Effect of Rare Earth Ce on Deep Stamping Properties of High-Strength Interstitial-Free Steel Containing Phosphorus

Abstract

The influence of rare earth Ce on the deep stamping property of high-strength interstitial-free (IF) steel containing phosphorus was analyzed. After adding 120 kg ferrocerium alloy (Ce content is 10%) in the steel, the inclusion statistics and the two-dimensional morphology of the samples in the direction of 1/4 thickness of slab and each rolling process were observed and compared by scanning electron microscope (SEM). After the samples in each rolling process were treated by acid leaching, the three-dimensional morphology and components of the second phase precipitates were observed by SEM and energy dispersive spectrometer (EDS). The microstructure of the sample was observed by optical microscope, and the grain size was compared. Meanwhile, the content and strength of the favorable texture were analyzed by X-ray diffraction (XRD). Finally, the mechanical properties of the product were analyzed. The results showed that: (1) The combination of rare earth Ce with activity O and S in steel had lower Gibbs free energy, and it was easy to generate CeAlO3, Ce2O2S, and Ce2O3. The inclusions size was obviously reduced, but the number of inclusions was increased after adding rare earth. The morphology of inclusions changed from chain and strip to spherical. The size of rare earth inclusions was mostly about 2–5 μm, distributed and dispersed, and their elastic modulus was close to that of steel matrix, which was conducive to improving the structure continuity of steel. (2) The rare earth compound had a high melting point. As a heterogeneous nucleation point, the nucleation rate was increased and the solidification structure was refined. The grade of grain size of products was increased by 1.5 grades, which is helpful to improve the strength and plasticity of metal. (3) Rare earth Ce can inhibit the segregation of P element at the grain boundary and the precipitation of Fe(Nb+Ti)P phase. It can effectively increase the solid solution amount of P element in steel, improve the solid solution strengthening effect of P element in high-strength IF steel, and obtain a large proportion of {111} favorable texture, which is conducive to improving the stamping formability index r90 value.

In Situ Observation of Microstructural and Inclusions Evolution in High-Strength Steel Deposited Metals with Various Rare Earth Pr Contents

“…With the addition of Pr 6 O 11 in the deposited metal, the inclusion phases in spherical forms normally have the maximum surface tension under the premise of the same volume. The spherical inclusions have the minimum thermodynamic driving force during their growing process in the weld pool [ 25 ]. Thus the inclusions in the deposited metal change their shape.…”

Effect of Cerium on the Microstructure and Inclusion Evolution of C-Mn Cryogenic Vessel Steels

“…The combination of Ce with [O] and [S] in steel has lower Gibbs free energy. It was easy to change the inclusion morphology from chains and strips to generate CeAlO 3 , Ce 2 O 2 S, and Ce 2 O 3 spherical inclusions [ 42 ]. The RE inclusions CeAlO 3 and Ce 2 O 2 S in molten steel were stable at 1873K, decreasing the mass fraction of dissolved oxygen in the molten steel, while Ce and S formed complex RE sulfides, resulting in a decrease in CeAlO 3 and increase in Ce 2 O 2 S [ 43 , 44 ].…”

“…( Combining Table 3 [40]. Both elements begin to aggregate and form high melting point oxides, oxysulfides and sulfides, thus having the ability to remove the deleterious types of inclusions that are formed [13,32,41] to change the inclusion morphology from chains and strips to generate CeAlO3, Ce2O2S, and Ce2O3 spherical inclusions [42]. The RE inclusions CeAlO3 and Ce2O2S in molten steel were stable at 1873K, decreasing the mass fraction of dissolved oxygen in the molten steel, while Ce and S formed complex RE sulfides, resulting in a decrease in CeAlO3 and increase in Ce2O2S [43,44].…”

Effect of Pr6O11 on the Microstructures and Mechanical Properties of High-Strength Steel Weld Metal

“…The addition of Pr6O11 can promote the formation of AF in the weld metal. The rare-earth elements can both spheroidize and refine inclusions because they usually enrich at inclusions in weld metal deposits [11]. For liquid metals, the new inclusion phases in spherical forms normally have the maximum surface tension under the premise of the same volume.…”

“…This is mainly ascribed to the fact that spherical inclusions have the minimum thermodynamic driving force during its growing process in weld pool. On the other hand, the amount of inclusions can be enhanced by the rare-earth elements, which accordingly provides more nucleation positions for AF [11,12]. AF is considered an excellent microstructure component to improve the toughness through effective grain refinement, and AF grains can divide large austenite grains into fine individual regions to form a mixed microstructure of fine particles [13,14,15].…”