Partitioning Steels

"The quenching and partitioning (Q&P) process is a two-stage heat-treatment procedure proposed for producing steel microstructures that contain carbon-enriched retained austenite."

That sentence is from the abstract of an article produced by an international panel of scientists, and the principal author is associated with both the Los Alamos National Laboratory and the Colorado School of Mines. If you want a more detailed explanation, read the article:

http://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-09-01639

Alloying steel with Niobium is a popular topic of metallurgical investigation nowadays. Niobium improves certain properties of steel by reducing grain size. Although it will cost you to read some of the research, there are many more articles, like the one cited above, which are free.