣ当量を下げ
るのが最も有効であるが、かかる鋼種は焼準状態では十
分な強度が望めないのが普通である。In order to solve the above-mentioned problems, a thick steel plate is required that has high strength in a normalizing state after cooling, or in a tempered state after normalizing, and has excellent weldability. In order to improve the weldability of steel, it is most effective to lower the C and C equivalents of alloy components, but such steel types usually cannot be expected to have sufficient strength in a normalized state.

このような問題点を解決するため本出願人は特願昭５２
−９１０４７号（特開昭５４−２５２１１号、特公昭５
７−２３７３９号）によりＣ量を０．０３〜０．１２％
と低くし、極微量（０，０００１５〜０．０００７０％
）のＢと０．０３０％〜０．１００％のｓｏｌ、ＡＩを
併用することによって低Ｃ且つ低ＰＣＭの鋼であって、
しかも高強度であり溶接性に優れた特に圧力容器用に好
適に用いられる鋼板を提案したものである。In order to solve these problems, the present applicant filed a patent application filed in 1983.
-91047 (Japanese Patent Publication No. 54-25211,
7-23739), the amount of C is 0.03 to 0.12%.
and a very small amount (0,00015 to 0.00070%
) B and 0.030% to 0.100% sol and AI are used together to produce a low C and low PCM steel,
Moreover, the present invention proposes a steel plate that has high strength and excellent weldability, and is particularly suitable for use in pressure vessels.

しかしながら、圧力容器用の厚鋼板では約０．０２％程
度のＮｂを添加していた。この結果、従来の圧力容器用
厚鋼板では、−４０℃付近の低温靭性が劣り、溶接部が
高硬度となり、耐硫化物応力腐蝕割れ性が低いという欠
点があった。However, about 0.02% of Nb has been added to thick steel plates for pressure vessels. As a result, conventional thick steel plates for pressure vessels have the drawbacks of poor low-temperature toughness near -40°C, high hardness of welded parts, and low resistance to sulfide stress corrosion cracking.

発明の解決しようとする問題点 本発明は、圧力容器用の鋼板において、高強度を維持し
ながら低温靭性を改善し、更に溶接部硬さを低減するこ
とを目的とし、このような鋼板の製造方法を提供せんと
するものである。Problems to be Solved by the Invention The present invention aims to improve the low-temperature toughness of a steel plate for pressure vessels while maintaining high strength, and further reduce the hardness of the welded part. The purpose is to provide a method.

更に詳細には、本発明は圧力容器用の厚鋼板の製造方法
において、Ｃ量の低減、Ｎｂの無添加、更にＰ　Ｃ）Ｉ
の低減を行うことによって溶接性と低温靭性を改善し、
これらによる強度の低下を、微量のＢの添加効果を最大
限有効に発揮せしめ且つ熱処理条件を制御することによ
り補償し、かくして高強度であり、溶接性および低温靭
性に優れた圧力容器用鋼板の製造方法を提供することを
目的とするものである。More specifically, the present invention provides a method for manufacturing a thick steel plate for pressure vessels, which reduces the amount of C, does not add Nb, and furthermore provides P C) I
Improves weldability and low-temperature toughness by reducing
The decrease in strength caused by these factors can be compensated for by maximizing the effect of adding a small amount of B and controlling the heat treatment conditions, thereby creating a steel plate for pressure vessels that has high strength and excellent weldability and low-temperature toughness. The purpose is to provide a manufacturing method.

問題点を解決するための手段 上記の問題点を解決するため、本発明に従うと、Ｃ：　
　　０．１２〜０．１９％、 Ｓｉ：　　０．１０〜０．３０％、 Ｍｎ　：　　　０．８０〜１．５０％、ｐ：　　　０．
０１５％以下、 Ｃｒ：　　　０．１５〜０．７５％、 Ｍｏ　：　　　０．１０〜０．３０％、ｓｏｌ、八１：
０．０２〜０．０８％、Ｂ　：　　　０．０００２〜０
．００１０％、を含有し、残部がＦｅおよび不可避的不
純物からなり、下記に定義されるＰＣＭが０．２２％〜
０．３０％の範囲にある鋼材を９５０〜１１７５℃の範
囲内の温度に加熱した後、熱間圧延を行い鋼板とし、該
鋼板を７８０℃から（Ａ３−１０℃）の間の温度に加熱
した後に空冷を行うことを特徴とする低温靭性の優れた
圧力容器用鋼板の製造方法が提供される。Means for Solving the Problems In order to solve the above problems, according to the present invention, C:
0.12-0.19%, Si: 0.10-0.30%, Mn: 0.80-1.50%, p: 0.
015% or less, Cr: 0.15-0.75%, Mo: 0.10-0.30%, sol, 81:
0.02-0.08%, B: 0.0002-0
．． 0.0010%, with the remainder consisting of Fe and unavoidable impurities, and PCM defined below from 0.22% to
After heating the steel material in the range of 0.30% to a temperature in the range of 950 to 1175°C, hot rolling is performed to form a steel plate, and the steel plate is heated to a temperature between 780°C and (A3-10°C). Provided is a method for producing a steel plate for a pressure vessel having excellent low-temperature toughness, which is characterized in that the steel plate is air-cooled after heating.

