Influence of sulphur content in Q345R steel plate

The internal control w(S)<0.015% of Q345R steel sheet is counted. The qualified rate of flaw detection in three ranges of w( S)≤50 × 10^-6 、w( S)  = ( 50 ～ 80)  × 10 10^-6 and w( S)  = ( 80～ 150) × 10^-6 and w(S)=80-150 *10^-6 for stripped and tailing rolled steel sheets in January-June 2012 is shown in Fig. 1. It can be seen that with the increase of sulphur content, the qualification rate of Q345R steel plate is gradually reduced. The qualified rate of flaw detection can reach 97.897% when w (S) <80 *10^-6, but only 95.676% when w (S) >80 *10^-6

Fig. 1 Influence of sulphur content on qualification rate of Q345R steel plate flaw detection
In addition, the statistical results of low sulphur (w (S) < 50 *10^-6 ) test on Q345R steel show that the qualified rate of In addition, the statistical results of low sulphur (w (S) < 50 *10^-6) test on Q345R steel show that the qualified rate of all low sulphur test on Q345R steel is 100%. The internal control requirement of Q345R slab for katalor steel rolling thickness less than or equal to 25 mm is 45% ~ 1.60%. Therefore, the effect of sulfur content on the qualified rate of Q345R steel is also reflected in the influence of manganese-sulfur ratio on the qualified rate of Q345R steel. The qualified rate of Q345R steel plate with different Mn/S ratios for stripping head and tail billet rolling volume from January to June 2012 is calculated as shown in Figure 2. It can be seen that with the increase of W (Mn) / w (S), the qualification rate of Q345R plate detection is increasing gradually. Statistical results show that the ratio of W (Mn) / W (S) < 300 in molten steel of Nangang is large at present. Therefore, while reducing the sulfur content in molten steel, the composition of manganese should be controlled according to the upper limit to ensure that W (Mn) / W (S) is more than 200, which will certainly help to improve the qualified rate of Q345R flaw detection.

Fig. 2 Influence of manganese to sulfur ratio on the qualification rate of Q345R steel plate flaw detection
Sulfur is the most serious element in the center segregation of continuous casting slab. With the increase of sulfur content, the center segregation of continuous casting slab is aggravated, and the probability and quantity of inclusions precipitated in the segregation zone of selective crystallization increase, which seriously affects the qualified rate of Q345R steel plate. It is very advantageous to improve the qualified rate of Q345R steel plate by controlling the final product W (S) below 80×10^-6