JP7607913B2 - Residual stress reduction method and residual stress reduction device - Google Patents
Residual stress reduction method and residual stress reduction device Download PDFInfo
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Description
本発明は、残留応力低減方法及び残留応力低減装置に関する。 The present invention relates to a method and device for reducing residual stress.
大型鋼構造物の建造には溶接が必要不可欠である。しかし、溶接の施工に伴い、溶接部近傍には高い引張り残留応力が発生する。この残留応力が疲労き裂や応力腐食割れ（Stress Corrosion Cracking：SCC）の原因の一つとされており、残留応力と構造物の健全性は深く関係している。したがって、引張り残留応力を低減することは重要であるといえる。溶接残留応力を緩和する方法としては、ピーニング手法や溶接後熱処理（Post Weld Heat Treatment: PWHT）などが挙げられる。
また、管の外表面を高温にし、管の内表面を低温にすることにより形成した温度勾配により管溶接部の残留応力を緩和する方法が知られている（例えば、特許文献１参照）。
Welding is essential for the construction of large steel structures. However, high tensile residual stress occurs near the welded parts during welding. This residual stress is considered to be one of the causes of fatigue cracks and stress corrosion cracking (SCC), and the residual stress is closely related to the soundness of the structure. Therefore, it is important to reduce the tensile residual stress. Methods for mitigating welding residual stress include the peening method and post-weld heat treatment (PWHT).
Also, a method is known in which the residual stress in a pipe weld is relieved by forming a temperature gradient by heating the outer surface of the pipe to a high temperature and the inner surface of the pipe to a low temperature (see, for example, Patent Document 1).
しかし、従来の残留応力緩和方法では、初期コストや施行時間の点で問題となる場合があり、低コストかつ簡易的な施行方法の提案が期待されている。
本発明は、このような事情に鑑みてなされたものであり、簡便な残留応力低減方法を提供する。
However, conventional residual stress relaxation methods can have problems in terms of initial cost and application time, and there is a need for a low-cost, simple application method.
The present invention has been made in view of the above circumstances, and provides a simple method for reducing residual stress.
本発明は、引張り残留応力を有する処理対象物の表面の一部に、－１００℃以下の温度に冷却した少なくとも１つの金属部材の表面の一部を直接的に又は間接的に接触させ、前記処理対象物を局部的に冷却する冷却ステップと、前記処理対象物を常温に戻すステップとを含み、前記冷却ステップは、前記少なくとも１つの金属部材の表面のうち前記処理対象物と接触する部分を変えながら前記処理対象物の表面の一部を局部冷却するステップであることを特徴とする残留応力低減方法を提供する。 The present invention provides a method for reducing residual stress, which includes a cooling step of locally cooling a surface of an object to be treated having tensile residual stress by directly or indirectly contacting a portion of the surface of at least one metal member cooled to a temperature of -100°C or lower with the surface of the object to be treated, and a step of returning the object to room temperature, the cooling step being characterized in that the cooling step is a step of locally cooling a portion of the surface of the object to be treated while changing the portion of the surface of the at least one metal member that comes into contact with the object to be treated.
金属は熱伝導率が高く、単位体積あたりの熱容量（比熱×密度）が大きい。このため、－１００℃以下の温度に冷却した少なくとも１つの金属部材の表面の一部を、処理対象物の表面の一部に直接的に又は間接的に接触させることのより、大きな熱エネルギーが処理対象物から金属部材へと移動することができる。また、金属部材の表面のうち処理対象物と接触する部分を変えることにより、さらに処理対象物の熱エネルギーを金属部材へと移動させることができる。このように接触部分を変えながら処理対象物を局部冷却することにより、処理対象物の一部を十分に低い温度まで急冷することできる。この急冷された処理対象物の一部（局部冷却部）は、熱収縮するため、局部冷却部とその他の部分との間に引張応力が発生する。この引張応力が降伏応力に達すると、処理対象物に引張りの塑性ひずみが発生する。処理対象物に引張りの塑性ひずみが生じた後、処理対象物の冷却をやめると、局部冷却部は常温へと戻っていく。この常温へと戻る過程において、局部冷却部は、熱膨張し引張応力は小さくなっていく。処理対象物に引張りの塑性ひずみが生じているため、常温よりも低い温度において引張応力がなくなる。そのため、引張応力がなくなったあとも局部冷却部が常温へと昇温することにより局部冷却部が熱膨張し、局部冷却部とその他の部分との間に圧縮応力が生じる。そして、常温に戻った処理対象物にこの圧縮応力が残留応力として残ることになる。
処理対象物が冷却前において有していた引張残留応力は、上述した冷却サイクルにより生じる圧縮残留応力により除去される又は相殺される。従って、本発明の残留応力低減方法により、処理対象物の引張残留応力を除去又は低減することができる。
Metals have high thermal conductivity and large heat capacity per unit volume (specific heat × density). Therefore, by directly or indirectly contacting a part of the surface of at least one metal member cooled to a temperature of -100°C or less with a part of the surface of the object to be treated, a large amount of thermal energy can be transferred from the object to be treated to the metal member. In addition, by changing the part of the surface of the metal member that contacts the object to be treated, the thermal energy of the object to be treated can be further transferred to the metal member. By locally cooling the object to be treated while changing the contact part in this way, a part of the object to be treated can be quenched to a sufficiently low temperature. Since the quenched part of the object to be treated (the locally cooled part) thermally contracts, a tensile stress is generated between the locally cooled part and the other parts. When this tensile stress reaches the yield stress, a tensile plastic strain is generated in the object to be treated. After the tensile plastic strain is generated in the object to be treated, when the cooling of the object to be treated is stopped, the locally cooled part returns to room temperature. In the process of returning to room temperature, the locally cooled part thermally expands and the tensile stress decreases. Since the object to be treated has tensile plastic strain, the tensile stress disappears at temperatures lower than room temperature. Therefore, even after the tensile stress disappears, the locally cooled part continues to expand due to the temperature rise to room temperature, and compressive stress occurs between the locally cooled part and other parts. Then, this compressive stress remains as residual stress in the object to be treated when it returns to room temperature.
The tensile residual stress that the treatment object had before cooling is eliminated or offset by the compressive residual stress that occurs during the cooling cycle described above. Therefore, the method for reducing residual stress of the present invention can eliminate or reduce the tensile residual stress in the treatment object.
本発明の残留応力低減方法は、引張り残留応力を有する処理対象物の表面の一部に、－１００℃以下の温度に冷却した少なくとも１つの金属部材の表面の一部を直接的に又は間接的に接触させ、前記処理対象物を局部的に冷却する冷却ステップと、前記処理対象物を常温に戻すステップとを含み、前記冷却ステップは、前記少なくとも１つの金属部材の表面のうち前記処理対象物と接触する部分を変えながら前記処理対象物の表面の一部を局部冷却するステップであることを特徴とする。 The residual stress reduction method of the present invention includes a cooling step in which a portion of the surface of a treatment object having tensile residual stress is directly or indirectly brought into contact with a portion of the surface of at least one metal member cooled to a temperature of -100°C or lower, thereby locally cooling the treatment object, and a step in which the treatment object is returned to room temperature, and the cooling step is characterized in that it is a step of locally cooling a portion of the surface of the treatment object while changing the portion of the surface of the at least one metal member that is in contact with the treatment object.
