JP2014101568A - HIGH TOUGHNESS HIGH CORROSION RESISTANCE Ni ALLOY CLAD STEEL SHEET EXCELLENT IN WELD ZONE TOUGHNESS AND PRODUCTION METHOD THEREOF - Google Patents
HIGH TOUGHNESS HIGH CORROSION RESISTANCE Ni ALLOY CLAD STEEL SHEET EXCELLENT IN WELD ZONE TOUGHNESS AND PRODUCTION METHOD THEREOF Download PDFInfo
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Abstract
Description
本発明は、溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板及びその製造方法に関するものである。 The present invention relates to a high toughness and corrosion resistant Ni alloy clad steel plate excellent in weld toughness and a method for producing the same.
近年、エネルギー問題から従来採掘が不可能であった難採掘環境と呼ばれる領域においてもエネルギー資源開発が進んでいる。このような環境は高温で硫化水素や炭酸ガスが多く存在しているため特に腐食環境も厳しく(以後、サワー環境と呼ぶ)、より耐食性に優れた材料の要求が高まっている。さらに難採掘環境下での、産業設備と構造物のニ−ズとしては耐久性及び長寿命化並びにメンテナンスフリ−化が指向されており、Alloy625、825に代表されるNi基合金またはNi合金は、これらニ−ズに適合した材料として注目を集めている。 In recent years, energy resource development has progressed also in an area called a difficult mining environment, where mining has been impossible due to energy problems. In such an environment, since there are a large amount of hydrogen sulfide and carbon dioxide at a high temperature, the corrosive environment is particularly severe (hereinafter referred to as a sour environment), and the demand for a material with higher corrosion resistance is increasing. Furthermore, as a need for industrial equipment and structures in difficult mining environments, durability, long life, and maintenance freeness are aimed at. Ni-based alloys or Ni alloys represented by Alloy 625 and 825 are These materials are attracting attention as materials that meet these needs.
一方で、Ni合金の主原料であるNiやMo、Crに代表される合金元素の価格は、時に高騰や大きな変動がある。そのため、無垢材(全厚が合わせ材の金属組成のような場合を云う)としての使用よりも高合金鋼の優れた耐食性能をより経済的に利用できるクラッド鋼が最近、注目されている。 On the other hand, the price of alloy elements represented by Ni, Mo, and Cr, which are the main raw materials for Ni alloys, sometimes rises and fluctuates. Therefore, recently, clad steel has attracted attention because it can more economically utilize the superior corrosion resistance of high alloy steel than use as a solid material (when the total thickness is like the metal composition of a laminated material).
Ni合金クラッド鋼とは、合わせ材にNi合金、母材に炭素鋼、低合金鋼等の普通鋼材と、二種類の性質の異なる金属を張り合わせた鋼材である。クラッド鋼は、異種金属を金属学的に接合させたもので、めっきとは異なり剥離する心配がなく単一金属及び合金では達し得ない新たな特性を持たせることができる。 The Ni alloy clad steel is a steel material in which two kinds of metals different from each other and a common steel material such as a Ni alloy and a base material such as carbon steel and low alloy steel are bonded together. The clad steel is obtained by metallographically bonding dissimilar metals, and unlike the plating, there is no fear of peeling, and it can have new characteristics that cannot be achieved by a single metal and alloy.
クラッド鋼は、使用環境毎の目的に合った機能を有する合わせ材を選択することにより無垢材と同等の機能を発揮させることができる。さらに、クラッド鋼の母材には、耐食性以外の高靭性、高強度といった厳しい環境に適した特性を有する炭素鋼・低合金鋼を適用することができる。 The clad steel can exhibit a function equivalent to that of a solid material by selecting a laminated material having a function suitable for the purpose of each use environment. Furthermore, carbon steel and low alloy steel having characteristics suitable for severe environments such as high toughness and high strength other than corrosion resistance can be applied to the base material of the clad steel.
このように、クラッド鋼は、無垢材よりも合金元素の使用量が少なく、かつ、無垢材と同等の耐食性能を確保でき、さらに炭素鋼・低合金鋼と同等の強度・靭性を確保できるため、経済性と機能性が両立できるという利点を有する。 In this way, clad steel uses less alloying elements than solid wood, and can ensure corrosion resistance equivalent to that of solid wood, as well as strength and toughness equivalent to carbon steel and low alloy steel. , It has the advantage that economics and functionality are compatible.
以上から、高合金の合わせ材を用いたクラッド鋼は非常に有益な機能性鋼材であると考えられており、近年そのニ−ズが各種産業分野で益々高まっている。 From the above, clad steel using a high alloy laminated material is considered to be a very useful functional steel material, and in recent years, its needs are increasing in various industrial fields.
クラッド鋼は、合わせ材によって用途が異なり、製造方法も異なる。クラッド鋼板の母材には、Nb、VまたはTi、B等の合金成分を微量添加した低炭素低合金鋼が用いられていることがあった。このような低炭素低合金鋼は所定の焼き入れ焼き戻し(以下、「調質」ということもある。)又は熱間圧延時の制御圧延・制御冷却等の加工熱処理技術(TMCP)により製造されている。 Clad steel has different uses depending on the laminated material, and its manufacturing method is also different. As a base material of a clad steel plate, a low carbon low alloy steel to which a small amount of an alloy component such as Nb, V or Ti, B is added has been used. Such low-carbon low-alloy steels are manufactured by predetermined heat treatment (TMCP) such as controlled tempering and controlled cooling during hot rolling (hereinafter also referred to as “tempering”). ing.
しかもクラッド鋼を造管しクラッド鋼管として製造する場合には、鋼板を成形してパイプ形状とし、パイプの表裏面からそれぞれに1パスの高能率溶接が施工される。 In addition, when the clad steel is produced and manufactured as a clad steel pipe, the steel plate is formed into a pipe shape, and one-pass high-efficiency welding is performed from the front and back surfaces of the pipe.
一般に、多層盛り溶接では被溶接鋼板(溶接用語では「母材」と呼ぶが、クラッド鋼板の母材と区別する必要がある場合には、以下「被溶接鋼板」または「母材(B.M.)」と記載する)及び溶接金属の境界、母材(B.M.)熱影響部(以下「HAZ」という)は次パスの熱影響で細粒化されるが、1パス溶接では母材(B.M.)と溶接金属の境界(以下「溶接ボンド部」という)やHAZの結晶粒は粗大化した状態となり、靭性の低下につながる。 Generally, in multi-layer welding, a steel plate to be welded (referred to as a “base material” in welding terms), but when it is necessary to distinguish from a base material of a clad steel plate, hereinafter, “steel to be welded” or “base material (BM .) ”) And the boundary of the weld metal, and the base metal (BM) heat affected zone (hereinafter referred to as“ HAZ ”) are refined by the heat effect of the next pass. The boundary between the material (BM) and the weld metal (hereinafter referred to as “weld bond part”) and the HAZ crystal grains become coarse, leading to a decrease in toughness.
そこで、例えば寒冷地(例えばロシア、カナダ、アラスカ等)のパイプラインの操業が緊急停止するときにはパイプの各部位が−40℃程度の低温の環境下に置かれるため母材(B.M.)及びHAZにおける−40℃でのシャルピー衝撃吸収エネルギー(vE−40℃)は、35(J)以上の仕様となりつつある。しかも母材(B.M.)においても脆性破壊停止温度を確認するためのDWTT試験:Drop Weight Tear Test(落重引き裂き試験)で、−20℃の試験で85%以上の延性破面の確保(85%SATT)等の仕様が要求されこともある。そのため、多くの検討が行われた。 Therefore, for example, when the operation of a pipeline in a cold district (for example, Russia, Canada, Alaska, etc.) is urgently stopped, each part of the pipe is placed in a low temperature environment of about -40 ° C., so that the base material (BM) And the Charpy impact absorption energy (vE-40 ° C.) at −40 ° C. in HAZ is becoming a specification of 35 (J) or more. Moreover, in the base material (BM), a DWTT test for confirming the brittle fracture stop temperature: In a drop weight tear test, a ductile fracture surface of 85% or more is secured in a test at −20 ° C. Specifications such as (85% SATT) may be required. Therefore, many studies have been conducted.
