JPS58197215A - Improvement of corrosion resistance of austenitic stainless steel - Google Patents

Improvement of corrosion resistance of austenitic stainless steel

Info

Publication number
JPS58197215A
JPS58197215A JP7774282A JP7774282A JPS58197215A JP S58197215 A JPS58197215 A JP S58197215A JP 7774282 A JP7774282 A JP 7774282A JP 7774282 A JP7774282 A JP 7774282A JP S58197215 A JPS58197215 A JP S58197215A
Authority
JP
Japan
Prior art keywords
stainless steel
stress
shot
austenitic stainless
diameter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP7774282A
Other languages
Japanese (ja)
Inventor
Makoto Hayashi
林　眞琴
Tasuku Shimizu
翼 清水
Koji Fujimoto
藤本　弘次
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Ltd
Original Assignee
Hitachi Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hitachi Ltd filed Critical Hitachi Ltd
Priority to JP7774282A priority Critical patent/JPS58197215A/en
Publication of JPS58197215A publication Critical patent/JPS58197215A/en
Pending legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • C21D7/06—Modifying the physical properties of iron or steel by deformation by cold working of the surface by shot-peening or the like

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

PURPOSE:To reduce the stress corrosion cracking, etc. of austenitic stainless steel by plastically working the steel by shot peening at a specified temp. or above to apply residual compressive stress to the surface of the steel and gradually reducing the diameter of shots during the shot peening. CONSTITUTION:In order to prevent the stress corrosion cracking and corrosion fatigue cracking of austenitic stainless steel, residual compressive stress is applied to the surface of the steel by plastically working the steel by shot peening at a temp. above the Md point which is the upper limit of temp. at which strain producing martensite is formed. When martensitic transformation is caused in the structure by the shot peening, the corrosion resistance is deteriorated and corrosion cracking is accelerated by the unfavorable influence of stress between martensite phase and austenite phase, so by gradually reducing the diameter of shots for the peening, said defects are eliminated and the stress corrosion cracking and corrosion fatigue cracking of the steel are prevented.

Description

【発明の詳細な説明】 本発明は、オーステナイト系ステンレス鋼が使用される
機器、配管等の耐食性を改善する金属材料表面の加工法
に関するものである。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of processing the surface of a metal material to improve the corrosion resistance of equipment, piping, etc. in which austenitic stainless steel is used.

一般に、原子炉再循環系配管等の腐食環境下で使用され
る金属材料については、耐食性の強いオーステナイト系
ステンレス鋼の使用されることが多いが、該オーステナ
イト系ステンレス鋼も引張応力下で使用された場合には
、応力腐食割れおよび疲労腐食割れの感受性の高くなる
ことが知られている。との引張応力による影響は、外部
からの応力の細円部応力によっても生ずるものであシ、
特に金属材料を加工したときに発生する残留応力は、溶
接、グラインダ加工、切削加工等一般に引張応力となる
から応力腐食割れについては不利な傾向となる。In general, austenitic stainless steel with strong corrosion resistance is often used as metal materials used in corrosive environments such as nuclear reactor recirculation system piping, but austenitic stainless steel is also used under tensile stress. It is known that the susceptibility to stress corrosion cracking and fatigue corrosion cracking increases when The effect of tensile stress on the surface is also caused by stress on the thin circle of external stress.
In particular, residual stress generated when metal materials are processed, such as during welding, grinding, cutting, etc., generally becomes tensile stress, which tends to be disadvantageous for stress corrosion cracking.

そこで従来よシ、部材の残留応力を圧縮応力として応力
腐食割れ強度を向上させる工夫がなされており、例えば
溶接部については、溶接後の配管に冷却水を流し、部材
外表面を高周波加熱コイルで加熱後冷却する方法が提案
されている。Conventionally, efforts have been made to improve the stress corrosion cracking strength by using the residual stress in the component as compressive stress. For example, in the case of welded parts, cooling water is run through the piping after welding, and the outer surface of the component is heated with a high-frequency heating coil. A method of heating and then cooling has been proposed.

しかしこの方法は、圧力容器のノズルコーナーのように
板厚の厚いもの、或いは各種軸のように中央相１のもの
に対しては適用できないとい５Ｈ点がある。However, this method cannot be applied to thick plates such as nozzle corners of pressure vessels, or to central phase 1 objects such as various shafts.

