Precipitation and Solid Solution of Titanium Carbonitride Inclusions in Hypereutectoid Tire Cord Steel

The properties of titanium carbonitride Ti（CxN1-x） inclusions precipitated during solidification of tire cord steels and the thermodynamic conditions for their decomposition and solid solution during billet heating were investigated using a thermodynamics method. The solid solution of Ti（CxN1-x） inclusions during high-temperature heating was also studied experimentally. The results revealed that： （1） the higher the content of carbon in the tire cord steel is, the greater the value of .r in the Ti（CxN1-x） inclusions is; （2） the higher the content of carbon in the tire cord steel is, the earlier the Ti（CxN1-x） inclusions precipitated during the solidification process and the lower the solidification front temperature is during precipitation; （3） when an 82A steel sample was heated to 1087℃, the Ti（CxN1-x） inclusions possess the thermodynamic conditions of decomposition and solid solution; and （4） when 82A samples were heated to 1150 and 1 250℃, the total number of Ti（CxN1-x） inclusions larger than 5μm in diameter decreased by 55.0% and 70.3%, respectively. In addition, although smaller inclusions with diameter less than 2 μm continued to decompose when the sample was heated at 1 250℃ for 2 h and then cooled to 1000℃ in the furnace, the number of inclusions larger than 5 μm in diameter increased.

Effect of Carbon Content on Ti Inclusion Precipitated in Tire Cord Steel

The precipitation of TiN inclusion during solidification of different carbon content of 0.72%, 0.82% and 0.95% in tire cord steel is thermodynamically studied respectively. The results show that the carbon content has obvious effect on TiN inclusion precipitated in tire cord steel of different strength levels. With the carbon content of tire cord steel increasing, the temperature before solidifying reduced gradually and the required activity product of titanium and nitrogen for TiN inclusion precipitation also declined gradually. With the same condition of initial Ti and N content in liquid steel, the size of TiN inclusion precipitated in tire cord steel of higher carbon content is bigger than that of lower carbon content. In order to control the harmful effects on processability of TiN inclusion precipitated in hypereutectoid tire cord steel of the ultra high strength level, the measures of smelting process must be taken to further reduce the titanium and nitrogen content in liquid steel.

帘线钢SWRH82A铸坯加热过程中钛夹杂的固溶

根据热力学和动力学理论，研究了过共析帘线钢SWRH82A铸坯中钛夹杂固溶的条件．研究表明：（1）当SWRH82A铸坯加热温度达到1347K时，奥氏体中TiN具备固溶的热力学条件；（2）当加热温度达到1360K时，Ti（C，N）夹杂将开始溶解；（3）在1423～1523K的加热升温阶段，由于钛夹杂的分解并向奥氏体中扩散固溶，使得小颗粒钛夹杂逐渐消失，大颗粒钛夹杂尺寸变小；在铸坯高温加热后的冷却降温过程中，固溶在奥氏体深处的Ti和N会重新结合析出TiN夹杂，但缺少继续长大的动力学条件；固溶在残余钛夹杂周边奥氏体中的n和N会以残余钛夹杂为核心不断析出长大．

碳含量对帘线钢凝固析出TiN夹杂的影响

对含碳量(质量分数)分别为0.72%、0.82%和0.95%的帘线钢凝固析出TiN夹杂进行热力学研究,结果表明:碳含量对于不同强度级别的帘线钢中TiN夹杂的析出有着明显的影响.随着帘线钢碳含量增加,凝固前沿温度逐渐降低,析出TiN夹杂所需的氮钛活度积也逐渐下降.在相同的钢液初始Ti、N含量条件下,较高碳含量的帘线钢中析出的TiN夹杂尺寸会大于较低碳含量帘线钢中析出的TiN夹杂尺寸.为了控制超高强度级别的过共析帘线钢中TiN夹杂的析出对帘线钢加工性能的有害影响,必须通过冶炼工艺进一步降低钢液中的钛、氮含量.

SWRH 92A帘线钢中异相形核TiN复合夹杂析出机制

高碳帘线钢中析出的非金属夹杂物如钛夹杂,对钢材疲劳强度影响巨大。系统分析过共析帘线钢中钛夹杂的析出行为对控制夹杂物形成及产品质量提升尤为重要。结合形核理论以及热力学耦合模型,对SWRH 92A帘线钢盘条存在的Al_(2)O_(3)-TiN复合夹杂物的形成机制进行了研究。结果表明:TiN夹杂在钢液凝固进程凝固分数约为0.866(温度为1457 K)时开始析出;凝固前期Ti、N偏析比基本相当,然而当凝固接近结束时Ti的偏析比明显大于N,分别为6.059和2.367×10^(-6)。TiN夹杂物形成过程中,其异相形核功小于均相形核功,异相形核半径大于均相形核半径,并且形核功与形核半径变化曲线在1457 K时均达峰值。呈球形形态的Al_(2)O_(3)夹杂在TiN析出之前就已经析出,并且尺寸较小的Al_(2)O_(3)将被推动至凝固前沿被TiN捕获并以此为核心析出长大最终形成Al_(2)O_(3)-TiN复合夹杂。

过共析帘线钢中Ti夹杂的析出热力学与形成机制

过共析帘线钢中析出的含Ti夹杂对钢丝拉拔性能产生有害影响,研究钢中Ti夹杂的析出行为对夹杂物性质控制以及钢材质量提高具有重要意义。考虑夹杂物析出对凝固前沿溶质浓度和温度影响下,基于传统Ohnaka模型建立了相应的耦合模型并以此计算了92级过共析帘线钢中TiN夹杂的析出热力学。结果表明,耦合模型条件下TiN夹杂的析出时间较传统Ohnaka模型有所提前,冷却速率越大,析出越早;析出之后,凝固前沿N浓度仍会增加,而Ti浓度逐渐减小。钢锭中含Ti夹杂存在形式复杂多样,既包含单相TiN,也包含Ti_(x)O_(y)-TiN、TiN-MnS、Ti_(x)O_(y)-TiN-MnS等复合夹杂。通过计算还发现Ti_(x)O_(y)在钢液中会优先析出;之后随着凝固的进行,TiN和MnS相继析出;结合原子错配度计算得出了钢中含Ti夹杂可能的析出机制。