JP4441295B2 - Manufacturing method of high strength steel for welding and high strength steel for welding with excellent corrosion resistance and machinability - Google Patents

Manufacturing method of high strength steel for welding and high strength steel for welding with excellent corrosion resistance and machinability Download PDF

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JP4441295B2
JP4441295B2 JP2004072438A JP2004072438A JP4441295B2 JP 4441295 B2 JP4441295 B2 JP 4441295B2 JP 2004072438 A JP2004072438 A JP 2004072438A JP 2004072438 A JP2004072438 A JP 2004072438A JP 4441295 B2 JP4441295 B2 JP 4441295B2
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corrosion resistance
welding
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steel
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直樹 斎藤
謙治 加藤
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Nippon Steel Corp
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Priority to PCT/JP2004/006663 priority patent/WO2005087964A1/en
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys

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Description

本発明は、耐食性および切削性に優れた溶接用高強度鋼および溶接用高強度鋼板の製造法に係るものである。   The present invention relates to a method for producing high-strength steel for welding and high-strength steel plate for welding excellent in corrosion resistance and machinability.

近年、各種建築構造物や貯槽容器等に、ステンレス鋼の使用が拡大されてきている。しかしながら、スレンレス鋼、特にオーステナイト系ステンレス鋼は、耐食性は優れているものの、高価であると同時に、降伏強度が低く、かつ切削、孔明けなどの機械加工がしにくいなどの欠点がある。近年、耐食性の向上あるいは耐食性と加工性の向上を目的としたCrにAlを添加した鋼が提案されている(例えば特許文献1〜8)。これらの鋼は、耐食性あるいは耐食性と加工性の向上を図るためになされた技術であり、ある程度有効性が認められるが、一方、粗大なフェライトの生成により溶接熱影響部に割れが発生したり、する場合があり、かつ、切削性などの機械加工性は、あまり改善されていない。
特開平5-279791号公報 特開平6-179949号公報 特開平6-179950号公報 特開平6-179951号公報 特開平6-212256号公報 特開平6-212257号公報 特開平7-3388号公報 特開平11-350082 号公報
In recent years, the use of stainless steel has been expanded in various building structures and storage containers. However, although stainless steel, particularly austenitic stainless steel, is excellent in corrosion resistance, it is expensive and has disadvantages such as low yield strength and difficulty in machining such as cutting and drilling. In recent years, steels in which Al is added to Cr for the purpose of improving corrosion resistance or improving corrosion resistance and workability have been proposed (for example, Patent Documents 1 to 8). These steels are technologies made to improve corrosion resistance or corrosion resistance and workability, and some effectiveness is recognized, but on the other hand, cracks occur in the heat affected zone due to the formation of coarse ferrite, In addition, the machinability such as machinability has not been improved so much.
JP 5-279791 A JP-A-6-179949 Japanese Patent Laid-Open No. 6-17950 JP-A-6-179951 JP-A-6-212256 JP-A-6-212257 Japanese Unexamined Patent Publication No. 7-3388 Japanese Patent Laid-Open No. 11-350082

本発明は、こうした現状に鑑みて、室内環境や、大気中環境において、腐食抵抗が大きくかつ切削性を改善すると同時に、溶接性が良好な低コストで製造可能な鋼板を提供することを目的としている。   In view of such a current situation, the present invention aims to provide a steel sheet that has a high corrosion resistance and improves machinability in an indoor environment or an atmospheric environment, and at the same time has a good weldability and can be manufactured at low cost. Yes.

