氮含量与终轧温度对钛微合金化高强钢CGLC700低温冲击韧性的影响

Effect of Nitrogen Content and Final Rolling Temperature on Low-temperature Impact Toughness of Titanium Microalloyed High-strength Steel CGLC700

针对钛微合金化高强钢CGLC700低温冲击韧性差的问题,通过热力学计算与高温原位观察,采用电子背散射衍射、透射电镜、扫描电镜和光学显微镜对含Ti高强钢的夹杂物、第二相粒子、断口形貌和低温冲击韧性等进行了研究。结果表明,含Ti高强钢低温冲击韧性差的原因与钢中大尺寸脆性夹杂物和Ti(C,N)、TiN析出相有关。将钢中w[N]从0.0049%降低至≤0.0035%时,可以有效降低钢中脆性夹杂物的数量和尺寸,从而提高钢材冲击韧性;终轧温度从885~895℃降低至875~885℃,可以促使纳米级TiC第二相粒子析出和大角度晶界的生成,并降低有效晶粒尺寸,从而明显改善钢材的低温冲击韧性;同时降低氮含量至≤0.0035%与终轧温度在875~885℃时,钛微合金化高强钢中平均晶粒尺寸从3.1μm降至2.7μm,小尺寸有效晶粒占比高,大尺寸夹杂物及数密度降低,大角度晶界中占比增长了16.6%,钢材低温冲击功可以从14.75 J提高到37.35 J。

Aiming at the problem of poor low-temperature impact toughness of titanium microalloyed high-strength steel CGLC700,by thermodynamic calculations and high-temperature in-situ observations,as well as the use of electron backscattering diffraction,transmission electron microscopy,scanning electron microscopy,and optical microscopy have been used to investigate inclusions,second-phase particles,fracture morphology,and low-temperature impact toughness of the Ti-bearing high-strength steel.The results show that the reasons for the poor low-temperature impact toughness of Tibearing high-strength steel are related to the large-size brittle inclusions and the precipitation phase of Ti(C,N)and TiN in the steel.When the nitrogen content in steel is reduced from 0.0049%to≤0.0035%,the number and size of brittle inclusions in steel can be effectively reduced,and the impact toughness of steel can be improved.Reducing the final rolling temperature from 885-895℃to 875-885°C can promote the precipitation of nanoscale TiC second phase particles and the formation of large-angle grain boundaries,and reduce the effective grain size,thereby significantly improving the lowtemperature impact toughness of steel.Compared with experimental steel 1#,when the nitrogen content was reduced to≤0.0035%and the final rolling temperature was 875-885°C,the average grain size in titanium microalloyed high-strength steel decreased from 3.1μm to 2.7μm,the proportion of small-size effective grains was higher,the large-size inclusions and number density decreased,the proportion in the large-angle grain boundary increased by 16.6%,and the lowtemperature impact energy of steel could be increased from 14.75 J to 37.35 J.