JP6127939B2 - Manufacturing method of austenitic stainless clad steel plate with excellent low temperature toughness and HAZ toughness of base metal and corrosion resistance of laminated material - Google Patents
Manufacturing method of austenitic stainless clad steel plate with excellent low temperature toughness and HAZ toughness of base metal and corrosion resistance of laminated material Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 60
- 239000010959 steel Substances 0.000 title claims description 60
- 230000007797 corrosion Effects 0.000 title claims description 47
- 238000005260 corrosion Methods 0.000 title claims description 47
- 239000002648 laminated material Substances 0.000 title claims description 38
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 239000010953 base metal Substances 0.000 title claims description 10
- 239000000463 material Substances 0.000 claims description 72
- 238000005096 rolling process Methods 0.000 claims description 43
- 238000001816 cooling Methods 0.000 claims description 22
- 239000012535 impurity Substances 0.000 claims description 12
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 10
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 229910052759 nickel Inorganic materials 0.000 claims description 9
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 6
- 230000001186 cumulative effect Effects 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 229910052698 phosphorus Inorganic materials 0.000 claims description 4
- 238000005098 hot rolling Methods 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 17
- 238000012360 testing method Methods 0.000 description 17
- 238000010438 heat treatment Methods 0.000 description 11
- 230000000694 effects Effects 0.000 description 10
- 238000000034 method Methods 0.000 description 8
- 239000000203 mixture Substances 0.000 description 7
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 229910001220 stainless steel Inorganic materials 0.000 description 6
- 239000010935 stainless steel Substances 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 238000003475 lamination Methods 0.000 description 5
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 229910000975 Carbon steel Inorganic materials 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 239000010962 carbon steel Substances 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 238000001556 precipitation Methods 0.000 description 4
- 239000007787 solid Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000005496 tempering Methods 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 239000011343 solid material Substances 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 239000002023 wood Substances 0.000 description 2
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
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- 229910000765 intermetallic Inorganic materials 0.000 description 1
- 238000005304 joining Methods 0.000 description 1
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- 238000007747 plating Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
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- 238000001953 recrystallisation Methods 0.000 description 1
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- 229910052720 vanadium Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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Description
本発明は、母材の低温靭性とＨＡＺ靭性並びに合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼板およびその製造方法に関する。 The present invention relates to an austenitic stainless clad steel plate excellent in low-temperature toughness and HAZ toughness of a base material and corrosion resistance of a laminated material, and a method for producing the same.
クラッド鋼板は母材の機械的特性と合せ材の耐食性を兼ね備え、かつ経済性に優れた高機能鋼板である。オーステナイト系ステンレスクラッド鋼板は、ケミカルタンカー用として多く用いられるが、エネルギー開発分野の成長とともにパイプライン用途として需要が期待されている。近年、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おり、このような環境は、今まで以上に母材の低温靭性、特に脆性破壊の伝播停止特性や合せ材の耐食性が求められている。 The clad steel plate is a high-performance steel plate that combines the mechanical properties of the base material with the corrosion resistance of the laminated material and is excellent in economy. Austenitic stainless clad steel plates are often used for chemical tankers, but demand is expected for pipeline applications as the energy development field grows. In recent years, the development of energy resources has progressed even in a region called difficult mining environment, and such an environment requires more than ever the low temperature toughness of the base metal, especially the propagation stop property of brittle fracture and the corrosion resistance of the laminated material. Yes.
クラッド鋼板とは合せ材にステンレス鋼やＮｉ基合金、母材に低合金鋼材と、二種類の性質の異なる金属を張り合わせた鋼板である。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 clad steel plate is a steel plate in which two kinds of metals different from each other, such as stainless steel or Ni-based alloy as a laminated material and a low alloy steel material as a base material, 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.
クラッド鋼板は、使用環境毎の目的に合った機能を有する合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炭素鋼や低合金鋼を適用することができる。 The clad steel plate 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 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、さらに炭素鋼や低合金鋼と同等の強度や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, can ensure the same corrosion resistance as solid wood, and can also ensure the same strength and toughness as carbon steel and low alloy steel. , It has the advantage that economics and functionality are compatible.
以上から、オーステナイト系ステンレス鋼を含めて、高合金の合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、近年そのニー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, including austenitic stainless steel, is considered to be a very useful functional steel material, and its needs have been increasing in various industrial fields in recent years.
このような背景から、以下に示すようなクラッド鋼板およびクラッド鋼板の製造方法が開示されている。 From such a background, the following clad steel plates and methods for producing clad steel plates are disclosed.
特許文献１および特許文献２には、Ｎｉ、Ｃｒ、Ｃｕ、Ｍｏ、Ｖ、ＮｂやＴｉを含有する合金炭素鋼を母材としてクラッド圧延した後、９００〜１１００℃のオーステナイト化温度域から調質を行い、その後５５０〜６５０℃の焼戻しを行うクラッド鋼の製造方法が開示されている。 In Patent Document 1 and Patent Document 2, the alloy carbon steel containing Ni, Cr, Cu, Mo, V, Nb, and Ti is clad-rolled as a base material, and then tempered from an austenitizing temperature range of 900 to 1100 ° C. And then a method for producing clad steel is disclosed in which tempering at 550 to 650 ° C. is performed.
特許文献３には、Ｎｂを０．０８〜０．１５質量％含有する母材とステンレス鋼またはニッケル合金からなる合わせ材とを有するクラッド鋼を１０００℃以下での圧下比を３以上、総圧下比を５以上として、圧延終了温度９００〜１０００℃で圧延し、３０〜２００秒間空冷した後、７５０℃以上の温度から５〜４０℃／秒の冷却速度で５５０℃以下の温度まで冷却するクラッド鋼板の製造方法が開示されている。 In Patent Document 3, a clad steel having a base material containing 0.08 to 0.15% by mass of Nb and a laminated material made of stainless steel or a nickel alloy has a reduction ratio of 3 or more at 1000 ° C. or less and a total reduction. The clad is rolled at a rolling end temperature of 900 to 1000 ° C. with a ratio of 5 or more, air-cooled for 30 to 200 seconds, and then cooled to a temperature of 550 ° C. or lower from a temperature of 750 ° C. or higher at a cooling rate of 5 to 40 ° C./second. A method for manufacturing a steel sheet is disclosed.
