A subsurface terrace and step-like crack in the base metal with a basic orientation parallel to the wrought surface caused by tensile stresses in the through thickness direction of the base metal weakened by the presence of small dispersed, planar shaped, nonmetallic inclusions parallel to the metal surface.

Lamellar tearing is a cracking phenomenon that occurs in welds joining rolled steel products. Lamellar cracks or tears occur most often during fabrication where weld shrinkage strains exceed the strength of the base metal in the through-thickness direction of the steel.

All steels contain nonmetallic inclusions in varying amounts. Hot-rolled steels may contain other internal imperfections such as porosity, seams, or laminations. When the steel is rolled to the desired shape for fabrication, these inclusions and imperfections are elongated in the direction of rolling. Internal seams and tears may or may not be “healed” (welded together by the rolling action). These defects are likely to occur in

thick sections where the mechanical deformation of the internal seams or tears may not be sufficiently worked to “heal” the defects. The specified strength of these steels is always measured in the direction of rolling. The strength of rolled steels in the through-thickness direction (perpendicular to the direction of rolling) is considerably less than the strength obtained in the direction of rolling.

The contraction or shrinkage of deposited weld metal during cooling sets up localized strains in the base metal. These strains may exceed the strength of the base metal in the through-thickness direction, resulting in lamellar tearing. Welds that require the deposition of large amounts of filler metal tend to degrade the tensile properties of the base metal and contribute to lamellar tearing. Highly restrained joints are also susceptible to lamellar tearing and should be welded with caution.

The design of welded joints must take into account the direction of rolling. Welding to members in the through-thickness direction must be avoided, if possible.

Where this is unavoidable, the joint should be detailed to reduce the possibility of lamellar tearing resulting from welding. Figure L- 1 illustrates susceptible joint details.

Recognizing lamellar tearing may be difficult since the tearing is internal, like underbead cracking. Corner joints and T-joints are the most susceptible to lamellar tearing, but joint details can be modified to minimize it. If there is any question that subsurface tearing exists, then nondestructive methods should be used to examine the base metal.

 

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