JPH0625742A - Manufacture of sour resistant steel sheet having excellent low temperature toughness - Google Patents

Abstract

PURPOSE:To obtain a sour resistant steel sheet having excellent low temp. toughness by specifying the componental compsn. of steel, heating and rolling conditions characterized by cooling in the process of rolling and cooling conditions immediately after the rolling. CONSTITUTION:The steel contg., as fundamental components, by weight, <=0.12% C, <=0.6% Si, 0.6 to 1.5% Mn, <=0.015% P, each 0.01 to 0.10% Al and Nb 0.005 to 0.030% Ti and each 0.1 to 0.5% Ni and Cu and contg. <=0.003% S, <=0.005% O and <=0.006% Ca as well as contg. components satisfying formula I, 0.7<=ICP<=1.5 and formula II, ICP=[Ca]/1.25[S]+0.625-[O] and the balance iron is used. This steel is cast, and after that, it is not formed into a cold slab or is formed into a cold slab and is heated to 1000 to 1250 deg.C. After its extraction, rolling is started and is once stopped at >=900 deg.C surface temp., and it is cooled to <=700 deg.C surface temp. at 5 to 40 deg.C/sec cooling rate. Next, it is allowed to stand till the surface temp. reaches Ac3 or below and the temp. of the central part of the sheet thickness reaches <=950 deg.C and is rolled down so as to regulate the cumulative draft to >=60% and the average rolling true strain per pass to <=0.2, and the rolling is finished when the average temp. of the sheet thickness reaches Ar3 or above. Immediately, it is cooled till the average temp. of the sheet thickness reaches 350 to 550 deg.C at 5 to 40 deg.C/sec cooling rate and is air-cooled.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】本発明は優れた低温靭性を有する
耐サワー鋼板の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing sour-resistant steel sheet having excellent low temperature toughness.

【０００２】[0002]

【従来の技術】近年、パイプラインの敷設が大規模に行
なわれているが、このようなパイプラインにおいて腐食
による材料の劣化が問題となっている。特に石油や天然
ガスのパイプライン輸送において、原油や天然ガスに硫
化水素（以後Ｈ₂ Ｓと言う）や二酸化炭素（以後ＣＯ₂
と言う）を含む場合が多く、これらのＨ₂ Ｓ，ＣＯ₂ は
水と共存し腐食作用により発生した原子状の水素が鋼中
に侵入して起る破壊が問題となっている。2. Description of the Related Art In recent years, pipelines have been laid on a large scale, but deterioration of materials due to corrosion has become a problem in such pipelines. Especially in pipeline transportation of oil and natural gas, hydrogen sulfide (hereinafter referred to as H ₂ S) and carbon dioxide (hereinafter CO ₂
In many cases, H ₂ S and CO ₂ coexist with water and atomic hydrogen generated by a corrosive action penetrates into the steel to cause destruction.

【０００３】この腐食作用により発生した原子状の水素
が鋼中に侵入して起る破壊には、板面に平行な割れであ
る水素誘起割れ（以後ＨＩＣと言う）と板面に垂直な割
れである硫化物応力腐食割れ（以後ＳＳＣと言う）とが
ある。Atomic hydrogen generated by this corrosive action penetrates into the steel to cause damage. Hydrogen-induced cracking (hereinafter referred to as HIC), which is a crack parallel to the plate surface, and cracks perpendicular to the plate surface, are included. Sulfide stress corrosion cracking (hereinafter referred to as SSC).

【０００４】ＨＩＣの発生機構は、サワー環境下で起る
鋼材表面の鉄の腐食によって生じた原子状の水素が鋼中
に侵入し、鋼材中のＭｎＳや酸化物系のクラスターのよ
うな層状の広がりをもつ介在物のまわりに集積して起る
ものである。The mechanism of HIC generation is that atomic hydrogen generated by corrosion of iron on the surface of a steel material in a sour environment penetrates into the steel to form a layered structure such as MnS or oxide-based clusters in the steel material. It occurs by accumulating around expansive inclusions.

【０００５】しかもかかる層状の介在物はしばしば偏析
帯の中に存在するために、介在物を起点に発生したＨＩ
Ｃが偏析帯によって助長されることが知られており、一
般にＨＩＣの発生は中心偏析部に多い。Moreover, since such layered inclusions are often present in the segregation zone, the HI generated from the inclusions as a starting point.
It is known that C is promoted by the segregation zone, and generally, HIC is often generated in the central segregation part.

【０００６】一方、ＳＳＣは特に高強度側で起る現象で
あり、更に、ラインパイプ等の製造、敷設に際しては溶
接施工が必須となるから、これらの用途に供される鋼の
溶接部の硬度は高くなり、パイプラインの操業化及び残
留応力と鋼中の原子状の水素によりＳＳＣが発生するこ
とが知られている。On the other hand, SSC is a phenomenon that occurs particularly on the high strength side, and since welding work is indispensable when manufacturing and laying line pipes, etc., the hardness of the welded portion of the steel used for these applications is high. Is higher, and it is known that SSC is generated due to pipeline operation and residual stress and atomic hydrogen in steel.

【０００７】従来、耐サワー用鋼板の製造方法として、
例えば特開昭６３−１３６９号公報のようにＳ含有量を
極端に下げると共にＣａ添加によりＭｎＳの形態制御処
理を実施し、Ｍｏ，Ｔｉ添加した鋼片を加熱し、オース
テナイト粒の再結晶域の圧延に加えて、９００℃以下の
未再結晶域で６０〜８０％の圧下を加え、Ａｒ₃ 変態点
以上で圧延を終了した後、直ちに比較的速い冷却速度２
０超〜４０℃/secで冷却し３５０℃以上５５０℃未満の
温度で水冷停止し、その後放冷する技術がある。Conventionally, as a method for producing a sour-resistant steel sheet,
For example, as in Japanese Patent Laid-Open No. 63-1369, the S content is extremely reduced and the morphology control treatment of MnS is performed by adding Ca, and the steel slabs added with Mo and Ti are heated to reduce the recrystallization area of austenite grains. In addition to the rolling, a reduction of 60 to 80% is applied in the unrecrystallized region of 900 ° C. or lower, and the rolling is completed at the Ar ₃ transformation point or higher, and immediately after that, a relatively high cooling rate 2
There is a technique of cooling at 0 to 40 ° C / sec, stopping water cooling at a temperature of 350 ° C or higher and lower than 550 ° C, and then allowing to cool.

