In the first half of this research, welding tests were made on two high tensile alloy steels with 0.32%C. 2.98%Ni, 1.31%Cr, 0.46% Mo and 0.42%C, 1.18%Mn, 1.60%Cr, 0.26%Mo under con-current heating at various temperatures, i. e., from the martensite formation range to the A
1.
And the relation between the cracks and the hardness and micro-structure in the zone adjacent to-the weld was surveyed systematically.
Thus it was conformed that the formation of cracks in the heat-affected zone could be perfectry avoided by the so-called hot welding.
In order to attain this object in a shorter heating time, suitable temperature ranges are to be adopted. Ni-Cr-Mo steel can be successfully welded with about 20 minute holding at 300-C to 400-C after depositing. Hearing to about 650-C may be also suitable but requires a considerably long time. Mn-Cr-Mo steel is to be held at about 650°C to 675°C and about 300°C to 400°C for about 40 and 10 minutes after welding respectively. The above-mentioned phenomena can be explained in the light of the so-called S-curves usually dealt with in physical metallurgy. But in welding a zone immediately adjacent to the weld is heated up to the solidus, and thus the maximum heating temperature is much higher than in the case of usual physical metallurgy.
Therefore there may be appreciable differences between the two cases (e.g. incubation periods before transformation begins may be longer in welding). Secondly, to compare with the prevention of the formation of the hardened zone by the so-called hot welding, the post-heating procedure, which tempering the martensite softens the hardened zone induced by welding, was carried out systematically.
The last results show that post-heating immediately below the Al can safely and sufficiently soften the hardened zone in a very short time. Namely, compared with the hot welding, the same degree of softening can be obtained with about one-sixtieth time holding in post-heating.
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