A method of forging and heat treatment of forged pieces of circular plates made of stainless CrNi austenitic steels alloyed with niobium

摘要

A method of forging and heat treatment of forged pieces of circular plates made of stainless CrNi austenitic steels alloyed with niobium, when the niobium content in the steel is eight times the weight percent of the carbon content, comprises these manufacturing steps: in the first stage, forging at a temperature from 1030 to 1070°C with the lowest degree of deformation in each operation of 25% is performed and, in the second stage, final forging of the circular plates is conducted at a maximum temperature from 1020 to 1040°C and the size of the applied deformation at the last forging operation is of at least 35%, whereupon the forged piece of the circular plate is controllably cooled by air to a temperature of about 400°C. This is followed by solution annealing during which the furnace is heated to a temperature of 880 to 920°C and the forged piece is charged in this furnace and heated to a solution temperature which is moving at a rate that is in the range of 30 to 65°C/h, wherein the length of heating the forged piece depends on its thickness, and the desired solution annealing temperature ranges from 1000 to 1040°C and lasts for 2 to 3 hours. Subsequently, the forged piece of the circular plate is directly cooled in water to a temperature of about 150°C. With lower strength of the forged piece and its lower yield point, the production is complemented with precipitation annealing of the forged piece.