Abstract
M.Ing.
3CR12 is a corrosion resistant steel that was developed in the 1980’s as an alternative to coated
mild steel in the construction industry. The low chromium content together with an absence of
nickel result in a competitative production cost. It has good welding characteristics when
compared to the other ferritic grades.
Because of the cost and difficulties involved, structural hot-rolled sections in 3CR12 (or any other
stainless steel for that matter) are not commercially available. Sections are either cold formed or
built-up through various welding techniques. Design in cold formed stainless steel sections are
done in accordance to the SABS 0162-4:1997 code of practice. In general welded built-up
sections should comply with the SANS 10162-1:2005 code of practice.
Little is known about the structural behaviour of built-up stainless steel and particularly 3CR12
fabricated sections. Currently sections are fabricated using both manual metal arc and laser
welding. The effect of using different welding techniques (which has become common practice) is
totally unexplored.
The aim of this research is therefore to investigate the structural behaviour of built-up 3CR12
sections when fabricated by using either manual metal arc or laser welding techniques.
The investigation was initiated by conducting a comprehensive literature review with specific
reference to built-up 3CR12 structural sections. This is followed by an experimental investigation
utilizing the neutron diffraction technique to determine the typical residual stress profile
associated with manual metal arc and laser-welded built-up 3CR12 sections. This data is then
used as input to a non-linear finite element investigation where the effect of the residual stress
profile on the structural integrity of selected axial structural members (columns) is evaluated. An
experimental program where a selected number of full scale fabricated sections were tested as
axial members was then conducted to act as comparison and validation of the numerical model.
The research found that both the welding techniques investigated may be successfully used to
fabricate the structural sections. There is however a distinct difference in the residual stress
profile within the sections between the two welding techniques. Laser welding induces smaller
compressive residual stresses in the flange end regions when compared to manual metal arc
welding. This has a beneficial effect on the axial buckling strength of the axial members. The
difference could be up to about 8 % depending on the slenderness ratio and the column in
question.
SANS 0162-1:2005 was found to adequately describe the column behaviour for the sections
tested as far as design is concerned.