Through process considerations for microalloyed steels used in naval ship construction

Abstract

A review has been carried out on the status of particular microalloying elements in plate used for the construction of naval ships. The potential problem area tends to be the heat affected zone (HAZ) toughness where the presence of niobium imparts no beneficial effects. Vanadium has been excluded historically on the basis of cost, but current trends indicate that the ferroniobiumferrovanadium cost differential has been decreasing. In addition, vanadium is known to reduce the incidence of transverse slab cracking, and this could potentially reduce through costs as the scarfing loss to remove the cracks can account for a yield loss of y3%. A detailed through cost evaluation is required to establish the exact status. In addition, a tentative relationship exists between the HAZ toughness effect of the microalloying element and its effect on the susceptibility to induce transverse slab cracking. Overall, the benefits improve in the order of niobium, vanadium and titanium. If cost is factored into these effects, then the microalloying element with the most potentially positive benefits is titanium. The effects of multimicroalloying have been briefly reviewed and this is clearly an area where further work is required. Although molybdenum has been extensively used in linepipe steels, its potentially positive effects as a microalloying element, and on transverse slab cracking in ship plate steels, has never been fully enough explored. This is related to its higher ferroalloy cost.

Micromechanism of Decrease of Impact Toughness in Coarse-Grain Heat-Affected Zone of HSLA Steel with Increasing Welding Heat Input

“…X f is identified using the method indicated by Figure 5 and is measured as shown in Figure 6. The nature of the (a) 1…”

“…Heavy thickness, extra-width, and extra-length steel plate with yield strength higher than 460 MPa is widely used for ship-building. [1][2][3][4][5] Due to the lower carbon content these steels show less sensitivity to hydrogen-induced cold crack (HICC) and can be welded without preheating, therefore reduce the time and cost of fabrication. However, for these steels, welding is still a critical process, which produces the coarse-grain heat-affected zone (CGHAZ) and deteriorates the property of the welded joint.…”

Microalloyed steels

“…In a review on the status of microalloying elements in plate used for the construction of naval ships, by McPherson, 206 it is recognised that the potential problem area tends to be the HAZ toughness. A tentative relationship exists between the HAZ toughness effect of the microalloying element and its effect on the susceptibility to induce transverse slab cracking.…”

F460 Heavy Steel Plates for Offshore Structure and Shipbuilding Produced by Thermomechanical Control Process

“…These plates are developed word wide to meet the market demand. 7,[11][12][13][14][15][16][17] The heavy plates with YS greater than 460 MPa and ductile fracture behaviour during Charpy V notch (CVN) impact tests at -40°C are of major developments. [13][14][15][16][17] Few steel producers have developed advanced steel plates with required CVN property at -60°C.…”

“…7,[11][12][13][14][15][16][17] The heavy plates with YS greater than 460 MPa and ductile fracture behaviour during Charpy V notch (CVN) impact tests at -40°C are of major developments. [13][14][15][16][17] Few steel producers have developed advanced steel plates with required CVN property at -60°C. 7,12) Recently, plates in conformity with Det Norske Veritas NV-F460 specifications, i.e., a minimum yield strength of 460 MPa, and secured minimum CVN impact energy of 31 J at temperatures down to -60°C, have been developed using TMCP with lean steel composition and low carbon equivalent to achieve maximized weldability.…”