JP4189359B2 - Anticorrosion method - Google Patents

Anticorrosion method Download PDF

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JP4189359B2
JP4189359B2 JP2004183711A JP2004183711A JP4189359B2 JP 4189359 B2 JP4189359 B2 JP 4189359B2 JP 2004183711 A JP2004183711 A JP 2004183711A JP 2004183711 A JP2004183711 A JP 2004183711A JP 4189359 B2 JP4189359 B2 JP 4189359B2
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stainless steel
valve
corrosion
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JP2006009052A (en
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正敏 岡野
克己 平野
寛 前岡
博行 末松
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Okano Valve Mfg Co Ltd
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Description

この発明は、防食方法に係り、とくに、弁棒や弁座(弁箱付弁座部)、弁体(弁体付弁座部)に使用される部材の防食方法に関する。   The present invention relates to an anticorrosion method, and more particularly, to an anticorrosion method for members used in valve stems, valve seats (valve seats with valve boxes), and valve bodies (valve seats with valve bodies).

ステライトは、強度が高く摺動性が良好であるといった特性を有しているため、弁の摺動部品や高い圧縮強度を要求される部品表面の硬化肉盛材に使用される。
従来から行われているステライトの硬化肉盛については、例えば図5に示されるように、マルテンサイト系ステンレス鋼製の安全弁の弁棒41の先端に、炭素を0.9〜3.0重量%、クロムを26.0〜33.0重量%及びタングステンを3.0〜14.0重量%含有するステライト42を硬化肉盛して高圧縮荷重に耐えられるようにしている。弁棒41及びステライト42間には、硬化肉盛境界部43が形成されている。
また、図6に示されるように、オーステナイト系ステンレス鋼製の仕切弁の弁体51に、図5のステライト42と同組成のステライトを硬化肉盛して弁体付弁座部52を形成し、その表面に摺動性を保たせるようにしている。弁体51及び弁体付弁座部52間には、硬化肉盛境界部53が形成されている。
Since stellite has characteristics such as high strength and good slidability, it is used as a hardened material on the surface of parts that require sliding parts of valves and high compressive strength.
As for the conventional hardening of stellite, as shown in FIG. 5, for example, as shown in FIG. 5, carbon is added to the tip of the valve stem 41 of the martensitic stainless steel safety valve 41 to 0.9 to 3.0% by weight. The stellite 42 containing 26.0 to 33.0% by weight of chromium and 3.0 to 14.0% by weight of tungsten is hardened to withstand a high compressive load. A hardfacing boundary 43 is formed between the valve stem 41 and the stellite 42.
Further, as shown in FIG. 6, a valve seat with valve body 52 is formed by hardening and hardening stellite having the same composition as the stellite 42 of FIG. 5 on the valve body 51 of the austenitic stainless steel gate valve. The surface is kept slidable. A hardened boundary portion 53 is formed between the valve body 51 and the valve seat with valve body 52.

弁部品の基材がマルテンサイト系ステンレス鋼やオーステナイト系ステンレス鋼の場合、基材にステライトを硬化肉盛すると、図7に示されるように、硬化肉盛境界部と隣接しているステンレス鋼の一部(以下、ステンレス鋼の熱影響部)が腐食を受けやすい状態となる。図7はオーステナイト系ステンレス鋼についての写真であるが、マルテンサイト系ステンレス鋼でも、類似した組織状態となる。
この原因としては、ステライトの炭素含有量が高く、ステンレス鋼の熱影響部に炭素の富化(浸炭)が生じて、孔食を生じやすいクロム炭化物の析出を促進するからである。また、ステライトの硬化肉盛時に、ステンレス鋼の熱影響部が高温に加熱されることにより結晶粒が粗大化されると共に、結晶粒界に粒界腐食や応力腐食割れを生じやすいクロム炭化物が析出するからである。
When the base material of the valve part is martensitic stainless steel or austenitic stainless steel, when hardening the stellite on the base material, as shown in FIG. A part (hereinafter referred to as a heat-affected zone of stainless steel) becomes susceptible to corrosion. FIG. 7 is a photograph of the austenitic stainless steel, but a martensitic stainless steel has a similar structure.
This is because the carbon content of stellite is high, and carbon enrichment (carburization) occurs in the heat-affected zone of stainless steel, promoting the precipitation of chromium carbides that are prone to pitting. In addition, when the stellite is hardened, the heat affected zone of the stainless steel is heated to a high temperature, resulting in coarsening of the crystal grains and precipitation of chromium carbide that easily causes intergranular corrosion and stress corrosion cracking at the crystal grain boundaries. Because it does.

