Application Research on Nb Microalloying of High-Carbon Pearlite Bridge Cable Wire Rods

Abstract

The application of Nb microalloying to high-carbon pearlite bridge cable wire rod steel has always been controversial, especially in the actual production process, which will be affected by the cooling rate, holding temperature and final bonding temperature. In this paper, the experimental characterization, finite element simulation and phase diagram calculation of the test steel were carried out, then the microstructure and properties of different parts of Nb microalloying of bridge cable wire rods were compared and analyzed. The phase transition interval of pearlite during the water-cooling process of bridge cable wire rods is increased due to the refinement of austenite grains, and the significant increase in the end temperature of the phase transition makes the average interlamellar spacing of pearlite increase. The cooling rate of different parts of bridge cable wire rods simulated by Abaqus has little difference. At the same time, Nb microalloying effectively increases the proportion of low-angle grain boundaries, so that the overall average misorientation representing the surface defects is reduced. This helps to reduce the surface energy and increase the stability of the microstructure. Combined with the mechanical properties of microtensile rods, it is found that the grain refinement effect of Nb is greater than that of coarsening interlamellar spacing during hot rolling deformation in actual production, which makes the tensile strength at the 1/4 section increase significantly. The overall tensile strength and area shrinkage of the steel wire have also been effectively improved.

The Effect of Niobium Addition and Pre-Annealing on the Tensile Properties of 52CrMoV4 Spring Steel

“…This is the way in which the dislocation locking mechanism works in conjunction with the development of tiny phases to produce materials with improved strength characteristics [6,21]. Similar to previous research, it was discovered that the production of Nb and C particles following heat treatment results in a higher Nb ratio material with a finer grain size [5,[7][8][9][10][11]. The mechanical properties of the steel are greatly affected by the size of the prior austenite grain [22].…”

“…It is understood that when the Nb ratio increases, pre-annealing is effective in reducing the grain size. When the relevant literature was examined, it was seen that the grain size decreased with the effect of Nb [5][6][7][8][9][10][11].…”

“…However, there are studies on the effects of Nb addition to other alloy steels. Zhu et al observed that Nb, as an alloying element, was effective at increasing the strength and toughness by delaying recrystallization and reducing the grain size [8]. In a study carried out by Zakir, niobium was found to have the highest grain refinement effect among all alloying elements studied.…”

The Performance of Niobium-Microalloying Ultra-High-Strength Bridge Cable Steel during Hot Rolling

“…Nb also affects the recrystallization behavior of materials, slowing down the recrystallization process, allowing for finer grain sizes at higher deformation temperatures [ 10 , 11 , 12 ]. Due to these benefits of Nb-microalloying, bridge cable steel in modern bridge engineering increasingly employs this approach [ 13 ].…”

Synergistic Effect of Alloying on the Strength and Ductility of High Carbon Pearlitic Steel

“…Many studies focused on the investigation of the effect of strong carbide formers, e.g., niobium and vanadium, which were proven to change the stoichiometric composition of pearlitic cementite and form additional carbide dispersions in the microstructure. Some researches indicate that the grain refinement effect of Nb is greater than that of coarsening interlamellar spacing during hot rolling deformation [17]. The effects of strong carbide formers on the mechanical properties of pearlitic steels can summarized as follows [17][18][19][20][21]: increase the strength by decreasing the lamellar spacing and the smaller nodule size and more uniform grain size distribution; decrease the reduction in area by increments in austenite grain size and carbide plate thickness.…”