| Summary: | 碩士 === 國立海洋大學 === 機械與輪機工程學系 === 85 === In this thesis, EH36 TMCP shipbuliding steel plate was
utilizedto study the crack propagation behavior of the weldment,
in which the low-heat input using Shielded Metal Arc Welding
(SMAW) process was applied. The result revealed TMCP steel
plates treated by on-lineaccelerated coding process obtained a
fine microstructure. However,it did not exhibit evident
difference in microstructure for specimensreceiving 600℃/2hr
tempering. The hardness test indicated that the fusion zone had
a higher hardness than the other regions in a weld and the
decline in hardness was obtained after postweld tempering
treatment.The harding phenomena were not obtained in the heat
affected zone(HAZ), owing to the low carbon content of the base
plate. The fatigue test showed the base plate with crack
propagatingonalong the rolling direction had a better resistance
to crack growth thanthat along the transverse direction.
However, the result were conversely for the tempered specimens.
The results also indicate the effect of tempering treatment on
the fatigue crack growth of TMCPbase plate was minor. In
addition, the HAZ had the lowest crackgrowth rates among the
various regions in aweld regardless of tempering treatment.
Meanwhile, the reduction in crack growth ratesin the HAZ was
obtained after tempering treatment. SEM fractograph
revealed the transgranular fatigue fracture wasobtained for all
the specimens. Fatigue striations were more clearespecially in
high △K ranges. The impact-fractured surface of all
thespecimens revealed a ductile dimple fracture.
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