Identification of Weld Residual Stresses Using Diffraction Methods and their Effect on Fatigue Strength of High Strength Steels Welds

2013 ◽  
Vol 768-769 ◽  
pp. 668-674 ◽  
Author(s):  
Lubos Mraz ◽  
Leif Karlsson ◽  
Pavol Mikula ◽  
Miroslav Vrána
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
High Strength Steel ◽  
Transformation Temperature ◽  
High Strength Steels ◽  
High Strength ◽  
Life Time ◽  
Filler Material ◽  
Phase Transformation Temperature ◽  
Steel Welds

It is well known that fatigue strength of welded joints does not depend on steel strength. Better fatigue strength of welded joints, e.g. longer life time of fatigue loaded weld structures, can be achieved with a smooth transition between the weld and the base material to minimize stress concentration. It has also been recognized that residual stresses play a critical role in the fatigue behaviour of welds. In the last decade an extensive research has been performed in order to increase the fatigue strength of high strength steel weldments. The martensite and bainite transformation start temperatures of weld metals have been shown to have a large effect on fatigue life time of high strength steel welds. This is of particular importance if the full potential of high strength steels is to be used in fatigue loaded constructions. A detailed investigation of the effect of phase transformation temperature on residual stress distribution in the vicinity high strength steel welds and its effect on fatigue life time has been performed. The transformation temperature of the weld metal was varied by changing the chemical composition of the filler material. Residual stress distributions have been measured by neutron as well as by X-ray diffraction and fatigue tests have been performed on the fillet welds. A strong effect of weld metal phase transformation temperature on residual stress level was observed. Fatigue strength increased approximately three times when an optimised low transformation temperature filler material was used in comparison to the application of conventional filler material.

Capability of martensitic low transformation temperature welding consumables for increasing the fatigue strength of high strength steel joints

2020 ◽  
Vol 62 (9) ◽  
pp. 891-900
Author(s):  
Jonas Hensel ◽  
Arne Kromm ◽  
Thomas Nitschke-Pagel ◽  
Jonny Dixneit ◽  
Klaus Dilger
Keyword(s):  
Residual Stress ◽  
Phase Transformation ◽  
Fatigue Strength ◽  
High Strength Steel ◽  
Transformation Temperature ◽  
Fatigue Cracks ◽  
High Strength ◽  
Filler Material ◽  
Phase Transformation Temperature ◽  
Filler Materials

Abstract The use of low transformation temperature (LTT) filler materials represents a smart approach for increasing the fatigue strength of welded high strength steel structures apart from the usual procedures of post weld treatment. The main mechanism is based on the effect of the low start temperature of martensite formation on the stress already present during welding. Thus, compressive residual stress formed due to constrained volume expansion in connection with phase transformation become highly effective. Furthermore, the weld metal has a high hardness that can delay the formation of fatigue cracks but also leads to low toughness. Fundamental investigations on the weldability of an LTT filler material are presented in this work, including the characterization of the weld microstructure, its hardness, phase transformation temperature and mechanical properties. Special attention was applied to avoid imperfections in order to ensure a high weld quality for subsequent fatigue testing. Fatigue tests were conducted on the welded joints of the base materials S355J2 and S960QL using conventional filler materials as a comparison to the LTT filler. Butt joints were used with a variation in the weld type (DY-weld and V-weld). In addition, a component-like specimen (longitudinal stiffener) was investigated where the LTT filler material was applied as an additional layer. The joints were characterized with respect to residual stress, its stability during cyclic loading and microstructure. The results show that the application of LTT consumables leads to a significant increase in fatigue strength when basic design guidelines are followed. This enables a benefit from the lightweight design potential of high-strength steel grades.

scholarly journals Formation of welding residual stresses in low transformation temperature (LTT) materials

2009 ◽  
Vol 14 (1) ◽  
pp. 74-81 ◽  
Author(s):  
Thomas Kannengiesser ◽  
Arne Kromm
Keyword(s):  
Residual Stress ◽  
Synchrotron Radiation ◽  
Residual Stresses ◽  
Transformation Temperature ◽  
Steel Structures ◽  
High Strength ◽  
High Energy ◽  
Phase Transformation Temperature ◽  
Filler Materials ◽  
Precise Knowledge

For the safety and cost efficiency of welded high-strength steel structures, precise knowledge of the level and distribution of welding- and cooling-specific stresses and residual stresses is essential, since they exert a decisive influence on strength, crack resistance, and finally on the bearable service load. This paper presents innovative filler materials, of which the phase transformation temperature was deliberately adjusted via the chemical composition. The transformation behaviour of these martensitic Low Transformation Temperature (LTT-) filler materials shows direct effects on the local residual stresses in the weld and the HAZ. These effects can purposefully be exploited to counteract the thermally induced shrinkage of the material and to produce significant compressive residual stresses in the weld. Comparative welding experiments were carried out on 690 MPa high-strength base materials using various LTT-filler materials. High energy synchrotron radiation was used for residual stress measurement. Particularly the use of high energy synchrotron radiation makes it possible to detect the residual stress condition fast without destruction of material. Thereby, residual stress depth gradients can be determined simultaneously without removing material. In steel, gradients of up to 150 µm can be resolved in such a way. Furthermore, the application of high energy radiation permits determination of residual stresses of any available residual austenite contents. Results show significant dependence of transformation temperatures on the resulting residual stress level and distribution.

scholarly journals Investigation on Residual Compressive Distribution of High-Strength Steel for Bridges by Base Metal Hammer Impact Peening

2021 ◽  
Vol 2 (4) ◽  
pp. 932-941
Author(s):  
Yasuyuki Kurihara ◽  
Yoshihiro Sakino ◽  
Tomoharu Kato
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Base Metal ◽  
High Strength Steel ◽  
Plate Thickness ◽  
Base Material ◽  
Steel Structures ◽  
High Strength ◽  
Hammer Impact ◽  
Ordinary Steel

Various peening techniques have been used to improve the fatigue strength of steel structures. Among them, base metal impact hammer peening shows significant improvement in fatigue strength in ordinary steel, but the effect on high-strength steel has not been sufficiently studied. Accordingly, this study applied base material hammer impact peening to test specimens of 780 MPa grade high-strength steel (HT780) and 490 MPa grade ordinary steel (SM490), and the residual stress was measured and simulated. The experimental results clarified that a large compressive residual stress was introduced into the inner part of the plate thickness near the indentation in the high-strength steel, although the range of introduction of residual stress was equivalent in both the ordinary steel and high-strength steel.

scholarly journals Development of New Low Transformation-Temperature Welding Consumable to Prevent Cold Cracking in High Strength Steel Welds

2005 ◽  
Vol 23 (1) ◽  
pp. 95-102 ◽  
Author(s):  
Satoru ZENITANI ◽  
Naoya HAYAKAWA ◽  
Junji YAMAMOTO ◽  
Kazuo HIRAOKA ◽  
Yasushi MORIKAGE ◽  
...  
Keyword(s):  
High Strength Steel ◽  
Transformation Temperature ◽  
High Strength ◽  
Cold Cracking ◽  
Welding Consumable ◽  
Steel Welds
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