臺灣博碩士論文加值系統

本研究主要目的，在研究 AISI 4130 鋼材之一系列微觀組織的氫助長疲
勞裂縫生長行為。包括肥粒鐵 / 波來鐵、回火麻田散鐵，及變韌鐵組織
。氫在各微觀組織之擴散係數，亦利用電化學實驗量測得知。 本研究之
主旨，在探討一些較為人少研究之氫助長疲勞裂縫生長的重要因素， 其
中包括微觀組織、強度、氫擴散係數、碳化物、肥粒鐵 / 波來鐵組織中
氫擴散之從優路徑、回火麻田散鐵組織之回火溫度， 以及變韌鐵組織之
恆溫處理溫度。 透過各微觀組織之氫助長疲勞裂縫生長，及氫滲透實驗
的分析，得到以下幾點結論: (1) 微觀組織明顯地影響著氫在鋼鐵中的擴
散。 然而，目前無法找出氫滲透行為與氫助長疲勞裂縫生長間的直接關
係。 (2) 對肥粒鐵 / 波來鐵組織的研究顯示，氫擴散路徑中肥粒鐵 /
波來鐵的排列對其擴散係數影響甚深。散亂肥粒鐵 / 波來鐵組織之氫擴
散係數的異向性甚小，而且其數值大於氫沿帶狀組織中之表面及橫斷面方
向之擴散係數， 但小於氫沿縱斷面方向之擴散係數。氫擴散的結果可成
功地解釋肥粒鐵 / 波來鐵之氫助長疲勞裂縫生長行為。(3) 肥粒鐵 / 波
來鐵散亂組織之氫助長疲勞裂縫生長之異向性，仍是很小。然而，肥粒
鐵 / 波來鐵帶狀組織之氫助長疲勞裂縫生長，具有強烈的異向性。 散亂
組織之不同取向試片，其氫助長疲勞裂縫生長速率皆比帶狀組織的高。
(4) 不同恆溫變態所得的變韌鐵組織，其明顯地具有不同的強度及氫滲透
性質。 然而，不同的變韌鐵組織，卻具有相似的氫助長疲勞裂縫生長行
為。 變韌鐵組織之氫助長疲勞裂縫生長速率皆較低溫回火麻田散鐵的高
， 但較高溫回火麻田散鐵組織的低。 (5)不同溫度回火之氫助長疲勞裂
縫生長速率，隨著回火溫度升高而降低。 且低溫回火麻田散鐵組織之氫
助長疲勞裂縫生長出現不尋常的破壞模式。(6)微觀組織因素對氫助長疲
勞裂縫生長具有明顯地影響， 碳化物也具有明顯的影響。 另外，強度因
素對氫助長疲勞裂縫生長的影響，目前無法有系統地歸納出。

The main objective of this research has been to carry out
a systematic study on the influences of various
microstructures of a popular structural steel, AISI 4130
steel, on hydrogen-enhanced fatigue crack propagation. Some
important effects have been discussed in this work,
including those of microstructure, strength, hydrogen
permeation, tempering temperature for tempered martensitic
structures, and isothermal treating temperature for bainitic
structures. In this work, some conclusions could be
outlined: (1) For ferrite/pearlitic structures, the
distribution of ferrite/pearlite along the path of
hydrogen penetration affected hydrogen diffusivity
deeply. Then the results of hydrogen diffusivity can
be applied to explain the hydrogen-assisted fatigue
crack propagation behavior of the banded and random ferrite/
pearlite structures successfully. (2) The variation of
hydrogen-assisted fatigue crack growth rates of specimens
sampled from different orientations for banded ferrite/
pearlitic structure was very significant, slight for
random in the random ferrite/pearlitic structure. (3) A
similar hydrogen-enhanced fatigue crack growth
behavior and a transgranular fracture mode were found in
bainitic structures, though they have different tensile
strength and hydrogen permeation rate. (4) The
hydrogen-assisted fatigue crack propagation rate of
tempered martensitic structures increased as yield strength
increased. In higher strength tempered martensites,
an irregular fracture mode, in which the
intergranular crack propagated easily near surface of
specimen, was found. (5) The microstructural effect was the
dominant factor on the hydrogen-assisted fatigue crack
growth behavior. Alternatively, the strength effects
could not been featured systematically.