TiとNの添加量を適正化することで溶接部靱性の向上を図る技術が特許文献1及び2に開示されている。TiNは、主として鋼の凝固時に形成されることから、粗大な析出物となりやすい。そのため、生成したTiNが固溶しないで残存する場合は、溶融部に近い1200℃を超える高温に加熱されるHAZ領域において組織の粗大化が抑制されるというピンニング効果が認められる。しかし、1000℃付近に加熱されるHAZではTiNは、粗大なままでピンニング効果が少なく、その領域の組織の粗大化抑制が十分に達成されず、HAZ靭性が低下するという問題がある。 Patent Documents 1 and 2 disclose techniques for improving weld toughness by optimizing the addition amounts of Ti and N. Since TiN is mainly formed during the solidification of steel, it tends to be coarse precipitates. Therefore, when the produced TiN remains without being dissolved, a pinning effect is observed in that the coarsening of the structure is suppressed in the HAZ region heated to a high temperature exceeding 1200 ° C. close to the melting part. However, in HAZ heated to around 1000 ° C., TiN remains coarse and has a small pinning effect, and there is a problem that the coarsening suppression of the structure in that region is not sufficiently achieved and the HAZ toughness is lowered.
また、さらに溶接ボンド部近傍のように最高到達温度が1400℃を超え高温にさらされる場合では、TiNはほとんど固溶してしまう。このため、この溶接ボンド部に近い領域では、TiNのピンニング効果が得られず十分に靭性を確保できないという問題がある。 Further, when the maximum temperature reaches more than 1400 ° C. and is exposed to a high temperature as in the vicinity of the weld bond portion, TiN is almost dissolved. For this reason, in the region close to this weld bond portion, there is a problem that the pinning effect of TiN cannot be obtained and sufficient toughness cannot be ensured.
また、非特許文献1には上記特許文献1及び2に基づいて製造した例が開示されているが、TiNのピンニング効果が十分に得られない領域に関する記載は見あたらない。 Further, Non-Patent Document 1 discloses an example manufactured based on Patent Documents 1 and 2, but no description is given regarding a region where the pinning effect of TiN is not sufficiently obtained.
また、特許文献3〜5には、合わせ材としてNi合金の成分が検討されている。特許文献3では、母材の脆性破壊伝播停止特性を確保するために必要な条件である最終圧下直前の鋼板表面温度が875℃〜925℃以下でも安定してクラッド合わせ材の再結晶組織が得られる0.01%≦Ti+Nb≦0.2%とする技術が開示されている。特許文献4には、再結晶温度900℃未満、且つ、熱処理無しで、サワー環境での応力腐食割れ感受性を低減する目的でCを0.03%以下、Pを0.02%以下、また熱間加工性を低下させるため、Sを0.0050%以下とする技術が開示されている。特許文献5には、耐食性に悪影響を及ぼす炭化物の析出抑制のためCを0.03%以下、応力腐食割れ感受性を低減させるためPを0.03%以下、熱間加工性を低下させるため、Sを0.005%以下とする技術が開示されている。 In Patent Documents 3 to 5, a component of Ni alloy is studied as a laminated material. In Patent Document 3, a recrystallized structure of a clad laminated material can be obtained stably even when the steel sheet surface temperature immediately before the final reduction, which is a necessary condition for ensuring the brittle fracture propagation stopping characteristics of the base material, is 875 ° C. to 925 ° C. or less. The technology of 0.01% ≦ Ti + Nb ≦ 0.2% is disclosed. In Patent Document 4, C is 0.03% or less, P is 0.02% or less, and P is 0.02% or less for the purpose of reducing stress corrosion cracking susceptibility in a sour environment without a recrystallization temperature of less than 900 ° C. and without heat treatment. In order to reduce the inter-workability, a technique for setting S to 0.0050% or less is disclosed. In Patent Document 5, C is 0.03% or less for suppressing the precipitation of carbides adversely affecting the corrosion resistance, P is 0.03% or less for reducing stress corrosion cracking sensitivity, and hot workability is reduced. A technique for reducing S to 0.005% or less is disclosed.
しかしながら、特許文献3では、NbとTi量が0.2%以下の範囲であるため、NbCやTiCが十分に析出せず、Cr、Mo、Ni等を含有した炭化物が多く析出してしまい、その結果、耐粒界腐食性や耐孔食性ならびに耐応力腐食割れ性が劣る要因となる。また、特許文献4と5では、C、P、S量を制限しているが、接合性確保のために900℃以上の再結晶領域ならびに部分再結晶領域で圧延する際に、PとSは不純物として粒界部に特に偏析してしまい、腐食環境下に曝されると粒界が脱落してしまい、甚大な耐食性劣化が生じてしまうため、より含有量として低減させる必要がある。 However, in Patent Document 3, since the Nb and Ti amounts are in the range of 0.2% or less, NbC and TiC are not sufficiently precipitated, and a large amount of carbides containing Cr, Mo, Ni, etc. are precipitated. As a result, intergranular corrosion resistance, pitting corrosion resistance and stress corrosion cracking resistance are factors. In Patent Documents 4 and 5, the amounts of C, P, and S are limited. When rolling in a recrystallization region and a partial recrystallization region at 900 ° C. or higher to ensure bondability, P and S are In particular, segregation occurs at the grain boundary as an impurity, and when exposed to a corrosive environment, the grain boundary falls off, resulting in a significant deterioration in corrosion resistance. Therefore, it is necessary to further reduce the content.
なお、以下の説明で、「母材」とは、クラッド鋼板の使用状態において合わせ材以外の部分を「クラッド鋼板の母材」または単に「母材」と云い、クラッド鋼板の製造工程の初期工程で用いられる母材を「母材素材」のように必要に応じて適宜区別して用いることとする。 In the following description, the term “base material” refers to a part other than the laminated material in the state of use of the clad steel plate as “base material of the clad steel plate” or simply “base material”, and is an initial step of the production process of the clad steel plate. The base material used in the above is used by appropriately distinguishing it as necessary, such as “base material”.
本発明は、クラッド鋼の母材及び合わせ材の合金元素を規定し、溶接部靭性に優れた高靭性高耐食Ni合金クラッド鋼板及びその製造方法を提供することを目的とする。 An object of the present invention is to provide a high-toughness, high-corrosion-resistant Ni-clad steel sheet having excellent weld zone toughness, and a method for producing the same, by defining the base material of the clad steel and the alloy element of the laminated material.
発明者らは、かかる事情に鑑み、Ni合金クラッド鋼板の母材において、TiNだけではHAZ靭性向上が図られない点に留意し、析出物の挙動を明確化することでクラッド鋼の母材とHAZ靭性が共に向上できることを明らかにした。 In view of such circumstances, the inventors have noted that in a base material of a Ni alloy clad steel plate, it is not possible to improve HAZ toughness by using only TiN, and by clarifying the behavior of precipitates, It was clarified that both HAZ toughness can be improved.
具体的には、従来技術で強度調整のために添加が必須とされていたVは、900℃程度で鋼中に固溶し、焼入れ性が著しく高くなり、溶接後の冷却時にHAZ部が硬化し、HAZ靭性の劣化の原因となることを確認し、クラッド鋼の母材の成分設計の際、このVを添加しないこととした。さらに、1000℃近傍の温度域に加熱されるクラッド鋼の母材のHAZ靭性の低下を抑制するため、TiNとNbCの析出量と形態を最適化して加熱時のγ粒径の粗大化を抑制できるようにした。 Specifically, V, which had been required to be added for strength adjustment in the prior art, dissolved in steel at about 900 ° C., and the hardenability was remarkably increased, and the HAZ part was hardened during cooling after welding. Then, it was confirmed that this would cause deterioration of the HAZ toughness, and this V was not added when designing the component of the base material of the clad steel. Furthermore, in order to suppress the decrease in the HAZ toughness of the base material of the clad steel heated in the temperature range near 1000 ° C., the precipitation amount and form of TiN and NbC are optimized to suppress the coarsening of the γ grain size during heating. I was able to do it.
これにより、1パス溶接による熱影響部(HAZ)においても、優れた低温靭性のクラッド鋼板の母材が得られることを見出した。該母材の厚さは、好適には50mm以下である。本発明の製造方法において、合金元素の複合添加と調質処理により、1パス溶接後の溶接ボンド部、熱影響部、母材の低温靱性を確保し、さらに溶接部靭性に優れた高靭性クラッド鋼板の母材を提供することを可能とした。 As a result, it was found that a base material of a clad steel sheet having excellent low temperature toughness can be obtained even in a heat-affected zone (HAZ) by one-pass welding. The thickness of the base material is preferably 50 mm or less. In the manufacturing method of the present invention, a high-toughness clad that ensures low-temperature toughness of the weld bond portion, heat-affected zone, and base metal after one pass welding by composite addition of alloying elements and tempering treatment, and further has excellent weld zone toughness It was possible to provide a base material for a steel plate.
