• Corrosion Science and Technology
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• 제9권6호
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• pp.294-299
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• 2010

Two types of welding methods were performed on austenitic 304 stainless steel: laser welding and TIG welding. The differences of the corrosion characteristics of the welded zones from the two welding methods were investigated with electrochemical methods, such as measurement of the corrosion potential, polarization curves, cyclic voltammogram, etc. The vickers hardness of all laser-welded zones (WM:Weld Metal, HAZ:Heat Affected Zone, BM:Base Metal) was relatively higher while their corrosion current densities exhibited a comparatively lower value than those which were TIG welded. In particular, the corrosion current density of the TIG-welded HAZ had the highest value among all other welding zones, which suggests that chromium depletion due to the formation of chromium carbide occurs in the HAZ, which is in the sensitization temperature range, thus it can easily be corroded with an active anode. Intergrenular corrosion was also observed at the TIG-welded HAZ and WM zones. Consequently, we can see that corrosion resistance of all austenitic 304 stainless steel welding zones can be improved via the use of laser welding.

• 한국기계가공학회지
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• 제10권6호
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• pp.128-133
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• 2011

In this study, the steel material for shipbuilding(LR-A class) was used, and FCAW was taken advantage of 3G attitude and they are welded by different welding ways. As a result of analyzing wave with welding monitoring system, the stable values are obtained which are the first floor(electronic current 164~182 A, voltage 24 V), the second floor(electronic current 174~190 A, voltage 22~25 V), the third floor(electronic current 158~188 A, voltage 22~25 V), and fourth floor(electronic current 172~184 A, voltage 22~25 V), at this time, the stable wave standard deviation and changing coefficient could be obtained. When the welding testing through nondestructive inspection was analyzed know defect of welding, there was no defect of welding in A, D, E, but some porosities in B, and slag conclusion near the surface in C, because the length of arc was not accurate, and the electronic current and voltage was not stable. After observing the change of heat affect zone through micro testing, each organization of floor formed as Grain Refinement, so welding part was fine, the distance of heat affect zone is getting wider up to change the values of the electronic current and voltage. As a result of degree of hardness testing, the hardness orders were the heat affect zone(HAZ), Welding Zone(WZ), and Base Metal(BM). When the distribution of degree of hardness is observed. B is the highest degree of hardness The reason why heat effect zone is higher than welding zone and base metal, welding zone is boiled over melting point($1539^{\circ}C$) and it starts to melt after the result of analysis through metal microscope, so we can know that delicate tissue is created at the welding zone. Therefore, in order to get the optimal conditions of the welding, the proper current of the welding and voltage is needed. Furthermore the precise work of welding is required.

• 한국해양공학회지
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• 제10권1호
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• pp.36-46
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• 1996

This paper deals with determinig the proper friction welding condition and analyzing various mechanical properties of friction welded joints of sintered carbide tool materials(K20, P25, and SKDX5 for the blade part of drill or press punch) to alloy steel (SKH4, SCM440 for the shank part of drill or press punch), the alloy steel to aluminum(A6061 for the interlayer material between the blade part and the shank) and sintered carbide tool materials to alumminum. And also acoustic emission test will be carried out during fiction welding to evaluate the weld quality.

• 한국해양공학회지
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• 제10권2호
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• pp.69-76
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• 1996

In-process quality control and high reliability of the weld are the major concerns in applying friction welding to the economical and qualified mass-production. Experimental examinations and quantitative analysis were performed for the optimiaztion of similar friction welding of hydraulic valve spool steels(SNCM220, SCM435, SACM645, SCM415, ${\varphi}24). The quantitative correlations were found between the initial cumulative counts of acoustic emission(AE) occurring during plastic deformation periods of the welding and the fatigue life as well as weld strength and welding conditions. A real-time evaluation system was developed for the friction weld quality by AE.

• 한국해양공학회지
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• 제30권1호
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• pp.51-56
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• 2016

In this study, for the tube-to-tube friction welding of hose nipple materials, the main parameters of friction welding were investigated using tensile tests, Vickers hardness surveys of the bond area (HAZ), and observations of the microstructure to increase the quality of friction welding based on visual examination. As-welded and post weld heat treated (PWHT) specimens were tested. The optimal welding conditions were found to be n = 1000 rpm, HP = 10 MPa, UP = 15 MPa, HT = 9 s, and UT = 5 s when the metal loss (Mo) was 7.5 mm. Furthermore, the peak of the hardness distribution of the friction welded joints could be eliminated by PWHT. Moreover, the two materials of the friction weld were thoroughly mixed with a well-combined structure of micro-particles, without any molten material, particle growth, or defects.

• 한국강구조학회 논문집
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• 제8권4호통권29호
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• pp.133-133
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• 1996

Application of the relationship $da/dN=C({\Delta}K)^{m}$ is effective in the analysis of fatigue crack growth life. The values of material constant C and m have great influences on the predicted fatigue life and the relationship between fatigue crack growth rate(da/dN) and stress intensity factor range(${\Delta}K$) is effective in fatigue crack growth behavior. In this paper, fatigue crack growth behavior of the welded joints in HT60 grade TMCP(Thermo Machanical Control Process) steel have been studied. To evalute the fatigue crack growth rates of HT60 grade TMCP steel, fatigue test was performed by base metal(BM), heat affected zone(HAZ) and weld metal(WM) in TMCP steel at room temperature. We determined the relationship of $da/dN-{\Delta}K$ by correlation between C and m obtained from the Paris-Erdogan power law data supplied HT60 grade TMCP steel. The obtained results from this study indicate that fatigue crack growth rate of TMCP steel is not influenced by softening effect which occurs in the HAZ when high heat input weld is carried out. Softening effects, which affect fatigue properties. are shown that it is not affected to the fatigue growth rates significantly.

