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Journal ArticleDOI

Metallurgical changes and mechanical behaviour during high temperature aging of welds between Alloy 800 and 316LN austenitic stainless steel

01 Oct 2003-Materials Science and Technology (Taylor & Francis)-Vol. 19, Iss: 10, pp 1411-1417
TL;DR: In this article, a trimetallic material with a coefficient of thermal expansion intermediate between the ferritic and austenitic steels was used to interpose a material with high thermal expansion between the two steels.
Abstract: In the use of ferritic to austenitic stainless steel transition joints for power plant applications, the difference in coefficients of thermal expansion constitutes a serious problem. One way to mitigate this is to use a trimetallic configuration by interposing a material with a coefficient of thermal expansion intermediate between the ferritic and austenitic steels. Modified 9Cr - 1Mo steel has been joined to 316LN austenitic stainless steel using Alloy 800 as an intermediate piece. In the work herein reported, welds between Alloy 800 and 316LN have been produced using Inconel 182 filler material. These have been subjected to high temperature exposure for up to 5000 h at 625 ° C. Results have shown that up to 500 h of aging the structure and mechanical properties remain unaffected. On treatment for 2000 and 5000 h, however, there is a noticeable increase in hardness and reduction in toughness. These have been found to be caused by precipitation of Ni3Ti and carbide phases including NbC and M23C6.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the microstructural evolution in dissimilar welds and the factors that contribute to premature failure are discussed, and failure is attributed to the steep micro-structural and mechanical property gradients.
Abstract: Dissimilar metal welds between ferritic and austenitic alloys are used extensively in power plants. Premature failure of such welds can occur below the expected creep life of either base metal. This article reviews microstructural evolution in dissimilar welds and describes factors that contribute to premature failure. The microstructure in the as welded condition consists of a sharp chemical concentration gradient across the fusion line. Martensite forms within this gradient due to high hardenability and rapid cooling rates from welding. Upon aging, carbon diffuses down the chemical potential gradient from the ferritic steel toward the austenitic alloy. This can lead to formation of a soft carbon denuded zone in the ferritic steel, and nucleation and growth of carbides in the austenitic steel that produce high hardness. These differences in microstructure and hardness occur over distances of about 50–100 μm. Failure is attributed to the steep microstructural and mechanical property gradients, the...

110 citations

Journal ArticleDOI
TL;DR: In this paper, the thermal properties of transition joints between 9Cr-1Mo steel and Alloy 800 steels are investigated for high-temperature components of power plant power plants, and the results show that the tendency for carbon to diffuse from the ferritic steel into the weld metal is much less pronounced than when 2.25Cr- 1Mo steel is used as the ferrite part.
Abstract: Transition joints between ferritic steel and austenitic stainless steel are commonly encountered in high-temperature components of power plants. Service failures in these are known to occur as a result, mainly, of thermal stresses due to expansion coefficient differentials. In order to mitigate the problem, a trimetallic configuration involving an intermediate piece of a material such as Alloy 800 between the ferritic and austenitic steels has been suggested. In our work, modified 9Cr-1Mo steel and 316LN stainless steel are used as the ferritic and austenitic components and the thermal behavior of the joints between modified 9Cr-1Mo steel and Alloy 800 is described in this article. The joints, made using the nickel-base filler material INCONEL 82/182 (INCONEL 82 for the root pass by gas-tungsten arc welding and INCONEL 182 for the filler passes by shielded-metal arc welding), were aged at 625 °C for periods up to 5000 hours. The microstructural changes occurring in the weld metal as well as at the interfaces with the two parent materials are characterized in detail. Results of across-the-weld hardness surveys and cross-weld tension tests and weld metal Charpy impact tests are correlated with the structural changes observed. Principally, the results show that (1) the tendency for carbon to diffuse from the ferritic steel into the weld metal is much less pronounced than when 2.25Cr-1Mo steel is used as the ferritic part; and (2) intermetallic precipitation occurs in the weld metal for aging durations longer than 2000 hours, but the weld metal toughness still remains adequate in terms of the relevant specification.

39 citations

Journal ArticleDOI
TL;DR: In this article, the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, and impact toughness of the dissimilar joints is discussed.
Abstract: Fundamental investigation of continuous drive friction welding of austenitic stainless steel (AISI 304) and low alloy steel (AISI 4140) is described. The emphasis is made on the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, notch tensile strength and impact toughness of the dissimilar joints. Hardness profiles across the weld show the interface is harder than the respective parent metals. In general, maximum peak hardness is observed on the stainless steel side, while other peak hardness is on the low alloy steel side. A trough in hardness distribution in between the peaks is located on the low alloy steel side. Peak hardness on the stainless steel and low alloy steel side close to the interface increases with a decrease in rotational speed. All transverse tensile joints fractured on stainless steel side near the interface. Notch tensile strength and impact toughness increase with increase in rotational speed up to 1 500 r/min and decrease thereafter. The mechanism of influence of rotational speed for the observed trends is discussed in the torque, displacement characteristics, heat generation, microstructure, fractography and mechanical properties.

