Electroslag Fusion Process for Manufacturing a Blade Slab having a Large Curved Surface

Abstract

The invention provides an electroslag fusion process for manufacturing a blade slab having a large curved surface, and it is more particularly effectively in making a blade slab which has a big width-to-thickness ratio, a large difference between the thin and the thick edges and a large curved surface. Firstly, dividing the blade slab into two or three regions according to the external shape and the sectional size of the blade slab, wherein the region which has difficulty in unilateral or bilateral mold-filling is pre-fabricated by the electroslag casting technology to produce a pre-fabricated curved slab, and then it is placed in advance in a side of an internal cavity of a mold, and then fusing the molten metal melted from a consumable electrode and one or two electroslag pre-fabricated slabs which are placed in advance in the mold by utilizing the electroslag fusion process, so as to produce the blade slab having a large curved surface. The large curved blade slab prepared by the process of the present invention has good internal and surface qualities, which can improve material utilization rate, shorten the processing period and improve quality, and in particular, has high anti-fatigue performance, high crack resistance and extensibility performances. The process of the present invention is more suitable for producing large or very large curved blade slab castings having a width-to-thickness ratio >10 and a single weight over 10 tons.

What is claimed is: 
     
         1 . An electroslag fusion process for manufacturing a blade slab having a large curved surface, comprising the following steps:
 dividing the blade slab into two or three regions according to the external shape and the sectional size of the blade slab, wherein the region which has great sectional thickness changes and difficulty in unilateral or bilateral mold-filling is pre-fabricated in advance by an electroslag casting technology to produce a pre-fabricated curved slab;   placing the pre-fabricated curved slab in advance at a side of an internal cavity of a mold; and   fusing a molten metal melted from a consumable electrode and one or two electroslag pre-fabricated slabs which are placed in advance inside the mold together, so as to produce the blade slab having a large curved surface.   
     
     
         2 . The electroslag fusion process, as recited in  claim 1 , wherein the specific steps for the electroslag fusion process are as follows:
 (1) controlling the main components and the content of the electroslag fusion system to be as follows: mass percentage of CaF 2 : 50-62%, Al 2 O 3 : 25-35%, CaO: 3-8% and a trace component: no more than 5% of the total mass of the electroslag fusion system, so as to define a multi-element electroslag fusion system, wherein the trace component is one or more of MgO, SiO 2  and TiO 2 , and the thickness of the slag layer is 12 to 25% of the equivalent diameter of the curved blade slab mold;   (2) the process parameters of the electroslag fusion process are as follows: voltage: 70˜120V, current density: 20000˜60000 A/m 2 ;   (3) the feeding process: employing the intermittent feeding, in feeding period, firstly lowing the normal current to a minimum feeding current within 2 to 5 minutes at a constant speed, maintaining for 1 to 2 minutes; and then rising the current from the minimum feeding current to 70 to 80% of the normal casting current within 3 minutes at a constant speed, repeating the cycle 4 to 5 times, and each time the maximum current is 70 to 80% of the previous maximum current, and at the last time, reducing the current to zero.   
     
     
         3 . The electroslag fusion process, as recited in  claim 1 , wherein the electroslag casting process is capable of fusing either the unilateral pre-fabricated slabs, or fusing the bilateral pre-fabricated slabs. 
     
     
         4 . The electroslag fusion process, as recited in  claim 1 , wherein the consumable electrode for electroslag casting is a sand casting electrode, the consumable electrode of the electroslag fusion process is a steel welding electrode, and the filling ratio of the consumable electrode is 0.15 to 0.4. 
     
     
         5 . The electroslag fusion process, as recited in  claim 1 , wherein the alloy materials of the blade slab having a large curved surface comprises: low carbon martensitic stainless steel 06Cr 13 Ni 4 Mo, 06Cr 13 Ni 5 Mo or 06Cr 16 Ni 5 Mo, and ultra-low carbon martensitic stainless steel 04Cr 13 Ni 4 Mo or 04Cr 13 Ni 5 Mo.