The law of increasing nitrogen by RH withdrawing pump and the effect of nitrogen content on inclusions in ultra-low carbon enamel steel are studied. The results show that the time of increasing nitrogen by RH withdrawing pump ≤ 25 min

the relationship between the time of withdrawing pump and the nitrogen content in steel is basically in accordance with a quadratic formula γ = -0. 226 x

2

+ 9.429 x +31.21. The inclusions in enamel steel are mainly the second phase precipitates containing Ti and a small amount of Al

2

0

3

particles. The main composition of small inclusions is TixS

and that of large inclusions is TiN. The nitrogen content of conventional enamel steel is 0.003 8%

and the nitrogen content of two nitrogen increased enamel steel is 0.010 8% and 0. 012 7%. The total inc

lusions in the corresponding steel are 355. 61

545. 74 and 558. 77μm

2

/mm

2

respectively. The number of inclusions in each size range in conventional enamel steel is the least. Considering hydrogen storage property and RH nitrogen increasing time of enamel steel

the nitrogen content in steel is suitably controlled around 0. 01% .