• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.33-38
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• 2012

The effects of the diffusible hydrogen content and hardness on the cold cracking in high strength weld metal were investigated. The diffusible hydrogen contents were influenced by welding parameters such as the voltage and contact tip-to-work distance (CTWD). The diffusible hydrogen content increased with an increase in voltage. However, it was decreased with an increase in CTWD. CTWD also influenced the weld metal hardness,especially when the wire used had a higher strength than the base metal. This showed that weld metal hardness had a more powerful effect on weld metal cold cracking than the diffusible hydrogen content in this experiment.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.49-56
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• 1999

Welding is a reliable process and is mainly adopted for fabricating heavy structures. Recently, transverse cracks in the weld metal is serious problem, and they affect cost, efficiency, safety and joint reliability for various welded structures. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained are as follows; 1) The content of diffusible hydrogen in the commercial flux cored are welding wire was remarkable change by manufacturer. 2) The diffusible hydrogen content was thd main factor for weld metal transverse cracks. 3) Weld metal was immune to transverse cracking under the condition of low diffusible hydrogen content of high restraint condition. 4) The factors for weld metal transverse crack would be the content of diffusible hydrogen and restraint of weld joint.

• Journal of Welding and Joining
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• v.31 no.6
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• pp.112-118
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• 2013

In this study, constant loading test (CLT) was performed to evaluate the hydrogen embrittlement resistance for multipass FCA weld metals of 600MPa tensile strength grade. The microstructures of weld metal-2 having the smallest carbon equivalent (Ceq=0.37) consisted of grain boundary ferrite and widmanstatten ferrite in the acicular ferrite matrix. The weld metal-1 having the largest Ceq=0.47, showed the microstructures of grain boundary ferrite, widmanstatten ferrite and the large amount of bainite (vol.%=19%) in the acicular ferrite matrix. The weld metal-3 having the Ceq=0.41, which was composed of grain boundary ferrite, widmanstatten ferrite, and the small amount of bainite (vol.%=9%) in the acicular ferrite matrix. Hydrogen desorption spectrometry (TDS) used to analyze the amount of diffusible hydrogen and trapping site for the hydrogen pre-charged specimens electrochemically for 24 hours. With increasing the current density of hydrogen pre-charging, the released amount of diffusible hydrogen was increased. Furthermore, as increasing carbon equivalent of weld metals, the released diffusible hydrogen was increased. The main trapping sites of diffusible hydrogen for the weld metal having a low carbon equivalent (Ceq=0.37) were grain boundaries and those of weld metals having a relatively high carbon equivalent (Ceq: 0.41~0.47) were grain boundaries and dislocation. The fracture time for the hydrogen pre-charged specimens in the constant loading test was decreased as the carbon equivalent increased from 0.37 to 0.47. This result is mainly due to the increment of bainite that is vulnerable to hydrogen embrittlement.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.18-21
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• 2014

Cold cracking of weldment is one of the most serious welding problems. A sufficient quantity of diffusible hydrogen, a residual stress, and a sensitive microstructure are the causes of cold cracking. Removal of any one of these factors can be used to prevent cold cracking. Application of flux cored arc welding process is increasing due to high productivity and easiness of welding. In addition, to prevent cold cracking in the HAZ or weldment, preheat temperature and interpass temperature have to be controlled. In this study, the effect of preheat temperature on the levels of diffusible hydrogen in the weld metal deposited using flux cored wire was examined. The levels of preheat temperature of base metal specimen were ambient temperature, 50, 100 and $150^{\circ}C$ respectively. The result showed that the increase of preheat temperature was a linear relationship with reduction of diffusible hydrogen content in weldment.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.3
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• pp.45-52
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• 1987

