Low welding crack sensitivity Q690CF steel plate

Q690CF steel plate refers to a kind of steel with yield strength grade higher than 690MPa and low welding crack sensitivity.

Q690CF steel plate, also known as CF (Crack Free) steel, is a kind of steel with low carbon equivalent, low Pcm value and excellent welding performance. Generally, no cracks will appear when welding Q690CF steel without preheating or under low preheating conditions.

Chemical composition of Q690CF steel plate:
Q690CF hot-rolled steel plate, the chemical composition is: C: 0.05-0.08%, Si: 0.22-0.30%, Mn: 1.6-2.0%, Al: 0.2-0.35%, Cr: 0.10-0.35%, Mo: 0.20-0.35%, Ni: 0.1-0.4%, Cu: 0.15-0.3%, Nb: 0.025-0.045%, V: 0.01-0.03%, Ti: 0.005-0.03%, P ≤ 0.010%, S ≤ 0.008%, and the remainder is Fe and inevitable impurities.
Note: The welding crack sensitivity index Pcm value is not greater than 0.20%.

C is the most important solid solution element in low carbon steel. It can even be supersaturated and dissolved in bainite matrix with high dislocation density, which has the effect of solution strengthening; In addition, it combines with the elements of strong carbon nitrogen compounds to form a dispersion fine separated phase, which has the effect of separation strengthening; However, the increase of carbon content will significantly deteriorate the welding function of the steel and is not conducive to impact resistance, so the carbon content in Q690CF steel is controlled at 0.05-0.08%.