Difference between austenitic and martensitic stainless steel thick-walled pipe

For example, the tensile strength range of 12Cr18Ni9 (302), Y12Cr18Ni9 (303), 06Cr19N10 (304) and 06Cr17N12Mo (316) under annealing conditions is approximately the same as the tensile strength range of carbon steel. However, the range between tensile strength and yield strength of austenitic stainless steels is much greater than for low or medium carbon ferritic steels. For example, there is a significant range between the tensile strength and yield strength of the annealed Y12Cr18Ni9 (303) steel, which causes “sticking” during cutting, resulting in accumulation at the tip of the tool, combined with poor precision, overheating and short tool life. 

In order to avoid work hardening and reduce the accumulation of chips before the tool, when cutting austenitic stainless steel, a larger feed rate than carbon steel and a slower cutting speed are used. It is also recommended to use a helical chip cutter to cut all austenitic steels, especially high alloy steels such as 16Cr23N13 (309) steel, because the austenitic steels are very flexible and look like long ropes.

Annealed low carbon martensitic stainless steels, such as 12Cr13 (410), have similar cutting characteristics to annealed low carbon alloy steels. However, the annealed low carbon martensitic stainless steel generally has a relatively high hardness range, and therefore, a larger cutting force is required for cutting martensitic stainless steel.

In most cases, 12Cr13 (410) martensitic stainless steel or similar grades of stainless steel thick-walled tubes must be cut in a quenched and tempered condition, typically with a hardness ranging from 26 to 32 Rockwell. Cutting in this hardness range should increase the cutting force proportionally and reduce the cutting speed and feed rate. Although the service life of the tool is shortened with increasing hardness, good surface finish and precision can be obtained when cutting the low-carbon martensitic stainless steel of the above hardness range. Martensitic steels with higher carbon content, such as 30Cr13 (420) and 68Cr17 (440A), especially 108Cr17 (440C) steel, are extremely difficult to cut. This is due to: high hardness after annealing (Brinell hardness 195 ~ 230); there are hard chromium carbide spots.