280D refers to a hot-finished 280-tube which has been further processed by cold working, usually cold drawing. The cold working increases both yield and tensile strength but elongation is lowered. In comparison with the 280 hot-rolled product, dimensional tolerances are improved. 280D has equivalent weldability to hot-finished 280 while machinability is improved as a result of the cold working.
The standard which covers cold-drawn, seamless tubes is SS-EN 10305 - 1. The grade closest to 280 which is referred to in this standard is E410 +C. However, for the latter, the only stipulation is a minimum level for tensile strength whereas 280D has guaranteed minimum levels for both yield and tensile strength. Furthermore, the minimum elongation for 280D is considerably better than for E410 +C in SS-EN 10305 - 1.
The tolerances on outside diameter and wall are somewhat tighter for 280D than the levels stipulated in SS-EN 10305 - 1. The inside and outside dimensions which can be achieved after machining are important parameters. Levels for these are defined in SS-EN 10294 - 1 for outer as well as inner chucking. The designations indicated relate to outer chucking and concur with those given in SS-EN 10294 - 1. The first 2 numbers denote the greatest guaranteed outside diameter while the final 2 relate to the lowest guaranteed inside diameter. These guaranteed dimensions apply over a length of 3 times the outside diameter or 200 mm whichever is the smaller. For inner chucking, the guaranteed dimensions after machining are generally somewhat less.