Brittle Fracture Initiation Characteristics of 9% Ni Steels and Welded Joint Deposited with Various Ni Content Electrodes

Abstract

Recently, employment of 9% Ni steels for low temperature structures such as liquid oxygen storage tank has been increasing. The most important problem for those structures is the brittle fracture characteristics of materials.
9% Ni steel has been welded with 70% Ni electrode such as Incoweld A. However, the electrode is very expensive, and reduction of nickel content has been strongly demanded.
In this paper, the brittle fracture initiation characteristics of 9% Ni steel plates quenched and tempered (QT) and doubly normalized and tempered (NNT) was investigated by the deep notch test.
In addition, the brittle fracture initiation characteristics of bond and weld metal deposited with 70, 50, 40, 35, 20 and 12% Ni electrodes was investigated.
It can be concluded that 9% Ni steel is excellent in brittle fracture initiation characteristics and can be applied safely to the liquid nitrogen storage tank, and all kinds of electrode tested provide similar quality of bond and weld metal. Weld metals with a notch never fracture in a brittle manner even at -196°C.