Effect of Ti on microstructure and strengthening behavior in press hardening steels

Abstract

Effect of Ti addition on the microstructure and strengthening behavior in press hardening steels (PHS) was analyzed by optical metallography (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the microstructure of PHS is martensite, and two sizes of particles disperse in the martensite matrix during the forming and quenching process. The size of the bigger particles is between 100 and 200 nm, and the small particles are nanometer-sized. The quantity of the particles has a positive relation with the Ti content. More importantly, the microstructure and strengthening mechanism are affected by the precipitating behavior of the particles. Besides the prior austenite grain, martensite packet, block and lath are refined by Ti addition. The steels are strengthened by the fine grains, martensite substructure and precipitates. The uniformly distributed dislocation in the martensite lath, the density of which is between 3.0×10¹⁴ cm^–2 and 5.0×10¹⁴ cm^–2, strengthens the steels through associating with fine carbide particles.

Keywords

martensite / particles / prior austenite grain / martensite lath / press hardening steel

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