hello
after hot rolling with 2 different reduction of thickness (60% and 85%) on haynes 188 (Carbide strengthened and solid solution Cobalt base alloy) we observed sample with 85% reduction of thickness had more volume fraction of carbide. what is reason of this Phenomenon؟
dear Mehdi Samie ,
The response of the HAYNES188 and other high-temperature alloys (HTA) to heat treatment is very dependent upon the right condition of the material prior to the treatment. When the material is not in a suitable cold- or warm-worked condition, the principal response is usually a change in the amount and morphology of the secondary carbide phases.
Rapid cooling is essential after annealing, to prevent the nucleation and growth of these deleterious second phase precipitates in the microstructure, particularly at the grain boundaries. Water quenching is preferred, and highly recommended for materials thicker than 3/8 in (9.5 mm). Rapid air cooling has been used for thin sections. The time between removal from the furnace and the start of quenching must be as short as possible (and certainly less than three minutes).
For more details see HAYNESS INT. website
Greetings, Ruediger
Thank you sir Rüdiger Rentsch
we hot rolled samples at same condition (1150 C heated and 2 different reduction of thickness 60 and 85%). but sample 85% reduction of thickness show more volume fraction of carbides. what is it reason? why under higher strain carbide precipitation increasing?
dear Mehdi Samie, are the reduction rates total reduction numbers or relative, meaning first 60%, second again 85% by considering the height after the first rolling step? What are the rolling Speeds you applied?
Best regards, R. Rentsch
we had 2 samples (50*10*2 cm) with same history, we rolled sample A with 1mm reduction of thickness in each pass of hot rolling. and finally sample A from 2 cm of thickness reduced to 8 mm (60%). and sample B with same dimension and same process with final thickness of 3 mm (85%).
dear Mehdi Samie, the temperature range starting from 1150°C seems o.k.; reduction numbers recommended are 15-20% per pass. With 5% increasing to 11% you are below it. Only during the last steps at sample B (below 6mm rest height) you reach this recommendation; But the Major Point is the heat Management, i.e. keeping the temperature range between 1177°C (at start) and 927°C (at end) during rolling. Your specimens are quite small and it could be difficult to Keep the temperature over so many steps (i.e. such a Long time) in the range. Since you observed the higher carbide Content in the 85%-totally reduced specimen (B), time respectively low rate quenching could be a reason for the growth of more secondary carbide phases. In principle thinner specimen experience much higher quenching rates than thicker ones, even during air quenching. Hence if the additional carbide amout would have been generated only at the end by quenching alone, than the higher quenching rate should have led to a lower carbide Content in specimen B. Since the opposite is the case, the Problem occurs most likely from the hot-rolling process. Have you been able to control the temperature during hot-rolling or did you apply reheating?
Best regards, R. Rentsch
Thank you dear Dr.Rüdiger Rentsch
yes we reheated samples. but we reheated them after each step of rolling process.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering