ASTM A570 covers hot-rolled carbon steel sheet and strip across six strength levels — Grades 30, 33, 36, 40, 45, and 50 — each defined by its own minimum yield and tensile requirement. This page covers Grade 40, the middle tier of the family, requiring a minimum yield strength of 40 ksi (276 MPa) and a minimum tensile strength of 55 ksi (379 MPa). It sits a step above Grades 33/36 in load-carrying capacity while remaining noticeably easier to form than Grade 50.

Like every grade in the A570 line, Grade 40 is a plain carbon-manganese steel with no significant alloy additions, so it stays weldable and forms cleanly by roll-forming, press-braking, or stamping. That combination of moderate strength and good formability makes it a common choice for structural sheet-metal parts that need more capacity than the lowest grades but don't require the extra strength — and extra forming difficulty — of Grade 50. Typical uses include structural framing components, machinery guarding, brackets, panels, and fabricated sheet-steel assemblies across general industrial and agricultural equipment.

As with other A570 grades, this material is normally supplied as coil or sheet rather than plate, and most shop work on it happens after forming: drilling, tapping, edge trimming, and light face work on a finished or partially formed part rather than heavy lathe turning on bar stock.

Grade 40's carbon content sits just above the lowest A570 grades, which gives it slightly more body in the chip without changing its fundamental behavior as a low-carbon steel. Chips still form long and stringy rather than breaking cleanly on their own, so chip control depends mainly on chipbreaker geometry rather than the material's own metallurgy.

Built-up edge remains the primary concern at low cutting speeds — soft, ductile material tends to smear across the rake face instead of shearing away, then tears off unevenly and leaves a rough surface. Running toward the upper end of the recommended speed range, maintaining feed rates high enough that the tool keeps cutting rather than rubbing, and using a sharp, positive-rake edge geometry all reduce that tendency.

Power requirements and steady-state tool wear are both modest on this material, and most shops find it forgiving to work with once BUE is under control. Because it typically arrives as a formed or partially formed sheet-metal part, secondary machining operations like drilling, tapping, and edge finishing benefit more from sharp, well-maintained cutting edges than from chasing higher spindle speeds.