【０００８】この方法に従えば冷却後の組織は微細なベ
イナイトあるいは微細なフェライト−ベイナイトの混合
組織となり板厚方向の硬度は一定となり、また中心偏析
部のミクロ組織も改善され、耐ＨＩＣ，耐ＳＳＣ性は非
常に改善される。According to this method, the microstructure after cooling becomes a fine bainite or a fine microstructure of ferrite-bainite, the hardness in the plate thickness direction becomes constant, the microstructure of the central segregation portion is improved, and HIC resistance and resistance are improved. The SSC property is greatly improved.

【０００９】一方、厚鋼板の低温靭性を向上させる加工
方法としては、特公昭４９−７２９１号公報、特公昭５
７−２１００７号公報、特公昭５９−１４５３５号公報
等があり、オーステナイトの未再結晶温度域において制
御圧延を行ない、引き続いて加速冷却を行なうことが有
効とされてきた。On the other hand, as a processing method for improving the low temperature toughness of a thick steel plate, Japanese Patent Publication Nos. 49-7291 and 5
7-21007, JP-B-59-14535, etc., it has been considered effective to carry out controlled rolling in the unrecrystallized temperature range of austenite, followed by accelerated cooling.

【００１０】しかしこの方法では板厚が厚くなった場合
に板厚中心部まで十分に圧下の効果がゆきわたらず、圧
下による靭性の向上効果は飽和してしまう。However, in this method, when the plate thickness is increased, the effect of reduction is not fully spread to the central portion of the plate thickness, and the effect of improving the toughness due to the reduction is saturated.

【００１１】耐サワー用鋼板の場合、耐サワー性の観点
から圧延終了温度がＡｒ₃ 以上に制限されるために低温
靭性に不利な高温圧延が強いられる。しかも、耐サワー
用厚手材においては高温圧延に加えて、圧下による靭性
の向上効果も飽和してしまうために、低温靭性に優れた
耐サワー用厚手鋼板を製造することは極めて困難であっ
た。In the case of a sour-resistant steel plate, the rolling end temperature is limited to Ar ₃ or higher from the viewpoint of sour resistance, so that high-temperature rolling which is disadvantageous in low temperature toughness is forced. Moreover, in the case of thick sour-resistant materials, in addition to high temperature rolling, the effect of improving the toughness due to reduction is saturated, so it has been extremely difficult to manufacture thick steel sheets for sour-resistant having excellent low temperature toughness.

【００１２】[0012]

【発明が解決しようとする課題】本発明は鋼の成分に特
別な条件を設けると共に圧延途中冷却を特徴とする加熱
圧延条件及び圧延直後の冷却条件を制御することによ
り、湿潤な硫化水素環境（以後サワー環境と言う）、と
くに高濃度の硫化水素あるいはさらに二酸化炭素を含む
湿潤環境下における優れた耐水素誘起割れ性及び耐硫化
物応力腐食割れ性と優れた低温靭性を有する耐サワー鋼
板の製造方法を提供するものである。SUMMARY OF THE INVENTION The present invention provides a wet hydrogen sulfide environment (by controlling special conditions for the composition of steel and controlling hot rolling conditions characterized by cooling during rolling and cooling conditions immediately after rolling). Hereinafter referred to as sour environment), especially the production of sour-resistant steel sheets with excellent hydrogen-induced cracking resistance and sulfide stress corrosion cracking resistance and excellent low temperature toughness in a humid environment containing high concentration of hydrogen sulfide or carbon dioxide. It provides a method.

【００１３】[0013]

【課題を解決するための手段】本発明の要旨は、重量％
でＣ：０．１２％以下、Ｓｉ：０．６％以下、Ｍｎ：
０．６〜１．５％、Ｐ：０．０１５％以下、Ａｌ：０．
０１〜０．１０％、Ｔｉ：０．００５〜０．０３０％、
Ｎｂ：０．０１〜０．１０％、Ｎｉ：０．１〜０．５
％、Ｃｕ：０．１〜０．５％、Ｖ：０．０１〜０．１０
％を基本成分としてＳ，Ｏ，Ｃａの含有量がＳ：０．０
０３％以下、Ｏ：０．００５％以下、Ｃａ：０．００６
％以下であって、かつ次式（１），（２） ０．７≦ＩＣＰ≦１．５ ………………………………………（１） ＩＣＰ＝〔Ｃａ〕／１．２５〔Ｓ〕＋０．６２５〔Ｏ〕 ……………（２） を満足する成分を含有し、残部がＦｅ及び不可避的不純
物よりなる鋼を鋳造後冷片にすることなく、あるいは冷
片を１０００〜１２５０℃の温度に加熱し、抽出後圧延
を開始して表面温度が９００℃以上で圧延を一旦中断
し、引続き５〜４０℃／秒の冷却速度で表面温度が７０
０℃以下になるまで冷却した後、表面温度がＡｃ₃ 以
下、板厚中心部温度が９５０℃以下になるまで放置し、
しかる後に累積圧下率が６０％以上でかつ平均の１パス
あたりの圧延真歪が０．２以下となる圧下を加え、板厚
平均温度がＡｒ₃ 以上で圧延を終了し、直ちに５〜４０
℃／秒の冷却速度で板厚平均温度が３５０〜５５０℃と
なるまで冷却し、その後空冷することを特徴とする低温
靭性に優れた耐サワー鋼板の製造方法である。SUMMARY OF THE INVENTION The gist of the present invention is the weight%
C: 0.12% or less, Si: 0.6% or less, Mn:
0.6 to 1.5%, P: 0.015% or less, Al: 0.
01 to 0.10%, Ti: 0.005 to 0.030%,
Nb: 0.01 to 0.10%, Ni: 0.1 to 0.5
%, Cu: 0.1 to 0.5%, V: 0.01 to 0.10.
% As a basic component, the content of S, O, Ca is S: 0.0
03% or less, O: 0.005% or less, Ca: 0.006
% Or less and the following equations (1) and (2) 0.7 ≦ ICP ≦ 1.5 ………………………………………… (1) ICP = [Ca] / 1 .25 [S] +0.625 [O] ............................................................................... Is heated to a temperature of 1000 to 1250 ° C., rolling is started after extraction, the rolling is temporarily stopped when the surface temperature is 900 ° C. or more, and then the surface temperature is 70 at a cooling rate of 5 to 40 ° C./sec.
After cooling to 0 ° C or lower, the surface temperature is Ac ₃ or lower, and the plate thickness center temperature is left to be 950 ° C or lower,
Then, a rolling reduction with a cumulative rolling reduction of 60% or more and an average rolling true strain per pass of 0.2 or less was added, and the rolling was terminated when the sheet thickness average temperature was Ar ₃ or more, and immediately 5 to 40
It is a method for producing a sour-resistant steel sheet having excellent low temperature toughness, which comprises cooling at a cooling rate of ° C / sec until the sheet thickness average temperature reaches 350 to 550 ° C, and then performing air cooling.

