Steels for Shipbuilding...

Steels for Shipbuilding Ship structures are determined by the ship’s mission and intended service. These determine a ship’s size, complexity and the function of the structural components. There are inherent uncertainties in the loads imposed on the ship structure because of the random nature of the loads imposed by the marine environment. Unlike a fixed, land-based structure, a ship derives its entire support from the buoyancy provided by a fluid, which transmits these loads to the hull structure. Iron hulls replaced wooden hulls in the second half of the 18th century, to be followed up by steel. Since then seagoing ships and inland barges are being regularly designed with several steel grades and shapes. Steels are the most common materials being used for shipbuilding. These steels are rather to meet strict requirements such as strength, flexibility, high manufacturability, weldability, and cost, reparability, etc.  Steels used in the shipbuilding industry also need high cold-resistance, good welding characteristics and increased fracture strength. Modern steel shipbuilding involves the fabrication of a complex steel structure, into which a wide range of ready-made equipment is fixed. Today the principal raw material is steel plate and the layout of  a modern shipyard is arranged to facilitate the flow of steel received from the steel plant through the various processes of making out, cutting, bending, welding, fabricating subassemblies, and final erection of the prefabricated units into the hull and the superstructure. In shipbuilding, there is usually a trade off in the use of material and complex structures. Typically, a complex structure requires more labour and fabrication than a simpler structure, which uses more material. There is also a tradeoff between using more complex structure and the lighter weight of the vessel, as a lighter ship can carry more cargo for a...

Thermo Mechanical Control Processing in Rolling Mills Jul07

Thermo Mechanical Control Processing in Rolling Mills...

Thermo Mechanical Control Processing in Rolling Mills Thermo mechanical controlled processing (TMCP) is a technique designed to improve the mechanical properties of materials by controlling the hot-deformation process in a rolling mill. This was originally designed to produce the required external shape of the product. Controlled rolling, controlled-cooling and direct-quenching are typical examples of thermo mechanical controlled processing. Such processing saves energy in the manufacture of steel by minimizing or even eliminating the heat treatment after hot-deformation, thus increasing the productivity for high grade steels. It normally requires a change in alloy design and often reduces the productivity of the hot deformation process itself, but at the same time makes it possible to reduce the total amount of alloying additions and to improve weldability, whilst sometimes producing new and beneficial characteristics in the steel. TMCP process has several advantages that can help overcome issues related to the addition of major alloying elements and conventional heat treatments. TMCP steels with added micro alloys have been developed to manage the conflicting requirements of strength, toughness and weldability through grain refinement. TMCP effectively enables a reduction of the preheating temperature, thus lowering the rolling cost. As TMCP steels afford good weldability, they are highly valued in industries such as shipbuilding, offshore structures, pipelines and building construction. TMCP is the sophisticated combination of well-defined deformation operations and well-defined heat treatment in a single production stage to control the microstructure of the steel being rolled. TMCP produces steels with the desired external qualities (dimensions, shape and surface quality) and acceptable mechanical properties. TMCP is normally considered as the final stage in the production of steels. TMCP is generally associated with hot rolling operations in hot strip mills, plate mills and bar and rod mills. For example, in case of...