従来の腐食防止方法の一例として、ステンレス鋼とステライトの硬化肉盛境界部にニッケルメッキを施す方法が、特許文献1に開示されている。   As an example of a conventional corrosion prevention method, Patent Document 1 discloses a method in which nickel plating is applied to a hardfacing boundary between stainless steel and stellite.

特開平6−254678号公報JP-A-6-254678

しかしながら、この方法は、塩化物、SOxまたはNOxを含んだ環境では、ニッケルメッキ部が腐食する場合があるといった問題点があった。   However, this method has a problem that the nickel plating portion may corrode in an environment containing chloride, SOx, or NOx.

この発明は、このような問題点を解決するためになされたもので、ステライトを硬化肉盛したマルテンサイト系ステンレス鋼やオーステナイト系ステンレス鋼の熱影響部に発生する孔食、粒界腐食及び応力腐食割れを防止するための防食方法を提供することを目的とする。   The present invention was made to solve such problems, and pitting corrosion, intergranular corrosion and stress generated in the heat-affected zone of martensitic stainless steel and austenitic stainless steel hardened by stellite. An object of the present invention is to provide an anticorrosion method for preventing corrosion cracking.

この発明に係るマルテンサイト系ステンレス鋼またはオーステナイト系ステンレス鋼にステライトを肉盛した部材の防食方法は、マルテンサイト系ステンレス鋼またはオーステナイト系ステンレス鋼ステライトとの間の硬化肉盛境界部を覆うように耐食性合金をTIG溶接または被覆アーク溶接によって肉盛し、耐食性合金の化学組成は、炭素が0.10重量%以下、クロムが17.0〜26.0重量%、ニッケルが40.0重量%以上、鉄が25.0重量%以下、タングステンが2.5重量%以下、シリコンが6.5重量%以下、マンガンが3.5重量%以下、モリブデンが10.0重量%以下、ニオブとタンタルの合計が5.5重量%以下、チタンが1.15重量%以下、アルミニウムが0.8重量%以下、ボロンが1.0重量%以下であることを特徴とする。
The corrosion process of members who NikuSakari stellite martensitic stainless steel or austenitic stainless steel according to the invention, so as to cover the hardfacing interface between the martensitic stainless steel or austenitic stainless steel and Stellite Corrosion-resistant alloy is deposited by TIG welding or coated arc welding, and the chemical composition of the corrosion-resistant alloy is 0.10% by weight or less for carbon, 17.0 to 26.0% by weight for chromium, and 40.0% by weight for nickel. As mentioned above, iron is 25.0% or less, tungsten is 2.5% or less, silicon is 6.5% or less, manganese is 3.5% or less, molybdenum is 10.0% or less, niobium and tantalum. Is 5.5% by weight or less, titanium is 1.15% by weight or less, aluminum is 0.8% by weight or less, and boron is 1.0% by weight or less. Characterized in that there.

この発明によれば、マルテンサイト系ステンレス鋼またはオーステナイト系ステンレス鋼とステライトの硬化肉盛境界部を覆うように耐食性合金を肉盛するので、マルテンサイト系ステンレス鋼またはオーステナイト系ステンレス鋼の熱影響部の腐食を防止することができる。   According to the present invention, since the corrosion-resistant alloy is built up so as to cover the hardened built-up boundary between martensitic stainless steel or austenitic stainless steel and stellite, the heat affected zone of martensitic stainless steel or austenitic stainless steel Corrosion can be prevented.

