湿式水中溶接における粗粒域のマルテンサイト量,硬さ及び低温割れ感受性に及ぼす鋼材の炭素当量の影響

抄録

The influence of chemical composition of steels on the proportions of martensite, hardnesses and critical rupture stresses of implant cracking tests (specified in WES 1104, Specimen: Type 1B) at coarse-grained regions in underwater wet welding was investigated by substituting the "equivalent carbon contents" Ceq (JIS G 3106 and WES-3001) or the "chemical composition for weld cracking susceptibility" Paz (WES-3002) for the chemical composition of the steels.
JIS-SM and some equivalent steels were employed as the materials to be tested. The test, welds ("autogenous welds" in the flat position) were deposited at a depth of 20 cm in fresh water, using a plasma arc as a source of heat.
The results summarized in empirical equations are as follows:
1) For cooling time from 800 to 500°C S(800-500°C) (s) ranging between some 3 and 11 s, the proportions of martensite M (%) in coarse-grained regions is given by;
M=(270×logS(800-500°C)-24.6)× Ceq-163×logS(800-500°C)+ 115.
2) For S(800-500°C) not exceeding 4s, the Vickers' hardness Hv with a load of 10 kgf is; Hv=563×POM-123×logS(800-500°C)+315
while for S(800-500°C) from 4 to 11s;
Hv=(885×logS(800-500-°C)-117) ×Ceq-449×logS(800-500°C)+483
3) Under the conditions. that the weld contains diffusible hydrogen of the level of 20-30 ml/"100 g of weld metal" (Collecting medium: Mercury), the critical rupture stress (σcr) imp (MPa), below which cracking does not lead to complete rupture of the implant, is;
(σcr)imp={(1.72×logS(800-500°C)-2.42)×Ceq-0.239×logS(800-500C)+0.956}×10³or,
(σcr)imp={(1.72×logS(P-100°C)-4.04)×Ceq-0.239×logS(P-100°C)+1.18}×10³
where S(P-100°C) is cooling time from peak temperature to 100°C (s) and ranges from about 20 to 100s.
In case (σcr)imp's calculated by the above-cited equations drop below 230 MPa, they can be estimated to be on the fixed level of 230 MPa.