A Study of Weld Cracking of Austenic Stainless Steel (Report 3)

Examination of The Results of FISCO Type Cracking Test and Comparison between Four Types of Cracking Test

Abstract

Weld cracking susceptibilities of various austenitic stainless steel electrodes in the market were investigated with FISCO type cracking test which was found very useful for the cracking test of austenitic stainless steel welds as shown in the previous report. The shape and microstructure of weld metals in the FISCO test were examined. Four types of hot cracking tests, including the FISCO test, were compared in respect to the sensitivity and reproducibility. The main conclusions are summarized as follows :
(1) D347 type electrodes were generally more hot-crack-sensitive than D308 type, D308 L type and 16 Cr-8 Ni-2 Mo type electrodes.
(2) Crack susceptibilities of D347 type electrodes varied in a wide range with the type of coating and description, regardless of the ferrite content from 6 to 9 % in weld metals.
(3) Longitudinal bead cracks in austenitic stainless steel welds are likely to be caused through a chain of micro-cracks in grain boundaries at or beneath the bead surface by shrinkage stresses and then propagated through weld metal within the temperature range from 1100°C to 500°C.
(4) Bead cracking increased with the ratio of width to depth in the bead section and was more serious in V-or U-groove than in I-groove.
(5) Crack-sensitive D347 type weld metals had heterogeneous and coarse-grained structures for a small heat input, while crack-insensitive weld metal was rather homogeneous and fine-grained. It seems to be attributed to a greater content of molybdenum in the latter.
(6) The FISCO type cracking test was more preferable to three other types of cracking test, that is, double fillet, segment circular groove and modified Lehigh restraint tests, in respect to the sensitivity and reproducibility for the hot cracking test of austenitic stainless steel welds.