Influences of cooling time (welding heat input) on microstructure, impact toughness and the fracture mechanism of the weakest CGHAZ (coarse-grained heat-affected zone) in a novel high-strength low-carbon microalloyed construction steel were studied for the purpose of laying a theoretical foundation for developing welding support technologies. When the cooling time (t8/5) was increased, the microstructure changed from dot shape M-A constituents and lath martensite/bainite to slender and blocky M-A constituents and coarse granular bainite. Accordingly, the impact toughness deteriorated. Large blocky M-A constituents seriously reduced the impact absorbed energy during crack initiation. For coarse bainite, the high-misorientation boundary almost disappeared. Therefore, crack initiation energy determines the cleavage fracture micromechanism of high heat input construction steel.
BakerTN.Processes, microstructure and properties of vanadium microalloyed steels. Mater Sci Technol. 2009; 25:1083–1107.
2.
LeeSI, LeeJ, HwangB.Microstructure-based prediction of yield ratio and uniform elongation in high-strength bainitic steels using multiple linear regression analysis. Mater Sci Eng A. 2019; 758:56–59.
3.
HulkaK, KernA, SchrieverU.Application of niobium in quenched and tempered high-strength steels. Mater Sci Forum. 2005; 500-501:519–526.
4.
ZhouYL, TaoJ, ZhangXJ, Microstructure and toughness of the CGHAZ of an offshore platform steel. J Mater Process Technol. 2015; 219:314–320.
5.
TakayamaN, MiyamotoG, FuruharaT.Chemistry and three-dimensional morphology of martensite–austenite constituent in the bainite structure of low-carbon low-alloy steels. Acta Mater. 2018; 145:154–164.
6.
KumarS, NathSK.Effect of weld thermal cycles on microstructures and mechanical properties in simulated heat affected zone of a HY 85 steel. Trans Indian Inst Met. 2016; 70(1):239–250.
7.
Lambert-PerladeA, GourguesAF, BessonJ, Mechanisms and modelling of cleavage fractures in simulated heat-affected zone microstructures in HSLA steel. Metall Mater Trans A. 2004; 35:1039–1053.
8.
KimS, KangD, KimT, Fatigue crack growth behavior of the simulated HAZ of 800 MPa grade high-performance steel. Mater Sci Eng A. 2011; 528(6):2331–2338.
9.
QiuC, LanL, ZhaoD, Microstructural evolution and toughness in the HAZ of submerged arc welded low welding crack susceptibility steel. Acta Metall Sin (Engl Lett). 2013; 26(1):49–55.
10.
ZhuZ, HanJ, LiH, High temperature processed high Nb X80 steel with excellent heat-affected zone toughness. Mater Lett. 2016; 163:171–174.
WanXL, WuKM, HuangG, Toughness improvement by Cu addition in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels. Sci Technol Weld Joi. 2016; 21(4):295–302.
13.
WangX, ChenC, WangH, Microstructure formation and precipitation in laser welding of microalloyed C–Mn steel. J Mater Process Technol. 2015; 226:106–114.
14.
ShanmugamS, RamisettiNK, MisraRDK, Microstructure and high strength-toughness combination of a new 700 MPa Nb-microalloyed pipeline steel. Mater Sci Eng A. 2008; 478(1-2):26–37.
15.
BayraktarE, KaplanD.Mechanical and metallurgical investigation of martensite–austenite constituents in simulated welding conditions. J Mater Process Technol. 2004; 153–154:87–92.
16.
KimBC, LeeS, KimNJ, Microstructure and local brittle zone phenomena in high-strength low-alloy steel welds. Metall Trans A. 1991; 22A(1):139–149.
17.
LuoX, ChenXH, WangT, Effect of morphologies of martensite–austenite constituents on impact toughness in intercritically reheated coarse-grained heat-affected zone of HSLA steel. Mater Sci Eng A. 2018; 710:192–199.
18.
HojnaA, FoscaDG, MichalC, Initiation of LME crack in ferritic martensitic steel in liquid lead-bismuth. J Nucl Mater. 2018; 511:459–472.
RykalinNN.Calculation of heat processes in welding. Moscow: Office for Official Publications of the European Communities; 1960.
21.
ShomeM.Effect of heat-input on austenite grain size in the heat-affected zone of HSLA-100 steel. Mater Sci Eng A. 2007; 445-446(2):454–460.
22.
ChristinaH, VitaliyB, AnV, High-resolution characterization of the martensite–austenite constituent in a carbide-free bainitic steel. Mater Charact. 2018; 144:182–190.
23.
GuXL, XuYB, PengF, Role of martensite/austenite constituents in novel ultra-high strength TRIP-assisted steels subjected to non-isothermal annealing. Mater Sci Eng A. 2019; 754:318–329.
24.
IrwinGR.Fracture dynamics, fracturing of metals. Cleveland: American Society for Metals; 1948, 147-166.
25.
TweedJH, KnottJF.Micromechanisms of failure in C–Mn weld metals. Acta Metall. Sin. 1987; 35:1401–1414.
26.
CurryDA, KnottJF.Effects of microstructure on cleavage fracture stress in steel. Met Sci. 1978; 12:511–514.
27.
MoritoS, HuangX, FuruharaT, The morphology and crystallography of lath martensite in alloy steels. Acta Mater. 2006; 54(19):5323–5331.
28.
LambertA, GaratX, SturelT, Application of acoustic emission to the study of cleavage fracture mechanism in a HSLA steel. Scripta Mater. 2000; 43:161–166.
29.
Diaz-FuentesM, Iza-MendiaA, GutierrezI.Analysis of different acicular ferrite microstructures in low-carbon steels by electron backscattered diffraction. Study of their toughness behavior. Metall Mater Trans A. 2003; 34A:2505–2516.
30.
KitaharaH, UejiR, TsujiN, Crystallographic features of lath martensite in low-carbon steel. Acta Mater. 2006; 54:1279–1288.