また、前述したグラインダ加工、切削加工等が部材に対
して残留引張応力を生じさせるのに比べて、鍛造、圧延
加工と、表面加工法としてのエメＩＪ　−ヘ−／４’〜
研磨、ショットピーニングが残留圧縮応力を生じさせる
加工として知られているが、このうち前者の鍛造、圧延
加工は既に部材として形造られたものには使用できない
という問題がある。In addition, compared to the grinding process, cutting process, etc. described above which generates residual tensile stress in the member, forging, rolling process, and surface processing method such as emery IJ-H/4'~
Polishing and shot peening are known as processes that produce residual compressive stress, but the former forging and rolling processes have a problem in that they cannot be used on parts that have already been formed.

したがって、オーステナイト系ステンレス鋼の応力腐食
割れ感受性を抑えるためには、前記したエメリーに−・
平−研磨やショットピーニングの加工を行なうことが、
前記ステンレス鋼の内表面残留応力を圧縮側とさせると
いう意味から有効であるということができる。Therefore, in order to suppress the stress corrosion cracking susceptibility of austenitic stainless steel, it is necessary to use the emery mentioned above.
It is possible to perform flat polishing and shot peening processing.
This can be said to be effective in the sense that the residual stress on the inner surface of the stainless steel is made to be on the compression side.

ところで、ここでオーステナイト系ステンレス鋼の耐食
性に関してはもう一つの問題がある。By the way, there is another problem regarding the corrosion resistance of austenitic stainless steel.

すなわち、とのオーステナイト系ステンレス鋼が優れた
耐食性をもつのはオーステナイト相が単相で存在する場
合について言えるものであって、変態によってマルテン
サイト相が形成されると、とのマルテンサイト相自身は
オーステナイト相忙比べて耐食性に劣るために亀裂発生
の虞れが増大する他、オーステナイト相との相聞応力の
悪影響、両相での局部電位による腐食割れの促進の可能
性、更には熱応力を受ける場合において両相の線膨張率
の差が熱疲労を増大させて強度を低下させるなど、耐食
性低下を招致する種々の問題を生ずるという点である。In other words, the austenitic stainless steel with and has excellent corrosion resistance only when the austenite phase exists as a single phase, and when the martensitic phase is formed by transformation, the martensite phase itself is The corrosion resistance of the austenite phase is inferior to that of the austenite phase, which increases the risk of cracking, as well as the negative effects of mutual stress with the austenite phase, the possibility of accelerating corrosion cracking due to local potentials in both phases, and the possibility of being subject to thermal stress. In some cases, the difference in coefficient of linear expansion between the two phases causes various problems such as increased thermal fatigue and decreased strength, which leads to a decrease in corrosion resistance.

このマルテンサイト変態は、既知の如く焼入れや塑性加
工によって生ずることが知られ、後者については加工条
件にもよるが前記したエメリーペー・９−研磨やショッ
トピーニングの場合に、前者で約３０チ程度、後者で約
４２％程度がマルテンサイトに変態するとされている。This martensitic transformation is known to be caused by quenching and plastic working, and the latter depends on the processing conditions, but in the case of the above-mentioned emery paper polishing and shot peening, the former is about 30 inches, It is said that about 42% of the latter is transformed into martensite.

このため、前記したエメリーペーパー研磨やショットピ
ーニングを行なって金属内表面に残留圧縮応力を生じさ
せても、別にこの加工がマルテンサイト変態を生じさせ
る原因となれば応力腐食割れ強度や腐食疲労割れ強度の
改善に結びつかないことが考えられるから、前記加工は
マルテンサイト変態を生じない状態で行なうことが必要
となる。Therefore, even if residual compressive stress is generated on the inner surface of the metal by the emery paper polishing or shot peening described above, if this process causes martensitic transformation, the stress corrosion cracking strength and corrosion fatigue cracking strength will increase. Since it is conceivable that this will not lead to an improvement in

そこでこの問題を考えるに、既知の如く、加工によシ歪
惹起マルテンサイト変態を生じさせるには温度条件があ
って、Ｍｄ点以下の温度でこれを行なうことが必要とさ
れているから、逆にこのＭｄ点以上の温度で残留圧縮応
力を生じさせるような前記加工を施せば、マルテンサイ
ト相を生成することなく所望する残留圧縮応力をオース
テナイト系ステンレス鋼で構成される部材に与えるとと
か（５） できることになる。Considering this problem, as is known, there are temperature conditions for strain-induced martensitic transformation to occur during processing, and it is necessary to perform this at a temperature below the Md point. If the processing is applied to generate residual compressive stress at a temperature above the Md point, the desired residual compressive stress can be applied to a member made of austenitic stainless steel without forming a martensitic phase ( 5) You will be able to do it.

