ASTM A516 is the standard workhorse specification for carbon steel pressure vessel plate at moderate and lower service temperatures, and it's the single most commonly ordered pressure vessel plate in North America. It covers welded boilers, storage tanks, separators, and process vessels where notch toughness at ambient-to-cold temperature is a design requirement. The specification defines four strength grades — 55, 60, 65, and 70 — with the grade number indicating minimum tensile strength in ksi; higher grade numbers mean higher strength but slightly lower elongation.

Plates 1.5 in. (40 mm) and under are normally supplied as-rolled, while thicker sections must be normalized to meet the specification's toughness intent — a heat treatment that refines grain structure without hardening the material. Because A516 stays in this normalized or as-rolled condition rather than being quenched and tempered, all four grades machine predictably with moderate cutting forces. Grade 70 is the most frequently stocked and specified grade in the family because it delivers the highest strength-to-cost ratio for typical pressure vessel design; Grade 60 is the next most common choice where a lower strength level is acceptable.

A516 is about as machinist-friendly as pressure vessel plate gets. All four grades are low-carbon, and none of them see a hardening heat treatment — they're delivered as-rolled or normalized, so hardness stays low and consistent across the family. Cutting forces rise only modestly from Grade 55 to Grade 70 as carbon and manganese content increase, and none of the grades introduce the abrasive carbide structures or work-hardening tendencies associated with heat-treated alloy steels.

The main variable that actually affects a machinist's day-to-day experience with A516 is condition, not grade: as-rolled mill scale is considerably harder and more abrasive than the clean steel beneath it, so the first pass into an unmachined face wears an edge faster than subsequent cuts. Normalized plate (required above 1.5 in.) has a slightly more uniform, fine-grained microstructure than thinner as-rolled stock, but this has little practical effect on cutting parameters.

Chip formation is continuous-to-segmented and easy to manage with standard chipbreaker geometries. A general-purpose coated carbide grade suited to low-carbon steel handles the entire A516 grade range without needing to be swapped between Grade 55 and Grade 70 — the practical differences in cutting speed between grades are smaller than the differences caused by scale, rigidity, or section thickness.