FIRST LAYER OR UPPER LAYER WELDING SECTION OF HIGH Cr STEEL TURBINE ROTOR, OVERLAY WELDING MATERIAL FOR WELDING SECTION, AND METHOD FOR MANUFACTURING OVERLAY WELDING SECTION

Abstract

The present invention relates to a multilayer overlay welding section in which a first layer of an overlay welding section to be formed on the bearing contact surface of a high Cr steel turbine rotor includes C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.5%, Cr: 4.0 to 7.7%, and Mo: 0.5 to 1.5% with a remainder including Fe and unavoidable impurities, a multilayer overlay welding section in which, in addition to the above layer, an upper layer welding section includes C: 0.05 to 0.2%, Si: 0.1 to 1.0%, Mn: 0.3 to 2.5%, Cr: 1.0 to 4.0%, and Mo: 0.5 to 1.5%, and a welding material therefor and a process for producing the multilayer overlay welding section.

Description

TECHNICAL FIELD[0001]The present invention relates to a multilayer overlay for forming a Cr-containing steel overlay on a surface with which bearings of a high Cr steel turbine rotor come into contact.BACKGROUND ART[0002]Since a high Cr steel is excellent in high-temperature strength and low-temperature toughness, the steel has been increasingly used as a material for high-pressure and medium-pressure turbine rotors of generators. However, the contact surface with the bearings of the high Cr steel turbine rotor is prone to develop seizure at the bearings during its use, so that there is a concern of inviting damage. Therefore, there has been proposed a method for preventing the generation of seizure by overlay welding a low alloy steel on the bearing part of the rotor (e.g., see Patent Document 1).[0003]Heretofore, with regard to such a kind of overlay welding, mainly welding materials and welding methods for submerge arc welding have been developed.[0004]For example, Patent Documen...

AI Technical Summary

Benefits of technology

The present invention relates to a welding method for a bearing part. The method prevents the formation of ferrite at the boundary part between layers and suppresses stress relief annealing cracks. It also prevents seizing of bearings and ensures sufficient strength and toughness for the bearing part. The strength balance among the layers is optimized to prevent strain concentration to the first layer during stress relief annealing. This method allows for stable quality of an overlay-strengthened high Cr steel turbine rotor and prevents the formation of pro-eutectoid ferrite.

Problems solved by technology

However, since the welding material used in the first layer welding material described in Patent Document 2 contains no Cr, accumulation of strain occurs in the first layer at shape discontinuous parts such as a thrust part during stress relief annealing and there is a possibility of generation of defects such as cracks in some cases, depending on the strength of the upper layer.

Also, in the shape discontinuous parts such as the thrust part at which stress concentration is prone to occur due to the shape, there is a concern of occurrence of defects.

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