ただし、 Ｐｃｘ＝Ｃ＋Ｓｉ／３０＋（Ｍｎ＋Ｃｕ＋Ｃｒ）　／２
０＋Ｍａ／１５＋　Ｖ　／１５＋　５　ＢＡ３　　＝９
１０　３００Ｃ＋６０Ｓｔ　　３０Ｍｎ＋３３０Ｐ−３
０Ｃｕ　−３Ｃｒ−３０Ｎｉ　−２Ｍｏ＋７０Ｖすなわ
ち、本発明の方法では、Ｂの添加効果を最大限有効に発
揮させるため圧延加熱温度を９５０〜１１７５℃とし、
更に７８０℃〜（Ａ、−１０℃）の範囲の加熱温度で規
準することにより鋼の組織をフェライト＋ベイナイトの
２相組織とし、所望の強度を与えつつ低温靭性を改善す
ることに成功したものである。However, Pcx=C+Si/30+(Mn+Cu+Cr)/2
0+Ma/15+V/15+ 5 BA3 =9
10 300C+60St 30Mn+330P-3
0Cu -3Cr-30Ni -2Mo+70V That is, in the method of the present invention, in order to maximize the effect of adding B, the rolling heating temperature is set at 950 to 1175 °C,
Furthermore, by standardizing the heating temperature in the range of 780℃ to (A, -10℃), the structure of the steel is made into a two-phase structure of ferrite + bainite, which successfully improves low-temperature toughness while providing the desired strength. It is.

発明の作用 以下、本発明の方法に於ける鋼の化学組成の限定理由お
よび圧延条件、熱処理条件の限定理由を説明する。Effects of the Invention The reasons for limiting the chemical composition of the steel and the rolling conditions and heat treatment conditions in the method of the present invention will be explained below.

（１）鋼の化学組成の限定理由 Ｃ：　Ｃは鋼板の強度を確保するために必要且有効な元
素であり、このため０．１２％を超える含有量が必要で
ある。一方、Ｃ含有量が０，１９％以上となると鋼板の
低温靭性が著しく劣化し、溶接部の最大硬さが大きくな
るのでＣ含有量を０．１９％未満とした。(1) Reason C for limiting the chemical composition of steel: C is a necessary and effective element for ensuring the strength of steel sheets, and therefore the content must exceed 0.12%. On the other hand, if the C content exceeds 0.19%, the low-temperature toughness of the steel plate will significantly deteriorate and the maximum hardness of the weld will increase, so the C content was set to less than 0.19%.

Ｓｉ：Ｓｉは低Ｐ。０の条件下で強度を確保するため０
．１０％を超える量を添加することが必要であるが、本
発明では特に低温靭性を改善するため、低温靭性を劣化
させるＳｌの含有量を極力抑えるため領３０％未満とし
た。Si:Si has low P. 0 to ensure strength under the condition of 0.
．． Although it is necessary to add an amount exceeding 10%, in the present invention, in order to particularly improve low temperature toughness, the content of Sl, which deteriorates low temperature toughness, is set to be less than 30% as much as possible.

Ｍｎ：Ｍｎは鋼板の強度を確保し熱間脆性を防止するの
に有効且つ必要な元素であるので、その含有量を０．８
０％以上とした。一方、１．５０％と超えてＭｎを含有
すると鋼板の低温靭性が著しく劣化し、且つ溶接部の最
高硬さが著しく大きくなるので、Ｍｎの含有量の上限を
１．５０％とした。Mn: Mn is an effective and necessary element for ensuring the strength of steel sheets and preventing hot embrittlement, so its content is set to 0.8
It was set to 0% or more. On the other hand, if the Mn content exceeds 1.50%, the low-temperature toughness of the steel plate will significantly deteriorate and the maximum hardness of the welded part will increase significantly, so the upper limit of the Mn content was set at 1.50%.

