Hammer forging method for producing alloy forgings using hammer forging lubricant

Abstract

The invention relates to a hammer forging method for producing alloy forgings using a hammer forging lubricant, and belongs to the technical field of alloy forging. The hammer forging method comprises uniformly throwing the hammer forging lubricant onto the surface of the lower mold cavity of the die to form a lubricating layer; wherein the thickness of the lubricating layer is 3 to 5 mm; hammer forging the forging blank or forging to obtain the alloy forging; the preparation of the hammer forging lubricant is to fully mix the oil-rich white pine sawdust, industrial salt and water in a mass ratio of 10: (0.5 to 1.5): (2 to 10) and soak for 20 to 60 min, and then drain until no obvious water is discharged. The hammer forging lubricant of the invention is uniformly dispersed without agglomeration, and can be uniformly dispersed on the lower die and the surface of the forging. When the hammer forging lubricant is used for hammer forging, there is no oxidation pit on the surface of the forging, and the surface texture is uniform and smooth, and the oxide scale on the surface of the forging can be effectively cleaned.

Description

Technical Field

[0001] The invention relates to a hammer forging method for producing alloy forgings by utilizing a lubricant for hammer forging, and belongs to the technical field of alloy forging. Background Art

[0002] Hammer forging is a forging process in which forgings are shaped by hammering with a hammer or forging hammer. A forging hammer is a forging device that uses a transmission mechanism such as air pressure or hydraulic pressure to make the falling part (piston, hammer rod, hammer head, upper anvil or upper die) move and accumulate kinetic energy, applying energy to the forging in a very short time to enable it to obtain plastic deformation energy. The forging machine that completes various forging processes is called a forging hammer. Based on the free forging hammer, hammer forging processes such as die forging and membrane forging can be carried out. In order to reduce the friction coefficient between the die and the forging, improve the surface quality and filling condition of the forging product, reduce die stress and wear, and increase the service life of the die, lubricants are often used in the process of hammer forging to prepare alloy forgings.

[0003] At present, commonly used lubricants include oily lubricants and dry lubricants. The main components of oily lubricants are mineral oil, synthetic oil, liquid wax, etc., which form a strong lubricating film at high temperature to reduce friction and wear; however, oily lubricants are relatively viscous and there is a risk of contaminating the machine. They may fail under higher temperature and high pressure conditions and cannot provide stable lubrication effects; dry lubricants are mainly composed of a mixture of graphite, metal powder, etc., which can form a fine oxide layer on the surface of the forging to achieve lubrication; the lubricating effect of dry lubricants is not as good as that of oily lubricants, which will accelerate the wear of the mold, and its lubricating effect will also decrease over time; both oily lubricants and dry lubricants are not conducive to removing oxide scale and impurities on the surface of forgings.

[0004] In the prior art, Zhang Shizhong proposed in "The Application of Wood Sawdust in Forging Production" (Forging Machinery, December 27, 1979) the use of a mixture of wood sawdust and water as a medium, evenly spread on the lower die and forging surface during the forging process to facilitate demolding and descaling. The principle is that when the forging blank, hot over a thousand degrees Celsius, comes into contact with the sawdust and water mixture, the latter burns and produces smoke and water vapor. At this point, the upper hammer strikes at a high speed of 7 meters per second, causing the water vapor and smoke between the upper and lower dies to explode under pressure, thereby vibrating off the oxide scale on the forging and sending it flying out through the dies. The sawdust and water mixture should be in an appropriate ratio (sufficient for being able to form a ball), and the sawdust particles should be less than 1 mm in diameter. The sawdust should be spread evenly, preferably when the forging is jumping, so that both the lower die and forging surface are simultaneously covered for optimal results. This method results in high-quality forgings with a bright surface and easy demolding. However, in actual production applications, due to the uneven particles of ordinary sawdust, the presence of many impurities, and poor water absorption, the wetted sawdust is easy to form a mass, but it is more likely to accumulate, resulting in uneven coverage on the lower die cavity and the surface of the forging. After hammer forging, pits and oxidation pits appear on the surface of the forging, and the effect of removing the oxide scale on the surface of the forging is poor. In addition, there is no standard for the use of wood sawdust in the hammer forging process, and there are no established standards for its preparation and use. This leads to differences in the quality of forgings processed by different operators. With the increase in the number of products, the increase in production tasks, the increase in mold temperature and other factors, the use of wood sawdust has failed in the actual production process, and the application of wood sawdust has been limited.

