US20190022746A1

US20190022746A1 - Electroslag Fusion Process for Manufacturing a Blade Slab having a Large Curved Surface

Info

Publication number: US20190022746A1
Application number: US15/756,024
Authority: US
Inventors: Yanchun LOU; Yunlong XIONG; Rui Chen; Zhaowei SONG; Anguo WANG; Yunxia Wang
Original assignee: Shenyang Research Institute of Foundry Co Ltd
Current assignee: Shenyang Research Institute of Foundry Co Ltd
Priority date: 2016-08-31
Filing date: 2016-10-27
Publication date: 2019-01-24
Also published as: CN107774962A; CN107774962B; WO2018039817A1

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.

Description

BACKGROUND OF THE PRESENT INVENTION

Field of Invention

The present invention relates to a process for manufacturing a casting having a big width-to-thickness ration and a large curved surface, and more particularly to an electroslag fusion process for manufacturing a blade slab having a large curved surface.

Description of Related Arts

In the field of equipment manufacture, a variety of irregular wide and thick plate castings and/or forgings are often used, which are characterized by a big width-to-thickness ration and an irregular cross-section shape. As one of the important basic components of high-level equipments, the quality requirements of this special-shaped plate casting are extremely strict. For example: the quality problem of a turbine blade casting almost decides the overall running life of the turbine.
At present, the methods for manufacturing such castings and forgings are mainly as follows: conventional sand casting process, forging process and electroslag fusion process, at home and abroad.
(1) Due to the limitations of the process itself, the conventional sand casting products are often difficult to meet the requirements of use, resulting from its poor internal quality; (2) the wide-thick plate castings and forgings produced by the forging process have good internal qualities, but the forging process has a very low metal utilization level and a sharp increase in production cost and time, and against the concept of green manufacturing; (3) the wide-thick plate castings and forgings meeting the requirements can be directly produced by an electroslag casting process, according to its product profile, which have excellent solidification quality and mechanical properties, and reach the quality standard of the same material wrought products. At present, the inventor has produced a compact of overall blade by the electroslag casting method and obtained an invention patent (an electroslag fusion method for manufacturing a compact of a turbine blade, Publication Number: CN 104174834A). However, the process is only effective in manufacturing plate slab castings having a relatively small width-to-thickness ration, and when it is used for manufacturing large plate slab castings (width to thickness ratio >10) having complicated cross-sectional shapes, the molten metal produced by the electroslag casting cannot fully overflow to the farthest thin edge area, limited by its consumable electrode fabrication and mold cooling conditions, which results in poor quality of the thin edge of the casting and limits its further application.
In addition to the above three methods for manufacturing wide and thick plate castings and forgings, Japanese Patent (JP 1999019791A) and Chinese Patent (Publication No.: CN 102029378A) respectively propose a new method of welding two original blanks together by an electroslag process. However, these two methods are only suitable for the welding of steel plates or ingots having an equal thickness, and it is very difficult to apply to the casting having a large width-to-thickness ratio and an irregular cross-sectional shape.

