Introduction to the mechanical properties and Z-direction properties of A572Gr50 steel plate

1.Mechnical property for A572Gr50 steel plate:
 

2.Chemical composition for A572Gr50 steel plate (Product Analysis Max%)
 

 3.Z-Directional Properties of A572Gr50 Steel Plate

 What is Z-Directional?

Z-Directional steel: Also known as "lamellar tearing resistant steel," this is commonly referred to as Z-direction performance. In steel structures connected by welding, when the steel plate thickness is 40 mm or greater and subjected to tension along the plate thickness, lamellar tearing-resistant steel (often referred to as "Z-Directional steel") is required to prevent lamellar tearing during welding. Lamellar tearing is a problem with thick plates, so Z-direction performance testing is required.

Z-Directional Properties and Their Impact on the Steel Plate

Steel plates and steel sections are formed by roll forming. Generally, steel used in multi-story steel structures is hot rolled. Hot rolling breaks down the cast structure of the steel ingot and refines the grain size. Bubbles and cracks formed during ingot casting can be welded together under high temperature and pressure, thereby improving the steel's mechanical properties. However, this improvement primarily occurs along the rolling direction. Non-metallic inclusions (primarily sulfides, oxides, and silicates) within the steel are compressed into thin sheets after rolling and remain in the steel plate (generally parallel to the plate surface), causing delamination (interlayering) in the steel plate. This non-metallic interlayering deteriorates the steel's tensile properties along the thickness direction. Consequently, the steel plate's mechanical properties vary in three directions: the best along the rolling direction; slightly worse perpendicular to the rolling direction; and the worst along the thickness direction.

Generally, thicker steel plates are more susceptible to lamellar tearing because thicker plates contain more non-metallic inclusions, thicker welds, and greater welding stress and deformation. To address this issue, Z-direction steel is the preferred choice. This type of steel is made from a specific grade of structural steel (called parent steel) and undergoes special smelting and treatment. Its sulfur content is less than one-fifth that of standard steel, and its reduction of section is greater than 15%. The mechanical properties of a steel plate along the thickness direction (primarily ductility) are referred to as Z-direction properties. The Z-direction properties of steel plates can be determined through tensile testing of specimens, generally measured by reduction of area. Z-direction steel plates produced in my country are designated by the Z-direction steel grade symbol Z25, Z25, or Z25 after the parent steel grade. The number following the Z represents the reduction of area (%).