特許文献４には、母材にＮｂ：０．００５〜０．０５質量％を含有し、Ｃｕ：１．５質量％以下、Ｎｉ：３．０質量％以下、Ｃｒ：０．３質量％以下、Ｍｏ：０．３質量％以下等を選択的に含有した低合金鋼を用いて、１１００℃以上に加熱した後に、１０００℃以上の温度範囲において圧下比で２．５以上、８５０℃以下母材のＡｒ３点−２０℃までの温度範囲において圧下率５０％以上の圧延を施し、その後直ちに４５０℃以下の温度まで水冷するオーステナイト系ステンレスクラッド鋼の製造方法が開示されている。 Patent Document 4 contains Nb: 0.005 to 0.05 mass% in the base material, Cu: 1.5 mass% or less, Ni: 3.0 mass% or less, Cr: 0.3 mass% or less. , Mo: Using a low alloy steel that selectively contains 0.3% by mass or less, etc., after heating to 1100 ° C. or higher, the rolling reduction ratio is 2.5 to 850 ° C. in a temperature range of 1000 ° C. or higher. A method for producing an austenitic stainless clad steel is disclosed in which rolling at a reduction rate of 50% or more is performed in a temperature range of Ar 3 point to -20 ° C of the material, and then immediately cooled to a temperature of 450 ° C or less.
しかしながら、特許文献１および特許文献２に開示された技術は、９００〜１１００℃のオーステナイト化温度域から調質後に、５５０〜６５０℃の焼戻し処理を行うために、合わせ材の耐食性が劣化するという問題がある。 However, the techniques disclosed in Patent Document 1 and Patent Document 2 are said to deteriorate the corrosion resistance of the laminated material in order to perform tempering at 550 to 650 ° C. after tempering from the austenitizing temperature range of 900 to 1100 ° C. There's a problem.
これは、合せ材であるオーステナイト系ステンレス鋼では、５００〜８００℃の温度域に保持すると、Ｃｒ２３Ｃ６といった炭化物やσ相といった金属間化合物が生じることで、析出物周辺部のＣｒ濃度が低くなり、粒界腐食や孔食が生じやすくなるためである。 This is because in the austenitic stainless steel that is a laminated material, when it is kept in a temperature range of 500 to 800 ° C., a carbide such as Cr 23 C 6 and an intermetallic compound such as a σ phase are generated, so that the Cr concentration in the periphery of the precipitate is reduced. This is because it becomes low and intergranular corrosion and pitting corrosion easily occur.
通常、無垢材であれば圧延後に溶体化処理を施し析出物を固溶させることができるが、クラッド鋼の場合には析出物が溶け込むような高温に加熱保持すると、母材である低合金鋼の結晶粒が粗大化し、機械的特性が著しく悪化するという問題が生じる。また、特許文献１および特許文献２に記載の焼入焼戻処理での製造方法では、母材の低温靭性、特に脆性破壊伝播停止性能を向上させるには限界があるという問題もある。 Normally, solid materials can be subjected to solution treatment after rolling to solidify the precipitates, but in the case of clad steel, the low alloy steel, which is the base material, can be heated to a high temperature where the precipitates melt. This causes the problem that the crystal grains become coarse and the mechanical properties are remarkably deteriorated. Moreover, in the manufacturing method by the quenching and tempering process described in Patent Document 1 and Patent Document 2, there is a problem that there is a limit to improving the low temperature toughness of the base material, particularly the brittle fracture propagation stopping performance.
特許文献３に開示された技術では、Ｎｂを０．０８質量％以上含有しているので、溶接熱影響部（ＨＡＺ）靭性が劣化するという問題がある。通常、溶接を伴う鋼構造物にクラッド鋼を用いる場合は、母材のＮｂ含有量は０．０８質量％未満とすることが望ましい。しかし、Ｎｂ含有量を低くした場合には、制御圧延による結晶粒の微細化達成のために、より低温での圧延が必要となるという問題がある。 In the technique disclosed in Patent Document 3, since Nb is contained in an amount of 0.08% by mass or more, there is a problem that the weld heat affected zone (HAZ) toughness deteriorates. Usually, when clad steel is used for a steel structure with welding, the Nb content of the base material is preferably less than 0.08% by mass. However, when the Nb content is lowered, there is a problem that rolling at a lower temperature is required to achieve refinement of crystal grains by controlled rolling.
特許文献４に開示された技術では、Ｃｕは０．５０質量％以上、Ｎｉは０．４５質量％以上含有すると、溶接性が劣化するという問題があり、鋼構造物として重要な溶接熱影響部（ＨＡＺ）靭性を確保する点について考慮されていない。 In the technique disclosed in Patent Document 4, when Cu is contained in an amount of 0.50% by mass or more and Ni is contained in an amount of 0.45% by mass or more, there is a problem that weldability deteriorates, and an important weld heat affected zone as a steel structure. (HAZ) No consideration is given to securing toughness.
本発明は、上記した現状に鑑みてなされたものであり、合せ材の耐食性、ＨＡＺ靭性並びに母材の低温靭性、特に脆性破壊伝播停止特性に優れたオーステナイト系ステンレスクラッド鋼板およびその製造方法を提供することを目的とする。 The present invention has been made in view of the above-mentioned present situation, and provides an austenitic stainless clad steel plate excellent in corrosion resistance of a laminated material, HAZ toughness and low temperature toughness of a base material, particularly brittle fracture propagation stopping properties, and a method for producing the same. The purpose is to do.
