Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar

Abstract

The effects of niobium and composite strengthening on the phase transformation characteristics and precipitation behavior of continuous cooling transformation of high-strength rebar during thermal deformation and subsequent cooling were investigated. The results show that when the cooling rate was within 0.3–5 °C/s, ferrite transformation and pearlite transformation occurred in the experimental steels. The Nb content increased to 0.062 wt.%, and the starting temperature of the ferrite transformation decreased. Meanwhile, the ferrite phase transformation zone gradually expanded, and the pearlite phase transformation zone gradually narrowed with the increase in the cooling rate. When the cooling rate was 1 °C/s, bainite transformation began to occur, and the amount of transformation increased with the increase in the cooling rate. It was found that the main precipitates in the experimental steels were (Nb, Ti, V)C, with an average particle size of about 10–50 nm. When the Nb content was increased to 0.062 wt.% and the cooling rate was increased to 5 °C/s, the ferrite grain size was reduced from 19.5 to 7.5 μm, and the particle size of the precipitate (Nb, Ti, V)C could be effectively reduced. The strength of the steel was significantly improved, but the elongation of the steel was reduced. However, the comprehensive mechanical properties of 0.062 wt.% Nb experimental steel was significantly improved at a cooling rate of 5 °C/s.

Microstructure and Mechanical Properties of Structural Steels and Alloys

“…A total of 10 papers cover a wide range of structural metals and alloys. The majority of these papers focus on the mechanisms of microstructure evolution and the mechanical properties of metallic materials subjected to various thermo-mechanical, deformation, or heat treatments [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Readers who are interesting in structural steels may learn from comprehensive investigations of microstructure evolution and its effect on the mechanical properties of diverse steel types [ 1 , 3 , 5 , 7 , 8 ].…”

“…The majority of these papers focus on the mechanisms of microstructure evolution and the mechanical properties of metallic materials subjected to various thermo-mechanical, deformation, or heat treatments [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Readers who are interesting in structural steels may learn from comprehensive investigations of microstructure evolution and its effect on the mechanical properties of diverse steel types [ 1 , 3 , 5 , 7 , 8 ]. Four of these papers [ 1 , 3 , 7 , 8 ] present experimental investigations of strengthening mechanisms operating in high-strength steels subjected to various promising treatments including tempforming [ 1 ] and quenching–partitioning processing [ 7 ].…”

“…Readers who are interesting in structural steels may learn from comprehensive investigations of microstructure evolution and its effect on the mechanical properties of diverse steel types [ 1 , 3 , 5 , 7 , 8 ]. Four of these papers [ 1 , 3 , 7 , 8 ] present experimental investigations of strengthening mechanisms operating in high-strength steels subjected to various promising treatments including tempforming [ 1 ] and quenching–partitioning processing [ 7 ]. Some crucial features related to structure–property relationships are detailed for high-strength rebar [ 3 ] and a high-speed axle steel [ 8 ].…”

“…Four of these papers [ 1 , 3 , 7 , 8 ] present experimental investigations of strengthening mechanisms operating in high-strength steels subjected to various promising treatments including tempforming [ 1 ] and quenching–partitioning processing [ 7 ]. Some crucial features related to structure–property relationships are detailed for high-strength rebar [ 3 ] and a high-speed axle steel [ 8 ]. Hydrogen-assisted deformation behavior was clarified by Astafurova et al [ 5 ] for a 316 L austenitic stainless steel.…”