Abstract
The effects of chromium additions on the microstructures and properties of submerged arc welded HSLA steels were examined using two different fluxes: a basic agglomerated flux and a recently developed flux designed to deposit titanium and boron.Instrumented impact tests were done on pre-fatigued Charpy specimens. These indicated that the titanium-boron flux was very beneficial to toughness, compared to the conventional flux. Metallographic examination showed that the major reasons for this were: (1) attainment of a 100 % acicular ferrite microstructure; (2) avoidance of the embrittlement of austenite grain boundaries which was found in all of the welds made using the conventional flux; (3) an increase in the upper shelf energy despite similar oxygen contents and (for a given Cr level) similar tensile properties and microhardness. Scanning Auger microprobe analysis showed segregation of P, C, N, Mo and Cr to brittle grain boundaries.Chromium additions were generally detrimental to toughness in both weld series. This decrease in toughness corresponded to a general increase in hardenability, indicated by microhardness and ultimate tensile strength, and by a deterioration of the microstructures, namely, increases in the fractions of martensite-austenite (M-A) and bainite phases.
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