JP6686645B2 - Steel quality assurance method and fatigue property estimation method - Google Patents
Steel quality assurance method and fatigue property estimation method Download PDFInfo
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Description
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 products.
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。 Various welded steel structures such as buildings and bridges, transportation machines such as ships and automobiles, industrial machines, construction machines, and many other parts of steel (hereinafter referred to as "mechanical / structural steel") .) Is used. Since mechanical and structural steel materials are usually subjected to repeated loads, attention must be paid to fatigue characteristics such as fatigue life in order to secure the strength and soundness of the structure or machine. The fatigue characteristics of the welded portion, whose fatigue strength is overwhelmingly 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。 2. Description of the Related Art Conventionally, regarding the prevention of fatigue fracture of mechanical / structural steel materials, various studies have been made by dividing the fatigue fracture into two damage processes, “generation of fatigue crack” and “propagation of fatigue crack”. In the examination, focus on the fatigue crack initiation process and the fatigue crack growth process according to the geometrical dimensions of the structure or machine, the operating environment, the load pattern, 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, in the case of a small-sized member, failure of the member leads to fatal damage to the entire machine / structure, and when there is only one load path, it is important to prevent fatigue cracks from occurring. . On the other hand, a member with a large size does not lead to direct and fatal destruction of the entire machine / structure due to the breakage of the member, and there are multiple load paths, that is, even if the single member breaks, other members In the case of bearing the load instead, fatigue crack initiation 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。 Thus, fatigue crack initiation and fatigue crack growth are both important characteristics for understanding fatigue fracture, but the occurrence of fatigue cracks is usually regarded as the fatigue fracture life, and load stress and fatigue Fatigue strength is evaluated from the relationship with fracture life, and fatigue crack growth is rarely 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 comparing the base material portion and the welded portion, the welded portion 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 having excellent joint fatigue characteristics that can change the fatigue design of the welded portion, it is necessary to evaluate the fatigue characteristics of the welded joint a lot. Further, when commercializing a steel material having excellent joint fatigue characteristics, it is necessary to evaluate the fatigue characteristics of the welded joint in order to directly assure the quality of the steel material.
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, in the case of evaluating the joint fatigue property of a specific steel material, the procedure is as follows.
(1) Welding a steel material according to the joint type to prepare a welded joint (large plate).
(2) From this welded joint (large plate), a test piece having a desired shape and size is sampled by a method such as machining.
(3) If necessary, after measuring the amount of angular deformation of the test piece or the shape of the weld toe toe, make it possible to chuck the fatigue tester with the gripped portion of the test piece as the same plane by straightening the bend etc. Then, 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 tester sends a proper electric signal to the loading part equipped with a hydraulic actuator, etc., the sensor part to detect load / displacement, etc. and the signal from the load detector while sending an appropriate electric signal to the servo valve attached to the actuator. And a closed loop control part so that the actual load value matches the load set value (load upper limit value, load lower limit value). In order to ensure the required load control accuracy, a load part, a sensor part, and a control part of excellent quality 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。 Further, although it largely depends 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 huge amount of time. It is clear from the early stages of the development plan that the fatigue test requires a huge amount of time, but it is believed that the fatigue properties of the joint can only be ascertained by carrying out the fatigue test. Since its inception, 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 correspondingly improved. The same tendency as the tensile strength dependency in the fatigue strength has been subjected to a heat treatment that reproduces the heat history of the welding heat affected zone (HAZ) of the actual joint during welding (also referred to as "reproduced HAZ material" in the following description). .) Is also recognized. That is, also 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 the quality of fatigue in a welded joint of steel materials and a method for estimating fatigue characteristics by a simple and quick 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 to solve the above problems, and has as its gist the following quality assurance method and fatigue property estimation method for steel materials.
（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 of guaranteeing that the fatigue-related quality of a welded joint manufactured using a steel material as a test material is superior to that of a welded joint manufactured using an arbitrary reference material,
The reference material, the test material and a plurality of comparative materials, after subjected to a heat treatment that reproduces the heat history that the welding heat-affected zone of the welded joint receives during welding, and a step of determining hardness and fatigue properties,
From the hardness and fatigue characteristics of at least a portion of the reference material and the comparative material after the reproduction heat treatment, deriving a reference expression between hardness and fatigue characteristics,
Hardness and fatigue characteristics of the test material after the reproduction heat treatment, and a step of guaranteeing the quality of the test material, based on the relationship between the reference formula,
Quality assurance method for steel products.
（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) a step of producing a welded joint using steel materials corresponding to the reference material and the plurality of comparative materials, subjecting the joint to a fatigue test, and obtaining fatigue characteristics of each welded joint;
From the plurality of comparative materials, further comprising the step of extracting a lower comparative material in which the fatigue characteristics of the welded joint are equal to or less than the reference material,
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 (1) above.
