CONSTRUCTING-AND-FORGING METHOD FOR PREPARING HOMOGENIZED FORGED PIECES

Abstract

A constructing-and-forging method for preparing homogenized forged pieces comprises: preparing preformed billets: cutting off a plurality of continuous casting billets, milling and smoothing surfaces of the billets to be welded, performing vacuum plasma cleaning operation to the surfaces to be welded, stacking the plurality of billets and sealing around the surfaces in a vacuum chamber by electron beam welding; forge-welding and homogenizing the preformed billets: heating the preformed billets to a certain temperature in a heating furnace and taking the heated preformed billets out of the heating furnace, forging the preformed billets by a hydraulic press, then using three-dimensional forging to disperse the welded surfaces such that composition, structure and inclusion of the interface areas are at the same level as those of the bodies of the billets. Cheap continuous casting billets are stacked and forge welded.

Claims

1. A constructing-and-forging method for preparing homogenized forged pieces, characterized by: firstly, preparing preformed billets: cutting off a plurality of continuous casting billets to have certain sizes milling and smoothing surfaces of the billets to be welded by a milling planer, performing vacuum plasma cleaning operation to the surfaces to be welded, stacking the plurality of billets and sealing around the surfaces to be welded in a vacuum chamber by electron beam welding; then forge-welding and homogenizing the preformed billets: heating the preformed billets to a certain temperature in a heating furnace and taking the heated preformed billets out of the heating furnace, forging the preformed billets by a hydraulic press, using pressure dwelling and temperature dwelling means during a first upsetting process to weld the surfaces completely together, then using three-dimensional forging to disperse the welded surfaces such that composition, structure and inclusion of the interface areas are at the same level as those of the bodies of the billets; final forming: forging the preformed billets to have final shape and size; the method comprises: a first step, cutting off the plurality of the continuous casting billets according to a certain specification; a second step, machining and cleaning the surfaces of the billets to be welded; a third step, welding the billets by vacuum electron beam welding to seal the billets; a fourth step, heating the billets before forging; a fifth step, upsetting and forge-welding the billets using a pressure dwelling and forge welding method; a sixth step, diffusion bonding the billets under a high temperature; a seventh step, stretching the billets in the Y direction; an eighth step, stretching the billets in the X direction; a ninth step, stretching the billets in the Z direction; and a tenth step, forging the billets to have final shape and size.

2. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the first step, when cutting off the continuous casting billets, a width-to-length ratio of the billets is 2:3, and the number of continuous casting billets is determined such that a total height of the stacked billets versus the width is 2:1, thus, after stacking, the ratio of width (X):length (Y):height (Z)=2:3:4, so as to facilitate performing the three-dimensional forging.

3. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the second step, the surfaces to be welded are processed by the milling planer and cleaned by a plasma in the vacuum chamber, so as to ensure high cleanliness of the surface and to expose fresh metal.

4. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the third step, the stacked billets are placed in the vacuum chamber and interfaces between the billets are sealed around by electron beam welding, and a welding depth is 1050 mm.

5. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the fourth step, the sealed billets are sent to the heating furnace and a heating temperature is 0.85T.sub.m, wherein T.sub.m is the melting point of the material of the billets and the unit of T.sub.m is C.

6. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the fifth step, placing the heated billets on an operation platform of the forging press and make the height direction of the billet vertical; upsetting the billets using an upsetting plate in the direction of height (Z direction); the upsetting is carried out in two steps: first, pressing the billets to reduce the total height of the billets by 10% and keep pressure on the billets for 5 min; then continuing the upsetting until the total height of the billets is reduced by 50%, and keeping pressure on the billets for 10 min.

7. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the sixth step, the upset billet is sent back to the heating furnace and heated at heating temperature of 0.85Tm, T.sub.m is the melting point of the material of the billets and has a unit in C., and the heating temperature is kept for 20T.sub.h hours after the billets are uniformly heated, T.sub.h is the height after upsetting and has a unit in meters.

8. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the seventh step, a flat anvil is used to stretch the billets in the Y direction and the billets are formed into a cuboid with a dimension ratio of width (X):length (Y):height (Z)=3:4:2.

9. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the eight step, upsetting the billets by 50% in the Y direction by a flat anvil, and after the billets are deformed to the certain dimension, stretching the billets in the X direction into a cuboid with a dimension ratio of width (X):length (Y):height (Z)=4:2:3.

10. The constructing-and-forging method for preparing homogenized forged pieces of claim 1, wherein: in the ninth step, upsetting the billets by 50% in the X direction by a flat anvil, and after the billets are deformed to the certain dimension, stretching the billets in the Z direction into a cuboid with a dimension ratio of width (X):length (Y):height (Z)=2:3:4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 shows the mechanism of interface defect's healing. It is included, (a) the initial deformation; (b) the void closing macroscopically; (c) crack defect becoming unstable and decomposing; (d) metallurgical bonding.