また、Ni合金クラッド鋼板の合わせ材において、耐食性元素のNi、Cr、Moの含有量のみではなく、実際のサワー環境で腐食の起点となる、炭化物や粒界に偏析する不純物の影響を調査し、C、P、S含有量を制御し、クラッド鋼板の接合性と耐食性の確保が可能な圧延と熱処理条件を限定することで、高耐食性を確保可能なことを明らかとした。なお、ここで言う高耐食性とは、耐粒界腐食性と耐孔食性と耐応力腐食割れ性を有することを意味する。 In addition, not only the contents of the corrosion-resistant elements Ni, Cr, and Mo, but also the influence of impurities segregating on carbides and grain boundaries, which are the starting points of corrosion in the actual sour environment, are investigated in the laminated materials of Ni alloy clad steel sheets. It has been clarified that high corrosion resistance can be secured by controlling the C, P, and S contents and limiting the rolling and heat treatment conditions capable of securing the bondability and corrosion resistance of the clad steel plate. In addition, the high corrosion resistance said here has having intergranular corrosion resistance, pitting corrosion resistance, and stress corrosion cracking resistance.
クラッド鋼板の製造時を考えると、圧延および熱処理の製造温度範囲内では、炭化物として、M6Cは約930℃、M23C6は約850℃、MCは約910℃にそれぞれ析出ノーズがあり、これらが析出することで耐食性が劣化する。なお、MはNi、Cr、Mo、Nb、Ti、Si、Al等の合金元素を意味する。実際の製造では、上記の析出ノーズの温度範囲にかかってしまうが、析出する炭化物量を低減することが耐食性を劣化させないためには重要であり、そのためにC含有量を極力抑えることが必要となる。また、接合性を考えると、圧延終了温度は鋼板表面温度で900℃以上が必要であるが、その温度範囲は合わせ材における再結晶と部分再結晶温度領域となる。その際に、粒界にはPとSといった不純物が偏析し、耐食性を劣化させることがわかったため、合わせ材の製造上可能な範囲でPとSの含有量を低く抑えることが重要である。 Considering the production time of the clad steel sheet, within the production temperature range of rolling and heat treatment, there are precipitation noses as carbides, M 6 C is about 930 ° C, M 23 C 6 is about 850 ° C, and MC is about 910 ° C. The corrosion resistance deteriorates due to the precipitation. Note that M means an alloy element such as Ni, Cr, Mo, Nb, Ti, Si, and Al. In actual production, it depends on the temperature range of the above-mentioned precipitation nose, but it is important to reduce the amount of precipitated carbide in order not to deteriorate the corrosion resistance, and therefore it is necessary to suppress the C content as much as possible. Become. Further, considering the bondability, the rolling end temperature needs to be 900 ° C. or higher at the steel sheet surface temperature, but the temperature range is a recrystallization and partial recrystallization temperature region in the laminated material. At that time, it has been found that impurities such as P and S are segregated at the grain boundaries and deteriorate the corrosion resistance. Therefore, it is important to keep the contents of P and S as low as possible in the production of the laminated material.
すなわち、上記課題を解決するため本発明の溶接部靱性に優れた高靭性高耐食Ni合金クラッド鋼板の発明及びその製造方法は、以下の通りである。 That is, the invention of the high toughness and corrosion-resistant Ni alloy clad steel plate excellent in weld toughness according to the present invention and the method for producing the same are as follows in order to solve the above problems.
[1]質量%で、C量が0.020%以下のNi合金を合わせ材とし、質量%で、C:0.030〜0.10%、Si:0.10〜0.30%、Mn:1.30〜1.80%、P:0.015%以下、S:0.003%以下、V:0.010%未満、Al:0.040%以下、N:0.0030〜0.010%を含有し、残部がFe及び不可避的不純物からなる鋼を母材としたことを特徴とする溶接部靱性に優れた高靱性高耐食性Ni合金クラッド鋼板。 [1] Ni alloy with a C content of 0.020% or less at a mass% is used as a combination material. C: 0.030 to 0.10%, Si: 0.10 to 0.30%, Mn : 1.30 to 1.80%, P: 0.015% or less, S: 0.003% or less, V: less than 0.010%, Al: 0.040% or less, N: 0.0030-0. A high-toughness, high-corrosion-resistant Ni alloy clad steel sheet excellent in weld toughness, characterized in that the base material is steel containing 010% and the balance being Fe and inevitable impurities.
[2]母材として、さらに、質量%で、Mo:0.05〜0.50%、Ni:0.01〜0.50%、Cr:0.01〜0.50%、Cu:0.01〜0.50%、Nb:0.010〜0.060%、Ti:0.005〜0.020%、Ca:0.0010〜0.0040%の中から選ばれる1種以上を含有することを特徴とする前記[1]に記載の溶接部靱性に優れた高靱性高耐食性Ni合金クラッド鋼板。 [2] Further, as a base material, in terms of mass%, Mo: 0.05 to 0.50%, Ni: 0.01 to 0.50%, Cr: 0.01 to 0.50%, Cu: 0.00. Contains one or more selected from 01 to 0.50%, Nb: 0.010 to 0.060%, Ti: 0.005 to 0.020%, Ca: 0.0010 to 0.0040% The high toughness and corrosion-resistant Ni alloy clad steel plate excellent in weld toughness according to [1] above.
[3]合わせ材として、さらに、質量%で、C:0.020以下、Si:0.50%以下、Mn:0.50%以下、P:0.010%以下、S:0.0010%以下、Cr:20.0%〜23.0%、Mo:8.0%〜10.0%、Fe:5.0%以下、Al:0.40%以下、Ti:0.40%以下を含有し、さらに、Nb+Taを3.15〜4.15%含有し、残部がNi及び不可避的不純物からなることを特徴とする前記[1]または[2]に記載の溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板。 [3] Further, as a laminated material, in mass%, C: 0.020 or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.010% or less, S: 0.0010% Hereinafter, Cr: 20.0% to 23.0%, Mo: 8.0% to 10.0%, Fe: 5.0% or less, Al: 0.40% or less, Ti: 0.40% or less Further, 3.15 to 4.15% of Nb + Ta is contained, and the balance is made of Ni and unavoidable impurities, and the weld joint toughness according to [1] or [2] is excellent. Tough, high corrosion resistance Ni alloy clad steel sheet.
[4]合わせ材として、さらに、C、PおよびSが下記式(1)を満たすことを特徴とする前記[3]に記載の溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板。
10×C+5×P+50×S≦0.25・・・・・(1)
ここで、元素記号は各元素の含有量(質量%)を表す。
[4] The high-toughness and corrosion-resistant Ni alloy clad steel plate excellent in weld toughness according to [3], wherein C, P and S further satisfy the following formula (1) as a laminated material.
10 × C + 5 × P + 50 × S ≦ 0.25 (1)
Here, the element symbol represents the content (% by mass) of each element.
[5]母材として、Tiを含有する場合は、さらに、TiおよびNが下記式(2)を満たすことを特徴とする前記[2]乃至[4]の何れかに記載の溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板。
Ti/N = 2.0〜3.5・・・・・(2)
ここで、元素記号は各元素の含有量(質量%)を表す。
[5] In the case where Ti is contained as a base material, Ti and N satisfy the following formula (2), and the weld joint toughness according to any one of the above [2] to [4] Excellent high toughness and corrosion resistant Ni alloy clad steel plate.
Ti / N = 2.0 to 3.5 (2)
Here, the element symbol represents the content (% by mass) of each element.
[6]母材として、Nbを含有する場合は、さらに、NbおよびCが下記式(3)を満たすことを特徴とする前記2]乃至[5]の何れかに記載の溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板。
Nb/C = 0.2〜2.0・・・・・(3)
ここで、元素記号は各元素の含有量(質量%)を表す。
[6] When Nb is contained as a base material, Nb and C satisfy the following formula (3), and the weld joint toughness according to any one of the above 2] to [5] is excellent. High toughness and corrosion resistant Ni alloy clad steel sheet.
Nb / C = 0.2-2.0 (3)
Here, the element symbol represents the content (% by mass) of each element.
[7]前記[1]乃至[6]の何れかに記載の成分組成を有する母材と合わせ材とからなるクラッド鋼の素材を用いて圧延後、850〜950℃に再加熱して焼入れし、その後、650℃未満で焼戻しを行うことを特徴とする溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板の製造方法。 [7] After rolling using a clad steel material composed of a base material having a component composition according to any one of [1] to [6] and a laminated material, the steel is reheated to 850 to 950 ° C. and quenched. Thereafter, tempering is performed at a temperature lower than 650 ° C., and a method for producing a high toughness and corrosion-resistant Ni alloy clad steel plate excellent in weld toughness.