（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 of estimating the fatigue characteristics of a welded joint produced using a steel material as a test material,
A process of producing a welded joint using a reference material and a plurality of comparative materials and subjecting it to a joint fatigue test, and determining the fatigue characteristics of each welded joint,
A step of obtaining hardness and fatigue properties after subjecting the steel materials corresponding to the reference material and the comparative material, and the test material to heat treatment that reproduces the heat history of the welded heat-affected zone of the welded joint during welding. When,
From the hardness and fatigue characteristics of at least a portion of the reference material and the comparative material after the reproduction heat treatment, deriving a reference expression between hardness and fatigue characteristics,
Hardness and fatigue characteristics of the comparative material and the test material after the reproduction heat treatment, and, from the reference formula, a step of determining the superiority or inferiority parameter as an index of the fatigue characteristics of the welded joint of each steel material,
From the superiority and inferiority parameter of the comparative material after the reproduction heat treatment, and the fatigue characteristic of the welded joint produced using a steel material corresponding to the comparative material, a step of deriving a fatigue characteristic estimation formula,
Based on the superiority and inferiority parameter of the test material after the reproduction heat treatment, and the fatigue characteristic estimation formula, a step of calculating an estimated value of the fatigue characteristic of a welded joint produced using the test material,
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 the welded joint equal to or lower than 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 fatigue property estimation method for steel 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, the fatigue characteristic estimation error is further obtained,
In the step of calculating the estimated value of the fatigue characteristic of the welded joint manufactured using the test material, based on the fatigue characteristic estimation error, the upper and lower limits of the fatigue characteristic are simultaneously calculated,
The fatigue property estimation method for steel according to (3) or (4) above.
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 the 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 reproduced 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 area in the graph) that deviate from that tendency. As described above, it was found that a steel material having a higher fatigue life even with the same level of hardness has excellent fatigue characteristics of actual joints.
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. Hereinafter, the present invention will be described in detail.
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 quality assurance method for a steel material according to the present invention ensures that the quality of fatigue of a welded joint manufactured using a steel material as a test material is superior to that of a welded joint manufactured using an arbitrary reference material. Further, the method for estimating the fatigue characteristics of a steel material according to the present invention is a method for estimating the fatigue characteristics of a welded joint produced using a steel material as a test material. That is, the test material to be subjected to quality assurance or fatigue characteristic estimation is specifically a steel material (welding steel) used for welding among machine / 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。 Further, the chemical composition of the steel material is not particularly limited, and for example, in mass%, C: 0.02 to 0.20%, Si: 0.1 to 0.8%, Mn: 0.5 to 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 of Al: 0.3% or less, the balance Fe and inevitable impurities can be used. In the examples described below, various steel materials having compositions within 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 in which the butt welded portion is damaged by fatigue. It is considered that this is because the joint shape has an influence, and specifically, the change in cross-sectional shape is small and the change is gradual. In comparison, fillet welded joints such as cross joints or gusset joints often regulate the fatigue strength of the entire structure. Therefore, the present invention is particularly useful for understanding 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 step in the quality assurance method for steel 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 heat history of the weld heat affected zone of the welded joint during welding. The reference material may be any steel material, but in order to evaluate the superiority or inferiority with respect to the reference material, it is preferable to select the steel material to be used as the criterion of superiority or inferiority.
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 a 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. The apparatus for carrying out this heat treatment is not particularly limited, but for example, an apparatus having an induction heating function and a He gas cooling function can be used. There are no particular restrictions on the heat cycle of the heat treatment, but for example, as shown in the example in FIG. After that, the heat cycle may be a heat cycle of cooling 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 the above-described reproduction heat treatment (hereinafter referred to as "reference reproduction HAZ material", "test reproduction HAZ material", and "comparison reproduction HAZ material", respectively). For, the hardness and fatigue properties are determined.
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。 There is no particular limitation on the method of measuring the hardness of the reproduced HAZ material, but the Vickers hardness can be measured, for example. Since the indentation dimension at Hv300 to 400, which is often observed as the hardness of the welding heat affected zone, is 68 to 79 μm in diagonal length, for example, the pressing load in Vickers hardness measurement is set to 1 kgf (98 N). Is good. The hardness is preferably measured according to JIS Z 2244 (2009) and corrected. In order to further improve accuracy, it is preferable to carry out the measurement at three or more points. In addition, if there is a special circumstance such that the above-mentioned measurement method cannot be carried out, the use of another measurement method is not hindered.