Ｐ：　Ｐは低温靭性および溶接性に極めて有害な元素で
あり、その含有量が少ないほど良好な低温靭性が得られ
、且つ溶接高温割れ感受性を低減することができる。従
ってＰの含有量は低ければ低いほど圧力容器用鋼板とし
て望ましいものである。しかしながら、低Ｐ鋼の製造は
コストが高く、複雑であるので、経済性を考慮して０．
０１５％を本発明で許容できるＰ含有量の上限とした。P: P is an element extremely harmful to low-temperature toughness and weldability, and the lower its content, the better low-temperature toughness can be obtained and the susceptibility to welding hot cracking can be reduced. Therefore, the lower the P content, the more desirable the steel sheet is for pressure vessels. However, since manufacturing low P steel is expensive and complicated, 0.
0.015% was set as the upper limit of the P content allowable in the present invention.

Ｃｒ：Ｃｒは鋼の強度、特に高温強度を向上するのに有
効な元素であるので０．１５％以上の量のＣｒを含有さ
せることとした。しかしながら、０．７５％以上のＣｒ
を含有すると、低温靭性に悪影響を及ぼし、更に溶接部
の最高硬さも大きくなるので、Ｃｒ含有量の上限を０．
７５％とした。Cr: Since Cr is an effective element for improving the strength of steel, especially high-temperature strength, it was decided to contain 0.15% or more of Cr. However, Cr of 0.75% or more
If it contains Cr, it will have an adverse effect on the low temperature toughness and will also increase the maximum hardness of the welded part, so the upper limit of the Cr content should be set to 0.
It was set at 75%.

Ｍｏ：Ｍｏは鋼の焼入性を向上せしめ且つ焼戻し軟化抵
抗を有するので、強度上昇には極めて有効な元素であり
、更にＭｏは焼戻し脆化を防止するので靭性の改善にも
有効である。このため、０．１０％以上のＭｏを含有さ
せることとした。一方、０．３０％を超えてＭＯを含有
すると、鋼の低温靭性を劣化せしめ、鋼板溶接部の最高
硬さを大きくするので、ＭＯ含有量の上限を０．３０％
とした。Mo: Mo improves the hardenability of steel and has resistance to temper softening, so it is an extremely effective element for increasing strength.Moreover, Mo prevents temper embrittlement, so it is also effective for improving toughness. For this reason, it was decided to contain 0.10% or more of Mo. On the other hand, if MO content exceeds 0.30%, the low-temperature toughness of the steel will deteriorate and the maximum hardness of the steel plate weld will increase, so the upper limit of the MO content should be set at 0.30%.
And so.

ｓｏｌ、Ａｌ　：　　本発明は上記した如くＢの添加効
果を最大限発揮せしめて低Ｃ且つ低Ｐ。Ｘ鋼の焼入性を
向上することを特徴とするものである。しかしながら、
ｓｏｌ、ＡＩが不足すると、ＢはＢＮとなり、その添加
効果が失われる。従って、本発明では０．０２％以上の
ｓｏｌ、ＡＩを含有せしめてＮをＡＩＮとして固定し、
組織を微細化して強度を上昇するとともにＢの焼入性向
上効果を確保するものである。しかしながら、ｓｏｌ、
ＡＩの添加量が０．０８％を超えるとＡＩＮが粗大化し
て鋼の低温靭性が著しく劣化すると同時にＢの添加効果
も失わる。従って、ｓｏｌ、　ＡＩの添加量を０゜０２
〜０，０８％の範囲とした。sol, Al: As described above, the present invention maximizes the effect of adding B to achieve low C and low P. It is characterized by improving the hardenability of X steel. however,
When sol and AI are insufficient, B becomes BN, and the effect of its addition is lost. Therefore, in the present invention, N is fixed as AIN by containing 0.02% or more of sol and AI,
The purpose is to refine the structure, increase strength, and ensure the hardenability improvement effect of B. However, sol,
When the amount of AI added exceeds 0.08%, AIN becomes coarse and the low-temperature toughness of the steel deteriorates significantly, and at the same time, the effect of B addition is also lost. Therefore, the amount of sol and AI added is 0°02
The range was 0.08%.

