JP2017187408A - Quality assurance method of steel material and fatigue characteristics estimation method - Google Patents
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本発明は、鋼材の品質保証方法および疲労特性推定方法に関する。 The present invention relates to a quality assurance method and a fatigue property estimation method for steel materials.
建築物、橋梁などの各種溶接鋼構造物、船舶、自動車などの輸送用機械、産業用機械、建築用機械などの各種機械における多くの部位に鋼材（以下、「機械・構造用鋼材」と呼ぶ。）が使用されている。機械・構造用鋼材には、通常、繰返し荷重が負荷されるため、構造物または機械の強度健全性を確保する上で、疲労寿命のような疲労特性に対する注意が必要不可欠である。母材部と比較して疲労強度が圧倒的に弱い溶接部の疲労特性は、特に重要である。 Steel materials (hereinafter referred to as “mechanical / structural steel materials”) in various parts of various machines such as various welded steel structures such as buildings, bridges, transport machinery such as ships and automobiles, industrial machinery, and construction machinery .) Is used. Since mechanical and structural steel materials are usually subjected to repeated loads, attention to fatigue properties such as fatigue life is indispensable for ensuring the strength and soundness of the structure or machine. The fatigue characteristics of the welded portion, where the fatigue strength is much weaker than that of the base metal portion, are particularly important.
従来、機械・構造用鋼材の疲労破壊の防止に関しては、疲労破壊を「疲労き裂の発生」および「疲労き裂の進展」という２つの損傷過程に分けて、種々の検討がなされてきた。その検討に際しては、構造物または機械の幾何学的寸法、使用環境、負荷形態、荷重経路の数などに従って、疲労き裂の発生過程に重点を置く場合と、疲労き裂の進展過程に重点を置く場合とがある。 Conventionally, various studies have been made on the prevention of fatigue fracture of mechanical and structural steel materials by dividing the fatigue fracture into two damage processes, “generation of fatigue crack” and “progress of fatigue crack”. In the examination, the emphasis is placed on the fatigue crack initiation process and the fatigue crack propagation process according to the geometrical dimensions of the structure or machine, the usage environment, the load configuration, the number of load paths, etc. There is a case to put.
例えば、寸法の小さな部材で、その部材の破断によって機械・構造物全体の致命的な損害に繋がり、荷重経路が一つしかない場合には、疲労き裂の発生を防止することが重要になる。一方、寸法の大きな部材で、その部材の破断によっては機械・構造物全体の直接かつ致命的な破壊には至らず、荷重経路が複数存在、つまり、その部材単体が破断しても他の部材が代わって荷重を受け持つ場合は、疲労き裂の発生はある程度までは許容でき、その後の疲労き裂の進展を防止することが重要となる。 For example, when a member with small dimensions leads to fatal damage to the entire machine / structure by breaking the member and there is only one load path, it is important to prevent the occurrence of fatigue cracks. . On the other hand, it is a large-sized member, and the fracture of the member does not cause a direct and fatal destruction of the entire machine / structure, and there are multiple load paths. However, if the load is handled instead, the occurrence of fatigue cracks can be tolerated to some extent, and it is important to prevent the subsequent growth of fatigue cracks.
このように、疲労き裂の発生および疲労き裂の進展は、疲労破壊を知る上で共に重要な特性であるが、通常、疲労き裂の発生をもって疲労破断寿命と見なされ、負荷応力と疲労破断寿命との関係から疲労強度が評価されており、航空機設計などの特殊な場合を除き、疲労き裂進展についてはほとんど考慮されていない。 As described above, the occurrence of fatigue cracks and the development of fatigue cracks are both important characteristics for knowing fatigue fracture. Normally, the occurrence of fatigue cracks is regarded as the fatigue fracture life, and the stress and fatigue Fatigue strength is evaluated from the relationship with fracture life, and fatigue crack growth is hardly considered except in special cases such as aircraft design.
前述のように、疲労強度に関しては、母材部と溶接部とを比較した場合、圧倒的に溶接部が弱い。そのため、溶接鋼構造物の疲労強度改善のためには、継手部の疲労特性を向上させることが重要となる。例えば、溶接部の疲労設計を変え得る、継手疲労特性に優れた鋼材を実用化するにあっては、溶接継手の疲労特性評価が数多く必要となる。また、継手疲労特性に優れた鋼材を商品化するに当たり、鋼材の品質を直接保証する上でも溶接継手の疲労特性評価を行なう必要がある。 As described above, regarding the fatigue strength, when the base metal part and the welded part are compared, the welded part is overwhelmingly weak. Therefore, in order to improve the fatigue strength of the welded steel structure, it is important to improve the fatigue characteristics of the joint. For example, in order to put into practical use a steel material with excellent joint fatigue characteristics that can change the fatigue design of welded parts, many fatigue characteristics evaluations of welded joints are required. In addition, when commercializing steel materials with excellent joint fatigue characteristics, it is necessary to evaluate the fatigue characteristics of welded joints in order to directly guarantee the quality of the steel materials.
ところで、ある特定の鋼材に対し、継手疲労特性を評価する場合、以下の手順で進められる。
（１）鋼材に対し継手形式に応じて溶接施工を行い、溶接継手（大板）を準備する。
（２）この溶接継手（大板）から、機械加工などの方法により所望の形状・寸法の試験片を採取する。
（３）必要に応じて、試験片の角変形量、または溶接余盛り止端形状の測定を行った後、曲げ矯正などで試験片の掴み部分を同一平面として疲労試験機にチャッキングできるようにして、疲労試験を開始する。
By the way, when evaluating a joint fatigue characteristic with respect to a specific steel material, it is advanced in the following procedures.
(1) Welding is performed on steel according to the joint type, and a welded joint (large plate) is prepared.
(2) From this welded joint (large plate), a test piece having a desired shape and size is collected by a method such as machining.
(3) After measuring the amount of angular deformation of the test piece or the shape of the toe of the weld, if necessary, the gripping part of the test piece can be chucked to the fatigue testing machine by bending correction etc. The fatigue test is started.