前記金属部材の材料は、１００Ｗ／（ｍ・Ｋ）以上の熱伝導率を有する金属であり、かつ、２．０Ｊ／（Ｋ・ｃｍ3）以上の単位体積あたりの熱容量（比熱×密度）を有する金属であることが好ましい。このことにより、処理対象物を急速に局部冷却することができる。
前記冷却ステップにおける冷却時間は０．１秒間以上１分間以下であることが好ましく、前記冷却ステップは、処理対象物の一部の温度を、処理対象物に引張りの塑性ひずみが生じる温度よりも低い温度にするステップであることが好ましい。このことにより、処理対象物に圧縮残留応力を発生させることができ、処理前の処理対象物が有していた引張り残留応力を低減することができる。
The material of the metal member is preferably a metal having a thermal conductivity of 100 W/(m·K) or more and a heat capacity per unit volume (specific heat x density) of 2.0 J/(K·cm 3 ) or more, which allows rapid localized cooling of the object to be processed.
The cooling time in the cooling step is preferably 0.1 seconds to 1 minute, and the cooling step is preferably a step of lowering the temperature of a part of the object to be treated to a temperature lower than the temperature at which tensile plastic strain occurs in the object to be treated. This makes it possible to generate compressive residual stress in the object to be treated and to reduce the tensile residual stress that the object had before the treatment.
本発明は、少なくとも１つの金属部材と、－１００℃以下の液化ガスにより前記少なくとも１つの金属部材を冷却するように設けられた冷却構造と、前記少なくとも１つの金属部材の表面のうち処理対象物と接触する部分を変えながら前記少なくとも１つの金属部材を前記処理対象物の表面の一部に直接的に又は間接的に接触させるように設けられた接触構造とを備える残留応力低減装置も提供する。
前記金属部材は、円柱形状又は円筒形状を有することが好ましく、前記接触構造は、前記金属部材を回転させるように設けられた構造であることが好ましく、前記金属部材は、処理対象物の表面の一部に前記金属部材の外周面の一部が直接的に又は間接的に接触するように設けられたことが好ましい。この金属部材を回転させることにより、金属部材の外周面を連続的に処理対象物に接触させることができ、処理対象物を急速に局部冷却することができる。
The present invention also provides a residual stress reduction device comprising: at least one metal member; a cooling structure arranged to cool the at least one metal member with a liquefied gas at -100°C or lower; and a contact structure arranged to bring the at least one metal member into direct or indirect contact with a part of a surface of an object to be treated while changing the part of the surface of the at least one metal member that comes into contact with the object to be treated.
The metal member preferably has a columnar or cylindrical shape, the contact structure is preferably a structure arranged to rotate the metal member, and the metal member is preferably arranged so that a part of the outer circumferential surface of the metal member directly or indirectly contacts a part of the surface of the object to be treated. By rotating the metal member, the outer circumferential surface of the metal member can be continuously brought into contact with the object to be treated, and the object to be treated can be rapidly locally cooled.
前記少なくとも１つの金属部材は、第１金属部材と第２金属部材とを含むことが好ましく、前記接触構造は、第１及び第２金属部材を吊り下げ移動させるように設けられたレールと、吊り下げられた第１又は第２金属部材を落とし前記処理対象物の表面に接触させるように設けられた落とし構造とを有することが好ましい。第１金属部材を処理対象物に接触させた後、さらに第２金属部材を処理対象物に接触させることにより、処理対象物を急速に局部冷却することができる。
前記少なくとも１つの金属部材は、複数の粒状の金属部材を含むことが好ましく、前記接触構造は、複数の粒状の金属部材を連続的に前記処理対象物に接触させるように設けられたことが好ましい。このことにより、処理対象物を急速に局部冷却することができる。
The at least one metal member preferably includes a first metal member and a second metal member, and the contact structure preferably includes a rail provided for suspending and moving the first and second metal members, and a drop structure provided for dropping the suspended first or second metal member into contact with the surface of the object to be treated. By contacting the first metal member with the object to be treated and then further contacting the second metal member with the object to be treated, the object to be treated can be rapidly locally cooled.
The at least one metal member preferably includes a plurality of granular metal members, and the contact structure preferably is provided so as to continuously contact the plurality of granular metal members with the object to be treated, thereby enabling rapid localized cooling of the object to be treated.
以下、複数の実施形態を参照して本発明をより詳細に説明する。図面や以下の記述中で示す構成は、例示であって、本発明の範囲は、図面や以下の記述中で示すものに限定されない。 The present invention will be described in more detail below with reference to several embodiments. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.
第１実施形態
図１は、本実施形態の残留応力低減方法における処理対象物及び金属部材の概略斜視図であり、図２は図１の破線Ａ－Ａにおける処理対象物及び金属部材の概略断面図であり、図３は、本実施形態の残留応力低減装置の概略断面図である。
本実施形態の残留応力低減方法は、引張り残留応力を有する処理対象物２の表面の一部に、－１００℃以下の温度に冷却した少なくとも１つの金属部材３の表面の一部を直接的に又は間接的に接触させ、処理対象物２を局部的に冷却する冷却ステップと、処理対象物２を常温に戻すステップとを含み、前記冷却ステップは、少なくとも１つの金属部材３の表面のうち処理対象物２と接触する部分を変えながら処理対象物２の表面の一部を局部冷却するステップであることを特徴とする。
また、残留応力低減方法は、液化ガス８により金属部材３の全体を－１００℃以下に冷却するステップを含んでもよい。
First embodiment FIG. 1 is a schematic perspective view of a treatment object and a metal member in a residual stress reduction method of this embodiment, FIG. 2 is a schematic cross-sectional view of the treatment object and the metal member taken along dashed line A-A in FIG. 1, and FIG. 3 is a schematic cross-sectional view of a residual stress reduction apparatus of this embodiment.
The residual stress reduction method of this embodiment includes a cooling step of locally cooling the treatment object 2 by directly or indirectly contacting a portion of the surface of at least one metal member 3 that has been cooled to a temperature of -100°C or lower with a portion of the surface of the treatment object 2 having tensile residual stress, and a step of returning the treatment object 2 to room temperature, wherein the cooling step is characterized in that it is a step of locally cooling a portion of the surface of the treatment object 2 while changing the portion of the surface of the at least one metal member 3 that comes into contact with the treatment object 2.
Moreover, the residual stress reducing method may include a step of cooling the entire metal component 3 to −100° C. or lower with liquefied gas 8.
本実施形態の残留応力低減装置２０は、少なくとも１つの金属部材３と、－１００℃以下の液化ガスにより少なくとも１つの金属部材３を冷却するように設けられた冷却構造１２と、少なくとも１つの金属部材３の表面のうち処理対象物２と接触する部分を変えながら少なくとも１つの金属部材３を処理対象物２の表面の一部に直接的に又は間接的に接触させるように設けられた接触構造１７とを備える。 The residual stress reduction device 20 of this embodiment comprises at least one metal member 3, a cooling structure 12 arranged to cool the at least one metal member 3 with liquefied gas at -100°C or lower, and a contact structure 17 arranged to bring the at least one metal member 3 into direct or indirect contact with a portion of the surface of the object to be treated 2 while changing the portion of the surface of the at least one metal member 3 that contacts the object to be treated 2.
