Non-isothermal prior austenite grain growth of a high-Nb X100 pipeline steel during a simulated welding heat cycle process

Mechanical Properties of High-Nb X80 Steel Weld Pipes for the Second West-to-East Gas Transmission Pipeline Project

“…Because the similar welding process parameters are adopted for the same size pipe manufactured in the mill, the chemical compositions of the pipeline steels become one of the most important factors to affect the mechanical properties of HAZ [14]. For the high-Nb X80 steels with high-Nb and bearing Ti, the prior austenite grain Advances in Materials Science and Engineering 11 in HAZ has lower coarse tendency, because the (TiNb)(CN) precipitates are not completely dissolved during the thermal cycle [20]. The undissolved (TiNb)(CN) particles in Nb steels can effectively restrain the austenite grain growth [20,21].…”

“…For the high-Nb X80 steels with high-Nb and bearing Ti, the prior austenite grain Advances in Materials Science and Engineering 11 in HAZ has lower coarse tendency, because the (TiNb)(CN) precipitates are not completely dissolved during the thermal cycle [20]. The undissolved (TiNb)(CN) particles in Nb steels can effectively restrain the austenite grain growth [20,21]. In this case, the transformed microstructure becomes a most important factor to affect the mechanical properties of HAZ.…”

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

“…When the peak temperature increases higher than 1000 °C, austenitizing has proceeded completely, the austenitic grain began to grow up, the hardenability of steel are rising and the phase transition temperature is reduced, the amount of GB increases after cooling, thus obtains higher strength but lower toughness (Figure 1). For high Nb steel, Nb (CN) fast dissolving temperature is above 1150 °C [18], therefore, when the peak temperature is above 1200 °C, the austenitic grains begin to rapidly grow up (Figure 3), phase transition temperature significantly decreases (Figure 6), the microstructure changes to GB, the toughness decreases further, and the strength increases. By the austenitic grain size, at 1350 °C, the primary austenite grain size remained about 60 μm (Figure 1), and toughness decreased significantly, which is related to the larger effective grain size in GB obtained after cooling (Figure 3).…”

Microstructure and Mechanical Characterization of X70 Steel Welded Joints Through Hardness Mapping and Tensile Strength Testing

“…With the increase of energy consumption in the recent years, pipeline steels have been developed due to their good toughness, high strength, superior weldability and sufficient deformation capacity [1][2][3][4]. Among the wide range of pipeline steels, API X70 is one of the most important steels extensively applied in oil and gas industries [5].…”