SUMMARY OF THE PRESENT INVENTION

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, wherein the method mainly fuses the molten metal melted by a consumable electrode and one or two electroslag pre-fabricated slabs which are placed in the mold in advance by utilizing the electroslag fusion process, so as to produce a plate slab casting having a large curved surface.
The technical scheme of the present invention is as follows:
An electroslag fusion process for manufacturing a blade slab having a large curved surface, which is characterized in that, comprising the following steps: firstly, dividing the blade slab into two or three regions according to the external shape and the sectional size of the blade slab (see FIGS. 1-2), wherein the region which has great sectional thickness changes and difficulty in unilateral or bilateral mold-filling is pre-fabricated by the electroslag casting technology to produce a pre-fabricated curved slab, and then 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 castings prepared by the process of the present invention have 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.
Specific steps of the electroslag fusion process are as follows:
(1) controlling the main slag components and the content of the electroslag fusion system to be as follows: mass percentage of CaF₂: 50-62%, Al₂O₃: 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, SiO₂and TiO₂, 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/m²;
(3) the feeding process: employing the intermittent feeding, in feeding period, firstly lowing the normal current to the 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.
The electroslag fusion process of the present invention, which is used for manufacturing a blade slab having a large curved surface, is characterized in that the electroslag casting process can fuse the unilateral pre-fabricated slabs and the bilateral pre-fabricated slabs.
The electroslag fusion process of the present invention, which is used for manufacturing a blade slab having a large curved surface, is characterized in that: since the pre-fabricated curved surface slab is relatively complicated, the consumable electrode for electroslag casting is a sand casting electrode, and the consumable electrode of the electroslag fusion process is a steel welding electrode. According to the size of the internal cavity of the blade slab mold, the filling ratio of the consumable electrode is 0.15 to 0.4.
The electroslag fusion process of the present invention, which is used for manufacturing a blade slab having a large curved surface, is characterized in that: the alloy materials of the blade slab having a large curved surface comprises: low carbon martensitic stainless steel 06Cr₁₃Ni₄Mo, 06Cr₁₃Ni₅Mo or 06Cr₁₆Ni₅Mo; ultra-low carbon martensitic stainless steel 04Cr₁₃Ni₄Mo or 04Cr₁₃Ni₅Mo.
Compared with the prior art, the present invention has the following advantages:
(1) The electroslag casting is a kind of special casting technology which combines refining, solidification and forming. It can further remove the inclusions in the consumable electrode and adjust its distribution, reducing P, S and other harmful elements and N, H, O and other gas content in the curved blade slab and improving the material purity thereof by adjusting the compositions of the electroslag and optimizing the process.
(2) the electroslag fusion blade slab can achieve the same mechanical properties and testing indicators of the same material forging and has a homogeneity of the chemical composition, dense tissue, no loose, shrinkage and other defects, dispersed inclusions, has high anti-fatigue performance, high crack resistance and extensibility performances.
(3) the curved blade slab is solidified in the mold, with high cooling speed, high crystallizer size and crystallizer accuracy, small deformation, so the external surface of the casting is smooth and has a small allowance, so as to achieve near-net shape forming.
(4) The electroslag fusion process is employed to effectively solve the problem of filling quality of large-scale blade slabs, and the prepared large-surface blade slab castings have good internal and surface qualities. And the process is more suitable for producing large or very large curved blade slab castings having width-to-thickness ratio >10 and weight over 10 tons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural schematic diagram of a unilateral fusion pre-fabricated slab.

FIG. 2 is a structural schematic diagram of a bilateral fusion pre-fabricated slab.

FIG. 3 is a flow chart of the electroslag fusion process for manufacturing a blade slab having a large curved surface.

Among the above FIGS. 1-3, the figure numbers respectively represent: 1: transformers, 2: combined water-cooled mold, 3: electrode, 4: bottom tank, 5: pre-fabricated slab I, 6: pre-fabricated slab II, 7: electroslag fusion region, 8: metal pool, 9: liquid slag.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Example 1