本発明者らは上記の目的を達成すべく、結露腐食環境、大気腐食環境、水道水腐食環境、コンクリート腐食環境、海水腐食環境等の腐食環境において優れた耐食性を有する鋼を開発するべく、種々の観点から検討を行った。まず、優れた溶接部靭性と同時に上記の該腐食環境において耐食性を向上させる手段を種々検討した結果、Crを2〜7%含有する鋼に、Alを0.1〜2%を添加した鋼が上述した多くの腐食環境で非常に優れた耐食性を示すことを見出した。しかしながら、このような鋼はフェライト相変態域が広く、例えば、溶接時に1200℃以上に加熱されると粗大フェライトが生成し、このために靭性が大きく低下する懸念がある。そこで、発明者らは、多くの実験を重ねた結果、溶接時に起こるフェライト相変態の生成を抑制するための手段として、添加合金元素量との関係を定量化することに成功し、次に示すTp なる式の範囲を満たす合金添加量の時に、高温域でのフェライトの生成が抑制されることを見出した。   In order to achieve the above object, the present inventors have developed various steels having excellent corrosion resistance in a corrosive environment such as a condensation corrosive environment, an atmospheric corrosive environment, a tap water corrosive environment, a concrete corrosive environment, and a seawater corrosive environment. We examined from the viewpoint of. First, as a result of various investigations on means for improving the corrosion resistance in the corrosive environment as well as excellent toughness of the welded portion, a steel in which 0.1 to 2% of Al is added to steel containing 2 to 7% of Cr is obtained. It has been found that it exhibits excellent corrosion resistance in many of the above-mentioned corrosive environments. However, such a steel has a wide ferrite phase transformation region. For example, when it is heated to 1200 ° C. or higher during welding, coarse ferrite is generated, and there is a concern that the toughness is greatly reduced. Therefore, as a result of repeating many experiments, the inventors succeeded in quantifying the relationship with the amount of additive alloy element as a means for suppressing the generation of ferrite phase transformation that occurs during welding, as shown below. It has been found that the formation of ferrite in the high temperature range is suppressed when the alloy addition amount satisfies the range of the expression Tp.

さらに、切削性の改善から、母材組織に着目し、単相組織よりも軟質相と硬質相と適切に混合させることが重要であるとの知見に基づき、熱間圧延後、鋼板空冷中に適切な母材組織を生成させるための合金添加量、Tc 式を導入した。すなわち、本発明では、このTc 式により、切削性を改善できる成分範囲が得られた。   Furthermore, focusing on the base material structure for improving machinability, based on the knowledge that it is more important to mix the soft phase and the hard phase appropriately than the single phase structure, after hot rolling, during the air cooling of the steel sheet An alloy addition amount for generating an appropriate matrix structure, a Tc formula, was introduced. That is, in this invention, the component range which can improve machinability by this Tc type | formula was obtained.

本発明の骨子は、
(1)、質量%で、
C :0.03%越え0.3%以下
Si:0.01〜1.0%
Mn:0.1〜3%未満
P :0.03%以下
S :0.01%以下
Cr:2〜7%
Al:0.1〜2%
N :0.02%以下
を含有し、残部Fe及び不可避的不純物とする鋼において、次式で示されるTp 値が1150以上で、かつ、Tc 値が600 以上となる成分を含有することを特徴とする耐食性および切削性に優れた溶接用高強度鋼。

Figure 0004441295
(2)、質量%で、
C :0.03%越え0.3%
Si:0.01〜1.0%
Mn:0.1〜3%未満
P :0.03%以下
S :0.01%以下
Cr:2〜7%
Al:0.1〜2%
N :0.02%以下
を含有し、かつ選択的に、
Cu:0.01〜5%
Ni:0.01〜5%
Mo:0.005〜1%
V :0.005〜0.1%
Nb:0.005〜0.050%
Ti:0.005〜0.03%
Ca:0.0005〜0.05%
Mg:0.0005〜0.05%
REM:0.001〜0.1%
の1種または2種を含有し、残部Fe及び不可避的不純物とする鋼において、次式で示されるTp 値が1150以上で、かつ、Tc 値が600 以上となる成分を含有することを特徴とする耐食性および切削性に優れた溶接用高強度鋼。
Figure 0004441295
(3)、前記した(1)または(2)記載の耐食性および切削性に優れた溶接用高強度鋼の鋼塊を加熱後、熱間圧延し700 ℃以上の温度から空冷することを特徴とする耐食性および切削性に優れた溶接用高強度鋼板の製造法、
(4)、熱間圧延後、Ac 1 変態点以下の温度で焼戻しをすることを特徴とする(3)に記載の耐食性および切削性に優れた溶接用高強度鋼板の製造法、
である。 The gist of the present invention is
(1) By mass%
C: 0.03% to 0.3% or less Si: 0.01 to 1.0%
Mn: Less than 0.1 to 3% P: 0.03% or less S: 0.01% or less Cr: 2-7%
Al: 0.1 to 2%
N: steel containing 0.02% or less, the balance being Fe and inevitable impurities , containing a component having a Tp value of 1150 or more and a Tc value of 600 or more represented by the following formula High strength steel for welding with excellent corrosion resistance and machinability.
Figure 0004441295
(2) By mass%
C: 0.03% over 0.3%
Si: 0.01 to 1.0%
Mn: less than 0.1 to 3%
P: 0.03% or less
S: 0.01% or less
Cr: 2-7%
Al: 0.1 to 2%
N: 0.02% or less
And optionally,
Cu: 0.01 to 5%
Ni: 0.01 to 5%
Mo: 0.005 to 1%
V: 0.005-0.1%
Nb: 0.005 to 0.050%
Ti: 0.005 to 0.03%
Ca: 0.0005 to 0.05%
Mg: 0.0005 to 0.05%
REM: 0.001 to 0.1%
A steel containing one or two of the above, the balance being Fe and inevitable impurities, containing a component having a Tp value of 1150 or more and a Tc value of 600 or more represented by the following formula: High strength steel for welding with excellent corrosion resistance and machinability.
Figure 0004441295
(3) characterized in that after heating the steel ingot of high strength steel for welding excellent in corrosion resistance and machinability as described in (1) or (2) above, it is hot-rolled and air-cooled from a temperature of 700 ° C. or higher. Manufacturing method of high strength steel sheet for welding with excellent corrosion resistance and machinability,
(4) The method for producing a high-strength steel sheet for welding excellent in corrosion resistance and machinability according to (3), characterized by tempering at a temperature not higher than the Ac 1 transformation point after hot rolling ,
It is.

