Austenite Grain Size Control During Welding of Line Pipe Steels

The aim of the present work is to investigate the microstructural behavior of austenite grain size (AGS) during the reheating process of two different API steel grades (X65 and X70). The steel samples were austenitized at 1150°C, 1200°C, and 1250°C for various holding times from 10 to 60 minutes and quenched in ice water. The samples were then annealed at 500°C for 24 hours to reveal the prior AGS using optical microscopy. It was noticed that the AGS in X65 grade is coarser than that of X70 grade. Additionally, the grain size increases with increasing the reheating temperature and time for both steels. The kinetics of grain growth was studied using the equationdn-d0n=Atexp-Q/RT, wheredis the measured grain size,dois the initial grain size,nis the grain size exponent,tis the heating time,Tis the heating temperature,Qis the activation energy,Ris the gas constant, andAis a constant. To characterize the grain growth process the values ofn,Q, andAwere determined. Good agreement is obtained between the prediction of the model and the experimental grain size values.

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Effects of Hot-rolling Conditions on Austenite Grain Size and Mechanical Properties of Hot-rolled Coil for High Test Line Pipe

Tetsu-to-Hagane ◽

10.2355/tetsutohagane1955.63.7_1116 ◽

1977 ◽

Vol 63 (7) ◽

pp. 1116-1125 ◽

Cited By ~ 2

Author(s):

Minoru NISHIDA ◽

Toshiyuki KATO ◽

Nobuo OHASHI ◽

Taisuke MORI

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Hot Rolling ◽

Test Line ◽

Austenite Grain Size ◽

Line Pipe ◽

Austenite Grain ◽

Hot Rolled ◽

Hot Rolling Conditions ◽

High Test

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Austenite Grain Size Model for the Coarse Grain Heat Affected Zone in Line Pipe Steels

Volume 3: Operations, Monitoring, and Maintenance; Materials and Joining ◽

10.1115/ipc2020-9687 ◽

2020 ◽

Author(s):

Nicolas Romualdi ◽

Matthias Militzer ◽

Warren Poole ◽

Laurie Collins ◽

Robert Lazor

Keyword(s):

Grain Size ◽

Grain Growth ◽

Heat Affected Zone ◽

Arc Welding ◽

Coarse Grain ◽

Austenite Grain Size ◽

Line Pipe ◽

Austenite Grain ◽

Girth Welding ◽

Austenite Grain Growth

Abstract Pipelines are the safest and most cost-effective method of oil and gas transportation to storage and processing facilities. Large diameter welded pipes fabricated by submerged arc welding (SAW) are the preferred product in many cases for pipeline construction. Furthermore, pipelines are constructed by welding segments of pipe, typically by single or dual torch Gas Metal Arc Welding (GMAW). During welding, both during pipe fabrication and girth welding, the Heat Affected Zone (HAZ) experiences rapid thermal cycles with peak temperatures up to the melting temperature of the base metal. Controlling the microstructure evolution in the HAZ during welding of line pipe steels is critical to ensure that these products meet the Charpy impact testing and CTOD requirements imposed by clients and specifications. In particular, the Coarse Grain Heat Affected Zone (CGHAZ) is of concern. Here, austenite grain growth occurs readily due to the combination of high temperature and precipitate dissolution. Controlling the CGHAZ austenite grain size is critical to obtain final microstructures with acceptable impact properties. In this study, austenite grain growth has been measured and modeled for thermal conditions relevant for the CGHAZ in 27 steels, including industrial as well as laboratory steels with systematic variations of alloying element content. Austenite grain size was measured using a Laser Ultrasonics for Metallurgy (LUMet) sensor attached to a Gleeble 3500 Thermomechanical Simulator, which enables high-throughput in-situ monitoring of austenite grain growth. A classical grain growth model has been developed based on a standard test. The grain growth kinetics are described by combining curvature driven grain growth with pinning due to TiN precipitates. A phenomenological relationship has been developed for the grain boundary mobility that decreases with C, Nb and Mo alloying which is consistent with their expected grain boundary segregation. The pinning parameter is rationalized in terms of volume fraction and size of TiN particles. The proposed model has been validated for CGHAZ heat treatment cycles including an industrial welding trial. The results of this study provide a model to predict the austenite grain size in the CGHAZ as a function of steel chemistries and heat treatment paths, i.e. welding parameters. Austenite grain size maps have been constructed as a function of peak local temperature and line pipe steel chemistry. The model can be used both for steel chemistry design and for optimizing welding of steels with known chemical composition to minimize the CGHAZ austenite grain size both during pipe fabrication and girth welding.

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Interfacial studies in Nb3Sn superconductors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087264 ◽

1991 ◽

Vol 49 ◽

pp. 590-591

Author(s):

Ernest L. Hall ◽

Lee E. Rumaner ◽

Mark G. Benz

Keyword(s):

Grain Size ◽

Grain Boundaries ◽

Flux Pinning ◽

Size Control ◽

High Magnetic Fields ◽

Type Ii ◽

Reaction Interface ◽

Liquid Diffusion ◽

Type Ii Superconductor ◽

Grain Size Control

The intermetallic compound Nb3Sn is a type-II superconductor of interest because it has high values of critical current density Jc in high magnetic fields. One method of forming this compound involves diffusion of Sn into Nb foil containing small amounts of Zr and O. In order to maintain high values of Jc, it is important to keep the grain size in the Nb3Sn as small as possible, since the grain boundaries act as flux-pinning sites. It has been known for many years that Zr and O were essential to grain size control in this process. In previous work, we have shown that (a) the Sn is transported to the Nb3Sn/Nb interface by liquid diffusion along grain boundaries; (b) the Zr and O form small ZrO2 particles in the Nb3Sn grains; and (c) many very small Nb3Sn grains nucleate from a single Nb grain at the reaction interface. In this paper we report the results of detailed studies of the Nb3Sn/Nb3Sn, Nb3Sn/Nb, and Nb3Sn/ZrO2 interfaces.

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Grain Size Evolution and Mechanical Properties of Nb, V–Nb, and Ti–Nb Boron Type S1100QL Steels

Metals ◽

10.3390/met11030492 ◽

2021 ◽

Vol 11 (3) ◽

pp. 492

Author(s):

Jan Foder ◽

Jaka Burja ◽

Grega Klančnik

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Grain Size ◽

Hot Forging ◽

Size Control ◽

High Strength ◽

Fatigue Properties ◽

Titanium Addition ◽

Austenite Grain Size ◽

Size Evolution

Titanium additions are often used for boron factor and primary austenite grain size control in boron high- and ultra-high-strength alloys. Due to the risk of formation of coarse TiN during solidification the addition of titanium is limited in respect to nitrogen. The risk of coarse nitrides working as non-metallic inclusions formed in the last solidification front can degrade fatigue properties and weldability of the final product. In the presented study three microalloying systems with minor additions were tested, two without any titanium addition, to evaluate grain size evolution and mechanical properties with pre-defined as-cast, hot forging, hot rolling, and off-line heat-treatment strategy to meet demands for S1100QL steel. Microstructure evolution from hot-forged to final martensitic microstructure was observed, continuous cooling transformation diagrams of non-deformed austenite were constructed for off-line heat treatment, and the mechanical properties of Nb and V–Nb were compared to Ti–Nb microalloying system with a limited titanium addition. Using the parameters in the laboratory environment all three micro-alloying systems can provide needed mechanical properties, especially the Ti–Nb system can be successfully replaced with V–Nb having the highest response in tensile properties and still obtaining satisfying toughness of 27 J at –40 °C using Charpy V-notch samples.

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