What is the steel with through-thickness properties?

In the steel structure using welding connection, when the thickness of the steel plate is not less than 40 mm and bears the tensile force along the thickness direction of the plate, in order to avoid laminar tearing during welding, it is necessary to use a steel that resists laminar tearing (usually referred to as "Z direction steel or steel with through-thickness properties). There is a problem of lamellar tearing of thick plates, so Z Direction (through thickness) test is proposed.

Marking 
The Z-direction steel plate (steel with through-thickness properties)produced in China is marked with Z-direction steel plate grade marks Z15, Z25, Z35 after the parent steel grade. The number after the Z is the index of section shrinkage (%).

The situation when the through-thickness properties of the steel are most likely to be important is in heavily-welded “cruciform” type joints. This is because when welds shrink on cooling the locally imposed strains can reach yield and the parent material must be ductile enough to redistribute these strains. This requires the steel to have an appropriate “Z-quality”.

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