本発明は室内環境をはじめとして、結露腐食環境、大気腐食環境、海水腐食環境等の種々の腐食環境において耐食性に優れると同時に、溶接構造物において重要な母材部および溶接熱影響部の靭性に優れる高強度鋼および高強度鋼板の製造法をきわめて低コストで提供することを可能としたものであり、産業の発展に貢献するところ極めて大きい。   The present invention is excellent in corrosion resistance in various corrosive environments such as an indoor environment, condensation corrosive environment, atmospheric corrosive environment, seawater corrosive environment, etc., and at the same time, toughness of an important base material part and weld heat affected zone in a welded structure. This makes it possible to provide excellent high-strength steel and high-strength steel sheet manufacturing methods at an extremely low cost, and is extremely important in contributing to industrial development.

(必須含有成分)
C: Cは、強度を改善する元素であると同時に、母材の硬質相の硬さを上昇させ、切削性を改善させることができる元素であるため、0.03%を越える添加が必要であるが、0.3%を超える添加では、HAZ 部が効果し溶接性を損ねるため、その上限を0.3%とした。
(Essential ingredients)
C: C is an element that improves the strength and at the same time increases the hardness of the hard phase of the base material and can improve the machinability. Therefore, it is necessary to add more than 0.03%. However, if added over 0.3%, the HAZ part is effective and the weldability is impaired, so the upper limit was made 0.3%.

Si: Siは、Crを2%以上含有する鋼に脱酸剤および強化元素として添加することが有効であるが、含有量が0.01%未満ではその脱酸効果が充分ではなく、1.0%を超えて含有するとその効果は飽和している上に、かえって溶接熱影響部靭性を低下させるので、含有量の範囲を0.01%以上1.0%以下に限定する。   Si: It is effective to add Si as a deoxidizer and strengthening element to steel containing 2% or more of Cr. However, if the content is less than 0.01%, the deoxidation effect is not sufficient. If the content exceeds 0%, the effect is saturated and the weld heat-affected zone toughness is lowered. Therefore, the content range is limited to 0.01% to 1.0%.

Cr: Crは、耐食性を確保するために2%以上を含有させることが必要であるが、7%を超えて含有させると、溶接熱影響部靱性などを阻害するので上限を7%とする。   Cr: Cr needs to be contained in an amount of 2% or more in order to ensure corrosion resistance, but if it exceeds 7%, the weld heat-affected zone toughness will be hindered, so the upper limit is made 7%.