以下、この発明の実施の形態を添付図面に基づいて説明する。
実施の形態1.
図1に示されるように、この発明に係る防食方法を施した安全弁10は、図示しない高圧容器に取り付けられる弁箱5の中に、高圧流体の通路が形成されている。この通路を閉じる弁体4を押えるマルテンサイト系ステンレス鋼製の弁棒3は、コイルスプリング6によって、下方に押付けられ、弁体4が閉止するように常時、力を加えることによって、流体の流れを遮断している。
一方、安全弁10が取付けられた図示しない高圧容器内の圧力が上昇し、設定圧力以上になると、弁体4および弁棒3はコイルスプリング6のばね力に抗して上方向に持ち上げられ、安全弁10の弁箱入口11の流体が、弁箱5内を通過し、弁箱出口12から放出される。
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Embodiment 1 FIG.
As shown in FIG. 1, the safety valve 10 subjected to the anticorrosion method according to the present invention has a high-pressure fluid passage formed in a valve box 5 attached to a high-pressure vessel (not shown). The martensitic stainless steel valve rod 3 that holds the valve body 4 closing the passage is pressed downward by the coil spring 6, and a force is constantly applied so that the valve body 4 is closed. Is shut off.
On the other hand, when the pressure in the high-pressure vessel (not shown) to which the safety valve 10 is attached rises and exceeds the set pressure, the valve body 4 and the valve stem 3 are lifted upward against the spring force of the coil spring 6, and the safety valve Ten fluids at the valve box inlet 11 pass through the valve box 5 and are discharged from the valve box outlet 12.

このような安全弁10による流体の出入りの制御において、弁棒3の先端には大きな圧縮力がかかる。そのため、図2に示されるように、安全弁10の弁棒3の先端部に、コバルト基合金であるステライト13を硬化肉盛する。弁棒3及びステライト13間には、硬化肉盛境界部14が形成される。
また、ステライト13を硬化肉盛する際に、ステライトに含有される炭素によって、熱影響部16に炭素の富化を生じさせて腐食させてしまうことを防止するため、この硬化肉盛境界部14を覆うように、耐食性合金15を肉盛する。
尚、ステライト13の硬化肉盛についてはガス溶接、TIG溶接、PTA溶接等により行い、耐食性合金15の肉盛については、TIG溶接、被覆アーク溶接等により行う。
In such control of the flow of fluid in and out by the safety valve 10, a large compressive force is applied to the tip of the valve stem 3. Therefore, as shown in FIG. 2, the stellite 13, which is a cobalt-based alloy, is hardened on the tip of the valve stem 3 of the safety valve 10. A hardened boundary portion 14 is formed between the valve stem 3 and the stellite 13.
Further, when the stellite 13 is hardened, the hardened boundary part 14 is prevented from being caused by carbon contained in the stellite to cause the heat-affected zone 16 to be enriched and corroded. The corrosion resistant alloy 15 is built up so as to cover the surface.
In addition, about the hardening buildup of the stellite 13, it performs by gas welding, TIG welding, PTA welding, etc., and buildup of the corrosion-resistant alloy 15 performs by TIG welding, covering arc welding, etc.

ステライト13の化学組成は、炭素が0.9〜3.0重量%、クロムが26.0〜33.0重量%、タングステンが3.0〜14.0重量%である。マルテンサイト系ステンレス鋼の炭素含有量は0.20重量%以下であるため、弁棒3に比べて炭素含有量が多く、クロムやタングステンの炭化物を形成して硬化するため、摺動性や圧縮強度を維持することができる。   The chemical composition of stellite 13 is 0.9 to 3.0% by weight of carbon, 26.0 to 33.0% by weight of chromium, and 3.0 to 14.0% by weight of tungsten. Since the carbon content of martensitic stainless steel is 0.20% by weight or less, it has a higher carbon content than the valve stem 3, and forms and hardens chromium and tungsten carbides. The strength can be maintained.