而して、オーステナイト系ステンレス鋼の応力腐食割れ
や腐食疲労割れを防止するためには、歪惹起マルテンサ
イトを生ずる温度の上限Ｍｄ点以上で、金属内表面に残
留圧縮応力を生じさせる塑性加工としてのエメリーペー
パー研磨やショットピーニングを行なうことが有効であ
るということができ、特にショットピーニングの方が表
面での残留圧縮応力が高く、かつ深い部分まで圧縮応力
に、なるという点で有利であるから、加工法としてはこ
のショットピーニングを主とし、更に必要に応じてエメ
リー（−・千−研磨を補助的に行なうことがよ込ものと
なる。Therefore, in order to prevent stress corrosion cracking and corrosion fatigue cracking in austenitic stainless steel, it is necessary to perform plastic working that produces residual compressive stress on the inner surface of the metal at a temperature above the upper limit Md of the temperature that produces strain-induced martensite. It can be said that emery paper polishing and shot peening are effective. In particular, shot peening is advantageous in that the residual compressive stress at the surface is higher and the compressive stress extends to the deeper parts. The main processing method is shot peening, and if necessary, emery polishing may be used as an auxiliary method.

ところで、以上のようなオーステナイト系ステンレス鋼
の耐食性改善手法につき更に詳細に検討してみると、シ
ョットピーニングで加工された金属表面の平均的な残留
応力は高い圧縮応力となっているのであるが、局所的に
は残留引張応力となっている部分のあることが考察され
た。By the way, when we examine in more detail the above methods for improving the corrosion resistance of austenitic stainless steel, we find that the average residual stress on the metal surface processed by shot peening is high compressive stress. It was considered that there were some areas with residual tensile stress locally.

これは、ショットピーニングした表面近傍の残（６） 留応力分布を測定した結果をみると、表面から０．１〜
０．２間の深さで残留圧縮応力は極大値を示して表面で
はこれよりもある程度近い値となっているから、塑性変
形の不均一さのために表面近傍では局所的に非常に低い
残留圧縮応力、ないし残留引張応力となっている部分の
あることが示唆されるためである。This is due to the residual stress distribution near the shot peened surface (6).
The residual compressive stress reaches its maximum value at a depth of between 0.2 and 0.2 mm, and the value at the surface is somewhat closer to this value, so the residual compressive stress is locally very low near the surface due to the non-uniformity of plastic deformation. This is because it suggests that there is a portion with compressive stress or residual tensile stress.

本発明は以上のような実状に鑑み、ショットピーニング
によって金属内表面に残留圧縮応力を付与する加工にお
いて、その塑性加工の不均一さに起因する前述した問題
点は、ショット径を順次小径のものに移行させてピーニ
ングを行なうととにより補正できることを見い出してな
されたものである。In view of the above-mentioned circumstances, the present invention aims to solve the above-mentioned problem caused by the non-uniformity of plastic working in the process of imparting residual compressive stress to the inner surface of a metal by shot peening, by gradually increasing the shot diameter to smaller diameters. This was done after discovering that it could be corrected by shifting the temperature to 1 and then performing peening.

而して本発明は、オーステナイト系ステンレス鋼を歪惹
起マルテンサイト変態の生ずる上限温度Ｍｄ点よりも高
い温度で塑性加工し、その表面に残留圧縮応力を付与さ
せるにあたり、その塑性加工法としてショットピーニン
グを採用すると共に、ショット径を大径のものから小径
のものに順次移行させてピーニングを行ない前記オース
テナイト系ステンレス鋼の耐食性を改善することを特徴
とするものである。Therefore, the present invention employs shot peening as a plastic working method for plastic working austenitic stainless steel at a temperature higher than the upper limit temperature Md at which strain-induced martensitic transformation occurs and imparting residual compressive stress to its surface. The present invention is characterized in that the corrosion resistance of the austenitic stainless steel is improved by peening the austenitic stainless steel by sequentially changing the shot diameter from a large diameter to a small diameter.

ｋお、ショットピーニングによシ加工された金属表面は
、更にエメリーペーパー研磨によって表面凹凸がなくな
るまで研磨するととて一層良好な残留圧縮応力状態とな
ることが確認されている。It has been confirmed that when the metal surface processed by shot peening is further polished with emery paper until the surface unevenness disappears, the residual compressive stress state becomes even better.

