Enhancement of Upper Shelf Energy through Delamination Fracture in 0.05 pct P Doped High-Strength Steel

An ultrafine elongated grain (UFEG) structure with strong aOE (c) 110 >//rolling direction (RD) fiber deformation texture was produced by warm-caliber rolling at 773 K (500 A degrees C) and final tempering at 823 K (550 A degrees C), namely tempforming in the 1200 MPa-class, medium-carbon, low-alloy steel with phosphorus (P) content of 0.053 wt pct. Charpy impact tests and tensile tests were performed at a temperature range of 77 K (-196 A degrees C) to 623 K (350 A degrees C) on the tempformed (TF) samples along with a conventional quenched and tempered (QT) samples. The QT structure showed a low upper shelf energy of 70 J and a high ductile-to-brittle transition temperature (DBTT) of 373 K (100 A degrees C) as a result of P segregation and intergranular fracture. A remarkable increase in the upper shelf energy to 150 J from 70 J and a low DBTT of approximately 103 K (-170 A degrees C) were obtained in the UFEG structure. P segregation embrittlement disappeared completely in the UFEG structure, and ductile fracture on the planes normal to RD along with delamination fracture on the planes along RD were observed at a temperature range of 123 K (-150 A degrees C) to 423 K (150 A degrees C). The enhanced delamination occurred because of the microstructural anisotropy of the UFEG structure, a strong aOE (c) 110 >//RD fiber deformation texture, and interfaces (i.e. ferrite grain boundaries and cementite particles-ferrite matrix interfaces) weakened by P segregation as feasible crack propagation paths. We studied the delamination (crack-arrester-type) fracture in 0.053 pct P doped high-strength steel along with upper shelf energy and DBTT obtained from the UFEG structure.