Transverse and z-Direction CVN Impact Tests of X65 Line Pipe Steels of Two Centerline Segregation Ratings

Wang

Liu

et al. 2018

steel research int.

Centerline segregation is an inherent phenomenon during solidification. It is controlled by optimizing the continuous casting process, but is not easy to be avoided. According to the severity of centerline segregation of the slab, it affects the mechanical properties and final microstructure of rolled strip. The objective of this paper is to study the influence of centerline segregation degree on the microstructure and mechanical properties of X70 pipeline steels. In this study, the mechanical properties of strips produced from the slabs are examined and the results show that centerline segregation is some adverse effect on Charpy impact toughness and tensile properties of hot‐rolled strips. The strips from slab with higher degree of segregation, exhibits lower Charpy impact toughness, higher tensile strength, higher microhardness. The segregated degree of slab is studied by using the method of Mannesmann, indicating that it could be up to class 3–4. Moreover, the results from Electron Probe Micro Analyzer (EPMA) shows that high level of Mn content is obtained at the centerline of strips processed from the slab with segregation degree of class 3–4. The corresponding microstructure is identified as lath martensite, which should be contributed to the undesirable mechanical properties.

Section: Discussioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Wang

Liu

et al. 2018

steel research int.

“…Therefore, the variability in toughness in the same plate was caused by centerline segregation of the slab. This result is consistent with Su et al [22,23] who suggested that centerline segregation in continuously cast slabs increased variability in mechanical properties of steel plates.…”

Section: Low Temperature Toughnesssupporting

confidence: 92%

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

Liu

Wang

et al. 2019

Metals

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).

“…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

Hou

Peng

et al. 2021

Metals

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.