Microstructures and mechanical properties in ultra-thick EH47  steel plates and heat affected zones

LIU Dong-sheng; CHENG Bing-gui; LUO Mi; QU Jin-bo

doi:10.13228/j.boyuan.issn0449-749x.20200335

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Iron and Steel ›› 2021, Vol. 56 ›› Issue (3) : 92-102. DOI: 10.13228/j.boyuan.issn0449-749x.20200335

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Microstructures and mechanical properties in ultra-thick EH47 steel plates and heat affected zones

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Abstract

A microalloyed low carbon MnCrNiCu steel has been proposed to develop EH47 steel plates via thermomechanical controlled processing(TMCP) route. The effect of hot deformation of austenite or cooling rate on phase transformation in the steel was investigated. Heavy steel plates with maximum thickness of 85 mm were rolled. Submerged arc welding(SMA) and flux-cored arc welding(FCAW)processes were employed in welding trials,respectively, to evaluate the weldability of the thickest plate. Microstructures in the plates and the coarse-grained heat affected zone(CGHAZ) were characterized. Ductile-to-brittle transition temperatures(DBTTs) in the plates were measured based on a series of instrumented Charpy V notch(CVN) impact tests, followed by the determination of the local cleavage fracture stresses(σ_f). Microhardness and CVN impact toughness in the heat affected zone(HAZ) produced by either SMA or FCAW were also tested. Full thickness crack tip open displacement(CTOD) in the mother plate or the weld joints was tested at -10 ℃ leading to evaluation on the crack-initiation toughness(K_c) in the ultra-thick plate or the weld joints. A temperature dependency of crack-arrest toughness(K_ca)in the ultra-thick plate was determined based on a series of large scale double tension(DT)tests across the entire thickness of the ultra-thick plate. The results show that:a mixture of polygonal ferrite(PF)+acicular ferrite(AF)associated with dispersed martensite-austenite constituents was produced in the plates. An increase in σ_f leads to a decrease in DBTT. The critical events of cleavage fracture during the CVN testing and DT crack arrest testing are identical being grain-sized cracks. In comparison with the CGHAZ where quasi-polygonal(QPF)+AF are produced by SMA,cleavage crack can be initiated more easily in the CGHAZ by FCAW due to the formation of brittle GB. As a result,K_c associated with the latter CGHAZ is lower than the former. K_ca at -10 ℃ is determined being 7 140 N/mm^3/2indicating satisfactory crack arrestability in the mother plate.

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TMCP / EH47 crack arrest steel / cleavage fracture stress / crack-initiation toughness / crack-arresttoughness

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LIU Dong-sheng, CHENG Bing-gui, LUO Mi, et al. Microstructures and mechanical properties in ultra-thick EH47 steel plates and heat affected zones[J]. Iron and Steel, 2021, 56(3): 92-102 https://doi.org/10.13228/j.boyuan.issn0449-749x.20200335

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