加热工艺对Nb-Ti微合金钢奥氏体晶粒长大的影响

 为了解加热制度对Nb Ti微合金钢的奥氏体晶粒长大和析出行为的影响，采用OM、TEM和EDS分析技术，研究了Nb Ti微合金钢在不同加热温度和保温时间的奥氏体晶粒长大行为，以及微合金元素碳氮化物析出行为。结果表明，随加热温度升高，奥氏体晶粒尺寸逐渐长大，当加热温度超过1 200 ℃时奥氏体晶粒尺寸快速长大。随保温时间延长，奥氏体晶粒尺寸逐渐长大，当保温时间超过2.0 h时奥氏体晶粒尺寸快速长大。EDS分析显示Nb Ti钢中的析出物为(Nb，Ti)(C，N)复合相，随着加热温度升高和保温时间延长，析出相体积分数减少，尺寸增大，从而减弱对奥氏体晶粒的细化作用；Nb Ti微合金试验钢合适的加热温度范围为1 150～1 200 ℃，保温时间低于2.0 h。

Effect of heating process on grain growth of#br# Nb Ti microalloyed steel

 In order to understand the effects of heating schedule on the austenite grain growth and precipitation behavior，the OM，TEM and EDS were used for studying austenite grain coarsening behavior and microalloying carbonitrides precipitation behavior of Nb Ti test steel at different of heating temperature(1 150，1 200 and 1 250 ℃) and holding time(0.5，1.0，2.0 and 3.0 h). The experimental results showed that the austenite grain size grew up gradually with the increasing of heating temperature，and the austenite grain grew rapidly when the heating temperature exceeded 1 200 ℃. With the increasing of holding time，the average austenite grain grew up gradually，and the austenite grain grew rapidly when the holding time exceeded 2.0 h. EDS results showed that the precipitates are composite phase (Nb，Ti)(C，N)，however the amounts of precipitate was reduced and the sizes of precipitate increased at higher heating temperature and longer holding time，consequently，the effects of precipitate on austenite grain was decreased. The heating temperature at 1 150 1 200 ℃ by holding less than 2.0 h will be more appropriate for Nb Ti test steel.