The demand of the most popular shipyard is the pur

2022-08-02
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The demand of shipyards is the pursuit of steel mills

the international shipbuilding industry believes that over the years, a series of serious accidents in the marine industry are directly or indirectly caused by brittle fracture, fatigue failure or corrosion of marine steel plates. In addition, in the process of globalization, the logistics volume is growing, and its demand for various ships will increase accordingly, such as oil tankers, LNG ships (special ships for transporting liquefied natural gas at low temperature), bulk carriers, container ships, LPG ships (special ships for transporting liquefied petroleum gas) and chemical carriers

the above development trend has not only led to the rapid growth of the demand for ship plates, but also led to the following trends in the quality of ship plates:

first, the specification range of shipbuilding steel has become larger, and the dimensional accuracy requirements are higher. Through investigation, shipyards generally reflect that the wider and longer the ship plate, the better. This is mainly due to the consideration of the requirements of shipbuilding technology. The wide and long ship plate is conducive to adapt to the requirements of shipbuilding technology such as large sections and improve shipbuilding efficiency

with the efficient shipbuilding production organization and the large-scale ships, in order to reduce the welding quantity and improve the hull quality, the shipyard has a trend of large-scale requirements for the ship plate specifications. The ships with a width ≥ 3M ensure that the MEG and PE prices will rise sharply in April, and the amount of maintenance plate will increase significantly, and the maximum ship plate specification is required to reach 4.5m × 22.5m。 However, the shipyard also pointed out that the requirement for width and length of ship plates is not simply because of the larger ship type, but to reduce welding seams and improve shipbuilding efficiency. In addition, the shipyard also requires that the shipboard manufacturer can provide the shipboard rolled with 0.5mm grade and negative tolerance, with the maximum length of 24m, especially with higher requirements for strength and surface quality

second, the use of high-strength ship plates is increasing. With the increase of ship tonnage, the shipbuilding industry feels that the strength of ordinary strength hull steel is insufficient. Because of the low strength, the steel plant must increase the thickness of the ship plate, so it has good tensile property during stretching, which not only increases the difficulty and cost of processing and welding in the manufacturing process, but also increases the dead weight of the hull and reduces the load. Therefore, shipyards put forward the requirement of using high-strength hull steel. The shipyard hopes that the steel plant can provide more common carbon ship plates produced by TMCP (thermal mechanical control process) technology, which have the characteristics of high strength, good welding performance and low stress

third, the proportion of low-alloy high-strength steel will increase significantly. The development trend of ship specialization puts forward requirements for lightweight. Therefore, a large number of low-alloy high-strength ship plates, especially microalloyed high-strength ship plates, will also be used. Low alloy high strength hull steel is an important kind of ordinary low alloy high strength structural steel. With the continuous development of ship and ocean engineering, especially the development of offshore oil on the continental shelf, more varieties and higher quality of marine steel, especially high-strength marine steel, are required, which is equivalent to Thailand. Therefore, classification societies of all countries have invested a large amount of money to develop low-alloy high-strength steel resistant to seawater corrosion, which can be fully and automatically connected within one day. It is basically based on the rich and cheap alloy elements in China, and is developing towards microalloying, forming a strength toughness matching grade series. The consumption of low alloy high strength steel in shipbuilding is increasing

fourth, the requirements for the performance and quality of ship plates are becoming higher and higher. In the past, bulk carriers generally required the quality level of ship plates to be below grade D, with more than 20 varieties. With the development of container ships and other ship types, the varieties of ship plates cover almost all levels, with more than 1200 varieties, and develop to F-class and Z-direction steel ship plates and profiles. In view of the high requirements of marine steel plates for seawater corrosion resistance, steel mills have adopted measures such as increasing the thickness of steel plates and increasing the coating. In this regard, the shipyard hopes that the steel plant can develop a thinner marine steel plate with less or no coating and good seawater corrosion resistance, so as to reduce the use of steel plate and coating workload. At the same time, good surface quality is still a quality index specially emphasized by shipyards. In addition, IMO (International Maritime Organization) has put forward new coating standard requirements, which should be paid attention to by relevant iron and steel enterprises

fifth, the requirements for the brittle failure resistance of ship plates are stronger. In recent years, accidents such as ship striking rocks and collision have occurred frequently, causing heavy casualties, economic losses and environmental pollution. In this regard, some developed countries have formulated new ship grade standards for high crack resistant steel plates used in hull structures, such as side plates, decks and stiffeners