また、オーステナイト系ステンレス鋼で構成される部材
のうち、軸のキー溝部等はその形状から割れの発生し易
い部分であり、このコーナ一部に対して前記ショットピ
ーニングの加工をそのまま施すと該コーナ一部の肩が垂
れ、ここが新たな割れの起点になることが考えられる。In addition, among members made of austenitic stainless steel, the key groove of the shaft is prone to cracking due to its shape. Some of the shoulders may droop, and this may become the starting point for new cracks.

したがってこれを防止するためには、部材の機能上にお
いて支障とならない範囲で前記コーナ一部の角を丸めて
おき、ショット径の小さなものでピーニングを行なって
加工硬化させながら順次ショット径を大きくしていくこ
とにより、肩の垂れを防止して高い残留圧縮応力を付与
し、この後ショット径を順次小径のものに移行しながら
ピーニングを行なって表面の塑性加工の不均一性を補正
し、更に必要に応じてエメリーペーパー研磨を施すよう
にすればよい。Therefore, in order to prevent this, some of the corners are rounded to the extent that it does not interfere with the functionality of the part, and the shot diameter is gradually increased while peening is performed with a small shot diameter and work hardened. This process prevents the shoulders from sagging and imparts high residual compressive stress, and then peening is performed while gradually changing the shot diameter to smaller diameters to correct the non-uniformity of the plastic working on the surface. Emery paper polishing may be performed as necessary.

以下図面を参照して、本発明を更に詳細に説明する。The present invention will be explained in more detail below with reference to the drawings.

第１図はオーステナイト系ステンレス鋼で構成される部
材（以下単に部材と称する）を旋削加工した場合の部材
表面深さ方向に関しての応力分布の一例を示しておυ、
同図から、部材表面では１００　ｋｇ”／　２に近い大
きな引張力の状態となシ、簡 約１５μｍの深さで残留応力は圧縮側となって約４０μ
ｍ付近で極小となった後、略零付近まで圧縮応力は漸減
していることが理解されよう。ことで表面で現われる高
い引張応力′が応力腐食割れの点で不利となるととは既
に述べた通りである。Figure 1 shows an example of the stress distribution in the depth direction of the surface of a member made of austenitic stainless steel (hereinafter simply referred to as the member) when turned.
From the same figure, it can be seen that there is a large tensile force close to 100 kg"/2 on the surface of the member, and at a depth of approximately 15 μm, the residual stress becomes compressive and reaches approximately 40 μm.
It will be understood that after reaching a minimum near m, the compressive stress gradually decreases to near zero. As already mentioned, the high tensile stress 'that appears on the surface is disadvantageous in terms of stress corrosion cracking.

第２図は、前記した旋削加工後の部材表面をす３２０の
二メリーペーパーで研磨したときの研磨回数と、部材表
面の残留応力変化の関係を示したものであり、前記した
部材表面の高い引張応力も研磨によって低下し、研磨５
回で圧縮側となった（９） 後、研磨２０回程度で圧縮応力３０　”ｆ４２程となっ
て飽和している。Figure 2 shows the relationship between the number of times of polishing and the change in residual stress on the surface of the component when the surface of the component after the turning process was polished using Su320-2 Merry Paper. Tensile stress is also reduced by polishing, and polishing 5
After reaching the compression side (9), the compressive stress became saturated at about 30"f42 after about 20 polishings.

そしてこのようなエメリー（−パー研磨を充分行なった
ときの部材表面の深さ方向での残留応力分布は、第１図
と第２図を重畳した第３図の形となシ、同第３図から理
解されるように、エメリーペーパー研磨による加工法で
は残留応力を圧縮側に補正する加工層が極めて薄い状態
となっている。The residual stress distribution in the depth direction of the surface of the member after sufficient emery polishing is shown in Figure 3, which is a superimposition of Figures 1 and 2. As can be understood from the figure, in the processing method using emery paper polishing, the processed layer that corrects the residual stress to the compressive side is extremely thin.

第４図は、前記した旋削加工した部材をショット径０．
５簡のものでピーニングした場合の部材深さ方向に関し
ての残留応力分布を示したものであり、同図から、部材
表面で約４５ｋｇ°ｆ４２の圧縮応力とな軌約１００μ
ｍの深さで７０　”’／−２の圧縮応力の極大値となっ
た後漸減するが、約７００μｍ・の深さでも圧縮側とな
っていることが理解されよう。なお同図で部材表面近傍
の圧縮応力が若干低くなっているのは、塑性加工による
表面粗さのために若干開放されているため等の理由が考
えられるが、この点については後述する。FIG. 4 shows the above-described turned member with a shot diameter of 0.
This figure shows the residual stress distribution in the depth direction of a member when peening is performed using a 5-strip piece. From the same figure, it can be seen that there is a compressive stress of about 45 kg° f42 on the surface of the member and a radius of about 100 μ
It is understood that the compressive stress reaches its maximum value of 70''/-2 at a depth of m and then gradually decreases, but it is still on the compressive side even at a depth of about 700 μm. The reason why the compressive stress in the vicinity is slightly lower may be that the surface is slightly opened due to surface roughness due to plastic working, but this point will be discussed later.

