• Journal of Welding and Joining
• /
• 제14권3호
• /
• pp.75-85
• /
• 1996

In this paper the influence of postweld heat treatment on mechanical properties of SMAW and FCAW stainless steel weldments was examined and the obtained results are as follows ; (1) The amount of $\delta$-ferrite formed by SMAW and FCAW process decreased with increasing holding temperature and time in post weld heat treatment(PWHT), and it was found that the reduced ferrite was transformed into sigma phase after $800^{circ}C{\times}50hr$ PWHT. This sigma phase, even though it was very small, resulted in brittleness of dissimilar weldment between carbon steel and stainless steel in bending test, however in similar weldment between stainless steel and stainless steel was not occured. (2) The chemical composition of sigma phase was measured to 28-30%Cr, 7-9%Mo, 4-6Ni in 316L weldment, and also 35-37%Cr, 0.9-1.0Mo, 6-8%Ni in 309L weldment by EDS analysis.

• 한국재료학회지
• /
• 제6권12호
• /
• pp.1257-1262
• /
• 1996

1.0Cr-1.0Mo-0.25V강 용접부의 크립 파단 시험시 파단 발생 원인에 관한 연구가 시행되었다. 파괴는 Intercritical Heat Affected Zone에서 발생하였으며 파단면에서 구상의조대한 M6C탄화물이 발견되었다. 모재는 molybdenum 주성분의 M2C, vanadium 주성분의 M4C3 및 chromium 주성분의 M23C6와 M7C3 탄화물이 존재하였다. 모의 실험 결과 준안정 상태인 M2C 탄화물은 85$0^{\circ}C$, 10oh에서 안정한 M6C탄화물로 변태하였다. M6C 탄화물은 주변의 molybdenum 농도를 떨어뜨려 강도의 저하를 가져오며 크립 기공의 발생 원인을 제공하였다.

• 공업화학
• /
• 제10권4호
• /
• pp.531-536
• /
• 1999

누출시험 장치를 이용하여 미량 물 누출 실험을 수행하였다. 2.25Cr-1Mo 시편의 누출경로는 나트륨-물 반응 생성물에 의해 plugging되는 경우가 발생하였으나, 대부분 re-open상태를 나타내었다. 또한 누출 경로가 완전 re-open된 후 나트륨 부위에서 시편의 self-wastage pattern은 온도에 영향을 받지 않음을 알 수 있었으며, 누출경로가 re-open 되면서 나타나는 defected 크기는 대략 5 mm 이내임을 알 수 있었다. 누출 경로가 완전 re-open 되는데 걸리는 시간은나트륨 온도가 높을수록 짧게 나타났으며, 평균적으로 $450^{\circ}C$에서 143분, $475^{\circ}C$의 경우 40.7분, $510^{\circ}C$의 경우 34.7분을 나타내었다.

• Corrosion Science and Technology
• /
• 제5권1호
• /
• pp.1-4
• /
• 2006

Martensitic stainless steel is used when mechanical properties such as high tensile strength and hardness are required. Medium carbon-contained martensitic stainless steel which contains more than 0.2 wt% of carbon should be heat-treated and quenched at the temperature where undissolved carbides are totally dissolved into the matrix. In particular, the dissolution and reprecipitation behaviors of various forms of carbides are affected by such parameters as heating rate, heating temperature, duration time and cooling rate. This study is to investigate the effects of heat treatment parameters of 14Cr-3Mo martensitic stainless on corrosion resistance and phase transformation in relation to the dissolution and reprecipitation of carbides.

• Journal of Welding and Joining
• /
• 제18권2호
• /
• pp.176-176
• /
• 2000

Recently developed Austenite stainless steel,309L was to overlay on 3Cr-1Mo-V-Ti-B steels, using Electroslag welding process, which wide electrodes were adopted. Transition region in welding interlayer relating to disbonding crack was investigated. Also. the effect of welding condition on the width of transition region and coarsening grains of the austenite were studied.1) With increasing welding speed the width of martensite at transient region was increased, but the amount of delta ferrite in weld metal was reduced, being fine grained.2) The form of martensite at the transition region was occured by reversible transition region, leading to increasing Ms point.3) With increasing welding speed, the grain of austenite formed at the welding interface was finer. With increasing welding current under the same welding speed, the grain size of the austenite was finer. At high current, original grain size of the austenite is coarse, but the austenite has fine grains because the austenite was transformed to martensite during cooling.4) In the case of high welding speed, the width of martensite at the welding interface was increased, but the grain size of austenite at the welding interface was finer. This indicates that the inhibition of disbonding crack may be achieved through dispersening fine carbides in the grain boudary.(Received August 3, 1999)