残留応力低減方法は、溶接などにより生じた引張り残留応力を低減する方法である。
処理対象物２は、残留応力低減方法の処理対象であり、処理前において引張応力を有する。処理対象物２は、例えば、溶接部を有する金属部材、溶接部を有する金属構造物などである。また、冷却する前の処理対象物２の温度は、常温（０℃以上４０℃以下）とすることができる。
冷却構造１２は、－１００℃以下の液化ガス８により金属部材３を冷却するように設けられた部分である。冷却構造１２は、例えば、金属部材３を液化ガス８に浸漬するように設けられる。冷却構造１２は、例えば、液化ガス容器９を備えることができる。この液化ガス容器９の液化ガス中に金属部材３を浸漬することにより、金属部材３を液化ガスとほぼ同じ温度まで冷却することができる。また、冷却構造１２は、管状の金属部材３の管内に液化ガスを流すことにより金属部材３を冷却する構造であってもよい。
図３に示した残留応力低減装置２０の冷却構造１２は、底に開口を有する液化ガス容器９を備え、この開口に円柱形状又は円筒形状の金属部材３が、外周面を下側にして嵌合している。
液化ガスは、例えば、液体窒素、液体酸素、液体アルゴン又はこれらの混合物である。
The residual stress reduction method is a method for reducing the tensile residual stress caused by welding or the like.
The treatment object 2 is a treatment target of the residual stress reduction method, and has tensile stress before treatment. The treatment object 2 is, for example, a metal member having a welded part, a metal structure having a welded part, etc. Furthermore, the temperature of the treatment object 2 before cooling can be room temperature (0° C. or higher and 40° C. or lower).
The cooling structure 12 is a portion provided to cool the metal member 3 with liquefied gas 8 at -100°C or lower. The cooling structure 12 is provided, for example, so as to immerse the metal member 3 in the liquefied gas 8. The cooling structure 12 may include, for example, a liquefied gas container 9. By immersing the metal member 3 in the liquefied gas in this liquefied gas container 9, the metal member 3 can be cooled to approximately the same temperature as the liquefied gas. The cooling structure 12 may also be a structure that cools the metal member 3 by flowing liquefied gas inside a tube of the tubular metal member 3.
The cooling structure 12 of the residual stress reducing device 20 shown in FIG. 3 includes a liquefied gas container 9 having an opening at its bottom, and a columnar or cylindrical metal member 3 is fitted into this opening with its outer circumferential surface facing downward.
The liquefied gas may be, for example, liquid nitrogen, liquid oxygen, liquid argon or a mixture thereof.
金属部材３は、－１００℃以下に冷却された後、処理対象物２に直接的に又は間接的に接触させる金属部材である。
金属部材３の材料は、例えば、１００Ｗ／（ｍ・Ｋ）以上の熱伝導率を有する金属であり、かつ、２．０Ｊ／（Ｋ・ｃｍ3）以上の単位体積あたりの熱容量（比熱×密度）を有する金属である。このことにより、大きな熱エネルギーを処理対象物２から金属部材３へと移動させることができ、処理対象物２を局部的に急冷することができる。
例えば、金属部材３の材料は、純銅、銅合金、アルミニウム、アルミニウム合金などである。
The metal member 3 is a metal member that is brought into direct or indirect contact with the treatment object 2 after being cooled to −100° C. or lower.
The material of the metal member 3 is, for example, a metal having a thermal conductivity of 100 W/(m·K) or more and a heat capacity per unit volume (specific heat×density) of 2.0 J/(K·cm 3 ) or more. This allows a large amount of thermal energy to be transferred from the processing object 2 to the metal member 3, and allows the processing object 2 to be locally rapidly cooled.
For example, the material of the metal member 3 is pure copper, a copper alloy, aluminum, an aluminum alloy, or the like.
金属部材３は、１つの部材から構成されてもよく、複数の部材から構成されてもよい。「少なくとも１つの金属部材３の表面」とは、金属部材３が１つの部材から構成される場合その部材の表面をいい、金属部材３が複数の部材から構成される場合複数の部材すべての表面をいう。また、金属部材３の形状は、金属部材３の表面の一部を直接的に又は間接的に処理対象物２に接触させることができれば特に限定されない。図１～図３に例示した図面では、金属部材３は、円柱形状又は円筒形状を有する。 The metal member 3 may be composed of one member or multiple members. "The surface of at least one metal member 3" refers to the surface of one member when the metal member 3 is composed of one member, and refers to the surfaces of all the multiple members when the metal member 3 is composed of multiple members. The shape of the metal member 3 is not particularly limited as long as a portion of the surface of the metal member 3 can be brought into contact with the processing object 2 directly or indirectly. In the drawings exemplified in Figures 1 to 3, the metal member 3 has a cylindrical or cylindrical shape.
図４は、冷却サイクルにより残留応力を低減するメカニズムの説明図である。図４の横軸は処理対象物２の局部冷却部の温度であり、縦軸は処理対象物２の局部冷却部で生じる応力である。図４の縦軸では、プラスの応力が引張応力であり、マイナスの応力が圧縮応力である。また、図４において、αは、線膨張係数であり、Ｅはヤング率であり、βは拘束パラメータ（β＜１）である。
金属部材３の全体を液化ガスなどにより－１００℃以下に冷却した後、金属部材３の表面の一部を処理対象物２の一部に直接的に又は間接的に接触させる。例えば、図１、図２のように金属部材３を処理対象物２に接触させることができる。例えば、処理対象物２に金属部材３を直接接触させてもよく、処理対象物２に金属部材３を熱伝導グリースを介して接触させてもよい。熱伝導グリースを介在させる場合、熱伝導グリースも金属部材３と一緒に液化ガスにより冷却することができる。
Fig. 4 is an explanatory diagram of the mechanism by which residual stress is reduced by a cooling cycle. The horizontal axis of Fig. 4 is the temperature of the locally cooled portion of the processing object 2, and the vertical axis is the stress generated in the locally cooled portion of the processing object 2. On the vertical axis of Fig. 4, positive stress is tensile stress, and negative stress is compressive stress. Also, in Fig. 4, α is the linear expansion coefficient, E is Young's modulus, and β is a constraint parameter (β<1).
After the entire metal member 3 is cooled to -100°C or lower by liquefied gas or the like, a part of the surface of the metal member 3 is directly or indirectly brought into contact with a part of the treatment object 2. For example, the metal member 3 can be brought into contact with the treatment object 2 as shown in Figures 1 and 2. For example, the metal member 3 may be brought into direct contact with the treatment object 2, or the metal member 3 may be brought into contact with the treatment object 2 via thermally conductive grease. When thermally conductive grease is interposed, the thermally conductive grease can also be cooled by the liquefied gas together with the metal member 3.
金属部材３を処理対象物２に局部的に接触させることにより、処理対象物２の接触部分の大きな熱エネルギーが処理対象物２から金属部材３へと移動することができる。このことにより、処理対象物２が局部的に急冷される。また、処理対象物２の急冷に伴い、金属部材３の温度も上昇するため、１回の接触では、処理対象物２を十分に低い温度まで冷却することは難しい。このため、本実施形態の方法では、金属部材３の表面のうち処理対象物２と接触する部分を変える。金属部材３の表面のうち新たに処理対象物２と接触する部分は十分に低い温度であるため、さらに処理対象物２の熱エネルギーを金属部材３へと移動させることができる。例えば、図１、図２に示した円柱形状又は円筒形状の金属部材３を位置を動かさずに所定の回転速度で回転させる。このことにより、金属部材３の表面のうち処理対象物２と接触する部分を連続的に変えることができ、処理対象物２の一部を十分に低い温度まで局部的に急冷することできる。 By locally contacting the metal member 3 with the processing object 2, a large amount of heat energy at the contact portion of the processing object 2 can be transferred from the processing object 2 to the metal member 3. This allows the processing object 2 to be locally quenched. In addition, the temperature of the metal member 3 also rises as the processing object 2 is quenched, so it is difficult to cool the processing object 2 to a sufficiently low temperature with a single contact. For this reason, in the method of this embodiment, the portion of the surface of the metal member 3 that comes into contact with the processing object 2 is changed. Since the portion of the surface of the metal member 3 that newly comes into contact with the processing object 2 has a sufficiently low temperature, the heat energy of the processing object 2 can be further transferred to the metal member 3. For example, the columnar or cylindrical metal member 3 shown in Figures 1 and 2 is rotated at a predetermined rotation speed without moving the position. This allows the portion of the surface of the metal member 3 that comes into contact with the processing object 2 to be continuously changed, and a portion of the processing object 2 can be locally quenched to a sufficiently low temperature.
