Usually 1.5% is the upper limit.

B can reduce the freedom of the state of the weld N, improve the HAZ toughness of coarse grained region. TiN particles at temperatures over 1450 ℃, easy to melt, the resulting free N atoms on the HAZ toughness of disadvantage. B and N with the formation of BN, to improve toughness.

Re2O3 of deposited metal in the inclusions are spherical, thinning, and improve the HAZ toughness. In flux after adding the right amount of Re2O3, reduce the number of inclusions. Moreover, REM in the steel to form a stable small O, S compounds, replacing the one hand, TiN particles

Inhibition of austenite grain coarsening, but also act as ferrite nucleation prevents the formation of upper bainite.
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Cr powder added in the welded joints can increase the number of AF, but weaken the impact toughness. Different alloy composition, with the increase in the amount of AF Cr with different degrees of increase, but further increase in Cr content, AF will be FS (ferritewithsecondphase) instead.

Some foreign researchers believe the increase will reduce the amount of Cr (usually suppressed) PF (primaryferrite) of nucleation, because in the AF before the nucleation of intragranular bainite have been free in the grain boundary nucleation.

4 advanced production process control organizations

In order to improve the HAZ toughness of thick plate, the researchers in addition to improving the alloy composition to reduce the Ceq and austenite grain refinement, but also from the production process control of the organization begin to analyze the toughness improvement.

TMCP (Thermo-mechanicalcontrolprocess) technology:  the technology to the deformation of steel, recrystallization and phase transformation effects combined to refine the grain-based, greatly improve the strength and toughness of steel, hot-rolled state to have good low temperature toughness of steel and strong

Degrees. To improve the toughness and weldability, must reduce the carbon content in steel and carbon equivalent, the use of TMCP can make up for the loss of strength, to ensure that steel has sufficient strength and toughness.

Super-OLAC controlled cooling technology: This is the so-called accelerated cooled TMCP application in the sheet production start. The technology in the process of accelerated cooling after rolling theory of cooling rate can be achieved, greatly expanded the traditional cooling technology cooling can

Force. Controlled rolling and controlled cooling technology combination can further reduce the thick of the alloying elements, thus reducing the carbon equivalent, improving welding performance. Do not heat because the process can improve the performance of sheet metal and welding strength, so in the world

Range is referenced. Using this technique, developed by Nippon  Steel to HBL385 HBL325 series from the new low-carbon steel equivalent to ensure the performance of the matrix material. In addition, the technology is also used to produce high-performance steel bridges, steel tanks and pressure vessels