• 한국해양공학회지
• /
• 제12권2호통권28호
• /
• pp.65-70
• /
• 1998

In this report, the creep properties and creep life estimation by Larson-Miller Parameter(LMP) Method for 2.25Cr1Mo steel to be used as power plant tubes or other components were presented at the high temperatures of 500, 550, and $600^{\circ}C$. It was confirmed experimentally and quantitatively that a creep life estimation equation at such various high temperatures was well derived by LMP and could be used very effectively within the creep life of 10$^3$ hours, but very unreliable and even dangerous for design in a long term of creep life such as 10$^4$ or $10^5$ hours.

• Journal of Welding and Joining
• /
• 제18권2호
• /
• pp.227-227
• /
• 2000

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, 2 ¼Cr-1Mo steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence. (Received December 2, 1999)

• 대한기계학회논문집A
• /
• 제24권7호
• /
• pp.1673-1680
• /
• 2000

The degradation of a boiler header constructed by a material, 1Cr-0.5Mo steel in a fossil power plant is observed when the header is exposed for a long period to the high temperature and pressure. The present investigations are for evaluating the effect of the degradation on the material, such as its strength changes. Reheat-treated metal is used to compare the mechanical properties of the degraded and that of reheat-treated materials. Through the investigation, following results are obtained 1) the area ratio of ferrite in the reheat-treated material is larger than that of the degraded material, 2) the hardness and tensile strength of the degraded material are lower than that of the reheat-treated material, 3) the ductile-brittle transition temperature(DBTT) increased toward high temperature region, 4) the fatigue crack growth rate(FCGR) of the degraded material is higher than that of the reheat-treated material in the region of low ΔK value while FCGR of the both materials are similar in high ΔK region.

• 한국산학기술학회논문지
• /
• 제9권6호
• /
• pp.1555-1559
• /
• 2008

$5{\sim}150{\mu}m$의 오스테나이트계 304(Fe-18%Cr-12%Ni) 및 316L(Fe-18%Cr-13%Ni-2.4%Mo)미립 분말을 사용하여 소결 특성을 평가한 결과, 다음과 같은 결론을 얻었다 (1) 3.6ks의 소결 시간으로는 어느 경우에 있어서나 소결조건에 관계없이 소결체의 상대밀도는 $95{\sim}98%$에서 포화하여 완전 치밀화된 소결체를 얻을 수 없었다. (2) $5{\mu}m$분말을 진공소결 하였을 경우, ts=57.6ks에서 거의 완전 치밀화된 소결체가 얻어졌다. (3) 소결 분위기에 상관없이 304 및 316L소결체에는 $0.5{\sim}0.6%$정도의 산소가 잔류하였다. (4) 진공 소결의 경우, 탄소분 첨가에 의해 소결체의 잔류 산소량은 무첨가 소결체에 비하여 0.375이상 감소하였고, 조직적으로도 산화물은 거의 관찰되지 않았다. 또한 탄소 첨가는 소결체의 밀도 향상 효과로 작용하여 목적하는 완전 치밀화된 고성능 소결체를 제조하는 것이 가능하게 되었다.

• 한국해양공학회지
• /
• 제4권2호
• /
• pp.250-250
• /
• 1990

In this paper, fatigue tests were carried out at stress test levels of 461 MPa, 441 MPa, and 431 MPa by using smooth specimen of$2_{1/4}$ Cr-1 Mo steel with the stress ratio(R) of 0.05. The initiation, growth and coalescense process of the major cracks and sub-cracks among the fatigue cracks on the smooth specimen are investigated and measured under each stress level at a constant cycle ratio by the replica technique with optical microscope. Some of the important results are as follows: In spite of the difference of stress levels, the major crack data gather into a small band in the curve of surface crack length and crack depth against cycle ratio N/Nf. The sub-crack data, however, deviate from the band of the major crack. The growth rates, da/dN, of major and sub-crack plotted against the stress intensity factor range, ${\Delta}K$, have the tendency to be compressed on a relatively small band. But it is more effective to predict fatigue life through major cracks. The propagation behavior of surface microcracks on the smooth specimens coincides with that of the specimen having an artificial small surface defect or through crack.