Effect of Hydrogen on Root Cracking of High Strength Steel Welds and Discussion about Repeating Number of Specimens
A Study of Root Cracking in High Strength Steel Welds (Report IV)
1964 Volume 33 Issue 3 Pages 191-202
Details
1964 Volume 33 Issue 3 Pages 191-202
The important role of hydrogen in root cracking of high strength steel welds had been already discussed in the previous report. In this report the quantitative effect of hydrogen was clarified with HT 60 welds and the effects of lower cooling process below 300°C on root cracking were discussed. The activation energy necessary for root cracking was measured with slotted cracking specimens which were quenched at various low temperatures. Difference in cracking behavior with a change of groove type or root opening was discussed and the repeating number of specimens necessary for a root cracking test was obtained.
The conclusions obtained in the study are as follows:
(1) There was ascertained an obvious difference in the iniation of root cracks when diffusible hydrogen contents in HT 60 welds varied from 1 to about 3 cc/100 gr
(2) Initiation of a root crack in a weld metal was remarkably affected, by chemical compositions of a weld metal, even with a diffusible hydrogen content of lcc/100gr.
(3) Propagation of a root crack in an HT 60 weld metal was little affected, even if the diffuible hydrogen content was increased from 3 to 6cc/100gr.
(4) It was the cooling process above 300°C that affected the initiation of root cracks in HT 60 welds. In HT 80 welds, however, the cooling process below 300°C also affected the initiation of root cracks.
(5) Through the measurement of incubation time for root cracking in slotted cracking specimens which were quenched at various low temperatures, the activation energy necessary for root cracking was estimated at about 10, 500 cal/g. atom, the value of which was in good agreement with the activation energy for the diffusion of hydrogen in a-Fe.
(6) Repeating number of specimens which was necessary and sufficient for estimation of cracking tendency was three or four, so far as the slotted cracking test was regarded as "go or no go test". At least eleven specimens were necessary in order that cracking percentage might be estimated in detail.
(7) It was understood with consideration of angles of inclination of fusion lines that a root crack occurred exclusively in HAZ with y-groove specimens and in a weld metal with U-groove specimens.
(8) It was also explained by the angle of inclination of a fusion line that cracking behavior was varied with the gap of root.