[0050] FIG. 2 shows in an exemplary embodiment of the present invention, the continuous casting billets are stacked and sealing welded.

[0051] FIG. 3 shows in an exemplary embodiment of the present invention, the billets are being forged.

[0052] FIG. 4 shows the process flow diagram of the present invention. It is included (a) cutting the continuous casting billet; (b) milling and smoothing the surfaces to be welded, exposing fresh metal and performing plasma cleaning; (c) sealing the interface around in a vacuum chamber by electron beam welding; (d) heating the billet in high temperature furnace; (e) using hydraulic press to upset the billet in a direction perpendicular to the to be welded interface; (f) when the upsetting reaches the expected position, keeping the pressure on the billet to make the defects completely welded; (g) returning the billet to the furnace for high temperature diffusion after upsetting; (h) (i) three-dimensional forging to guarantee the billet's large deformation in each direction; (j) forging the billet to the final shape and size.

[0053] FIG. 5 shows in an exemplary embodiment of the present invention, the microstructure of the welded interface after forging.

[0054] FIG. 6 shows in the comparative embodiment 1, the microstructure on the central area of the forged pieces forged from traditional ingot.

[0055] FIG. 7 shows in the comparative embodiment 2, the microstructure of the welded interface after cladding rolling. It is including, (a) the central area of the billet, (b) the edge region of the cladding rolled billet.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] As shown in FIG. 4, in the present invention, the process flow of the method for preparing homogenizing forging by forge-welding stacked continuous casting billets is as follows:

[0057] (a) cutting the continuous casting billet; (b) milling and smoothing the surfaces to be welded, exposing fresh metal and performing plasma cleaning; (c) sealing the interface around in a vacuum chamber by electron beam welding; (d) heating the billet in high temperature furnace; (e) using hydraulic press to upset the billet in a direction perpendicular to the to be welded interface; (f) when the upsetting reaches the expected position, keeping the pressure on the billet to make the defects completely welded; (g) returning the billet to the furnace for high temperature diffusion after upsetting; (h) (i) three-dimensional forging to guarantee the billet's large deformation in each direction; (j) forging the billet to the final shape and size by traditional free forging process like upsetting, stretching, rounding, punching, broaching and core bar stretching.

[0058] The present invention is further illustrated by exemplary embodiment, comparative embodiment, and experimental embodiment.

Exemplary Embodiment 1

[0059] Using continuously casted method, the continuously casted slab billet with width 1200 mm and thickness 200 mm is casted. The steel is 25Cr2Ni4MoV and the chemical composition is listed in Table 1. This steel is commonly used for pressure vessel. Cutting the billet to a certain size, after machining and cleaning, sealing and welding the billets in the vacuum chamber and then forge it. The specific steps are as follows:

TABLE-US-00001 TABLE 1 measured chemical composition of 25Cr2Ni4MoV steal (mass percentage, %) element C Si Mn P S Cr Ni Mo V percentage 0.21 0.039 0.27 0.005 0.005 1.64 3.46 0.39 0.095

[0060] A first step, cutting off the continuous casting billets according to a certain specification. Three pieces of 200450300 mm continuous casting billets are cut and stacked together. Making the dimensions of the stacked billets as width=300 mm, length=450 mm, height=600 mm, which can be easily forged in three directions.

[0061] A second step, machining and cleaning the surface to be welded. The surface to be welded is processed by milling planer and cleaned by plasma in a vacuum chamber, which can guarantee the surface's high cleanliness and expose fresh metal.

[0062] A third step, sealing the billets by vacuum electron beam welding. The stacked billets are placed in the vacuum chamber and the interfaces between the billets are sealed around by electron beam welding. The welding depth is 1050 mm (FIG. 2).

[0063] A fourth step, heating the billets before forging. The sealed billet is sent to the heating furnace and the heating temperature is 1250 C.

[0064] A Fifth step, upsetting and forge-welding the billets using a pressure dwelling forge welding method. Placing the heated billets on the operation platform of forging press and making the height direction of the billet vertical; upsetting the billets using upsetting plate in the direction of height (Z direction); upsetting is carried out in two steps: first, pressing the billets to reduce the total height of the billets by 10% and keep pressure on the billets for 5 min; then continuing the upsetting until the total height of the billets is reduced by 50%, and keeping pressure on the billets for 10 min (FIG. 3).

[0065] A sixth step, diffusion bonding the billets under a high temperature. The upset billets are sent back to the heating furnace and the heating temperature is 1250 C. The temperature holding time is 6 hours.

[0066] A seventh step, stretching the billets in the Y direction and deforming it to width=450 mm, length=600 mm and height=300 mm.

[0067] An eighth step, stretching the billet in the X direction and deforming it to width=600 mm, length=300 mm and height=450 mm.

[0068] A ninth step, stretching the billet in the Z direction and deforming it to width=300 mm, length=450 mm and height=600 mm.