ここで、疲労試験機は、油圧アクチュエーターなどを備えた載荷部分と、荷重・変位などを検出するセンサー部分と、アクチュエーターに取付けられたサーボバルブに適切な電気信号を送るとともに荷重検出器からの信号を受け取り、荷重の実績値が荷重設定値（荷重上限値、荷重下限値）に一致するよう閉ループで制御している制御部分とからなる。必要とされる荷重の制御精度を確保するためには、優れた品質の負荷部分、センサー部分、制御部分が必要で、疲労試験機は一般に高価な装置となる。 Here, the fatigue testing machine sends an appropriate electrical signal to the loading part equipped with a hydraulic actuator, a sensor part that detects load / displacement, etc., and a servo valve attached to the actuator, and a signal from the load detector. And a control part that is controlled in a closed loop so that the actual load value matches the load setting value (load upper limit value, load lower limit value). In order to ensure the control accuracy of the required load, an excellent quality load part, sensor part, and control part are required, and the fatigue testing machine is generally an expensive device.
さらに、評価対象とする疲労破断寿命の領域にも大きく依存するものの、疲労試験結果を疲労設計に活かすためには、通常、疲労試験には膨大な時間を要することが多い。疲労試験に膨大な時間を要することは、開発計画の初期段階から明らかではあるが、疲労試験を実施するしか継手疲労特性を把握できないと考えられているため、溶接施工法が工業的に活用され始めて以来、このような膨大な時間を要する評価が続けられてきた。 Furthermore, although it depends greatly on the fatigue fracture life region to be evaluated, in order to utilize the fatigue test result for fatigue design, the fatigue test usually requires a lot of time. It is clear from the initial stage of the development plan that the fatigue test requires an enormous amount of time, but since it is thought that the fatigue characteristics of the joint can only be grasped by performing the fatigue test, the welding method is used industrially. Since beginning, such a time-consuming evaluation has been continued.
上記の問題を解決するため、特許文献１では、溶接熱影響部の硬度を測定するという簡便な方法により、溶接継手の疲労特性を推定する方法が提案されている。
In order to solve the above problem,
母材の平滑材では、母材の引張強度すなわち硬度が上昇すると、それに対応して疲労強度も同時に向上する。この疲労強度における引張強度依存性と同じ傾向は、実継手の溶接熱影響部（ＨＡＺ）が溶接時に受ける熱履歴を再現した熱処理を施した材料（以下の説明において、「再現ＨＡＺ材」ともいう。）においても認められる。すなわち、再現ＨＡＺ材においても、硬度が高いほど疲労特性は良好である。 In the smooth material of the base material, when the tensile strength, that is, the hardness of the base material is increased, the fatigue strength is also improved at the same time. The same tendency as the tensile strength dependency in the fatigue strength is a material subjected to heat treatment that reproduces the thermal history that the weld heat affected zone (HAZ) of the actual joint undergoes during welding (in the following description, it is also referred to as “reproduced HAZ material”). )). That is, even in the reproduced HAZ material, the higher the hardness, the better the fatigue characteristics.
しかしながら、特許文献１に開示されているように、実継手において疲労き裂はＨＡＺから発生するものの、溶接継手の疲労特性は、再現ＨＡＺ材の疲労特性とは全く異なる。つまり、再現ＨＡＺ材では硬度が高いほど疲労特性が良好であったが、実際の溶接継手では逆に、それに対応する再現ＨＡＺ材の硬度が低い方が、溶接継手の疲労特性が良好となる。
However, as disclosed in
特許文献１ではこのような関係性に着目し、再現ＨＡＺ材の硬度に基づいて継手疲労強度の推定を行っている。しかしながら、より高精度な継手疲労強度の推定を行うにあたっては、改善の余地が残されている。
In
本発明は、簡便かつ迅速な方法により、鋼材の溶接継手における疲労に関する品質を保証する方法および疲労特性を推定する方法を提供することを目的とする。 An object of the present invention is to provide a method for guaranteeing fatigue-related quality in a welded joint of steel and a method for estimating fatigue characteristics by a simple and rapid method.
本発明は、上記の課題を解決するためになされたものであり、下記の鋼材の品質保証方法および疲労特性推定方法を要旨とする。 The present invention has been made in order to solve the above-described problems, and provides the following steel material quality assurance method and fatigue property estimation method.
（１）試験材となる鋼材を用いて作製した溶接継手の疲労に関する品質が、任意の基準材を用いて作製した溶接継手より優れることを保証する方法であって、
前記基準材、前記試験材および複数の比較材に対して、溶接継手の溶接熱影響部が溶接時に受ける熱履歴を再現した熱処理を施した後、硬度および疲労特性を求める工程と、
前記再現熱処理後の前記基準材および前記比較材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する工程と、
前記再現熱処理後の前記試験材の硬度および疲労特性と、前記基準式との関係に基づき、前記試験材の品質を保証する工程と、を備える、
鋼材の品質保証方法。
(1) A method for ensuring that the quality related to fatigue of a welded joint produced using a steel material as a test material is superior to a welded joint produced using an arbitrary reference material,
Steps for obtaining hardness and fatigue characteristics after performing heat treatment that reproduces the thermal history that the weld heat-affected zone of the welded joint undergoes during welding with respect to the reference material, the test material, and the plurality of comparative materials;
Deriving a standard expression between hardness and fatigue characteristics from hardness and fatigue characteristics of at least a part of the reference material and the comparative material after the reproduction heat treatment;
A step of assuring the quality of the test material based on the relationship between the hardness and fatigue characteristics of the test material after the reproduction heat treatment and the reference formula,
Quality assurance method for steel.
（２）前記基準材および前記複数の比較材に対応する鋼材を用いて溶接継手を作製して継手疲労試験に供し、各溶接継手の疲労特性を求める工程と、
前記複数の比較材のうちから、溶接継手の疲労特性が前記基準材と同等以下である下等比較材を抽出する工程と、をさらに備え、
前記基準式を導出する工程における、前記比較材のうちの少なくとも一部が、前記下等比較材に対応する鋼材である、
上記（１）に記載の鋼材の品質保証方法。
(2) producing a welded joint using steel materials corresponding to the reference material and the plurality of comparative materials, and subjecting the joint to a joint fatigue test, and determining fatigue characteristics of each welded joint;
A step of extracting a lower comparative material having a fatigue characteristic of a welded joint equal to or lower than that of the reference material from the plurality of comparative materials, and further comprising:
In the step of deriving the reference formula, at least a part of the comparison material is a steel material corresponding to the lower comparison material,
The quality assurance method of the steel material as described in said (1).
