Welding procedure to improve the fatigue characteristics of the welded parts of high-tension steel


January 4, 2021

A new welding procedure which is capable of introducing residual compressive stress

Key Word : Welding procedure, high-tension steel, fatigue, welding technology

Background / Context / Abstract:

High-tension steel is a steel material with heightened tensile strength greater than that of normal steel materials through composition and structure control, and it has a tensile strength of 500 MPa to 1 GPa as well as high fatigue characteristics. It therefore offers advantages in weight reduction and safety, and is popularly used in railroads, shipbuilding, bridges and so forth. However, parts that were welded using the conventional welding technology were lower in fatigue characteristics than the high-tension steel, resulting in a problem in which fractures began at the welded parts.
To improve the fatigue characteristics of the welded parts mentioned above, welding materials with low martensitic transformation temperatures have been developed in the past. However, these only addressed a fatigue life of approximately twice that of the conventional welded parts. A technology to improve the fatigue characteristics by introducing residual compressive stress with an ultrasonic shot peening process (ultrasonic impact treatment: UIT) into the welded parts has also been put into practical application, but the processing involved a lot of trouble and cost, and also left the issue of release in the residual compressive stress (decrease in strength) caused by the large fluctuations in stress.

Technology Overview:

This is a new welding procedure which improves the fatigue characteristics of the welded parts to 2 to 15 times higher in the welding of steel material stiffeners and gusset plates, and is capable of introducing residual compressive stress while also mitigating the concentration of stress.


This invention delivers the following advantages compared to conventional welding technology as well as UIT.
・Addresses a fatigue life characteristic of 2 to 15 times higher (under a load of 100 to 150 MPa) than that of simple conventional welding technology.
・Fatigue characteristics equivalent to those of UIT
・Less prone to go through residual compressive stress release (decrease in strength) due to large fluctuations in the load, which is a weakness in UIT, as the residual compressive stress is generated down to a deep position in the toe of the weld.
・Easier introduction and processing than UIT
・Similar improvement in the fatigue characteristics is possible for repair welding on the gusset welding parts of operating structures.

Potential Applications / Potential Markets:

・Construction and repair for structures using high-tension steel such as railroads, shipbuilding and bridges

State of Development / Opportunity / Seeking:

・Available for exclusive and non-exclusive licensing
・Exclusive/non-exclusive evaluation for defined period (set up for options)
・Collaborative/supportive research
・Development partner

IP Status:

WO2013/069484 (Issued: JP, EP (GB, DE), CN)


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