また、耐食性合金15の化学組成は、炭素が0.10重量%以下、クロムが17.0〜26.0重量%、ニッケルが40.0重量%以上、鉄が25.0重量%以下、タングステンが2.5重量%以下、シリコンが6.5重量%以下、マンガンが3.5重量%以下、モリブデンが10.0重量%以下、ニオブとタンタルの合計が5.5重量%以下、チタンが1.15重量%以下、アルミニウムが0.8重量%以下、ボロンが1.0重量%以下である。
この耐食性合金15は、弁棒3よりもクロム含有量が多いため、耐食性を有することになる。また、炭素含有量が0.10重量%以下であるため、肉盛により弁棒3の熱影響部16に腐食を受けやすいクロム炭化物を生成しにくくなる。さらに、ニッケル含有量が多いため、肉盛時に鉄やクロム等と融合してマルテンサイト等の有害な金属組織を形成しないようにすることができる。
The chemical composition of the corrosion resistant alloy 15 is as follows: carbon is 0.10% by weight or less, chromium is 17.0 to 26.0% by weight, nickel is 40.0% by weight or more, iron is 25.0% by weight or less, tungsten Is 2.5 wt% or less, silicon is 6.5 wt% or less, manganese is 3.5 wt% or less, molybdenum is 10.0 wt% or less, the total of niobium and tantalum is 5.5 wt% or less, titanium is 1.15% by weight or less, aluminum is 0.8% by weight or less, and boron is 1.0% by weight or less.
Since this corrosion resistant alloy 15 has a higher chromium content than the valve stem 3, it has corrosion resistance. Moreover, since carbon content is 0.10 weight% or less, it becomes difficult to produce | generate the chromium carbide which is easy to receive the corrosion in the heat affected zone 16 of the valve stem 3 by overlaying. Furthermore, since the nickel content is high, it can be prevented from forming a harmful metal structure such as martensite by fusing with iron, chromium, or the like during building.

このように、マルテンサイト系ステンレス鋼製の弁棒3及びステライト13間の硬化肉盛境界部14を覆うように、耐食性合金15を肉盛したので、熱影響部16の腐食を防止することができる。   Thus, since the corrosion-resistant alloy 15 was built up so as to cover the hardened built-up boundary 14 between the valve rod 3 and the stellite 13 made of martensitic stainless steel, corrosion of the heat affected zone 16 can be prevented. it can.

実施の形態2.
次に、この発明の実施の形態2に係る防食方法を、図3に基づいて説明する。この防食方法は、防食する対象物として、実施の形態1における安全弁の弁棒の代わりに、仕切弁の弁体に適用したものである。
図3(a)に示される仕切弁の弁体21は、ほぼ円板状であるが、炭素含有量0.08重量%以下のオーステナイト系ステンレス鋼製弁体21の両面のそれぞれの外周部に、円輪状に実施の形態1のステライト13と同組成のステライトを硬化肉盛し、弁体弁座部22を形成する。また、図3(b)に示されるように、弁体21及び弁体弁座部22間には、硬化肉盛境界部23が形成される。この硬化肉盛境界部23を覆うように、実施の形態1と同組成の耐食性合金15を肉盛する。
尚、ステライト(弁体弁座部22)の肉盛についてはガス溶接、TIG溶接、PTA溶接等により行い、耐食性合金15の肉盛については、TIG溶接、被覆アーク溶接等により行う。
Embodiment 2. FIG.
Next, the anticorrosion method according to Embodiment 2 of the present invention will be described with reference to FIG. This anticorrosion method is applied to the valve body of the gate valve instead of the valve stem of the safety valve in the first embodiment as an object to be anticorrosive.
The valve body 21 of the gate valve shown in FIG. 3 (a) has a substantially disc shape, but is formed on each outer peripheral portion of both surfaces of the austenitic stainless steel valve body 21 having a carbon content of 0.08% by weight or less. The stellite having the same composition as that of the stellite 13 of the first embodiment is hardened and formed in a ring shape to form the valve body valve seat portion 22. Further, as shown in FIG. 3B, a hardfacing boundary portion 23 is formed between the valve body 21 and the valve body valve seat portion 22. The corrosion-resistant alloy 15 having the same composition as that of the first embodiment is built up so as to cover the cured build-up boundary 23.
The build-up of stellite (valve valve seat 22) is performed by gas welding, TIG welding, PTA welding or the like, and the build-up of the corrosion-resistant alloy 15 is performed by TIG welding, covered arc welding or the like.

