Effect of Restraint Intensity of Joint on Lamellar Tearing (Report 1)

Assessment by Multirun RRC Test and Modified Cranfield Test

Abstract

Generally, it is suggested for the prevention of lamellar tearing that steel plate is selected and weldfabrication method is modified. In this paper, the selection of plate is dealt with. To obtain a criterion of selection of plate, RRC (Rigid Restraint Cracking) test method with multirun fillet weld is applied for 50 kg/mm² class high tensile steel plates, and susceptibility of lamellar tearing is given by critical reaction stress or critical restraint intensity for crack intiation. From this result, in order to select the plate for . prevention of lamellar tearing, it became clear that plate would be selected in proportion to the actul restraint intensity of joints.
Modified Cranfield test, that is, simple crack susceptibility test for lamellar tearing, is experimented and its susceptibility is given by critical volume of angular distortion for crack initiation or critical preheat and interpass temperature for crack arrest, and the result of Modified Cranfield test is compared with that of prior RRC test.
Further, investigated is the effect of some properties of steel plate, that is, inclusions and tensile properties of through thickness direction, on the susceptibility of lamellar tearing.
Conclusions obtained are as follows.
(1) Sulphur content in steel plate is closely related to the susceptibility of lamellar tearing and it may be regarded as appropriate that sulphur content is substituted for selection-criterion of steel plate.
Cleanliness and average length and volume fraction of inclusions, which are related to sulphur content, have good correlation with the susceptibility of lamellar tearing. However, classification of sulphur print has no correlation.
(2) From the result of through thickness tensile test experimented by square-type, roundtype and Brodeau-type specimen, it has been clear that the value of reduction of area has good correlation with susceptibility of lamellar tearing. Therefore, round-type and Brodeau-type specimen, which is able to estimate by the value of reduction of area, may be adapted for through thickness specimen.
(3) Decrease of plate thickness increases susceptibility of lamellar tearing in order that inclusions may be elongated by hot rolling. Generally, however, it would be considered that thicker plate increases susceptibility of lamellar tearing, because of a lot of deposition volume which causes local strain at the weld.
(4) Result of Modified Cranfield test has good correlation with that of RRC test, and Modified Cranfield test method is proper method for the estimation of susceptibility of lamellar tearing.