Enhancement of Heat-Affected Zone Toughness of a Low Carbon Steel by TiN Particle
- PDF / 6,110,922 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 82 Downloads / 190 Views
ODUCTION
RECENTLY, high heat input welding methods, such as sub-merged arc welding, electro-gas welding, and electro-slag welding, have gained engineering applications due to construction efficiency improvement and cost reduction.[1–3] However, increasing welding heat input usually leads to deteriorated impact toughness of weld joints, especially in heat-affected zone (HAZ).[4–6] Two distinct groups of methods[7–13] were put forwarded to improve HAZ toughness. The first one adopts low carbon, low carbon equivalent chemistry design along with TiN pinning austenite grain growth to refine HAZ grain structure, and hence to improve low-temperature toughness. The second one is fabrication of densely distributed fine oxide particles with high-temperature stability to improve HAZ impact toughness through oxide metallurgy, such as the use of strong de-oxidant Ti, Mg, Zr, and Ca. The latter relates to oxide metallurgy, which requires delicate control of steel-making process with narrow operating window. This is difficult for mill production. From the point of industrial production, the first one is more reliable for quality control. Positive effect of TiN particles on steel weldability is frequently reported.[14–19] But the fact is that TiN particles dissolve with exposure to temperature higher than 1623 K (1350 C), and the pinning effect on austenite grain boundary loses.[20,21] Therefore, high-temperature stability of TiN particles is critical for weldability improvement. Increasing nitrogen and nitrogen/titanium ratio YU ZHANG, Group Manager, Senior Researcher, XIAO-BAO LI, Assistant Researcher, and HAN MA, Deputy Director, Senior Researcher, are with the Institute of Research of Iron and Steel, Sha-steel, Zhangjiagang, 215625 Jiangsu, China. Contact e-mail: [email protected] Manuscript submitted September 9, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
improves high-temperature stabilities of TiN and hence heat-affected zone toughnesses were reported.[22–25] However, effect of TiN on microstructural and toughness of HAZ are not well understood. The objective of this study is to clarify the mechanism of HAZ toughness changes resultant from TiN particles.
II.
EXPERIMENTAL PROCEDURES
Two 150-mm-thick steel ingots were prepared by 80 kg vacuum induction melting furnace, and then were hot rolled into 30-mm-thick plates on a rolling machine with a force of 1000 kN. Prior to hot rolling, the ingots were reheated to 1473 K (1200 C) with a soaking time of 3 hours. Twostage thermo-mechanically controlled processing and accelerated cooling technique was employed for rolling, and cooling rate is about 15 K/s (15 C/s). Chemical composition of the rolled plates is shown in Table I. The plate A# shows a microstructure of polygonal ferrite (PF) plus bainite, while a mixture of PF and pearlite (P) was observed in the plate B#, as shown in Figure 1. The plate A# exhibits a yield strength of 465 MPa, a tensile strength of 564 MPa, and an elongation ‡25 pct. In contrast, the plate B# shows a yield strength of 372 MPa and a tensile stren
Data Loading...