Generally the factors affected largely by the cold cracking sensitivity of the weld are the quantity of the diffusible hydrogen, the brittleness and hardness of the bond area and the tensile restraint stress. These factors have relation each other, and if we can reduce one of these factors, it becomes instrumental to the root cracks prevention of weld. This study deals with the gravity type-underwater-welding of KR Grade A-3 marine steel plate using E4303 welding electrode in order to compare wet-underwater-welding with in-air- welding, resulting in obtaining the tensile restraint characteristics, the hardness distribution, the quantity of diffusible hydrogen and the macro- and micro-crack properties in both underwater and in-air welds. The main results obtained are as follows: 1) The quantity of diffusible hydrogen measured for 48 hours is about 18cc/100g-weld-metal for the in-air-weld of one pass and about 48cc/100g-weld-metal for the underwater-weld of one pass which is about 3 times penetration of diffusible hydrogen compairing with the case of the in-air-weld. However, it was experimentally confirmed that, by the multi-pass welding of 2 to 5 passes, the diffusible hydrogen in the underwater weld metal can be reduced as much as 27 to 49%. 2) The hardness of the weld metal indicates the highest value in the heat affected zones of underwater weld for more rapid cooling rate, resulting in the higher sensitivity of cold cracking. So, it is desirable to soften the higher hardness in the HAZ by tempering effect such as the multi-pass welding in the underwater welding. 3) At the bond vicinity of the underwater weld HAZ, micro cracks were found as resulted by both more rapid cooling rate and more diffusible hydrogen and also by the stress corrosion cracking under the tensile restraint stress in the underwater. But this could be prevented by the tempering effect of the following weld bead such as the multi-pass welding.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.55-62
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• 1998

While excellent joint quality has been obtained using dry chamber underwater welding methods, the size limitations imposed by this process restrict its use for underwater construction work. The wet underwater shielded metal-arc welding eliminates this restriction but suffers from poor weld properties by the 1-pass bead-on-plate welding due to the excessive diffusible hydrogen. On the other hand, in the wet underwater welding, it is well known that the quantity of diffusible hydrogen in multi-pass welded parts reduce to less than that in 1-pass welded parts. Therefore, in this paper, welding experiments are made the 3-pass bead-on-plate welds by using TMCP and normalized steel plates and E4301 and cellulose coated electrode. After that, The amounts of the hydrogen absorbed into the 3-pass welded area were measured according to the JIS Z 3118 specification. The microstructural changes as well as the microhardness distribution after the underwater 3-pass welding were also investigated using Vickers microhardness tester and S.E.M and O.M. The results indicated that the quantity of diffusible hydrogen in 3-pass welded areas was reduced little less than a half of one of that in 1-pass welded areas at the specific welding condition. As a result, the cold cracking of 3-pass welded areas decreased by reduced effect of diffusible hydrogen. In the underwater 3-pass welding, the micrography of cold cracking fracture surface showed mainly the cleavage of hydrogen embrittlement.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.830-836
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• 1986

In this study, the effect of hydrogen absorbed in welding process on the fatigue behaviour of the weld bond was quantitatively made clear. The influence of cyclic loading rate on the fatigue characteristics of the manual arc weld bond was inspected under the condition of constant amount of hydrogen. Moreover, the fatigue cracking mechanism concerning the diffusible hydrogen in the welded part was discussed in connection with fractographs of the fracture surfaces.

• Journal of Ocean Engineering and Technology
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• v.27 no.5
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• pp.77-81
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• 2013

The effects of the welding parameters, contact tip-to-workpiece distance (CTWD), current, and voltage on the diffusible hydrogen content in weld metal deposited by self-shielded flux cored arc welding were investigated and rationalized by comparing the amount of heat generated in the extension length of the wire. This showed that as CTWD increased from 15mm to 25mm, the amount of heat generated was increased from 71.1J to 174.8J, and the hydrogen content was decreased from 11.3mL/100g to 5.9mL/100 g. Even if little difference was observed in the amount of heat generated, the hydrogen content was increased with an increase in voltage because of the longer arc length. A regression analysis showed that the regression coefficient of voltage in self-shielded flux cored arc welding is greater than that in $CO_2$ arc welding. This implies that voltage control is more important in self-shielded flux cored arc welding than in $CO_2$ arc welding.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.57-67
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• 1999

Welding is widely applicable and reliable process and is mainly adopted for fabricating heavy structures. Recently, weld metal transverse cracks in butt and fillet weld joint is a serious problem, and they must be eliminated for improving weld joint reliability. The weld metal transverse crack susceptibility of butt and fillet joint was carried out by cantilever type tensile crack testing jig and CTS test. In this view of point, this study investigated the potential factors for weld metal transverse crack. The main results obtained were as follows: 1. The content o fdiffusible hydrogen in weld metal played an important role for weld metal transverse cracks. 2. From cantilever type tensile crack tests, it was pointed out that the higher the diffusible hydrogen content and tensile restraint, the more susceptible to weld metal transverse craking. 3. The TSN(thermal severity number) and diffusible hydrogen were important factors for determining weld metal transverse cracks in fillet weld joints.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.52-58
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• 2012

Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-to-failure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.