氮含量对10B21冷镦钢Φ12mm线材淬火硬度的影响

Effect of Nitrogen Content on Quenched Hardness of Φ12 mm Rod Products of Cold Heading Steel 10B21

10821冷镦钢（／％：0．18—0．23C，≤0．10Si，0．60～0．90Mn，≤0．030P，≤0．035S，0．0008～0．0030B，≥0．02A1）的生产流程为50t顶底复吹转炉-LF-280mm×325mm连铸坯-连轧成Ф12mm材。通过检测得出，当钢中氮含量为0．0046％时，该钢淬火后的HRC硬度值为41～43，而当钢中氮含量为0．0081％时，其淬火后HRC硬度值为21～27，小于技术条件要求HRC值38。通过试验得出Ti／N≤8时，随Ti/N增加，钢中硼的收得率显著增加，如钢中氮含量0．0046％时，Ti／N为7．4，硼收得率达90％，钢中氮含量0．0081％时，Ti／N为4．3，硼的收得率不到70％，造成钢中B含量低，淬火后HRC值降低。通过改进BOF和LF操作，使钢中氮含量控制在0．005％以下（0．0039％～0．0041％），Ti／N为7．5—8．1，钢材心部淬火HRC值为40—42，达到用户要求。

The production flowsheet for cold heading steel 10B21 （/% ： 0. 18 -0. 23C, ≤0. 10Si, 0. 60 -0. 90Mn, ≤0. 030P,≤0. 035S, 0. 000 8 - 0.003 0B, ≥0. 02A1） is 50 t top and bottom combined blowing converter-LF-280 mm× 325 mm casting bloom-continuous rolling to Ф12 mm rod products. It is obtained by examination that as nitrogen content in steel is 0. 004 6%, the HRC hardness value of quenched steel is 41 - 43, while as the nitrogen content in steel is 0. 008 1%, the HRC value of quenched steel is 21 -27 that is less than the specification requirement HRC value 38. And it is obtained by test that as Ti/N ≤8, with increasing Ti/N the yield of boron in steel increases obviously, for instance on condition that the nitrogen content in steel is 0.004 6% with Ti/N being 7.4, the yield of boron is up to 90%, and on this condition the nitrogen in steel is 0. 008 1% with Ti/N being 4. 3, the yield of boron in steel is less than 70% led to low bo- ron content in steel and lower HRC value of quenched steel. By improving the BOF and LF operation to control the nitrogen in steel less than 0. 005% （0. 003 9% -0.004 1% ） with Ti/N being 7.5 - 8. 1, the quenched HRC value of core of rod product is 40 - 42 to meet the requirement of user.