| Summary: | 碩士 === 國立中正大學 === 機械系 === 88 === Thermomechanical controlled process steel (TMCP steel) was manufactured by controlled rolling and accelerated cooling process for lower alloy content and higher strength. Higher strength can be achieved by adding Ni, V, and Ti elements. The weldability of TMCP steel may be affected by these elements.
In this work, the weldability of 60kg/mm2-grade TMCP steel was studied at high heat input. Thermal simulation of the real welding processes was conducted using Gleeble 1500. Simulated microstructure of heat affect zone was observed. Simulated specimens were tested for hardness, strength, and toughness in order to understand the HAZ degradation under different heat input. Furthermore, hot ductility test and nil-strength test were carried out to analyze the mechanism of hot crack. Observation on the crack surface of hot ductility specimen was conducted and the results of hot ductility test were confirmed. Hot ductility curves and ultimate strength curves were plotted and hot crack susceptible region in HAZ was predicted.
Comparing the weldability between the 50kg/mm2 grade and 60kg/mm2 grade TMCP steel, it has been found that the 60kg/mm2 grade TMCP steel exhibited better weldability than 50kg/mm2 grade TMCP steel.
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