この急冷された処理対象物２の一部（局部冷却部）は熱収縮するため、局部冷却部とその他の部分との間に引張応力が発生する。この引張応力が降伏応力に達すると、処理対象物に引張りの塑性ひずみが発生する。例えば、図４のグラフのように、局部冷却部の温度が急速に低くなっていくと、引張応力が徐々に大きくなっていく。そして、局部冷却部の温度が降伏温度Ｔ１（引張応力が降伏応力に達した時の温度）より低くなると、引張応力はほぼ一定となり（σY）局部冷却部に引張りの塑性ひずみが生じ、この塑性ひずみが徐々に大きくなっていく。処理対象物２から金属部材３を離し冷却をやめると、局部冷却部は常温へと戻っていく。この常温へと戻る過程において、図４のグラフのように、局部冷却部は熱膨張し引張応力は小さくなっていく。引張りの塑性ひずみが生じているため、常温よりも低い温度において引張応力がなくなる。そのため、引張応力がなくなったあとも局部冷却部が常温へと昇温することにより局部冷却部は熱膨張し、局部冷却部とその他の部分との間に圧縮応力が生じる。この圧縮応力は、降伏応力に達するまで大きくなる。この降伏応力と同等の圧縮応力が残留応力として処理対象物２に残る。
また、圧縮応力が降伏応力に達する前に局部冷却部が常温へと戻った場合は、常温に戻るまでに生じた圧縮応力が残留応力として処理対象物２に残る。
このような温度サイクルで処理対象物２の局部的な急速な冷却と、常温への昇温とを行うことにより、処理対象物２に圧縮残留応力を発生させることができる。
Since a part (locally cooled part) of the object 2 that has been quenched thermally shrinks, tensile stress occurs between the locally cooled part and the other parts. When this tensile stress reaches the yield stress, tensile plastic strain occurs in the object. For example, as shown in the graph of FIG. 4, when the temperature of the locally cooled part drops rapidly, the tensile stress gradually increases. When the temperature of the locally cooled part drops below the yield temperature T1 (the temperature when the tensile stress reaches the yield stress), the tensile stress becomes almost constant (σ Y ), and tensile plastic strain occurs in the locally cooled part, and this plastic strain gradually increases. When the metal member 3 is removed from the object 2 and cooling is stopped, the locally cooled part returns to room temperature. In the process of returning to room temperature, the locally cooled part thermally expands and the tensile stress decreases, as shown in the graph of FIG. 4. Because tensile plastic strain occurs, the tensile stress disappears at temperatures lower than room temperature. Therefore, even after the tensile stress is removed, the locally cooled portion continues to expand due to the temperature rise to room temperature, and compressive stress is generated between the locally cooled portion and other portions. This compressive stress increases until it reaches the yield stress. A compressive stress equivalent to this yield stress remains in the treatment object 2 as residual stress.
Furthermore, if the locally cooled portion returns to room temperature before the compressive stress reaches the yield stress, the compressive stress generated before the temperature returns to room temperature remains in the treatment object 2 as residual stress.
By performing localized rapid cooling of the treatment object 2 and then heating it to room temperature in such a temperature cycle, compressive residual stress can be generated in the treatment object 2.
処理対象物２が冷却前において有していた引張残留応力は、上述した温度サイクルにより生じる圧縮残留応力により除去される又は相殺される。従って、本実施形態の残留応力低減方法により、処理対象物２の引張残留応力を除去又は低減することができる。
金属部材３による処理対象物２の冷却時間は、０．１秒間以上１分間以下とすることができ、好ましくは、０．５秒間以上３０秒間以下とすることができる。このことにより、局部冷却部とその他の部分との間の温度差が大きくなり、局部冷却部をより低い温度まで冷却することができる。
金属部材３を処理対象物２に接触させることにより局部冷却部を、局部冷却部に引張りの塑性ひずみが生じる温度よりも低い温度にまるまで冷却することができる。このことにより、上述の温度サイクル後に局部冷却部に圧縮残留応力を発生させることができる。
The tensile residual stress that the treatment object 2 had before cooling is eliminated or offset by the compressive residual stress that occurs due to the above-mentioned temperature cycle. Therefore, the residual stress reduction method of the present embodiment can eliminate or reduce the tensile residual stress of the treatment object 2.
The cooling time of the treatment object 2 by the metal member 3 can be from 0.1 seconds to 1 minute, and preferably from 0.5 seconds to 30 seconds. This increases the temperature difference between the locally cooled portion and the other portions, and allows the locally cooled portion to be cooled to a lower temperature.
By bringing the metal member 3 into contact with the treatment object 2, the locally cooled portion can be cooled to a temperature lower than the temperature at which tensile plastic strain occurs in the locally cooled portion, thereby generating compressive residual stress in the locally cooled portion after the above-mentioned temperature cycle.
接触構造１７は、金属部材３の表面のうち処理対象物２と接触する部分を変えながら金属部材３を処理対象物２の表面の一部に直接的に又は間接的に接触させるように設けられた構造である。
図３に例示した残留応力軽減装置２０の接触構造１７は、モーター５と、歯車６ａ、６ｂと、ベルト７とを含む回転構造４である。金属部材３は、円柱形状又は円筒形状を有し、金属部材３の外周面の一部が直接的に又は間接的に処理対象物２に接触させることができるように設けられている。
例えば、引張残留応力を有する処理対象物２に図３に示した金属部材３の外周面を接触させることにより、処理対象物２の局部冷却を開始し、回転構造４を用いて金属部材３を回転させることにより金属部材３の外周面の接触部分を変える。そして、金属部材３の外周面を処理対象物２から離すことにより局部冷却を終了し、処理対象物２を常温に戻す。このような一連の操作により、処理対象物２の引張残留応力を除去又は軽減することができる。
The contact structure 17 is a structure provided so as to bring the metal member 3 into direct or indirect contact with a part of the surface of the object 2 to be treated while changing the part of the surface of the metal member 3 that comes into contact with the object 2 to be treated.
3 is a rotating structure 4 including a motor 5, gears 6a and 6b, and a belt 7. The metal member 3 has a columnar or cylindrical shape and is provided so that a part of the outer circumferential surface of the metal member 3 can be brought into contact with the treatment object 2 directly or indirectly.
3 is brought into contact with the treatment object 2 having tensile residual stress, localized cooling of the treatment object 2 is started, and the contact portion of the outer circumferential surface of the metal member 3 is changed by rotating the metal member 3 using a rotating structure 4. Then, the outer circumferential surface of the metal member 3 is separated from the treatment object 2 to end the localized cooling and return the treatment object 2 to room temperature. By such a series of operations, the tensile residual stress of the treatment object 2 can be removed or reduced.
