Effects Of Zr On The Microstructure And Mechanical Properties Of EH36 Shipbuilding Steel

In 2014.global containerized trade was estimated to have increased by 5.3 percent and reached 171 million TEUs(twentyfoot equivalent unit).The total main lane container trade is estimated to have grown by 9.0 percent between 2007 and 2014.The need to reduce both environmental burden operating costs has led to an increased demand for larger and higher performance vessels.For container ships.hull girder strength must be ensured by using a limited number of longitudinal strength members because of the large openings in the strength deck.Therefore,thick steel plates are used for the strength deck structures.In particular,extremely thick steel plates exceeding 50 mm in thickness are now being used in large container ships.Totally.40%of working hours are spent for the welding process used in the construction of the hull.In order to join these heavy section plates,high heat input welding is adopted to prevent the low building efficiency.During high heat input welding.microstructures in the heat-affected zone(HAZ)become extremely coarse.and the toughness of welded joints decreases drastically.To solve these problems.oxides metallurgy has been applied as one of the techonlogies in the 1990s.which was developed as a method of metallurgical technology that employs fine inclusion particles for improving the microstructure of HAZ.Numerous studies have indicated that in the process of welding heat cycle,fine dispersed inclusions can pin the austenite grains and promote the nucleation of intragranular ferrite.These inclusions are invariably products of the steel refining deoxidization process.The size,quantity and composition of inclusions all have influence on the optimization of the microstructure of the heat affected zone.Further studies have shown that ZrO2 which is the product of Zr deoxidization can effectively promote the nucleation of intragranular ferrite and pin austenite grain boundaries.Finally it can refine the microstructure of HAZ.In the prior study.very few authors have investigated large heat input welding steel with a holistic perspective,i.e,from production to application.Therefore,this paper aims to tackle the effect of Zr on the mechanical properties and microstructures after continuous casting,rolling,and welding.Emphasis has been placed on the size,quantity and composition of the inclusions,in conjunction with microstructure and mechanical properties of steel ship plate.And DSC thermal analysis were carried out to study the decomposition of austenite temperature and the eutectoid reaction temperature.The study found that.Zr which the concentration is 34 ppm can effectively increase the number of inclusions in EH36 slab and plate,refining the microstructure and improving the mechanical properties of steel.However,after the high heat input welding thermal simulation experiment,this content Zr does not inhibit austenite grain growth,or promote the nucleation of intragranular ferrite.This content Zr cannot effectively optimize the welding heat affected zone microstructure.Further examinations are called for in order to make better use of the Zr in the oxide metallurgy technical strategy.