ここで第３図と第４図を対比すると、部材表面（１０） に残留圧縮応力を付与する加工としてのエメリーヘー・
り一研磨とショットピーニングは、後者ショットピーニ
ングの方が残留圧縮応力が高く、かつ深い所まで圧縮側
となるので、応力腐食割れ等の耐食性改善法として有利
であることは明らかであシ、前者エメリーペーパー研磨
については、必要に応じてこれを補助的に採用すること
がよい。Comparing Fig. 3 and Fig. 4, we can see that emery hair is a process that imparts residual compressive stress to the surface (10) of the member.
It is clear that the latter is more advantageous as a method for improving corrosion resistance such as stress corrosion cracking, as the latter has a higher residual compressive stress and is compressed to a deeper depth. Emery paper polishing may be used as a supplement if necessary.

また、これらの加工については、加工時の温度条件によ
って部材にマルテンサイト変態を生じさせることがあっ
て、との変態によって生じたマルテンサイト相は既に述
べたように応力腐食割れ強度の上では不利な傾向のもの
となるから、前記したショットピーニング、エメリ−ヘ
−ノ＋−研磨ハ、部材の歪惹起マルテンサイト変態を生
じさせる上限温度Ｍｄ点よυも高い温度で行たっている
ことは言うまでもない。Additionally, these processes may cause martensitic transformation in the component depending on the temperature conditions during processing, and the martensitic phase produced by this transformation is disadvantageous in terms of stress corrosion cracking strength, as mentioned above. Therefore, it goes without saying that the above-mentioned shot peening and emery polishing are performed at a temperature υ higher than the upper limit temperature Md point at which strain-induced martensitic transformation of the member occurs. .

次ぎに、第４図の説明において、部材表面近傍、１ の残留圧縮応力が若干低くな鬼ているのは表面粗さのた
め若干開放しているためとした点につき述べると、第５
図に示すように、ショットピーニングを充分時間をかけ
て行なった場合にも、局所的には表面にショットが当ら
ない部分（第５図の符号２の部分）があると考えられ、
ショットが当った真下の部分（第５図の符号１の部分）
は表面に平行する方向に引張を受けるような形で変形す
るので、結果として充分大きな残留圧縮応力となるが、
他方前記ショットの当らなかった部分ではこの場合反対
に圧縮変形を受けることになるから、結果として部材表
面に残留引張応力が残されることも考えられ、これが結
局部材表面の平均的残留圧縮応力の低下として現われる
ことになっていると理解されるのである。Next, in the explanation of Fig. 4, we will discuss the fact that the residual compressive stress near the surface of the member, 1, is slightly low because it is slightly open due to surface roughness.
As shown in the figure, even if shot peening is carried out for a sufficient amount of time, it is thought that there are localized areas where the shot does not hit the surface (parts marked 2 in Figure 5).
The area directly below where the shot hit (the area marked 1 in Figure 5)
deforms in such a way that it is under tension in the direction parallel to the surface, resulting in a sufficiently large residual compressive stress, but
On the other hand, in this case, the parts that were not hit by the shot will undergo compressive deformation, so it is possible that residual tensile stress will remain on the surface of the component as a result, which will eventually reduce the average residual compressive stress on the surface of the component. It is understood that it is supposed to appear as.

この傾向は、ショット径が大きいものほど大きく生じ、
このことは小径のショットを部材表面に、当てた場合と
して示した第６図との対比からも明らかであろう。This tendency occurs more strongly as the shot diameter becomes larger.
This will be clear from a comparison with FIG. 6, which shows the case where a small-diameter shot hits the surface of a member.

したがって小径のショットを用いてピーニングを行なえ
ば、表面粗さに基づく前述の難点も解消されるが、反面
、付与すべき残留圧縮応力の大きさ、および部材の深い
所までの圧縮応力付与のためにはショット径が大きい方
が有利である。Therefore, if peening is performed using a small-diameter shot, the above-mentioned difficulties due to surface roughness can be solved, but on the other hand, it is difficult to apply the residual compressive stress to the deep part of the part. It is advantageous to have a larger shot diameter.