ステンレスクラッド鋼は、無垢のステンレスや無垢の低合金鋼と異なり、合せ材の耐食性の確保、母材の機械的特性の確保、複合材料としての接合性の確保の３つの特性を同時に満たす必要がある。発明者らは、かかる事情に鑑み、合せ材の耐食性については、炭化物を抑制するために、低Ｃ量とし、さらに製造条件で圧延終了温度の低温化の防止、また、母材の機械的特性、特に低温靭性と溶接熱影響部の靭性の確保のために、母材の成分と製造条件の加熱温度と制御圧延条件の適正化、また、接合性については、製造条件のスラブ加熱温度と圧延の温度範囲とその際の圧下比について鋭意検討し、全ての特性を満足する条件を求めた。 Stainless steel clad steel, unlike solid stainless steel and solid low alloy steel, must satisfy the three characteristics of ensuring the corrosion resistance of the laminated material, ensuring the mechanical properties of the base material, and ensuring the bondability as a composite material. is there. In view of such circumstances, the inventors have made the low corrosion amount of the laminated material low in order to suppress carbides, and further prevent the rolling end temperature from being lowered under manufacturing conditions, and the mechanical properties of the base material. Especially, to ensure the low temperature toughness and the toughness of the weld heat affected zone, optimize the base material components, the heating temperature of the manufacturing conditions and the controlled rolling conditions, and the joinability, the slab heating temperature of the manufacturing conditions and the rolling The temperature range and the reduction ratio at that time were intensively studied, and the conditions satisfying all the characteristics were obtained.
本発明の要旨は、以下の通りである。 The gist of the present invention is as follows.
［１］ オーステナイト系ステンレス鋼を合せ材とし、低合金鋼を母材とするクラッド鋼板において、前記母材が、質量％で、Ｃ：０．０２０〜０．１００％、Ｓｉ：０．１０〜０．５０％、Ｍｎ：０．７５〜１．８０％、Ｐ：０．０１５％以下、Ｓ：０．００３０％以下、
Ｃｕ：０．０１〜０．５０％、Ｎｉ：０．０１〜０．４５％、Ｃｒ：０．０１〜０．５０％、
Ｍｏ：０．０１〜０．５０％、Ｎｂ：０．００５〜０．０８０％、Ｔｉ：０．００５〜０．０３０％、Ｎ：０．００１０〜０．００６０％、Ａｌ：０．０７０％以下、Ｃａ：０．００１０〜０．００４０％を含有し、残部Ｆｅ及び不可避的不純物からなることを特徴とする母材の低温靭性とＨＡＺ靭性並びに合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼板。
[1] In a clad steel plate using austenitic stainless steel as a combination material and low alloy steel as a base material, the base material is in mass%, C: 0.020 to 0.100%, Si: 0.10 0.50%, Mn: 0.75-1.80%, P: 0.015% or less, S: 0.0030% or less,
Cu: 0.01 to 0.50%, Ni: 0.01 to 0.45%, Cr: 0.01 to 0.50%,
Mo: 0.01-0.50%, Nb: 0.005-0.080%, Ti: 0.005-0.030%, N: 0.0010-0.0060%, Al: 0.070% Hereinafter, an austenitic stainless clad steel plate excellent in low-temperature toughness and HAZ toughness of the base material and corrosion resistance of the laminated material, characterized in that it contains Ca: 0.0010 to 0.0040% and consists of the balance Fe and inevitable impurities. .
［２］ さらに、前記母材のＴｉとＮの含有量（質量％）の比（Ｔｉ／Ｎ）が２．００〜４．００であることを特徴とする［１］に記載の母材の低温靭性とＨＡＺ靭性並びに合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼板。 [2] Furthermore, the ratio (Ti / N) of the content (% by mass) of Ti and N in the base material is 2.00 to 4.00. An austenitic stainless clad steel plate with excellent low-temperature toughness, HAZ toughness and corrosion resistance of laminated materials.
［３］ 前記オーステナイト系ステンレスクラッド鋼板の合せ材が、質量％で、Ｃ：０．０２０％以下、Ｓｉ：１．００％以下、Ｍｎ：１．４０％以下、Ｐ：０．０４５％以下、Ｓ：０．０３０％以下、Ｎｉ：１２．００〜１５：００％、Ｃｒ：１６．００〜１８．００％、Ｍｏ：２．００〜３．００％を含有し、残部Ｆｅ及び不可避的不純物からなることを特徴とする［１］または［２］に記載の母材の低温靭性とＨＡＺ靭性並びに合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼板。 [3] The laminated material of the austenitic stainless clad steel plate is in mass%, C: 0.020% or less, Si: 1.00% or less, Mn: 1.40% or less, P: 0.045% or less, S: 0.030% or less, Ni: 12.00 to 15: 00%, Cr: 16.00 to 18.00%, Mo: 2.00 to 3.00%, the balance Fe and inevitable impurities An austenitic stainless clad steel sheet excellent in the low temperature toughness and HAZ toughness of the base material and the corrosion resistance of the laminated material according to [1] or [2].
［４］ ［１］乃至［３］の何れかに記載のクラッド鋼板の素材を用いて、１０５０〜１１５０℃に加熱後、板表面の温度で９５０℃以上での圧下比を１．５以上とし、９００℃以下の温度域における制御圧延において、累積圧下率を５０％以上、圧延終了温度を７５０℃以上とする熱間圧延を行った後に、冷却速度３℃／ｓ以上、冷却停止温度５５０℃以下とする加速冷却を行い、その後放冷することを特徴とする母材の低温靭性とＨＡＺ靭性並びに合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼板の製造方法。 [4] Using the material of the clad steel plate according to any one of [1] to [3], after heating to 1050 to 1150 ° C., the rolling ratio at 950 ° C. or higher at the plate surface temperature is 1.5 or higher. In a controlled rolling in a temperature range of 900 ° C. or lower, after performing hot rolling with a cumulative reduction ratio of 50% or more and a rolling end temperature of 750 ° C. or higher, a cooling rate of 3 ° C./s or higher and a cooling stop temperature of 550 ° C. The manufacturing method of the austenitic stainless clad steel plate excellent in the low temperature toughness of a base material, HAZ toughness, and the corrosion resistance of a laminated material characterized by performing the accelerated cooling set forth below and then allowing to cool.
本発明によれば、母材の化学成分としてＣｕ、Ｎｉ、Ｃｒ、Ｍｏを必須元素として全て含有し、あるいはＴｉ／Ｎの範囲を限定し、また、制御圧延の条件を適正化することで、母材の低温靭性と溶接熱影響部靭性と合せ材の耐食性に優れたオーステナイト系ステンレスクラッド鋼を得ることができる。 According to the present invention, Cu, Ni, Cr, and Mo are all contained as essential elements as chemical components of the base material, or the range of Ti / N is limited, and the conditions of controlled rolling are optimized. An austenitic stainless clad steel excellent in low-temperature toughness of the base metal, weld heat-affected zone toughness and corrosion resistance of the laminated material can be obtained.
