Influence of Boron Addition on the Hot Ductility of Low-Carbon Aluminum-Killed Steel

Abstract

The hot ductility of low-carbon aluminum-killed steel with different boron contents was investigated. The hot tensile experiment was conducted using Gleeble3500 simulator. The reduction of area of each specimen was determined to estimate the quality of hot ductility. The changes of precipitates in studied steel were calculated by Thermo-Calc software. The microstructures of specimens were observed using optical microscopy (OM), sanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the experimental results, the fracture types of specimens were analyzed. The results show that the hot ductility improves with increase in boron content. In the experimental condition of this study, the combining ability of boron with nitrogen is greater than that aluminum and nitrogen in the energetics point of view. Coarse BN particles decrease the effect of pinning grain boundary by fine AlN. Boron in solid solution plays a role of inhibiting the austenite/ ferrite transformation. The improvement of hot ductility is caused by the formation of coarse BN and existence of boron in solid solution.

Effect of Boron on the Hot Ductility of Low-Carbon Nb-Ti-Microalloyed Steel

“…These coarse precipitates are about several hundred nanometers, and invalid for pinning grain boundary. 18) It appears from Fig. 6 that the amount of ne Nb-Ti-containing precipitates increases with the decrease in temperature.…”

Effect of Boron on Mechanical Properties and Fatigue Life of Spring Steel for Automobile Suspension

“…While, only a little of proeutectoid ferrite began to form around the prior austenite grain boundaries in 2# and 3# samples at 750 °C and could not form networks. The segregation of boron in grain boundaries decreased austenite grain boundary energy and BN forming along grain boundaries occupied the forming positions of ferrite, thereby impeding formation of proeutectoid ferrite [3,7,8,11,13,[17][18]. Therefore, the fracture of 2# sample was still obvious dimple morphology.…”

“…Why the DRX in 2# and 3# samples could happen was related with that boron decreased activation energy for DRX [15] and changed the precipitates in steels. As shown in figure 6(a), through thermodynamics calculation by Thermo-Calc software, though the Als content of 1# steel was low to 0.001%, there was still a little of AlN precipitating in steel, the nano-sized AlN could pin in grain boundaries and prevent the DRX from happening [18]. As shown in figure 6(b), (c), figure 7(b), (c) and figure 8(a), (b), large blocky BN occurred at grain boundaries in 2# and 3# samples, whose size was large to 1.5 μm, which prevented the formation of AlN and decreased its pinning effect in grain boundaries.…”

“…Therefore, improving the ductility, toughness, elastic sag resistance and so on of spring steel becomes especially important so that spring can have good fatigue resistance performance when it works under the high periodic alternating stress [2]. Many studies showed that the ductility and toughness of low and medium carbon steel could be increased by a proper addition of boron [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The elastic sag resistance and delayed fracture resistance of Al-killed spring steel could be improved by the introduction of boron [19][20].…”

Effect of cooling rate on microstructure and mechanical properties of CB2 tempered martensitic steel

“…The free energy of BN formed at the front of the solid-liquid interface in CB2 molten steel is shown in Eq. (1) [28] . The relationship between the solidification rate f s and the temperature T S-L of the solid-liquid interface front is established as shown in Eq.…”