Abstract
E36 ship plate steel was, respectively, produced by as rolling and normalizing process (ARNP), and EH36 and FH36 ship plate steel was produced by the thermo-mechanical control process (TMCP) with low carbon and multi-element micro-alloying. The microstructure of the three grades of ship plate steel was composed of ferrite, pearlite, and carbides at room temperature. The average grain size on 1/4 width sections (i.e., longitudinal sections) of the three grades of ship plate steel was, respectively, 5.4 μm, 10.8 μm, and 11.9 μm. EH36 and FH36 ship plate steel had the higher strength due to precipitation and grain boundary strengthening effect, while the E36 ship plate steel had the lower strength due to the recovery phenomenon in the normalizing process. EH36 and FH36 ship plate steel had higher impact toughness due to lower carbon (C) and silicon (Si) content and higher manganese (Mn) content than E36 ship plate steel. E36 ship plate steel had the best plasticity due to the two strong {110} and {111} texture components. The fracture toughness KJ0.2BL(30) values of E36 and EH36 and KJ0.2BL value of FH36 ship plate steel were, respectively, obtained at 387 MPa·m1/2, 464 MPa·m1/2 and 443 MPa·m1/2. EH36 and FH36 ship plate steel had higher KJ0.2BL(30) due to lower C and Si and higher Mn, niobium (Nb), vanadium (V), and aluminum (Al) content than the E36 ship plate steel. The fatigue crack growth rate of E36 ship plate steel was higher than that of EH36 and FH36 ship plate steel due to its higher carbon content and obviously smaller grain size. The analysis results and data may provide a necessary experimental basis for quantitatively establishing the relationship between fracture toughness, yield strength and impact toughness, as well as the relationship between fatigue crack growth rate and both strength and fracture toughness.
Highlights
It was well known that ship plates were subjected to the strong wind and wave impact and alternating loads in the process of transporting goods
As can be seen from the images, the microstructure of the three grades grades of plate steel plate was all composed of white ferrite black-and-white pearlite which of steel was all composed of white ferrite and and black-and-white pearlite which were were distributed at intervals
The results show that the strength increment caused by precipitation strengthening of
Summary
It was well known that ship plates were subjected to the strong wind and wave impact and alternating loads in the process of transporting goods. From the perspective of resource conservation and environmental protection, ships need to be lighter, which requires ship steel plates to have higher strength and toughness. Ship plate steel with high strength and toughness at the grade of AH, EH, DH or FH has become a research hot-spot [1]. In order to obtain high strength and toughness, low-carbon, high-manganese, composite microalloying of Nb, V, titanium (Ti), nickel (Ni) and other elements, TMCP, or the normalizing process after hot rolling have been studied for ship plate steel at higher grades. The strength of the DH40 steel plate was improved by adding Nb and Ti elements, whose precipitates played a role in precipitation strengthening and restraining the austenite grain growth [3]. The volume fraction of pearlite in the as-cast structure of the FH40 steel plate was reduced by adding Mg and
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