このように、オーステナイト系ステンレス鋼の弁体21においても、硬化肉盛境界部23を覆うように、耐食性合金15を肉盛することで、実施の形態1と同様の防食効果を得ることができる。   Thus, also in the valve body 21 of austenitic stainless steel, the same anticorrosion effect as Embodiment 1 can be acquired by building up the corrosion-resistant alloy 15 so that the hardening buildup boundary part 23 may be covered. .

実施の形態3.
次に、この発明の実施の形態3に係る防食方法を、図4に基づいて説明する。この防食方法は、防食する対象物として、実施の形態1における安全弁の弁棒の代わりに、玉形弁の弁箱に適用したものである。
図4に示されるように、炭素含有量0.08重量%以下のオーステナイト系ステンレス鋼製の玉形弁の弁箱31に、実施の形態1と同組成のステライト13を硬化肉盛し、弁箱付弁座部32を形成する。また、弁箱31及び弁箱付弁座部32間には、硬化肉盛境界部33が形成される。この硬化肉盛境界部33を覆うように、実施の形態1と同組成の耐食性合金15を肉盛する。
尚、ステライト(弁箱付弁座部32)の肉盛についてはガス溶接、TIG溶接、PTA溶接等により行い、耐食性合金15の肉盛については、TIG溶接、被覆アーク溶接等により行う。
このように、玉形弁の弁箱31にも、この発明に係る防食方法を適用することで、実施の形態1及び2と同様の効果を得ることができる。
Embodiment 3 FIG.
Next, the anticorrosion method according to Embodiment 3 of the present invention will be described with reference to FIG. This anticorrosion method is applied to a valve box of a ball valve instead of the valve stem of the safety valve in the first embodiment as an object to be anticorrosive.
As shown in FIG. 4, a stellite 13 having the same composition as that of the first embodiment is hardened on a valve box 31 of an austenitic stainless steel ball valve having a carbon content of 0.08% by weight or less, and the valve A valve seat portion 32 with a box is formed. Further, a hardfacing boundary portion 33 is formed between the valve box 31 and the valve seat portion 32 with a valve box. The corrosion-resistant alloy 15 having the same composition as that of the first embodiment is built up so as to cover the hardfacing boundary portion 33.
The build-up of stellite (valve seat portion 32 with valve box) is performed by gas welding, TIG welding, PTA welding, and the like, and the build-up of the corrosion resistant alloy 15 is performed by TIG welding, covered arc welding, or the like.
Thus, the effect similar to Embodiment 1 and 2 can be acquired also by applying the anticorrosion method which concerns on this invention also to the valve box 31 of a ball-shaped valve.

