複合組織鋼의 摩擦 熔接部 및 熱影響部의 疲勞破壞特性에 관한 硏究 = (A) Study on the Characteristics of Fatique-Crack of Welded Zone and Heat Affected Zone of Friction-Welded Dual Phase Steel

다국어 초록 (Multilingual Abstract)

The weight reduction and reliability, stability of various steel materials has been used in industrial machinery have become a great of importance under the influence of development in industry.
For this reason, a study on affection of microscopic structure come up to fatigue strength and mechanical properties of dual phase steel have been performed by the reporter at great interest. But there are few paper for the characteristics of welded dual phase steel. It is necessary to study the change of phase and the characteristics of fatigue strength of welded zone and heat affected zone of welded dual phase steel.
In this study, dual phase steel be welded by friction welding machine of brake type, and each of tensile specimens and fatigue specimens were conducted by universal testing machine and rotary bending fatigue test machine.
This paper described an experimental study of friction-welded dual phase steel on change of phase, tensile strength, hardness test, fatigue strength and fracture behaviours.
Dual phase steel were fabricated by SS 41 steel.
Main results obtained from this study are as follows;
1. Microstructure of welded zone is changed to ferrite and pearlite from ferrite and martensite by welding heat. micro-vickers hardness of welded zone is higher than that of base metal zone and heat affected zone.
2. Micro-vickers hardness of heat affected zone is lower than that of welded zone and microstructure of heat affected zone is changed to fine martensite and ferrite by heating cycle of welding.
3. Fatigue limits of heat affected zone is a little higher than that of welded zone and base metal zone. There are no difference of fatigue limit of base metal zone and welded zone.
Fatigue strength of welded zone is similar to that of base metal zone.
4. At high ΔK region (ΔK>19MPa·√(m)), fatigue-crack propagation velocity of heat affected zone is slower than that of welded zone and base metal zone, and the difference of fatigue-crack propagation velocity is smaller than that of high ΔK region.
5. The crack occure to the notch in heat affected zone first, but the final fracture surface is the surface of welded zone.
6. It is obvious that heat affected zone of friction-welded dual phase steel superior to welded zone and base metal zone in fatigue strength and resistance of fatigue crack propagation. The above mentioned facts are contrary to theory that heat affected zone of general metals is weaker than welded zone and base metal zone.

목차 (Table of Contents)

• 目次
• Ⅰ. 緖論 = 2
• Ⅱ. 實驗裝置 및 方法 = 4
• 1. 素材熱處理 및 試驗片 = 4
• 2. 實驗裝置 = 12
• 3. 實驗方法 = 14
• Ⅲ. 實驗結果 및 考察 = 15
• 1. 摩擦熔接部의 組織變化 및 硬度分布 = 15
• 2. 疲勞强度 및 疲勞크랙傳播 特性 = 18
• 3. 疲勞破斷面 考察 = 22
• Ⅳ. 結論 = 28
• 參考文獻 = 30
• SUMMARY = 33