High Temperature Properties and Weldability of 1Cr-1Mo-1/4V-B Heat Resistant Steel

Abstract

For the purpose of application to boiier main steam pipes, the continuous cooling transformation, high temperature strength, weldability by restrained crack test, creep-rupture strength and the oxidation resistance of a newly-developed 1Cr-1Mo-1/4V-0.003B steel have been investigated.
This steel has a better hardenability than 1Cr-1Mo-1/4V steel. The high temperature strength of this steel does not decrease with the decrease of cooling rate from 1400°C/h to 300°C/h and does not change appreciably by the hot bending thermal cycle. The 10⁵h creep-rupture strength at 600°C of this steel as the base metal is 8.4kg/mmmm² and that as a welded joint is 6.1kg/mmmm². These values are 2 times and 1.5 times higher than those of 21/4Cr-1Mo steel respectively. The improvement of high temperature strength is mainly due to the upper bainite structure with uniformly dispersed fine VC carbides. Furthermore, the weldability and the oxidation resistance at temperatures below 650°C of this steel are comparable to those of 21/4Cr-1Mo steel. Thus this steel is favourable for the boiler main steam pipe application.