Hardening mechanisms and impact toughening of a high-strength steel containing low Ni and Cu additions. (15th June 2019)

• Record Type: Journal Article
• Authors: Kong, H.J.; Xu, C.; Bu, C.C.; Da, C.; Luan, J.H.; Jiao, Z.B.; Chen, G.; Liu, C.T.
• Is Part Of: Acta materialia. Volume 172(2019)
• Page Start: 150
• Page End: 160
• Publication Date: 2019-06-15
• Subjects: Multiple strengthening mechanisms -- Impact toughening -- Temper-embrittlement -- Cu-rich nanocluster-strengthened high-strength low alloy (HSLA) steel -- Dislocation-precipitate interactions; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2019.04.041
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Aging treatments at 400–550 °C are commonly used to attain a peak strengthening for the Cu-rich nanocluster-strengthened high-strength low-alloy (HSLA) steels. However, these temperatures fall within the dangerous 300–600 °C temper-embrittlement regime, leading to poor impact toughness. On the other hand, aging at temperatures above the embrittlement regime can improve the impact toughness but at a great expense of strength. In this work, the strengthening mechanisms as well as the toughening of a low cost weldable HSLA steel with a low content of carbon (C ∼0.08 wt.%), nickel (Ni = 0.78 wt.%), and copper (Cu = 1.3 wt.%) were carefully investigated. Our findings show that the low-C-Ni-Cu HSLA steel is insensitive to the aging temperatures and can achieve a yield strength (YS) and ultimate tensile strength (UTS) over 1000 and 1100 MPa, respectively, with tensile ductility >10% (reduction of area >60%) at a heat-treat temperature of 640 °C through multiple strengthening mechanisms. Besides, a good low-temperature (−40 °C) impact performance (∼200 J) with high YS (∼900 MPa) and UTS (∼1000 MPa) can be obtained by seeking a strength balance among the fine grain size (∼2.5 μm), medium-sized (∼14 nm) overaged Cu-rich precipitates, tempered martensite, and fresh martensite (or carbides). Moreover, a relatively lower YS (∼800 MPa) and UTS (∼900 MPa) useful for steel manufacturing can be attained by a prolonged aging at 640 °C. In addition, the dislocation-precipitate interactions were also explored based on the dislocation theories in this study. Graphical abstract: Image 1