[8]前記[1]乃至[6]の何れかに記載の成分組成を有する母材と合わせ材とからなるクラッド鋼の素材を用いて、1050〜1225℃の範囲に加熱し、圧下比を5以上とし、クラッド鋼板の表面温度で、900℃以上で圧延を終了後、850〜950℃に再加熱して焼入れし、その後、650℃未満で焼戻しを行うことを特徴とする溶接部靭性に優れた高靭性高耐食性Ni合金クラッド鋼板の製造方法。 [8] Using a clad steel material composed of a base material and a laminated material having the component composition according to any one of [1] to [6] above, the steel is heated to a range of 1050 to 1225 ° C., and a reduction ratio is set. 5 or more, after finishing rolling at 900 ° C. or higher at the surface temperature of the clad steel plate, reheating to 850 to 950 ° C. and quenching, and then tempering at less than 650 ° C. A method for producing an excellent high toughness and corrosion resistant Ni alloy clad steel sheet.
本発明によれば、母材のHAZ靭性の劣化原因のV含有量を極力低減し、Nb、Al、Ti、N等を適正量添加してクラッド鋼の母材の結晶粒を超微細化することにより、母材及び1パス溶接による熱影響部において、結晶粒度の粗大化を抑制して優れた低温靱性を得ることができる。また、合わせ材の耐食性劣化要因となるC、P、Sを適正量とすることで、高耐食のNi合金クラッド鋼を得ることができる。 According to the present invention, the V content that causes deterioration of the HAZ toughness of the base metal is reduced as much as possible, and an appropriate amount of Nb, Al, Ti, N, etc. is added to make the crystal grains of the base steel of the clad steel ultrafine. Thereby, in the base material and the heat-affected zone by 1-pass welding, it is possible to obtain excellent low-temperature toughness by suppressing the coarsening of the crystal grain size. In addition, by making C, P, and S, which are factors that deteriorate the corrosion resistance of the laminated material, into appropriate amounts, a highly corrosion-resistant Ni alloy clad steel can be obtained.
1.母材の成分組成について
以下、本発明における母材の成分組成を規定した理由を説明する。なお、成分%は、特に記載が無い限り全て質量%を意味する。
1. About the component composition of a base material Hereinafter, the reason which prescribed | regulated the component composition of the base material in this invention is demonstrated. In addition, all the component% means the mass% unless there is particular description.
C:0.030〜0.10%
Cは鋼の強度を向上させる有効な成分であり、0.030%未満であると一般溶接用鋼材としての強度が得られないため0.030%以上の含有を必要とする。しかし、0.10%を超える含有は母材ならびに熱影響部の靭性の劣化を招き、また、溶接性の観点からC量の低減が望ましいためC量は0.030〜0.10%の範囲とする。なお、溶接性及びHAZ靭性の観点から、好ましくは0.030〜0.08%の範囲とする。
C: 0.030 to 0.10%
C is an effective component for improving the strength of the steel, and if it is less than 0.030%, the strength as a general welding steel material cannot be obtained, so the content of 0.030% or more is required. However, if the content exceeds 0.10%, the toughness of the base metal and the heat-affected zone is deteriorated, and from the viewpoint of weldability, it is desirable to reduce the C content. And In addition, from the viewpoint of weldability and HAZ toughness, the range is preferably 0.030 to 0.08%.
Si:0.10〜0.30%
Siは製鋼時の脱酸のために添加され、また、母材の強度確保に必要な成分であるため0.10%以上の含有が必要である。一方、0.30%を超えて含有すると溶接熱影響部の靭性と溶接性の劣化を引き起こすため、Si量は0.10〜0.30%の範囲とする。なお、脱酸の効果及びHAZ靭性の観点から、好ましくは0.13〜0.20%の範囲である。
Si: 0.10 to 0.30%
Si is added for deoxidation at the time of steelmaking, and since it is a component necessary for ensuring the strength of the base material, it must contain 0.10% or more. On the other hand, if the content exceeds 0.30%, the toughness of the heat affected zone and the weldability are deteriorated, so the Si content is in the range of 0.10 to 0.30%. In addition, from the viewpoint of deoxidation effect and HAZ toughness, it is preferably in the range of 0.13 to 0.20%.
Mn:1.30〜1.80%
Mnは母材の強度及び靭性の確保に有効な成分として1.30%以上の含有が必要であるが、1.80%を超えて含有すると溶接部の靭性を劣化させ、溶接割れを助長するため、Mn量は1.30〜1.80%の範囲とする。なお、母材靭性およびHAZ靭性の観点から、好ましくは1.40〜1.70%の範囲である。
Mn: 1.30 to 1.80%
Mn needs to be contained in an amount of 1.30% or more as an effective component for securing the strength and toughness of the base material. However, if it exceeds 1.80%, the toughness of the welded portion is deteriorated and weld cracking is promoted. Therefore, the Mn content is set to 1.30 to 1.80%. In addition, from a viewpoint of base material toughness and HAZ toughness, it is preferably in the range of 1.40 to 1.70%.
P:0.015%以下
母材ならびに溶接熱影響部靭性を確保するため、Pを極力低減することが望ましいが、過度の脱Pはコスト上昇を招くためP量は0.015%以下とする。
P: 0.015% or less It is desirable to reduce P as much as possible in order to secure the toughness of the base metal and the weld heat affected zone. However, excessive P removal causes an increase in cost, so the amount of P is 0.015% or less. .
S:0.003%以下
Sは鋼中不純物として不可避な元素であるが、0.003%を超えると溶接部靭性が損なわれるのでS量は0.003%以下とする。
S: 0.003% or less S is an element that is unavoidable as an impurity in steel, but if over 0.003%, the toughness of the welded portion is impaired, so the S content is made 0.003% or less.
V:0.010%未満
Vは本発明において、最も注目すべき元素であり、できるだけ少ないことが必要である。従来、Vは、VC、VN等の微細析出物による析出強化を意図して積極的に添加されてきた。しかし、本発明のクラッド鋼の製造過程に、850℃以上に加熱して焼入れを実施する工程がある場合、母材中のVC、VN等の微細析出物は加熱した時に解離して固溶する。
本発明のC含有範囲においては、VC、VN等の微細析出物は低い温度で鋼中へ固溶する性質があるからである。従って、添加されたVは、焼入れ加熱時に微細析出物として存在しなくなるので、焼入れ性元素として作用し、母材、HAZのいずれの領域においても著しく硬化して、靭性劣化の原因となる。この靭性劣化はVを0.010%以上含有すると顕著となる。そのため、V量は0.010%未満とする。より好ましくは、0.004%未満であり、工業的に可能なレベルで含有させないことがさらに好ましい。
V: Less than 0.010% V is the most notable element in the present invention and needs to be as small as possible. Conventionally, V has been positively added with the intention of strengthening precipitation by fine precipitates such as VC and VN. However, when the production process of the clad steel of the present invention includes a step of quenching by heating to 850 ° C. or higher, fine precipitates such as VC and VN in the base material are dissociated and dissolved when heated. .
This is because in the C-containing range of the present invention, fine precipitates such as VC and VN have a property of being dissolved in steel at a low temperature. Accordingly, the added V does not exist as fine precipitates during quenching heating, so that it acts as a hardenable element and is significantly hardened in both regions of the base material and HAZ, causing toughness deterioration. This toughness deterioration becomes significant when V is contained by 0.010% or more. Therefore, the V amount is less than 0.010%. More preferably, it is less than 0.004%, and it is further more preferable not to contain it in the industrially possible level.
Al:0.040%以下
Alは、脱酸剤として有効な元素であるが、0.040%を超えて含有すると靭性が劣化するため、上限を0.040%とする。好ましくは0.015%未満である。
Al: 0.040% or less Al is an element effective as a deoxidizing agent, but if it exceeds 0.040%, the toughness deteriorates, so the upper limit is made 0.040%. Preferably it is less than 0.015%.