以下に本発明の各構成要件の限定理由について説明する。 The reasons for limiting the respective constituent requirements of the present invention will be described below.
１．母材の成分組成について
はじめに、本発明のクラッド鋼の母材の成分組成を規定した理由を説明する。なお、各元素の成分％は、特に記載が無い限りすべて質量％を意味する。
1. About the component composition of a base material First, the reason which prescribed | regulated the component composition of the base material of the clad steel of this invention is demonstrated. In addition, unless otherwise indicated, the component% of each element means the mass%.
Ｃ：０．０２０〜０．１００％
Ｃは鋼の強度を向上させる有効な成分であり、０．０２０％未満であると一般溶接用としては強度が得られないため０．０２０％以上とする。一方、０．１００％を超えて含有すると鋼材の溶接性やＨＡＺ靭性等を著しく劣化させるため、Ｃ量は０．０２０〜０．１００％の範囲とする。好ましくは０．０３０〜０．０８０％の範囲である。
C: 0.020 to 0.100%
C is an effective component for improving the strength of the steel, and if it is less than 0.020%, the strength cannot be obtained for general welding, so the content is made 0.020% or more. On the other hand, if the content exceeds 0.100%, the weldability and HAZ toughness of the steel material are remarkably deteriorated, so the C content is in the range of 0.020 to 0.100%. Preferably it is 0.030 to 0.080% of range.
Ｓｉ：０．１０〜０．５０％
Ｓｉは母材の強度確保、脱酸等に必要な成分であり、その効果を得るためには少なくとも０．１０％以上の含有が必要である。一方、０．５０％を超えて含有するとＨＡＺの硬化により靭性が低下するため、Ｓｉ量は０．１０〜０．５０％の範囲とする。なお、ＨＡＺ靭性の観点から、好ましくは０．２０〜０．４０％の範囲である。
Si: 0.10 to 0.50%
Si is a component necessary for securing the strength of the base material, deoxidation, and the like, and in order to obtain the effect, it is necessary to contain at least 0.10% or more. On the other hand, if the content exceeds 0.50%, the toughness decreases due to the hardening of the HAZ, so the Si content is in the range of 0.10 to 0.50%. In addition, from the viewpoint of HAZ toughness, the range is preferably 0.20 to 0.40%.
Ｍｎ：０．７５〜１．８０％
Ｍｎは母材の強度及び靭性の確保に有効な成分として０．７５％以上の含有が必要であるが、１．８０％を超えて含有すると、靭性、溶接性に悪影響を与えるため、上限値を１．８０％とする。よって、Ｍｎ量は０．７５〜１．８０％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１．００〜１．７０％の範囲である。
Mn: 0.75 to 1.80%
Mn needs to be contained in an amount of 0.75% or more as an effective component for ensuring the strength and toughness of the base material. However, if it exceeds 1.80%, it will adversely affect toughness and weldability. Is 1.80%. Therefore, the amount of Mn is made into the range of 0.75 to 1.80%. In addition, from a viewpoint of base material toughness and HAZ toughness, it is preferably in the range of 1.00 to 1.70%.
Ｐ：０．０１５％以下
Ｐは鋼中不純物として不可避な元素であるが、母材ならびに溶接熱影響部靭性を確保するためにはＰ量は０．０１５％以下とする。好ましくは０．０１０％以下である。
P: 0.015% or less P is an element that is unavoidable as an impurity in the steel, but in order to ensure the toughness of the base metal and the weld heat affected zone, the amount of P is 0.015% or less. Preferably it is 0.010% 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、低温靭性を確保するためにはＳ量は０．００３％以下とする。好ましくは０．００１０％以下である。
S: 0.003% or less S is an element that is unavoidable as an impurity in steel, but in order to ensure low temperature toughness, the amount of S is made 0.003% or less. Preferably it is 0.0010% or less.
Ｃｕ：０．０１〜０．５０％
Ｃｕは靭性の改善と強度の上昇に有効な元素の１つであるため、０．０１％以上の含有とする。しかし、０．５０％を超えて含有すると溶接性を阻害することがあるので、Ｃｕ量は０．０１〜０．５０％の範囲とする。好ましくは、０．１０〜０．４０％の範囲である。
Cu: 0.01 to 0.50%
Since Cu is one of the elements effective for improving toughness and increasing strength, the Cu content is 0.01% or more. However, if the content exceeds 0.50%, weldability may be hindered, so the Cu content is in the range of 0.01 to 0.50%. Preferably, it is 0.10 to 0.40% of range.
Ｎｉ：０．０１〜０．４５％
Ｎｉは靭性の改善と強度の上昇に有効な元素の１つであるため、０．０１％以上の含有とする。しかし、０．４５％を超えて含有すると効果が飽和し、また、Ｎｉの含有は製造コストを上昇させるため、Ｎｉ量は０．０１〜０．４５％の範囲とする。好ましくは、０．１０〜０．４０％の範囲である。
Ni: 0.01 to 0.45%
Since Ni is one of the elements effective for improving toughness and increasing strength, the Ni content is 0.01% or more. However, if the content exceeds 0.45%, the effect is saturated, and the content of Ni increases the manufacturing cost, so the Ni content is in the range of 0.01 to 0.45%. Preferably, it is 0.10 to 0.40% of range.
Ｃｒ：０．０１〜０．５０％
Ｃｒは靭性の改善と強度の上昇に有効な元素の１つであるため、０．０１％以上の含有とする。しかし、０．５０％を超えて含有すると、溶接熱影響部靭性を劣化させるので、Ｃｒ量は０．０１〜０．５０％の範囲とする。好ましくは、０．０５〜０．３５％の範囲である。
Cr: 0.01 to 0.50%
Since Cr is one of elements effective for improving toughness and increasing strength, the content is 0.01% or more. However, if the content exceeds 0.50%, the weld heat-affected zone toughness is deteriorated, so the Cr content is in the range of 0.01 to 0.50%. Preferably, it is 0.05 to 0.35% of range.