【００１４】以下、本発明について詳細に説明する。ま
ず、Ａｒ₃ 以上の高温圧延において厚手材の低温靭性の
向上を図る技術思想について述べる。The present invention will be described in detail below. First, a technical idea for improving the low temperature toughness of a thick material in high temperature rolling of Ar ₃ or more will be described.

【００１５】一般に高温からの冷却による降温過程で生
じる変態温度域と、低温からの加熱による昇温過程で生
じる変態温度域との間には１００℃から２００℃程度の
温度差があり、昇温過程で生じる変態温度域の方が高
い。Generally, there is a temperature difference of about 100 ° C. to 200 ° C. between the transformation temperature range generated in the temperature lowering process by cooling from high temperature and the transformation temperature region generated in the temperature rising process by heating from low temperature. The transformation temperature range that occurs during the process is higher.

【００１６】そのため本発明の場合のように図１に示す
ごとく厚鋼板を適切な温度域まで一度冷却した後に復熱
させる過程においては、板厚表層部は昇温中にフェライ
トからオーステナイトへ変態し、板厚中心部はいまだに
フェライト変態が開始せずに、オーステナイト一相の状
態である。Therefore, as in the case of the present invention, in the process of cooling the thick steel plate once to an appropriate temperature range and then reheating it as shown in FIG. 1, the surface portion of the plate thickness transforms from ferrite to austenite during the temperature rise. The central part of the plate thickness is still in the austenite one phase state without the ferrite transformation starting yet.

【００１７】そのため復熱がある程度進行して両者の温
度差が小さくなった時点でも、板厚表層部ではフェライ
ト主体の金属組織を有し、板厚中心部ではオーステナイ
ト主体の金属組織を有するため、両者の間には大きな変
形抵抗差が生じ、板厚表層部の変形抵抗の方が極めて大
きい。Therefore, even when the recuperating heat progresses to some extent and the temperature difference between the two becomes small, the surface layer part of the plate thickness has a metal structure mainly composed of ferrite, and the center part of the plate thickness has a metal structure mainly composed of austenite. A large difference in deformation resistance occurs between the two, and the deformation resistance in the surface layer portion of the plate thickness is extremely large.

【００１８】これは図２に示すように、フェライト主体
の金属組織とオーステナイト主体の金属組織とではその
応力−歪関係が異なり、圧延真歪で０．２以下の範囲で
はフェライト主体の金属組織の方が同じ歪を与えた場合
の変形抵抗が大きいためである。As shown in FIG. 2, the stress-strain relationship is different between the metal structure mainly composed of ferrite and the metal structure mainly composed of austenite, and the metal structure mainly composed of ferrite is present in the rolling true strain range of 0.2 or less. This is because the deformation resistance is larger when the same strain is applied.

【００１９】本発明ではこの板厚方向の変形抵抗差を利
用した板厚中心部の強圧下により、高温圧延における厚
手材の低温靭性の向上を図る。In the present invention, the low temperature toughness of the thick material in the high temperature rolling is improved by the strong reduction of the central portion of the thickness utilizing the difference in deformation resistance in the thickness direction.

【００２０】次に加熱、圧延、冷却条件について説明す
る。本発明においては鋳造後冷片にすることなく鋳片を
直接圧延してもよいし、また鋳造後冷片としたものを再
加熱して用いてもよい。加熱温度は１０００〜１２５０
℃の範囲である。Next, heating, rolling and cooling conditions will be described. In the present invention, the cast pieces may be directly rolled without forming the cold pieces after casting, or the cold pieces after casting may be reheated and used. Heating temperature is 1000-1250
It is in the range of ° C.

【００２１】これは母材の強度、低温靭性を確保するた
めに必要である。加熱温度が１０００℃未満になると、
Ｎｂ，Ｖ，Ｔｉ等の固溶が不十分となり、良好な強度、
低温靭性が確保できない。しかし再加熱温度が１２５０
℃超になると、オーステナイト（γ）粒が粗大化、圧延
後の結晶粒も大きくなって低温靭性が劣化する。したが
って適切な再加熱温度は１０００〜１２５０℃である。This is necessary to secure the strength and low temperature toughness of the base material. When the heating temperature is less than 1000 ° C,
The solid solution of Nb, V, Ti, etc. becomes insufficient, resulting in good strength,
Low temperature toughness cannot be secured. However, the reheating temperature is 1250
If the temperature exceeds ℃, the austenite (γ) grains become coarse and the crystal grains after rolling become large, and the low temperature toughness deteriorates. Therefore, a suitable reheating temperature is 1000 to 1250 ° C.

