• Journal of Welding and Joining
• /
• 제27권2호
• /
• pp.27-31
• /
• 2009

Ferritic stainless steels have a good heat resistance and economic advantage. They are used for applications such as automotive exhaust systems where resistance to general corrosion is superior to carbon steels. However, there are not enough research for ferritic stainless steels on weldability mainly used as automotive exhaust manifolds. In this study, mechanical and microstructure properties of as-welded STS 429L and STS 444 ferrite stainless steels were confirmed by tensile, bending, hardness test, optical microscopy and scanning electron microscopy. Tensile strength of the STS 444 is higher than the STS 429L when it is a raw material. In contrast to this fact, STS 429L indicated higher tensile strength after butt welded. In addition, the hardness have a increasing tendency as getting down on the bead.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.107-112
• /
• 2002

Ferritic stainless steels would be the most important alloys under the chloride environment. They are a cheaper alternative to austenitic stainless steels [1]. The present study is related to gas tungsten arc welding (GTAW) characteristics of Type 444 stainless steels. The heat of welding leads to grain coarsening in the HAZ and in the weld metal of ferritic stainless steels because they solidify directly from the liquid to the ferritc phase without any intermediate phase transformation. It is therefore recommended that these alloys be welded with a low heat input and at high welding speeds. Attempts to improve weldability were made by using of direct current straight polarity (DCSP) and pulsed current GTAW processes in this study. Measuring weld bead, grain size and Erichsen test were performed and the effects of heat input, pulse frequency on the weld metal and HAZ were studied. The main results were obtained as followings: decreasing heat input was effective to control the width of weld both in DCSP welding and in pulsed current welding; pulsed current welding was found to refine the grain size effectively and the finest grain size was found at the frequency of 150Hz in pulsed current welding; it was found that decreasing heat input also refine the HAZs effectively and the frequency had no different effect on HAZ at the same heat input; the ductility could be improved effectively in pulsed current welding.

• Corrosion Science and Technology
• /
• 제6권1호
• /
• pp.1-6
• /
• 2007

Ferritic stainless steels for the SOFC interconnect applications are required to possess not only a good oxidation resistance, but also a high electrical conductivity of the oxide scale that forms during exposure at the SOFC operating environment. In order to understand the effects of alloying elements on the oxidation behavior of ferritic stainless steels and on the electrical properties of oxide scales, two kinds of commercial ferritic stainless steels, STS 430 and STS 444, were investigated by performing isothermal oxidations at $800^{\circ}C$ in a wet air containing 3% $H_{2}O$. The results showed that STS 444 was superior to STS 430 in both of the oxidation resistance and the area specific resistance. Although STS 444 contained a less amount of Mn for the $(Mn,Cr)_{3}O_{4}$ spinel formation than STS 430, the minor alloying elements of Al and Mo in STS 444, which were accumulated in the base metal region adjacent the scale, were suggested to reduce the scale growth rate and to enhance the scale adherence to the base metal.

• Journal of Advanced Marine Engineering and Technology
• /
• 제33권6호
• /
• pp.860-866
• /
• 2009

It is very important to choose optimal material having good corrosion resistance and capabilities for the part materials such as the automotive exhaust system under a hot salt corrosion atmosphere. Generally, two types of corrosion come into the automotive exhaust system. One is 'Condensate Corrosion', which is occurred by exhaust gas condensate formed at the inner surface of exhaust system heated up during driving, which results in the acid condensate pitting. The other is 'High Temperature Salt Corrosion' occurring from the interaction between the chloride ion coming from salt at the seaside district or snow salt and the outer surface of exhaust system. By the corrosion attack, the main muffler is firstly damaged and the life cycle of an automobile is significantly decreased. It has been investigated that the hot salt corrosion properties of a STS 409L and 436L ferritic stainless steels which are well-known for the materials of the automotive exhaust system. In addition, the corrosion properties of hot dip aluminum coated STS 409L have been compared with uncoated steels. Aluminum coated STS 409L showed a superior corrosion resistance than uncoated STS 409L, and futhermore showed a better corrosion resistance than a STS 436L, which is an expensive ferritic stainless steel having a excellent corrosion resistance caused from more chromium content of an alloying element.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 1993년도 특별강연 및 추계학술발표 개요집
• /
• pp.79-81
• /
• 1993

• 대한금속재료학회지
• /
• 제49권1호
• /
• pp.64-72
• /
• 2011

The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.

