焊接接頭是焊縫和熱影響區的總稱。
Welding joint is the floorboard of welding seam and heat affected zone.
電弧焊接時，焊接電弧使焊件局部加熱和熔化，同時加入填充金屬(焊條或焊絲)，形成金屬熔池，並不斷把熱量傳給周圍冷的母材金屬。
Arc welding, the welding arc make welding and local heating and melting, while adding a filler metal (welding rod or wire), the formation of metal molten pool, cold and constantly pass quantity of heat to the surrounding of the base metal.
當電弧移開後
，熔池的溫度迅速降低，熔池中液體金屬凝固成焊縫。
After the arc removed, quickly reduce the temperature of the molten pool, liquid metal in the molten pool solidified into a weld.
由於熱傳導的作用，母材将受到不同程度的加熱和冷卻，相當於進行瞭一次熱處理，使其組織和性能發生瞭變化，這部分金屬所占的區域就稱爲焊縫的熱影響區。
Due to the effect of heat conduction, the base will be subject to different degree of heating and cooling, equivalent to a heat treatment, the microstructure and property has changed, this part of the metal of the area is called the weld heat affected zone.