N:0.0030〜0.010%
NはTiNとして析出することでHAZ靭性の向上に効果があるが、Nの含有量が0.0030%未満では効果が薄れるため下限を0.0030%とする。しかしながら0.010%を超えると固溶Nが増大しHAZ靭性の低下がおこる。よってN量は0.0030〜0.010%の範囲とする。好ましくは0.0030〜0.0060%の範囲である。
N: 0.0030 to 0.010%
N precipitates as TiN and is effective in improving the HAZ toughness. However, if the N content is less than 0.0030%, the effect is reduced, so the lower limit is made 0.0030%. However, if it exceeds 0.010%, the solid solution N increases and the HAZ toughness decreases. Therefore, the N amount is in the range of 0.0030 to 0.010%. Preferably it is 0.0030 to 0.0060% of range.
以上が本発明の母材の基本成分であるが、更に特性を向上させるため、上記成分に加えて、選択的にMo、Ni、Cr、Cu、Nb、Ti、Caの中から選ばれる一種以上を以下の範囲で含有してもよい。 The above are the basic components of the base material of the present invention, but in order to further improve the characteristics, in addition to the above components, one or more selected selectively from Mo, Ni, Cr, Cu, Nb, Ti, Ca May be contained in the following range.
Mo:0.05〜0.50%
Moは焼入れ熱処理後の母材の強度と靭性を安定的に向上させる元素であるが、0.05%未満ではその効果が得られないため0.05%以上を含有させることが好ましい。また、0.50%を超えて含有すると効果が飽和し、また、過剰な含有は溶接熱影響部靭性や溶接性を阻害するため、Moを含有する場合は、Mo量は0.05〜0.50%の範囲とすることが好ましい。なお、母材強度とHAZ靭性の観点から、さらに好適には、0.08〜0.20%の範囲である。
Mo: 0.05 to 0.50%
Mo is an element that stably improves the strength and toughness of the base material after quenching heat treatment, but if less than 0.05%, the effect cannot be obtained, so 0.05% or more is preferably contained. Further, if the content exceeds 0.50%, the effect is saturated, and excessive content inhibits the weld heat affected zone toughness and weldability. Therefore, when Mo is contained, the amount of Mo is 0.05 to 0. It is preferable to be in the range of 50%. In addition, from a viewpoint of base material strength and HAZ toughness, the range is more preferably 0.08 to 0.20%.
Ni:0.01〜0.50%
Niは母材の強度及び靭性を向上させるために有効であり、0.01%以上含有することが好ましい。しかし、0.50%を超えて含有すると効果が飽和し、Niの含有は製造コストを上昇させるため、Niを含有する場合は、Ni量は0.01〜0.50%の範囲とすることが好ましい。さらに好適には、0.01〜0.30%の範囲である。
Ni: 0.01 to 0.50%
Ni is effective for improving the strength and toughness of the base material, and is preferably contained in an amount of 0.01% or more. However, if the content exceeds 0.50%, the effect is saturated, and the inclusion of Ni increases the manufacturing cost. Therefore, when Ni is contained, the Ni content should be in the range of 0.01 to 0.50%. Is preferred. More preferably, it is 0.01 to 0.30% of range.
Cr:0.01〜0.50%
Crは母材の強度及び靭性を向上させるために有効であり、0.01%以上を含有することが好ましい。しかし、0.50%を超えて含有するとHAZ靭性を低下させることがあるため、Crを含有する場合は、Cr量は0.01〜0.50%の範囲とすることが好ましい。さらに好適には、0.01〜0.30%の範囲である。
Cr: 0.01 to 0.50%
Cr is effective for improving the strength and toughness of the base material, and preferably contains 0.01% or more. However, if the content exceeds 0.50%, the HAZ toughness may be reduced. Therefore, when Cr is contained, the Cr content is preferably in the range of 0.01 to 0.50%. More preferably, it is 0.01 to 0.30% of range.
Cu:0.01〜0.50%
Cuは靭性の改善と強度の上昇に有効であり、0.01%以上含有することが好ましい。一方、0.50%を超えて含有すると溶接性を阻害することがある。従って、Cuを含有する場合は、Cu量は0.01〜0.50%の範囲とすることが好ましい。さらに好適には、0.01〜0.30%の範囲である。
Cu: 0.01 to 0.50%
Cu is effective for improving toughness and increasing strength, and is preferably contained in an amount of 0.01% or more. On the other hand, if it exceeds 0.50%, weldability may be impaired. Therefore, when it contains Cu, it is preferable to make Cu amount into the range of 0.01 to 0.50%. More preferably, it is 0.01 to 0.30% of range.
Nb:0.010〜0.060%
Nbは、NbCを生成することで結晶粒の細粒化に効果があり、本発明のように焼入焼戻処理した母材、およびHAZの靭性向上に寄与するので、0.010%以上の含有が好ましい。しかし、0.060%を超えるとその効果が認められないだけでなく、鋼片に表面庇が生じやすい。従って、Nbを含有する場合は、0.010〜0.060%の範囲とすることが好ましい。さらに好適には、0.025〜0.050%の範囲である。
Nb: 0.010 to 0.060%
Nb produces NbC, which is effective in reducing the grain size, and contributes to the improvement of the toughness of the base material that has been quenched and tempered as in the present invention, and HAZ. Containing is preferable. However, when it exceeds 0.060%, not only the effect is not recognized, but also surface flaws are likely to occur in the steel piece. Therefore, when it contains Nb, it is preferable to set it as the range of 0.010 to 0.060%. More preferably, it is 0.025 to 0.050% of range.
Ti:0.005〜0.020%
TiはTiNを形成してスラブ加熱時や溶接熱影響部の粒成長を抑制し、結果としてミクロ組織の微細化をもたらして靭性を改善する効果がある。その効果を発揮するには0.005%以上の含有が好ましい。しかし、0.020%を超えると溶接熱影響部靭性の劣化を引き起こす。従って、Tiを含有する場合は、0.005〜0.020%の範囲とすることが好ましい。さらに好適には、0.010〜0.016%の範囲である。
Ti: 0.005-0.020%
Ti forms TiN and has the effect of suppressing grain growth during slab heating and welding heat affected zone, resulting in refinement of the microstructure and improving toughness. In order to exhibit the effect, the content is preferably 0.005% or more. However, if it exceeds 0.020%, the weld heat-affected zone toughness is deteriorated. Therefore, when it contains Ti, it is preferable to set it as 0.005 to 0.020% of range. More preferably, it is in the range of 0.010 to 0.016%.
Ca:0.0010〜0.0040%
Caは硫化物系介在物の形態を制御し溶接熱影響部靭性を改善し,また、それに伴いMnSの形態制御に効果があり、衝撃値を向上させる。また、耐水素誘起割れ感受性を改善する。この効果を発揮するには0.0010%以上の含有が好ましい。しかし、0.0040%を超えると効果が飽和し、逆に清浄度を低下させ溶接熱影響部靭性を劣化させる。従ってCaを含有する場合は0.0010〜0.0040%とすることが好ましい。さらに好適には、0.0020〜0.0030%の範囲である。
Ca: 0.0010 to 0.0040%
Ca controls the form of sulfide inclusions and improves the toughness of the heat affected zone, and accordingly, it has an effect on the form control of MnS and improves the impact value. It also improves the resistance to hydrogen-induced cracking resistance. In order to exhibit this effect, 0.0010% or more is preferable. However, if it exceeds 0.0040%, the effect is saturated, conversely, the cleanliness is lowered and the weld heat affected zone toughness is deteriorated. Therefore, when it contains Ca, it is preferable to set it as 0.0010 to 0.0040%. More preferably, it is 0.0020 to 0.0030% of range.
本発明のクラッド鋼板の母材は、上記組成に加えて、さらに靭性を向上する目的でTi/N、Nb/Cを規定してもよい。 In addition to the above composition, the base material of the clad steel plate of the present invention may further define Ti / N and Nb / C for the purpose of further improving toughness.
Ti/N:2.0〜3.5
Ti及びNは、上記のようにTiNを生成してHAZの靱性を改善するのに重要な元素であり、該効果を充分に発揮するためには両元素の含有量の相関関係も重要となる。すなわち、質量%比で、Ti/Nが2.0未満であると結晶粒が粗大化し、靱性値が大きく低下することがある。また、Ti/Nが3.5を超えると同様の理由により靭性値が低下することがある。したがって、Ti/Nは2.0〜3.5の範囲とすることが好ましい。
Ti / N: 2.0 to 3.5
Ti and N are elements that are important for generating TiN and improving the toughness of HAZ as described above, and the correlation between the contents of both elements is also important in order to fully exhibit this effect. . That is, when the Ti / N ratio is less than 2.0 by mass%, the crystal grains become coarse and the toughness value may be greatly reduced. Moreover, when Ti / N exceeds 3.5, the toughness value may decrease for the same reason. Therefore, Ti / N is preferably in the range of 2.0 to 3.5.