実施の形態1〜3において、安全弁10の弁棒3、仕切弁の弁体21及び玉形弁の弁箱31へこの発明に係る防食方法を適用した場合を説明したが、これらに限定されるものではなく、流体の出入りを制御する弁の種類や部品の形状が異なる弁部材についても、この防食方法を適用することによって同様の効果を得ることができる。   In the first to third embodiments, the case where the anticorrosion method according to the present invention is applied to the valve stem 3 of the safety valve 10, the valve body 21 of the gate valve and the valve box 31 of the ball valve is described, but the present invention is limited to these. The same effect can be obtained by applying this anticorrosion method to valve members that are different from each other and have different valve types and parts shapes for controlling the flow of fluid.

<実施例1〜8>
試験片については、直径52mm、長さ150mmのマルテンサイト系ステンレス鋼又はオーステナイト系ステンレス鋼の素材の片方の端部を、直径が38mmとなる円錐台形状に機械加工を行った。次に、その端面にガス溶接によってステライトの硬化肉盛を行なった後、先端部を略円錐状に加工して試験片を作製した。さらに、基材及びステライト間の硬化肉盛境界部を覆うように、耐食性合金をTIG溶接によって肉盛した。
<比較例1〜3>
実施例1〜8に対して、耐食性合金の肉盛がない場合の試験片を作製した。
実施例1〜6と比較例1及び2とは、基材をマルテンサイト系ステンレス鋼としたものである。これらの各試験片について、基材、ステライト及び耐食性合金の化学組成を表1に示す。一方、実施例7及び8と比較例3とは、基材をオーステナイト系ステンレス鋼としたものである。これらの各試験片について、基材、ステライト及び耐食性合金の化学組成を表2に示す。
<Examples 1-8>
For the test piece, one end of a martensitic stainless steel or austenitic stainless steel material having a diameter of 52 mm and a length of 150 mm was machined into a truncated cone shape having a diameter of 38 mm. Next, after hardening the stellite on the end face by gas welding, the tip portion was processed into a substantially conical shape to prepare a test piece. Furthermore, the corrosion-resistant alloy was built up by TIG welding so as to cover the hardfacing boundary between the base material and stellite.
<Comparative Examples 1-3>
For Examples 1 to 8, test pieces were prepared when there was no buildup of the corrosion resistant alloy.
In Examples 1 to 6 and Comparative Examples 1 and 2, the base material is martensitic stainless steel. Table 1 shows the chemical compositions of the base material, stellite, and the corrosion-resistant alloy for each of these test pieces. On the other hand, in Examples 7 and 8 and Comparative Example 3, the base material is austenitic stainless steel. Table 2 shows the chemical compositions of the base material, stellite, and the corrosion-resistant alloy for each of these test pieces.

Figure 0004189359
Figure 0004189359

Figure 0004189359
Figure 0004189359

<加速腐食試験方法>
表1に示した条件の各試験片を、室温の3%食塩水、pH4の硫酸溶液及びpH4の硝酸溶液のそれぞれに、1000時間浸漬させた。浸漬後、各試験片の硬化肉盛境界部に、腐食孔が発生しているか否かを目視、液体浸透探傷検査および代表的なものについては断面の顕微鏡組織の観察等で確認した。
<Accelerated corrosion test method>
Each test piece under the conditions shown in Table 1 was immersed in a 3% saline solution at room temperature, a sulfuric acid solution at pH 4 and a nitric acid solution at pH 4 for 1000 hours. After immersion, whether or not corrosion holes were generated at the hardfacing boundary portion of each test piece was confirmed by visual inspection, liquid penetration inspection, and observation of a microscopic structure of a cross-section for representative ones.

