通过观察焊接热循环冷却过程中不同温度取样直接淬火后的微观组织, 研究了焊接热影响区(HAZ)晶内针状铁素体(IAF)的形核长大过程, 论证了针状铁素体分割原奥氏体晶粒及细化晶内组织的机理. Auger电子能谱(AES)证实, 在TiOx-MnS型复合夹杂物边界附近存在贫Mn区, IAF易于在这类复合夹杂物上形核, 单个复合夹杂物能够诱导多个IAF形核, 随着冷却过程中温度的降低, 形核后的IAF逐渐长大. 淬火马氏体和贝氏体在生长过程中会与IAF发生碰撞, 使其发生变形, 但不能穿过IAF. 正是由于IAF分割了原奥氏体晶粒, 阻碍了晶内其它微观组织的生长, 焊接热影响区的微观组织得到细化.
Nucleation and growth of intragranular acicular ferrites (IAFs) in heat-affected-zone (HAZ) have been investigated by the observation of microstructures quenched at different temperatures during the cooling process of welding thermal cycle. It is proved that IAFs can divide the prior austenite grains and refine the intragranular microstructures. AES show that there is a Mn-depleted-zone near the interface of TiOx-MnS complex inclusion. IAFs prefer to nucleate on the complex inclusion, and a single inclusion can usually induce several IAFs to nucleate. IAFs grow up with lowering of the temperature during the cooling process. Quenched martensite and bainite could collide with the IAFs and make them deform, but the< quenched martensite and bainite can not penetrate through the IAFs. IAFs divide the prior austenite grain and restrain the growth of other intragranular microstructures, and therefore HAZ's microstructure is finally refined effectively.
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