Microstructural Characterization and Mechanical Properties across Thickness of Ultra‐Heavy Steel Plate

Abstract

The microstructural homogeneity across thickness and the interior toughness are significant factors challenging the development of ultra-heavy steel plate (above 200 mm) limited by the thermal transfer capacity of material and the loading capacity of mill. A complete understanding of the relationship between processing, structure, and property is essential for the optimization of alloying and heat treatment of ultra-heavy steel plate. Hence, in the present work, the authors focus on the microstructural evolution and resultant mechanical properties across the thickness of ultra-heavy steel plate under three potential heat treatment technologies, including quenching and tempering, double quenching and tempering, and intercritical quenching and tempering. The results show that the refined signal-phase lath martensite microstructure after double quenching technology can improve toughness stability, while dual-phase intercritical ferrite-martensite microstructure resulted from intercritical quenching technology achieves excellent toughness stability and ductility, and a potential optimal combination of strength and toughness for ultra-heavy steel plate. However, limited cooling capacity of the interior leads to the formation of massive coarse martensite/austenite constituents with high carbon concentration, which significantly deteriorate the toughness. Thus, the control or suppression of coarse martensite/austenite constituents is critical for optimization of lowalloyed ultra-heavy steel plate.

Effect of cooling rate on the microstructure and mechanical properties of a low-carbon low-alloyed steel

“…Other material fields dealing with the mechanical properties of components with processing related heterogeneous microstructure deal with similar difficulties. While this has been known for quite some time [60,61], efforts to overcome the associated uncertainties have only started recently [11,[62][63][64]. Composite approaches will have to be used to progress this technologically important field.…”

Superior Through‐Thickness Homogeneity of Microstructure and Mechanical Properties of Ultraheavy Steel Plate by Advanced Casting and Quenching Technologies

“…Heavy thickness steel plates with high strength and good lowtemperature toughness have been increasingly required for large-scale offshore structures such as jack-up legs of offshore platforms and offshore wind power installation vessels. [1][2][3][4] The ultraheavy steel plates have been conventionally produced by mold ingot casting, hot rolling, immersion quenching in the water tank, and final tempering treatment. There have been two key issues existing for producing heavy gauge steel plates.…”

Thickness Dependence of Toughness in Ultra-Heavy Low-Alloyed Steel Plate after Quenching and Tempering

“…The maximum thickness, however, of the steel plates that can be produced from this technology is still limited [2]. On the other hand, heavy and ultra-heavy steel plates (thickness from 50 mm to 200 mm or even greater) are essential in many industrial sections such as nuclear, hydropower, offshore and so on [3,4]. With the improvement of heat treatment technology in steel mills, these heavy steel plates can at present be manufactured through heat treatment including normalizing, quenching and tempering.…”

“…With the improvement of heat treatment technology in steel mills, these heavy steel plates can at present be manufactured through heat treatment including normalizing, quenching and tempering. Among them, quenching and tempering has the advantage of achieving higher strength together with better toughness compared with other treatments [3,4].…”

“…An inhomogeneous microstructure is usually considered undesirable as it may lead to property fluctuation and scattering and affect ultimate service performance; however, the effect of microstructural inhomogeneity of this kind, through the thickness direction of ultra-heavy steel plate on property performance, is still unclear [5]. Although some work has been done on the difference in microstructure as well as properties of ultra-heavy steel plate, they tended to employ simulated lab samples rather than ultra-heavy plate itself [4,6]. The aim of this study is to investigate accurately the thickness-dependent properties in a practical low-alloyed ultra-heavy steel plate manufactured by quenching and tempering and the correlations with microstructural features, so that a reliable conclusion can be made on the consequence of such inhomogeneous microstructure on the steel's performance.…”