加速腐食試験の結果を表3に示す。
実施例1〜4は、ステライトを硬化肉盛したマルテンサイト系ステンレス鋼に、硬化肉盛境界部を覆うように、化学組成の異なる4種類の耐食性合金を肉盛したものである。比較例1は、硬化肉盛境界部に耐食性合金を肉盛しない、実施例1〜4と同じ組成のステライトを硬化肉盛したマルテンサイト系ステンレス鋼である。実施例1〜4については、3%食塩水、pH4の硫酸溶液及びpH4の硝酸溶液のいずれに浸漬させても、腐食孔は確認されなかったのに対し、比較例1については、3%食塩水及びpH4の硫酸溶液に浸漬させた場合に、腐食孔の発生が確認された。
また、実施例5及び6は、実施例1〜4に対して、ステライトの化学組成を変更したものであり、硬化肉盛境界部を覆うように化学組成の異なる2種類の耐食性合金を肉盛したものである。比較例2は、実施例5及び6に対して、硬化肉盛境界部に耐食性合金を肉盛しない、実施例5及び6と同じ組成のステライトを硬化肉盛したマルテンサイト系ステンレス鋼である。実施例5及び6については、3%食塩水、pH4の硫酸溶液及びpH4の硝酸溶液のいずれに浸漬させても、腐食孔は確認されなかったのに対し、比較例2については、3%食塩水及びpH4の硫酸溶液に浸漬させた場合に、腐食孔の発生が確認された。
Table 3 shows the results of the accelerated corrosion test.
In Examples 1 to 4, four types of corrosion-resistant alloys having different chemical compositions are built up on a martensitic stainless steel hardened by stellite so as to cover the hardened built-up boundary. Comparative Example 1 is a martensitic stainless steel that has been hardened with stellite having the same composition as in Examples 1 to 4, which does not build up a corrosion-resistant alloy at the hardfacing boundary. For Examples 1 to 4, no corrosion pores were observed when immersed in any of 3% saline, pH 4 sulfuric acid solution and pH 4 nitric acid solution, whereas for Comparative Example 1, 3% sodium chloride was used. When immersed in water and a sulfuric acid solution of pH 4, the generation of corrosion pores was confirmed.
Moreover, Example 5 and 6 is what changed the chemical composition of stellite with respect to Examples 1-4, and builds up two types of corrosion-resistant alloys from which a chemical composition differs so that a hardfacing boundary part may be covered. It is a thing. Comparative Example 2 is a martensitic stainless steel that is hardened and hardened with stellite having the same composition as in Examples 5 and 6 and does not build up a corrosion-resistant alloy at the hardfacing boundary with respect to Examples 5 and 6. In Examples 5 and 6, no corrosion pores were observed when immersed in any of 3% saline, pH 4 sulfuric acid solution, and pH 4 nitric acid solution, whereas in Comparative Example 2, 3% sodium chloride was used. When immersed in water and a sulfuric acid solution of pH 4, the generation of corrosion pores was confirmed.

一方、実施例7及び8は、ステライトを硬化肉盛したオーステナイト系ステンレス鋼に、硬化肉盛境界部を覆うように、化学組成の異なる2種類の耐食性合金を肉盛したものである。比較例3は、実施例7及び8に対して、硬化肉盛境界部に耐食性合金を肉盛しない、実施例7及び8と同じ組成のステライトを硬化肉盛したオーステナイト系ステンレス鋼である。実施例7及び8については、3%食塩水及びpH4の硫酸溶液に浸漬させても、腐食孔は確認されなかったのに対し、比較例3については、3%食塩水及びpH4の硫酸溶液に浸漬させた場合に、腐食孔の発生が確認された。   On the other hand, Examples 7 and 8 are obtained by depositing two types of corrosion-resistant alloys having different chemical compositions on an austenitic stainless steel obtained by hardening and hardening stellite so as to cover the hardening and building-up boundary. Comparative Example 3 is an austenitic stainless steel that is hardened and hardened with stellite having the same composition as in Examples 7 and 8 and does not build up a corrosion-resistant alloy at the hardfacing boundary with respect to Examples 7 and 8. In Examples 7 and 8, no corrosive pores were observed even when immersed in a 3% saline solution and a sulfuric acid solution at pH 4, whereas in Comparative Example 3, a 3% saline solution and a pH 4 sulfuric acid solution were used. When immersed, the formation of corrosion holes was confirmed.

