Ship building materials:

Posted:10/4/2013 10:28:06 PM

In ship building there are a variety of materials used depending upon the location the material is being used and the amount of stress the material is expected to take at various stages. The following are commonly used amongst them, Steel- There is a different type of steel used in the ship building depending on the location it is to be used. For hull construction usually mild steel containing 0.15 to 0.23 % carbons and a high manganese content is used. Sulphur and phosphorus content in the mild steel are kept to a minimum, as low as 0.05 %. High tensile steel have greater strength than that of the mild steel and are used in the regions where high stress concentrations are expected to occur. Using high tensile steel also allow the thickness of the plate to be reduced. During the design stage only it is recommended to consider the weld ability of the steel. Stainless Steel -steel is mixed with alloy elements to form corrosion resistant. This kind of steel is normally not used because of its high initial and fabrication costs. Only the ships which are designed to carry high corrosive cargoes are fabricated with this type of steel. Steel castings are produced by open hearth, electric furnace or oxygen process is poured into a carefully constructed mould and then allowed to solidify to the shape required after removal this type of steel need to be heat treated by the following process annealing, or normalizing and tempering to reduce the brittleness. Example of locations where this type of steel is used is rudder frames, stern frames, spectacle frames for bossing etc. Steel which is being used for ship building is approved by the classification society after carrying out the entire required test. The properties required for steel used in ship building are as follows: Reasonable cost, easy to weld with simple equipment, easy to do repairs on, ductility and homogeneity, yield point to be a high proportion of ultimate tensile strength, while flame cutting it shouldn't harden, comparatively resistant to corrosion. Properties of steel can be altered by the following processes. Annealing: This is done by heating the steel at a slow rate to a temperature of 850 deg C and then cooled in a furnace at a slow rate. This is done to relieve an internal stress, to soften the steel or to bring to a suitable condition for subsequent heat treatment. Normalizing: This is done by heating the steel at a slow rate to a temperature same as that of annealing (850 deg C) then cooled down in air, this result in faster cooling and hence the steel becomes harder and stronger than the annealing process. Quenching: This is done by a similar way like the above but cooled by water or oil. Hence cools faster than the above two process leading to a very hard structure with high tensile strength. Tempering: In this process the steel is heated to a temperature of about 650 deg C and then cooled down very rapidly by quenching in oil or water. This relieves the internal stresses caused by the heat treatment for hardening. Makes the steel less brittle and retains the high tensile strength.