The Role of Intercritical Annealing in Enhancing Low-temperature Toughness of Fe-C-Mn-Ni-Cu Structural Steel
- PDF / 2,698,201 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 95 Downloads / 180 Views
INTRODUCTION
HIGH-STRENGTH low-alloyed steels with improved low-temperature toughness and good weldability are preferred as constructural materials for offshore structures, bridges, ship hull, and pressure vessels.[1–3] In regard to alloy design, low-carbon design is preferentially adopted for consideration of weldability and low-temperature toughness. Moreover, micro-alloying elements, such as Nb, V, and Ti, are usually added for carbide formation with aim to precipitation strengthening.[4–6] Cu is added to compensate for the loss of strength due to carbon reduction.[7] Additionally, Cu is helpful to improve the corrosion resistance of the marine structural steels.[8] Although a balance of strength, ductility, toughness, and weldability has been
XIAOHUI XI, JINLIANG WANG, XING LI, LIQING CHEN, and ZHAODONG WANG are with the State Key Laboratory of Rolling and Automation, Northeastern University, 3-11 Wenhua Road, Shenyang 110819, P.R. China. Contact e-mail: lqchen@mail. neu.edu.cn Manuscript submitted December 9, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
obtained in structural steels, higher requirements for strength–toughness combination are proposed due to their severer service conditions, stricter demands for safety and reliability, long-term service, etc. In order to meet the requirement for higher performance, numerous approaches have been developed for various alloying steels, such as the addition of alloy elements, thermal mechanical controlled processing (TMCP), and heat treatments.[1,9,10] Presently, one of the most effective heat treatments is quenching and tempering in the production of ultrahigh-strength steels.[11] The quenching process is a common way to increase the strength of high-strength steels by generating a high density of dislocations in martensite, which are obtained during the rapidly cooling to room temperature after reheating hot-rolled steels to the austenization temperature.[12] The subsequent tempering process can improve the toughness of the quenched steels by relaxing dislocations,[13] accompanied with the loss of strength, which is attributed to the intrinsic conflict between strength and toughness. Meanwhile, the brittle cementite is inevitable to precipitate during conventional quenching and tempering, causing initial cracks and thus decreasing the low-temperature toughness.[14] Another problem to be solved for high-strength steels is the high yield-to-tensile ratio (Y/T ratio). It has
been found that the Y/T ratio increases with the increase of yield strength.[1,12,15,16] When the yield strength is higher than 690 MPa, the Y/T ratio increases up to 0.9 or more. However, the higher Y/T ratio definitely means the poorer formability, which seriously limits the industrial application of ultrahigh-strength steels. Intercritical annealing has been demonstrated as a new method capable of producing multi-phase microstructure in low-carbon steels, which are characterized by high strength, ductility, and toughness. Therefore, the intercritical annealing has long been receiving more
Data Loading...