Ｂ：　Ｂは本発明に於いて極めて重要な元素である。す
なわち、低Ｃ１低ＰＣＭの鋼組織において所望の強度を
達成するにはＢの焼入性向上効果を最大限有効に発揮さ
せねばならず、０．０００２％以上のＢの含有量を必要
とする。一方、Ｂ含有量が０．００１０％を超えると、
熱処理時にＢ析出物が粒界に形成され鋼の靭性が低下す
るばかりか、規準時に溶接部の割れが発生しやすくなる
。B: B is an extremely important element in the present invention. In other words, in order to achieve the desired strength in a steel structure with low C1 and low PCM, the hardenability improving effect of B must be maximized, and a B content of 0.0002% or more is required. . On the other hand, when the B content exceeds 0.0010%,
During heat treatment, B precipitates are formed at grain boundaries, which not only reduces the toughness of the steel, but also makes it easier for cracks to occur in the weld during standardization.

従って、Ｂ含有量を０．０００２〜０．００１０％の範
囲とした。Therefore, the B content was set in the range of 0.0002 to 0.0010%.

ＰＣ）ｌ：　　ＰＣＭは鋼板の溶接時の低温割れ感受性
を示す指標であり、Ｐ　０Ｍ値が低いほど溶接時の低温
割れが発生しにくい。一方、Ｐ　０Ｍ値が高いほど一般
的に鋼の強度が大きくなり、それに比例して靭性が劣化
する。従って、本発明に於いては鋼の強度を所望のレベ
ル以上に確保するためＰ　Ｃａｌ値が０．２２％以上の
鋼組成とし、他方、鋼板の低温靭性の確保および溶接部
の最高硬さ低減のためにＰＣ１Ｌ値の上限を０．３０％
とした。PC) l: PCM is an index showing the susceptibility to cold cracking during welding of steel plates, and the lower the P 0M value, the less likely cold cracking will occur during welding. On the other hand, the higher the P 0M value, the greater the strength of the steel in general, and the toughness deteriorates proportionally. Therefore, in the present invention, in order to ensure the strength of the steel at a desired level or higher, the steel composition has a P Cal value of 0.22% or more, while ensuring the low temperature toughness of the steel plate and reducing the maximum hardness of the welded part. Therefore, the upper limit of PC1L value is set to 0.30%.
And so.

（２）圧延加熱温度範囲の限定理由 上記した化学組成の鋼材を熱間圧延するに際し、圧延加
熱温度が９５０℃未満のときは鋼組織がオーステナイト
とならず、圧延抵抗が大きく且つ異常組織となる恐れが
ある。一方、圧延加熱温度が１１７５℃を超えると、鋼
中のＮがＡＩＮとならず、Ｂと結合してＢの添加による
焼入性向上効果がなくなる。(2) Reason for limiting the rolling heating temperature range When hot rolling steel materials with the above chemical composition, if the rolling heating temperature is less than 950°C, the steel structure will not become austenite, and the rolling resistance will be large and the structure will be abnormal. There is a fear. On the other hand, when the rolling heating temperature exceeds 1175° C., N in the steel does not become AIN, but combines with B, and the hardenability improvement effect due to the addition of B disappears.

従って、本発明の方法では鋼材の圧延加熱温度を９５０
〜１１７５℃の範囲とした。Therefore, in the method of the present invention, the rolling heating temperature of the steel material is set to 950°C.
-1175°C.

（３）規準加熱温度範囲の限定理由 上記した如く本発明の方法ではＮｂを添加しない低Ｃ１
低Ｐ。、４の鋼に微量のＢを添加して焼入性を向上せし
め、強度を確保すると同時に低温靭性及び溶接性を改善
している。しかしながら低Ｃ１低Ｐ。０のため強度は依
然として低目であり、これを規準条件を選択することに
より鋼をフェライト＋ベイナイトの２相組織とすること
゛により解決している。(3) Reason for limiting the standard heating temperature range As mentioned above, the method of the present invention uses low C1 without adding Nb.
Low P. A small amount of B is added to the steel of No. 4 to improve hardenability, ensure strength, and at the same time improve low temperature toughness and weldability. However, low C1 and low P. 0, the strength is still low, but this problem was solved by selecting standard conditions to make the steel a two-phase structure of ferrite and bainite.

すなわち、焼準加熱が７８０℃未満のときはフェライト
＋ベイナイトの２相組織のフェライト率が５０％以上と
なり、靭性及び強度が著しく劣化する。That is, when the normalizing temperature is lower than 780° C., the ferrite ratio of the two-phase structure of ferrite + bainite becomes 50% or more, and the toughness and strength deteriorate significantly.

