بررسي آزمون خستگي و شكست نگاري با سيكل كم جوش لب به لب الكترود دستي فولاد كم آلياژ در نقاط توقف و شروع قوس

Fatigue Testing and Fractography of Manual Butt Fusion Welding of Low-Alloy Steel for Stopping and Starting Arc

در اﯾﻦ ﺗﺤﻘﯿﻖ آزﻣﻮن ﺧﺴﺘﮕﯽ و ﺷﮑﺴﺖ ﻧﮕﺎري ﮐﻢ ﭼﺮﺧﻪ در ﻣﻨﺎﻃﻖ ﭘﯿﻮﺳﺘﻪ ﺟﻮﺷﮑﺎري اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﺑﺪﯾﻦ ﻣﻨﻈﻮر ﻓﻮﻻد ASTM A633 ﮔﺮﯾﺪ D، ﺑﻪ روش ﺟﻮﺷﮑﺎري ﻗﻮس اﻟﮑﺘﺮﯾﮏ دﺳﺘﯽ ﺑﻪ ﺻﻮرت ﻟﺐ ﺑﻪ ﻟﺐ ﺟﻮﺷﮑﺎري ﺷﺪه اﺳﺖ. از ﻧﻘﺎﻃﯽ ﮐ ﻗﻮس ﭘﯿﻮﺳﺘﻪ ﺗﺪاوم داﺷﺘﻪ و از ﻧﻘﺎﻃﯽ ﮐﻪ ﻗﻮس ﻗﻄﻊ و دوﺑﺎره ﺑﺮﻗﺮار ﺷﺪه ﺑﻮد، ﻧﻤﻮﻧﻪ ﻫﺎﯾﯽ ﺑﺮ اﺳﺎس اﺳﺘﺎﻧﺪارد ASTM E466 ﺑﺮاي اﻧﺠﺎم آزﻣﻮن ﺧﺴﺘﮕﯽ ﺗﺤﺖ ﺳﯿﮑﻞ ﮐﻢ و ﻫﻤﭽﻨﯿﻦ ﺷﮑﺴﺖ ﻧﮕﺎري ﺑﺮ روي ﻧﻤﻮﻧﻪ ﻫﺎ اﻧﺠﺎم ﭘﺬﯾﺮﻓﺖ. ﻧﺘﺎﯾﺞ ﺣﺎﺻﻠﻪ ﻧﺸﺎن ﻣﯽ دﻫﺪ ﮐﻪ ﺳﯿﮑﻞ ﺣﺮارﺗﯽ ﺟﻮﺷﮑﺎري ﻧﺎﻣﻨﺎﺳﺐ ﺑﺎﻋﺚ اﯾﺠﺎد ﺳﺎﺧﺘﺎر ﻓﺮﯾﺖ داﻧﻪ درﺷﺖ و ﻓﺮﯾﺖ وﯾﺪﻣﻦ اﺷﺘﺎﺗﻦ در ﻧﻘﺎط ﺗﻮﻗﻒ و ﺷﺮوع ﻗﻮس ﮔﺮدﯾﺪه اﺳﺖ. در ﻧﻘﺎط ﺗﻮﻗﻒ و ﺷﺮوع ﻗﻮس ﺑﻪ دﻟﯿﻞ اﯾﺠﺎد ﺳﺎﺧﺘﺎرﻫﺎي ﻓﺮﯾﺖ ﻣﺮزداﻧﻪ اي درﺷﺖ، آﺧﺎل و ﺗﺨﻠﺨﻞ ﭘﺪﯾﺪ آﻏﺎز ﺗﺮك ﺗﺸﺪﯾﺪ ﮔﺮدﯾﺪه و اﯾﺠﺎد ﺳﺎﺧﺘﺎرﻫﺎي ﻓﺮﯾﺖ وﯾﺪﻣﻦ اﺷﺘﺎﺗﻦ ﺑﺎﻋﺚ ﺗﺴﺮﯾﻊ در رﺷﺪ ﺗﺮك ﺷﺪه اﺳﺖ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن دﻫﻨﺪ ﮐﺎﻫﺶ اﺳﺘﺤﮑﺎم در اﯾﻦ ﻧﻤﻮﻧﻪ ﻫﺎ ﻣﯽ ﺑﺎﺷﺪ. اﮔﺮ ﭼﻪ در اﯾﻦ ﻧﻘﺎط ﺳﺨﺘﯽ و اﺳﺘﺤﮑﺎم ﮐﺸﺸﯽ ﺑﯿﺸﺘﺮ از ﻧﻤﻮﻧﻪ ﻫﺎﯾﯽ اﺳﺖ ﮐﻪ ﻗﻮس ﭘﯿﻮﺳﺘﻪ ﺑﺮﻗﺮار ﺑﻮده اﺳﺖ.

In this study, the low-cycle fatigue properties and fractography for continuously welded areas have been investigated. For this purpose, ASTM A633 steel grade D is welded by manual butt fusion welding. From continued arc points as well as interrupted and re-established arc points, samples were prepared according to the ASTM E466 standard for low cycle fatigue testing and fractography. According to the result, inappropriate welding thermal cycles have resulted in the formation of a large grain ferrite and Widmanstätten ferrite at the stopping and starting of the arc. At the stopping and starting of the arc due to the creation of large granular ferrite structures, the inclination and porosity phenomenon has intensified, and the formation of Widmanstätten ferrite has accelerated the growth of cracks. The results indicate decreased strength in these samples, while the stiffness and tensile strength are more than continued arc samples.