Ti-Mo FERRITE MATRIX MICRO-ALLOY STEEL WITH NANOMETER-SIZED PRECIPITATES

The morphology, size, distribution and types of precipitate particles were studied by using OM, SEM, TEM, EDS and SAEDP for Ti-Mo low-carbon ferrite matrix micro-alloy steel with four different titanium contents. Experimental results indicated that there were two kinds of particles with obvious different sizes in ferrite matrix, one was nanometer sized particles, which were smaller than 10 nm, the composition of these particles was compound carbonitride of Ti and Mo. These particles precipitated in chains or dispersed in the interior of grains. Dislocation nodes and the dislocation network were preferential nucleation sites for these particles. Another kind of particles was titanium carbonitride larger particles with a "cap" and few in number in ferrite matrix. Their size was about 200 to 300 nm and morphology was square. Tensile experimental results at room temperature and high temperatures showed that ferrite matrix micro-alloy steel with nanometer sized had good mechanical properties. No.4 steel had good performance at 600 degrees C with a yield strength of about 300 MPa.