一方、焼準加熱が（Ａ３−１０℃）以上の場合、フェラ
イト＋ベイナイトの２相組織中のフェライト率が１０％
以下となり、はぼづイナイト単相の組織となるので低温
靭性が急激に劣化する。On the other hand, when the normalization heating is above (A3-10℃), the ferrite percentage in the two-phase structure of ferrite + bainite is 10%.
As a result, the structure becomes a single phase of habozu inite, and the low-temperature toughness rapidly deteriorates.

従って本発明の方法では焼型加熱温度を７８０℃〜（Ａ
３１０℃）の範囲とする。Therefore, in the method of the present invention, the heating temperature of the baking mold is 780℃~(A
310°C).

実施例 以下、本発明の方法を比較例と対照しながら実施例によ
り説明する。なお、こさらの実施例は本発明の単なる例
示であって本発明の技術的範囲を何隻制限するものでは
ない。Examples Hereinafter, the method of the present invention will be explained by examples in comparison with comparative examples. It should be noted that these embodiments are merely illustrative of the present invention and do not limit the technical scope of the present invention.

表１に示す化学組成の鋼スラブ試片をそれぞれ表２に示
す温度まで均一加熱した後、熱間圧延を行い厚さ１００
ｍｍの厚鋼板を得た。これらの厚鋼板をそれぞれ表３に
示す温度に加熱し、３０分間保持した後、空冷すること
により焼型処理を行った。After uniformly heating the steel slab specimens with the chemical compositions shown in Table 1 to the temperatures shown in Table 2, they were hot rolled to a thickness of 100 mm.
A steel plate with a thickness of mm was obtained. These thick steel plates were heated to the temperatures shown in Table 3, held for 30 minutes, and then air-cooled to perform a baking process.

表２　鋼板の熱間圧延時の加熱温度 表３　鋼板の熱処理条件 ただし、 Ａ３＝　９１０−３００Ｃ＋　６０Ｓｉ　−３０Ｍｎ＋
　３３０Ｆ　−３０Ｃｕ　−３Ｃｒ　−３０Ｎｉ−２Ｍ
ｏ　　＋７０Ｖ 得られた鋼板に第１図に示す如き開先加工を施し、下記
の条件で溶接及び溶接後熱処理を行溶接施行条件 溶接法；被覆アーク溶接法 溶接材料：被覆アーク溶接棒ＪＩＳＤ　５０１６、棒径
４．　Ｏｍｍφ 溶接条件：電流１７０Ａ、、電圧２５Ｖ、溶接速度１５
ｃｍ／ｍｉｎ、溶接人熱量１７０００Ｊ／ｃｍ予熱温度
：１００℃ 層間温度：１００〜１５０℃ 溶接後熱処理条件二６２５℃×１４ｈ炉冷得られた溶接
鋼板について表４に示す項目の機械的特性の試験を行い
、それらの結果を表５および第２図〜第５図に示す。Table 2 Heating temperature during hot rolling of steel plate Table 3 Heat treatment conditions of steel plate However, A3 = 910-300C+ 60Si -30Mn+
330F -30Cu -3Cr -30Ni-2M
o +70V The obtained steel plate was grooved as shown in Fig. 1, and welding and post-welding heat treatment were performed under the following conditions. Welding conditions Welding method: Covered arc welding method Welding material: Covered arc welding rod JISD 5016, Rod diameter 4. Ommφ Welding conditions: current 170A, voltage 25V, welding speed 15
cm/min, welder's heat amount 17000 J/cm Preheating temperature: 100°C Interlaminar temperature: 100-150°C Post-weld heat treatment conditions 2 625°C x 14h Furnace cooling The obtained welded steel plate was tested for mechanical properties on the items shown in Table 4. The results are shown in Table 5 and FIGS. 2 to 5.