【００２２】加熱後、圧延を行ない表面温度が９００℃
以上で圧延を一旦中断し、５〜４０℃／秒の冷却速度で
表面温度が７００℃以下まで冷却する必要がある。After heating, rolling is performed and the surface temperature is 900 ° C.
As described above, it is necessary to suspend rolling once and cool the surface temperature to 700 ° C. or lower at a cooling rate of 5 to 40 ° C./sec.

【００２３】粗圧延を必要とするのは、オーステナイト
再結晶温度域での圧延によって、組織の細粒化、均一化
を図るためである。The reason why the rough rolling is required is to make the structure finer and more uniform by rolling in the austenite recrystallization temperature range.

【００２４】スラブの表面温度が９００℃未満から冷却
すると、鋼板中心部の温度も低下するために、圧延終了
時に板厚平均温度をＡｒ₃ 以上に確保するのが困難とな
る。冷却により到達する温度域を表面温度で７００℃以
下とした理由は、７００℃を超える温度では板厚中心部
の温度が復熱過程で未再結晶温度域まで下がらないため
である。When the surface temperature of the slab is cooled from less than 900 ° C., the temperature of the central portion of the steel plate is also lowered, so that it becomes difficult to secure the plate thickness average temperature at Ar ₃ or higher at the end of rolling. The reason why the temperature range reached by cooling is 700 ° C. or less in surface temperature is that the temperature at the center of the plate thickness does not drop to the non-recrystallized temperature range in the recuperation process at a temperature exceeding 700 ° C.

【００２５】冷却速度が小さ過ぎると板厚表層部でαへ
変態する部分の割合が小さくなり過ぎて、板厚中心部を
強圧下できなくなるため、冷却速度の下限は５℃／秒と
した。冷却速度が大き過ぎると板厚平均温度が低下し過
ぎて、圧延終了時に板厚平均温度をＡｒ₃ 以上に確保で
きなくなるため、上限を４０℃／秒とした。If the cooling rate is too low, the ratio of the portion transformed to α in the surface layer of the sheet thickness becomes too small, and the central portion of the sheet thickness cannot be strongly pressed. Therefore, the lower limit of the cooling rate was set to 5 ° C./sec. If the cooling rate is too high, the sheet thickness average temperature will be too low, and it will not be possible to secure the sheet thickness average temperature above Ar ₃ at the end of rolling. Therefore, the upper limit was set to 40 ° C / sec.

【００２６】冷却後、表面温度がＡｃ₃ 以下、板厚中心
部温度が９５０℃以下の温度域になるまで放置し、その
後累積圧下率で６０％以上でかつ平均の１パスあたりの
圧延真歪が０．２以下となるような圧下を加えなければ
ならない。After cooling, the plate was left to stand until the surface temperature was Ac ₃ or less and the plate thickness center temperature was 950 ° C. or less, and then the rolling reduction was 60% or more in cumulative reduction and the average rolling true strain per pass. Must be applied so that the value becomes 0.2 or less.

【００２７】冷却後の圧延開始時の表面温度がＡｃ₃ 以
下である理由は、Ａｃ₃ を超えてしまうと板厚表層部の
αがγへ逆変態してしまい、本発明の基本思想であるα
とγの変形抵抗差の利用が不可能となるからである。The reason the surface temperature at the start of rolling after cooling is Ac ₃ or less, when exceeds the Ac ₃ alpha of sheet thickness surface layer portion ends up reverse transformation to gamma, is the basic idea of the present invention α
This is because it is impossible to use the deformation resistance difference between γ and γ.

【００２８】また冷却終了後板厚中心部の温度が９５０
℃以下の温度域に低下するまで放置する理由は、板厚中
心部の温度をオーステナイトの未再結晶温度域に低下さ
せた後圧下を加えるためである。After cooling, the temperature at the center of the plate thickness is 950.
The reason for leaving until the temperature falls to a temperature range of ℃ or less is to reduce the temperature of the central portion of the plate thickness to the austenite unrecrystallized temperature range and then apply reduction.

【００２９】冷却後の圧延の累積圧下率を６０％以上と
する理由は、６０％未満では板厚表層部（α）と板厚中
心部（γ）の変形抵抗差による強圧下の効果は小さく、
板厚中心部へ導入される加工歪量が少ないためである。The reason for setting the cumulative rolling reduction after cooling to 60% or more is that if it is less than 60%, the effect of strong reduction due to the difference in deformation resistance between the sheet thickness surface layer portion (α) and the sheet thickness center portion (γ) is small. ,
This is because the amount of processing strain introduced into the center of the plate thickness is small.

【００３０】また平均の１パスあたりの圧延真歪を０．
２以下に制限した理由は、圧延真歪が０．２超となると
板厚中心部と板厚表層部の変形抵抗の大きさが逆転して
しまうためであり、これについては図２に示したとおり
である。Further, the true rolling true strain per pass is 0.
The reason why it is limited to 2 or less is that when the rolling true strain exceeds 0.2, the magnitudes of the deformation resistances of the central portion of the sheet thickness and the surface layer portion of the sheet thickness are reversed, which is shown in FIG. It is as follows.

【００３１】冷却後の圧延は板厚平均温度がＡｒ₃ 以上
で終了し、その後直ちに５〜４０℃／秒の冷却速度で板
厚平均温度が３５０〜５５０℃となるまで加速冷却し、
その後空冷する。After cooling, the rolling ends at a plate thickness average temperature of Ar ₃ or more, and immediately thereafter, accelerated cooling is performed at a cooling rate of 5 to 40 ° C./sec until the plate thickness average temperature reaches 350 to 550 ° C.
Then air cool.