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, the method for measuring the fatigue characteristics of the reproduced HAZ material is not particularly limited, but, for example, the rotational bending fatigue characteristics can be measured. Specifically, the rotational bending fatigue property is performed 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 reproducible heat treatment is higher than that of the base material. Therefore, when the reproduced heat treatment part and the base material are evaluated equally using the 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 reproduced heat treatment portion, it is desirable to provide an annular notch in the reproduced heat treatment portion 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 measured values of hardness and fatigue characteristics of the reproduced HAZ material are obtained, the reference expression between the hardness and the fatigue characteristics is calculated from the hardness and fatigue characteristics of at least a part of the reference reproduced HAZ material and the comparative reproduced HAZ material. Derive.
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 standard reproduced HAZ material and the comparative reproduced 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 standard reproduction HAZ material, it becomes possible to draw the standard formula 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 reproduced 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 those of the welded joint manufactured using the reference material. I do. Specifically, when the measured values of hardness and fatigue properties of the test reproduced HAZ material are plotted on the graph, when plotted in the area above the reference formula, the quality is better than in the reference material and in the area below. If it is, 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 above 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 highly 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 a steel material corresponding to a reference material and a plurality of comparative materials. Incidentally, the steel material corresponding to the reference material and the like, as well as the steel material having the same chemical composition and base steel plate structure as the reference material, etc., the substantially same chemical in the relationship between the reference material and the fatigue strength characteristics. A steel material having a composition and a base material steel sheet structure is also 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 welded joint, for example, a load non-transmission cross joint as shown in FIG. 4 can be used. A rib plate made of the same material as the main plate is prepared, the rib plates are installed on the front and back surfaces of the main plate, and the main plate and the rib plate are temporarily welded together at a position that does not affect the fatigue test. After that, a welding material corresponding to the strength of the base material is selected. It is desirable that the welding method and welding conditions match the welding adopted in the welded structure under evaluation.
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, a carbon dioxide shield arc welding method can be adopted. Further, as a welding condition, a small heat input condition in which fatigue characteristics often cause a problem, and about 1.5 kJ / mm can be adopted. If the welding length of the joint is about 500 to 1000 mm, it is easy to handle. A test piece was processed into a strip shape from the welded joint. The size of the test piece is restricted by the load capacity of the fatigue tester used, the plate thickness, etc., but the welding length of the parallel part of the test piece can be set to, for example, 30 mm.
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。 Then, the welded joints produced by using the steel materials corresponding to the reference material and the plurality of comparative materials (in the following description, referred to as “reference joint material” and “comparative joint material”) were subjected to joint fatigue test, and fatigue characteristics 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 the stress range Δσ (= σ max −σ min ), which is obtained by subtracting the minimum stress σ min in the repeated stress waveform from the maximum stress σ max in the repeated stress waveform. Especially in the case of 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。 Regarding the joint fatigue test condition, when the welding length of the parallel portion of the test piece is 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 supplement the released portion with repeated stress. Specifically, it is preferable that the maximum stress σ max of cyclic stress be constant at 350 MPa and the minimum stress be variously changed in order to set the stress range Δσ. For the fatigue test, for example, an electrohydraulic closed loop fatigue tester may be used. The fatigue test is carried out under load control, and the moment when the displacement at the maximum load increases 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 above-mentioned joint fatigue test compares the fatigue characteristics of the standard joint material and the comparative joint material. 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 the variation in the test results, first, a reference SN diagram as shown in FIG. 5 is created from the joint fatigue test results for a plurality of reference joint materials, and then each comparative joint material is different. By obtaining the fatigue rupture life in three or more stress ranges Δσ and comparing it with the reference SN line as shown in FIG. 6, the fatigue life extension ratio for the reference joint material can be calculated. In the example shown in FIG. 6, when the stress range Δσ was set to 100 MPa, 130 MPa, and 160 MPa, the fatigue rupture lives were 1.7 times, 2.8 times, and 2.5 times the reference SN line, respectively, so that the comparative joint The fatigue life extension ratio of the material is calculated as 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, from the comparative joint materials subjected to the joint fatigue test, those whose fatigue life extension ratio is 1.0 or less are extracted as lower comparative materials whose fatigue properties of the welded joint are equal to or less than the reference material. . Then, when deriving the standard expression between the hardness and the fatigue property of the above-mentioned reproduced HAZ material, the measured values of the hardness and fatigue property of the reproduced HAZ material of the steel material corresponding to the lower comparison 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 comparison 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 expression.
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 the fatigue characteristics of the steel material 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 standard joint material and a plurality of comparative joint materials are subjected to a joint fatigue test, and the fatigue characteristics of each welded joint are obtained. Then, the hardness and fatigue characteristics of the standard reproduced HAZ material, the comparative reproduced HAZ material and the test reproduced HAZ material are obtained. Then, a standard expression between the hardness and the fatigue property is derived from the hardness and the fatigue property of at least a part of the standard reproduced HAZ material and the comparative reproduced 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 property estimation method, superiority / inferiority parameters are further determined from the hardness and fatigue properties of the comparative reproduced HAZ material obtained by the above steps and the reference formula.
