強靱鋼材の熔接割れについて(第4報)

熔接変質部附近割れに及ぼす局部後熱の影響について

抄録

In this research, the correlation between cracks in the, heat-affected zone of alloy steels, welding conditions; the maximum hardness in the heat-affected zone and the local post-beating was investigated.
In the first place, single beads were deposited on (8 mm thick) rectangular plates of alloy steel and the following facts were ascertained.
(1) In the case of the 200 mm/min speed of bead-progress, if large diameter electrodes are used, large longitudinal cracks are apt to occur, and with small diameter electrodes small longitudinal cracks and transverse cracks are apt to occur.
(2) In the case of 3.2 mm diameter electrodes, the larger the speed of bead-progress to is, the more difficult the occurrence of learge longitudinal cracks is and the easier th occurrence of transverse cracks is.
(3) if the neighbourhood of a welded part is post-heated with a gas flame, both longitudinal and transverse cracks may be prevented.
(4) But if the local post-heating is not performed in a suitable time after welding, good effect can not be expected.
In the next place, the rectangular. specimen deposited with single beads and the special rectangular specimens having grooves slit in the center which were arc-welded, were cut perpendicular to the bead, and the hardness distribution on these sections was surveyed. Such procedures were also performed in the specimens which were deposited or welded and then post-heated. In this way, the following facts were found.
(5) According to the hardness distribution on the above-mentioned section of specimens in which cracks did not occur, the maximum hardness is lower compared with those of-specimens in which cracks occurred.
(6) If suitable heating is performed after welding, the maximum hardness in the heat-affected zone drops to a very low value, and cracks do not occur. But if the temperature and period of heating are not appropriate and consequently the softening of the hardened zone by welding is insufficient or on the contrary a new hardened zone appears again, the prevention of cracks is difficult. And even if post-heating is performed, when the time of heating after welding is not suitable, namely when it is after the occurrence of cracks, the good result can not be expected.
In this manner, the relation between the maximum hardness of the heat-affected zone and cracks in the neighbourhood of this zohe, was claritied. Accordingly it is understood that if the maximum hardness is brought down to a suitable value by the local post-heating with sufficient means and cares, cracks can be prevent perfectly.
But with the above-mentioned method, cracks in weld metals and unaffected parts can not be prevented.
In order to prevent these cracks, other suitable methods are to be adopted.