1973 Volume 42 Issue 9 Pages 879-889
Occurring and developing mechanism of longitudinal hot cracking due to rotational deformation of specimen of thin aluminum plate is studied experimentally based on the results in previous report.Fursthermore, a new method of assessment of hot cracking susceptibility is suggested basedon the above experimental results and modification of Houldcroft hot cracking test.
It is observed that in welding a rectangular specimen starting rom edge, longitudinal cracking occurs in weld bead and when the width of specimen is increased, the cracking ratio changes abruptly from 100% to 0% at a certain width of specimen-critical width-in high speed welding, but at low welding speed, the cracking ratio decreases gradually from 100% and drops to 0%. In these cases, it is observed that the cracking occurs in the brittle area behind the molten pool in the start part of weld bead and it develops from A to B in Fig. 2 with the molten pool.
The above mentioned results may be understood from the existence of minimum deformation -l for thecracking (which is described in 1st report) and the actual deformation. The latter is affected bythe rigidity of the plate and the temperature distribution in the width direction.
From above results, it is concluded that the factor which stops the cracking in Houldcroft type cracking test is uniformity of temperature distribution in the width direction due to the decrease of effective width by a slit inserted. On the other hand, there is another tendency of the development of cracking being accelerated by the decrease of rigidity due to the slit. Accordingly, it is understood that Houldcroft type cracking test is an obscure one with an inconsistent factor in stopping mechanism of cracking. From above results, a new improved hot cracking test is suggested.
