Solidification Cracking in Low Alloy Steel Weld Metals

Abstract

A study has been made of the effects of material composition
and welding variables, particularly speed, on weld metal
solidification cracking. This has involved low alloy steels
to specifications En24, SAE4130, ASTM A387B, and several
aircraft steels. Existing relationships between composition
and cracking have been critically examined, and an improved
expression, based on regression analysis, has been developed
using data relating to some 80 Steels. Practical cracking
tests were carried out using the Huxley test, and a comparison
of these results with the predictions of the regression
analysis confirmed the crack-promoting influences of sulphur,
phosphorus and carbon, and isolated the important crack inhibiting
effect of oxygen.

The influence of welding speed was found to be complex
and varied with the composition of the steel. In general an
increase in speed is detrimental at low speeds, but becomes
beneficial when the speed is raised. This phenomenon is
explained by a model in which changes of speed are shown to
cause opposing effects, which interact to give the characteristic
relationship.

The morphology of inclusions was also examined, and
crack susceptibility was found to be associated with sulphide
films.

The practical significance of the work is also discussed.
Apart from exposing important new effects, the results
facilitate the assessment of chemical effects on cracking; and demonstrate the importance of selecting welding variables
appropriate to the particular materials being used.

Two different tests have been used in the work for
specific purposes. The results demonstrate the overwhelming
importance of selecting a test suitable for the situation
under examination.

Date of Award	1972
Original language	English