Al: Alは、本発明において耐食性を確保するためにCrと並んで重要な元素であって、Alの含有量は、耐食性を確保する観点から0.1%以上の必要であるが、一方、2%を超えて添加すると固溶して溶接熱影響部靭性阻害するので、その含有量は0.1%以上2%以下に限定する。   Al: Al is an important element along with Cr in order to ensure corrosion resistance in the present invention, and the content of Al is required to be 0.1% or more from the viewpoint of ensuring corrosion resistance, If added over 2%, it dissolves and inhibits the weld heat affected zone toughness, so its content is limited to 0.1% or more and 2% or less.

Mn: Mnは本発明においては、主として強度の改善とオーステナイト形成元素として作用し、耐食性の観点から添加されているCrおよびAlにより助長される粗大フェライトの形成を抑制するために添加される。すなわち、CrおよびAlは周知のようにフェライト形成元素であり、これらが多量に添加されると、凝固から室温に至るまで変態を経ずしてフェライト単相組織となり、母材のみならず、溶接熱影響部においても著しく溶接性を阻害する場合がある。そこで、発明者らは、耐食性を損なわずに母材および靭性の改善を目的として、系統的に実験を行った結果、Mnの添加によりそれが回避できることを見出した。その具体的な制約条件は後に述べるが、それによると、Mn量は0.1%以上添加することが必要であるが、3%以上の添加量では、母材組織が硬化性が上昇するために3%未満の添加とする。   Mn: In the present invention, Mn is added mainly to improve the strength and to act as an austenite forming element, and to suppress the formation of coarse ferrite promoted by Cr and Al added from the viewpoint of corrosion resistance. That is, as is well known, Cr and Al are ferrite-forming elements, and when they are added in large amounts, they undergo a transformation from solidification to room temperature and become a ferrite single-phase structure. In the heat affected zone, weldability may be significantly impaired. Therefore, the inventors have conducted a systematic experiment for the purpose of improving the base material and toughness without impairing the corrosion resistance, and as a result, found that it can be avoided by adding Mn. The specific constraint conditions will be described later. According to this, it is necessary to add 0.1% or more of Mn, but the addition of 3% or more increases the hardenability of the base material structure. Less than 3%.

N: Nは、鋼板の多量に添加されると母材および溶接熱影響部の靭性を低下させるので、少ない方が望ましく、上限の含有量は、0.02%とする。   N: If N is added in a large amount in the steel sheet, the toughness of the base metal and the weld heat-affected zone is lowered, so a smaller amount is desirable, and the upper limit content is 0.02%.

P: Pは、多量に存在すると靭性を低下させるので少ない方が望ましく、上限の含有量は0.03%とする。不可避的に混入する含有量をできる限り少なくするのがよい。   P: If P is present in a large amount, the toughness is lowered, so a smaller amount is desirable, and the upper limit content is 0.03%. It is preferable to reduce the content inevitably mixed in as much as possible.

S: Sも多量に存在すると耐孔食性を低下させるので少ない方が望ましく、上限の含有量は0.01%とする。SもPと同様に不可避的な混入量をできる限り少なくするのがよい。   S: When S is also present in a large amount, the pitting corrosion resistance is deteriorated, so the smaller one is desirable. The upper limit content is 0.01%. S, like P, should have the unavoidable amount of contamination as small as possible.

さらに、本発明では以下の元素の1種または2種以上をを選択して添加できる。
Cu、Ni: Cu、Niともに強度を改善するとともに、フェライト生成を抑制する効果があり、特に、Niは母材および熱影響部の靭性を改善する効果がある。その効果は、いずれも0.01%以上の添加を必要とするが、いずれも5%を越えて添加されると脆化が生じるために、両者ともに、その限定範囲を0.01〜5%とする。
Furthermore, in the present invention, one or more of the following elements can be selected and added.
Cu, Ni: Both Cu and Ni have the effect of improving the strength and suppressing the formation of ferrite. In particular, Ni has the effect of improving the toughness of the base material and the heat-affected zone. Both of these effects require the addition of 0.01% or more. However, since the embrittlement occurs when both are added in excess of 5%, in both cases, the limited range is 0.01 to 5%. And

Mo: Moは、CrおよびAlが添加された鋼において、0.01%以上添加されると、母材の靭性を損なうことなく孔食の発生と成長を抑制する効果が認められるが、 1.0%を超えて添加しても効果が飽和するばかりか靭性を低下させるので、その範囲を0.005%〜1.0%とする。   Mo: When steel is added with 0.01% or more in steel to which Cr and Al are added, the effect of suppressing the occurrence and growth of pitting corrosion is recognized without impairing the toughness of the base material. Even if added over 0%, the effect is not only saturated but also the toughness is lowered, so the range is made 0.005% to 1.0%.