（３）試験材となる鋼材を用いて作製した溶接継手の疲労特性を推定する方法であって、
基準材および複数の比較材を用いて溶接継手を作製して継手疲労試験に供し、各溶接継手の疲労特性を求める工程と、
前記基準材および前記比較材に対応する鋼材、ならびに、前記試験材に対して、溶接継手の溶接熱影響部が溶接時に受ける熱履歴を再現した熱処理を施した後、硬度および疲労特性を求める工程と、
前記再現熱処理後の前記基準材および前記比較材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する工程と、
前記再現熱処理後の前記比較材および前記試験材の硬度および疲労特性、ならびに、前記基準式から、各鋼材の溶接継手の疲労特性の指標となる優劣パラメータを求める工程と、
前記再現熱処理後の前記比較材の前記優劣パラメータと、前記比較材に対応する鋼材を用いて作製した前記溶接継手の前記疲労特性とから、疲労特性推定式を導出する工程と、
前記再現熱処理後の前記試験材の前記優劣パラメータと、前記疲労特性推定式とに基づき、前記試験材を用いて作製した溶接継手の疲労特性の推定値を算出する工程と、を備える、
鋼材の疲労特性推定方法。
(3) A method for estimating fatigue characteristics of a welded joint produced using a steel material as a test material,
Producing a welded joint using a reference material and a plurality of comparative materials and subjecting the joint to a joint fatigue test, and determining the fatigue characteristics of each welded joint;
A step of obtaining hardness and fatigue characteristics after subjecting the steel material corresponding to the reference material and the comparative material, and the test material to heat treatment that reproduces the thermal history that the weld heat affected zone of the welded joint undergoes during welding. When,
Deriving a standard expression between hardness and fatigue characteristics from hardness and fatigue characteristics of at least a part of the reference material and the comparative material after the reproduction heat treatment;
From the hardness and fatigue characteristics of the comparative material and the test material after the reproducible heat treatment, and a step of obtaining a superior / inferior parameter serving as an index of fatigue characteristics of the welded joint of each steel material from the reference formula,
Deriving a fatigue property estimation formula from the superiority and inferiority parameters of the comparative material after the reproduction heat treatment and the fatigue properties of the welded joint produced using a steel material corresponding to the comparative material;
Calculating an estimated value of fatigue characteristics of a welded joint produced using the test material based on the superiority / inferiority parameters of the test material after the reproduction heat treatment and the fatigue property estimation formula,
A method for estimating fatigue properties of steel.
（４）前記複数の比較材のうちから、溶接継手の疲労特性が前記基準材と同等以下である下等比較材を抽出する工程、をさらに備え、
前記基準式を導出する工程における、前記比較材のうちの少なくとも一部が、前記下等比較材に対応する鋼材である、
上記（３）に記載の鋼材の疲労特性推定方法。
(4) a step of extracting a lower comparative material having a fatigue characteristic of a welded joint equal to or lower than that of the reference material from the plurality of comparative materials,
In the step of deriving the reference formula, at least a part of the comparison material is a steel material corresponding to the lower comparison material,
The method for estimating fatigue characteristics of a steel material according to (3) above.
（５）前記疲労特性推定式を導出する工程において、疲労特性推定誤差をさらに求め、
前記試験材を用いて作製した溶接継手の前記疲労特性の推定値を算出する工程において、前記疲労特性推定誤差に基づき、前記疲労特性の上下限を同時に算出する、
上記（３）または（４）に記載の鋼材の疲労特性推定方法。
(5) In the step of deriving the fatigue characteristic estimation formula, a fatigue characteristic estimation error is further obtained,
In the step of calculating the estimated value of the fatigue characteristics of the welded joint produced using the test material, the upper and lower limits of the fatigue characteristics are simultaneously calculated based on the fatigue characteristic estimation error.
The method for estimating fatigue characteristics of a steel material according to the above (3) or (4).
本発明によれば、溶接熱影響部の硬度および疲労寿命を測定するという簡便な方法により、溶接継手の疲労特性を迅速に知ることができる。 According to the present invention, the fatigue characteristics of a welded joint can be quickly known by a simple method of measuring the hardness and fatigue life of the weld heat affected zone.
上述のように、溶接継手の疲労特性は、それに対応する再現ＨＡＺ材の硬度が低い方が良好となる。そして、本発明者らがさらに検討を重ねた結果、溶接継手の疲労特性は、再現ＨＡＺ材の硬度に加えて、再現ＨＡＺ材の疲労特性にも強く依存していることを見出した。 As described above, the fatigue characteristics of the welded joint are better when the hardness of the corresponding HAZ material is lower. As a result of further studies by the present inventors, it was found that the fatigue characteristics of the welded joint strongly depend on the fatigue characteristics of the reproduced HAZ material in addition to the hardness of the reproduced HAZ material.
図１は、各種鋼材を用いた再現ＨＡＺ材における、硬度と疲労寿命との関係の一例を示した図である。図１から分かるように再現ＨＡＺ材の硬度と疲労寿命との間には、正の相関関係が存在することが分かる。その一方で、その傾向から外れてくる鋼材（グラフにおいて左上の領域にプロットされる試料）が存在している。このように、同レベルの硬度であっても、より高い疲労寿命を示す鋼材は、実継手の疲労特性にも優れることが分かった。 FIG. 1 is a diagram showing an example of the relationship between hardness and fatigue life in a reproduced HAZ material using various steel materials. As can be seen from FIG. 1, there is a positive correlation between the hardness of the reproduced HAZ material and the fatigue life. On the other hand, there are steel materials (samples plotted in the upper left region in the graph) that deviate from the tendency. Thus, it was found that a steel material having a higher fatigue life even at the same level of hardness is excellent in the fatigue characteristics of an actual joint.
本発明は、上記の知見に基づいてなされたものである。以下、本発明について詳しく説明する。 The present invention has been made based on the above findings. The present invention will be described in detail below.
本発明に係る鋼材の品質保証方法は、試験材となる鋼材を用いて作製した溶接継手の疲労に関する品質が、任意の基準材を用いて作製した溶接継手より優れることを保証するものである。また、本発明に係る鋼材の疲労特性推定方法は、試験材となる鋼材を用いて作製した溶接継手の疲労特性を推定する方法である。すなわち、品質保証または疲労特性推定の対象となる試験材は、具体的には、機械・構造用鋼材のうち溶接に供される鋼材（溶接用鋼）である。 The steel material quality assurance method according to the present invention guarantees that the quality related to fatigue of a welded joint produced using a steel material as a test material is superior to a welded joint produced using an arbitrary reference material. Moreover, the fatigue property estimation method of the steel material which concerns on this invention is a method of estimating the fatigue property of the welded joint produced using the steel material used as a test material. That is, the test material that is the target of quality assurance or fatigue property estimation is specifically a steel material (welding steel) used for welding among mechanical and structural steel materials.
