氮化物对齿条钢强度及冲击韧性的影响

Effect of nitride on strength and impact property of rack stee

钢锭冶炼齿条钢时,由于浇铸过程中吸氮,钢中的氮含量偏高,影响钢中固溶硼含量,降低了钢板淬透性,影响了钢板心部性能。为了提高钢锭轧制齿条钢的心部强韧性,通过添加铝或者钛元素消耗钢中的氮,确保钢板中有足够的固溶硼,提高钢板淬透性,增加钢板心部的回火索氏体比例。通过钢板性能与组织对比发现加铝和加钛均能提高钢板的淬透性和强度,加钛的钢板淬透性更好,强度更高,但是钢板的低温冲击吸收能量下降。分析钢板的冲击断口发现钢板中有大颗粒的TiN夹杂物,夹杂物与基体之间或者夹杂物本身就存在裂纹,成为冲击试验的裂纹源,降低了钢板的韧性。对比加铝与加钛钢板中尺寸为2μm以上夹杂物,加钛钢中存在大量的大颗粒TiN夹杂,最大夹杂物尺寸超过15μm,加铝钢板中仍有少量的TiN夹杂,但是TiN夹杂物数量和尺寸变小,同时AlN并未明显增加。对加铝钢板中铝元素与加钛钢板中钛元素进行原位分析对比,发现铝元素为心部负偏析,并且偏聚程度较低,钛元素为心部正偏析,并且钛元素的均匀性更差,存在局部偏聚。热力学计算表明,通过钛元素固氮时,将在凝固前沿析出TiN,析出温度较高;而采用铝固氮时,若铝的质量分数不小于0.08%,AlN在固态中析出,析出温度高于BN,能够保证钢板中的固溶硼含量,确保钢板的淬透性,并控制钢中TiN析出物的尺寸。

When smelting rack steel with steel ingots,due to the absorption of N during the casting process,the N content in the steel is relatively high,which affects the solid solution B content in the steel,reduces the hardenability of the steel plate,and affects the performance of the center the steel plate.In order to improve the strength and toughness matching of the steel ingot rolling gear steel,the addition of Al or Ti elements to reaction with N in the steel ensures sufficient solid solution B in the steel plate,improves the hardenability of the steel plate,and increases the proportion of tempered sorbite in the center of the steel plate.By comparing the properties and microstructure of steel plates,it was found that both adding Al and Ti can improve the hardenability and strength of the steel plate.The steel plate with Ti has better hardenability and higher strength,but its low-temperature impact absorption energy decreases.Analyzing the impact fracture surface of the steel plate,it was found that there are large particles of TiN inclusions in the steel plate.Cracks exist between the inclusions and the matrix or between the inclusions themselves,which become the source of cracks in the impact test and reduce the toughness of the steel plate.Comparison of steel plates with Al and Ti added Statistical analysis of inclusions above 2μm shows that there are a large number of large particle TiN inclusions in Ti steel,with a maximum inclusion size exceeding 15μm.There are still a small amount of TiN inclusions in the Al added steel plate,but the number and size of TiN inclusions have decreased,and AlN has not significantly increased.In situ analysis and comparison were conducted between the Al element in the Al steel plate and the Ti element in the Ti steel plate.It was found that the Al element is negatively segregated at the center and has a lower degree of segregation.The Ti element is positively segregated at the center and has poorer uniformity,with local segregation.Thermodynamic calculations indicate that when titanium is used for nitrogen fixation,TiN will precipitate at the solidification front,resulting in a higher precipitation temperature;when using aluminum nitrogen fixation,if the mass fraction of aluminum is not less than 0.08%,AlN precipitates in the solid state at a temperature higher than BN,which can ensure the solid solution boron content in the steel plate,ensure the hardenability of the steel plate,and control the size of TiN precipitates in the steel.