Nb: Nbは耐食性を損なわずに強度および靭性を改善する元素であり、その効果は0.005%から認められるが、0.05%を越えると溶接熱影響部の靭性低下が顕著になるためにその範囲を0.005%〜0.05%とする。   Nb: Nb is an element that improves the strength and toughness without impairing the corrosion resistance, and its effect is recognized from 0.005%, but if it exceeds 0.05%, the toughness of the weld heat-affected zone becomes remarkable. The range is 0.005% to 0.05%.

V: Vは、同じく耐食性を損なわずに強度を改善する元素であり、0.005%以上で効果が認められるが、多量の添加は周知のように靭性を阻害するので、その上限を0.1%とする。   V: V is an element that improves the strength without impairing the corrosion resistance, and an effect is recognized at 0.005% or more. However, as is well known, addition of a large amount inhibits toughness. 1%.

Ti: Tiは窒化物の生成を通じて高温での結晶粒径の細粒化に寄与する元素であるので、0.005%以上の添加が必要となるが、0.03%を越えると、粗大な析出物が生成するために、特に靭性の著しい低下を招く。従って、その範囲を両元素ともに0.005%〜0.03%とする。   Ti: Ti is an element that contributes to the refinement of the crystal grain size at a high temperature through the formation of nitrides. Therefore, addition of 0.005% or more is necessary, but if it exceeds 0.03%, it is coarse. Since precipitates are generated, the toughness is particularly significantly reduced. Therefore, the range is set to 0.005% to 0.03% for both elements.

Ca、Mg: CaおよびMgはCrおよびAlを含有する鋼において、耐食性を改善できる元素である。現在のところその機構には不明点が多いが、両者がそれぞれ5ppm以上で耐食性が一層向上し、その量の増大とともに、耐食性の向上が認められるが、500ppmを越えて添加すると耐食性向上効果が飽和するばかりではなく、靭性が低下する傾向が明らかとなっており、その添加量を5ppm以上500ppm以下に限定する。   Ca, Mg: Ca and Mg are elements that can improve the corrosion resistance of steel containing Cr and Al. At present, there are many unclear points in the mechanism, but the corrosion resistance is further improved when both of them are 5 ppm or more, and as the amount increases, the improvement of the corrosion resistance is recognized. However, when the amount exceeds 500 ppm, the effect of improving the corrosion resistance is saturated. In addition to this, the tendency to lower the toughness has been clarified, and the addition amount is limited to 5 ppm or more and 500 ppm or less.

REM: さらに、本発明では、希土類元素(REM)を適宜添加してもその耐食性を損なわずに、母材および溶接部の特性を改善することが可能である。その添加量は、0.001%以上を必要とするが、多量の添加は靭性などの阻害するので、その上限を0.1%とする。   REM: Furthermore, in the present invention, it is possible to improve the properties of the base material and the welded part without damaging the corrosion resistance even if a rare earth element (REM) is added as appropriate. The addition amount needs to be 0.001% or more, but addition of a large amount inhibits toughness and the like, so the upper limit is made 0.1%.

さらに本発明では、本発明の骨子となる溶接性の向上および切削性の改善を図るためにTp 、Tc の両式を導入した。

Figure 0004441295
図1は、0.035 %C−0.15%Si−0.0050N%の鋼を基本として、Mn、Cr、Alまた、場合によりCu、Ni添加した素材に溶接サイクルを与え、その時の変態点と粗大なフェライトの生成挙動を観察した結果である。すなわち、横軸で示すTp 式が、1150以上になると、粗大なフェライト相の生成が抑制されることが分かる。 Further, in the present invention, both Tp and Tc are introduced in order to improve the weldability and the machinability that are the core of the present invention.
Figure 0004441295
Figure 1 shows 0.035% C-0.15% Si-0.0050N% steel as a base, Mn, Cr, Al, and optionally Cu and Ni-added materials are subjected to a welding cycle, the transformation point and coarse ferrite at that time. It is the result of having observed the production | generation behavior of. That is, it can be seen that when the Tp expression shown on the horizontal axis is 1150 or more, the formation of a coarse ferrite phase is suppressed.

