Behaviors of Embrittlement and Softening in Heat Affected Zone of High Strength X90 Pipeline Steels

Gu, Yu; Xiao, Furen; Zhou, Yongsheng; Jin, Li; Xu, Caiyun; Zhou, Xiaodong

doi:10.1590/0104-9224/si24.15

Cited by 4 publications

(4 citation statements)

References 20 publications

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“…This softening reported by the literature is usual in API X80 steel 14,65,[68][69][70][71][72][73][74] , and is due to the predominance of polygonal ferrite 65,72,73 . However, some works 14,68,74 state that the softening of HAZ may be more serious and a study on high-strength pipeline steel should not only pay attention to the embrittlement but also to the softening of the welding heat affected zone 73 , because the reduction in hardness can be around 10-20% in comparison to the base metal 70 . Other works 14,[68][69][70][71] have shown that differences inferior to 10% are not problematic.…”

Section: Mechanical Properties and Microstructural Characterizationmentioning

confidence: 80%

“…The former is not a problem for impact toughness because the presence of polygonal ferrite promotes high Charpy-V results, although it can impair the mechanical strength when the difference in hardness is 20% greater than the base metal 14,65,68,74 . However, the latter can be a significant problem because the toughness is indubitably affected by the presence of a 'necklace' of micro-phases around the prior austenite grain boundaries 65,73,76 . Recently, MA constituents have been under scrutiny because their significance on mechanical properties is ambiguous, particularly in terms of tensile and toughness properties.…”

Section: Concerns About Safe Welding Proceduresmentioning

confidence: 99%

See 1 more Smart Citation

Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

et al. 2020

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API 5L X80 steels are widely used in welded pipes in the petroleum industry. However, microstructural changes in the heat affected zone are a concern when welding such pipes due to the potential formation of regions with low toughness. Despite all the research concerning mechanical properties of welded joints, the acceptance criteria for the qualification of welding procedures are still limited. Welded joints do not always guarantee the safe operation of industrial equipment, because the current Standards adopted are not able to evaluate the properties at some critical regions of the welded joint. This work studied the characteristics of a girth welded joint and showed evidences of low toughness at 0.5 mm from the fusion line due to the micro-phases necklacing the prior austenite grain boundaries. As this feature is not considered by the current Standards for approval of welding procedures, this work proposes an alternative approach to improve the safety of welded structures.

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Section: Mechanical Properties and Microstructural Characterizationmentioning

confidence: 80%

Section: Concerns About Safe Welding Proceduresmentioning

confidence: 99%

Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

et al. 2020

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“…The hardness values in the HAZ and the FZ of the welded stainless steel shows that the hardness of the HAZ and FZ are reasonably comparable within same weld region (HAZ or FZ) irrespective of the heat input. The higher the heat input the slower the cooling rate which allows for grain refinement within the HAZ and leads to the formation of coarse grains (Jovicic et al, 2015;Gu et al 2019;Amuda et al 2020) that should engender relatively softer HAZ.…”

Section: F Hardness Testmentioning

confidence: 99%

Influence of Heat Inputs on Weld Profiles and Mechanical Properties of Carbon and Stainless Steel

Osoba¹,

Ayoola²,

Adegbuji³

et al. 2021

Nig. J. Technol. Dev.

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This study examines the effect of heat input on the weld bead profile, microstructure and mechanical properties of single V- joint welded carbon and stainless-steel plates. The as-received sample steel plates were sectioned into eight pieces; dimension 75 X 30 X 10 mm thicknesses. Shielded metal arc welding (SMAW) of heat inputs 1250 and 2030 J/mm was used to produce full penetration bead on the plates. Although visual inspection indicated that some of the welds were macro defect free, austenitic stainless steel exhibited more weld distortions than the carbon steel and this was partially attributed to its lower carbon content and the width to depth aspect ratio of the weld profile aside the magnitude of the induced stress. For the carbon steel, as the heat input increased, the hardness value of both the heat affected zone and fusion zone increased. In contrast, for stainless steel, the hardness values were reasonably comparable within same weld region (HAZ or FZ) irrespective of heat input. Furthermore, the ultimate tensile strength of the stainless steel decreased as heat input increased while the ductility increased with an increase in heat input, in contrast to carbon steel, where both ductility and ultimate tensile strength generally decreased.

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“…Usually, the softening phenomenon potentially appeared in the coarse-grained zone, intercritical zone or fine-grained zone of HAZ, namely, CGHAZ, ICHAZ and FGHAZ, respectively [11][12][13]. Gu et al [14] suggested that the larger-size polygonal ferrite (PF) and granular ferrite formed from the ununiform prior austenite resulted in softening phenomenon. In order to reduce the HAZ softening, researchers have put forward many methods [15,16].…”

Section: Introductionmentioning

confidence: 99%

Effect of Nb Addition and Heat Input on Heat-Affected Zone Softening in High-Strength Low-Alloy Steel

et al. 2022

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The effect of both Nb content and heat input on the softening phenomenon of the heat-affected zone (HAZ) of low-alloy high-strength steel was studied through welding thermal simulation experiments. The microstructure evolution, density variation of geometrically necessary dislocation, microhardness distribution and the second phase precipitation behavior in HAZ was characterized and analyzed by combining the optical microscope, scanning electron microscope, high-resolution transmission electron microscope with microhardness tests. The results showed that the softening appeared in the fine-grain HAZ (FGHAZ) of the low-alloy high-strength steel with the polygonal ferrite and bainite microstructure. With an increase in Nb content, the FGHAZ softening was inhibited even with high heat input; however, the hardness shows little variation. On the one hand, the increase in the Nb content increased the volume fraction of high-strength bainite in the FGHAZ. On the other hand, the remarkable strengthening was produced by the equally distributed precipitation nanoparticles. As a result, the two factors were the main reason for the solution of the FGHAZ softening problem in the low-alloyed high-strength steel with the mixed microstructure of ferrite and bainite.

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Behaviors of Embrittlement and Softening in Heat Affected Zone of High Strength X90 Pipeline Steels

Cited by 4 publications

References 20 publications

Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

Investigation into the Impact Toughness of API 5L X80 Steel Weldments and its Relationship with Safe Welding Procedures

Influence of Heat Inputs on Weld Profiles and Mechanical Properties of Carbon and Stainless Steel

Effect of Nb Addition and Heat Input on Heat-Affected Zone Softening in High-Strength Low-Alloy Steel

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