Cover
CONTENT
ABSTRACT
CHINESE ABSTRACT
ACKNOWLEDGMENTS
CONTENTS
FIGURE LIST
TABLE LIST
CHAPTER 1 INTRODUCTION
1.1 Microstructural aspects on failure
1.1.1 Microstructural importance in fatigue
1.1.2 Microstructural importance in hydrogen embrittlement
1.2 Motivation of this research
1.3 Objective
CHAPTER 2 OVERVIEW
2.1 Analysis of fatigue crack propagation
2.1.1 Historical development of fatigue sudies
2.1.2 Approaches of fracture mechanics on fatigue
2.1.3 Empirical fatigue crack propagation equations
2.2 Factors influemcing fatigue crack propagation
2.2.1 Stress ratio effects
2.2.2 Crack colsure phenomena
2.2.3 Environmental effects and corrosion fatigue
2.2.4 Typees of corrosion fatigue crack growth
2.3 Hydrogen assisted fatigue crack propagation
2.3.1 Mechanisms of corrosion fatigue
2.3.2 Jjstification for hydrogen embrittlement
2.3.3 Quantitative hydrogen embrittlement models
2.3.4 Importance of bulk charging in hydrogen assisted cracking
2.4 Effects of metallurgical factors on HE and hydrogen assisted FCP
2.4.1 Relationship among CFMHE and SCC
2.4.2 Microstructural effects on CF
2.4.3 HE behavior of ferrite/pearlite steels
2.4.4 Effects of martensitic morphologies on the HE of steels
2.4.5 Microstructural effects on HE
CHAPTER 3 FCP AND PERMEATION TESTS
3.1 AISI 4130 steel
3.2 Fatigue crack propagation test
3.2.1 Selection of test specimens
3.2.2 Servohydraulic fatigue testing systems
3.2.3 Crack length measurenemt techniques
3.2.4 Testing procedures
3.2.5 Set-up of hydrogen charging environment
3.3 Electrochemical permeation test
3.3.1 Trapping theory
3.3.2 Experimental set-up
3.3.3 Mathematical background
3.3.4 Specimen preparing
CHAPTER 4 MICROSTRUCTURES AND PROPERTIES
4.1 Ferrite/pearlite structure
4.1.1 Banded ferrite/pearlite structure
4.1.2 Elimination of banded structure(formation of random F/P structure)
4.1.3 Mechanical properties
4.2 Tempered martensitic structure
4.2.1 Introduction
4.2.2 Tempering of plain carbon steels
4.2.3 Tempering of alloy steels
4.2.4 Effects of heat treatment on the mechanical properties of the tempered martensitic structure
4.3 Bainitic structure
4.3.1 Introduction
4.3.2 Morphology of bainitic structure
4.3.3 Effects of heat treatment on the mechanical properties of the bainitic struct1ure
CHAPTER 5 HYDROGEN PERMEATION AND HYDROGEN ASSISTED FCP BEHAVIOR OF F/P STRUCTURE
5.1 Introduction
5.2 Permeation behavior
5.2.1 Specimen sampling
5.2.2 Effect of banding and inclusion
5.2.3 Effect of ferrite/pearlite alignment
5.3 FCP behavior
5.3.1 Specimen preparation
5.3.2 Anisotropy of FCP behavior
5.4 Hydrogen assisted FCP behavior
5.4.1 Hydrogen assisted FCP behavior
5.4.1 Test condition
5.4.2 Effect of hydrogen-charging environment
5.4.3 Rleative dominance of banding and inclusion
5.4.4 Comparison of banded F/P structure and random F/P structure
5.5 Conclusions
CHAPTER 6 HYDROGEN PERMEATION AND HYDROGEN ASSISTED FCP BEHAVIOR OF TEMPERED MARTENSITIC AND BAINITIC STRUCTURES
6.1 Introduction
6.2 Permeation behavior
6.2.1 Specimen preparation
6.2.2 Effects of tempering temperature for empered martensitic structure
6.2.3 Effects of isothermally treated temperature for bainitic structure
6.2.4 Comparison of tempered martensitic and bainitic structure
6.3 FCP behavior
6.3.1 Specimen preparation
6.3.2 Fatigue crack propagation in air
6.3.3 Fatigue crack propagation under hydrogen charging environment
6.4 Comparison of microstructural effect and strength effect
6.5 Conclusions
CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER WORK
7.1 Conclusions
7.2 Recommendations for furtheer work ]
REFERENCE
INTRODUCTION OF AUTHOR