第２実施形態
図５は第２実施形態の残留応力軽減装置２０の概略断面図である。第２実施形態の残留応力軽減装置２０は、複数の金属部材３ａ～３ｃを含む。図５には、冷却構造１２を示していないが、冷却構造１２として液化ガス容器９を備える。
接触構造１７は、複数の金属部材３ａ～３ｃを吊り下げ移動させるように設けられたレール１１と、吊り下げられた複数の金属部材３ａ～３ｃを落とし、処理対象物２の表面に接触させるように設けられた落とし構造１０ａ～１０ｃとを有する。落とし構造１０ａ～１０ｃは、金属部材３ａ～３ｃの重力を利用して金属部材３ａ～３ｃを落下させる構造である。落とし構造１０ａ～１０ｃは、自動で金属部材３ａ～３ｃを落とす構造であってもよく、手動で金属部材３ａ～３ｃを落とす構造であってもよい。
Second embodiment Fig. 5 is a schematic cross-sectional view of a residual stress relief device 20 of a second embodiment. The residual stress relief device 20 of the second embodiment includes a plurality of metal members 3a to 3c. Although the cooling structure 12 is not shown in Fig. 5, a liquefied gas container 9 is provided as the cooling structure 12.
The contact structure 17 has rails 11 provided to suspend and move the multiple metal members 3a to 3c, and drop structures 10a to 10c provided to drop the suspended multiple metal members 3a to 3c and bring them into contact with the surface of the processing target 2. The drop structures 10a to 10c are structures that use the gravity of the metal members 3a to 3c to drop the metal members 3a to 3c. The drop structures 10a to 10c may be structures that automatically drop the metal members 3a to 3c, or may be structures that manually drop the metal members 3a to 3c.
まず、液化ガス容器９の液化ガス中に複数の金属部材３ａ～３ｃを浸漬し、複数の金属部材３ａ～３ｃの全体が－１００℃以下になるまで十分に冷却する。引張残留応力を有する処理対象物２の上に配置したレール１１に冷却した複数の金属部材３ａ～３ｃを取り付け、処理対象物２の冷却対象領域の直上に配置した金属部材３ａを落とし冷却対象領域と接触させる。このことにより、処理対象物２の熱エネルギーを金属部材３ａへと移動させることができる。所定の時間（例えば１秒間）が経過した後、金属部材３ａを引き上げ、レール１１を用いて金属部材３ｂが冷却対象領域の直上にくるように金属部材３ａ～３ｃを移動させる。そして、金属部材３ｂを落とし冷却対象領域と接触させ、処理対象物２の熱エネルギーを金属部材３ｂへと移動させる。所定の時間（例えば１秒間）が経過した後、金属部材３ｂを引き上げ、レール１１を用いて金属部材３ｃが冷却対象領域の直上にくるように金属部材３ａ～３ｃを移動させる。そして、金属部材３ｃを落とし冷却対象領域と接触させ、処理対象物２の熱エネルギーを金属部材３ｃへと移動させる。このように、金属部材３ａ～３ｃを変えながら処理対象物２の冷却対象領域を冷却することにより、冷却対象領域の温度を、処理対象物２に引張りの塑性ひずみが生じる温度よりも低い温度まで急速に低下させることができる。また、金属部材３ａ～３ｃの数は、冷却対象領域の冷却温度や金属部材３ａ～３ｃの大きさなどに応じて適宜変更することができる。
その後、金属部材３ｃを処理対象物２から離すことにより局部冷却を終了し、処理対象物２を常温に戻す。このような一連の操作により、処理対象物２の引張残留応力を除去又は軽減することができる。
First, the plurality of metal members 3a to 3c are immersed in the liquefied gas in the liquefied gas container 9, and the plurality of metal members 3a to 3c are sufficiently cooled until the entirety of the plurality of metal members 3a to 3c is at or below −100° C. The cooled plurality of metal members 3a to 3c are attached to the rails 11 arranged on the processing object 2 having tensile residual stress, and the metal member 3a arranged directly above the area to be cooled of the processing object 2 is dropped to contact the area to be cooled. This allows the thermal energy of the processing object 2 to be transferred to the metal member 3a. After a predetermined time (for example, 1 second) has elapsed, the metal member 3a is lifted, and the metal members 3a to 3c are moved using the rails 11 so that the metal member 3b is directly above the area to be cooled. Then, the metal member 3b is dropped to contact the area to be cooled, and the thermal energy of the processing object 2 is transferred to the metal member 3b. After a predetermined time (for example, 1 second) has elapsed, the metal member 3b is lifted, and the metal members 3a to 3c are moved using the rails 11 so that the metal member 3c is directly above the area to be cooled. Then, the metal member 3c is dropped and brought into contact with the cooling target area, and the thermal energy of the treatment object 2 is transferred to the metal member 3c. In this way, by cooling the cooling target area of the treatment object 2 while changing the metal members 3a to 3c, it is possible to rapidly lower the temperature of the cooling target area to a temperature lower than the temperature at which tensile plastic strain occurs in the treatment object 2. In addition, the number of metal members 3a to 3c can be appropriately changed depending on the cooling temperature of the cooling target area and the size of the metal members 3a to 3c.
Thereafter, the local cooling is terminated by separating the metal member 3c from the processing object 2, and the processing object 2 is returned to room temperature. Through such a series of operations, the tensile residual stress in the processing object 2 can be removed or reduced.
その他の構成は第１実施形態と同様である。また、第１実施形態についての記載は矛盾がない限り第２実施形態についても当てはまる。 The rest of the configuration is the same as in the first embodiment. Furthermore, the description of the first embodiment also applies to the second embodiment unless there is a contradiction.
第３実施形態
図６は第３実施形態の残留応力軽減装置２０の概略断面図である。第３実施形態の残留応力軽減装置２０は、複数の粒状の金属部材３を含む。図６には、冷却構造１２を示していないが、冷却構造１２として液化ガス容器９を備える。
複数の粒状の金属部材３の粒径は、例えば、１０μｍ以上１０ｃｍ以下とすることができる。また、粒状の金属部材３の形状は球状であってもよい。
Third embodiment Fig. 6 is a schematic cross-sectional view of a residual stress relief device 20 of a third embodiment. The residual stress relief device 20 of the third embodiment includes a plurality of granular metal members 3. Although the cooling structure 12 is not shown in Fig. 6, a liquefied gas container 9 is provided as the cooling structure 12.
The particle size of the plurality of granular metal members 3 may be, for example, 10 μm to 10 cm. The shape of the granular metal members 3 may be spherical.
接触構造１７は、複数の粒状の金属部材３を輸送するように設けられたダクト１６を有する。ダクト１６は、入口と、出口と、管壁に設けられた開口とを有し、処理対象物２の冷却対象領域がこの開口を塞ぐようにダクト１６と処理対象物２とが接続される。また、ダクト１６は、ダクト１６の内部を流れてきた粒状の金属部材３がこの開口において冷却対象領域に接触し、その後、ダクト１６の下流に流れていくように設けられる。ダクト１６内の金属部材３の輸送は、重力を利用してもよく、気体の流れを利用してもよい。例えば、ダクト１６の出口から金属部材３を気体と共に吸引してもよい。ダクト１６の材料は例えばプラスチックとすることができる。 The contact structure 17 has a duct 16 that is provided to transport a plurality of granular metal members 3. The duct 16 has an inlet, an outlet, and an opening provided in the pipe wall, and the duct 16 is connected to the object 2 to be treated so that the area to be cooled of the object 2 to be treated blocks this opening. The duct 16 is also provided so that the granular metal members 3 that have flowed inside the duct 16 come into contact with the area to be cooled at this opening, and then flow downstream of the duct 16. The transport of the metal members 3 in the duct 16 may be performed by using gravity or a gas flow. For example, the metal members 3 may be sucked together with the gas from the outlet of the duct 16. The material of the duct 16 may be, for example, plastic.