【００３２】板厚平均の圧延終了温度をＡｒ₃ 以上とす
る理由は、Ａｒ₃ 未満ではＭｎＳ系介在物が残存した
場合に延伸しやすい、Ｍｎ等の偏析により周囲よりも
Ａｒ₃ が低下している中心偏析部へ、その周囲のγ→α
変態に伴なうＣの濃縮が起り中心偏析部に硬化組織が形
成される等により耐サワー性を劣化させるからである。The reason for setting the rolling end temperature of the plate thickness average to be Ar ₃ or higher is that if it is less than Ar ₃ , it tends to be stretched when MnS inclusions remain, and segregation of Mn causes Ar ₃ to fall below the surroundings. Γ → α around the center segregation part
This is because the sour resistance is deteriorated due to the concentration of C that accompanies the transformation and the formation of a hardened structure in the center segregated portion.

【００３３】圧延終了後の加速冷却及び空冷は、耐サワ
ー性と良好な強度、靭性を確保するために行なう。加速
冷却において、５℃／秒以下の冷却速度あるいは５５０
℃を超える冷却停止温度ではγ→α変態に伴なう中心偏
析部へのＣ濃縮やパーライトの生成により硬化組織が形
成されるために耐サワー性が劣化する。Accelerated cooling and air cooling after the completion of rolling are performed to ensure sour resistance and good strength and toughness. In accelerated cooling, cooling rate of 5 ° C / sec or less or 550
When the cooling stop temperature is higher than 0 ° C, the sour resistance deteriorates because a hardened structure is formed due to C concentration in the central segregation portion and the formation of pearlite accompanying the γ → α transformation.

【００３４】４０℃／秒以上の冷却速度あるいは３５０
℃未満の冷却停止温度では焼きの入りが大きくマルテン
サイト等の硬化組織が形成されるために耐サワー性が劣
化する。加速冷却後の空冷では焼戻し処理と同等の効果
が得られ、良好な強度、靭性を確保できる。Cooling rate of 40 ° C./sec or more or 350
If the cooling stop temperature is lower than ℃, quenching is large and a hardened structure such as martensite is formed, so that the sour resistance is deteriorated. Air-cooling after accelerated cooling has the same effect as tempering treatment, and can secure good strength and toughness.

【００３５】次に各成分の限定理由について説明する。
Ｃの上限を０．１２％としたのは母材及び溶接部の強度
確保のためであるが、０．１２％を超えると制御冷却し
た場合島状マルテンサイトが生成し、延靭性に悪影響を
及ぼすばかりでなく、内質、溶接性及びＨＡＺ靭性も劣
化させるため上限を０．１２％とした。なお、Ｃは０．
０３％未満であれば中心偏析部を非常に改善することか
ら０．０３％未満が好ましい。Next, the reasons for limiting each component will be described.
The upper limit of C is set to 0.12% in order to secure the strength of the base metal and the welded portion, but if it exceeds 0.12%, island martensite is generated when controlled cooling, which adversely affects ductility. The upper limit was set to 0.12% because it not only adversely affects the internal quality, weldability and HAZ toughness. C is 0.
If it is less than 03%, the central segregation portion is greatly improved, so less than 0.03% is preferable.

【００３６】Ｓｉは脱酸上鋼に必然的に含まれる元素で
あるが、溶接性及びＨＡＺ部靭性を劣化させるため上限
を０．６％とした（鋼の脱酸はＡｌだけでも可能であり
好ましくは０．２％以下が望ましい）。Si is an element necessarily contained in the deoxidized upper steel, but its upper limit is set to 0.6% in order to deteriorate the weldability and the toughness of the HAZ part (the deoxidation of the steel is possible only with Al. It is preferably 0.2% or less).

【００３７】Ｍｎは強度、靭性を同時に向上せしめる極
めて重要な元素である。Ｍｎが０．６％未満では低Ｃで
あるため強度が確保できず、靭性改善効果も少ないため
下限を０．６％とした。Mn is an extremely important element that simultaneously improves strength and toughness. When Mn is less than 0.6%, the strength cannot be ensured because of low C and the effect of improving toughness is small, so the lower limit was made 0.6%.

【００３８】しかしＭｎが多過ぎて焼入性が増加する
と、マルテンサイトが多量に生成し易くなると共に、中
心偏析が著しくなり、ＨＩＣ伝播停止能力が低下する。
また、母材及びＨＡＺの靭性を劣化させるため、その上
限を１．５％とした。However, if the Mn content is too large and the hardenability increases, a large amount of martensite is likely to be formed, the center segregation becomes remarkable, and the HIC propagation stopping ability decreases.
Moreover, in order to deteriorate the toughness of the base material and HAZ, the upper limit was made 1.5%.

【００３９】Ｐについては、中心偏析を助長する元素で
あるから上限を０．０１５％以下とした。The upper limit of P is 0.015% or less because it is an element that promotes center segregation.

【００４０】Ａｌは脱酸上この種のキルド鋼に必然的に
含有される元素であるが、Ａｌ０．０１％未満では脱酸
が不十分となり、母材靭性が劣化するため下限を０．０
１％とした。Al is an element that is inevitably contained in this type of killed steel for deoxidation, but if Al is less than 0.01%, deoxidation becomes insufficient and the base metal toughness deteriorates, so the lower limit is 0.0.
It was set to 1%.

【００４１】一方Ａｌが０．１０％を超えるとクラスタ
ー状の酸化物系介在物が増加し、ＨＩＣに悪影響を及ぼ
すと共に、ＨＡＺ靭性が劣化するため上限を０．１０％
にした。On the other hand, if Al exceeds 0.10%, cluster-shaped oxide inclusions increase, which adversely affects HIC and deteriorates HAZ toughness, so the upper limit is 0.10%.
I chose

【００４２】Ｔｉは添加量が少ない範囲（Ｔｉ０．００
５〜０．０３０％）では微細なＴｉＮを形成し、圧延組
織及びＨＡＺの細粒化、つまり靭性向上に効果的であ
る。またＴｉ，Ｃａの相乗効果によりＨＩＣの発生原因
であるＭｎＳを球状化する効果もある。Ti is added in a small amount (Ti0.00
5 to 0.030%) forms fine TiN, and is effective for making the rolling structure and HAZ finer, that is, improving the toughness. Further, due to the synergistic effect of Ti and Ca, there is also an effect of spheroidizing MnS, which is a cause of HIC.

