According to ASTM(ASME) standard, it mentions that tubes shall be reheated to a temperature of 1200˚F[650˚C] or higher and cooled. Which means that manufacture must have tempering heat treatment to have martensite structure. Some manufacturers have annealing heat treatment on TP410 but not have tempering and it’s not proper procedure. To have martensite structure, the material must be quenched. The temperature 726˚C above, steel structure is changed to austenite. When it’s cooled rapidly by air, water or oil etc, structure is changed to martensite. Martensite itself has high value of hardness, it must be tempered to low hardness and increase ductility. If annealing is applied to the material and cooled in room temperature, steel structure will be deformated to ferrite, pearlite and bainite. Temperature of tempering could be different to chemical composition of material.
Alloy steels undergo temper brittleness or a reduction in toughness that occurs when the steel is tempered in (or slowly cooled through) the temperature range of 950 to 1100˚F (510 to 593˚C ). This phenomenon does not occure in plain carbon steels, but the degree of embrittlement is enhanced by nickel, manganese, and chromium content. Tempring should be carried out beloe this range for steels susceptible to this embrittlement or above the range, followed by rapid quenching through the range.(comment 1) The material TP410 includes manganese 1.00 Max, chromium 11.5~13.5. That is why heat treatment condition for reheating is 1200˚F[650˚C] or higher.
In case of an unalloyed steel containing .045% C, Austenitization temperature is 880˚C (1620˚F). The temperature A1 is where tranformation to austenite begins, and temperature A3 is where the transformation to austenite is complete. And the temperature where martensite apearing is much lower than alloy steel.
Fig. 1 Courtesy of Verlag Stahlessen mbH Dusseldor.
It is important to apply right heat treatment to have right structure. Based on method of heat treatment, structure can be different as the pictures below.
Fig.2 Smith, William F. Principles of Materials Science and Engineering. McGraw Hill, 3rd Ed., 1996. (p. 128-132)
Comment 1: Failure Related to Heat Treating Operations, G.E. Totten, G.E. Totten & Associates, LLC M. Narazaki, Utsunomiya University (Japan) R.R. Blackwood and L.M. Jarvis, Tenaxol Inc. page 4 temperting.
The Original Posted by Jethro