まず、液化ガス容器９の液化ガス中に複数の粒状の金属部材３を浸漬し、複数の粒状の金属部材３が－１００℃以下になるまで十分に冷却する。引張残留応力を有する処理対象物２の冷却対象領域でダクト１６の開口を塞ぐようにダクト１６を処理対象物２に接続する。そして、十分に冷却した複数の粒状の金属部材３を入口からダクト１６に流し込み、ダクト１６内に複数の粒状の金属部材３を流す。管壁の開口に達した粒状の金属部材３は処理対象物２の冷却対象領域に接触し、処理対象物２の熱エネルギーが粒状の金属部材３へと移動する。熱エネルギーを受け取った金属部材３はダクト１６の出口へと流れ、回収部（例えば、回収容器）により回収される。多数の粒状の金属部材３を連続的にダクト１６に流すことにより、処理対象物２の冷却対象領域の熱エネルギーを連続して金属部材３へと移動させることができ、冷却対象領域の温度を、処理対象物２に引張りの塑性ひずみが生じる温度よりも低い温度まで急速に低下させることができる。
その後、ダクト１６の入口への金属部材３の供給を止めることにより、局部冷却を終了し、処理対象物２を常温に戻す。このような一連の操作により、処理対象物２の引張残留応力を除去又は軽減することができる。
First, a plurality of granular metal members 3 are immersed in the liquefied gas in the liquefied gas container 9, and the plurality of granular metal members 3 are sufficiently cooled until the temperature becomes −100° C. or lower. The duct 16 is connected to the processing object 2 so that the opening of the duct 16 is blocked in the area to be cooled of the processing object 2 having tensile residual stress. Then, the plurality of granular metal members 3 that have been sufficiently cooled are poured into the duct 16 from the inlet, and the plurality of granular metal members 3 are caused to flow in the duct 16. The granular metal members 3 that reach the opening of the pipe wall come into contact with the area to be cooled of the processing object 2, and the thermal energy of the processing object 2 is transferred to the granular metal members 3. The metal members 3 that have received the thermal energy flow to the outlet of the duct 16, and are collected by a collection unit (e.g., a collection container). By continuously flowing a large number of granular metal components 3 through duct 16, the thermal energy of the area to be cooled of the object to be treated 2 can be continuously transferred to the metal components 3, and the temperature of the area to be cooled can be rapidly reduced to a temperature lower than the temperature at which tensile plastic strain occurs in the object to be treated 2.
Thereafter, the supply of the metal member 3 to the inlet of the duct 16 is stopped to terminate the local cooling and return the treatment object 2 to room temperature. Through such a series of operations, the tensile residual stress in the treatment object 2 can be removed or reduced.
その他の構成は第１又は第２実施形態と同様である。また、第１又は第２実施形態についての記載は矛盾がない限り第３実施形態についても当てはまる。 The rest of the configuration is the same as in the first or second embodiment. Furthermore, any description of the first or second embodiment also applies to the third embodiment unless there is a contradiction.
ＦＥＭ熱弾塑性解析
図７は、熱弾塑性解析の解析モデルであり、図８は図７の破線Ｂ－Ｂにおける解析モデルの概略断面図である。処理対象物２の材料を溶接構造用延鋼材ＳＭ４９０とし、処理対象物２の寸法を幅１５０ｍｍ、長さ３００ｍｍ、厚さ１５ｍｍとした。また、電流４００Ａ、電圧３０Ｖ、溶接速度２０mm/secのアーク溶接を溶接部１３に施す熱弾塑性解析を実施し、この解析の結果生じる残留応力を有する処理対象物２を解析モデルとして用いた。溶接部１３は、処理対象物２の中央部の領域であり、処理対象物２の長さ方向に伸びる。
金属部材３の材料を純銅とし、金属部材３の寸法を幅４０ｍｍ、長さ４０ｍｍ、厚さ８０ｍｍとした。
FEM Thermoelastic-Plastic Analysis Figure 7 shows an analytical model for thermoelastic-plastic analysis, and Figure 8 shows a schematic cross-sectional view of the analytical model taken along the dashed line B-B in Figure 7. The material of the object 2 to be treated was SM490, a rolled steel material for welded structures, and the dimensions of the object 2 to be treated were 150 mm wide, 300 mm long, and 15 mm thick. A thermoelastic-plastic analysis was also carried out in which arc welding was performed on the welded portion 13 with a current of 400 A, a voltage of 30 V, and a welding speed of 20 mm/sec, and the object 2 to be treated having residual stress resulting from this analysis was used as the analytical model. The welded portion 13 is a central region of the object 2 to be treated, and extends in the longitudinal direction of the object 2 to be treated.
The material of the metal member 3 was pure copper, and the dimensions of the metal member 3 were 40 mm in width, 40 mm in length, and 80 mm in thickness.
２０℃の処理対象物２の上面の中央部（溶接部１３）に、－１９６℃の金属部材３（液体窒素により冷却）の下面（４０ｍｍ×４０ｍｍ）を１秒間接触させ処理対象物２を冷却しその後処理対象物２を２０℃に戻す解析を実施した（繰り返し回数：１回）。この解析では、処理対象物２の熱エネルギーが金属部材３へと移動し金属部材３の温度は上昇するため、処理対象物２の冷却効率は徐々に低下する。
また、２０℃の処理対象物２の上面の中央部（溶接部１３）に、－１９６℃の金属部材３の下面（４０ｍｍ×４０ｍｍ）を接触させ、金属部材３を連続的に－１９６℃の新たな金属部材３に取り換えながら（１秒間に∞回取り換える）処理対象物２を１秒間冷却しその後処理対象物２を２０℃に戻す解析を実施した（繰り返し回数：∞回）。この解析では、金属部材３の温度は常に－１９６℃であり、処理対象物２を急速により低い温度に冷却することができる。
An analysis was performed in which the underside (40 mm x 40 mm) of a metal member 3 (cooled by liquid nitrogen) at -196°C was brought into contact with the center (welded portion 13) of the upper surface of a processing object 2 at 20°C for one second to cool the processing object 2, and then the processing object 2 was returned to 20°C (repeated once). In this analysis, the thermal energy of the processing object 2 was transferred to the metal member 3, causing the temperature of the metal member 3 to rise, and therefore the cooling efficiency of the processing object 2 gradually decreased.
In addition, an analysis was performed in which the bottom surface (40 mm x 40 mm) of a metal member 3 at -196°C was brought into contact with the center (welded portion 13) of the top surface of a treatment object 2 at 20°C, and the treatment object 2 was cooled for 1 second while the metal member 3 was continuously replaced with a new metal member 3 at -196°C (replaced ∞ times per second), and then the treatment object 2 was returned to 20°C (repeated number of times: ∞). In this analysis, the temperature of the metal member 3 was always -196°C, and the treatment object 2 could be rapidly cooled to a lower temperature.
図９～図１１は解析結果を示すグラフである。図９～図１１の縦軸は、図８に破線Ｃ－Ｃで示したＺ方向における処理対象物２の位置座標である。この位置座標では、処理対象物２と金属部材３との接触面が０ｍｍであり、処理対象物２の下面が－１５ｍｍである。図９は温度分布であり、図１０は残留塑性ひずみ（溶接を施す解析を実施する前の処理対象物２からのひずみ）の分布であり、図１１は残留応力分布である。なお、図１１において、プラスの残留応力が引張残留応力であり、マイナスの残留応力が圧縮残留応力である。
図９の温度分布のように、繰り返し回数を１回とした解析では、処理対象物２の接触面を１秒間で約－７０℃まで冷却することができた。繰り返し回数を∞回とした解析では処理対象物２の接触面を－１９６℃まで冷却することができた。
9 to 11 are graphs showing the analysis results. The vertical axis in Fig. 9 to 11 is the position coordinate of the processing object 2 in the Z direction shown by the dashed line CC in Fig. 8. In this position coordinate, the contact surface between the processing object 2 and the metal member 3 is 0 mm, and the bottom surface of the processing object 2 is -15 mm. Fig. 9 shows the temperature distribution, Fig. 10 shows the distribution of residual plastic strain (strain from the processing object 2 before performing the analysis of welding), and Fig. 11 shows the residual stress distribution. In Fig. 11, positive residual stress is tensile residual stress, and negative residual stress is compressive residual stress.
