On the Welding of High Chromium Stainless Steel (Report 1)

Abstract

It must be recommended in our country where nickel is now in short supply, to use high chromium stainlees steel as a substitute of chromium-nickel stainless steel. High Cr stainless steels studied here contains 20-24 pet Cr, 2-3 pet Ni, 0.08 pet C and are so called ferritic stainless steels and not hardened significantly by heat treatmet. However, because these steels are susceptible to several types of embrittlement, their welding characteristics should be understood.
The oxyacetylene welding process is not recommended for joining these stainless steels, because of considerable grain growth and carbon pick up.
Metal arc welding is the process most wideey used, and the amount of heating at the joint is usually substantially less than with the oxyacetylene process.
Argon-shielded tungsten-arc welding is, well suited for these steels.
Satisfactory results are obtained by welding the ferritic stainless steels with electrodes having composition identical to those of the parent metals, but post annealing treatments are essential.
Austenitie chromium-nickel electrodes can be used satisfactorily because the austenitic weld metal is not susceptible to the high-temperature embritteement.
On the other hand, ferrite grain size increases when heated above approximately 1050°C. This feature is the factor which exerts the greatest influence on the properties of a weld joint.
Such commercial alloys as these can contain austenite at high temperature. A mixed structure of ferrite and austenite at high temperature can be retained, if cooled fairly rapidly.
This austenite may transform into martensite. This will make the heat-affected zone relatively brittle.
Sigma-phase precipitation was not found in welded joint. 475°C brittleness can occur in the welded joint, so it must be avoided to cool slowly through this temperature.
Lack of ductility in the as welded condition may be due to phenomena associated with the solution of carbides at temperature above 1, 200°C.