Nb/C:0.2〜2.0
Nb、Cは、NbCを生成することで結晶粒の細粒化に効果があり、本発明のように焼入焼戻処理時には靭性向上に寄与する。しかし、その効果はNb/Cが0.2以上で発揮され、Nb/Cが2.0を超えると効果が認められない。したがって、質量%比で、Nb/Cは0.2〜2.0の範囲とすることが好ましい。より好ましくは0.3〜1.9の範囲である。さらに好ましくは0.3〜1.8の範囲である。
Nb / C: 0.2 to 2.0
Nb and C are effective in reducing the crystal grains by generating NbC, and contribute to the improvement of toughness during the quenching and tempering treatment as in the present invention. However, the effect is exhibited when Nb / C is 0.2 or more, and when Nb / C exceeds 2.0, the effect is not recognized. Therefore, Nb / C is preferably in the range of 0.2 to 2.0 in terms of mass%. More preferably, it is the range of 0.3-1.9. More preferably, it is the range of 0.3-1.8.
2.合わせ材の成分組成について
以下、本発明における合わせ材は、Cが0.020%以下のNi合金であれば良いが、更に好適な成分組成として以下のように規定した。なお、成分%は、特に記載が無い限り全て質量%を意味する。
2. About the component composition of a laminated material Hereinafter, although the laminated material in this invention should just be Ni alloy whose C is 0.020% or less, it prescribed | regulated as follows as a more suitable component composition. In addition, all the component% means the mass% unless there is particular description.
C:0.020%以下
Cはクラッド鋼板の製造において、圧延および熱処理工程の熱履歴で炭化物として粒界に析出し、耐食性を阻害するため多量の含有は避けるべき元素である。0.020%を超えて含有すると、耐食性が劣化するため、C量は0.020%以下とする。好ましくは、0.017%以下である。
C: 0.020% or less C is an element that should be avoided in the production of clad steel sheets because it precipitates at the grain boundaries as carbides due to the thermal history of the rolling and heat treatment processes and inhibits corrosion resistance. If the content exceeds 0.020%, the corrosion resistance deteriorates, so the C content is 0.020% or less. Preferably, it is 0.017% or less.
Si:0.50%以下
Siは脱酸成分として必要な成分である。しかしながら、0.50%を超えて含有すると非金属介在物として残存し、耐食性が劣化し、また熱間加工性も劣化するため、Si量は0.50%以下とする。好ましくは0.20%以下である。なお、脱酸材としては0.02%以上から効果が発現する。
Si: 0.50% or less Si is a necessary component as a deoxidizing component. However, if it exceeds 0.50%, it remains as a non-metallic inclusion, the corrosion resistance is deteriorated, and the hot workability is also deteriorated, so the Si amount is 0.50% or less. Preferably it is 0.20% or less. In addition, as a deoxidizer, the effect is manifested from 0.02% or more.
Mn:0.50%以下
Mnは脱酸成分として必要な成分である。しかしながら、0.50%を超えて含有すると非金属介在物として残存し、耐食性が劣化し、また熱間加工性も劣化するため、Mn量は0.50%以下とする。好ましくは0.15%以下である。なお、脱酸材としては0.02%以上から効果が発現する。
Mn: 0.50% or less Mn is a necessary component as a deoxidizing component. However, if it exceeds 0.50%, it remains as a non-metallic inclusion, the corrosion resistance is deteriorated, and the hot workability is also deteriorated. Therefore, the Mn amount is 0.50% or less. Preferably it is 0.15% or less. In addition, as a deoxidizer, the effect is manifested from 0.02% or more.
P:0.010%以下
Pは不純物元素であり、クラッド鋼板の接合性確保のため、900℃以上で圧延する際に、粒界に偏析し、耐食性を劣化させる元素である。したがって、P量は0.010%以下とする。好ましくは、0.005%以下とする。
P: 0.010% or less P is an impurity element, and is an element that segregates at grain boundaries and deteriorates corrosion resistance when rolled at 900 ° C. or more in order to ensure the bonding property of the clad steel plate. Therefore, the P content is 0.010% or less. Preferably, the content is 0.005% or less.
S:0.0010以下
SはPと同様で不純物元素であり、クラッド鋼板の接合性確保のため、900℃以上で圧延する際に、粒界に偏析し、耐食性を劣化させる元素である。したがって、S量は0.0010%以下とする。好ましくは、0.0005%以下とする。
S: 0.0010 or less S is an impurity element similar to P, and is an element that segregates at the grain boundaries and deteriorates the corrosion resistance when rolled at 900 ° C. or more in order to secure the bondability of the clad steel plate. Therefore, the S content is 0.0010% or less. Preferably, it is 0.0005% or less.
Cr:20.0〜23.0%
Crは、金属の表面に保護性の高い酸化物皮膜を形成し、耐孔食性や耐粒界腐食性を向上させる元素である。また、Niとの複合添加によって、サワー環境中での耐応力腐食割れ感受性も改善するため、Niやその他の合金とのバランスも考え、Cr量は20.0〜23.0%の範囲とする。
Cr: 20.0-23.0%
Cr is an element that forms a highly protective oxide film on the surface of metal and improves pitting corrosion resistance and intergranular corrosion resistance. In addition, the combined addition with Ni improves the stress corrosion cracking susceptibility in the sour environment, so considering the balance with Ni and other alloys, the Cr content is in the range of 20.0 to 23.0%. .
Mo:8.0〜10.0%
Moは、耐孔食性、耐隙間腐食性を向上させる。また、Niとの複合添加によって、サワー環境中での耐応力腐食割れ感受性も改善するため、Niやその他の合金とのバランスも考え、Mo量は8.0〜10.0%の範囲とする。
Mo: 8.0 to 10.0%
Mo improves pitting corrosion resistance and crevice corrosion resistance. In addition, the combined addition with Ni improves the stress corrosion cracking susceptibility in the sour environment, so considering the balance with Ni and other alloys, the Mo amount is in the range of 8.0 to 10.0%. .
Fe:5.0%以下
Feは、フェロクロム、フェロモリブデン等を用いた場合、不可避的に混入する不純物であり、5.0%を超えるとNi量が低下して耐食性が低下するため、Fe量は5%以下とする。好ましくは3.5%以下である。
Fe: 5.0% or less Fe is an impurity inevitably mixed when ferrochromium, ferromolybdenum, or the like is used, and if it exceeds 5.0%, the Ni content decreases and the corrosion resistance decreases, so the Fe content Is 5% or less. Preferably it is 3.5% or less.
Al:0.40%以下
Alは有効な脱酸元素であるが、0.40%を超えて含有すると耐応力腐食割れ性が劣化するため、Al量は0.40%以下とする。好ましくは0.25%以下である。なお、脱酸材としては0.02%以上から効果が発現する。
Al: 0.40% or less Al is an effective deoxidizing element, but if it exceeds 0.40%, the stress corrosion cracking resistance deteriorates, so the Al amount is 0.40% or less. Preferably it is 0.25% or less. In addition, as a deoxidizer, the effect is manifested from 0.02% or more.
Ti:0.40%以下
TiはCの固定化元素として有効であり、クラッド鋼板製造時の熱履歴で炭化物として析出する。しかしながら、多量に含有すると、クラッド鋼板の接合界面で金属間化合物として析出し、接合性を阻害するため、Ti量は0.40%以下とする。好ましくは0.30%以下である。
Ti: 0.40% or less Ti is effective as a fixing element for C, and precipitates as carbides in the thermal history during the production of the clad steel plate. However, if it is contained in a large amount, it precipitates as an intermetallic compound at the bonding interface of the clad steel plate and inhibits the bonding property, so the Ti amount is set to 0.40% or less. Preferably it is 0.30% or less.
Nb+Ta:3.15〜4.15%
NbとTaはCの固定化元素として有効であり、クラッド鋼板製造時の熱履歴で炭化物として析出する。しかし、多量に含有すると低融点の金属間化合物を形成し、熱間加工性が低下するため、Nb+Taは3.15〜4.15%の範囲とする。
Nb + Ta: 3.15-4.15%
Nb and Ta are effective as C-fixing elements, and precipitate as carbides in the thermal history during the production of the clad steel plate. However, if it is contained in a large amount, an intermetallic compound having a low melting point is formed and hot workability is lowered. Therefore, Nb + Ta is set to a range of 3.15 to 4.15%.