[0005] Chinese patent CN102618378A discloses a lubricant for high-temperature pipe rolling. Specifically, the lubricant's components, graphite powder, sawdust, and salt, are formulated in a weight ratio of 3:1:0.1. The sawdust rapidly burns at high temperatures, depleting the oxygen within the bore of the hot-rolled steel pipe. This prevents oxidation of the steel pipe to form iron oxide chips, thus eliminating the formation of a rough surface. The lubricant's purpose is to prevent the formation of oxide scale within the capillary tube. Therefore, the salt's lubricating effect facilitates the movement of graphite powder and sawdust within the tube.

[0006] In view of this, it is of great significance to solve the problems of uneven particles, high impurities, poor water absorption and poor lubrication effect when using white pine sawdust as a lubricant for hammer forging to produce alloy forgings. Summary of the Invention

[0007] In order to overcome the above technical defects, the present invention provides a lubricant for hammer forging, a preparation method and use thereof. The lubricant for hammer forging is evenly dispersed without agglomeration and can be evenly dispersed on the lower die and the surface of the forging. When the lubricant for hammer forging is used for hammer forging, there are no oxidation pits and excess residual oxide scale on the surface of the forging, and the surface texture is uniform and smooth, which can effectively clean the oxide scale on the surface of the forging.

[0008] The object of the present invention is to provide a hammer forging method for producing alloy forgings using a hammer forging lubricant, the hammer forging method comprising the following steps:

[0009] 1) preparing a forging hammer and a die, and evenly spreading the hammer forging lubricant on the surface of the lower die cavity of the die to form a lubricating layer; wherein the thickness of the lubricating layer is 3 to 5 mm;

[0010] 2) transferring the forging blank or forging to the lower die cavity where the lubricating layer is formed, evenly spreading the hammer forging lubricant on the upper surface of the forging blank or forging, and hammer forging the forging blank or forging to obtain the alloy forging;

[0011] The preparation of the hammer forging lubricant comprises the following steps:

[0012] a. Fully mix oil-rich white pine sawdust, industrial salt, and water in a mass ratio of 10:(0.5-1.5):(2-10), and soak for 20-60 minutes to obtain a mixture;

[0013] b. draining the mixed material from step a to obtain a drained material;

[0014] c. Press the drained material from step b until no obvious water is released and the particles are loose and uniform, thereby obtaining the lubricant for hammer forging.

[0015] In a specific embodiment of the present invention, the white pine sawdust is sawdust from white pine trees that are 10 to 15 years old, and is white, soft, loose and free of debris.

[0016] In a specific embodiment of the present invention, the particle size of the white pine sawdust is 1 to 3 mm.

[0017] In a specific embodiment of the present invention, the industrial salt is any one or both of sodium chloride and potassium chloride.

[0018] In a specific embodiment of the present invention, the industrial salt is industrial grade sodium chloride or potassium chloride with a content of ≥99%.

[0019] In a specific embodiment of the present invention, in step b, the draining time is 5 to 10 minutes.

[0020] In a specific embodiment of the present invention, in step c, the pressing pressure is 0.4-0.5 MPa.

[0021] In a specific embodiment of the present invention, step 2) during the hammer forging process of the forging blank or forging, the hammer forging lubricant is continuously sprinkled according to the number of hammer blows, specifically:

[0022] From the first hammering, before each hammer falls, evenly sprinkle the hammer forging lubricant on the upper surface of the forging blank or forging until the hammer forging is completed;

[0023] From the first hammering, every 5 to 8 hammerings of the high-strength alloy steel, the forging blank or forging is tilted from the lower mold cavity, and the hammer forging lubricant is sprinkled on the upper surface of the lower mold cavity until the hammer forging is completed.

[0024] In a specific embodiment of the present invention, the alloy forging is a complex titanium alloy forging or a high-strength steel forging.

