The Effects of Finish Rolling Temperature and Cooling Interrupt Conditions on Precipitation in Microalloyed Steels Using Small Angle Neutron Scattering

Small angle neutron scattering (SANS) was used to quantify the precipitate characteristics (i.e., mean precipitate size, number of precipitates, and distribution broadening) in X-70 and X-80 pipeline steel and in grades 80 and 100 microalloyed steel plate. The precipitate distributions measured for the different steels were correlated with the finish rolling temperature (FRT) and cooling interrupt temperature (CT) as a means of identifying processing conditions that may enhance fine precipitate evolution. It was observed that for some combinations of processing conditions two distinct precipitation events—based on size of the precipitates—were occurring. The first precipitation event (larger size) was strongly associated with the FRT, where a decrease in the mean precipitate radius with decreasing FRT was observed. The second (finer size) precipitation event was affected by both the CT and the FRT. Both the size and volume of the second precipitation event was observed to decrease with decreasing CT. The precipitate distribution predicted from the SANS data for grade 100 steel compared favorably to precipitation data obtained from particle counting analysis conducted with a transmission electron microscopy (TEM).