As shown in the temperature distribution in Figure 9, in an analysis in which the number of repetitions was 1, the contact surface of the treatment object 2 could be cooled to approximately -70°C in 1 second. In an analysis in which the number of repetitions was infinite, the contact surface of the treatment object 2 could be cooled to -196°C.
図１０の残留塑性ひずみの分布のように、冷却前の処理対象物２では溶接部１３において約－０．００２の残留塑性ひずみが生じていたが、繰り返し回数を１回とした解析では残留塑性ひずみが０に近づき、繰り返し回数を∞回とした解析では残留塑性ひずみがさらに０に近づいた。このように、金属部材３により処理対象物２を局部的に冷却することにより、溶接を施すことにより生じた塑性ひずみを小さくできることがわかった。 As shown in the distribution of residual plastic strain in Figure 10, the treatment object 2 had a residual plastic strain of approximately -0.002 at the welded part 13 before cooling, but in an analysis where the number of repetitions was 1, the residual plastic strain approached 0, and in an analysis where the number of repetitions was infinite, the residual plastic strain approached 0 even more. In this way, it was found that the plastic strain caused by welding can be reduced by locally cooling the treatment object 2 with the metal member 3.
図１１の残留応力分布のように、冷却前の処理対象物２では、溶接により表面から内部の広範囲に亘り引張り残留応力が発生していたが、繰り返し回数を１回として金属部材３により処理対象物２を局部的に冷却した解析では、接触面において圧縮残留応力とすることができ、処理対象物２の内部においても引張残留応力を小さくすることができた。また、繰り返し回数を∞回として金属部材３により処理対象物２を局部的に冷却した解析では、処理対象物２の内部の引張残留応力をさらに小さくすることができた。
このように金属部材３により処理対象物２を局部的に冷却することにより、溶接により生じた引張残留応力を軽減することができることがわかった。
As shown in the residual stress distribution in Fig. 11, in the treatment object 2 before cooling, tensile residual stress was generated over a wide range from the surface to the inside due to welding, but in an analysis in which the treatment object 2 was locally cooled by the metal member 3 with the number of repetitions being one, it was possible to make the residual stress compressive at the contact surface, and it was also possible to reduce the tensile residual stress inside the treatment object 2. Moreover, in an analysis in which the treatment object 2 was locally cooled by the metal member 3 with the number of repetitions being infinite, it was possible to further reduce the tensile residual stress inside the treatment object 2.
It has been found that by locally cooling the object 2 with the metal member 3 in this manner, the tensile residual stress caused by welding can be reduced.
残留応力低減装置作製実験
図３に示したような残留応力低減装置を作製した。図１２は、作製した残留応力低減装置の写真であり、図１３は残留応力低減装置の内部構造を示す分解立体図である。金属部材３の形状は円柱状であり、金属部材３の材料は純銅である。また、液化ガスは液体窒素である。作製した残留応力軽減装置により、液体窒素により冷却した円柱状の金属部材３をモーター５を用いて回転させることにより金属部材３の外周面のうち処理対象物２と接触する部分を変えながら処理対象物２の表面の一部を局部的に急速に冷却することができた。
Experiment to fabricate a residual stress reduction device A residual stress reduction device as shown in Figure 3 was fabricated. Figure 12 is a photograph of the fabricated residual stress reduction device, and Figure 13 is an exploded view showing the internal structure of the residual stress reduction device. The metal member 3 has a cylindrical shape, and is made of pure copper. The liquefied gas is liquid nitrogen. With the fabricated residual stress reduction device, the cylindrical metal member 3 cooled by liquid nitrogen is rotated by a motor 5, and a part of the surface of the treatment object 2 can be locally and rapidly cooled while changing the part of the outer circumferential surface of the metal member 3 that comes into contact with the treatment object 2.
残留応力低減試験
図１４（ａ）に示したような解析モデルを用いたＦＥＭ熱弾塑性解析を行った。処理対象物２の材料を溶接構造用延鋼材ＳＭ４９０とし、処理対象物２の寸法を幅２００ｍｍ、長さ２００ｍｍ、厚さ１０ｍｍとした。円柱状の金属部材３の材料を純銅とし、金属部材３の直径を３０ｍｍとし高さを２０ｍｍとした。２０℃の処理対象物２の上面の中央部に、－１９６℃の金属部材３（液体窒素により冷却）の下面（直径３０ｍｍ）を８秒間接触させ処理対象物２を局部冷却した際の処理対象物２の温度及びひずみを解析した。温度計測点及びひずみ計測点は図１４（ａ）に示している。
Residual stress reduction test: FEM thermal elastic-plastic analysis was performed using an analysis model as shown in FIG. 14(a). The material of the processing object 2 was SM490, a rolled steel material for welded structures, and the dimensions of the processing object 2 were 200 mm wide, 200 mm long, and 10 mm thick. The material of the cylindrical metal member 3 was pure copper, and the diameter and height of the metal member 3 were 30 mm and 20 mm. The temperature and strain of the processing object 2 were analyzed when the bottom surface (diameter 30 mm) of the metal member 3 (cooled by liquid nitrogen) at −196° C. was brought into contact with the center of the top surface of the processing object 2 at 20° C. for 8 seconds to locally cool the processing object 2. The temperature measurement points and strain measurement points are shown in FIG. 14(a).
常温の溶接構造用延鋼材ＳＭ４９０（幅２００ｍｍ、長さ２００ｍｍ、厚さ１０ｍｍ）（処理対象物２）の上面の中央部に、液体窒素により十分に冷却した円柱状の純銅（直径３０ｍｍ、高さ２０ｍｍ）（金属部材３）の下面を接触させ処理対象物２を局部冷却した際の処理対象物２の温度及びひずみを測定した。温度計測点及びひずみ計測点は図１４（ａ）と同様の位置に設けた。図１４（ｂ）は、測定装置の写真である。 The temperature and strain of the treatment object 2 were measured when the underside of a cylindrical pure copper (diameter 30 mm, height 20 mm) (metal member 3) sufficiently cooled with liquid nitrogen was brought into contact with the center of the top surface of SM490 (width 200 mm, length 200 mm, thickness 10 mm) (treatment object 2) for welding construction at room temperature, and the treatment object 2 was locally cooled. The temperature and strain measurement points were set at the same positions as in Figure 14(a). Figure 14(b) is a photograph of the measurement device.
常温の溶接構造用延鋼材ＳＭ４９０（幅２００ｍｍ、長さ２００ｍｍ、厚さ１０ｍｍ）（処理対象物２）の上面の中央部に、液体窒素を入れるための円筒１５（内径３０ｍｍ）を設置し、円筒内に注ぎ込んだ液体窒素により処理対象物２を局部冷却した際の処理対象物２の温度を測定した。処理対象物２と液体窒素の接触面から液体窒素の液面までの深さは２０ｍｍに保った。温度計測点は図１４（ａ）と同様の位置に設けた。図１４（ｃ）は、測定装置の写真である。 A cylinder 15 (inner diameter 30 mm) for holding liquid nitrogen was placed in the center of the top surface of SM490 (width 200 mm, length 200 mm, thickness 10 mm) (processing object 2) for welded structures at room temperature, and the temperature of the processing object 2 was measured when the processing object 2 was locally cooled by the liquid nitrogen poured into the cylinder. The depth from the contact surface between the processing object 2 and the liquid nitrogen to the liquid nitrogen surface was kept at 20 mm. The temperature measurement points were set up in the same positions as in Figure 14 (a). Figure 14 (c) is a photograph of the measurement device.