• 한국해양공학회지
• /
• 제11권3호
• /
• pp.48-55
• /
• 1997

The steel for automotive exhaust system needs a good corrosion resistance at the atmosphere of high temperature NaCl. Effect of the alloying elements Me, Ti, Nb on the NaCl induced hot corrosion behavior was investigated at the temperatures between 55$0^{\circ}C$ and 75$0^{\circ}C$ for 18Cr ferritic stainless steels. The weight loss by corrosion has increased linearly with corrosion cycle time, and the corrosion rate has accelerated at higher temperature. The alloying of Mo significantly improved corrosion resistance of the steel and the effect was more pronounced at higher temperature. The addition of alloying elements Ti, Nb have also shown improved corrosion resistance by formation of Ti(C,N) or Nb(C, N) precipitates.

• 한국강구조학회 논문집
• /
• 제28권5호
• /
• pp.303-312
• /
• 2016

최근에 스테인리스강의 우수한 연성과 내식성 등의 재료적 특성으로 건축물의 구조용 강재로 적용하기 위한 많은 연구들이 수행되어 오고 있다. 특히, 니켈을 거의 함유하고 있지 않은 페라이트계 스테인리스강은 재료비 측면에서 니켈을 함유하고 있는 오스테나이트계 스테인리스강에 비해 저렴하고 탄소강에 비해서는 월등한 내식성능과 구조성능을 제공하기 때문에 그 사용성이 증대되고 있다. 본 연구에서는 페라이트계 스테인리스강 용접접합부에 있어 용착금속이 아닌 모재 블록전단파단의 구조적 거동을 조사하기 위해 용접길이와 용접방법(아크, 티그)을 변수로 하여 단순인장 실험을 실시하였다. 용접접합부의 블록전단 거동은 용접에 의한 삼축응력효과 때문에 볼트접합부의 블록전단 거동과 상이하며, 현행설계기준식은 이러한 특성을 반영하지 못하고 있다. 티그용접 접합부의 변형능력과 최대내력이 아크용접 접합부보다 높게 나타났고, 현행기준식과 기존연구자에 의해 제시된 내력식에 의한 예측내력과 실험결과 최대내력을 비교 검토하였다.

• Journal of Welding and Joining
• /
• 제20권5호
• /
• pp.63-71
• /
• 2002

One of the shortcoming of ferritic stainless steels is their limited toughness. The most important factor governing the toughness of ferritic stainless steels is hewn to be their interstitial contents. Due to the limited solubility of carbon and nitrogen in the ferrite matrix, it is difficult to avoid carbide and nitride precipitates. In the study, the role of nitrogen on the toughness of 260r-2Mo superferritic stainless steel welds has been investigated using alloys containing various nitrogen levels between 100 and 1640 ppm. Mechanical properties of weld metals have been evaluated by microhardness, Charpy impact test and notch tensile test. The alloys are mainly embrittled by the grain boundary and intragranular nitride precipitation. Grain boundary precipitates are considered to be more deleterious than intrauanular nitrides. Fracture mechanism have been elucidated through microscopic evaluation of notch tensile test

• 소성∙가공
• /
• 제6권2호
• /
• pp.110-117
• /
• 1997

Sticking behavior under the hot rolling conditions for ferritic stainless steels have been studied. Sticking, which is a phenomenon that the naked metal exposed to the surface by scale breakaway during hot rolling sticks to the roll surface, was affected by both high temperature tensile strength and oxidation resistance of the steels. A steel having higher tensile strength and lower oxidation resistance exhibits better resistance to the sticking. It is due to that higher tensile strength increases localized deformation resistance and lower oxidation resistance creates lower friction between steel and roll by forming thicker scale as a lubricant during hot rolling. So, the sticking tends to occur more severely in the order of 430J1L, 436L, 430 and 409L. The most sensitive temperature to the sticking was found to be 90$0^{\circ}C$ for all grade of steels. It was also found that the high speed steel(HSS) roll compared to the Hi-Cr roll was more beneficial to prevent sticking. Because higher surface hardness of HSS roll compared to that of Hi-Cr roll provides less nucleation sites for sticking such as scratch on the roll surface.