Strengthening and toughening mechanism of a Cu-bearing high-strength low-alloy steel with refined tempered martensite/ba
- PDF / 3,498,314 Bytes
- 15 Pages / 595.276 x 790.866 pts Page_size
- 28 Downloads / 228 Views
(0123456789().,-volV)(0123456789(). ,- volV)
ORIGINAL PAPER
Strengthening and toughening mechanism of a Cu-bearing highstrength low-alloy steel with refined tempered martensite/bainite (M/ B) matrix and minor inter-critical ferrite Fei Zhu1 • Feng Chai1 • Xiao-bing Luo1 • Zheng-yan Zhang1 • Cai-fu Yang1 Received: 14 January 2020 / Revised: 19 July 2020 / Accepted: 21 July 2020 China Iron and Steel Research Institute Group 2020
Abstract The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel, subjected to a novel multistage heat treatment including quenching (Q), lamellarization (L) and tempering (T), is presented. Yield strength of 989.5 MPa and average toughness at - 80 C of 41 J were obtained in this steel after quenching and tempering (QT) heat treatments. Specimen QLT gained a little lower yield strength (982.5 MPa), but greatly enhanced average toughness at - 80 C (137 J). To further clarify the strengthening and toughening mechanisms in specimen QLT, parameters of microstructural characteristic and crack propagation process were compared and analyzed for specimens Q, QL, QT and QLT. The microstructure of tempered martensite/bainite (M/B) in specimen QT changed to refined tempered M/B matrix mixed with minor IF (inter-critical ferrite) in specimen QLT. Cu-rich precipitates existed in tempered M/B for both specimens QT and QLT, as well as in IF. Compared with QT, adding a lamellarization step before tempering made the effective grains of specimen QLT refined and also led to coarser Cu-rich precipitates in tempered M/B matrix. The weaker strengthening effect of coarser Cu-rich precipitates should be a key reason for the slightly lower yield strength in specimen QLT than in specimen QT. No austenite was found in all specimens Q, QL, QT and QLT. Specimen QLT showed purely ductile fracture mode at - 80 C due to the refined effective grains. The greatly improved toughness is mainly attributed to the enhanced energy of crack propagation. The combination of refined microstructure, softened matrix and deformation of minor ‘soft’ IF during crack propagation led to the most superior toughness of specimen QLT among all specimens. Keywords High-strength low-alloy steel Multistage heat treatment Low-temperature toughness Strengthening mechanism Grain refinement Crack propagation
1 Introduction Low-carbon, Cu-strengthened high-strength low-alloy steel (HSLA steel) with excellent combination of strength, toughness, superior weldability and corrosion resistance has been widely used for marine engineering application, mining and dredging equipment, and so on [1–6]. It was developed on the basis of high yield strength (HY) steel in order to improve its poor weldability caused by high carbon content as well as high hardenability agents such as
& Cai-fu Yang [email protected] 1
Department of Structural Steels, Central Iron and Steel Research Institute, Beijing 100081, China
chromium, nickel and molybdenum. Improved weldability has been achieved in Cu-s
Data Loading...