これらのととからして、本発明においては、初めに所定
の大径ショットを用いてピーニングすることによシ、付
与する残留圧縮応力の大きさ、圧縮応力側とする深さに
ついて、望ましい応力分布の状態を定め、この後、大径
のショットを用いた場合の難点となる部材表面の粗さを
、ピーニングするショット径を順次小径のものに移行さ
せることによって補正し、更には、必要に応じて最終段
階の表面加工としてエメリーペーパー研磨を施すように
したのである。Considering these points, in the present invention, by first peening using a predetermined large-diameter shot, the desired stress can be determined with respect to the magnitude of the residual compressive stress to be applied and the depth of the compressive stress side. After determining the state of the distribution, the roughness of the surface of the part, which is a problem when using a large diameter shot, is corrected by gradually shifting the diameter of the shot to be peened to a smaller diameter shot, and further, as necessary, Accordingly, emery paper polishing was applied as the final surface treatment.

第７図は、このようにしてピーニングするショット径を
順次小さくしていき（本例では、図の符号＆、１ｂ１ｅ
ｌｄに対応してショット径を、０．５　ｍ。FIG. 7 shows how the shot diameter to be peened is gradually reduced (in this example, the symbols &, 1b1e
The shot diameter is 0.5 m corresponding to ld.

０．３ｍ　、　０．２ｍ　、　Ｏ１１箭とした）、最終
段階としてエメリーペー・や−研磨（図の符号ｅ）した
場合の部材深さ方向に関しての応力分布を示しておシ同
図から明らかであるように、部材表面近傍の残留圧縮応
力は順次増大して、結果として部材表面の残留応力が均
一化されることが解かる。これら（１３） の加工を、いずれも温度条件Ｍｄ点以上で行なっている
ことは言うまでもない。It is clear from the figure that the stress distribution in the depth direction of the member is shown when the final step is emery polishing (reference numeral e in the figure). It can be seen that the residual compressive stress near the surface of the member gradually increases, and as a result, the residual stress on the surface of the member becomes uniform. It goes without saying that these processes (13) are all carried out under temperature conditions of Md point or higher.

なお、前記第７図の応力分布において、深さ０、１　ｍ
以上の所では初めの０．５　ｖｍ径のショットによって
加工硬化を生ずるために、以後の小径ショットによるピ
ーニングでは殆んど変化は生じていない。In addition, in the stress distribution shown in FIG. 7, depths of 0 and 1 m
In the above case, since work hardening occurs due to the initial 0.5 vm diameter shot, almost no change occurs in subsequent peening using small diameter shots.

以上述べた本発明方法におけるショット径を順次大径の
ものから小径のものに移行させるについては、その順次
段階のショット径変化、必要な順次段数を、対象となる
部材の形状・組成等に応じて適宜選定して行なえばよい
。　。In order to gradually shift the shot diameter from a large diameter to a small diameter in the method of the present invention described above, the shot diameter change in the sequential steps and the necessary number of sequential steps are determined depending on the shape and composition of the target member. It is sufficient to select and carry out the process as appropriate. .

第８図は、本発明を適用する対象部材の一つであるオー
ステナイト系ステンレス鋼で構成される゛キー溝をもっ
た軸を示しているが、このような段差部があってコーナ
一部分を有する部材に対しては、前述し゛たショット径
を大径のものから順次小径のものに移行させるというシ
ョットピーニングの加工をそのまま適用するには問題を
生ずる。Fig. 8 shows a shaft with a keyway made of austenitic stainless steel, which is one of the target members to which the present invention is applied. Problems arise when applying the above-mentioned shot peening process, in which the shot diameter is gradually changed from a large diameter shot to a small diameter shot, to a member as is.

この問題は既に述べているように、初期の大径（１４） ショットによってコーナ一部の肩が垂れ（第９図参照）
、第９図の矢印３ないし４に示す部分から亀裂を発生さ
せる虞れが大きくなるからである。As already mentioned, this problem is caused by the initial large-diameter (14) shots that cause the shoulders in some corners to sag (see Figure 9).
This is because there is a greater possibility that cracks will occur from the portions indicated by arrows 3 and 4 in FIG.

