Production and properties of modified 9Cr-1Mo steel forging (F91) for valve bodies

In order to conserve the energy resources and to reduce the dependence to o il, the large coal fired power plant which was improved heat efficiency has been currently developed. A very effective method of improving the heat ef ficiency of steam power plant is the raise of steam conditions, it is impor tant to develop the high temperature turbine valve forging which is used as the major structural material of this steam power plant. Modified 9Cr-1Mo (Grade 91) steel has been incorporated to the parts of boiler in thermal pl ants due to its excellent properties at high temperatures. In recent years, this steel has also been applied to the parts of turbine in ultra super cr itical plants, Former experience with a process for manufacturing forged va lves of low alloy steel in thermal power plants have enabled the applicatio n of F91 steel to forge as valves. A 25-ton ingot was made by the basic ele ctric furnace and was molded to valve bodies by combination of forging and shaping with Gas. The manufacture of trial valve with F91 steel have succes sfully been performed. They exhibited high quality, good creep rupture prop erties and excellent toughness.