Metal Cutting

We cut steel plate, tube and angle to your dimensions, for people doing their own build who want parts that start out square and to size. Bring the cut list. You do the assembly.

How a piece is cut matters more than most people expect, because the common methods are thermal. Oxy-fuel, plasma and laser all melt their way through the steel, and the heat changes the metal beside the cut. How much that matters depends on the steel. For hardened abrasion resistant plate it can undo part of the reason the plate was bought.

SSAB, which makes Hardox abrasion resistant plate, publishes what happens. Thermal cutting leaves a heat affected zone along the cut, and SSAB divides it in two. Right at the cut edge is a re-quenched zone. Beyond it is a tempered zone, heated to below 900°C by the cut, and SSAB notes that this tempered zone is where residual tensile stresses build up and where hydrogen cracks start. For oxy-fuel cutting, SSAB gives the heat affected zone as 4 to 10 mm wide.

Plate thickness decides the method. SSAB recommends a minimum thickness of 10 mm for oxy-fuel cutting, and says thinner material should be cut with low heat methods such as plasma or laser to minimize deformation and loss of hardness. The abrasion resistant plate in our dump bodies runs 3/16 to 3/8 inch, about 4.8 to 9.5 mm, so all of it sits under that line.

For that thickness range, plasma is the practical thermal method. SSAB states there is no difference in plasma cutting its wear steel compared with ordinary mild steel, and that plasma cutting needs less preheating or postheating than oxy-fuel. The cleanest option of all for hardness is a cold one: SSAB names abrasive water jet cutting as the best way to eliminate the risk of softening.

Small parts carry their own risk. SSAB says that the smaller the piece that is thermally cut, the greater the risk of the whole component softening, because the heat from the cut builds up in the piece. On plate 30 mm or thicker cut with oxy-fuel, its rule of thumb is that cuts closer together than 200 mm risk softening the entire part. It also notes that most of its grades are sensitive to cut edge cracking at sharp geometries, so inside corners are worth a thought on the drawing.

Preheating only enters the picture on thick plate. In SSAB's table for oxy-fuel cutting, Hardox 400 needs no preheat below 45 mm and Hardox 500 none below 25 mm, and neither should be heated past 225°C when preheat is used.

Structural steel to a specification such as ASTM A36 is the other common request, and the same principle applies to it: a square, clean cut saves fitting time later. Bring the cut list with the material, thickness, dimensions and quantity for each piece. Cutting is done at both shops, and parts that need joining afterwards can go straight on to custom fabrication.