Ni
上記した合わせ材の成分の残部はNiおよび不可避的不純物である。Niは耐食性を向上させる元素であり、特に、サワー環境での耐応力腐食割れ性を著しく改善する。前述したように、CrとMoとの複合添加効果でさらに耐食性は向上する。
Ni
The balance of the components of the above-mentioned laminated material is Ni and inevitable impurities. Ni is an element that improves corrosion resistance, and remarkably improves stress corrosion cracking resistance in a sour environment. As described above, the corrosion resistance is further improved by the combined effect of Cr and Mo.
3.クラッド鋼の製造方法について
本発明のクラッド鋼に用いる母材と合わせ材は、前記した成分範囲に調整され、常法等により溶製することができる。クラッド圧延を行うために、事前にクラッドスラブを組み立てる。クラッド鋼板の最終板厚が25mm以下の場合は、母材/合わせ材/合わせ材/母材の順番で重ね合わせ、母材と合わせ材の間には接合性確保のためにNiフォイルを挿入し、高真空に引きながら、端部の四周溶接を行う、サンドイッチ方式のスラブ形態をとる。
3. About the manufacturing method of clad steel The base material and laminated material used for the clad steel of this invention are adjusted to the above-mentioned component range, and can be melted by a conventional method. The clad slab is assembled in advance to perform clad rolling. When the final thickness of the clad steel sheet is 25 mm or less, the base material / lamination material / lamination material / matrix material is overlapped in order, and Ni foil is inserted between the base material and the laminating material to ensure the bonding property. The sandwich-type slab is formed by performing four-round welding at the end while drawing a high vacuum.
クラッド鋼板の最終板厚が25mmを超える場合には、犠牲材/合わせ材/母材の順番で重ね合わせ、母材と合わせ材の間には接合性確保のためにNiフォイルを挿入し、高真空に引きながら、端部の四周溶接を行う、犠牲材方式のスラブ形態をとる。製造条件によっては接合性確保が十分な場合は、Niフォイルを挿入しなくても良い。なお、もちろん,クラッドの組立方法は前記に限ったことではなく、圧延可能なスラブ組立をしていれば良い。 When the final thickness of the clad steel plate exceeds 25 mm, the sacrificial material / laminated material / base material are stacked in this order, and Ni foil is inserted between the base material and the laminated material to ensure the bonding property. It takes a sacrificial material slab form in which the end is subjected to four-round welding while being evacuated. Depending on the manufacturing conditions, the Ni foil need not be inserted if sufficient bondability is ensured. Of course, the method of assembling the clad is not limited to the above, and any slab assembly that can be rolled may be used.
上記により得られたクラッドスラブについて、常法による熱間圧延を行えばよい。なお、クラッド鋼板としての接合性を確保するためには、スラブ加熱温度、圧延終了温度、圧下比は以下の条件が好ましい。 What is necessary is just to perform hot rolling by a conventional method about the clad slab obtained by the above. In order to secure the bondability as a clad steel plate, the following conditions are preferable for the slab heating temperature, rolling end temperature, and rolling reduction ratio.
スラブ加熱温度:1050〜1225℃
クラッド鋼板は固相拡散接合によって接合される。よって、高温の方が接合界面での拡散が起こり、接合性が向上するため、スラブ加熱温度は1050℃以上が好ましい。しかしながら、1225℃以上では本発明の合わせ材は無延性となるため、最適加熱温度範囲は1050〜1225℃とする。より好ましい温度範囲は1100〜1200℃である。
Slab heating temperature: 1050-1225 ° C
The clad steel plate is joined by solid phase diffusion bonding. Therefore, the slab heating temperature is preferably 1050 ° C. or higher because diffusion at the bonding interface occurs at a higher temperature and bonding properties are improved. However, since the laminated material of the present invention becomes non-ductile at 1225 ° C. or higher, the optimum heating temperature range is set to 1050 to 1225 ° C. A more preferable temperature range is 1100 to 1200 ° C.
圧延終了温度:鋼板表面温度で900℃以上
本発明のクラッド鋼板は、通常のステンレスやNi合金に比べて、非常に変形抵抗が高いため、通常のステンレスクラッド鋼板より接合性の確保が難しい。高温の方が接合界面での拡散が起こり、また、合わせ材の再結晶や部分再結晶が起こることで、接合性が向上するため、圧延終了温度は通常のステンレスクラッド鋼より高い900℃以上とする。圧延終了後は空冷以上の速度で冷却すれば、合わせ材の耐食性は確保可能である。
Rolling end temperature: 900 ° C. or more at the steel sheet surface temperature The clad steel sheet of the present invention has a very high deformation resistance as compared with ordinary stainless steel and Ni alloy, and therefore it is difficult to ensure the bonding property than the ordinary stainless clad steel sheet. Higher temperature causes diffusion at the bonding interface, and recrystallization or partial recrystallization of the laminated material improves bonding properties. Therefore, the rolling end temperature is 900 ° C. or higher, which is higher than that of ordinary stainless clad steel. To do. The corrosion resistance of the laminated material can be ensured by cooling at a rate higher than air cooling after the end of rolling.
圧下比:5以上
本発明のクラッド鋼板は、通常のステンレスやNi合金に比べて、非常に変形抵抗が高いため、通常のステンレスクラッド鋼板より接合性の確保が難しい。そのため、通常のステンレスクラッド鋼板より圧下比を高くすることで、合わせ材表面の新生金属面の現出や母材と合わせ材の圧着を促進するため、圧下比は5以上とする。
Rolling ratio: 5 or more Since the clad steel sheet of the present invention has a very high deformation resistance as compared with ordinary stainless steel and Ni alloy, it is difficult to ensure the bondability than ordinary stainless clad steel sheet. For this reason, the reduction ratio is set to 5 or more in order to promote the appearance of the new metal surface on the surface of the laminated material and the press bonding of the base material and the laminated material by increasing the reduction ratio compared to a normal stainless clad steel plate.
なお圧下比は、組立てスラブの板厚/圧延後のクラッド鋼板厚として定義される。 The reduction ratio is defined as the thickness of the assembled slab / the thickness of the clad steel plate after rolling.
焼入れ温度:850〜950℃
上記により得られたクラッド鋼板は、焼入れ処理のため、850〜950℃の温度範囲に加熱する。加熱温度が850℃未満では十分な母材強度が確保できず、950℃を超えると母材の靭性が劣化する。したがって、焼入れ処理のため、850〜950℃の範囲に加熱する。さらに好ましくは、900〜930℃の範囲である。焼入れ処理の時間はクラッド鋼板の板厚にもよるが、10〜30分とすることが好ましい。しかし、高温長時間の保持は合わせ材中に析出物が生成するため、10分より短時間としても良い。焼入れ処理後の冷却方法としては、水冷、油冷(例えば冷却速度2℃/s以上)により行うことができる。
Quenching temperature: 850-950 ° C
The clad steel plate obtained as described above is heated to a temperature range of 850 to 950 ° C. for quenching treatment. If the heating temperature is less than 850 ° C., sufficient base material strength cannot be secured, and if it exceeds 950 ° C., the toughness of the base material deteriorates. Therefore, it heats in the range of 850-950 degreeC for a quenching process. More preferably, it is the range of 900-930 degreeC. The quenching time is preferably 10 to 30 minutes, although it depends on the thickness of the clad steel plate. However, holding for a long time at a high temperature may be shorter than 10 minutes because precipitates are generated in the laminated material. As a cooling method after the quenching treatment, water cooling or oil cooling (for example, a cooling rate of 2 ° C./s or more) can be performed.
焼戻し温度:650℃未満
次いで、650℃未満の温度に加熱し、焼戻し処理を行う。650℃以上ではDWTT特性が劣化するので、650℃未満とする。さらに、焼戻し処理温度は、好ましくは500〜600℃の範囲である。なお、焼戻し加熱時間は5〜35分とするのがよい。
上記一連の熱処理により、クラッド鋼板の母材組織を微細化することができる。
Tempering temperature: less than 650 ° C. Next, heating to a temperature of less than 650 ° C. to perform a tempering treatment. Since the DWTT characteristics deteriorate at 650 ° C. or higher, the temperature is set to less than 650 ° C. Furthermore, the tempering temperature is preferably in the range of 500 to 600 ° C. The tempering heating time is preferably 5 to 35 minutes.
By the above series of heat treatments, the base metal structure of the clad steel plate can be refined.