図１５、図１６に解析結果及び測定結果を示す。図１５は、処理対象物２の温度変化を示すグラフである。図１５及び図１６では、金属部材３又は液体窒素を処理対象物２に接触させた時点を０秒としている。
図１５のグラフのように、液体窒素を処理対象物２に１秒間接触させたとき測定温度はほとんど変化しなかったのに対し、純銅を処理対象物２に接触させたとき（実験）及びＦＥＭ解析では、純銅を処理対象物２に接触させると処理対象物２の温度は同じように低下していき、接触させてから１秒後に約－８℃に達した。
このように金属部材３を処理対象物２に接触させることにより、処理対象物２を局部的に急冷できることがわかった。また、液体窒素では処理対象物２を急冷することはできなかった。これは、液体窒素の熱容量が小さいため及び液体窒素と処理対象物２との間に窒素ガスが発生するためと考えられる。
The analysis results and the measurement results are shown in Figures 15 and 16. Figure 15 is a graph showing the temperature change of the treatment object 2. In Figures 15 and 16, the time when the metal member 3 or liquid nitrogen is brought into contact with the treatment object 2 is set as 0 seconds.
As shown in the graph of Figure 15, when liquid nitrogen was brought into contact with the treatment object 2 for 1 second, the measured temperature hardly changed, whereas when pure copper was brought into contact with the treatment object 2 (experiment) and in the FEM analysis, when pure copper was brought into contact with the treatment object 2, the temperature of the treatment object 2 similarly decreased, reaching approximately -8°C 1 second after contact.
It was found that the object 2 can be locally quenched by contacting the metal member 3 with the object 2. Furthermore, the object 2 could not be quenched with liquid nitrogen. This is believed to be because the heat capacity of liquid nitrogen is small and because nitrogen gas is generated between the liquid nitrogen and the object 2.
図１６は、Ｘ軸方向のひずみの変化を示すグラフである。図１６のグラフのように、冷却した純銅を処理対象物２に接触させることにより処理対象物２に生じるひずみ（実験で測定されたひずみ）は、ＦＥＭ解析と同じように変化することがわかった。 Figure 16 is a graph showing the change in strain in the X-axis direction. As shown in the graph in Figure 16, it was found that the strain (strain measured in the experiment) that occurs in the treatment object 2 when cooled pure copper is brought into contact with the treatment object 2 changes in the same way as in the FEM analysis.
２： 処理対象物 ３、３ａ～３ｃ：金属部材 ４：回転構造 ５：モーター ６ａ、６ｂ：歯車 ７：ベルト ８：液化ガス ９：液化ガス容器 １０ａ～１０ｃ：落とし構造 １１：レール １２：冷却構造 １３：溶接部 １５：液体窒素用円筒 １６：ダクト １７：接触構造 ２０：残留応力低減装置 2: Processing object 3, 3a-3c: Metal parts 4: Rotating structure 5: Motor 6a, 6b: Gears 7: Belt 8: Liquefied gas 9: Liquefied gas container 10a-10c: Drop structure 11: Rail 12: Cooling structure 13: Welded part 15: Liquid nitrogen cylinder 16: Duct 17: Contact structure 20: Residual stress reduction device
Claims (7)
前記処理対象物を常温に戻すステップとを含み、
前記冷却ステップは、前記少なくとも１つの金属部材の表面のうち前記処理対象物と接触する部分を変えながら前記処理対象物の表面の一部を局部冷却するステップであり、前記少なくとも１つの金属部材の表面の第１部分を直接的又は間接的に接触させた接触部分に、前記少なくとも１つの金属部材の表面の第１部分とは異なる第２部分を接触させるステップを含み、
前記冷却ステップにおいて冷却する前の前記処理対象物の温度は、常温であることを特徴とする残留応力低減方法。 A cooling step of directly or indirectly contacting a part of a surface of at least one metal member cooled to a temperature of −100° C. or lower with a part of a surface of the treatment object having tensile residual stress, thereby locally cooling the treatment object;
The object to be treated is returned to room temperature,
The cooling step is a step of locally cooling a part of the surface of the object to be treated while changing a part of the surface of the at least one metal member that is in contact with the object to be treated, and includes a step of contacting a second part of the surface of the at least one metal member, which is different from the first part, with a contact part that is in direct or indirect contact with a first part of the surface of the at least one metal member,
A residual stress reducing method , characterized in that the temperature of the treatment object before cooling in the cooling step is room temperature .
前記冷却ステップは、前記処理対象物の一部の温度を、前記処理対象物に引張りの塑性ひずみが生じる温度よりも低い温度にするステップである請求項１又は２に記載の残留応力低減方法。 The cooling time in the cooling step is 0.1 seconds or more and 1 minute or less,
3. The residual stress reducing method according to claim 1, wherein the cooling step is a step of lowering a temperature of a part of the object to be treated to a temperature lower than a temperature at which tensile plastic strain occurs in the object to be treated.
前記接触構造は、前記少なくとも１つの金属部材の表面の第１部分を直接的又は間接的に接触させた接触部分に、前記少なくとも１つの金属部材の表面の第１部分とは異なる第２部分を接触させるように設けられた残留応力低減装置。 The cooling structure is provided to cool the at least one metal member by a liquefied gas at -100°C or less, and the contact structure is provided to locally cool the treatment object at room temperature by directly or indirectly contacting the at least one metal member with a part of the surface of the treatment object while changing a part of the surface of the at least one metal member that contacts the treatment object ,
The contact structure is a residual stress reduction device configured to contact a second portion, different from the first portion of the surface of the at least one metal member, with a contact portion that directly or indirectly contacts a first portion of the surface of the at least one metal member .
前記接触構造は、前記金属部材を回転させるように設けられた構造であり、
前記金属部材は、処理対象物の表面の一部に前記金属部材の外周面の一部が直接的に又は間接的に接触するように設けられた請求項４に記載の残留応力低減装置。 The metal member has a columnar or cylindrical shape,
the contact structure is a structure provided to rotate the metal member,
5. The residual stress reducing device according to claim 4, wherein the metal member is provided so that a part of an outer circumferential surface of the metal member directly or indirectly contacts a part of a surface of the processing object.
前記接触構造は、第１及び第２金属部材を吊り下げ移動させるように設けられたレールと、吊り下げられた第１又は第２金属部材を落とし前記処理対象物の表面に接触させるように設けられた落とし構造とを有する請求項４に記載の残留応力低減装置。 the at least one metal member includes a first metal member and a second metal member;
5. The residual stress reduction device according to claim 4, wherein the contact structure comprises a rail arranged to suspend and move the first and second metal members, and a drop structure arranged to drop the suspended first or second metal member into contact with the surface of the object to be treated.
前記接触構造は、複数の粒状の金属部材を連続的に前記処理対象物に接触させるように設けられた請求項４に記載の残留応力低減装置。 the at least one metal member includes a plurality of granular metal members;
5. The residual stress reducing apparatus according to claim 4, wherein the contact structure is provided so as to continuously bring a plurality of granular metal members into contact with the object to be treated.
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