On the Choice of Material and Requrements in Heat treatment in the Specification

Abstract

In respect to welding of penstocks, there should be confirmed the conditions of crack free fabrication. Among them, choice of materials is primary importance. Proper preheating and post treatment of welded part are expected to get favorable effect to prevent crack initiation and its propagation.
Rimmed Steel has a higher transition temperature and top part of a rimmed ingot usually shows a considerable seggregation. Under welding process, the top part is apt to bring about some cracks, especially, sulphur cracks sometimes occur in submerged arc welding.
Therefore it has been decided in this specification that steel plates used for should be better than a certain grade as shown in table.
Plate thickness t mm. Kinds of steel
t≤12.7 ship plate(S.M.)
12.7<t≤25.4 ship plate(S.M.W.)
holding composition ratis of Mn/C>2.5
t>25.4 Killed steel plate
Preheating temperature required is above 70°C for the plate thicker than 25.4 mm. post-heating in furnace at temperature 600-650°C shall be applied to the plate of which thickness is more than 25.4 mm. However, if it is impossible to do, local heating such as induction heating may be allowed to use in place of furnace heating with the order's approval.