また、鋼材の化学組成についても特に制限は設けず、例えば、質量％で、Ｃ：０．０２〜０．２０％、Ｓｉ：０．１〜０．８％、Ｍｎ：０．５〜２．０％、Ｐ：０．０３％以下、Ｓ：０．０１％以下、Ｃｕ：０．５％以下、Ｎｉ：２．０％以下、Ｃｒ：０．７％以下、Ｍｏ：０．３％以下、Ｖ：０．３％以下、Ｔｉ：０．３％以下、Ｎｂ：０．３％以下、ｓｏｌ．Ａｌ：０．３％以下、残部Ｆｅおよび不回避的不純物からなる化学組成を有する鋼材を用いることができる。なお、以下に説明する例においては、上記の範囲の組成を有する鋼材を各種用いている。 Moreover, there is no restriction | limiting in particular also about the chemical composition of steel materials, For example, by mass%, C: 0.02-0.20%, Si: 0.1-0.8%, Mn: 0.5-2. 0%, P: 0.03% or less, S: 0.01% or less, Cu: 0.5% or less, Ni: 2.0% or less, Cr: 0.7% or less, Mo: 0.3% or less V: 0.3% or less, Ti: 0.3% or less, Nb: 0.3% or less, sol. A steel material having a chemical composition comprising Al: 0.3% or less, the balance Fe and unavoidable impurities can be used. In the example described below, various steel materials having compositions in the above range are used.
ここで、突合せ溶接部が疲労損傷する例は極めて少ない。これは、継手形状が影響していると考えられ、具体的には断面形状の変化が少なく、かつ変化が緩やかであるためと考えられる。それに比べ、十字継手またはガセット継手などの隅肉溶接継手が構造物全体の疲労強度を律則している場合が多い。そのため、本発明は、隅肉溶接継手の疲労特性を把握するのに特に有用である。 Here, there are very few examples where the butt welds are damaged by fatigue. This is considered to be due to the influence of the joint shape, specifically because the change in the cross-sectional shape is small and the change is gradual. In comparison, fillet welded joints such as cruciform joints or gusset joints often govern the fatigue strength of the entire structure. Therefore, the present invention is particularly useful for grasping the fatigue characteristics of fillet welded joints.
本発明に係る鋼材の品質保証方法における各工程について説明する。 Each process in the quality assurance method for steel materials according to the present invention will be described.
まず、基準材、試験材および複数の比較材を用意し、それぞれの鋼材に対して、溶接継手の溶接熱影響部が溶接時に受ける熱履歴を再現した熱処理を施す。基準材は任意の鋼材で構わないが、基準材に対する優劣を評価するため、優劣の基準としたい鋼材を選択することが好ましい。 First, a reference material, a test material, and a plurality of comparative materials are prepared, and each steel material is subjected to a heat treatment that reproduces the thermal history that the weld heat affected zone of the weld joint receives during welding. The reference material may be any steel material, but in order to evaluate superiority or inferiority with respect to the reference material, it is preferable to select a steel material to be used as a superiority or inferiority reference.
隅肉溶接は、突合せ溶接に比べ溶接入熱が低いことが多く、通常、１．２ｋＪ／ｍｍ程度である。したがって、上記の熱処理における加熱は、例えば、１．２ｋＪ／ｍｍの熱を付与するのがよい。この熱処理を実施する装置には、特に制約はないが、例えば、誘導加熱機能とＨｅガス冷却機能を備えた装置を用いることができる。熱処理の熱サイクルについては、特に制約はないが、例えば図２にその一例を示すように、３０〜４５℃／ｓの加熱速度で１２００〜１４００℃の温度域まで加熱し、２〜１０秒保持した後、３０〜５０℃／ｓの冷却速度で冷却する熱サイクルであればよい。 Fillet welding often has lower welding heat input than butt welding, and is usually about 1.2 kJ / mm. Therefore, for the heating in the above heat treatment, for example, heat of 1.2 kJ / mm is preferably applied. There is no particular limitation on the apparatus for performing the heat treatment, but an apparatus having an induction heating function and a He gas cooling function can be used, for example. Although there is no restriction | limiting in particular about the heat cycle of heat processing, For example, as shown in the example in FIG. 2, it heats to the temperature range of 1200-1400 degreeC with the heating rate of 30-45 degreeC / s, and hold | maintains for 2 to 10 seconds After that, it is sufficient if it is a thermal cycle that cools at a cooling rate of 30 to 50 ° C./s.
続いて、上記の再現熱処理を施した後の基準材、試験材および比較材（以下の説明において、それぞれ「基準再現ＨＡＺ材」、「試験再現ＨＡＺ材」および「比較再現ＨＡＺ材」という。）について、硬度および疲労特性を求める。 Subsequently, the reference material, the test material, and the comparative material after being subjected to the above reproducible heat treatment (in the following description, referred to as “reference reproducible HAZ material”, “test reproducible HAZ material”, and “comparative reproducible HAZ material”, respectively). For hardness and fatigue properties.
再現ＨＡＺ材の硬度を測定する方法について特に制約はないが、例えば、ビッカース硬さを測定することができる。そして、溶接熱影響部の硬度としてよく観察されるＨｖ３００〜４００での圧痕寸法が対角線長さで６８〜７９μｍであることから、例えば、ビッカース硬度測定での押付け荷重を１ｋｇｆ（９８Ｎ）に設定するのがよい。また、硬度の測定はＪＩＳ Ｚ ２２４４（２００９）に準じて実施し、補正して求めることが好ましい。さらに精度向上のためには、測定は３点以上で実施することが好ましい。また、前記測定方法が実施できない等の特別な事情がある場合は、他の測定方法を用いることを妨げない。 Although there is no restriction | limiting in particular about the method of measuring the hardness of reproduction HAZ material, For example, a Vickers hardness can be measured. And since the indentation dimension in Hv300-400 often observed as the hardness of a welding heat affected zone is 68-79 micrometers in diagonal length, for example, the pressing load in a Vickers hardness measurement is set to 1 kgf (98N). It is good. Further, it is preferable that the hardness is measured according to JIS Z 2244 (2009) and corrected. Furthermore, in order to improve accuracy, it is preferable to carry out measurement at three or more points. In addition, when there is a special circumstance such that the measurement method cannot be performed, the use of other measurement methods is not prevented.