また、Tc 式は、鋼板の冷却中での変態点に関係する式であるが、この式が600未満になると、圧延後の鋼板空冷中にフェライト組織が生成せず、適切な混合組織が得られない。   The Tc equation is related to the transformation point during cooling of the steel sheet. When this equation is less than 600, a ferrite structure is not generated during air cooling of the steel sheet after rolling, and an appropriate mixed structure is obtained. I can't.

なお、本発明鋼は製造するに際して、造塊分塊法あるいは連続鋳造法およびその他の方法で鋼塊として製造し、その後に、熱間圧延あるいは熱間鍛造によって鋼板とし、そのまま空冷するか、場合によっては、熱間圧延後、変態点以下の温度で焼戻しが実施されるのが望ましい。熱間圧延後の空冷は、母材の切削性付与に必要なフェライトを含む混合組織を得るために必要な処理であり、Tc 式が600以上の成分を有する場合、切削性が改善される。また、焼戻しは、鋼板の強度を低下させ、切削性の改善にも効果がある。
このようにして製造された鋼板は、優れた耐食性と切削性を有する溶接用高強度鋼板
として適用が可能である。
In addition, when producing the steel of the present invention, it is produced as a steel ingot by the ingot-splitting method or the continuous casting method and other methods, and then is made into a steel plate by hot rolling or hot forging, and then air-cooled as it is. In some cases, it is desirable that tempering is performed at a temperature equal to or lower than the transformation point after hot rolling. Air cooling after hot rolling is a process necessary for obtaining a mixed structure containing ferrite necessary for imparting machinability of the base material. When the Tc formula has 600 or more components, the machinability is improved. Tempering also reduces the strength of the steel sheet and is effective in improving machinability.
The steel plate produced in this way can be applied as a high strength steel plate for welding having excellent corrosion resistance and machinability.

表1に示す成分系の鋼を溶製後、その鋼塊を板厚20mm〜50mmの鋼板となるように熱間圧延し、表2に示す製造条件にて適宜、圧延まま、圧延後焼戻し処理、圧延直後水冷し焼戻し処理、あるいは、圧延後再加熱して焼入れおよび焼戻し処理を施した鋼板について、下記の試験を実施した。   After melting the component steels shown in Table 1, the steel ingot is hot-rolled to a steel plate with a thickness of 20 mm to 50 mm, and tempering after rolling as appropriate under the production conditions shown in Table 2. The following tests were carried out on steel plates that had been subjected to water-cooling and tempering immediately after rolling, or subjected to quenching and tempering by reheating after rolling.

(1) 母材引張特性評価
圧延ままの鋼板から、板厚1/2 部−C方向からJIS4号試験片を採取し、試験を実施し た。
(2) 溶接性評価
12mmφの試験片を板厚中央部より切り出し、溶接熱サイクル後[最高加熱温度;140 0 ℃冷却速度:15℃/s]、円周切欠き(10mmφ 0.25mmVノッチ深さ1mm)試験片を 取した後、0 ℃で荷重を増加させていき、破断時の荷重から応力を求めた。その破断 応力と材料の降伏強度を比較することで、評価した。
(3) 耐食性評価
試験鋼板から切削により、厚さ5mmの腐食試験を採取し、以下の条件にて試験を実施 した。
室内環境:冷暖房設置の室内にて無塗装にて100日間暴露試験を実施
湿潤環境:20℃に2時間保持後、湿度95%−25℃の環境に4時間保持することを1300 回繰返す。
塩害環境:海岸飛沫帯に試験片を12ケ月間暴露する。
いずれも錆スポットの大きさを評点としてあらわす。
(4) 切削性評価
鋼板表層部下1mmより板厚18mm厚みの鋼板(表面は、機械切削まま)を採取し、市販 のハイスドリル(6mmφ)を用い、回転数:890rpm 送り速度:0.1/Rev. 水溶性の切削 油を供給しながら貫通孔を明け、工具を変更せずに明けられた孔明け個数を記録して いく。◎:200 個超、△:100 〜200 個、X:100 個未満 として、評価する。
(1) Evaluation of base metal tensile properties JIS4 specimens were sampled from as-rolled steel sheet from 1/2 part thickness-C direction and tested.
(2) Weldability evaluation
A 12mmφ test piece is cut out from the center of the plate thickness, and after the welding heat cycle [maximum heating temperature: 140 ° C cooling rate: 15 ° C / s], a circumferential notch (10mmφ 0.25mm V notch depth 1mm) test piece is taken. After that, the load was increased at 0 ° C., and the stress was obtained from the load at the time of fracture. The fracture stress was evaluated by comparing the yield strength of the material.
(3) Corrosion resistance evaluation A 5 mm thick corrosion test was sampled by cutting from a test steel sheet and tested under the following conditions.
Indoor environment: 100-day exposure test without painting in an air-conditioned room Wet environment: Hold for 2 hours at 20 ° C and then hold for 4 hours in an environment of 95%-25 ° C for 1300 times.
Salt damage environment: Expose the specimen to the coastal splash zone for 12 months.
In both cases, the size of rust spots is expressed as a score.
(4) Evaluation of machinability A steel plate with a thickness of 18mm was collected from 1mm below the surface of the steel plate (the surface was machine-cut), and a commercially available high-speed drill (6mmφ) was used. Drill through holes while supplying the appropriate cutting oil, and record the number of holes drilled without changing the tool. ◎: More than 200 pieces, Δ: 100 to 200 pieces, X: less than 100 pieces are evaluated.