そこでこのようなコーナ一部を有する部材に対してショ
ット径を大径のものから小径のものに順次移行させなが
らショットピーニングするという加工を行なうにあたっ
ては、この加工に先立って為まずコーナ一部の肩を例え
ば最大ショット径の５０〜７０％程度の曲率半径で丸め
る前処理加工を施しく第１０図参照）、次ぎにショット
ピーニングを小径のものから始めて順次最大径のものに
至るまで移行させんから、該コーナ一部分を徐々に加工
硬化させてその肩が垂れるのを防ぎ、この後、表面の粗
さが局所的な残留引張応力を残すことの原因となる点を
補正解消するために、前記第７図で示したと同様の手法
、すなわちショット径を大径のものから小径のものに順
次移行させながらショットピーニングを行ない、更に必
要に応じてエメリーペーパー研磨を行なうようにすれば
よく、このことによってショットピーニングによるコー
ナ一部の肩の垂れの問題は効果的に解消されるものとな
った。Therefore, when performing shot peening on a member with such a part of the corner by sequentially changing the shot diameter from a large diameter to a small diameter, it is necessary to first peen a part of the corner prior to this processing. A pretreatment process is performed to round the shoulder to a radius of curvature of, for example, 50 to 70% of the maximum shot diameter (see Figure 10), and then shot peening is applied starting from the small diameter one and gradually progressing to the maximum diameter one. Then, in order to gradually work harden the corner part to prevent the shoulder from sagging, and then to correct and eliminate the point where the surface roughness causes local residual tensile stress, Shot peening can be performed using the same method as shown in Figure 7, in which the shot diameter is gradually changed from large to small, and if necessary, polishing with emery paper can be used. This effectively solved the problem of sagging shoulders in some corners caused by shot peening.

以上の説明から理解されるように、本発明によれば、例
えば原子炉機器、配管等のように腐食環境下で使用され
るオーステナイト系ステンレス鋼の応力腐食割れの防止
、腐食疲労強度の増大など耐食性の向上に効果があり、
特に原子カプラントのような装置類に対しての信頼性の
向上、運転時間の延長、定期検査等の保守点検作業頻度
の低減などには極めて有益なものとなシ、その有用性は
犬なるものである。As can be understood from the above description, according to the present invention, it is possible to prevent stress corrosion cracking of austenitic stainless steel used in corrosive environments such as nuclear reactor equipment, piping, etc., increase corrosion fatigue strength, etc. Effective in improving corrosion resistance,
In particular, it is extremely useful for improving the reliability of equipment such as nuclear couplants, extending operating hours, and reducing the frequency of maintenance inspections such as periodic inspections. It is.

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

図面はいずれもオーステディト系ステンレス鋼によって
構成される部材の加工による残留応力変化、又は応力分
布を説明するだめの図であシ、第１図は部材表面を旋削
加工した場合の表面近傍の残留応力分布図、第２図は旋
削加工後の部材表面をエメリーペーパー研磨したときの
研磨回数と表面残留応力変化の関係を示しだ図、第３図
は同研磨後の部材表面近傍の残留応力分布図、第４図は
旋削加工後にショットピーニングを行なったときの部材
表面近傍の残留応力分布図、第５図は大径のショットで
ピーニングしたときの部材表面性状を示す図、第６図は
小径のショットでピーニングしたときの部材表面性状を
示す図、第７図は本発明を適用した場合の部材表面近傍
の残留応力分布の変化を示した図、第８図はキー溝を有
する軸の断面図、第９図はショットピーニングによって
コーナ一部分の肩が垂れた状態を示す図、第１０図はシ
ョットピーニングに先立ってコーナ一部の角を丸めた状
態を示す図である。 １ニジヨツトの当たる部分 ２ニジヨツトの当らない部分 （１７） １ ０　　　　ノｏｏ　　　　：２ｏｏ　　　　、３ｏ。 着　Ｑ　（ｐが） ｋ升磨回数 第５図 ０妥４ １χ 第８図 第６図 第７図 ３鼠で仏プ） 第９図 第１０図All drawings are for explaining residual stress changes or stress distribution due to machining of a member made of austedite stainless steel. Figure 1 shows the residual stress near the surface of the member when the surface of the member is turned. Distribution diagram. Figure 2 shows the relationship between the number of polishing times and changes in surface residual stress when the surface of a component after turning is polished with emery paper. Figure 3 is a distribution diagram of residual stress near the surface of the component after polishing. , Fig. 4 is a residual stress distribution diagram near the surface of a part when shot peening is performed after turning, Fig. 5 is a diagram showing the surface properties of a part when peening is performed with a large-diameter shot, and Fig. 6 is a diagram showing the surface properties of a part when peening is performed with a large-diameter shot. A diagram showing the surface properties of a member when peened with shot, Figure 7 is a diagram showing changes in residual stress distribution near the member surface when the present invention is applied, and Figure 8 is a cross-sectional view of a shaft with a keyway. , FIG. 9 is a diagram showing a state in which the shoulder of a portion of the corner is drooped due to shot peening, and FIG. 10 is a diagram showing a state in which the shoulder of a portion of the corner is rounded prior to shot peening. 1. Part where the rainbow yawn hits 2. Part where the rainbow yacht doesn't hit (17) 1 0 nooo: 2oo, 3o. Arrival Q (p) k square number of times Fig. 5 0 - 4 1χ Fig. 8 Fig. 6 Fig. 7 3 mouse and Buddha) Fig. 9 Fig. 10