【００４３】したがってＴｉ添加量の下限は材質上の効
果が発揮される最少量であり、上限は微細なＴｉＮが鋼
片中に通常の製造法で得られ、またＴｉＣによる靭性劣
化が起きない条件から０．０３０％とした。Therefore, the lower limit of the amount of Ti added is the minimum amount at which the material effect is exerted, and the upper limit is the condition that fine TiN can be obtained in a steel slab by an ordinary manufacturing method and the toughness deterioration due to TiC does not occur. To 0.030%.

【００４４】Ｎｂは圧延組織の細粒化、焼入性の向上と
析出硬化のため含有させるもので強度、靭性を共に向上
させる重要な元素であり、０．０１％以下では実質的に
効果がないため、下限を０．０１％とした。Nb is an important element for improving both strength and toughness because it is contained for the purpose of grain refinement of the rolling structure, improvement of hardenability, and precipitation hardening. Therefore, the lower limit was made 0.01%.

【００４５】制御冷却材では０．１０％を超えて添加し
ても材質上効果なく、また溶接性及びＨＡＺ靭性に有害
であるため上限を０．１０％に限定した。In the case of the controlled cooling material, even if added in excess of 0.10%, there is no material effect and it is harmful to the weldability and HAZ toughness, so the upper limit was limited to 0.10%.

【００４６】Ｎｉは耐食性、耐ＨＩＣ特性等に効果的な
元素であり、しかも母材の強度、靭性を向上させる。し
かし、０．１％未満ではこの効果は小さいため下限を
０．１％とした。０．５％を超えると耐ＳＳＣ性及びＨ
ＡＺの硬化性、靭性に好ましくないため上限を０．５％
とした。Ni is an element effective in corrosion resistance, HIC resistance and the like, and further improves the strength and toughness of the base material. However, if less than 0.1%, this effect is small, so the lower limit was made 0.1%. If it exceeds 0.5%, SSC resistance and H
The upper limit is 0.5% because it is not favorable for the hardenability and toughness of AZ.
And

【００４７】ＣｕはＮｉとほぼ同様の効果と共に耐食
性、耐水素誘起割れ性等にも効果があり０．１％未満で
はこの効果は小さいため下限を０．１％とした。過剰な
添加は熱間圧延時にＣｕ−クラックが発生し製造困難と
なる。このため上限を０．５％とした。Cu has an effect similar to that of Ni, as well as an effect on corrosion resistance, hydrogen-induced cracking resistance, etc. If less than 0.1%, this effect is small, so the lower limit was made 0.1%. Excessive addition causes Cu-cracks during hot rolling, which makes manufacturing difficult. Therefore, the upper limit is set to 0.5%.

【００４８】ＶはＮｂと同様析出硬化に寄与するもので
あるが、Ｎｂに比べて母材強度の強化代は小さいため
０．０１％未満では効果が少なく、上限は０．１０％ま
で許容できる。またＶはＨＡＺ硬さをほとんど変化させ
ないためＮｂとの複合添加が望ましい。V, like Nb, contributes to precipitation hardening, but since the strengthening margin of the base metal strength is smaller than that of Nb, the effect is small at less than 0.01% and the upper limit is 0.10%. . Further, V hardly changes the HAZ hardness, so that it is desirable to add it in combination with Nb.

【００４９】本発明鋼において不純物であるＳを０．０
０３％以下、Ｏを０．００５％以下、Ｃａを０．００６
％以下に限定し、更にこの３成分の関係が０．７≦〔Ｃ
ａ〕／１．２５〔Ｓ〕＋０．６２５〔Ｏ〕≦１．５の条
件を満足するように規定した。In the steel of the present invention, the impurity S is 0.0
03% or less, O 0.005% or less, Ca 0.006
% Or less, and the relationship of these three components is 0.7 ≦ [C
a] /1.25 [S] +0.625 [O] ≦ 1.5 is defined as being satisfied.

【００５０】この主なる理由は、ＨＩＣの発生主因であ
るＭｎＳの球状化と主に低ｐＨ域でＨＩＣの起点となる
クラスター状の酸化物系介在物の減少にある。The main reason for this is the spheroidization of MnS, which is the main cause of HIC generation, and the reduction of cluster-like oxide inclusions, which are the starting point of HIC mainly in the low pH range.

【００５１】この対策として鋼中のＳ量、即ち、ＭｎＳ
の絶対量を減少させ、更にＣａ添加によりＭｎＳを形態
制御すると共に、Ｏ量即ちＡｌ₂ Ｏ₃ の絶対量を減少さ
せ、Ｃａ添加によりクラスター状の酸化物であるＡｌ₂
Ｏ₃ を還元させ、球状のＣａＯ・Ａｌ₂ Ｏ₃ に転化させ
る。As a countermeasure against this, the amount of S in steel, that is, MnS
The absolute amount reduces, the further morphology control of MnS by addition of Ca decreases the absolute amount of O amount, or Al ₂ O _3, Al ₂ is a cluster-like oxides upon addition of Ca
O ₃ is reduced and converted into spherical CaO · Al ₂ O ₃ .

【００５２】このための条件を鋭意検討した結果、本発
明者らは、Ｓを０．００３％以下と少なくした上で、
〔Ｃａ〕／１．２５〔Ｓ〕＋０．６２５〔Ｏ〕を０．７
以上にすることにより、伸長介在物ＭｎＳを極端に減少
させることが可能である。同様に〔Ｃａ〕／１．２５
〔Ｓ〕＋０．６２５〔Ｏ〕を１．５以下に抑えることに
よりクラスター状の酸化物系介在物の発生量を最少に抑
えることが可能であり、耐ＨＩＣに顕著な効果が認めら
れることを見出した。As a result of diligent examination of the conditions for this, the present inventors reduced S to 0.003% or less, and
[Ca] /1.25 [S] +0.625 [O] 0.7
By the above, it is possible to extremely reduce the elongation inclusion MnS. Similarly [Ca] /1.25
By suppressing [S] +0.625 [O] to 1.5 or less, it is possible to minimize the amount of cluster-like oxide-based inclusions generated, and it is confirmed that HIC resistance is significantly effective. I found it.

