scholarly journals Effects of Microstructural Modification Using Friction Stir Processing on Fatigue Strength of Butt-Welded Joints for High-Strength Steels

2018 ◽  
Vol 09 (07) ◽  
pp. 625-636
Author(s):  
Hajime Yamamoto ◽  
Kazuhiro Ito
Keyword(s):  
Fatigue Strength ◽  
Friction Stir Processing ◽  
Welded Joints ◽  
High Strength Steels ◽  
High Strength ◽  
Friction Stir ◽  
Microstructural Modification

A review of fatigue strength improvement methods

1985 ◽  
Vol 12 (1) ◽  
pp. 166-183 ◽  
Author(s):  
Ian F.C. Smith ◽  
Manfred A. Hirt
Keyword(s):  
Quality Control ◽  
Finite Element ◽  
Fatigue Strength ◽  
Structural Steel ◽  
Welded Joints ◽  
Three Dimensional ◽  
High Strength Steels ◽  
High Strength ◽  
High Yield ◽  
Element Analysis

Improving the fatigue strength of welded joints may be economically interesting in many situations, especially in those cases where high-strength steels are used. However, widespread use of a method is, in many cases, restricted by a lack of knowledge of its reliability. Previous work has focused only on the effectiveness of improvement methods to increase fatigue strength; cost studies and quality control instructions are rarely given.In this report, several methods for structural steel are summarized. A review of existing test results shows that improved connections made from a high yield strength steel reveal a higher percentage improvement than mild steel connections using the same improvement method. In addition, improved joints may be sensitive to the applied stress ratio. Finally, the most efficient method depends on the type of welded joint.Residual stress methods have relatively inexpensive application costs whereas some grinding methods are very costly. Quality control depends upon fabrication, loading, and environmental conditions. Examination of four types of fillet-welded joints has identified several methods that require further research. A three-dimensional finite element study of these joints predicts that at crack locations, under service loading, a very small plastic zone is formed. Therefore, residual stress methods may remain effective under variable-amplitude load conditions. Key words: structural steel, welded joints, fatigue, improvement methods, fillet welds, finite element analysis.

scholarly journals Comprehensive Analysis of the Microstructure and Mechanical Properties of Friction-Stir-Welded Low-Carbon High-Strength Steels with Tensile Strengths Ranging from 590 MPa to 1.5 GPa

2021 ◽  
Vol 11 (12) ◽  
pp. 5728
Author(s):  
HyeonJeong You ◽  
Minjung Kang ◽  
Sung Yi ◽  
Soongkeun Hyun ◽  
Cheolhee Kim
Keyword(s):  
Mechanical Properties ◽  
Tensile Test ◽  
Joint Strength ◽  
Solid Phase ◽  
Welding Process ◽  
High Strength Steels ◽  
High Strength ◽  
Low Carbon ◽  
Friction Stir ◽  
Welding Processes

High-strength steels are being increasingly employed in the automotive industry, requiring efficient welding processes. This study analyzed the materials and mechanical properties of high-strength automotive steels with strengths ranging from 590 MPa to 1500 MPa, subjected to friction stir welding (FSW), which is a solid-phase welding process. The high-strength steels were hardened by a high fraction of martensite, and the welds were composed of a recrystallized zone (RZ), a partially recrystallized zone (PRZ), a tempered zone (TZ), and an unaffected base metal (BM). The RZ exhibited a higher hardness than the BM and was fully martensitic when the BM strength was 980 MPa or higher. When the BM strength was 780 MPa or higher, the PRZ and TZ softened owing to tempered martensitic formation and were the fracture locations in the tensile test, whereas BM fracture occurred in the tensile test of the 590 MPa steel weld. The joint strength, determined by the hardness and width of the softened zone, increased and then saturated with an increase in the BM strength. From the results, we can conclude that the thermal history and size of the PRZ and TZ should be controlled to enhance the joint strength of automotive steels.

Investigations on the Mechanical Properties and Formability of Friction Stir Welded Tailored Blanks

2007 ◽  
Vol 344 ◽  
pp. 143-150 ◽  
Author(s):  
Gianluca Buffa ◽  
Livan Fratini ◽  
Marion Merklein ◽  
Detlev Staud
Keyword(s):  
Mechanical Properties ◽  
Stress Condition ◽  
Research Effort ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Friction Stir ◽  
Tailored Blanks ◽  
Sheet Stamping ◽  
Wide Range

Tight competition characterizing automotive industries in the last decades has determined a strong research effort aimed to improve utilized processes and materials in sheet stamping. As far as the latter are regarded light weight alloys, high strength steels and tailored blanks have been increasingly utilized with the aim to reduce parts weight and fuel consumptions. In the paper the mechanical properties and formability of tailored welded blanks made of a precipitation hardenable aluminum alloy but with different sheet thicknesses, have been investigated: both laser welding and friction stir welding have been developed to obtain the tailored blanks. For both welding operations a wide range of the thickness ratios has been considered. The formability of the obtained blanks has been characterized through tensile tests and cup deep drawing tests, in order to show the formability in dependency of the stress condition; what is more mechanical and metallurgical investigations have been made on the welded joints.

Metallurgical Study of Friction Stir Welded High Strength Steels for Shipbuilding

2014 ◽  
Vol 783-786 ◽  
pp. 2798-2803 ◽  
Author(s):  
Marion Allart ◽  
Alexandre Benoit ◽  
Pascal Paillard ◽  
Guillaume Rückert ◽  
Myriam Chargy
Keyword(s):  
Cubic Boron Nitride ◽  
High Strength Steels ◽  
High Strength ◽  
High Yield ◽  
Friction Stir ◽  
Polycrystalline Cubic Boron Nitride ◽  
Recent Developments ◽  
Metallurgical Study ◽  
Welding Processes ◽  
Pcbn Tools

Friction Stir Welding (FSW) is one of the most recent welding processes, invented in 1991 by The Welding Institute. Recent developments, mainly using polycrystalline cubic boron nitride (PCBN) tools, broaden the range of use of FSW to harder materials, like steels. Our study focused on the assembly of high yield strength steels for naval applications by FSW, and its consequences on the metallurgical properties. The main objectivewas to analyze the metallurgical transformations occurring during welding. Welding tests were conducted on three steels: 80HLES, S690QL and DH36. For each welded sample, macrographs, micrographs and micro-hardness maps were performed to characterize the variation of microstructures through the weld.

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