29 citations

ReportDOI
01 Mar 2010

25 citations


Cites background or methods from "Metallurgical changes and mechanica..."

  • ...SEM photomicrographs of the charpy impact specimens in the (a) as-welded condition and (b) aged for 5,000 hours at 625°C.(67)...

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  • ...Variation in hardness and impact toughness of the fusion zone for welds between 9Cr--1Mo steel and alloy 800H (made using ERNiCr-3 filler) that were aged at 625°C.(67)...

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  • ...Variation in hardness and impact toughness of the fusion zone for welds between 9Cr‐‐1Mo steel and alloy 800H (made using ERNiCr‐3 filler) that were aged at 625°C.(67) ....

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  • ...SEM photomicrographs of the charpy impact specimens in the (a) as‐welded condition and (b) aged for 5,000 hours at 625°C.(67) ....

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  • ...This has been investigated by Klueh and King65,66 and more recently Sireesha et al.18,67....

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Journal ArticleDOI
TL;DR: The consequence of friction stir welding (FSW) and activated-gas tungsten arc welding (A-GTAW) processes on the evolution of microstructure and mechanical properties of 9Cr-1Mo (P9) steel to 316LN was discussed in this article.
Abstract: The consequence of friction stir welding (FSW) and activated-gas tungsten arc welding (A-GTAW) processes on the evolution of microstructure and mechanical properties of 9Cr–1Mo (P9) steel to 316LN ...

17 citations


Cites background from "Metallurgical changes and mechanica..."

  • ...Therefore, the welding parameters need to be optimised appropriately to overcomehot-cracking issues [1,6]....

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References
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Journal ArticleDOI
TL;DR: In this article, a trimetallic joint involving modified 9Cr-1Mo steel and 316LN austenitic stainless steel as the base materials and Alloy 800 as the intermediate piece was investigated.

150 citations

Journal ArticleDOI
TL;DR: In this article, an improved transition metal joint (TMJ) with a trimetallic configuration of austenitic stainless steel/Alloy 800/Cr-Mo ferritic steel is discussed.

101 citations

Journal ArticleDOI
TL;DR: In this article, cross-weld tensile specimens were machined from welds made in 2·25 Cr-1 M 0 steel plate using either AISI 316 or Inconel 182 filler metals.
Abstract: Cross-weld tensile specimens were machined from welds made in 2·25 Cr-1 M 0 steel plate using either AISI 316 or Inconel 182 filler metals. Low-ductility failures, close to the ferritic steel/weld metal interface, were produced by iso-stress temperature-acceleration tests at either 62 or 100 MN m−2 over the temperature range 575°-640°C. The endurances of joints made using Inconel 182 weld metal were greater than those made using AISI 316 weld metal by factors of ∼2·5 and 3 for tests at 62 and 100 MN m−2, respectively. The fracture morphology has been studied by optical and scanning electron microscopy. By comparison with previous investigations, a change in the short- and long-term fracture mechanism of nickelbased joints is identified. The interfacial damage has been measured and is used to discuss the relative importance of creep-strength mismatch and thermal-expansion coefficient differences between the weld metal and ferritic steel in controlling the fracture of the joint.

32 citations

Journal ArticleDOI
TL;DR: In this paper, three commercial heats of Alloy 800 have been tested at 838 K in simple tension and in fatigue at constant plastic strain ranges from 0.2 pct. to 1.4 pct, and it was found that significant additional precipitation occurred during the fatigue testing of two of the heats, and this was correlated with secondary hardening behavior found during the mechanical tests.
Abstract: Three commercial heats of Alloy 800 have been tested at 838 K in simple tension and in fatigue at constant plastic strain ranges from 0.2 pct. to 1.4 pct. Although all three heats met the ASTM specifications for Alloy 800, the heats exhibited significant differences in elevated temperature mechanical properties. These differences were functions not only of heat-to-heat chemistry variations, but also of the final annealing treatment given during their manufacture. The microstructures of several samples cycled to failure in the above tests were examined by transmission electron microscopy and compared with the microstructures of the as-received heats. It was found that significant additional precipitation occurred during the fatigue testing of two of the heats, and this was correlated with secondary hardening behavior found during the mechanical tests. The observed precipitation behavior could be explained using suggested isothermal transformation curves and solvus curves taken from the literature.

23 citations

01 Aug 1962
TL;DR: In this article, the following metallurgical factors must be considered in the joining process are described: thermal cycling and shock, galvanic corrosion, metallurgy stability, compatibility of base metals, and dilution by base metal.
Abstract: General rules and precautions that were developed for joining dissimilar metals are discussed. The following metallurgical factors which must be considered in the joining process are described: thermal cycling and shock, galvanic corrosion, metallurgical stability, compatibility of base metals, and dilution by base metal. Rules for brazing and soldering are given. A table of 170 dissimilar metal joints is presented. (M.C.G.)

9 citations