また、再現ＨＡＺ材の疲労特性を測定する方法についても特に制約はないが、例えば、回転曲げ疲労特性を測定することができる。具体的には、回転曲げ疲労特性は、ＪＩＳ Ｚ ２２７４（１９７８）に準じて実施し、図３に形状の一例を示すように、試験片の直径ｄは６ｍｍ、曲げモーメントは４２０ＭＰａとすることができる。再現熱処理を施した部分は、母材よりも硬度が上昇する場合が多い。そのため、平滑試験片を用いて再現熱処理部と母材とを対等に評価すると、母材側で破断する可能性がある。そこで、破壊起点を再現熱処理部に限定するため、試験片の再現熱処理部に環状切欠きを設けることが望ましい。 Further, there is no particular limitation on the method for measuring the fatigue characteristics of the reproduced HAZ material, but for example, the rotational bending fatigue characteristics can be measured. Specifically, the rotational bending fatigue characteristics are implemented according to JIS Z 2274 (1978), and as shown in an example of the shape in FIG. 3, the diameter d of the test piece is 6 mm and the bending moment is 420 MPa. it can. In many cases, the hardness of the portion subjected to the reproduction heat treatment is higher than that of the base material. Therefore, if the reproducible heat treatment part and the base material are evaluated on an equal basis using a smooth test piece, there is a possibility of fracture on the base material side. Therefore, in order to limit the fracture starting point to the reproduction heat treatment part, it is desirable to provide an annular notch in the reproduction heat treatment part of the test piece.
再現ＨＡＺ材の硬度および疲労特性の測定値が得られた後、基準再現ＨＡＺ材および比較再現ＨＡＺ材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する。 After the measurement values of the hardness and fatigue characteristics of the reproduced HAZ material are obtained, a standard expression between the hardness and the fatigue characteristics is obtained from the hardness and fatigue characteristics of at least a part of the reference reproduced HAZ material and the comparative reproduced HAZ material. Is derived.
図１には、基準再現ＨＡＺ材および比較再現ＨＡＺ材の硬度と疲労特性との関係が示されている。例えば、図１に示す例においては、比較再現ＨＡＺ材のうちの一部の鋼材において、硬度と疲労寿命との間に、正の相関関係が認められる。この傾向と基準再現ＨＡＺ材の測定値に基づき、図１に示すような基準式を引くことが可能となる。 FIG. 1 shows the relationship between the hardness and fatigue characteristics of the reference reproduction HAZ material and the comparative reproduction HAZ material. For example, in the example shown in FIG. 1, a positive correlation is recognized between hardness and fatigue life in some steel materials of the comparative reproduction HAZ materials. Based on this tendency and the measured value of the reference reproduction HAZ material, it is possible to draw a reference expression as shown in FIG.
そして、試験再現ＨＡＺ材の硬度および疲労特性と、基準式との関係に基づき、試験材を用いて作製した溶接継手の疲労特性が、基準材を用いて作製した溶接継手より優れるかどうかの判定を行う。具体的には、試験再現ＨＡＺ材の硬度および疲労特性の測定値をグラフ上にプロットした時に、基準式より上の領域にプロットされた場合は基準材より品質が優れ、下の領域にプロットされた場合は基準材より品質が劣ると判定することができる。上記判定結果に基づいて試験材の品質を保証することができる。 Then, based on the relationship between the hardness and fatigue characteristics of the test reproduction HAZ material and the reference formula, it is determined whether the fatigue characteristics of the welded joint manufactured using the test material are superior to the welded joint manufactured using the reference material. I do. Specifically, when the measured values of hardness and fatigue properties of the test reproduction HAZ material are plotted on the graph, the quality is superior to the reference material when plotted in the region above the reference formula, and is plotted in the region below. In such a case, it can be determined that the quality is inferior to the reference material. The quality of the test material can be guaranteed based on the determination result.
より客観的かつ精度の高い基準式を得るためには、以下の手順に従って基準式を導出することがより好ましい。 In order to obtain a more objective and accurate reference expression, it is more preferable to derive the reference expression according to the following procedure.
まず、基準材および複数の比較材に対応する鋼材を用いて溶接継手を作製する。なお、基準材等に対応する鋼材とは、基準材等と同一の化学組成と母材鋼板組織を有する鋼材はもちろんのこと、基準材等と疲労強度特性との関係で実質的に同一の化学成分と母材鋼板組織を有する鋼材をも含むものとする。 First, a welded joint is produced using steel materials corresponding to a reference material and a plurality of comparative materials. Note that the steel material corresponding to the reference material and the like is not only a steel material having the same chemical composition and base steel plate structure as the reference material, but also substantially the same chemical in relation to the reference material and the fatigue strength characteristics. The steel material which has a component and a base-material steel plate structure shall also be included.
溶接継手としては、例えば、図４に示すような荷重非伝達十字継手を用いることができる。主板と同材質のリブ板を用意し、主板の表裏面にリブ板を設置し疲労試験時に影響しない位置で主板とリブ板とを仮付け溶接する。その後、母材強度に対応した溶接材料を選択する。溶接方法、溶接条件は評価対象としている溶接構造物で採用されている溶接に合致させるのが望ましい。 As the weld joint, for example, a load non-transmission cross joint as shown in FIG. 4 can be used. Prepare a rib plate of the same material as the main plate, install the rib plate on the front and back of the main plate, and temporarily weld the main plate and the rib plate at a position that does not affect the fatigue test. Thereafter, a welding material corresponding to the base material strength is selected. It is desirable to match the welding method and welding conditions to those used in the welded structure being evaluated.