Figure 0004189359
Figure 0004189359

以上の結果より、この発明に係る防食方法では、従来の防食方法において問題となっていた、塩化物、SOxまたはNOxを含んだ環境でも、硬化肉盛境界部を覆うように肉盛された耐食性合金が腐食されることなく、防食効果を得られることが確認された。   From the above results, in the anticorrosion method according to the present invention, even in an environment containing chloride, SOx or NOx, which has been a problem in the conventional anticorrosion method, the corrosion resistance is built up so as to cover the hardfacing boundary portion. It was confirmed that the anticorrosion effect can be obtained without the alloy being corroded.

この発明の実施の形態1に係る防食方法を施した安全弁の断面図である。It is sectional drawing of the safety valve which gave the anticorrosion method which concerns on Embodiment 1 of this invention. 実施の形態1に係る防食方法の図である。It is a figure of the anticorrosion method concerning Embodiment 1. FIG. 実施の形態2に係る防食方法の図である。It is a figure of the anticorrosion method which concerns on Embodiment 2. FIG. 実施の形態3に係る防食方法の図である。It is a figure of the anticorrosion method which concerns on Embodiment 3. FIG. 従来の方法により、マルテンサイト系ステンレス鋼製の弁棒の先端部にステライトを硬化肉盛した図である。It is the figure which hardened the stellite at the front-end | tip part of the valve rod made from a martensitic stainless steel by the conventional method. 従来の方法により、オーステナイト系ステンレス鋼製の仕切弁の弁体にステライトを硬化肉盛した図である。It is the figure which hardened the stellite on the valve body of the austenitic stainless steel gate valve by the conventional method. ステンレス鋼の熱影響部に発生した腐食の写真である。It is the photograph of the corrosion which generate | occur | produced in the heat affected zone of stainless steel.

符号の説明Explanation of symbols

13 ステライト、14,23,33 硬化肉盛境界部、15 耐食性合金、16 熱影響部。   13 Stellite, 14, 23, 33 Hardfacing boundary, 15 Corrosion resistant alloy, 16 Heat affected zone.

Claims (1)

マルテンサイト系ステンレス鋼またはオーステナイト系ステンレス鋼に、ステライトを硬化肉盛した部材の防食方法であって、
前記マルテンサイト系ステンレス鋼または前記オーステナイト系ステンレス鋼前記ステライトとの間の硬化肉盛境界部を覆うように耐食性合金をTIG溶接または被覆アーク溶接によって肉盛し、
前記耐食性合金の化学組成は、
炭素が0.10重量%以下、
クロムが17.0〜26.0重量%、
ニッケルが40.0重量%以上、
鉄が25.0重量%以下、
タングステンが2.5重量%以下、
シリコンが6.5重量%以下、
マンガンが3.5重量%以下、
モリブデンが10.0重量%以下、
ニオブとタンタルの合計が5.5重量%以下、
チタンが1.15重量%以下、
アルミニウムが0.8重量%以下、
ボロンが1.0重量%以下
であることを特徴とする防食方法。
A martensitic stainless steel or austenitic stainless steel is a method for preventing corrosion of a member formed by hardening stellite,
The martensitic stainless steel or the austenitic stainless steel with hardfacing boundary so as to cover corrosion resistant alloy between the stellite to overlay by TIG welding or shielded metal arc welding,
The chemical composition of the corrosion resistant alloy is:
Carbon is 0.10% by weight or less,
17.0 to 26.0% by weight of chromium,
40.0% by weight or more of nickel,
Iron is 25.0% by weight or less,
2.5% by weight or less of tungsten,
6.5% by weight or less of silicon,
Manganese is not more than 3.5% by weight,
Molybdenum is 10.0% by weight or less,
The total of niobium and tantalum is 5.5% by weight or less,
1.15% by weight or less of titanium,
0.8% by weight or less of aluminum,
An anticorrosion method, wherein boron is 1.0% by weight or less.
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