A PRECISE QUANTITATIVE-ANALYSIS OF PRECIP ITATES IN TI-BEARING INTERSTITIAL-FREE STEEL

A more precise quantitative analysis of precipitates in Ti-bearing Int erstitial-Free(IF) steel is made through the combination of both a Fie ld-Emission Transmission Electron Microscope(FE-TEM) analysis and an a nalysis based upon chemical extraction and isolation. The non-stoichio metry of precipitates is precisely determined using either Energy Disp ersive X-ray spectroscopy(EDX) or a new method by plasmon energy in El ectron Energy-Loss Spectroscopy(EELS) attached to FE-TEM. The non-stoi chiometric compositions of each precipitate are taken into considerati on in the quantitative analysis. The precise quantitative method is ap plied to both the hot-rolled and the annealed steels in the process co ndition: the reheating temperature: 1220 deg.C, the finishing hot-roll ing temperature: 890 deg.C, the hot-rolling coiling temperature : 680 deg.C and the annealing temperature : 770 deg.C. The precipitates are quantitatively analysed from the viewpoint of the interstitial element s; nitrogen, sulfur and carbon. All the nitrogen is precipitated as Ti N when hot-rolling is completed. Most of the sulfur-related precipitat e is TiS1.25 in the hot-rolled steel. The rest are Ti4C2S2 and (Mn,Fe) S-1.25. After annealing, TiS1.25 decreases, while Ti4C2S2 increases si gnificantly and (Mn,Fe)S-1.25 slightly increases, Not all the carbon i s combined with Ti in the hot-rolled steel and a lot of ''free carbon' ' still remains even after the hot-rolling process is finished. After the annealing process, both TiC0.85 and Ti4C2S2 increase in quantity d ramatically.