On the Brittleness of Heat-Affected Zone (Report 1)

Effect of Heat-Treatment on the Rimmed and Killed Steel

Abstract

There are several methods to judge the weldability, but the results determined by some method does not coincide necessarily with the result by the other method. The authors want to investigate the relation among the results of different methods about the brittleness of Heat-affected zone, and the results attained will be reported in the succeeding announcements. In the experiments Izod impact test, Hardness measurement, Microscopic and Xray observations are used, and the new method of Izod impact test revieled some interesting facts about the methods judging weldability of welded part.
In this report, as the fundamental test, the variation of properties by heat-treatment about Killed and Rimmed steels are investigated.
As the results of this experiment it was concluded that:
1) Rimmed steel of low carbon content became most brittle state by the water quench from 700°C., and Killed steel by the same quench from 800°C.
2) The most brittle state attained by 700°C. water quench will mainly be caused by the precipitation of carbide from Ferrite super-saturated with carbon, and the brittle ness after 800°C. water quench is mainly caused by the fundamental variation of the microstructures of Eutectoid.
3) Oxygen in steel accerelates extremely the precipitation and coagulation of cabide.