溶接方法としては、例えば炭酸ガスシールドのアーク溶接法を採用することができる。また、溶接条件として、疲労特性が問題となることが多い小入熱条件として、１．５ｋＪ／ｍｍ程度を採用することができる。継手の溶接長さは５００〜１０００ｍｍ程度がハンドリングしやすい。溶接継手から短冊状に試験片を加工した。試験片の寸法は、使用する疲労試験機の荷重容量と、板厚等から制約を受けるが、試験片平行部の溶接長さは、例えば、３０ｍｍとすることができる。 As a welding method, for example, an arc welding method of a carbon dioxide gas shield can be employed. Further, as a welding condition, about 1.5 kJ / mm can be adopted as a small heat input condition in which fatigue characteristics often cause a problem. The weld length of the joint is easily handled at about 500 to 1000 mm. A test piece was processed into a strip shape from the welded joint. Although the dimension of a test piece receives restrictions from the load capacity of a fatigue testing machine to be used, plate thickness, etc., the weld length of a test piece parallel part can be 30 mm, for example.
そして、基準材および複数の比較材に対応する鋼材を用いて作製した溶接継手（以下の説明において、それぞれ「基準継手材」および「比較継手材」という。）を継手疲労試験に供し、疲労特性を求める。 A welded joint produced using steel materials corresponding to the reference material and a plurality of comparative materials (hereinafter referred to as “reference joint material” and “comparative joint material”, respectively) is subjected to a joint fatigue test, and fatigue characteristics are obtained. Ask for.
ここで、疲労特性は、例えば、繰返し負荷応力とその応力での疲労破断寿命との関係で評価することができる。この応力のパラメータとして、通常は、繰返し応力波形の中で、最大応力σｍａｘから、繰返し応力波形の中の最小応力σｍｉｎを差引いた、応力範囲Δσ（＝σｍａｘ−σｍｉｎ）で表示されることが、特に、溶接継手の場合には多い。溶接残留応力が付与される溶接継手においては、最大応力σｍａｘおよび最小応力σｍｉｎの個々の絶対値より相対的な差が重要となるためである。 Here, the fatigue characteristics can be evaluated by, for example, the relationship between the cyclic load stress and the fatigue rupture life at the stress. As a parameter of this stress, it is usually displayed in a stress range Δσ (= σ max −σ min ) obtained by subtracting the minimum stress σ min in the repeated stress waveform from the maximum stress σ max in the repeated stress waveform. This is especially true for welded joints. This is because, in a welded joint to which welding residual stress is applied, a relative difference is more important than individual absolute values of the maximum stress σ max and the minimum stress σ min .
継手疲労試験条件については、試験片平行部の溶接長さを３０ｍｍとする場合、該溶接長さは比較的短く、試験片の加工途中で継手に存在していた溶接残留応力が解放されていると考えられるため、繰返し応力で解放分を補填することが好ましい。具体的には、繰返し応力の最大応力σｍａｘを３５０ＭＰａで一定とし、応力範囲Δσの設定のため、最小応力を種々変化させることが好ましい。疲労試験には、例えば電気油圧式閉ループ疲労試験機を用いればよい。荷重制御下で疲労試験を実施し、最大荷重時の変位が試験開始時に比べ１ｍｍ増加した瞬間を疲労破断寿命と定義することができる。 As for the joint fatigue test conditions, when the weld length of the parallel part of the test piece is set to 30 mm, the weld length is relatively short, and the welding residual stress existing in the joint during the processing of the test piece is released. Therefore, it is preferable to compensate for the released portion with repeated stress. Specifically, it is preferable that the maximum stress σ max of the repeated stress is constant at 350 MPa, and the minimum stress is variously changed for setting the stress range Δσ. For the fatigue test, for example, an electrohydraulic closed loop fatigue tester may be used. A fatigue test is performed under load control, and the moment when the displacement at the maximum load is increased by 1 mm compared to the start of the test can be defined as the fatigue fracture life.
上記の継手疲労試験により基準継手材および比較継手材の疲労特性を比較する。ここで、疲労特性を比較するに際しては、所定の応力範囲Δσでの基準継手材および比較継手材の疲労破断寿命を比較してもよい。しかしながら、試験結果のばらつきの影響を低減するためには、まず複数の基準継手材における継手疲労試験結果から、図５に示すような基準ＳＮ線図を作成した後、各比較継手材について、異なる３つ以上の応力範囲Δσでの疲労破断寿命を求め、図６に示すように、上記の基準ＳＮ線と比較することによって、基準継手材に対する疲労寿命延伸率を算出することができる。図６に示す例では、応力範囲Δσを１００ＭＰａ、１３０ＭＰａおよび１６０ＭＰａとした際の疲労破断寿命がそれぞれ基準ＳＮ線の１．７倍、２．８倍および２．５倍となったため、当該比較継手材の疲労寿命延伸率はその平均値である２．３３と算出される。 The fatigue characteristics of the reference joint material and the comparative joint material are compared by the above joint fatigue test. Here, when comparing the fatigue characteristics, the fatigue fracture lives of the reference joint material and the comparative joint material in a predetermined stress range Δσ may be compared. However, in order to reduce the influence of variation in test results, first, a reference SN diagram as shown in FIG. 5 is created from the joint fatigue test results of a plurality of reference joint materials, and then different for each comparative joint material. The fatigue life at breakage in three or more stress ranges Δσ is obtained, and as shown in FIG. 6, the fatigue life extension ratio for the reference joint material can be calculated by comparing with the reference SN line. In the example shown in FIG. 6, the fatigue fracture life when the stress range Δσ is 100 MPa, 130 MPa, and 160 MPa is 1.7 times, 2.8 times, and 2.5 times the reference SN line, respectively. The fatigue life elongation ratio of the material is calculated to be 2.33 which is the average value.
そして、継手疲労試験に供した比較継手材のうちから、前記疲労寿命延伸率が１．０以下になるものを、溶接継手の疲労特性が基準材と同等以下である下等比較材として抽出する。そして、上述の再現ＨＡＺ材の硬度と疲労特性との間の基準式を導出するに際しては、該下等比較材に対応する鋼材の再現ＨＡＺ材の硬度および疲労特性の測定値を用いればよい。 Then, among the comparative joint materials subjected to the joint fatigue test, those having the fatigue life elongation ratio of 1.0 or less are extracted as lower comparative materials whose fatigue characteristics of the welded joint are equal to or lower than the reference material. . Then, in deriving a reference expression between the hardness and fatigue characteristics of the above-described reproduced HAZ material, the measured values of the hardness and fatigue characteristics of the reproduced HAZ material of the steel material corresponding to the lower comparative material may be used.