[0025] In the method for preparing alloy forgings by hammer forging of the present invention, when manually spreading the lubricant for hammer forging, the operation method is as follows: when the hammer head is raised, the lubricant for hammer forging is grabbed, the arm is immediately positioned at 30 to 45 degrees with the palm facing upward, and the arm is swung backward. Before the hammer head falls, sawdust is evenly spread to cover most of the forging, and finally the arm is retracted to cover the surface to prevent oxide scale debris from popping out.

[0026] In the method for preparing alloy forgings by hammer forging of the present invention, when throwing the hammer forging lubricant, if the local oxide scale of the forging is thick or the forging has a deep cavity, the throwing frequency should be increased by 1 to 2 times on the local surface of the forging.

[0027] In the present invention, white pine sawdust, industrial salt and water are mixed and then allowed to stand. Pinus tabulaeformis is rich in oil, and the wood sawdust can fully absorb the industrial salt and water. At the same time, the addition of industrial salt can not only improve the water absorption of the white pine sawdust, but also reduce the surface tension of water. The white pine sawdust, industrial salt and water are mixed and then soaked for 20 to 60 minutes, thereby improving the contact between the oily hydrophobic substance on the surface of the white pine sawdust and water, increasing the contact area between the surface of the white pine sawdust and water, improving the water absorption effect of the wood sawdust, and increasing the explosion force under high temperature and high pressure; when water adheres to the surface of the wood sawdust or wood chips, the water absorbs heat and directly vaporizes without causing expansion. Therefore, it is necessary to adopt the soaking method to make the wood sawdust or wood chips absorb more water. After the surface of the wood sawdust absorbs heat, the water inside it is instantly vaporized, and then exploded under high temperature and high pressure. At the same time, the shock wave of the explosion and the wood sawdust or wood chip particles can also have an impact on the forgings, which can better remove the oxide scale on the surface of the forgings; at the same time, since industrial salt is added to the lubricant for hammer forging, the mixture is neutral and not easy to cause corrosion; in the hammer forging process, industrial salt can produce "salt explosion", which can not only reduce the amount of lubricant for hammer forging, but also enhance the compressive explosion force of water vapor and smoke, and improve the effect of vibrating off the oxide scale on the forgings.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention can effectively solve the problems of uneven particles, high impurities, poor water absorption, and poor lubrication effect of lubricants used in hammer forging, and effectively removes oxide scales on the surface of alloy forgings. The surface of the alloy forgings is free of oxidation pits and has a uniform and smooth surface texture. By soaking in water, the lubrication properties of white pine sawdust can be improved, thereby improving the quality of removing oxide scales from white pine sawdust during the hammer forging process.

[0030] 2. The lubricant for hammer forging of the present invention effectively improves the problem of poor water absorption of wood sawdust. The introduction of industrial salt can delay lubrication failure. At the same time, the pine sawdust that absorbs water and industrial salt has a good granulation effect. After removing free water, the white pine sawdust is loose and can be evenly sprinkled on the surface of the lower mold cavity and the surface of the forging without accumulation when used, avoiding local accumulation that affects the size difference of the alloy forgings produced by hammer forging, and can improve the quality of the alloy forgings produced by hammer forging.

[0031] 3. The white pine sawdust of the present invention can be carbonized into particles when heated, and contains a large amount of oil. Under the action of water vapor and smoke pressure explosion and "salt explosion", the carbonized particles of the white pine sawdust are promoted, causing the carbonized particles to impact the surface of the forging, which helps to further improve the effect of removing the oxide scale on the surface of the forging. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flowchart of the method for preparing the lubricant for hammer forging of the present invention;

[0033] Figure 2 Schematic diagram of the results of the porosity test of the balls of Example 1 and Comparative Examples 1-2 of the present invention;

[0034] Figure 3 The effect diagram of the loose test balls after falling to the ground in Example 1 of the present invention and Comparative Examples 1-2 is shown;

[0035] Figure 4 Statistical graph of the results of the scattering effect test of Example 1 of the present invention and Comparative Example 1;

[0036] Figure 5 These are the effect diagrams before and after a gripping force of 4-5 kg ​​is applied to the drained material by hand in Example 1 of the present invention;

[0037] Figure 6 These are the effect diagrams before and after applying a gripping force of 4-5 kg ​​to the drained material by hand in Comparative Example 1 of the present invention;