【００５３】このためＳの上限を０．００３％とし、
〔Ｃａ〕／１．２５〔Ｓ〕＋０．６２５〔Ｏ〕の上限を
１．５、下限を０．７とした。またＳは低い程改善効果
が大きく、０．００１％以下にすることにより飛躍的に
向上する。Therefore, the upper limit of S is set to 0.003%,
The upper limit of [Ca] /1.25 [S] +0.625 [O] was set to 1.5 and the lower limit was set to 0.7. Further, the lower the S is, the greater the improvement effect is, and when it is 0.001% or less, it is dramatically improved.

【００５４】なお、圧延後の鋼板を靭性改善、脱水素等
の目的でＡｃ₁ 以下の温度に再加熱（焼戻し処理）する
ことは何ら本発明の特徴を損なうものではない。Reheating (tempering) the rolled steel sheet to a temperature of Ac ₁ or lower for the purpose of improving toughness, dehydrogenation, etc. does not impair the characteristics of the present invention.

【００５５】[0055]

【実施例】転炉−連鋳工程で製造した表１の化学成分の
鋼を用い、表２のごとく加熱、圧延、冷却の条件を変え
て、板厚２５〜４０mmの鋼板を製造した。表３には機械
的性質、及び耐ＨＩＣ特性、耐ＳＳＣ特性を示す。EXAMPLES Steels having a chemical composition shown in Table 1 produced in a converter-continuous casting process were used, and steel sheets having a thickness of 25 to 40 mm were produced by changing heating, rolling and cooling conditions as shown in Table 2. Table 3 shows mechanical properties, HIC resistance, and SSC resistance.

【００５６】ＨＩＣ試験は鋼板より表裏面１mm切削した
厚さで、幅２０mm、長さ１００mmの試験片を用い、また
ＳＳＣ試験は厚さ３mm、幅１０mm、長さ１１５mmの試験
片を用いて行なった。The HIC test was carried out using a test piece having a thickness of 1 mm cut from the front and back sides of a steel plate and having a width of 20 mm and a length of 100 mm, and the SSC test was carried out using a test piece having a thickness of 3 mm, a width of 10 mm and a length of 115 mm. It was

【００５７】試験条件としてはＨＩＣ試験は外部応力を
負荷せずに行ない、ＳＳＣ試験は４点曲げ治具により降
伏応力に相当するたわみを試験片に負荷した。As the test conditions, the HIC test was carried out without applying external stress, and the SSC test was carried out by applying a flexure corresponding to the yield stress to the test piece by a 4-point bending jig.

【００５８】浸漬条件としては２５℃のＨ₂ Ｓ飽和で
０．５％ＣＨ₃ ＣＯＯＨ−５％ＮａＣｌ水溶液（ｐＨ約
３）中に、ＨＩＣ試験片は４日間、ＳＳＣ試験片は２１
日間浸漬した。浸漬結果を表２に示す。ＤＷＴＴは板厚
を１９．１mmに減厚して試験を行なった。As the immersion conditions, HIC test pieces were immersed in a 0.5% CH ₃ COOH-5% NaCl aqueous solution (pH about 3) at 25 ° C. for H ₂ S saturation for 4 days, and SSC test pieces were taken for 21 days.
Soaked for a day. The immersion results are shown in Table 2. The DWTT was tested by reducing the plate thickness to 19.1 mm.

【００５９】[0059]

【表１】 [Table 1]

【００６０】[0060]

【表２】 [Table 2]

【００６１】[0061]

【表３】 [Table 3]

【００６２】[0062]

【表４】 [Table 4]

【００６３】比較鋼中、鋼１１は圧延途中に冷却を行な
わない従来方法であり、本発明鋼に比べて低温靭性が劣
る。鋼１２は加熱温度が高いために、低温靭性が劣化す
る。鋼１３は逆に加熱温度が低いために、強度、低温靭
性が劣化する。鋼１４は仕上圧延における累積圧下率が
低いために低温靭性が劣化する。Among the comparative steels, Steel 11 is a conventional method in which cooling is not performed during rolling, and its low temperature toughness is inferior to that of the steels of the present invention. Since the heating temperature of steel 12 is high, the low temperature toughness deteriorates. On the contrary, since the steel 13 has a low heating temperature, its strength and low temperature toughness deteriorate. Steel 14 has a low low-temperature toughness because of a low cumulative rolling reduction in finish rolling.

【００６４】鋼１５は圧延途中冷却の冷却開始表面温度
が低いために、圧延終了温度がＡｒ₃ 以下となり、耐サ
ワー特性が劣化する。鋼１６は圧延途中冷却の冷却速度
が小さいために、仕上圧延での変形抵抗差による強圧下
効果が小さく、低温靭性が劣化する。鋼１７は逆に冷却
速度が大きいために圧延終了温度がＡｒ₃ 以下となり、
耐サワー特性が劣化する。Since the steel 15 has a low cooling start surface temperature during cooling during rolling, the rolling end temperature becomes Ar ₃ or less and the sour resistance is deteriorated. Steel 16 has a low cooling rate during cooling in the middle of rolling, so the effect of strong reduction due to the difference in deformation resistance during finish rolling is small, and the low temperature toughness deteriorates. On the other hand, Steel 17 has a high cooling rate, so the rolling end temperature is below Ar ₃
The sour resistance is deteriorated.

【００６５】鋼１８は圧延途中冷却の冷却停止表面温度
が高いために仕上圧延開始時の板厚中心部温度がγ未再
結晶温度域まで下がらず、鋼１９は仕上圧延開始表面温
度が高いために強圧下効果が小さく、鋼２０は仕上圧延
での各パス平均圧延真歪が大きいために、強圧下効果が
効かず、低温靭性が劣化する。Since Steel 18 has a high cooling stop surface temperature during cooling during rolling, the temperature at the center of the plate thickness at the start of finish rolling does not fall to the γ unrecrystallized temperature range, and Steel 19 has a high finish rolling start surface temperature. In addition, since the strong rolling-down effect is small, and the steel 20 has a large average rolling true strain in each pass in finish rolling, the strong rolling-down effect is not effective and the low temperature toughness is deteriorated.