Ｍｏ：０．０１〜０．５０％
Ｍｏは母材の強度と靭性を安定的に向上させる元素であり、０．０１％以上の含有とする。しかし、０．５０％を超えて含有すると溶接熱影響部靭性や溶接性を阻害するため、Ｍｏ量は０．０１〜０．５０％の範囲とする。なお、母材強度と靭性の観点から、好ましくは、０．０５〜０．３５％の範囲である。
Mo: 0.01 to 0.50%
Mo is an element that stably improves the strength and toughness of the base material, and is contained in an amount of 0.01% or more. However, if the content exceeds 0.50%, the weld heat affected zone toughness and weldability are hindered, so the Mo content is in the range of 0.01 to 0.50%. In addition, from a viewpoint of base material strength and toughness, it is preferably in the range of 0.05 to 0.35%.
Ｎｂ：０．００５〜０．０８０％
Ｎｂは細粒化による析出強化を通じて母材の強度および靭性を向上させるのに有効であるが、その量が０．００５％未満ではその効果を有効に発揮することができない。一方、０．０８０％を超えて含有すると溶接熱影響部の靭性を劣化させるため、Ｎｂ量は０．００５〜０．０８０％の範囲とする。好ましくは、０．０１０％〜０．０５０％の範囲である。
Nb: 0.005 to 0.080%
Nb is effective in improving the strength and toughness of the base material through precipitation strengthening by refining, but if the amount is less than 0.005%, the effect cannot be exhibited effectively. On the other hand, if the content exceeds 0.080%, the toughness of the weld heat-affected zone is deteriorated, so the Nb content is in the range of 0.005 to 0.080%. Preferably, it is 0.010% to 0.050% of range.
Ｔｉ：０．００５〜０．０３０％
ＴｉはＴｉＮを形成してスラブ加熱時の粒成長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強度と母材ならびに溶接熱影響部の靭性を改善する効果があるので、０．００５％以上の含有とする。しかし、０．０３０％を超えて含有すると、かえって上記効果が得られないのみならず、靭性も劣化させる。したがって、Ｔｉ量は０．００５〜０．０３０％の範囲とする。好ましくは、０．０１０〜０．０２０％の範囲である。
Ti: 0.005-0.030%
Ti forms TiN to suppress grain growth during slab heating and grain growth in the weld heat affected zone, resulting in refinement of the microstructure and improving strength, base material and toughness of weld heat affected zone Therefore, the content is 0.005% or more. However, if the content exceeds 0.030%, the above effect is not obtained, but the toughness is also deteriorated. Therefore, the Ti amount is in the range of 0.005 to 0.030%. Preferably, it is 0.010 to 0.020% of range.
Ｎ：０．００１０〜０．００６０％
ＮはＴｉＮとして析出することで溶接熱影響部靭性の向上に効果があるが、Ｎの含有量が０．００１０％未満では効果が薄れるため下限を０．００１０％とする。しかしながら０．００６０％を超えると固溶Ｎが増大し溶接熱影響部靭性の低下がおこる。Ｔｉの含有量と対応させるＴｉＮの微細析出によるＨＡＺ靭性の向上を考慮してＮ量は、０．００１０〜０．００６０％の範囲とする。
N: 0.0010 to 0.0060%
N precipitates as TiN and is effective in improving the weld heat-affected zone toughness. However, if the N content is less than 0.0010%, the effect decreases, so the lower limit is made 0.0010%. However, if it exceeds 0.0060%, the solute N increases and the weld heat affected zone toughness decreases. Considering the improvement of HAZ toughness due to the fine precipitation of TiN corresponding to the Ti content, the N content is set in the range of 0.0010 to 0.0060%.
Ａｌ：０．０７０％以下
Ａｌは、製鋼過程の脱酸用として重要な元素であるとともに、溶接熱影響部の靭性向上にも効力を有する。しかし、０．０７０％を超えて含有しても溶接熱影響部の靭性改善効果は飽和するので、Ａｌ量は０．０７０％以下とする。溶接熱影響部の靭性改善効果のために、好ましくは、０．０１％以上とする。
Al: 0.070% or less Al is an important element for deoxidation in the steelmaking process, and has an effect on improving the toughness of the weld heat affected zone. However, even if the content exceeds 0.070%, the effect of improving the toughness of the weld heat affected zone is saturated, so the Al content is 0.070% or less. In order to improve the toughness of the heat affected zone, the content is preferably 0.01% or more.
Ｃａ：０．００１０〜０．００４０％
Ｃａは硫化物系介在物の形態を制御し母材の靭性と溶接熱影響部靭性を改善する効果があるため、０．００１０％以上の含有とする。しかし、０．００４０％を超えて含有すると効果が飽和し、逆に清浄度を低下させ溶接熱影響部靭性を劣化させるので、Ｃａ量は０．００１０〜０．００４０％の範囲とする。好ましくは０．００２０〜０．００３０％の範囲である。
Ca: 0.0010 to 0.0040%
Ca has the effect of controlling the form of sulfide inclusions and improving the toughness of the base metal and the toughness of the heat affected zone of the base metal, so it is contained in an amount of 0.0010% or more. However, if the content exceeds 0.0040%, the effect is saturated, and conversely, the cleanliness is lowered and the weld heat affected zone toughness is deteriorated. Therefore, the Ca content is in the range of 0.0010 to 0.0040%. Preferably it is 0.0020 to 0.0030% of range.
以上が本発明のクラッド鋼の母材の基本成分であり、残部はＦｅおよび不可避的不純物であが、上記成分に加えて、ＴｉおよびＮについてはさらに、以下の制限を設けることができる。 The above are the basic components of the base material of the clad steel of the present invention, and the balance is Fe and inevitable impurities. In addition to the above components, the following restrictions can be further provided for Ti and N.
Ｔｉ／Ｎ：２．００〜４．００
なお、ＴｉおよびＮは、各元素の含有量（質量％）を表す。
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２．００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４．００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２．００〜４．００の範囲とすることが好ましい。
Ti / N: 2.00 to 4.00
In addition, Ti and N represent content (mass%) of each element.
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 2.00 by mass%, the crystal grains are coarsened and the toughness value may be greatly reduced. Moreover, when Ti / N exceeds 4.00, the toughness value may decrease for the same reason. Therefore, Ti / N is preferably in the range of 2.00 to 4.00.
２．合せ材の成分組成について
次に、本発明のクラッド鋼の合せ材の成分組成を規定した理由を説明する。なお、各元素の成分％は、特に記載が無い限りすべて質量％を意味する。
2. Next, the reason why the component composition of the clad steel of the present invention is defined will be described. In addition, unless otherwise indicated, the component% of each element means the mass%.