[0069] A tenth step, forging the billet to have final shape and size, which is thickness=180 mm, length=1000 mm and width=1000 mm.

Comparative Embodiment 1

[0070] The material's chemical composition and final work piece size in comparative embodiment 1 are the same as that of exemplary embodiment 1. Conventional mould casting ingot and forging process are used in the comparative embodiment 1. The specific steps are as follows:

[0071] A first step, making ingot mould, chassis, hot top box and central casting pipe. The grey iron is used to produce ingot mould, chassis, hot tops box and central casting pipe for a 2-ton ingot. The hot top insulation board, mould powder, carbonized rice hull, heating agent and other auxiliary materials should be prepared.

[0072] A second step, assembling the ingot mould. Bricks are built on the chassis to make runner. The ingot mould and central casting pipe are set on the chassis, the hot top box is set on the ingot mould and the mould powder is hanged inside the ingot mould.

[0073] A third step, smelting and pouring. A 2 tons of steel is smelted and poured. After pouring, the carbonized rice hull is placed on the upper part of the hot top for heat preservation.

[0074] A forth step, demoulding. 5 hours after pouring, a steel ingot of 2801000 mm can be got after demoulding.

[0075] A fifth step, cutting off. After cutting the hot top and nozzle, the billet can be got.

[0076] A sixth step, heating. The billet is put into the heating furnace and the heating temperature is 1250 C. The temperature holding time is 6 hours.

[0077] A seventh step, stretching the billet in the Y direction and deforming it to width=450 mm, length=600 mm and height=300 mm.

[0078] An eighth step, stretching the billet in the X direction and deforming it to width=600 mm, length=300 mm and height=450 mm.

[0079] A ninth step, stretching the billet in the Z direction and deforming it to width=300 mm, length=450 mm and height=600 mm.

[0080] A tenth step, forging the billet to have final shape and size, which is thickness=180 mm, length=1000 mm and width=1000 mm.

Comparative Embodiment 2

[0081] The material's chemical composition and final work piece size in comparative embodiment 2 are the same as that of exemplary embodiment 1. Conventional cladding rolling process is used in the comparative example 2. The specific steps are as follows:

[0082] A first step, cutting off the plurality of the continuous casting billets according to a certain specification

[0083] 3 pieces of 200450300 mm continuous casting billets are cut and stacked together. Make dimensions of the stacked billets as width=300 mm, length=450 mm, height=600 mm.

[0084] A second step, machining and cleaning the surfaces of the billets to be welded. The surface to be welded is processed by milling planer and cleaned using alcohol or acetone.

[0085] A third step, welding the billets by vacuum electron beam welding to seal the billets. The stacked billets are placed in the vacuum chamber and the interfaces between the billets are sealed around by electron beam welding. The welding depth is 50 mm.

[0086] A fourth step, heating the billets before forging. The sealed billet is sent to the heating furnace and the heating temperature is 1250 C.

[0087] A fifth step, rolling the billet. The heated billet is placed on heavy plate rolling mill for rolling. The average reduction depth for each press is 30 mm. Both transverse rolling and longitudinal rolling are used. After rolling for 14 times, the billet is rolled to the thickness of 180 mm, length of 1000 mm and width of 1000 mm.

Experimental Embodiment 1

[0088] Forgings in exemplary embodiment 1, comparative embodiment 1 and comparative embodiment 2 are sawed in the center line. Specimens of welded interface area can be got and corroded by nitric acid in alcohol. The specific macrostructure is shown in FIGS. 5, 6 and 7. It can be seen from the figures that the microstructure of the forging using the method of stacked continuous casting billet forge welding of the present invention are basically the same as that of the forging using conventional forging method. No abnormal microstructure is found at the original interface position, while compared with conventional forging method, the method of stacked continuous casting billets forge welding of the present invention can improve material utilization rate by 30%. Meanwhile, the interface has not been fully roll welded at the center of the billet produced by continuous casting billets cladding rolling method (FIG. 7a). During the first several passes of the multiple passes rolling, there is shear stress at the edge of the billet interface, which will fracture the electron beam welding area and lead to the oxidation of the to be welded surface. After deformation, obvious interface structure exists, as shown in FIG. 7b.

[0089] The result of experimental embodiment shows that the present invention breaks through the conventional method of using mould casting steel ingot to make large forgings. Using vacuum cleaning and electron beam welding on continuous casting billets, and pressure dwelling and temperature dwelling method during forging, the interface is completely welded. Then three-dimensional forging is used in the subsequent upsetting and stretching process to disperse the welded interface, which makes the composition, microstructure and inclusion level of the interface area reach that of the matrix's level. The present invention can largely reduce the manufacturing cost, improve the material utilization rate and solve conventional ingot's problems of segregation, coarse crystal, inclusion, shrinkage cavity and porosity, so manufacturing of homogenized forgings can be achieved. In addition, the present invention can also be used for bonding different kinds of metals.