報告書番号

T97019

タイトル（和文）

ボイラ溶接部余寿命評価法の開発（第３報：溶接熱影響部タイプＩＶき裂発生メカニズムの解明）

タイトル（英文）

DEVELOPMENT OF A REMAINING LIFE ASSESSMENT METHOD FOR BOILER WELDMENT PARTS (PART3: CLARIFICATION OF TYPE IV CRACKING MECHANISM IN HEAT AFFECTED ZONE OF WELDMENTS UNDER CREEP-FATIGUE LOADING CONDITION)

概要 （図表や脚注は「報告書全文」に掲載しております）

ボイラ機器の経年化が進む中で，溶接熱影響部細粒域でのタイプＩＶき裂の発生が報告されており，ボイラ溶接部に対する的確な余寿命評価法の開発が重要な課題とされている。本研究では，クリープ疲労条件下でのタイプＩＶき裂の発生メカニズムを明らかにするため走査型電子顕微鏡内試験による損傷過程の連続観察およびキャビティ成長の理論的検討を行った。細粒部において損傷初期に発生した擬球状キャビティが４ｍｍ程度で，き裂状キャビティへと遷移して１０ｍｍ程度まで成長を続け，その後微小き裂として成長しタイプＩＶき裂の発生に到ることが明らかとなった。観察結果と理論的検討に基づき，擬球状およびき裂状キャビティ成長モデルを提案した。同モデルによってタイプＩＶ領域のキャビティ成長過程を定量的に推定できることを示した。

概要 （英文）

UNDER THE CONDITION THAT AGING OF BOILER COMPONENTS PROCEEDS AND SOME TYPE IV CRACKING INCIDENTS WERE RECENTLY REPORTED, DEVELOPMENT OF AN ACCURATE REMAINING LIFE EVALUATION METHOD FORBOILER WLDMENT PARTS IS ONE OF THE IMPORTANT SUBJECTS FOR THE UTILITIES. IN THIS STUDY, IN ORDER TO CLARIFY TYPE IV CRACKING MECHANISM UNDER CREEP-FATIGUE LOADING CONDITION, CONTINUOUS OBSERVATIONS OF EXTENSIONPROCESSES BY A TESTING MACHINE IN A SEM WERE PERFORMED AND CAVITY GROWTH MECHANISM WAS DISCUSSED BASED ON THEORETICAL CONSIDERATION. MICRO DAMAGE EXTENSION PROCESS OF TYPE IV CRACKING WAS CLARIFIED AS FOLLOWS. SPHERICAL SHAPE CAVITIES INITIATE AND GROW UP TO THEIR LENGTH OF 2MM ONGRAINBOUNDARIES IN FINE GRAIN REGIONS AT INITIAL STAGE OF DAMEGE AND THESE CAVITIES CHANGE THEIR SHAPE TO CRACK-LIKE TO GROWTH UNTIL THEIR LENGTH REACH 10MM. THEN MICROCRACKS ARE FORMED ON THE GRAINBOUNDARIES ANDGROW TO MACRO CRACKS BY COALESCING EACH OTHER. BOTH SPHERICAL AND CRACK-LIKE CAVITY GROWTH MODELS WERE PROPOSED BASED ON THE OBSERVATION RESULTS AND THE THEORETICAL CONSIDERATIONS. IT WAS DEMONSTRATED THAT CAVITYGROWTH BEHAVIOR COULD BE PREDICTED QUANTITATIVELY BY THE PROPOSED MODELS.

報告者

キーワード