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Fusion Welding of Perlite and Austenite Steels

#3555


Fusion Welding Methods for Joining of Austenite Class Steels with Perlite Steels with Use of Perlite Material

Tech Area / Field

  • OTH-BIT/Building Industry Technology/Other
  • MAN-MAT/Engineering Materials/Manufacturing Technology

Status
3 Approved without Funding

Registration date
28.06.2006

Leading Institute
NIKIMT (Institute of Assembly Technology), Russia, Moscow

Supporting institutes

  • NPO TsNIITMASH (Machine-Building Technology), Russia, Moscow

Collaborators

  • Otto-von-Guericke-Universität Magdeburg, Germany, Magdeburg

Project summary

For manufacture of modern structures a lot of metals and alloys have wide application. For their welding by a fusion process it is difficult sometimes to find a material, which can meet all necessary requirements including economical ones. Thus there is a problem how to joint non-similar metals and alloys. As more applicable, there are welded structures combining perlite and austenite steels.

Such combinations have wide application in power engineering, for example, for joining of reactor vessels with coolant circuit pipelines, channel joints in channel-type reactors, joints of coolant circuit pipelines with internal cladding made of corrosion-resistant steel, etc. Application of joints of non-similar steels gives economical and other advantages.

The problem relating to fusion welding of austenite and perlite steels has the same nature as for welding of non-similar materials. Usually, each welded joint has chemical-, structural- and mechanical non-homogeneity, which appears in process of welding and during in-service period. Besides that, mechanical stresses in non-similar joints can be higher then in joints of similar materials.

These factors have a very negative influence on service characteristics of welds. In order to reduce such influence, some metallurgical and technological methods can be used, which allow produce welds with optimal properties. At present time, the mainly applicable method to weld a composition of perlite and austenite steels is usage of Cr-Ni-, austenite-, austenite-ferrite- and high nickel-alloyed welding materials. For thickness over 6 – 10 mm to be welded, a welding process can provide a provisional intermediate layer welded over perlite layer. Otherwise, non-similar steels with thickness within 10 mm can be joined directly together. By welding of perlite steels with austenite cladding, a perlite material shall be welded first and a cladding layer shall be welded next. Another way to weld a two-layered steel is welding of perlite layer using austenite materials.

Using of such technologies, however, does not exclude a possibility of deterioration of a non-similar joint. In some cases, for example – for welding of thick cladding pipes with valve fittings or housing elements, there is a very difficult or practically impossible task to fulfill welding of a thick part with restricted access to internal austenite cladding caused by limitation of space or presence of contaminants. So it is impossible to realize a classical welding process for both sides of such joint: first, welding of external layers shall be performed, then, welding of internal austenite cladding layer inside of a structure shall be made. Welding process performed in such condition can give reducing of welds quality, sufficient increase of labor consumption and relevant expenses.

In order to solve this problem, basing on a long-year experience in reactor building, the project’s authors propose to develop a one-sided fusion welding process instead the available double-sided technology. This method provides welding of internal cladding layer first with use of an austenite filler material, and then – welding of main perlite layer with use of special perlite filler materials. In this case, a transitional layer between root austenite layer and perlite layers, can be made with use of perlite filler materials welded directly over the austenite cladding layer. We also propose to weld austenite-class welds for non-cladding perlite steels using special perlite filler materials, as well as using a provisional perlite overlaying on edges of austenite parts.

There is no sufficient data on possible ways how to realize the proposed processes, so the project’s authors offer the working program including the following investigations:

  1. Production of welded joins by manual arc welding and machined TIG welding; thickness to be welded: up to 100 mm; heat treatment can be provided after welding.
  2. Study of welded joints properties will be performed using specimens welded by the proposed processes.

The project provides the following investigations:
  • distribution of chemical elements and structural non homogeneity through cross-section of welds by mean of metal-graphic, micro-Roentgen structural analysis and electronic microscopy;
  • mechanical properties of welds (strength, impact strength, thermal and cyclic fatigue);
  • critical brittleness temperature of transitional zone metal in initial condition, after welding thermal cycles, after heat treatment and aging;
  • withstanding of cladding weld root against inter-crystalline corrosion in boiling solution of CuSO4 and H2SO4 with addition of copper chips or copper disks, according to ISO 3651-1998.

On base of obtained research and testing results, technical recommendations will be issued, in order to apply developed process for welding of non-similar steels.

Research data to be obtained will allow to apply one-sided welding with easy external access through perlite layer, instead difficult “classic” double-sided welding process for steels with internal cladding, which is to be made by restricted internal access in contaminated area.

Application of proposed processes in industry will make welding production significantly easier regarding manufacture, mounting and repair of such structures, excluding hazardous procedures for personnel relating to internal overlaying by restricted access and presence of contaminants. They allow improve repair conditions and quality, shorten working period two or more times and reduce significantly costs of works.

Scope and results of investigations will also allow estimate functional properties of non-similar steels joints, estimate prospects of their application and introduce them in several industries: power plants, chemical- and oil/gas facilities, civil sector, etc. All mentioned above will ensure complete conversion of the project’s participating institutions by minimal expenses and saving their scientific potential.


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