Papers by Keyword: TMCP Steel

Abstract: In this paper an influence of simulated thermal cycle on properties and HAZ structure of 10 mm thick S700MC steel plates. The introduction of thermomechanically processed steels with high yield and relatively low carbon equivalent, will significantly reduce the time of welding works by reducing the preheating temperature, or even complete removal of this processing step, furthermore reduction of cross-sectional areas of structural elements, making welded structures with the same capacity will be more slender and lighter. The simulation of thermal cycles was carried out on a specially built test stand equipped with resistive heating source infrared camera VarioCam Head HR with 50 mm lens and a computer with software IRBIS 3 plus. Simulation was prepared for simple and complex thermal cycle. Simulation studies of thermal cycles consisted of resistive heating of samples prepared for the impact test. Single thermal cycles were simulated at temperatures ranging from 400 to 1300 oC, 100 oC and the cycle complex. For each temperature three repeats were carried out. Specimens were tested on impact, strength test and also hardness and metallographical tests. The study showed that there is a possibility to use a purpose built system to simulate simple and complex thermal cycles of S700 MC steel in specific ranges of the cooling time t_8/5. Analysis of the results of the study showed that the welding thermal cycle strongly influences the structural changes and phase in the HAZ zone of S700 MC steel. Areas of HAZ heated to high temperatures above 1000 [°C], show a sudden drop of toughness to unacceptable levels of impact strength (27 [J/cm²]). This sharp decrease in toughness is associated with uncontrolled separation processes of MX phases and dissolution of carbides, niobium and vanadium carbonitrides in austenite during heating. The study also showed that the chemical composition of steel and especially titanium and aluminium content is sufficient to bind in the HAZ free nitrogen and reduce the aging process. The control of the amount of heat introduced into the joint area during welding will reduce the adverse separation processes in the weld and HAZ which will ensure adequate toughness of the connection. Precise knowledge of the phenomena occurring in the HAZ during the thermal cycle can impact the ability to control properties and structure of the welded joint.

Abstract: A new lower cost 600MPa TMCP steel with high strength,good low temperature impact toughness,low yield ratio and excellent weldability has been developed successfully by design of alloy composition and thermal mechanical control process technology, and the welding heat affected zone(HAZ) have been investigated. The systematic studies show that the new developed steels gather high strength, high low temperature toughness, good seismic performance(low yield ratio) and excellent weldability, and the base steels have a good match of strength and toughness. A large number of fine acicular ferrite in HAZ can ensure that the welding plate has high strength and good low temperature impact toughness. The comprehensive performance of steel can meet fully the high-technical requirements of large-scale engineering.

Abstract: The purpose of this study is to identify the principal factors controlling the formability of TMCP steel for curved hull plate. In order to do it, the initial residual stress in TMCP steel was evaluated using flatness measured in the flat bar cut by flame and analytical approach. Changes of the curved profiles in conventional steel and EH 36 TMCP steel of 50mm thick during cold bending and local heating were investigated using 3 dimensional measuring instruments. It was found that the formability in TMCP steel was mainly determined by the excessive distortion by the relaxation of residual stress during cold bending.

Abstract: In recent time there are vigorous requirements for the use of thick steel plate in various industrial fields, including shipbuilding industry. Especially, application of TMCP steel plates on steel structure is progressively increasing now. Welding process with high heat input is necessary to be used in thick steel assembly for the purpose of the high productivity. However, HAZ softening of TMCP steel plates has a possibility to reduce the strength of welded joint. In this study, therefore, the tensile strength of TMCP weldments, having softened HAZ, was examined using the numerical calculation and experiments.

Abstract: In this research, corrosion fatigue tests using tensile strength of 490MPa TMCP steel were performed in synthetic seawater condition to investigate the corrosion fatigue crack propagation characteristics. The influence of cathodic protection at -800mV vs. SCE on the corrosion fatigue crack propagation behavior was investigated. Relationships between da/dN versus ΔK for the material were obtained by two types of test specimens. In the present study, F(α,β) versus α(= 2a/W) relationship for the CCT specimen was calculated by J integral approach, while that for the CT specimen was determined from ASTM E647. It is found that the fatigue crack propagation rate of TMCP steel in synthetic seawater condition is faster than that in air condition at least twice. Also, it is observed that the fatigue crack propagation rate of steel with cathodic protection is in between those of seawater condition without cathodic protection and air condition.

Abstract: TMCP steels produced by thermo-mechanical control process are now spot lighted due to the excellent combinations of strength, toughness and weldability. Recently, in Korea, high strength SM570-TMCP steel whose tensile strength is 600MPa has been developed and applied to steel structures due to its excellent nature. But, for the application of the TMCP steel to steel structures, it is necessary to elucidate not only the material characteristics but the mechanical characteristics of welded joints. In this study, high temperature tensile properties of the SM570-TMCP steel were investigated through the elevated temperature tensile test and the characteristics of residual stresses in welded joints of the TMCP steel were studied through the three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis on the basis of mechanical properties at high temperatures obtained from the experiment. The results are then compared with the conventional quenched and tempered high strength SM570 steel.

Abstract: In this research, corrosion fatigue tests using 490MPa TMCP steel were performed in synthetic seawater condition to investigate the corrosion fatigue crack propagation characteristics of TMCP steel plate which is often used for ships and offshore structures from its weldability and weight reduction purpose. In addition, relationships between boundary correlation factor F(α,β) and α(= 2a/W) of the fracture mechanics formula for the test specimen which was exerted by the pin load were calculated for the evaluation of da/dN-.K. To get the boundary correlation factor F(α,β), the calculation of J as a path-independent line integral was carried out. The solutions of J integral showed similar value in spite of the different path. Crack propagation tests for the same steel in air condition was carried out also for comparison. Finally, it was clear from the crack propagation test results that the propagation rate of TMCP steel plate in synthetic seawater condition is faster than that of in air condition at least twice.

Abstract: The wire for high strength and toughness TMCP steels of submerged arc welding was developed. The low carbon and micro-alloying with Ti-B system was adopted to obtain the acicular ferrite dominated deposited metals. Experimental results show that the carbon equivalent (Pcm) should be higher than 0.17, which can ensure the high strength and high toughness of the deposited metals. In the alloy system, Oxygen and Nitrogen contents, micro-alloyed elements (C, Mn) and its mixture ratio are the key factors that affect the deposited metals toughness. With increasing C, Mn content, the acicular ferrite is increased and toughness is improved. Oxygen and Nitrogen are deleterious to the toughness of deposited metals.