表2にその試験の結果を合わせて示す。
A鋼〜K鋼は、すべて本発明範囲のものである。すなわち、母材の引張強さもすべて、600MPa以上、かつ溶接性として評価した溶接熱影響を模擬した切欠き付丸棒引張試験の結果でも、母材の降伏強さの(0℃)の80%以上の高い破断応力を有しており、かつ、耐食性についても、一部に2mm以下の微小の発錆が観察されたのみであり、すべて良好な特性を示している。さらに、切削性もすべて、200 個以上の孔明けが可能である。
Table 2 also shows the results of the test.
Steels A to K are all within the scope of the present invention. That is, all the tensile strengths of the base metal are 600 MPa or more, and the result of the notched round bar tensile test simulating the influence of welding heat evaluated as weldability is 80% of the base material yield strength (0 ° C). In addition to the above-mentioned high breaking stress, only a small amount of rusting of 2 mm or less was observed in part of the corrosion resistance, and all showed good characteristics. In addition, all of the machinability can drill more than 200 holes.

それに反し、L鋼〜V鋼は、すべて比較鋼である。すなわち、L、M、N、O、P、Q、R、UおよびT鋼は、本発明範囲の中で添加元素が本発明範囲を逸脱したものである。すなわち、L鋼およびU鋼はそれぞれC量が下限および上限をはずれたものであり、いずれも耐食性および溶接性は良好であるが、L鋼は強度が500MPa以下と低く、U鋼は溶接性が低下している。V鋼はSi添加量が発明範囲の上限を超えて添加された場合であり、溶接性が低下している。   On the other hand, L steel to V steel are all comparative steels. That is, L, M, N, O, P, Q, R, U, and T steels are those in which the additive element deviates from the scope of the present invention within the scope of the present invention. That is, L steel and U steel each have C amount deviating from the lower limit and the upper limit, and both have good corrosion resistance and weldability, but L steel has a strength as low as 500 MPa or less, and U steel has weldability. It is falling. V steel is a case where Si addition amount exceeds the upper limit of the invention range, and weldability is lowered.

さらに、M鋼は、Mnの上限を逸脱していると同時に、そのためにTc 値が526 と本発明範囲以下であるために、溶接性および切削性が低下している。N、O鋼は、PおよびSが上限を超えて添加されているものであり、両者ともに、溶接性が低い。PおよびQは、CrおよりAl添加量が本発明より低い場合である。この場合は、耐食性が顕著に低下している。R鋼は、Al量が上限を超え添加された場合であり、溶接性が低下している。   Further, the M steel deviates from the upper limit of Mn, and at the same time, because the Tc value is 526, which is below the range of the present invention, the weldability and the machinability are deteriorated. N and O steels have P and S added in excess of the upper limit, and both have low weldability. P and Q are cases where the amount of Al added from Cr is lower than that of the present invention. In this case, the corrosion resistance is significantly reduced. In the case of R steel, the amount of Al exceeds the upper limit, and the weldability is reduced.