[0038] Figure 7 This is the surface morphology effect after the model cavity is hammer forged 10 times in Example 1 of the present invention and Comparative Examples 1-2. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0040] Based on the attached Figure 1 A hammer forging method for producing alloy forgings using a hammer forging lubricant comprises the following steps:

[0041] 1) preparing a forging hammer and a die, and evenly spreading the hammer forging lubricant on the surface of the lower die cavity of the die to form a lubricating layer; wherein the thickness of the lubricating layer is 3 to 5 mm;

[0042] 2) transferring the forging blank or forging to the lower die cavity where the lubricating layer is formed, evenly spreading the hammer forging lubricant on the upper surface of the forging blank or forging, and hammer forging the forging blank or forging to obtain the alloy forging;

[0043] The preparation of the hammer forging lubricant comprises the following steps:

[0044] a. Fully mix oil-rich white pine sawdust, industrial salt, and water in a mass ratio of 10:(0.5-1.5):(2-10), and soak for 20-60 minutes to obtain a mixture;

[0045] b. draining the mixed material from step a to obtain a drained material;

[0046] c. Press the drained material from step b until no obvious water is released to obtain the lubricant for hammer forging.

[0047] In some examples, the white pine sawdust is sawdust from white pine trees that are 10 to 15 years old, and is white, soft, loose and free of debris.

[0048] In some examples, the particle size of the white pine sawdust is 1 to 3 mm.

[0049] In some examples, the industrial salt is any one or both of sodium chloride and potassium chloride.

[0050] In some examples, the industrial salt is industrial grade sodium chloride with a content of ≥99%.

[0051] In some examples, in step b, the draining time is 5 to 10 minutes.

[0052] In some examples, in step c, the pressing pressure is 0.4-0.5 MPa.

[0053] In some examples, in step 2), the hammer forging lubricant is continuously sprinkled during the hammer forging process of the forging blank or forging according to the number of hammer blows, specifically:

[0054] From the first hammering, before each hammer falls, evenly sprinkle the hammer forging lubricant on the upper surface of the forging blank or forging until the hammer forging is completed;

[0055] From the first hammering, every 5 to 8 hammerings, the forging blank or forging is tilted from the lower mold cavity, and the hammer forging lubricant is sprinkled on the upper surface of the lower mold cavity until the hammer forging is completed.

[0056] In some examples, the titanium alloy is hammered every 3 to 6 times.

[0057] In some examples, the alloy forging is a complex titanium alloy forging or a high-strength steel forging.

[0058] In some instances, the pressing method may be to use a press to remove some of the free water in the drained material. Of course, manual operation may also be performed, specifically: grab the drained material by hand and apply a gripping force of 4 to 5 kg (0.4 to 0.5 MPa) to the drained material until no obvious water is released.

[0059] The pressing pressure should not be too large or too small. If the pressing pressure is too large, the water absorbed by the pine sawdust will overflow, which is not conducive to ensuring the water absorption; if the pressing pressure is too small, the water between the sawdust particles cannot be discharged.

[0060] In some embodiments, the draining process uses a 0.5 mm filter to drain.

[0061] In some instances, if the hammer forging lubricant has not been used for a long time and is subject to evaporation and dehydration, water can be sprayed onto the surface of the hammer forging lubricant using a spray bottle to keep the lubricant moist.

[0062] In some instances, during hammer forging, a handful of drained material is grabbed by hand and a gripping force of about 4 to 5 kg (0.4 to 0.5 MPa) is applied until no water is noticeably released from the drained material. The grabbed drained material is then evenly sprinkled on the cavity surface of the lower die, or on the upper surface of the forging during the hammer forging process, thereby providing lubrication and effectively removing oxide scale from the forging surface until the forging completes the hammer forging process.

[0063] In order to further demonstrate the effect of the hammer forging lubricant of the present invention in improving the hammer forging process of alloy forgings, the following examples and comparative examples are provided:

[0064] Example 1

[0065] This embodiment first provides a method for preparing a lubricant for hammer forging, comprising the following steps:

[0066] 1. Take 20 kg of white pine sawdust, 2 kg of industrial-grade sodium chloride and 10 kg of water, mix them thoroughly for 5 minutes, and then let them stand for 30 minutes to obtain a mixture;

[0067] 2. Drain the mixture through a 0.5 mm sieve to obtain a drained material;

[0068] 3. Press the drained material at 0.45 MPa until no water is released to obtain lubricant for hammer forging.