Claims (2)

【特許請求の範囲】[Claims] （１）オーステナイト系ステンレス鋼を、歪惹起マルテ
ンサイト変態の生ずる上限温度Ｍｄ点よシも高い温度で
塑性加工し、その表面に残留圧縮応力を付与させるオー
ステナイト系ステンレス鋼の表面加工法において、前記
塑性加工としてショットピーニングを採用すると共に、
そのピーニングするショット径を大径のものから小径の
ものに順次移行させることを特徴とするオーステナイト
系ステンレス鋼の耐食性改善法。(1) In the surface processing method for austenitic stainless steel, the austenitic stainless steel is plastically worked at a temperature higher than the upper limit temperature Md at which strain-induced martensitic transformation occurs, and residual compressive stress is imparted to the surface of the austenitic stainless steel. In addition to adopting shot peening as plastic processing,
A method for improving the corrosion resistance of austenitic stainless steel, which is characterized by sequentially changing the shot diameter for peening from a large diameter shot to a small diameter shot. （２）　　オーステ”ナイト系ステンレス鋼を、歪惹起
マルテンサイト変態の生ずる上限温度Ｍｄ点よシも高い
温度で塑性加、工し、その表面に残留圧縮応力を付与さ
せるオーステナイト系ステンレス鋼の表面加工法におい
て、６前記塑性加工としてショットピーニングを採用す
ると興に、前記ステンレス鋼で構成される部材のコーナ
一部に対しては、そのコーナ一部の曲率・半径を大きく
した後、前記ピーニングするショット径を小径のものか
ら大径のものに移行させ更にこの後小径のものに順次移
行させることを特徴とするオーステナイト系ステンレス
鋼の耐食性改善法。(2) Surface processing of austenitic stainless steel by plastic forming and processing the austenitic stainless steel at a temperature higher than the upper limit temperature Md at which strain-induced martensitic transformation occurs, and imparting residual compressive stress to the surface. In the method, when shot peening is adopted as the above-mentioned plastic working, after increasing the curvature and radius of a part of the corner of the member made of stainless steel, the above-mentioned shot peening is applied. A method for improving the corrosion resistance of austenitic stainless steel, which is characterized by shifting the diameter from a small diameter to a large diameter, and then sequentially shifting to a small diameter.
JP7774282A 1982-05-10 1982-05-10 Improvement of corrosion resistance of austenitic stainless steel Pending JPS58197215A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP7774282A JPS58197215A (en) 1982-05-10 1982-05-10 Improvement of corrosion resistance of austenitic stainless steel

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP7774282A JPS58197215A (en) 1982-05-10 1982-05-10 Improvement of corrosion resistance of austenitic stainless steel

Publications (1)

Publication Number Publication Date
JPS58197215A true JPS58197215A (en) 1983-11-16

Family

ID=13642357

Family Applications (1)

Application Number Title Priority Date Filing Date
JP7774282A Pending JPS58197215A (en) 1982-05-10 1982-05-10 Improvement of corrosion resistance of austenitic stainless steel

Country Status (1)

Country Link
JP (1) JPS58197215A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5598730A (en) * 1994-08-30 1997-02-04 Snap-On Technologies, Inc. Pre-forge aluminum oxide blasting of forging billets as a scale resistance treatment
CN110763612A (en) * 2018-07-25 2020-02-07 中国石油化工股份有限公司 Method for researching influence of martensite on stress corrosion cracking performance of austenitic steel

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5598730A (en) * 1994-08-30 1997-02-04 Snap-On Technologies, Inc. Pre-forge aluminum oxide blasting of forging billets as a scale resistance treatment
CN110763612A (en) * 2018-07-25 2020-02-07 中国石油化工股份有限公司 Method for researching influence of martensite on stress corrosion cracking performance of austenitic steel
CN110763612B (en) * 2018-07-25 2022-10-11 中国石油化工股份有限公司 Method for researching influence of martensite on stress corrosion cracking performance of austenitic steel

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