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(σf). 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(Kc) in the ultra-thick plate or the weld joints. A temperature dependency of crack-arrest toughness(Kca)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 σf 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,Kc associated with the latter CGHAZ is lower than the former. Kca at -10 ℃ is determined being 7 140 N/mm3/2indicating satisfactory crack arrestability in the mother plate.
[1] Hase K,Handa T,Eto T. Development of YP 460 N/mm2class heavy thick plate with excellent brittle crack arrestability for mega container carriers[J].JFE Technical Report,2015(20):14. [2] 孙德顺,陈益华,张珂,等. EH47船板钢热加工图的建立[J]. 钢铁,2015,50(11):93.(SUN De-shun,CHEN Yi-hua,ZHANG Ke,et al. Establishment of the hot processing map of shipbuilding steel EH47[J]. Iron and Steel, 2015, 50(11): 93.) [3] International Association of Classification Societies. Requirements Concerning Strength of Ships:S33 Requirements for Use of Extremely Thick Steel Plates[S]. London:[s.n.], 2013. [4] Wiesner C S. Predicting structural crack arrest behavior using small-scale material characterization tests[J]. International Journal Pressure Vessels and Piping,1996,69(2):185. [5] Morris J W. On the ductile-brittle transition in martensitic steels[J].ISIJ International,2011,51(10):1569. [6] CAO R,ZHANG X B,WANG Z,et al. Investigation of microstructural features determining the toughness of 980 MPa bainitic weld metal[J].Metallurgical and MaterialsTransactions A,2014,45(2):815. [7] CAO R,LI J,LIU D S,et al. Micromechanism of decrease of impact toughness in coarse-grain heat-affected zone of HSLA steel with the increasing weld heat input[J]. Metallurgical Materials Transactions A,2015,46(7):2999. [8] LIU D S,LUO M,CHENG B G,et al. Microstructural evolution and ductile-to-brittle transition in a low carbon MnCrMoNiCu heavy plate steel[J]. Metallurgical and Materials Transactions A,2018,49(10):4918. [9] CHEN J H,CAO R. Micromechanism of Cleavage Fracture of Metals:A Comprehensive Microphysical Model for Cleavage Cracking in Metals[M]. Oxford, UK:Elsevier,2014. [10] Yanagimoto F,Shibanuma K,Suzuki K,et al. Local stress in the vicinity of the propagating cleavage crack tip in ferritic steel[J]. Materials and Design,2018,144:361. [11] Yanagimoto F,Shibanuma K,Suzuki K,et al. A physics based model to simulate brittle crack arrest in steel plates incorporating experimental and numerical evidences[J]. Engineering Fracture Mechanics,2019,221:1. [12] 马江南,王瑞珍,杨才福,等.中厚板表面超细晶粒对止裂性能的影响[J].金属学报,2017,53(5):549.(MA Jiang-nan,WANG Rui-zhen,YANG Cai-fu,et al. Effect of surface layer with ultrafine grains on crackarrestability of heavy plate[J]. Acta Metallurgica Sinica,2017,53(5):549.) [13] WU J Y,WANG B,WANG B X,et al. Toughness and ductility improvement of heavy EH47 plate with grain refinement through inter-pass cooling[J]. Materials Science and Engineering A,2018,733:117. [14] WANG H T,TIAN Y,YE Q B,et al. Determining role of microstructure on crack arrest and propagation phenomenon in low-carbon microalloyed steel[J]. Materials Science and Engineering A,2019,761:1. [15] 牛延龙,刘清友,贾书君,等. 控冷工艺下组织及M/A岛对管线钢韧性的影响[J].钢铁,2020,55(6):91(NIU Yan-long,LIU Qing-you,JIA Shu-jun,et al. Influence of microstructure and M/A island evolution on toughness of pipeline steel under controlled cooling process[J]. Iron and Steel,2020,55(6):91.) [16] Lambert-Perlade A,Gourgues A F,Besson J,et al. Mechanisms and modeling of cleavage fracture in simulated heat-affected zone microstructures of a high-strength low alloy steel[J].Metallurgical and Materials Transactions A,2004,35(3):1039. [17] LIU D S,CHENG B G,LUO M. F460 heavy steel plates for offshore structure and shipbuilding produced by thermomechanical control process[J]. ISIJ International,2011,51(4):603. [18] LIU D S,LI Q L,Emi T. Microstructure and mechanical properties in hot rolled extra-high-yield-strength steel plates for offshore structure and shipbuilding[J].Metallurgical and Materials Transactions A,2011,42(5):1349. [19] 周成,严玲,张鹏,等. 集装箱船用EH47高止裂钢的组织和性能[J]. 材料热处理学报,2017,38(8):83.(ZHOU Cheng,YAN Ling,ZHANG Peng,et al. Microstructure and mechanical properties of EH47 high strength brittle crack arrest steel for container ship[J]. Transactions of Materials Heat Treatment,2017,38(8):83.) [20] Server W L. General yielding of Charpy V-notch and precracked Charpy specimens[J]. Journal of Engineering Materials Technology,1978,100(4):183. [21] British Standard Institution. British Standard BS 7448:Fracture Mechanics Toughness Tests,Method for Determination of KIC,Critical CTOD and Critical J Values of Metallic Materials[S]. London:British Standard Institution,1991. [22] The Japan Welding Engineering Society. WES 2815:Test Method for Brittle Crack Arrest Toughness,Kca[S]. Tokyo:The Japan Welding Engineering Society,2014. [23] Jang J I,Lee B W,Ju J B,et al. Crack-initiation toughness and crack-arrest toughness in advanced 9 Pct Ni steel welds containing local brittle zones[J]. Metallurgical and Materials Transactions A,2002,33(8):2615. [24] Choi D,Lee H,Cho Sung-K,et al. Microstructure and Charpy impact properties of FCAW and SMW heat affected zones of 100 mm thick steel plate for offshore platforms[J]. Metals and Materials International,2020,26(2):867.