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 or 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 standard formula. Specifically, it can be obtained by dividing the measured value of the fatigue characteristic of each reproduced HAZ material by the value of the fatigue characteristic obtained by substituting the hardness of the reproduced HAZ material into the reference formula. 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 value of the superiority / inferiority parameter of the comparative reproduced HAZ material thus obtained and the fatigue characteristic 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-mentioned fatigue life extension rate. FIG. 8 is a diagram showing the relationship between the value of the superiority / inferiority parameter of the comparative reproduced 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 observed between the value of the superiority / inferiority parameter of the comparative reproduced HAZ material and the fatigue life extension rate of the corresponding comparative joint material. From the above relationship, the fatigue characteristic estimation formula can be derived by using, for example, the least squares 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 and the fatigue life of the test reproduced HAZ material. Similarly, for the HAZ material reproduced in the test, superiority and 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 superiority / inferiority parameter of the test reproduction HAZ material and the fatigue characteristic estimation formula derived by the above-described process, estimation of the fatigue characteristic of the welded joint produced using the test material is performed. 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 manufactured using a steel material corresponding to the test material and subjected to a joint fatigue test to determine the fatigue characteristics of each welded joint. FIG. 11 is a diagram comparing the estimated value and the experimental value of the fatigue life extension rate in the test material. As is clear from FIG. 11, 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 deriving the fatigue characteristic estimation formula, as shown in FIG. 8, if the fatigue characteristic estimation error is further calculated based on the variation of the plots, the fatigue characteristic of the welded joint manufactured using the test material can be estimated. When calculating the value, it becomes possible to simultaneously calculate the upper and lower limits of the fatigue characteristic.
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, by a simple method of measuring the hardness and fatigue life of the weld heat affected zone, it is possible to quickly know the fatigue properties of the welded joint, and therefore to guarantee and estimate the fatigue properties of the welded joint of steel materials. It is 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と、前記比較材のうちの少なくとも一部と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 of guaranteeing that the quality of fatigue of a welded joint manufactured using a steel material as a test material is superior to that of a welded joint manufactured using any reference material,
The reference material, the test material and a plurality of comparative materials, after subjected to a heat treatment that reproduces the heat history that the welding heat-affected zone of the welded joint receives during welding, and a step of determining hardness and fatigue properties,
With the reference material after the reproduction heat treatment, the hardness and fatigue properties of at least a portion of said comparison member, a step of deriving a reference expression between the hardness and the fatigue properties,
Hardness and fatigue characteristics of the test material after the reproduction heat treatment, and a step of guaranteeing the quality of the test material, based on the relationship between the reference formula,
Quality assurance method for steel products.
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, subjected to a joint fatigue test, and a step of determining the fatigue characteristics of each welded joint,
From the plurality of comparative materials, further comprising the step of extracting a lower comparative material in which the fatigue characteristics of the welded joint are equal to or less than the reference material,
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 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と、前記比較材のうちの少なくとも一部と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 of estimating the fatigue characteristics of a welded joint produced using a steel material as a test material,
A process of producing a welded joint using a reference material and a plurality of comparative materials and subjecting it to a joint fatigue test, and determining the fatigue characteristics of each welded joint,
A step of obtaining hardness and fatigue properties after subjecting the steel materials corresponding to the reference material and the comparative material, and the test material to heat treatment that reproduces the heat history of the welded heat-affected zone of the welded joint during welding. When,
With the reference material after the reproduction heat treatment, the hardness and fatigue properties of at least a portion of said comparison member, a step of deriving a reference expression between the hardness and the fatigue properties,
Hardness and fatigue characteristics of the comparative material and the test material after the reproduction heat treatment, and, from the reference formula, a step of determining the superiority or inferiority parameter as an index of the fatigue characteristics of the welded joint of each steel material,
From the superiority and inferiority parameter of the comparative material after the reproduction heat treatment, and the fatigue characteristic of the welded joint produced using a steel material corresponding to the comparative material, a step of deriving a fatigue characteristic estimation formula,
Based on the superiority and inferiority parameter of the test material after the reproduction heat treatment, and the fatigue characteristic estimation formula, a step of calculating an estimated value of the fatigue characteristic of a welded joint produced using the test material,
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。 From the plurality of comparative materials, further comprising the step of extracting a lower comparative material whose fatigue properties of the welded joint are equal to or less than the reference material,
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 steel 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 characteristic estimation formula, the fatigue characteristic estimation error is further obtained,
In the step of calculating the estimated value of the fatigue characteristic of the welded joint manufactured using the test material, based on the fatigue characteristic estimation error, the upper and lower limits of the fatigue characteristic are simultaneously calculated,
The fatigue property estimation method for steel according to claim 3 or 4.
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