Indian Welding Journal

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Microstructure Evolution and Mechanical Properties of Friction Stir Welded Thick HSLA Steel


Affiliations
1 Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India
     

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Friction stir welding (FSW) is known for joining low softening alloys metals such as aluminum, magnesium and copper, however joining of high softening alloys like steel, titanium and nickel base alloys is still a challenge due to tool material stringent property requirements and its availability. Presently, due to development new generation tool material FSW of high softening alloys is possible and also reported. FSW can effectively join different grade of low thickness steel, however the questions about joining thick section steel still remains a challenge.

In this paper, FSW of 7 mm, 12 mm and 24 mm thick HSLA steel in single and double pass was carried out to develop the processing window for defect free weld joints and understanding the structure-property correlation. The increase in thickness of the base metal resulted in generation of higher load, higher heat input and consequently lower cooling rate. Therefore, the microstructure obtained after FSW in different thickness of steel also shows varying microstructures (grain boundary ferrite, acicular ferrite, widmensttan ferrite and upper bainite). Optical and scanning electron microscope (SEM) with electron back scattered diffraction (EBSD) detector was utilized to characterize the microstructure of FSW nugget zone. Tensile and hardness properties were also evaluated and correlated with the microstructure.


Keywords

Friction Stir Welding, High Strength Low Alloy Steel (HSLA), Microstructure, Tensile Properties, Scanning Electron Microscopy.
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  • Shinoda T and Takegami H (2005); Development of FSW process for steel assembly to shipbuilding and offshore structure, Proc. 15th Int. Offshore and Polar Eng. Conf., Seoul, pp.19-24.

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  • Microstructure Evolution and Mechanical Properties of Friction Stir Welded Thick HSLA Steel

Abstract Views: 427  |  PDF Views: 11

Authors

A. Gourav Rao
Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India
A. P. Singh
Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India
S. Parida
Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India
A. Kumar
Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India
V. P. Deshmukh
Naval Metallurgy Division, Naval Materials Research Laboratory, Ambernath, Thane - 421 506, Maharashtra, India

Abstract


Friction stir welding (FSW) is known for joining low softening alloys metals such as aluminum, magnesium and copper, however joining of high softening alloys like steel, titanium and nickel base alloys is still a challenge due to tool material stringent property requirements and its availability. Presently, due to development new generation tool material FSW of high softening alloys is possible and also reported. FSW can effectively join different grade of low thickness steel, however the questions about joining thick section steel still remains a challenge.

In this paper, FSW of 7 mm, 12 mm and 24 mm thick HSLA steel in single and double pass was carried out to develop the processing window for defect free weld joints and understanding the structure-property correlation. The increase in thickness of the base metal resulted in generation of higher load, higher heat input and consequently lower cooling rate. Therefore, the microstructure obtained after FSW in different thickness of steel also shows varying microstructures (grain boundary ferrite, acicular ferrite, widmensttan ferrite and upper bainite). Optical and scanning electron microscope (SEM) with electron back scattered diffraction (EBSD) detector was utilized to characterize the microstructure of FSW nugget zone. Tensile and hardness properties were also evaluated and correlated with the microstructure.


Keywords


Friction Stir Welding, High Strength Low Alloy Steel (HSLA), Microstructure, Tensile Properties, Scanning Electron Microscopy.

References





DOI: https://doi.org/10.22486/iwj%2F2018%2Fv51%2Fi3%2F175006