EFFECT OF HEAT-TREATMENT AND MICROALLOYING ON THE STRUCTURE AND PROPERTIES OF CONTROLLED ROLLED TYPE 20K BOILER-GRADE CARBON-STEEL

This paper deals with a study of the effect of heat treatment (normali zing for 1 h in air at 930 degrees C or tempering for 1 h in air at 65 0 degrees C) on the structure and characteristics of short-term (sigma (T), sigma(0.2), sigma(T)(450), sigma(0.2)(450) and long-term (sigma(1 0000)(450)) strength of type 20K boiler steel microalloyed with vanadi um (less than or equal to 0.06%)) and/or niobium (less than or equal t o 0.03%) after controlled rolling (T-fin = 750, 800, 850 degrees C). C ontrolled rolling and microalloying with niobium (or V + Nb) increased the strength of 20K steel by 40-45%; microalloying only with vanadium increased the strength by 30-35%. The difference in the plasticity of carbon and microalloyed steel is insignificant. The most favorable co mbination of short-term strength, long-term strength, plasticity and i mpact strength was achieved by controlled rolling in the temperature r ange close to Ar-3, (T-fin = 800 degrees C).