【００６６】鋼２１は圧延終了後の加速冷却の冷却速度
が小さいために、鋼２２は逆に冷却速度が大きいため
に、鋼２３は加速冷却停止温度が高いために、鋼２４は
逆に冷却停止温度が低いために耐サワー特性が劣化す
る。Steel 21 has a low cooling rate for accelerated cooling after the completion of rolling, steel 22 has a high cooling rate, and steel 23 has a high accelerated cooling stop temperature, and steel 24 has a reverse cooling rate. Since the stop temperature is low, the sour resistance is deteriorated.

【００６７】鋼２５はＭｎが高いために、鋼２６はＰが
高いために耐サワー特性が劣化する。鋼２７はＮｂが低
いために低温靭性が劣化する。鋼２８はＩＣＰが高いた
めに、鋼２９は逆にＩＣＰが低いために耐サワー特性が
劣化する。Since the steel 25 has a high Mn and the steel 26 has a high P, the sour resistance is deteriorated. Steel 27 has a low Nb, and therefore its low temperature toughness deteriorates. Steel 28 has a high ICP, and steel 29 has a low ICP, which deteriorates the sour resistance.

【００６８】[0068]

【発明の効果】本発明により、低温靭性に優れた耐サワ
ー鋼板を大量かつ安価に製造することが可能になった。
その結果、耐サワー鋼管を主とするサワー環境用鉄鋼構
造物の安全性を大きく向上させることができた。Industrial Applicability According to the present invention, it becomes possible to mass-produce inexpensive sour-resistant steel sheets excellent in low temperature toughness at low cost.
As a result, it was possible to greatly improve the safety of sour environment steel structures, which are mainly sour resistant steel pipes.

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

【図１】鋼板製造プロセスにおける鋼板表面と板厚中心
部の温度履歴模式図表である。FIG. 1 is a schematic diagram of temperature history of a steel plate surface and a plate thickness center portion in a steel plate manufacturing process.

【図２】αとγの組織の差による変形抵抗差を示す図表
である。FIG. 2 is a chart showing a difference in deformation resistance due to a difference in texture between α and γ.

Claims (1)

【特許請求の範囲】[Claims] 【請求項１】 重量％で Ｃ ：０．１２％以下、 Ｓｉ：０．６％以下、 Ｍｎ：０．６〜１．５％、 Ｐ ：０．０１５％以下、 Ａｌ：０．０１〜０．１０％、 Ｔｉ：０．００５〜０．０３０％、 Ｎｂ：０．０１〜０．１０％、 Ｎｉ：０．１〜０．５％、 Ｃｕ：０．１〜０．５％、 Ｖ ：０．０１〜０．１０％ を基本成分としてＳ，Ｏ，Ｃａの含有量が Ｓ ：０．００３％以下、 Ｏ ：０．００５％以下、 Ｃａ：０．００６％以下 であって、かつ次式（１），（２） ０．７≦ＩＣＰ≦１．５ ………………………………………（１） ＩＣＰ＝〔Ｃａ〕／１．２５〔Ｓ〕＋０．６２５〔Ｏ〕 ……………（２） を満足する成分を含有し、 残部がＦｅ及び不可避的不純物よりなる鋼を鋳造後冷片
にすることなく、あるいは冷片を１０００〜１２５０℃
の温度に加熱し、抽出後圧延を開始して表面温度が９０
０℃以上で圧延を一旦中断し、引続き５〜４０℃／秒の
冷却速度で表面温度が７００℃以下になるまで冷却した
後、表面温度がＡｃ₃ 以下、板厚中心部温度が９５０℃
以下になるまで放置し、しかる後に累積圧下率が６０％
以上でかつ平均の１パスあたりの圧延真歪が０．２以下
となる圧下を加え、板厚平均温度がＡｒ₃ 以上で圧延を
終了し、直ちに５〜４０℃／秒の冷却速度で板厚平均温
度が３５０〜５５０℃となるまで冷却し、その後空冷す
ることを特徴とする低温靭性に優れた耐サワー鋼板の製
造方法。1. By weight%, C: 0.12% or less, Si: 0.6% or less, Mn: 0.6 to 1.5%, P: 0.015% or less, Al: 0.01 to 0. 10%, Ti: 0.005 to 0.030%, Nb: 0.01 to 0.10%, Ni: 0.1 to 0.5%, Cu: 0.1 to 0.5%, V: 0.01 to 0.10% as a basic component, the content of S, O, Ca is S: 0.003% or less, O: 0.005% or less, Ca: 0.006% or less, and Formulas (1) and (2) 0.7 ≦ ICP ≦ 1.5 ………………………………………… (1) ICP = [Ca] /1.25 [S] +0.625 [O] ……………… Cold piece after casting of steel containing components satisfying (2), with the balance being Fe and unavoidable impurities
Or without cold pieces at 1000-1250 ° C
The temperature of the surface is 90
Rolling is temporarily interrupted at 0 ° C or higher, and then continued for 5 to 40 ° C / sec.
Cooled at a cooling rate until the surface temperature fell below 700 ° C.
After that, the surface temperature is Ac ₃ Below, the temperature at the center of the plate thickness is 950 ° C
Let it stand until it becomes below, and then the cumulative rolling reduction is 60%.
Above, and the average rolling true strain per pass is 0.2 or less
Is applied to reduce the average thickness of the plate to Ar. ₃ Roll over
Immediately after the completion, the plate thickness average temperature at a cooling rate of 5 to 40 ° C / sec
Cool to 350-550 ° C, then air cool
Of sour-resistant steel plate with excellent low temperature toughness
Build method.