図７に示すように、図中の白プロットが下等比較材に対応する鋼材の再現ＨＡＺ材の測定結果を示したものである。これらの鋼材の測定結果に基づき例えば最小二乗法により近似直線を引く。そして、基準ＨＡＺ材のプロットを通過し、上記の近似直線と傾きが同一である直線を基準式とすることができる。 As shown in FIG. 7, the white plot in the figure shows the measurement result of the reproduced HAZ material of the steel material corresponding to the lower comparative material. Based on the measurement results of these steel materials, an approximate straight line is drawn by, for example, the least square method. Then, a straight line that passes through the plot of the reference HAZ material and has the same inclination as the above approximate straight line can be used as the reference formula.
次に、本発明に係る鋼材の疲労特性推定方法における各工程について説明する。 Next, each step in the method for estimating fatigue characteristics of steel according to the present invention will be described.
まず、基準継手材および複数の比較継手材を継手疲労試験に供し、各溶接継手の疲労特性を求める。そして、基準再現ＨＡＺ材、比較再現ＨＡＺ材および試験再現ＨＡＺ材について硬度および疲労特性を求める。その後、基準再現ＨＡＺ材および比較再現ＨＡＺ材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する。これらの工程については、上述の品質保証方法における工程と同様である。 First, a reference joint material and a plurality of comparative joint materials are subjected to a joint fatigue test, and fatigue characteristics of each welded joint are obtained. Then, hardness and fatigue characteristics are obtained for the reference reproduction HAZ material, the comparative reproduction HAZ material, and the test reproduction HAZ material. Thereafter, a reference equation between the hardness and the fatigue characteristics is derived from the hardness and fatigue characteristics of at least a part of the reference reproduction HAZ material and the comparative reproduction HAZ material. These steps are the same as those in the quality assurance method described above.
疲労特性推定方法においては、さらに、上述の工程によって求められた、比較再現ＨＡＺ材の硬度および疲労特性ならびに基準式から、優劣パラメータを求める。 In the fatigue characteristic estimation method, the superiority / inferiority parameter is further obtained from the hardness and fatigue characteristics of the comparatively reproduced HAZ material and the reference formula obtained by the above-described steps.
優劣パラメータは各鋼材の溶接継手の疲労特性の指標となるものであり、基準式からのずれの程度によって表現されるものである。具体的には、各再現ＨＡＺ材の疲労特性の測定値を、当該再現ＨＡＺ材の硬度を基準式に代入することによって求められる疲労特性の値で除することによって求めることができる。すなわち、図７に示すグラフ上においては、左上に行くほど優劣パラメータの値は高くなる。 The superiority / inferiority parameter is an index of the fatigue characteristics of the welded joint of each steel material, and is expressed by the degree of deviation from the reference formula. Specifically, the measured value of the fatigue property of each reproduced HAZ material can be obtained by dividing the measured value of the fatigue property obtained by substituting the hardness of the reproduced HAZ material into a reference equation. That is, on the graph shown in FIG. 7, the value of the superiority / inferiority parameter increases toward the upper left.
このようにして求められた比較再現ＨＡＺ材の優劣パラメータの値と、対応する比較継手材の疲労特性との関係から、疲労特性推定式を導出する。この時、比較継手材の疲労特性としては、例えば、上述の疲労寿命延伸率で代表させることができる。図８は、比較再現ＨＡＺ材の優劣パラメータの値と、対応する比較継手材の疲労寿命延伸率との関係を示した図である。図８から分かるように、比較再現ＨＡＺ材の優劣パラメータの値と、対応する比較継手材の疲労寿命延伸率との間には良好な正の相関関係が認められる。上記の関係から、例えば最小二乗法を用いることによって、疲労特性推定式を導出することができる。 A fatigue characteristic estimation formula is derived from the relationship between the superior / inferiority parameter values of the comparatively reproduced HAZ material thus obtained and the fatigue characteristics of the corresponding comparative joint material. At this time, the fatigue characteristics of the comparative joint material can be represented by, for example, the above-described fatigue life extension rate. FIG. 8 is a diagram showing the relationship between the superior / inferior parameter value of the comparative reproduction HAZ material and the fatigue life extension rate of the corresponding comparative joint material. As can be seen from FIG. 8, a good positive correlation is recognized between the value of the superior / inferiority parameter of the comparative reproduction HAZ material and the fatigue life elongation of the corresponding comparative joint material. From the above relationship, the fatigue characteristic estimation formula can be derived by using, for example, the least square method.
図９は、試験再現ＨＡＺ材の硬度と疲労寿命との関係を示した図である。試験再現ＨＡＺ材についても同様にして、硬度および疲労特性ならびに基準式から、優劣パラメータを求める。そして、図１０に示されるように、試験再現ＨＡＺ材の優劣パラメータの値と、上述の工程によって導出された疲労特性推定式とに基づき、試験材を用いて作製した溶接継手の疲労特性の推定値を算出する。 FIG. 9 is a diagram showing the relationship between the hardness of the test reproduction HAZ material and the fatigue life. Similarly, for the test reproduction HAZ material, the superiority / inferiority parameters are obtained from the hardness and fatigue characteristics and the reference formula. Then, as shown in FIG. 10, based on the value of the superior / inferiority parameter of the test reproduction HAZ material and the fatigue property estimation formula derived by the above-described process, the fatigue property of the welded joint produced using the test material is estimated. Calculate the value.
上記の推定方法によって算出される推定値の精度を検証するため、実際に試験材に対応する鋼材を用いて溶接継手を作製して継手疲労試験に供し、各溶接継手の疲労特性を求めた。図１１は、試験材における疲労寿命延伸率の推定値と実験値とを比較した図である。図１１から明らかなように、再現ＨＡＺ材の特性から継手疲労特性を実用的な精度で推定できていることが分かる。 In order to verify the accuracy of the estimated value calculated by the above estimation method, a welded joint was actually produced using a steel material corresponding to the test material and subjected to a joint fatigue test, and the fatigue characteristics of each welded joint were obtained. FIG. 11 is a diagram comparing an estimated value and an experimental value of the fatigue life extension rate in the test material. As is apparent from FIG. 11, it can be seen that the joint fatigue characteristics can be estimated with practical accuracy from the characteristics of the reproduced HAZ material.
