Effect of rare earth cerium on inclusions, microstructure and mechanical properties in high-strength rebar

High-temperature smelting, rolling, and room-temperature tensile testing were conducted on high-strength rebar steels containing 0∼0.01% rare earth cerium. The rolling start temperature is 1128°C∼1160°C and the rolling start temperature for pass nine is 840°C∼850°C. The carbon/sulfur analyzer, oxygen/nitrogen determinator, inductively coupled plasma mass spectrometer and scanning electron microscopy with energy-dispersive spectroscopy were employed to detect steel composition. With increasing Ce amounts, inclusions were primarily composed of MnS, accompanied by oxides/ sulfides, as well as their MnS-complex counterparts, which is consistent with thermodynamic predictions. The addition of cerium significantly promoted ferrite formation. In the steel without Ce, the ferrite fraction was relatively low at 29.9%, whereas the steel with 0.01% Ce exhibited the highest ferrite content at 37.3%. Trace amounts of Ce facilitated grain refinement by forming Ce-Al-O inclusions, which served as nucleation sites for austenite. The Ce-Al-O inclusions also contributed to the precipitation of VN, enhancing ferrite formation and achieving an optimized balance between strength (874 MPa) and toughness (17.88%). However, excessive cerium content adversely affected steel cleanliness, leading to the formation of coarse Ce-O-S inclusions that compromised elongation to 7.37%.