Evaluation of Hydrogen-Assisted Cracking Behavior of HV670 Steel using Elastic Wave, and Fatigue Life
- Abstract
- The elastic waves generated in ultra-high strength steel (UHSS) under various corrosive solutions were investigated. The threshold stress intensity factor (K_IHAC) for HAC was obtained from ultra-high strength steel (SKD11: HV670) by applying different loads in a solution of 0.057M acetic acid. The frequency characteristics by hydrogen aggregation and crack propagation were analyzed by the time-frequency analysis method using LabVIEW. The K_IHAC of the specimen was determined from the cumulative elastic wave and fracture surface, and the static fatigue limit based on the crack depth was determined using K_IHAC. Regardless of the corrosion solution, elastic waves in a low frequency band, less than 40 kHz, and in a high frequency band, more than 60 kHz, were obtained. The low frequency below 40 kHz was caused by corrosion, while the high frequency above 60 kHz are caused by crack initiation and propagation. The elastic wave in the specimens under the acetic acid solution were caused by HAC-induced crack propagation, but the elastic wave in the specimens under 1.5M H2SO4 + NaCl 0.5M solution or distilled water were strongly affected by corrosion. The frequency band of the elastic wave was divided into dominant frequency below about 50 kHz and above about 60 kHz, regardless of the value of Kc. The low-frequency band below about 50 kHz is the elastic wave due to corrosion, while the high-frequency band above about 60 kHz is the elastic wave caused by crack occurrence and propagation. When K_C was the smallest, the crack in the surface direction propagated slightly, but the crack in the depth direction did not propagate at all. The stress intensity factor at this time was determined as the HAC threshold stress intensity factor (K_IHAC). That is, K_IHAC was determined to be 1.96 MPa√m. The static fatigue limit was determined to be 400 MPa, and the static fatigue limit of the crack specimen can be evaluated using K_(IHAC(a)) = 1.96 MPa√m). The experimental results agreed well with the evaluation results.
- Issued Date
- 2023
- Awarded Date
- 2023-02
- Type
- Dissertation
- Publisher
- 부경대학교
- Affiliation
- 부경대학교 대학원
- Department
- 대학원 재료공학과
- Advisor
- 남기우
- Table Of Contents
- Chapter 1 Introduction 1
References 3
Chapter 2 Elastic Wave Properties in Ultra-High Strength Steel (HV670) exposed to Various Corrosive Solutions 5
2.1 Introduction 5
2.2 Materials and experimental method 6
2.3 Results and Discussion 10
2.3.1 Frequency band under corrosive solution 10
2.3.2 Frequency band under a corrosive solution of 1.5M H2SO4 + 0.5M NaCl 12
2.3.3 Frequency band under distilled water 19
2.3.4 Frequency band under 0.057M acetic acid 26
2.4 Summary 33
References 34
Chapter 3 Threshold Stress Intensity Factor of Ultra-High Strength Steel (HV670) containing Surface Crack by Hydrogen-Assisted Cracking and Cumulative Elastic Wave 36
3.1 Introduction 36
3.2 Material and Experiment Method 38
3.3 Results and discussion 41
3.3.1 Elastic wave obtained from the stress intensity factor K_c=8.11 MPa√m and K_a= 5.56 MPa√m, 41
3.3.2 Elastic wave obtained from the stress intensity factor K_c=3.02MPa√m and K_a= 2.07 MPa√m 48
3.3.3 Elastic wave obtained from the stress intensity factor K_c=2.86MPa√m and K_a= 1.96 MPa√m 55
3.4 Summary 63
References 64
Chapter 4 Evaluation of Fatigue Life of Ultra-High Strength Steel Under Stress Corrosion Environment 67
4.1 Introduction 67
4.2 Material and experimental method 69
4.2.1 Specimen 69
4.2.2 Determination of K_IHAC based on elastic wave 71
4.2.3 Determination of static fatigue limit 73
4.2.4 Fatigue limit evaluation of stress corrosion cracking 73
4.2.5 Fracture surface observation 74
4.3 Results and discussion 75
4.3.1 K_(IHAC(s)) 75
4.3.2 Static fatigue limit of smooth specimen 81
4.3.3 Static fatigue limit of cracked specimen 83
4.4 Summary 87
References 88
Chapter 5 Conclusions 90
Publication Paper of Journal 92
Publication Paper of Proceeding 92
Acknowledgement 94
- Degree
- Doctor
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