An isotropic material, by definition, is one which has the same properties in all directions. An

anisotropic material in contrast is one which has unequal properties in at least two directions. Many hot-rolled, normalized, annealed, quenched, and tempered structural and pressure vessel steels are three dimensionally anisotropic to some degrees. Some are anisotropic to such an extent that their weldability is degraded in the through-thickness direction.

(1)Thermomechanical-control process .

(TMCP) steels are widely used in steel constructions for their high qualities such as fine grain, high strength, and excellent weldability. However, it is found that during manufacturing, rolling causes anisotropy in the TMCP steel plate where material properties such as elastic constants as well as tensile and fracture strengths change in the testing direction

(2)Anisotropic properties of rolled steel plates are related to pancake inclusions in the rolling direction, residual stresses, and mechanical fibering.

(3)S355N is a type of high strength and lowalloyed normalized steel. It is widely used in ship

structures, bridge constructions, and offshore structures in which weldability is a more important

parameter in the soundness of the construction.

 

And microalloyed S355N steel plates of a thickness range of 12-50mm are being widely used in its construction. Regarding the fact that anisotropy in thin plates is more noticeable in the event of complicated and detrimental defects or in lamellar tearing, a thin plate of 25mm was selected as a candidate material to study its properties in three directions and the results were compared with other anisotropic steel plates currently used in similar structures.

 

The chemical composition of the S355N steel as followings:

C: 0.2, Si:0.5, Mn:1.15, Al: 0.02, V :0.12, Ti:0.03, Nb:0.05, S :0.017, Cr:0.3

Nowadays, rare earth elements are used to control inclusion morphology in spite of high levels

of sulfur in steels so that the reduction in area remains considerably high and does not decrease

severely by increasing sulfur content. Even though S355N steel had a sulfur content of 0.017%, it was tougher showing the progress made in manufacturing modern fine grained and rare earth treated steels.

 

However recent developments in steel processing have resulted in reduced inclusion levels

and more controlled shapes of inclusion such as is observed in S355N steel. The elongated shape of inclusions had great detrimental effects on mechanical properties.What's more the modern clean steels such as S355N are more isotropic and have better mechanical properties in the through-thickness direction.