Primary processing Discontinuities

Question 1

Burst

Answer 1

Rolling, forging and extruding. A burst is a crack or split that opens up during forming when the material can’t deform plastically fast enough and instead tears.

Question 2

Cupping

Answer 2

Rolling, forging and extruding. Cupping occurs when internal tensile stresses during drawing or extrusion cause the center of the material to pull apart, opening up at the ends.

Question 3

Flash line cracks/tears

Answer 3

Rolling, forging and extruding. In closed-die forging, excess metal squeezes out between the die halves—this thin excess is called flash.
The flash line is the seam where the dies meet. Cracks or tears that develop along this seam are called flash line cracks/tears.

Question 4

Forging laps

Answer 4

Rolling, forging and extruding. A lap is created when excess or misdirected metal flow causes the surface to fold, trapping an unbonded seam. It looks like a crack but is actually a folded-over surface.

Question 5

Hydrogen flake (MT)

Answer 5

Rolling, forging and extruding. Internal cracks formed when dissolved hydrogen collects at inclusions or high-stress regions, creating pressure that fractures the steel.

Question 6

Inclusions (stringers)

Answer 6

Rolling, forging and extruding. Non-metallic particles trapped inside a metal during melting or solidification.

Question 7

Laminations

Answer 7

Rolling, forging and extruding. Planar internal discontinuities in wrought products, usually parallel to the surface, caused by non-metallic inclusions, porosity, or gas voids that were flattened during rolling or forging.

Question 8

Seams

Answer 8

Rolling, forging and extruding. Long, narrow, surface-connected discontinuities in wrought products, typically running parallel to the direction of rolling or drawing.

Question 9

Unfused porosity (PT)

Answer 9

Rolling, forging and extruding. Unfused porosity is a surface-breaking cluster of pores caused by voids that failed to weld together during mechanical working of metal.

Question 10

Seams (rolled threads)

Answer 10

Rolling, forging and extruding. Elongated surface defects that follow the thread profile, formed when existing seams in the raw material are exposed and spread during thread rolling.