SおよびT鋼は、それぞれの合金量は本発明範囲内であるが、溶接性を示すTp 値および切削性を表すTc 値がそれぞれ発明範囲を逸脱している場合である。その結果、S鋼は溶接性が、T鋼は切削性の低下が認められる。   In S and T steels, the amount of each alloy is within the range of the present invention, but the Tp value indicating weldability and the Tc value indicating machinability deviate from the range of the invention. As a result, it is recognized that S steel has poor weldability and T steel has low machinability.

Figure 0004441295
Figure 0004441295

Figure 0004441295
Figure 0004441295

Tp で定義された値とオーステナイト→デルタ・フェライト変態点の関係を示す図である。It is a figure which shows the relationship between the value defined by Tp, and an austenite-> delta ferrite transformation point.

Claims (4)

質量%で、
C :0.03%越え0.3%
Si:0.01〜1.0%
Mn:0.1〜3%未満
P :0.03%以下
S :0.01%以下
Cr:2〜7%
Al:0.1〜2%
N :0.02%以下
を含有し、残部Fe及び不可避的不純物とする鋼において、次式で示されるTp 値が1150以上で、かつ、Tc 値が600 以上となる成分を含有することを特徴とする耐食性および切削性に優れた溶接用高強度鋼。
Figure 0004441295
% By mass
C: 0.03% over 0.3%
Si: 0.01 to 1.0%
Mn: Less than 0.1 to 3% P: 0.03% or less S: 0.01% or less Cr: 2-7%
Al: 0.1 to 2%
N: steel containing 0.02% or less, the balance being Fe and inevitable impurities , containing a component having a Tp value of 1150 or more and a Tc value of 600 or more represented by the following formula High strength steel for welding with excellent corrosion resistance and machinability.
Figure 0004441295
質量%で、% By mass
C :0.03%越え0.3%C: 0.03% over 0.3%
Si:0.01〜1.0%Si: 0.01 to 1.0%
Mn:0.1〜3%未満Mn: less than 0.1 to 3%
P :0.03%以下P: 0.03% or less
S :0.01%以下S: 0.01% or less
Cr:2〜7%Cr: 2-7%
Al:0.1〜2%Al: 0.1 to 2%
N :0.02%以下N: 0.02% or less
を含有し、かつ選択的に、And optionally,
Cu:0.01〜5%Cu: 0.01 to 5%
Ni:0.01〜5%Ni: 0.01 to 5%
Mo:0.005〜1%Mo: 0.005 to 1%
V :0.005〜0.1%V: 0.005-0.1%
Nb:0.005〜0.050%Nb: 0.005 to 0.050%
Ti:0.005〜0.03%Ti: 0.005 to 0.03%
Ca:0.0005〜0.05%Ca: 0.0005 to 0.05%
Mg:0.0005〜0.05%Mg: 0.0005 to 0.05%
REM:0.001〜0.1%REM: 0.001 to 0.1%
の1種または2種を含有し、残部Fe及び不可避的不純物とする鋼において、次式で示されるTp 値が1150以上で、かつ、Tc 値が600 以上となる成分を含有することを特徴とする耐食性および切削性に優れた溶接用高強度鋼。A steel containing one or two of the above, the balance being Fe and inevitable impurities, containing a component having a Tp value of 1150 or more and a Tc value of 600 or more represented by the following formula: High strength steel for welding with excellent corrosion resistance and machinability.
Figure 0004441295
Figure 0004441295
請求項1または2記載の耐食性および切削性に優れた溶接用高強度鋼塊を、加熱後、熱間圧延し700 ℃以上の温度から空冷することを特徴とする耐食性および切削性に優れた溶接用高強度鋼板の製造法。The welding high-strength steel ingot excellent in corrosion resistance and machinability according to claim 1 or 2 is heated and then hot-rolled and air-cooled from a temperature of 700 ° C or higher. Of manufacturing high-strength steel sheets for industrial use. 熱間圧延後、AcAfter hot rolling, Ac 1 1 変態点以下の温度で焼戻しをすることを特徴とする請求項3記載の耐食性および切削性に優れた溶接用高強度鋼板の製造法。The method for producing a high-strength steel sheet for welding excellent in corrosion resistance and machinability according to claim 3, wherein tempering is performed at a temperature below the transformation point.
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