Ｃ：０．０２０％以下
Ｃはクラッド鋼の製造において、圧延中の熱履歴で炭化物として析出し、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、炭化物の析出が促進されて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、０．０１５％以下である。
C: 0.020% or less C is an element that should be avoided in the production of clad steel because it precipitates as carbides due to the thermal history during rolling and inhibits corrosion resistance. If the content exceeds 0.020%, precipitation of carbides is promoted and corrosion resistance deteriorates, so the C content is 0.020% or less. Preferably, it is 0.015% or less.
Ｓｉ：１．００％以下
Ｓｉは製造時の脱酸に有効な成分である。しかしながら、１．００％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１．００％以下とする。好ましくは、０．７５％以下である
Ｍｎ：１．４０％以下
Ｍｎも製鋼時の脱酸に有効な成分である。しかしながら、１．４０％を超えて含有すると、ＭｎＳといった非金属介在物が残存し、耐食性が劣化し、また熱間加工性も劣化するため、１．４０％以下とする。好ましくは１．００％以下とする。
Si: 1.00% or less Si is a component effective for deoxidation during production. However, if the content exceeds 1.00%, it remains as a non-metallic inclusion, the corrosion resistance deteriorates, and the hot workability also deteriorates, so the Si amount is made 1.00% or less. Preferably, it is 0.75% or less Mn: 1.40% or less Mn is also an effective component for deoxidation during steelmaking. However, if the content exceeds 1.40%, non-metallic inclusions such as MnS remain, corrosion resistance deteriorates, and hot workability also deteriorates, so the content is made 1.40% or less. Preferably it is 1.00% or less.
Ｐ：０．０４５％以下
Ｐは不純物であり、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０．０４５％以下とする。好ましくは、０．０３０％以下とする。
P: 0.045% or less P is an impurity, and is an element that segregates at grain boundaries and degrades corrosion resistance. Therefore, the P content is 0.045% or less. Preferably, it is 0.030% or less.
Ｓ：０．０３０％以下
ＳはＰと同様で不純物元素であり、ＭｎＳといった非金属介在物が析出して耐食性を劣化させる。したがって、Ｓ量は０．０３０％以下とする。好ましくは、０．０１０以下とする。
S: 0.030% or less S is an impurity element similar to P, and non-metallic inclusions such as MnS are precipitated to deteriorate the corrosion resistance. Therefore, the S amount is 0.030% or less. Preferably, it is 0.010 or less.
Ｎｉ：１２．００〜１５．００％
Ｎｉはオーステナイト系ステンレス鋼の主要元素であり、耐食性を向上させる元素である。後述する、Ｃｒによって形成される酸化皮膜の密着性が増し、Ｃｒとの複合添加によって耐食性が向上する。しかし、高価な元素であるため、耐食性能と価格のバランスを考慮して、Ｎｉ量は、１２．００〜１５．００％の範囲とする。好ましくは、１２．５０〜１４．５０％の範囲である。
Ni: 12.00 to 15.00 %
Ni is a main element of austenitic stainless steel and is an element that improves corrosion resistance. The adhesion of an oxide film formed of Cr, which will be described later, is increased, and the corrosion resistance is improved by the combined addition with Cr. However, since it is an expensive element, the Ni content is set in the range of 12.00 to 15.00% in consideration of the balance between corrosion resistance and price. Preferably, it is 12.50 to 14.50% of range.
Ｃｒ：１６．００〜１８．００％
Ｃｒは、金属の表面に保護性の高い酸化皮膜を形成し、耐孔食性や耐粒界腐食性といった耐食性を向上させる元素である。しかし、高価な元素であるため、耐食性能と価格のバランスを考慮して、Ｃｒ量は１６．００〜１８．００％の範囲とする。好ましくは、１６．５０〜１４．５０％の範囲である。
Cr: 16.00-18.00%
Cr is an element that forms a highly protective oxide film on a metal surface and improves corrosion resistance such as pitting corrosion resistance and intergranular corrosion resistance. However, since it is an expensive element, the amount of Cr is set in the range of 16.00 to 18.00% in consideration of the balance between corrosion resistance and price. Preferably, it is 16.50 to 14.50% of range.
Ｍｏ：２．００〜３．００％
Ｍｏは、耐孔食性、耐隙間腐食性を向上させる元素である。ＣｒとＮｉとの複合効果によって耐食性が向上するが、高価な元素であり、ＣｒとＮｉの添加量と価格のバランスを考慮して、Ｍｏ量は２．００〜３．００％の範囲とする。好ましくは、２．２０〜２．８０％の範囲である。
Mo: 2.00 to 3.00%
Mo is an element that improves pitting corrosion resistance and crevice corrosion resistance. Although the corrosion resistance is improved by the combined effect of Cr and Ni, it is an expensive element, and considering the balance between the addition amount of Cr and Ni and the price, the Mo amount is in the range of 2.00 to 3.00%. . Preferably, it is 2.20 to 2.80% of range.
上記した合せ材の成分の残部はＦｅおよび不可避的不純物である。また、不可避的不純物としては、Ｃｕ、Ｂ、Ｃａ、Ｎ、Ｏ等が挙げられ、それぞれ、Ｃｕ：０．５０％以下、Ｂ：０．００１０％以下、Ｃａ：０．００５０％以下、Ｎ：０．０５％以下、Ｏ：０．００５０％以下の範囲内で含有しても耐食性に何ら影響を与えるものではない。当然ながら、その他の不可避的不純物が含有されても特性に影響しないので、含有してもかまわない。 The balance of the components of the above-mentioned laminated material is Fe and inevitable impurities. Inevitable impurities include Cu, B, Ca, N, O, etc., Cu: 0.50% or less, B: 0.0010% or less, Ca: 0.0050% or less, N: Even if it is contained within the range of 0.05% or less and O: 0.0050% or less, it does not affect the corrosion resistance. Of course, the inclusion of other inevitable impurities does not affect the characteristics, so it may be contained.
３．製造方法について
本発明のオーステナイト系ステンレスクラッド鋼の製造方法について以下に述べる。
3. About a manufacturing method The manufacturing method of the austenitic stainless clad steel of this invention is described below.