なお、疲労特性推定式を導出するに際して、図８に示しているように、プロットのばらつきに基づき疲労特性推定誤差をさらに求めておけば、試験材を用いて作製した溶接継手の疲労特性の推定値を算出する際に、疲労特性の上下限を同時に算出することが可能になる。 When the fatigue property estimation formula is derived, as shown in FIG. 8, if the fatigue property estimation error is further obtained based on the variation of the plot, the fatigue property of the welded joint manufactured using the test material is estimated. When calculating the value, the upper and lower limits of fatigue characteristics can be calculated simultaneously.
本発明によれば、溶接熱影響部の硬度および疲労寿命を測定するという簡便な方法により、溶接継手の疲労特性を迅速に知ることができるため、鋼材の溶接継手における疲労特性の保証および推定に有用である。 According to the present invention, since the fatigue characteristics of the welded joint can be quickly known by a simple method of measuring the hardness and fatigue life of the weld heat affected zone, it is possible to guarantee and estimate the fatigue characteristics of the steel welded joint. Useful.
Claims (5)
前記基準材、前記試験材および複数の比較材に対して、溶接継手の溶接熱影響部が溶接時に受ける熱履歴を再現した熱処理を施した後、硬度および疲労特性を求める工程と、
前記再現熱処理後の前記基準材および前記比較材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する工程と、
前記再現熱処理後の前記試験材の硬度および疲労特性と、前記基準式との関係に基づき、前記試験材の品質を保証する工程と、を備える、
鋼材の品質保証方法。 A method for ensuring that the quality related to fatigue of a welded joint produced using a steel material as a test material is superior to a welded joint produced using an arbitrary reference material,
Steps for obtaining hardness and fatigue characteristics after performing heat treatment that reproduces the thermal history that the weld heat-affected zone of the welded joint undergoes during welding with respect to the reference material, the test material, and the plurality of comparative materials;
Deriving a standard expression between hardness and fatigue characteristics from hardness and fatigue characteristics of at least a part of the reference material and the comparative material after the reproduction heat treatment;
A step of assuring the quality of the test material based on the relationship between the hardness and fatigue characteristics of the test material after the reproduction heat treatment and the reference formula,
Quality assurance method for steel.
前記複数の比較材のうちから、溶接継手の疲労特性が前記基準材と同等以下である下等比較材を抽出する工程と、をさらに備え、
前記基準式を導出する工程における、前記比較材のうちの少なくとも一部が、前記下等比較材に対応する鋼材である、
請求項１に記載の鋼材の品質保証方法。 Producing a welded joint using a steel material corresponding to the reference material and the plurality of comparative materials and subjecting it to a joint fatigue test, and determining fatigue characteristics of each welded joint;
A step of extracting a lower comparative material having a fatigue characteristic of a welded joint equal to or lower than that of the reference material from the plurality of comparative materials, and further comprising:
In the step of deriving the reference formula, at least a part of the comparison material is a steel material corresponding to the lower comparison material,
The quality assurance method for steel according to claim 1.
基準材および複数の比較材を用いて溶接継手を作製して継手疲労試験に供し、各溶接継手の疲労特性を求める工程と、
前記基準材および前記比較材に対応する鋼材、ならびに、前記試験材に対して、溶接継手の溶接熱影響部が溶接時に受ける熱履歴を再現した熱処理を施した後、硬度および疲労特性を求める工程と、
前記再現熱処理後の前記基準材および前記比較材のうちの少なくとも一部についての硬度および疲労特性から、硬度と疲労特性との間の基準式を導出する工程と、
前記再現熱処理後の前記比較材および前記試験材の硬度および疲労特性、ならびに、前記基準式から、各鋼材の溶接継手の疲労特性の指標となる優劣パラメータを求める工程と、
前記再現熱処理後の前記比較材の前記優劣パラメータと、前記比較材に対応する鋼材を用いて作製した前記溶接継手の前記疲労特性とから、疲労特性推定式を導出する工程と、
前記再現熱処理後の前記試験材の前記優劣パラメータと、前記疲労特性推定式とに基づき、前記試験材を用いて作製した溶接継手の疲労特性の推定値を算出する工程と、を備える、
鋼材の疲労特性推定方法。 A method for estimating fatigue characteristics of a welded joint produced using a steel material as a test material,
Producing a welded joint using a reference material and a plurality of comparative materials and subjecting the joint to a joint fatigue test, and determining the fatigue characteristics of each welded joint;
A step of obtaining hardness and fatigue characteristics after subjecting the steel material corresponding to the reference material and the comparative material, and the test material to heat treatment that reproduces the thermal history that the weld heat affected zone of the welded joint undergoes during welding. When,
Deriving a standard expression between hardness and fatigue characteristics from hardness and fatigue characteristics of at least a part of the reference material and the comparative material after the reproduction heat treatment;
From the hardness and fatigue characteristics of the comparative material and the test material after the reproducible heat treatment, and a step of obtaining a superior / inferior parameter serving as an index of fatigue characteristics of the welded joint of each steel material from the reference formula,
Deriving a fatigue property estimation formula from the superiority and inferiority parameters of the comparative material after the reproduction heat treatment and the fatigue properties of the welded joint produced using a steel material corresponding to the comparative material;
Calculating an estimated value of fatigue characteristics of a welded joint produced using the test material based on the superiority / inferiority parameters of the test material after the reproduction heat treatment and the fatigue property estimation formula,
A method for estimating fatigue properties of steel.
前記基準式を導出する工程における、前記比較材のうちの少なくとも一部が、前記下等比較材に対応する鋼材である、
請求項３に記載の鋼材の疲労特性推定方法。 A step of extracting a lower comparative material having a fatigue characteristic of a welded joint equal to or lower than that of the reference material from the plurality of comparative materials,
In the step of deriving the reference formula, at least a part of the comparison material is a steel material corresponding to the lower comparison material,
The method for estimating fatigue characteristics of a steel material according to claim 3.
前記試験材を用いて作製した溶接継手の前記疲労特性の推定値を算出する工程において、前記疲労特性推定誤差に基づき、前記疲労特性の上下限を同時に算出する、
請求項３または請求項４に記載の鋼材の疲労特性推定方法。 In the step of deriving the fatigue property estimation formula, further obtaining a fatigue property estimation error,
In the step of calculating the estimated value of the fatigue characteristics of the welded joint produced using the test material, the upper and lower limits of the fatigue characteristics are simultaneously calculated based on the fatigue characteristic estimation error.
The method for estimating fatigue characteristics of a steel material according to claim 3 or 4.
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