表４　機械的特性の調査項目 第２図は、得られた溶接鋼板の母材部についてのＰｃｘ
値と常温引張強度及び低温衝撃値との関係を示すグラフ
である。図中・印は比較例の鋼を示し、○印は本発明の
方法により規定された化学組成の鋼を示し、これらの鋼
を１０５０℃の圧延加熱温度、８１０℃の焼準加熱温度
で熱間圧延および規準を施したものである。図示の如く
、比較例の鋼の場合は、１０ｋｇｆ−ｍ以上の一４０℃
に於ける低温衝撃値Ｖ　Ｅ−４０、及び５０ｋｇｆ／ｍ
ｍ２以上の常温における引張強さＴＳ、アを同時に満足
する鋼はない。Table 4 Investigation items for mechanical properties Figure 2 shows the Pcx of the base material of the obtained welded steel plate.
It is a graph showing the relationship between the tensile strength at room temperature and the low-temperature impact value. In the figure, the marks indicate steels of comparative examples, and the marks ○ indicate steels with chemical compositions specified by the method of the present invention. These steels were heated at a rolling heating temperature of 1050°C and a normalizing heating temperature of 810°C. It has been subjected to inter-rolling and standardization. As shown in the figure, in the case of the steel of the comparative example, the
Low temperature shock value V E-40 and 50kgf/m
There is no steel that simultaneously satisfies the tensile strength TS and A at room temperature of m2 or more.

これに対して本発明の規定する範囲内の化学成分を有す
る鋼板の母材部はいずれもＴＳＲ，及びＷＥ−４゜の目
標値を同時に満足している。On the other hand, all base metal parts of steel sheets having chemical compositions within the range prescribed by the present invention simultaneously satisfy the target values of TSR and WE-4°.

更に、第２図に示す結果より本発明の規定する化学組成
の範囲内の鋼ではＰ。、４値の増加とともに低温衝撃値
が低下し、引張強さが増加することが理解できる。Furthermore, the results shown in FIG. 2 show that steel within the chemical composition range defined by the present invention has a P content. It can be seen that as the 4 value increases, the low temperature impact value decreases and the tensile strength increases.

第３図は、試片７の母材部に付いての圧延加熱温度とＴ
ＳＲ□およびｖＥ−４ｏのの関係を示すグラフである。Figure 3 shows the rolling heating temperature and T of the base material of specimen 7.
It is a graph showing the relationship between SR□ and vE-4o.

この試片７は、熱間圧延後、７８０℃（・印）、８１０
℃（○印）及び８３５℃（菱形で右半分が黒い印）でそ
れぞれ３０分間加熱後、空冷することによって規準した
ものである。ただし、この鋼試片のＡ３は８４５℃であ
る。This sample 7 was hot rolled at 780°C (・mark) and 810°C.
℃ (marked with ○) and 835°C (diamond with black right half) for 30 minutes, respectively, and then cooled in the air. However, A3 of this steel specimen is 845°C.

第３図に示す如く、鋼試片７は圧延加熱温度が９５０〜
１１７５℃の範囲でＴＳＲＴおよびＷＥ−４０の目標値
を同時に満足する。これに対して圧延加熱温度が９００
℃の場合には鋼組織が細粒化して十分な焼入性が得られ
ず、ＴＳＲＴおよびＷＥ−４゜がともに低い値となる。As shown in FIG. 3, the steel specimen 7 has a rolling heating temperature of 950 to
The target values of TSRT and WE-40 are simultaneously satisfied within the range of 1175°C. On the other hand, the rolling heating temperature is 900
℃, the steel structure becomes fine-grained and sufficient hardenability cannot be obtained, and both TSRT and WE-4° become low values.

一方、圧延加熱温度が１２２５℃と高い場合には、八Ｉ
Ｎが再固溶し、Ｂが固溶したＮと結合してＢＮとなるた
め、Ｂ添加効果が失われ、焼入性が低下し、得られる鋼
板のＴＳＲＴが低くなる。On the other hand, when the rolling heating temperature is as high as 1225°C,
Since N re-dissolves and B combines with the dissolved N to form BN, the effect of B addition is lost, the hardenability decreases, and the TSRT of the resulting steel sheet becomes low.

第４図は試片７を１０５０℃で加熱した後、熱間圧延し
、次いで種々の加熱温度で規準した鋼板の母材部につい
ての焼準加熱温度とｖ　Ｅ−＜。及びＴＳＲＴとの関係
を示すグラフである。FIG. 4 shows the normalizing heating temperature and v E-< of the base material of the steel plate, which was heated at 1050° C. and then hot rolled, and then standardized at various heating temperatures. and TSRT.

第４図に示す如く、本発明で規定する化学組成の範囲内
の鋼試片７は、７８０〜８３５℃の範囲の規準加熱を行
ったときＴＳ、、および、Ｅ−４゜の目標値を同時に満
足している。As shown in FIG. 4, the steel specimen 7 having a chemical composition within the range specified by the present invention achieved target values of TS and E-4° when subjected to standard heating in the range of 780 to 835°C. I'm satisfied at the same time.

