Surface Ferrite Grain Refinement and Mechanical Properties of Low Carbon Steel Plates

Mechanical properties and microstructure of longitudinal submerged arc welded joint of a new C–Mn steel sheet cladding fine grained ferrite in surface layer for a long distance transport pipeline

“…The microstructure of the LSAW joint is mainly made up of the coarse martensite phase and the bainite phase. These researches show that the size of prior austenite grain, the volume fraction of bainitic ferrite, and M/A constituent increase with increasing the cooling time, moreover the martensite's volume fraction decreases [14][15][16][17][18]. Remarkable of toughness decrease observes with increasing the size of austenite grain and the volume fraction of M/A constituent.…”

“…This kind of metal-filled zone's phases is characterized by a brittle microstructure that greatly hinders the mechanical properties of the welded joint. The ferrite phase generally exhibits a lower strength than that of the bainite and martensite phases [16][17][18][19][20]. As the Hall-Petch relationship suggests, a reduction in grain size will improve mechanical properties, including hardness and yield stress.…”

“…Since the end of the twentieth century, many materials research projects have focused on ultra-fine grain (UFG) steel. Some research results of the laboratory have applied in the metallurgical industry [14][15][16][17][18]. The smallest ferrite grain size approaches 5.5 μm in the surface layers, and can reaches 6.5 μm on average in the whole thickness of the plates.…”

“…The LSAW is one of basic welding technology for the pipeline duo to its low cost, high efficiency, and good applicability [1]. However, because the characteristics of the LSAW, the properties of the metal-filled zone and the heat-affected zone are more difficult to control than that of the base metal, so the welding seam or welding joint is a weak for manufacturing the pipeline [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24].…”

“…One is the addition of small alloying element or reactive elements can have a significant effect on metal-filled zone, which is very expensive and complicated manufacturing process. The other is the post welding heat treatment method, which is low-cost and have a significant effect on all welding joint [10][11][12][13][14][15][16]. On the other hand, it is necessary to analyze the microstructure and fracture in different areas of LSAW joints.…”