Referring to FIGS. 2 and 3, the electroslag fusion process of the present invention, which is used for manufacturing a blade slab having a large curved surface, selects the martensitic stainless steel 06Cr₁₃Ni₄Mo as the original material of the blade slab, wherein the maximum width of the blade is about 4300 mm, the maximum height of the blade is 3400 mm, the maximum thickness of the blade is 310 mm, and the minimum thickness of the blade is 65 mm.
Firstly, a pre-fabricated slab I 5 and a pre-fabricated slab II 6 are respectively placed in a region I and a region III inside the mold, the transformer 1 is connected to the bottom tank 4 through a wire, the region II and the electrode 3 define a loop, the electrode 3 is melted by resistance heat resistance from a liquid slag 9, the liquid metal passes through the slag pool and defines a metal pool 8, and the pre-fabricated slab I 5 and the pre-fabricated slab II 6 are fused together by a strong water-cooled mold (the copper plate provided at the inner wall of the mold has a certain angle spiral groove for increasing the cooling strength). Finally, the region I, the region II and the region III form the curved blade slab meeting the experiment required.
According to the size of the region II of the internal cavity of the mold, the steel plate electrode having a corresponding shape is prepared, wherein the selected filling ratio is 0.3; {circle around (1)} The proportion of the components of the slag system is: CaF₂: 60%, Al₂O₃: 32%, CaO: 6%, MgO: 2%, so as to define a quaternary slag system, wherein the thickness of the slag layer is 20% equivalent diameter of the curved blade slab mold; {circle around (3)} power supply parameters: power voltage is determined to be 115V, the current density is determined to be 22000 A/m², according to the size of the casting, the geometric parameters of the electrode and the mold and the casting process; {circle around (4)} during the feeding period, reducing the normal current to a minimum feeding current within four minutes at a constant speed, maintaining for 1 minute, and then rising the current from the minimum feeding current to 70% of the normal casting current within 2 minutes at a constant speed, repeating the cycle 4 times, and each time the maximum current is 70% of the previous maximum current, and at the last time, reducing the current to zero.
The large-scale curved blade slab prepared by the process of the process invention has a dimension conforming to the drawing requirements and good internal and external qualities. The mechanical properties of the compact treated by the conventional heat treatment are RP0.2/650 Mpa, Rm/845 Mpa, A/26%, Z/62%, KV2/101J.

Example 2

This example illustrates manufacturing of a X-shaped curved blade slab of a power plant, the materials is martensitic stainless steel 06Cr16Ni5Mo. The maximum width of the prepared blade slab is about 2600 mm, the maximum height of the blade is 2100 mm, the maximum thickness of the blade is 220 mm, and the minimum thickness of the blade is 30 mm.
Firstly, a pre-fabricated slab is placed at an inner side of the mold, the electrode is melted by resistance heat resistance from a liquid slag, the liquid metal passes through the slag pool and defines a metal pool, and then the liquid metal and the pre-fabricated slab placed in the mold in advance are fused together by a water-cooled mold, so as to form the curved blade slab meeting the experiment required.
According to the remaining size of the mold, the steel plate electrode having a corresponding shape is prepared, wherein the selected filling ratio is 0.26; {circle around (2)} The proportion of the components of the slag system is: CaF₂: 60%, Al₂O₃: 35%, CaO: 5%, so as to define a ternary slag system, wherein the thickness of the slag layer is 21% equivalent diameter of the curved blade slab mold; {circle around (3)} power supply parameters: power voltage is determined to be 85V, the current density is determined to be 35000 A/m², according to the size of the casting, the geometric parameters of the electrode and the mold and the casting process; {circle around (4)} during the feeding period, reducing the normal current to a minimum feeding current within three minutes at a constant speed, maintaining for two minute, and then rising the current from the minimum feeding current to 70% of the normal casting current within 2 minutes at a constant speed, repeating the cycle 4 times, and each time the maximum current is 70% of the previous maximum current, and at the last time, reducing the current to zero.
The prepared large-scale curved blade slab is tested by profile line and its size meets the requirements of the drawing, and has no ditching on the surface. And the mechanical properties of the compact treated by the conventional heat treatment are RP0.2/634 Mpa, Rm/810 Mpa, A/25%, Z/55%, KV2/105J, which can meet the requirements of use.
The above embodiments are only used for illustrating the technical concept and features of the present invention to enable those skilled in the art to understand and implement the present invention, and they are not intended to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

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 CaF₂: 50-62%, Al₂O₃: 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, SiO₂and TiO₂, 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/m²;

(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 06Cr₁₃Ni₄Mo, 06Cr₁₃Ni₅Mo or 06Cr₁₆Ni₅Mo, and ultra-low carbon martensitic stainless steel 04Cr₁₃Ni₄Mo or 04Cr₁₃Ni₅Mo.