これに対し、焼準加熱温度が７５０℃と本発明で規定す
る範囲を超えて低いときは、フェライト＋ベイナイト組
織中のフェライトが５０％を超えてしまいＴＳＲＴおよ
びＶＥ−４゜がともに低下する。On the other hand, when the normalization heating temperature is 750°C, which is lower than the range defined by the present invention, the ferrite in the ferrite+bainite structure exceeds 50%, and both TSRT and VE-4° decrease.

一方、焼準加熱温度が８６５℃と高いときには、規準後
の鋼組織はベイナイト組織のみとなり、高強度は得られ
るものの低温衝撃値ＶＥ−４０は著しく低下する。On the other hand, when the normalizing temperature is as high as 865° C., the steel structure after normalization becomes only a bainite structure, and although high strength is obtained, the low-temperature impact value VE-40 is significantly lowered.

第５図は、本発明の規定する範囲の化学組成の！！Ｉ　
（Ｎｂ＜０．０１％）とＮｂ＜０．０１％及びＮｂ＝０
．０２％の比較鋼についてのＰ。＋４の値と溶接部の最
高硬さとの関係を示すグラフである。FIG. 5 shows the chemical composition within the range defined by the present invention! ! I
(Nb<0.01%) and Nb<0.01% and Nb=0
．． P for 02% comparison steel. It is a graph showing the relationship between the value of +4 and the maximum hardness of the welded part.

一般に溶接部の耐硫化物応力腐蝕割れ性は溶接部の硬さ
の上昇に従って低下し、ビッカース硬さｌｌｖが２００
を超えると著しく劣化する。In general, the resistance to sulfide stress corrosion cracking of welds decreases as the hardness of the weld increases, and the Vickers hardness llv is 200
Exceeding this will result in significant deterioration.

しかるに、第５図に示す通り、溶接部の最高硬さはＰ。However, as shown in Figure 5, the maximum hardness of the welded part is P.

、、値の増加およびＮｂ添加によって上昇する。従って
、優れた耐硫化物応力腐蝕割れ性の溶接部を得るには、
溶接部の最高ビッカース硬さを２００以下とすることが
必要であり、このためには第５図に示す結果よりＰ。、
４≦０．３０％とし、且つＮｂ＜０．０１％とすること
が必要である。, , increases with increasing value and Nb addition. Therefore, to obtain a weld with excellent sulfide stress corrosion cracking resistance,
It is necessary to set the maximum Vickers hardness of the welded part to 200 or less, and for this purpose, P from the results shown in FIG. ,
It is necessary to satisfy 4≦0.30% and Nb<0.01%.

発明の効果 上記した如く、本発明は圧力容器用鋼板の製造に於いて
、該鋼板の低温靭性と溶接部の耐硫化物応力腐蝕割れ性
を改善し、同時に引張強度を高レベルに維持することを
目的とするものであり、この目的を従来この種の鋼材に
添加されていたＮｂを添加せず、Ｃ看及びＰ。Ｘ値を低
減し、更にこれらによる強度の低下をＢの添加効果を最
大発揮することにより解決したものである。Effects of the Invention As described above, the present invention improves the low-temperature toughness of the steel plate and the resistance to sulfide stress corrosion cracking of the welded part, and at the same time maintains the tensile strength at a high level in the production of steel plates for pressure vessels. This purpose was achieved by adding C and P without adding Nb, which was conventionally added to this type of steel. The X value was reduced, and the resulting decrease in strength was resolved by maximizing the effect of B addition.

このため本発明に於いては圧延加熱温度及び焼準加熱温
度を制限し、強度、低温靭性及び溶接性の優れた低合金
鋼を提供することに成功した。For this reason, in the present invention, the rolling heating temperature and normalizing heating temperature were limited, and it was possible to provide a low-alloy steel with excellent strength, low-temperature toughness, and weldability.

