The Influence of Centerline Segregation on the Mechanical Performance and Microstructure of X70 Pipeline Steel

Self Cite

Low variability in mechanical properties is required for pipeline project designs to meet a strain-based design, which is used in regions of large ground movements. The objective of this study is to elucidate the influence of centerline segregation in continuously cast slab on variability in the mechanical property of pipeline steel, and controlling centerline segregation can meet the requirements of a strain-based design. Mannesmann rating method was used to evaluate the degree of segregation of two slabs and its effect on variability in mechanical properties of corresponding plates. Microstructural characterization indicated that bainite/martensite was formed in a segregated area where the content of C and Mn enriched. The mechanical property results indicated that controlling the degree of centerline segregation can reduce tensile strength variability and improve ductile-brittle transition temperature (DBTT).

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Controlling Variability in Mechanical Properties of Plates by Reducing Centerline Segregation to Meet Strain-Based Design of Pipeline Steel

Guo

Liu

Wang

et al. 2019

Self Cite

“…This is related to the continuous casting production process. The centerline segregation can lead to local embrittlement [29].…”

Section: Hole Surface Evaluationmentioning

confidence: 99%

Failure Mechanisms of Mechanically and Thermally Produced Holes in High-Strength Low-Alloy Steel Plates Subjected to Fatigue Loading

Jiménez-Peña

Goulas

Preußner

et al. 2020

High-strength low-alloy steels (HSLA) are gaining popularity in structural applications in which weight reduction is of interest, such as heavy duty machinery, bridges, and offshore structures. Since the fatigue behavior of welds appears to be almost independent of the base material and displays little improvement when more resistant steel grades are employed, the use of bolted joints is an alternative joining technique which can lead to an increased fatigue performance of HSLA connections. Manufacturing a hole to allocate the fastener elements is an unavoidable step in bolted elements and it might induce defects and tensile residual stresses that could affect its fatigue behavior. This paper studies and compares several mechanical (punching, drilling, and waterjet-cut) and thermal (plasma and laser-cut) hole-making procedures in HSLA structural plates. A series of 63 uniaxial fatigue tests was completed, covering three HSLA grades produced by thermomechanically controlled process (TMCP) with yield strength ranging from 500 to 960 MPa. Samples were tested at single load level, which was considered representative in HSLA typical applications, according to the input received from end users. The manufactured holes were examined by means of optical and electron microscopy, 3D point measurement, micro hardness tests, X-ray diffraction, and electron backscatter diffraction (EBSD). The results give insight on cutting processes in HSLA and indicate how the fatigue failure is dominated by macro defects rather than by the steel grade. It was shown that the higher yield strength of the HSLA grades did not lead to a higher fatigue life. Best fatigue results were achieved with laser-cut specimens while punched samples withstood the lowest amount of cycles.

“…However, central carbon segregation along the casting direction occurs due to the carbon solubility difference between the liquid phase and solid phase, which can induce tremendous quality control issues in high-end steel products [1,2]. Moreover, this kind of defect is difficult to eliminate in reheating and rolling processes and will be left into the subsequent products, which will affect the tensile yield strength and low-temperature impact toughness [3,4]. Therefore, the control of central segregation along the casting direction is important to improve the quality stability of high-end steel products.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Correlation and Control Strategy for Element Content Fluctuation along Casting Direction in Central Area of Continuous Casting Billet

Guo

Hou

Peng

et al. 2021

The statistical correlation was applied to analyze the specific and quantitative correlation relationship between the solidification structure and central segregation along the casting direction in carbon steel billet. On this basis, the segregation formation mechanism of the solute element and related control strategy were investigated. It is found that the equiaxed crystal zone fluctuation along the casting direction determines the fluctuation degree of central segregation. At the same time, the central segregation at a certain position is mostly affected by the equiaxed crystal zone width at the hysteretic position. Moreover, the casting speed can influence the columnar to equiaxed transition (CET) fluctuation along the casting direction by affecting the flow of molten steel in the billet. Overall, the segregation mechanism of solute elements along the casting direction can be summarized into two aspects: First, with the growth of columnar crystals in the initial stage, the segregated solutes are continuously enriched and distributed in the equiaxed crystal zone after CET. The fluctuation of the equiaxed crystal zone will affect the distribution of the enriched solute in the billet and cause the fluctuation of the central segregation. Second, due to the solidification shrinkage at the end of solidification, the solute-enriched liquid phase at the hysteretic position is pumped to the solidification endpoint and forms the central V-shaped segregation. Meanwhile, the stable solidification structure (columnar crystal length or equiaxed crystal zone width) along the casting direction and control measures preceded equiaxed crystal zone formation are beneficial to reduce the central V-shaped segregation.