In the current study,the standard and production status of rack steel for offshore platform at home and abroad were described from the view of manufacturing of extra-thick plate blanks,and the production technology and difficul-ties of the extra-thick plate blanks were analyzed. Based on this,the water-cooled mould casting technology with sequen-tial solidification and the result of pilot test were introduced,and the feasibility of casting plate blanks of rack steel with water-cooled mould casting technology was predicted by simulation. The simulation results show that the rack steel plate blanks of large piece weight and high quality can be generated by water-cooled mould casting technology with sequential solidification,which explores a economical and practical process for producing rack steel plate blanks.

An analysis on width to thickness ratio of flat ingot at home and abroad has been carried out to get the effect of width to thickness ratio on quality of ingot. And the 60 t flat ingot with large width to thickness ratio and large water-cooling mould casting equipment are developed. The casting test of 61 t flat ingot with width 3 070 mm, thickness 1 022 mm, width to thickness ratio 3. 0 and casting temperature 1 580℃ of steel Q345B (/% : 0. 19C, 0. 36Si, 1. 39Mn, 0. 010P, 0. 003S) steelmaking by EAF-LF-VD process and rolled to 220 mm heavy plate has been carried out. Results by non-destructive testing and sampling analysis show that the quality of ingot is better； the heavy plate mechanical properties are yield strength 348 ~373 MPa, tensile strength 562 ~588 MPa, impact energy at -40 °C 40. 76 ~88・80 J, elongation 17. 00% ~28. 50% , Z direction reduction of area 33. 79% -60. 88% and rating of grain size 8 ~9 to meet the requirement of standard ； and the non-destructive testing results of heavy plate meets the requirement of JB/T4730-2005I -grade detection of defect. The commercial test shows that the technology of flat ingot water-cooling mould for large width heavy plate has the ability to provide bloom for high quality extra-heavy plate.

Large ingots are mainly used for the production of supper thickness plate,and with the increase of the ingot mass,the porosity is deep on the upper of the ingot,which reduces the metal yield,and makes the organization density relatively poor and the segregation serious.The large-rectangular ingot quality becomes the bottlenech of the heavy plate mill capacity.Based on a large deal of foreign literatures,combined with the domestic current situation of the water-cooled mould casting technical,the patents of the water-cooled mould casting technology were summarized,and the influences of water-cooled mould casting technical on the solidification speed of ingot,the uniformity of solidified shell of ingot,the solidified structure and loose shrinkage cavity,and the segregation of ingot were elaborated.Industrial tests of ingot casting with water-cooled mould casting technical and rolling were introduced,and the performance of the steel plate was clarified.The intensive water-cooled mould casting technology for producting large rectangular ingot can provide the blanks for the high quality supper thickness plate.

The-application-of-heavy-gauge-plate-and-the-manufacturing-enterprise-was-summarized,and-the-advantage-and-disadvantage-of-different-production-methods-for-large-ingot-and-slab-were-compared-and-analyzed.The-present-situation-of-manufacturing-technologies-and-major-product-of-large-ingot-and-slab-for-heavy-gauge-plate-atdomestic-and-abroad-were-both-analyzed-in-detail,including-conventional-ingot-slab,electroslag-remelted-flat-ingot,unidirec-tionally-solidified-ingot,directionally-solidified-ingot,extra-gauge-casting-slabs,clad-continuous-casting-slab,forg-ing-rolling-stock.Rectangular-ingot-producted-with-water-cooling-mold-under-electromagnetic-fields-will-become-the-development-tendecy-of-the-production-of-large-ingot-and-slab-for-heavy-gauge-plate.

大型扁钢锭主要用于生产特厚板,随着钢锭吨位增大,钢锭上部缩孔较深,影响成材率,同时疏松等级高,偏析严重,因此大型扁钢锭的质量问题成为发挥特厚板轧机能力的瓶颈.针对该难题,采用大型钢锭水冷模铸装置,成功地浇注了60t级大型扁钢锭.钢锭被轧制成220 mm厚钢板,尽管钢种成分为Q345B,但各项性能指标达到了超厚板Q345E-Z35的要求,屈服强度为348～373MPa,抗拉强度为562～588MPa,伸长率为17％～28.5％,-40℃横向冲击功为56.57～71.65 J、纵向冲击功为40.76～88.80 J,1/2处断面收缩率平均为63.04％,1/4处断面收缩率为57.93％,夹杂物级别总和不超过2.0,晶粒度达到8.0～9.0级.表明该大型扁钢锭水冷模铸技术具备为高品质特厚板提供坯料的能力.

Temperature measurements have been carried out on a 17.5 ton experimental steel casting to determine the thermophysical properties of sand mold for heavy steel castings. The determined thermophysical data are used in the solidification simulation to predict shrinkage porosity in a 300 ton lower cross-head casting of rapid forging press. Results demonstrate that the thermal conductivity of sand mold is the minimum at 400 ℃, while the increase of the specific heat with temperature slows down after 600 ℃. Furthermore, the optimization of chill and padding design leads to desirable feeding which eliminates the shrinkage cavity and porosity of the lower cross-head casting.

The mould filling and solidification process of the casting of 80MN rapid forging press upper beam were simulated with MAGMA.The effect of gating system design,setting of feeder,position and the size of surface chill on the solidification defect was analyzed.Basing on these results,we have predicted the position of shrinkage and porosity in the casting,and have successfully optimized the casting technique of rapid forging press upper beam.