Effect of Tensile Strain Rate on Hot Ductility of Synthetic Heat-Affected-Zones Reproduced Reheating Weld Thermal Cycles
1972 Volume 41 Issue 10 Pages 1162-1171
Details
1972 Volume 41 Issue 10 Pages 1162-1171
Hot ductility and tensile strength are investigated on the synthetic heat-affected-zones (HAZ) simulating weld thermal and reheating cycles in relation to tensile strain rate dependency.
Four commercial steels, three, high strength and one mild steel, are used for testing.
Four programs of weld thermal cycles A, B, C, and D are compared, but the main experiments are conducted on thermal cycle C, which is a tensile test at various strain rates on each holding temperature with subsequent reheating of the first weld thermal cycle of 1400°C peak temperature. The main results are as follows :
(1) Hot ductilities of synthetic HAZ specimens tested at various temperatures generally fall after subsequnt reheating thermal cycle.
(2) Hot ductilities of synthetic HAZ specimens generally decrease at slower strain rates. Especially, in case of 80 kg/mm2 high strength steel 8A, the hot ductility of synthetic HAZ specimen falls to almost zero after subseouent reheatine at about 700°C and/or 900°C.
(3) In various hot ductility curves, three distinct temperatures are found, that is, one of maximum ductility Tit and two of minimum TL, and TL2.
(4) The maximum ductility temperature TH exists in 700-800°C range, and their hot ductilities are not affected by strain rates.
However, in the other temperature ranges, hot ductilily decreases rapidly with an increasing strain rate.
(5) Hot tensile strength in reheating weld thermal cycle increases straightly with an increase of strain rate on a logarithmic scale.
(6) Fractographic observations of reheating weld HAZ specimens showed that an intergranular fracture mostly occurred in case of testing in TH temperature range, and was more significant with an increasing strain rate.