本発明のクラッド鋼の母材素材ならびに合せ材素材は、上述した成分範囲に調整され、常法により溶製することができる。なお、本発明のステンレスクラッド鋼の母材としては、炭素鋼や低合金鋼を用いることができる。そして、本発明のステンレスクラッド鋼は、この母材の片面または両面に合せ材として上記成分範囲のステンレス鋼がクラッドされたものである。 The base material and the laminated material of the clad steel of the present invention are adjusted to the above-described component ranges and can be melted by a conventional method. Carbon steel or low alloy steel can be used as the base material of the stainless clad steel of the present invention. The stainless clad steel of the present invention is obtained by clad stainless steel having the above component range as a laminated material on one side or both sides of the base material.
クラッド圧延用組立スラブ（クラッド鋼板の素材）は、母材／合せ材／合せ材／母材というように重ね合わせた形式が製造上効率的であり、また冷却時の反りを考慮すると、母材同士、合せ材同士は等厚であることが望ましい。もちろん、上記した組立方式に限定されるものではない。 As for the assembly slab for clad rolling (clad steel plate material), the superposition type of base material / lamination material / lamination material / base material is efficient in manufacturing, and considering the warping during cooling, the base material It is desirable that the thicknesses are equal to each other. Of course, it is not limited to the assembly method described above.
加熱温度：１０５０〜１１５０℃
加熱時に合せ材を十分溶体化するために１０５０℃以上に加熱する。クラッド鋼の接合性の観点からは、加熱温度は高温である方が好ましいが、高温に加熱しすぎると合せ材中にδフェライトが生成し耐食性の低下が起こり、また、１１５０℃以上に加熱すると、母材の結晶粒粗大化によって靭性劣化を招く。よって、耐食性、低温靭性、接合性の観点から、加熱温度は１０５０〜１１５０℃の範囲とする。
Heating temperature: 1050-1150 ° C
Heating to 1050 ° C. or higher in order to sufficiently dissolve the laminated material during heating. From the viewpoint of the bondability of the clad steel, it is preferable that the heating temperature is high. However, if heated to a high temperature, δ ferrite is generated in the laminated material, resulting in a decrease in corrosion resistance. In addition, toughness deterioration is caused by the coarsening of crystal grains of the base material. Therefore, from the viewpoint of corrosion resistance, low temperature toughness, and bondability, the heating temperature is set to a range of 1050 to 1150 ° C.
９５０℃以上での圧下比：１．５以上
クラッド鋼は高温域での圧延によって、接合性が確保される。高温域での圧延が重要な意味としては、合せ材であるオーステナイト系ステンレス鋼と母材である低合金鋼の変形抵抗差が小さくなるため、圧延で理想的な接合界面となる点と、高温域では合せ材と母材両者の元素相互拡散が進行しやすいためである。
Rolling ratio at 950 ° C. or higher: 1.5 or higher Clad steel is secured by rolling in a high temperature region. The important meaning of rolling in a high temperature range is that the difference in deformation resistance between the austenitic stainless steel that is the laminated material and the low alloy steel that is the base material is small. This is because the interdiffusion of both the laminated material and the base material easily proceeds in the region.
よって、クラッド圧延用組立スラブを作製する段階で、組立スラブ内の真空度が１０−４ｔｏｒｒ以上の高真空を確保できれば、合せ材／母材界面で十分な金属接合を得るためには、９５０℃以上での圧下比が１．５以上であれば良い。ここで、圧下比は、圧延前の板厚／圧延後の板厚 と定義する。 Therefore, if a high vacuum with a degree of vacuum of 10 −4 torr or more can be secured at the stage of manufacturing the clad rolling assembly slab, 950 is sufficient to obtain a sufficient metal joint at the laminated material / base metal interface. It is sufficient that the reduction ratio at 1.5 ° C. or higher is 1.5 or higher. Here, the reduction ratio is defined as the thickness before rolling / the thickness after rolling.
接合性の確保のためには、好ましくは、温度範囲は１０００℃以上であり、圧下比は２．０以上である。 In order to ensure the bondability, the temperature range is preferably 1000 ° C. or higher and the rolling ratio is 2.0 or higher.
次に、発明者らの検討によれば、母材の強度、低温靭性、特に脆性破壊の伝播停止特性を改善するには、オーステナイト低温域での高圧下と圧延直後の水冷が有効であることが明らかとなった。そこで制御圧延と圧延後の冷却条件について以下に述べる。 Next, according to the study by the inventors, water cooling under a high pressure in the austenite low temperature region and immediately after rolling is effective in improving the strength of the base material, low temperature toughness, especially the propagation stop property of brittle fracture. Became clear. Therefore, control rolling and cooling conditions after rolling will be described below.
制御圧延：９００℃以下において累積圧下率５０％以上、圧延終了温度：７５０℃以上
オーステナイト未再結晶にて累積圧下率が５０％以上の圧延を行うことにより、オーステナイト粒が伸展し、その後の加速冷却で変態生成するベイナイトが微細化し靭性が向上する。圧延仕上げ温度は低下しすぎると、元素拡散の進行が生じにくく接合性の劣化に繋がり、また、７５０℃以下での圧延は合せ材中の炭化物やσ相の析出が促進される。よって、制御圧延は、母材の強度、低温靭性と合せ材の耐食性、クラッド鋼の接合性を全て確保するために、制御圧延開始温度は９００℃以下、累積圧下率は５０％以上とし、７５０℃以上の温度で仕上げ圧延を終了することとする。
Controlled rolling: Cumulative rolling reduction at 900 ° C. or lower, rolling reduction temperature: 750 ° C. or higher Rolling at a cumulative rolling reduction of 50% or higher by austenite non-recrystallization causes austenite grains to expand, and subsequent acceleration The bainite transformed by cooling is refined and the toughness is improved. If the rolling finish temperature is too low, the element diffusion is unlikely to proceed, leading to deterioration of the bondability, and rolling at 750 ° C. or less promotes precipitation of carbides and σ phase in the laminated material. Therefore, in the controlled rolling, in order to ensure all of the strength of the base metal, the low temperature toughness, the corrosion resistance of the laminated material, and the weldability of the clad steel, the controlled rolling start temperature is 900 ° C. or less, the cumulative rolling reduction is 50% or more, 750 Finish rolling is finished at a temperature of ℃ or higher.