クラッド鋼板は、板状のまま及び鋼管に成型してクラッド鋼管として使用することができる。上記クラッド鋼板では、溶接時に、それぞれ表裏1パスで溶接することができ、該1パス溶接によってもHAZ部での微細な組織が維持され、良好な靱性が確保される。 The clad steel plate can be used as a clad steel pipe in the form of a plate and formed into a steel pipe. The clad steel sheet can be welded in one pass on the front and back sides at the time of welding, and the fine structure in the HAZ portion is maintained even by the one pass welding, and good toughness is ensured.
以下に本発明の実施例を比較例と対比しつつ説明する。ここで、溶接部靱性の評価は、シャルピー試験で行った。シャルピー試験片のノッチ位置は、溶接金属と母材の境界であるボンド部から、母材側へ3mm(HAZ3mm)の位置とした。試験温度は、−20℃で実施した。本発明では−20℃の吸収エネルギー(vE−20℃)が100J以上を靭性に優れているものとした。 Examples of the present invention will be described below in comparison with comparative examples. Here, the toughness of the welded portion was evaluated by a Charpy test. The notch position of the Charpy test piece was set to a position of 3 mm (HAZ 3 mm) from the bond part, which is the boundary between the weld metal and the base material, to the base material side. The test temperature was -20 ° C. In the present invention, the absorbed energy (vE-20 ° C.) at −20 ° C. is 100 J or more, and the toughness is excellent.
また、母材の靭性は、−20℃におけるDWTT試験(落重特性)で評価した。本発明では、−20℃におけるDWTT試験で、延性破面率85%以上を母材の靭性に優れているものとした。 The toughness of the base material was evaluated by a DWTT test (falling weight characteristic) at −20 ° C. In the present invention, in the DWTT test at −20 ° C., a ductile fracture surface ratio of 85% or more is assumed to be excellent in the toughness of the base material.
なお、本願発明の目標値は、API 5L X65相当以上とし、YS≧450MPa、TS≧600MPa とした。 The target values of the present invention were equivalent to API 5L X65 or more, and YS ≧ 450 MPa and TS ≧ 600 MPa.
合わせ材の耐食性は、耐粒界腐食性と耐孔食性と耐応力腐食割れ性について評価した。耐粒界腐食性は、JIS G0573で規格化されているヒューイ試験(65%硝酸腐食試験)を行い、1.0g/m2・hr以下を耐食性良好と判断とした(無垢の溶体化材は、0.50g/m2・hr)。耐孔食性は、JIS G0578で規格化されている塩化第二鉄腐食試験において、孔食発生臨界温度試験を行い、CPT(孔食発生臨界温度)が80℃以上を合格と判断した。(無垢の溶体化材は、85℃以上)。耐応力腐食割れ性については、ラインパイプの使用環境としては厳しい条件である、NACE TM−01−77溶液(5%NaCl+0.5%CH3COOH)、5atmH2S−20atmCO2、150℃、720時間浸漬、4点曲げSCC試験を行い、試験後の割れ発生の有無で評価を行った。 The corrosion resistance of the laminated material was evaluated with respect to intergranular corrosion resistance, pitting corrosion resistance, and stress corrosion cracking resistance. Intergranular corrosion resistance was determined by performing Huey test (65% nitric acid corrosion test) standardized by JIS G0573 and judging that corrosion resistance was good at 1.0 g / m 2 · hr or less (solid solution material is 0.50 g / m 2 · hr). The pitting corrosion resistance was determined by performing a pitting corrosion critical temperature test in the ferric chloride corrosion test standardized in JIS G0578 and determining that CPT (pitting corrosion critical temperature) was 80 ° C. or higher. (The solid solution material is 85 ° C or higher). Regarding stress corrosion cracking resistance, NACE TM-01-77 solution (5% NaCl + 0.5% CH 3 COOH), 5 atm H 2 S-20 atm CO 2 , 150 ° C., 720, which is a severe condition as the use environment of the line pipe A time immersion, 4-point bending SCC test was performed, and evaluation was performed based on whether or not cracking occurred after the test.
接合性は、JIS G0601で規格化されている剪断強さ試験で行い、300MPa以上を目標範囲とした。 The bondability was measured by a shear strength test standardized by JIS G0601, and the target range was 300 MPa or more.
表1に示す母材の化学成分と表2に示す合わせ材の化学成分を用いて、表3に示す製造条件でクラッド鋼板を製造した。製造時は、母材と合わせ材を重ねて一組とし、加熱炉で所定の温度で加熱後、熱間圧延によりクラッド比1/10(例えば、合わせ材3mmに対して、全厚が30mm)となるように圧延し、圧延完了後、焼入焼戻処理を行った。焼入れ処理は、加熱炉にて所定の温度で10分間加熱後に約5℃/sで水冷した。次いで、焼戻し処理は所定の温度まで加熱後に30分間保持し、その後放冷した。一連の熱処理後のクラッド鋼板を冷間で成形して外径500mmのクラッド鋼管を製造し、母材部と母材の溶接熱影響部について諸特性を調べた。試験結果を表3に示す。 Using the chemical composition of the base material shown in Table 1 and the chemical composition of the laminated material shown in Table 2, a clad steel plate was produced under the production conditions shown in Table 3. At the time of manufacture, the base material and the laminated material are overlapped to form a set, heated at a predetermined temperature in a heating furnace, and then hot-rolled to have a cladding ratio of 1/10 (for example, the total thickness is 30 mm with respect to 3 mm of the laminated material) And after quenching, a quenching and tempering treatment was performed. The quenching treatment was performed by heating at a predetermined temperature in a heating furnace for 10 minutes and then water cooling at about 5 ° C./s. Subsequently, the tempering treatment was held for 30 minutes after heating to a predetermined temperature, and then allowed to cool. A clad steel plate after a series of heat treatments was cold-formed to produce a clad steel pipe having an outer diameter of 500 mm, and various characteristics of the base metal part and the weld heat affected zone of the base material were examined. The test results are shown in Table 3.
母材の化学成分がいずれも本発明の範囲を満足する鋼は、母材部、HAZ部共に目標特性を満足するのに対し、Mnが発明の範囲の下限値を外れた場合は、強度、母材のDWTT特性が目標値以下となった。また、V、Nb、Ti/Nの値が発明の範囲から外れた場合は、HAZ靭性が目標値以下となった。また、合わせ材のC、P、Sの値が発明の範囲から外れた場合は、耐食性が目標値以下となった。また、製造条件において、スラブ加熱温度と圧延終了温度と圧下比が発明の範囲から外れた場合は、剪断強度値が低く、焼入焼戻条件が発明の範囲から外れた場合は、機械的特性が劣っていた。 Steel whose chemical composition of the base material satisfies the range of the present invention satisfies the target characteristics for both the base material part and the HAZ part, whereas when Mn is outside the lower limit of the range of the invention, the strength, The DWTT characteristic of the base material was below the target value. Moreover, when the values of V, Nb, and Ti / N deviated from the scope of the invention, the HAZ toughness was less than the target value. Moreover, when the values of C, P, and S of the laminated material deviated from the scope of the invention, the corrosion resistance was below the target value. Also, in the manufacturing conditions, when the slab heating temperature, the rolling end temperature and the reduction ratio are out of the scope of the invention, the shear strength value is low, and when the quenching and tempering conditions are out of the scope of the invention, the mechanical characteristics Was inferior.
Claims (8)
10×C+5×P+50×S≦0.25・・・・・(1)
ここで、元素記号は各元素の含有量(質量%)を表す。 4. The high toughness and corrosion-resistant Ni alloy clad steel sheet having excellent weld toughness according to claim 3, wherein C, P and S further satisfy the following formula (1) as a laminated material.
10 × C + 5 × P + 50 × S ≦ 0.25 (1)
Here, the element symbol represents the content (% by mass) of each element.
Ti/N = 2.0〜3.5・・・・・(2)
ここで、元素記号は各元素の含有量(質量%)を表す。 When Ti is contained as a base material, Ti and N satisfy the following formula (2), and high toughness and corrosion resistance excellent in weld zone toughness according to any one of claims 2 to 4 Ni alloy clad steel sheet.
Ti / N = 2.0 to 3.5 (2)
Here, the element symbol represents the content (% by mass) of each element.
Nb/C = 0.2〜2.0・・・・・(3)
ここで、元素記号は各元素の含有量(質量%)を表す。 When Nb is contained as a base material, Nb and C satisfy the following formula (3), and the toughness and corrosion resistance excellent in weld zone toughness according to any one of claims 2 to 5 Ni alloy clad steel sheet.
Nb / C = 0.2-2.0 (3)
Here, the element symbol represents the content (% by mass) of each element.
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