[0069] The steps of preparing alloy forgings using the hammer forging lubricant of this embodiment include:

[0070] First spreading: Before the forging billet or forging is transferred to the die, a handful of hammer forging lubricant is manually grabbed and evenly spread on the surface of the lower mold cavity of the die until the lower mold cavity is fully covered.

[0071] Transfer forgings: transfer the forging blank or forging to the die, grab a handful of hammer forging lubricant by hand, evenly sprinkle it on the upper surface of the forging blank or forging, and start hammer forging;

[0072] Forging and scattering: After the first hammer forging, before each subsequent hammer drop, grab a handful of hammer forging lubricant and sprinkle it evenly on the upper surface of the forging blank or forging; from the first hammer forging, every 5-8 hammers, tilt the forging blank or forging and sprinkle a handful of hammer forging lubricant into the lower mold cavity.

[0073] Example 2

[0074] This embodiment first provides a method for preparing a lubricant for hammer forging, comprising the following steps:

[0075] 1. Take 20kg of pine sawdust, 1kg of industrial-grade sodium chloride and 10kg of water, mix and stir thoroughly for 5 minutes, mix and stir thoroughly for 5-10 minutes, and then let it stand for 30 minutes to obtain a mixture;

[0076] 2. Drain the mixture through a 0.5 mm sieve to obtain a drained material;

[0077] 3. Press the drained material at 0.45 MPa until no water is released to obtain lubricant for hammer forging.

[0078] The steps of preparing alloy forgings using the hammer forging lubricant of this embodiment include:

[0079] First spreading: Before the forging billet or forging is transferred to the die, a handful of hammer forging lubricant is manually grabbed and evenly spread on the surface of the lower mold cavity of the die until the lower mold cavity is fully covered.

[0080] Transfer forgings: transfer the forging blank or forging to the die, grab a handful of hammer forging lubricant by hand, evenly sprinkle it on the upper surface of the forging blank or forging, and start hammer forging;

[0081] Forging and scattering: After the first hammer forging, before each subsequent hammer drop, grab a handful of hammer forging lubricant and sprinkle it evenly on the upper surface of the forging blank or forging; from the first hammer forging, every 5-8 hammers, tilt the forging blank or forging and sprinkle a handful of hammer forging lubricant into the lower mold cavity.

[0082] Example 3

[0083] This embodiment first provides a method for preparing a lubricant for hammer forging, comprising the following steps:

[0084] 1. Take 20 kg of white pine sawdust, 3 kg of industrial-grade sodium chloride and 10 kg of water, mix them thoroughly for 5 minutes, and then let them stand for 30 minutes to obtain a mixture;

[0085] 2. Drain the mixture through a 0.5 mm sieve to obtain a drained material;

[0086] 3. Press the drained material at 0.45 MPa until no water is released to obtain lubricant for hammer forging.

[0087] The steps of preparing alloy forgings using the hammer forging lubricant of this embodiment include:

[0088] First spreading: Before the forging billet or forging is transferred to the die, a handful of hammer forging lubricant is manually grabbed and evenly spread on the surface of the lower mold cavity of the die until the lower mold cavity is fully covered.

[0089] Transfer forgings: transfer the forging blank or forging to the die, grab a handful of hammer forging lubricant by hand, evenly sprinkle it on the upper surface of the forging blank or forging, and start hammer forging;

[0090] Forging and scattering: After the first hammer forging, before each subsequent hammer drop, grab a handful of hammer forging lubricant and sprinkle it evenly on the upper surface of the forging blank or forging; from the first hammer forging, every 5-8 hammers, tilt the forging blank or forging and sprinkle a handful of hammer forging lubricant into the lower mold cavity.

[0091] Comparative Example 1

[0092] This comparative example differs from Example 1 in that no industrial grade sodium chloride is added.

[0093] Comparative Example 2

[0094] This comparative example differs from Example 1 in that no industrial-grade sodium chloride is added, and the particle size of the pine sawdust is in the range of 0.5-0.8 mm.