in order to comply with the above development trend, steel mills at home and abroad are actively implementing new technologies to provide users with high-performance ship plates, so as to improve productivity; By improving the strength, fracture toughness, fatigue strength, corrosion and weather resistance of the material, the welding efficiency of steel plate can be improved

niobium plays an important role in TMCP

in the research and development of ship plates, steel mills pay great attention to carefully designing alloy composition, and use the strain and thermal cycle during thermomechanical treatment, rolling and cooling to obtain the desired microstructure. TMCP technology combines rolling and post rolling cooling processes, which can significantly expand the control range of steel plate production and significantly reduce the grain size of steel. TMCP represents an innovation of control process, which is completely different from the traditional hot rolling and heat treatment processes

tmcp technology is characterized by the combination of controlled rolling and controlled cooling technology, that is, the comprehensive treatment means of controlled rolling and heat treatment. TMCP technology enables the traditional heat treatment process to be completed in the rolling production of deformation strengthening, thus rolling pipeline steel, ship plate steel and high-strength structural steel with high strength, high toughness and high weldability

microalloyed elements such as Nb and Ti play an important role in controlling the structure of ship plate. In fact, adding a small amount of any microalloying element to the steel will help refine the grain size of the steel plate in each link of heating, rolling and controlled cooling, and can improve the strength of the steel. The reason is that niobium exists in the form of solid solution or precipitates combined with carbon and nitrogen in steel, and the interaction between niobium and recrystallization

the dispersed niobium precipitates prevent austenite grain growth and coarsening through pinning during slab heating before rolling. In the subsequent rolling processes, when the rolling temperature reaches 900 ℃ or higher, austenite recombines in the recrystallization process and is continuously refined. At the same time, the strain produced in the rolling process can promote the formation of fine precipitates in niobium, nail the austenite grains in the later stage of rolling, prevent their recrystallization, effectively ensure that the austenite is continuously flattened, and make the strain and dislocation accumulate. Therefore, at the end of rolling, accumulated strains and dislocations provide many nucleation points (grain boundary protrusions, deformation bands, etc.) for ferrite transformation

in the process of Cooling Austenite to ferrite transformation after rolling, niobium in the steel increases the phase transformation supersaturation by delaying the transformation from austenite to ferrite, and niobium precipitates in the ferrite matrix further improve the strength of the steel through precipitation strengthening mechanism. Therefore, it is very useful to add a very small amount (0.01% NB) of microalloyed elements to the steel

strive to prevent brittle cracks in high-strength thick steel plates

in recent years, with the continuous improvement of the requirements of the logistics industry for transportation efficiency, the number of large ships is gradually increasing, and the demand for high-strength thick plates with heavy loads is also increasing. For container ships, 400MPa steel plate is used for ships that can carry 8000TEU containers, which means that the thickness of steel plate should exceed 70mm

at present, the method of single pass welding with large linear energy has been widely used, so that the shipbuilding efficiency will not decline when shipyards adopt thicker steel plates. Therefore, by comprehensively optimizing the alloy composition and TMCP conditions, the steel with high toughness in the welding heat affected zone (HAZ) can be developed, and the large line energy welding can be implemented. Using TMCP technology to refine the structure of base metal and improve HAZ toughness are two important technologies to prevent brittle fracture. With the large-scale ships, it is more difficult to prevent brittle cracks. Especially for container ships, from the point of view of dual safety assurance (to prevent brittle crack cracking and crack propagation), shipyards very much expect the steel plate to have sufficient crack arrest performance. Most of the brittle cracks start in the welding area, so it is particularly important to prevent crack propagation along the welded joint

at present, high-quality ship plates and their welding methods have been developed at home and abroad. The products can be used for giant container ships, which can successfully solve the following three problems: first, by preventing the occurrence of brittle cracks and improving the base metal, preventing the propagation of brittle cracks and improving the fracture toughness; The second is to improve the transportation and fuel efficiency by improving the hull size and strength (reducing the thickness of steel plate); Third, improve shipbuilding productivity by welding with large heat input

in addition to meeting the necessary conditions such as chemical composition and mechanical properties involved in the specification, the hull steel plate shall also have the properties such as strength, toughness, yield ratio, welding adaptability and excellent process properties. It is a systematic project for the iron and steel industry to ensure the properties of ship plates, and its purpose is to meet the explicit and implicit requirements of users

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