• Journal of Advanced Marine Engineering and Technology
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• 제24권4호
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• pp.460-469
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• 2000

A study on the corrosion behavior of RE36 steel for marine structure was investigated with parameters such as micro-Vickers hardness, corrosion potential and corrosion current density measurement of weld metal(WM), base metal (BM) and heat affected zone(HAZ), Al anode generating current and Al anode weight loss quantity in case of cathodic protection. And we carried out slow strain rate test(SSRT) in order to research mechanical properties such as stress at maximum load, percent strain, time to fracture and strain to failure ratio etc and to find out limiting cathodic polarization potential for hydrogen embrittlement with applied cathodic polarization potential. Hardness of HAZ part was the highest among those three parts and also galvanic corrosion susceptibility was the highest in HAZ part among those three parts due to the lowest corrosion potential than other parts. However corrosion current density was the highest in WM part among those three parts. And the optimum cathodic polarization potential showing the best mechanical properties obtained by SSRT method with applied constant cathodic potential was from - 770mV to - 875mV(SCE). However it is suggested that limiting cathodic polarization potential indicating hydrogen embrittlement on the mechanical properties was under - 900mV(SCE).

• Journal of Welding and Joining
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• 제15권1호
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• pp.92-100
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• 1997

손상된 ASTM A-470 class 8 고압 증기 터어빈 로터강의 수명 연장을 위해 보수 용접이 행하여졌다. SAW 용접부의 미세경도 측정결과 모재의 경도는 VHN 253이었으나 모재에 근접한 열영향부의 경도는 VHN 227로 떨어졌다. 이와 같이 경도가 떨어진 영역을 "연화층"이라 정의하였으며 약 0.5-0.6mm의 크기를 나타내었다. 한편 크립 파단 시험시 파괴는 연화층 부근에서 일어났으며 593.deg. C와 19Ksi(132 Mpa)에서 파단시간은 772.4hr이었다. 연화층의 크기를 줄이기 위해서 MIG 및 TIG 용접이 행하여졌는데 연화층 크기는 MIG의 경우 0.3-0.4mm이고, TIG의 경우에는 입열량의 크기에 따라 0부터 0.4mm의 크기를 나타내었다. 그러나 크립 파단시간은 연화층 크기가 작아질수록 감소하였다. 특히 TIG 용접부의 경우 크립 파단시간은 입열량과 밀접한 관계를 나타내었는데 입열량이 클수록 파단시간은 길어졌다. 대부분의 파괴는 ICHAZ에서 발생되었으나 입열량이 감소함에 따라 파단부는 CGHAZ으로 이동하였다. 파단면은 tearing과 dimple을 갖는 입내파괴를 나타내었다.파괴를 나타내었다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권8호
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• pp.1162-1169
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• 2009

22APU 스테인리스강에 대해서 두가지의 용접법이 적용 되었으며, 그중 한 방법은 레이저 용접법이며 다른 하나는 TIG 용접법이다. 이 경우 상기한 두 용접을 적용할 경우 용접부의 부식특성의 차이점에 대해서 전기화학적인 방법 예를 들면 부식전위, 분극곡선 및 사이클릭볼타모그램 등의 측정에 의해서 고찰되어졌다. 레이저용접의 경우 모든 용접부(용접금속,열영향부, 모재부)의 경도가 TIG용접의 경우에 비해서 상대적으로 높은 값을 나타내었다. 더욱이 모든 용접부의 부식전류밀도 역시 TIG용접에 비해서 낮은 값이 관찰되었다. 특히 모재부의 부식전류밀도는 용접방법에 관계없이 가장 낮은 값을 나타내었다. 그리고 레이저용접의 경우 부식된 모든 용접부에서 입계부식이 관찰 되지 않았으나, TIG용접에서는 용접금속부와 열영향부에서 입계부식이 관찰되었는데 이것은 크롬카바이드의 형성에 의한 크롬결핍이 감수성온도영역에 있는 용접금속부와 열영향부에 나타났기 때문으로 사료된다. 따라서 이들 영역은 더욱 활성화된 양극으로 부식되기쉽다. 결과적으로 22APU 스테인리스강의 용접부의 내식성은 레이저용접에 의해서 확실히 개선될 수 있다는 사실을 알 수 있다.

• 한국해양공학회지
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• 제26권4호
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• pp.64-69
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• 2012

Laser welding was carried out on austenitic 304 (STS 304) and 22 APU stainless steels. In this case, the differences between the corrosion characteristics of the welding zones of the two stainless steels were investigated using electrochemical methods. The Vickers hardness values of the weld metal (WM) zones in both cases, the STS 304 and 22 APU stainless steels, showed relatively higher values than those of other welding zones. The corrosion current densities of the heat affected zone (HAZ) of the 22 APU and the base metal (BM) zone of the STS 304 exhibited the highest values compared to the other welding zones. It is generally accepted that when STS 304 stainless steel is welded using a general welding method, intergranular corrosion is often observed at the grain boundary because of its chromium depletion area. However, when laser welding was performed on both the STS 304 and 22 APU stainless steels, no intergranular corrosion was observed at any of the welding zones. Consequently, it is considered that the intergranular corrosion of stainless steel can be controlled with the application of laser welding.