Properties and homogeneity of 550-MPa grade TMCP steel for ship hull

Abstract

Ultra low carbon steels by the thermal mechanical control process (TMCP) with less Ni, Cr, and Mo contents have been developed for 550 MPa grade heavy gauge ship hulls and offshore structures. The relationships among microstructures, process, and properties of the studied steel have been investigated. A series of accurate control technologies have been developed for this kind of steel. Cu microalloying and TMCP+relaxation precipitation control (RPC)+accelerated cooling process were employed to optimize the mechanical properties and ensure the homogeneity of the 80-mm thick plate. The microstructures of thin plates slightly changed from surface to center, but the microstructures of the heavy gauge plate (80 mm) changed notably. Adopting the simple composition, it can meet the requirement of thin plates by adopting a few microalloys. As for thick plates (80 mm), a little higher Cu and Ni contents should be adopted. These steels can meet the needs without tempering. By these ways, the properties of the steels can be optimized, and the cost can be decreased notably.

The Effect of Cooling Rate on the Microstructure Evolution and Mechanical Properties of Ti-Microalloyed Steel Plates

“…While in TMCP of advanced heavy steel plates, the deformation and cooling are rarely uniform over the entire thickness, which then leads to inhomogeneous microstructure and mechanical properties being obtained in the plate. Thus, In order to enhance the homogeneity of the heavy steel plate, expensive elements, such as Ni, Cr, Mo, and Cu were added to improve the hardenability of the steel plate [16][17][18]. Although a satisfactory strength-toughness combination is obtained in the steel plate arising from the combined effect of refined ferrite grain size and precipitation strengthening, the weldability is still a tough problem that needs to be overcome due to the enhanced carbon equivalent by the addition of expensive microalloying elements.…”

The Significance of Central Segregation of Continuously Cast Billet on Banded Microstructure and Mechanical Properties of Section Steel

“…Compared to plates, the rolling reduction and, consequently, deformation accumulation of section steels are relatively low, which lead to insufficient recrystallization and coarse prior austenite grains [1]. Moreover, the microstructures of ferrite and perlite are difficult to refine due to the lack of controlled cooling process [2,3]. Therefore, low temperature toughness is always a challenge for section steel [4].…”

Interplay between reversed austenite and plastic deformation in a directly quenched and intercritically annealed 0.04C-5Mn low-Al steel

“…Heavy plates of advanced high-strength steels are known for high ductility, good low-temperature impact toughness, ease of weldability and safety. They are widely considered for buildings, pressure vessels, bridges, ship hull, and offshore structures [1][2][3][4][5]. The principal application of high-strength offshore steels with nominal yield strength in the range of ~500-800 MPa is in the fabrication of jack-up legs, rack, and pinions [6].…”

“…With increased annealing temperature, the stability of reversed austenite was decreased because of less enrichment of C and Mn in reversed austenite and grain growth. At 0.05 tensile strain, reversed austenite improved weldability [5,7]. Currently used low alloy heavy plate steels for high-strength structural applications are essentially quenched and tempered steels with low-to medium-carbon content [8].Generally expensive alloying elements, such as Ni, Cr, Cu, and Mo, are added to obtain required high strength in the mid-thickness of the plate to improve the microstructure, mechanical properties and homogeneity.…”