[0095] Performance Testing

[0096] 1. Porosity test

[0097] The hammer forging lubricants obtained in Example 1 and Comparative Examples 1-2 were grabbed by hand and rolled into balls with a diameter of about 80 cm. The balls were then allowed to fall freely onto a cement floor at a height of 100 cm to observe whether the balls collided and broke. The porosity test was conducted three times for each of Example 1 and Comparative Examples 1-2.

[0098] The structures of the balls in Example 1 and Comparative Examples 1-2 are as follows Figure 2 shown.

[0099] The effects of the balls in Example 1 and Comparative Example 1-2 after landing are as follows: Figure 3 shown.

[0100] The statistics of the scattering area and scattering state of the balls in Example 1 and Comparative Examples 1-2 are shown in Table 1.

[0101] Table 1

[0102]

[0103] 2. Spreading effect test

[0104] Grab a handful of hammer forging lubricant of Example 1 and Comparative Example 1 with your hand, with your palm facing inward and your arm at an angle of 30-45 degrees, and swing your arm to sprinkle the hammer forging lubricant on the surface of the lower die. Observe and record the situation of the hammer forging lubricant sprinkled on the surface of the die cavity.

[0105] The test results of Example 1 and Comparative Example 1 are as follows: Figure 4 shown.

[0106] Example 1 The results before and after applying a grip of 4-5 kg ​​to the drained material are as follows Figure 5 shown.

[0107] Comparative Example 1 The results before and after applying a grip of 4-5 kg ​​to the drained material are as follows: Figure 6 shown

[0108] 3. Test of alloy forgings produced by lower die

[0109] Using the hammer forging lubricants of Example 1 and Comparative Examples 1-2, according to the method for producing alloy forgings, 10 alloy forgings were continuously hammer forged in each lower mold cavity, and one forging was randomly selected to observe the oxide scale condition of the lower mold.

[0110] After forging with the lubricants of Example 1 and Comparative Examples 1-2, one piece was randomly selected to observe the adhesion of oxide scale on the lower die. The results are as follows: Figure 7 shown.

Claims

1. A hammer forging method for producing alloy forgings using a hammer forging lubricant, characterized in that: The hammer forging method comprises the following steps: 1) preparing a forging hammer and a die, and evenly spreading the hammer forging lubricant on the surface of the lower mold cavity of the die to form a lubricating layer; wherein the thickness of the lubricating layer is 3 to 5 mm; 2) transferring the forging blank or forging to the lower mold cavity where the lubricating layer is formed, evenly spreading the hammer forging lubricant on the upper surface of the forging blank or forging, and hammer forging the forging blank or forging to obtain the alloy forging; The preparation of the lubricant for hammer forging comprises the following steps: a. Fully mix oil-rich white pine sawdust, industrial salt and water in a mass ratio of 10:(0.5-1.5):(2-10) and soak for 20-60 minutes to obtain a mixture; wherein the particle size of the white pine sawdust is 1-3 mm; and the industrial salt is industrial-grade sodium chloride with a content of ≥99%; b. Drain the mixed material of step a to obtain a drained material; the draining time is 5 to 10 minutes; c. Press the drained material from step b at 0.4-0.5 MPa until no obvious water is released, thereby obtaining the lubricant for hammer forging.

2. The hammer forging method according to claim 1, characterized in that: The white pine wood sawdust is the sawdust of white pine trees with a tree age of 10 to 15 years, and is white, soft, loose and free of debris.

3. The hammer forging method according to claim 1, characterized in that: Step 2), during the hammer forging process of the forging blank or forging, the lubricant for hammer forging is continuously sprinkled according to the number of hammer blows, specifically: From the first hammering, before each hammer falls, evenly sprinkle the hammer forging lubricant on the upper surface of the forging blank or forging until the hammer forging is completed; From the first hammering, every 5 to 8 hammerings, the forging blank or forging is lifted up from the lower mold cavity, and the lubricant for hammer forging is sprinkled on the upper surface of the lower mold cavity until the hammer forging is completed.

4. The hammer forging method according to claim 1, characterized in that: The alloy forging is a complex titanium alloy forging or a high-strength steel forging.

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