Chart groups carbon content, Typical uses and weldability.

Group	Content %	Typical usage	Weldability
Low carbon steel	0.15 Maximum	Welding electrodes, rivets and nails softer easily formed shapes.	Excellent weldability with all processes usually no preheat interpass or postheat necessary
Mild steel Plain carbon	0.15 to 0.30	Plate, angle, and bar stock for general fabrication. Mild steel accounts for a large segment of welded parts of Industry where good plasticity and ductility is required.	Readily weldable with all processes without preheat, interpass, or postheat except for very thick sections.
Medium carbon steel	0.30 to 0.50	Used for Machine parts, gears, and where parts may be hardened by heat treating.	Parts may be readily welded with all process if preheat, interpass temperature controls, and post heat recommendations are followed. Use Low hydrogen Electrodes and appropriate filler wire. Heat treating after welding may be applied
High carbon steels	0.50 To 1.0	Springs, Dies, Railroad Track, Many tools, Band saws, and Knives. Also used where a sharp edge is required.	Usually require preheat interpass temperature control and postheat. Special heating and cooling procedures in a furnace such as normalizing may be required to restore the properties of the metal after welding. High carbon Electrodes designed for welding tool steels or the specific alloy are readily available from welding supply companies.

Note: As carbon increases steel toughness and welding precautions increase

Radiograph Interpretation - Welds (part 5)

Discontinuities in Gas Metal Arc Welds (GMAW)

The following discontinuities are most commonly found in GMAW welds.

Whiskers are short lengths of weld electrode wire, visible on the top or bottom surface of the weld or contained within the weld. On a radiograph they appear as light, "wire like" indications.

Burn-Through results when too much heat causes excessive weld metal to penetrate the weld zone. Often lumps of metal sag through the weld, creating a thick globular condition on the back of the weld. These globs of metal are referred to as icicles. On a radiograph, burn-through appears as dark spots, which are often surrounded by light globular areas (icicles).