TMCP steels were developed in Japanese steel makers about 20 years ago. They are extensively used in ship building industry and are diversifying to other industries such as marine structures, bridges and soon. Reentry European and Korean steel makers produce TMCP steel also. They have not only great merits but also possible demerits. In this paper, these merits and demerits are explained in addition to recent topics in Japan about TMCP steel.
For recent years, ships with extensive use of high tensile steels with tensile strength of 5OOMPa class (HT-500) have increased more and more in number in Japan for the purpose of reducing their hull weight, thus leads to reduce its material cost. This is because Thermo- Mechanical Control Process (TMCP) has been developed and TMCT steels have good weldability due to their low C,, Though Japanese steel makers developed TMCP steels that meet the extensive demand of strength and toughness for line pipe had become a center of attraction from Japanese shipbuilders. The shipbuilders have utilized various highly efficient welding technologies in their fabrication. Accordingly, a great deal of joint work among them including university professors has been carried out to put such steel and welding technology into practical use in the Shipbuilding Research Association of Japan (SR193), that has resulted in the accumulation of an abundance of useful data. This paper shows the characteristics of TMCP steels and their welded joints from the viewpoints of welding procedures, fracture toughness and fatigue strength, which is summarized mainly in the SR193 committee (1985). Moreover recent topics about TMCP steels are also explained.
TMCP steels are basically classified into two types: non-accelerated cooling (Non-AcC) and accelerated cooling (AcC) processes. Fig.1 shows a schematic diagram of TMCP in comparison with conventional rolled process.