• 대한조선학회논문집
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• 제45권4호
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• pp.426-431
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• 2008

The high-strength low-alloy(HSLA) steels have low carbon contents($0.05{\sim}0.25%$ C) in order to produce adequate formability and weldability, and they have manganese contents up to 1.7%. Small quantities of silicon, chromium, nickel, copper, aluminum, molybdenum are used in various combinations. The results contained in this paper can provide the valuable information on the development of $-40^{\circ}C$ low temperature HSLA. Furthermore, the present experimental data will provide important database for casting steel materials of the offshore structure.

• 열처리공학회지
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• 제14권5호
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• pp.267-274
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• 2001

Microalloyed steels, which substituted by conventional quenched and tempered steels, have been used in a wide variety of structural and engineering application. The main driving force for preference of MA steels is a cost reduction which can be achieved by an omission of heat treatment. In this study, low carbon martensitic MA steels in 0.18C-0.30(0.60)Si-2.00(1.80)Mn-0.05S-1.5Cr-0.05(0.10)V-0.015Ti(wt%) were investigated to know the effects of cooling method on the mechanical properties and microstructures of Si, Mn, V added microalloyed steel at different reheating temperature. Microstructure of oil quenched steels which were comprised lath martensite, auto-tempered martensite and retained austenite, had more various structure than that of air cooled steel made of mainly bainite. Therefore, oil quenched steels, which had more various microstructure, had better strength-toughness balance compare to air cooled steels. In the impact test, fracture mode of oil quenched steels, which showed good mechanical properties, were dimple, but that of air cooled steels were cleavage.

• Advances in materials Research
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• 제7권3호
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• pp.195-201
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• 2018

High Strength low alloy steels containing various levels of C, Nb and Mn were used and for each of which, a simulated double thermal cycle was applied with the same first peak temperature and different second peak temperatures to produce HAZ microstructure corresponding to multi-pass weld. Effect of double cycle second temperature on the microstructure was observed and compared with single cycle results obtained from previous works, it was found that the percentage of martensite austenite constituent (MA) increases by Nb addition for all steels with the same Mn content and the increase in Mn content at the same Nb content shows an increase in MA area fraction as well. MA area fraction obtained for the double cycle is larger than that obtained for the single cycle for all steels used which imply that MA will have great role in the brittle fracture initiation for double cycle and the inter-pass temperature should be controlled for medium and high-carbon Mn steel to avoid large area fraction of MA. The beneficial effects of Niobium obtained in single pass weld were not observed for the double cycle or multi pass welds.