本発明の方法により圧力容器用鋼板を低価格且つ簡便な
方法で提供することが可能となり、従来技術では低合金
鋼では得られなかった機械的特性のものを提供すること
ができる。The method of the present invention makes it possible to provide a steel plate for pressure vessels at a low cost and in a simple manner, and it is possible to provide mechanical properties that could not be obtained with low alloy steel using conventional techniques.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は、実施例に於ける鋼板の開先加工を示す図であ
り、 第２図は、実施例で得られた溶接鋼板の母材邪について
のＰ　Ｃ１ｌ値と常温引張強度及び低温衝撃値との関係
を示すグラフであり、 第３図は、試片７の母材邪に付いての圧延加熱温度とＴ
ＳＲ，およびＶＥ−４０のの関係を示すグラフであり、 第４図は試片７を１０５０℃で加熱した後、熱間圧延し
、次いで種々の加熱温度で規準した鋼板の母材邪につい
ての焼準加熱温度とｖ　Ｅ　−４０及びＴＳＲ，との関
係を示すグラフであり、第５図は、本発明め規定する範
囲の化学組成の鋼（Ｎｂ　＜０．０１％）とＮｂ＜０．
０１％及びＮｂ＝０．０２％の比較鋼についてのＰ。０
の値と溶接部の最高硬さとの関係を示すグラフである。 １１５　Ｆ！Ｒ ＰａＭ　（ぞ） ＰＣＭ　（Ｚ） ｗ１２図 第１１１ 改：枚Ｎ　１００％％　　　ｂ：ｒ’／ｌｔ濯さ９０鵠
１１４図Fig. 1 is a diagram showing the bevel processing of the steel plate in the example, and Fig. 2 shows the P C1l value, room temperature tensile strength, and low temperature impact of the base material of the welded steel plate obtained in the example. FIG. 3 is a graph showing the relationship between the rolling heating temperature and the T value for the base material of specimen 7.
Fig. 4 is a graph showing the relationship between SR and VE-40, and Fig. 4 shows the relationship between the base material of the steel plate which was heated at 1050°C, hot rolled, and then standardized at various heating temperatures. FIG. 5 is a graph showing the relationship between normalization heating temperature, v E -40 and TSR, and FIG.
P for comparative steels with 0.01% and Nb=0.02%. 0
2 is a graph showing the relationship between the value of and the maximum hardness of the welded part. 115 F! R PaM (Zo) PCM (Z) w12 Figure 111 Revised: Sheet N 100%% b: r'/lt Rinse 90 Mouse Figure 114

Claims (1)

【特許請求の範囲】 Ｃ：０．１２〜０．１９％、 Ｓｉ：０．１０〜０．３０％、 Ｍｎ：０．８０〜１．５０％、 Ｐ：０．０１５％以下、 Ｃｒ：０．１５〜０．７５％、 Ｍｏ：０．１０〜０．３０％、 ｓｏｌ．Ａｌ：０．０２〜０．０８％、 Ｂ：０．０００２〜０．００１０％、 を含有し、残部がＦｅおよび不可避的不純物からなり、
下記に定義されるＰ＿Ｃ＿Ｍが０．２２％〜０．３０％
の範囲にある鋼材を９５０〜１１７５℃の範囲内の温度
に加熱した後、熱間圧延を行い鋼板とし、該鋼板を７８
０℃から（Ａ＿３−１０℃）の間の温度に加熱した後に
空冷を行うことを特徴とする低温靭性の優れた圧力容器
用鋼板の製造方法。 ただし、 Ｐ＿Ｃ＿Ｍ＝Ｃ＋Ｓｉ／３０＋（Ｍｎ＋Ｃｕ＋Ｃｒ）／
２０＋Ｍｏ／１５＋Ｖ／１５＋５Ｂ Ａ＿３＝９１０−３００Ｃ＋６０Ｓｉ−３０Ｍｎ＋３３
０Ｐ−３０Ｃｕ−３Ｃｒ−３０Ｎｉ−２Ｍｏ＋７０Ｖ[Claims] C: 0.12 to 0.19%, Si: 0.10 to 0.30%, Mn: 0.80 to 1.50%, P: 0.015% or less, Cr: 0 .15-0.75%, Mo: 0.10-0.30%, sol. Al: 0.02 to 0.08%, B: 0.0002 to 0.0010%, the remainder consists of Fe and inevitable impurities,
P_C_M defined below is 0.22% to 0.30%
After heating the steel material in the range of 950 to 1175°C, hot rolling is performed to form a steel plate, and the steel plate is heated to a temperature of 78°C.
A method for producing a steel plate for a pressure vessel having excellent low-temperature toughness, the method comprising heating to a temperature between 0°C and (A_3-10°C) and then air cooling. However, P_C_M=C+Si/30+(Mn+Cu+Cr)/
20+Mo/15+V/15+5B A_3=910-300C+60Si-30Mn+33
0P-30Cu-3Cr-30Ni-2Mo+70V