Effects of S and TO on strength and toughness of high purification low alloy steel plates

The effect ofS on strength and toughness of low alloy steel plates in which sum ofP,N, TO is less than 8×10^-5 and the effect of TO on strength and toughness of the steel plates in which sum ofS,P,N is less than 7×10^-5 were investigated. It is found that the strength of the steel plates decreases with increasingS content whenS is less than 4×10^-5. WhenS varies within the range of 4×10^-5-1.2×10^-4,S has no significant effect on strength of the steel. The strength of the steel plates increases with increasing TO content when TO is less than 30×10^-6, but decreases with increasing TO when TO is more than 3×10^-5.The difference between the LETT in plate length direction and LETT in width direction decreases with decreasingS content. However, even whenS is decreased to 9×10^-6, the difference of the LETT is still 16℃. When TO varies between 1.8×10^-5 and 5.2×10^-5, the low temperature impact toughness of the steel plates slowly decreases with TO increasing. When TO increases to more than 5.2×10^-5, the low temperature toughness of the steel rapidly decreases with increasing TO content.