冷却速度：３℃／ｓ以上、冷却停止温度：５５０℃以下
圧延終了後に５５０℃以下まで加速冷却するのは、母材の強度、低温靭性を担保するためである。冷却速度は、耐食性に大きく影響し、冷却速度は３℃／ｓ未満では、圧延直後からの冷却過程において、合せ材中に炭化物やσ相が析出し、耐食性が劣化する。よって、冷却停止温度は５５０℃以下とし、冷却速度は３℃／ｓ以上とする。冷却速度は、好ましくは、５℃／ｓ以上である。
Cooling rate: 3 ° C./s or more, cooling stop temperature: 550 ° C. or less Accelerated cooling to 550 ° C. or less after completion of rolling is to ensure the strength and low temperature toughness of the base material. The cooling rate greatly affects the corrosion resistance. When the cooling rate is less than 3 ° C./s, carbides and σ phases are precipitated in the laminated material in the cooling process immediately after rolling, and the corrosion resistance deteriorates. Therefore, the cooling stop temperature is set to 550 ° C. or lower, and the cooling rate is set to 3 ° C./s or higher. The cooling rate is preferably 5 ° C./s or more.
以下に本発明の実施例を説明する。 Examples of the present invention will be described below.
表１に示す成分組成からなる母材と、表２に示す成分組成からなる合せ材を用いて、クラッド鋼を製造した。製造条件は、母材／合せ材／合せ材／母材を重ねて一組のスラブに組み立てた。スラブにおける母材の厚みは１３０ｍｍ、合せ材の厚みは１８ｍｍとした。ついで、表３に示す加熱、圧延、冷却条件で熱間圧延を行い、その後空冷することで、厚みが（母材２３．５０ｍｍ＋合せ材３．２５ｍｍ）の片面クラッド鋼板を製造した。
そして、各クラッド鋼板から引張試験、ＤＷＴＴ試験、塩化第二鉄腐食試験の試験片を採取し、各試験に供した。
Clad steel was manufactured using a base material having the component composition shown in Table 1 and a laminated material having the component composition shown in Table 2. The manufacturing conditions were as follows. The base material / lamination material / lamination material / base material was stacked and assembled into a set of slabs. The thickness of the base material in the slab was 130 mm, and the thickness of the laminated material was 18 mm. Next, hot rolling was performed under the heating, rolling, and cooling conditions shown in Table 3, and then air cooling was performed to produce a single-side clad steel plate having a thickness (base material 23.50 mm + lamination material 3.25 mm).
And the test piece of the tension test, the DWTT test, and the ferric chloride corrosion test was extract | collected from each clad steel plate, and it used for each test.
ここで、溶接部靭性の評価は、ＪＩＳ Ｚ２２０２のＶノッチシャルピー試験により行った。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。 Here, the evaluation of the weld zone toughness was performed by the V-notch Charpy test of JIS Z2202. 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、ＡＰＩ規格に準拠したＤＷＴＴ試験片を採取し、−２０℃におけるＤＷＴＴ試験（落重試験）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％以上を母材の低温靭性に優れているものとした。
Further, the toughness of the base material was evaluated by a DWTT test (falling weight test) at −20 ° C. by collecting a DWTT test piece based on the API standard.
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 low temperature toughness of the base material.
母材の引張試験は、ＡＰＩ−５Ｌに準拠した引張試験片を採取して引張試験を行い、本発明の引張強度の目標はＡＰＩ ５Ｌ Ｘ６５相当以上とし、ＹＳが４５０ＭＰａ以上、ＴＳが５３５ＭＰａ以上を母材強度に優れているものとした。 The tensile test of the base material is performed by taking a tensile test piece based on API-5L and conducting a tensile test. The target tensile strength of the present invention is API 5L X65 or higher, YS is 450 MPa or higher, and TS is 535 MPa or higher. It was assumed that the base material strength was excellent.
また、クラッド鋼としての接合性は、ＪＩＳ Ｇ０６０１：２０１２のクラッド鋼の試験方法に記載のせん断強さ試験に準拠して行った。評価基準はせん断強さが３００ＭＰａ以上のものを接合性が良好であると判断した。 Moreover, the joining property as clad steel was performed based on the shear strength test described in the test method of clad steel of JIS G0601: 2012. The evaluation criteria were determined to be good bondability when the shear strength was 300 MPa or more.
一方、合せ材の耐食性試験は、ＪＩＳ Ｇ０５７８：２０００のステンレス鋼の塩化第二鉄腐食試験方法に準拠し、試験温度５０℃での浸漬試験を行い、腐食減少量が５０ｇ／ｍ２・ｈｒ未満を合せ材の耐食性に優れているものとした。 On the other hand, the corrosion resistance test of the laminated material is based on the ferric chloride corrosion test method of stainless steel of JIS G0578: 2000, and an immersion test is performed at a test temperature of 50 ° C., and the corrosion reduction amount is less than 50 g / m 2 · hr. The laminated material has excellent corrosion resistance.
表４に試験結果を示す。 Table 4 shows the test results.
母材の化学成分と合せ材の化学成分と製造条件が本発明の範囲を満足する発明例である実施例Ｎｏ．１〜１６は、母材部の引張特性、ＤＷＴＴ特性（低温靭性）およびＨＡＺ靭性（溶接熱影響部靭性）と合せ材の耐食性とクラッド鋼としての接合性を満足する。 Example No. which is an invention example in which the chemical composition of the base material, the chemical composition of the laminated material and the production conditions satisfy the scope of the present invention. Nos. 1 to 16 satisfy the tensile properties, DWTT properties (low temperature toughness) and HAZ toughness (welding heat affected zone toughness) of the base metal part, the corrosion resistance of the laminated material, and the bondability as clad steel.
一方、比較例である実施例Ｎｏ．１７、１８、２１〜２５は、本発明の範囲を外れているので引張特性、ＤＷＴＴ特性等のいずれかの項目を満たしていない。 On the other hand, Example No. which is a comparative example. Nos. 17 , 18, and 21 to 25 are out of the scope of the present invention and do not satisfy any of the items such as tensile properties and DWTT properties.
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