Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

Raath, Neill D.; Norman, D; McGregor, Iain; Hepple, S.; Dashwood, R. J.; Hughes, Darren J.

doi:10.1007/s11661-018-4502-x

Cited by 8 publications

(4 citation statements)

References 36 publications

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“…Bolt matrix zone shows mainly a bainitic phase, and the Vickers hardness was 286 HV as shown in Figure 13(a). The HAZ presented crystal grain coarsening towards the weld zone, becoming island martensite (M) or coarse bainite (B U ) + ferrite structures near the weld boundary (weld interface, WI), 5,17,18 and the highest Vickers hardness was 458 HV. Meanwhile, the plate matrix zone shown in Figure 13(c) shows mainly a ferritic phase (F), and the Vickers hardness was 169 HV.…”

Section: Resultsmentioning

confidence: 99%

“…The hardness was 292 HV, and it is inferred that the carbon content was increased by weld penetrations from the plate and the bolt, as well as that the cooling rate was considerably fast after the welding. Based on Fe-C equilibrium phase diagram and continuous cooling transformation diagram of austenite phase (A), 5,16–18 the phase transformation process cooling from high temperature liquid (L) in the weld zone with the analysed alloying composition is expressed as follows …”

Section: Resultsmentioning

confidence: 99%

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Bending fatigue behaviour and microstructure in welded high-strength bolt structures

Oh¹,

Akiniwa

2018

Proceedings of the Institution of Mechanical Engineers, Part C:

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Welded high-strength bolts are recently being applied to automobile part fixations, and it is important to clarify their fatigue behaviours and to carry out the fatigue strength designs for preventing fatigue failures. Using the spot and full-circled welded bracket samples in four kinds of weld shapes, bending fatigue strength properties of welded high-strength bolt structures were examined. Factors affecting fatigue to failure, such as weld bead shapes and metal structures, were identified through local stress measurements with strain gauges and X-ray diffractions, microscope observations and chemical composition analyses, as well as stress concentrations of finite element method computational simulation. Differences of bending fatigue strengths at 2 × 105 cycles in welded bolt structure samples when based on nominal stress are 15% to 60% compared with the bolt itself. Fatigue strengths corresponded to four kinds of fracture modes and did not decline greatly in the full-circled welded structure. The spot P sample, in which the connecting line between the two centres of the weld beads was perpendicular to the load direction, has higher strength due to the crack initiating from the weld zone of the gap between the plate and the bolt flange which has hard mixed phases of ferrite + martensite + bainite with high fatigue resistance, and its strength divided by weld length does not deteriorate. The strengths and fracture modes were analysed from the viewpoints of the shape effect relating to the stress concentration and residual stress and the material effect relating to the microstructure of the weld as well.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Bending fatigue behaviour and microstructure in welded high-strength bolt structures

Oh¹,

Akiniwa

2018

Proceedings of the Institution of Mechanical Engineers, Part C:

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“…The most widely used joining method in automotive applications is resistance spot welding (RSW) due to its high speed, robustness, and low-cost. [1][2][3] The high heating and cooling rates during RSW destroy the original AHSSs microstructures. As a result of the weld thermal cycle combined with high alloying content, the final weld nugget and HAZ microstructure of most AHSSs are almost fully martensitic.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Effect of a Paint Bake Cycle on the Microstructure–Mechanical Properties Relationship of a Resistance Spot Welded Advanced High Strength Steel

Eftekharimilani

Petrov

et al. 2018

Metall Mater Trans A

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The effect of an automotive paint bake (PB) thermal cycle on the microstructural evolution and the mechanical properties of resistance spot welded advanced high strength steel is presented in this work. Mechanical behavior of the heat-treated welds reveals an increase in maximum cross-tension strength, displacement and subsequently energy absorption capability when 453 K (180°C)-20 minutes a bake thermal cycle is applied after welding. The microstructures of resistance spot welds with and without a PB heat treatment were characterized using scanning and transmission electron microscopy (TEM). TEM analysis revealed that the weld nugget and HAZ of the resistance spot welds consist of a martensitic microstructure. The microstructural analysis of the post-weld heat-treated samples shows the presence of e carbides in a martensitic matrix within the weld nugget and the HAZ. It is shown that the improved mechanical response of the paint-baked welds is associated with carbide precipitation during heat treatment.

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“…The mechanical properties of advanced steels are controlled by microstructure-based thermomechanical processing routes. [6][7][8] However, the rapid heating and cooling during RSW can affect the strengthening/toughening mechanisms of the base metal. [9] The two important phase transformations in the resistance spot welds comprised of AHSS are as follows:…”

mentioning

confidence: 99%

The Role of HAZ Softening on Cross-Tension Mechanical Performance of Martensitic Advanced High Strength Steel Resistance Spot Welds

Tamizi

Pouranvari

Movahedi

2021

Metall Mater Trans A

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Giga-grade martensitic advanced high-strength steels are prone to sub-critical heat-affected zone (SCHAZ) softening during resistance spot welding. The article aims at understanding the role of HAZ softening on the fracture mode, load-bearing capacity, and energy absorption capability of MS1400 resistance spot welds during the cross-tension test. The highest load-bearing capacity was obtained when pullout failure was initiated from the martensitic coarse-grained HAZ. However, more severe HAZ softening and formation of a wider softened zone, promoted at high heat input conditions, encourages strain localization in SCHAZ, promoting transition in failure location to sub-critical HAZ. This change in pullout failure location is responsible for the observed reduction in the weld peak load at high welding currents. Therefore, control of martensite tempering in the HAZ is critical to obtain strong and reliable resistance spot welds in martensitic advanced high-strength steel sheets. To preclude the detrimental effect of the martensite tempering on the weld strength, the minimum welding current, which enables pullout failure mode, should be used for resistance spot welding of MS1400 advanced martensitic steel.

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Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

Cited by 8 publications

References 36 publications

Bending fatigue behaviour and microstructure in welded high-strength bolt structures

Bending fatigue behaviour and microstructure in welded high-strength bolt structures

Understanding the Effect of a Paint Bake Cycle on the Microstructure–Mechanical Properties Relationship of a Resistance Spot Welded Advanced High Strength Steel

The Role of HAZ Softening on Cross-Tension Mechanical Performance of Martensitic Advanced High Strength Steel Resistance Spot Welds

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