Seamless bearing steel pipe piercing plug material and preparation method thereof

Abstract

The invention discloses a seamless bearing steel pipe piercing plug material which comprises the following chemical components in percentage by weight: 0.35 to 0.42 percent of C, 0.80 to 1.30 percent of Si, 0.40 to 0.50 percent of Mn, 4.90 to 5.50 percent of Cr, 0.10 to 0.50 percent of Ni, 1.20 to 1.90 percent of Mo, 1.0 to 1.2 percent of V, 0.8 to 1.2 percent of Al, 1.5 to 2.0 percent of W, 0.05 to 0.50 percent of Ti, 0.001 to 0.005 percent of Mg and the balance of iron and inevitable trace impurities. According to the material formula, by optimizing the proportion of alloy elements, the high-temperature strength, wear resistance and oxidation resistance of the plug are remarkably improved, and the service life is prolonged.

Description

Technical Field

[0001] This invention relates to the field of seamless bearing steel tube manufacturing technology, and more specifically to a piercing mandrel material for seamless bearing steel tubes and its preparation method. Background Technology

[0002] Piercing is a crucial process in the production of seamless bearing steel pipes. During piercing, the mandrel must withstand immense axial force, compressive stress, shear stress, and friction with the rolled piece. Operating in alternating hot and cold temperatures ranging from 25℃ to 1000℃, it is highly susceptible to failure, significantly impacting its service life. With the continuous increase in billet alloy content and steel grade, deformation resistance has also increased substantially, placing higher demands on mandrel performance. Its quality and service life directly affect the quality, production efficiency, and profitability of seamless steel pipes. Therefore, research on high-quality, long-life, and low-cost mandrel piercing has been a focus of widespread attention in seamless steel pipe production.

[0003] Currently, H13 hot work die steel is the most commonly used material for mandrels used in the piercing of seamless steel pipes for bearings in my country. H13 steel mainly contains alloying elements such as Cr, Mo, and V, meeting the performance requirements of various hot work dies. Compared to high-toughness hot work die steels 5CrMnMo and 5CrNiMo, H13 steel has higher heat strength, thermal stability, and hardenability. Therefore, it can be used to replace 5CrMnMo and 5CrNiMo steels, which have insufficient heat strength, in the manufacture of hot forging dies to improve service life. Compared to high-heat-strength hot work die steel 3Cr2W8V, H13 steel has higher toughness and thermal shock resistance. Therefore, H13 hot work die steel has successfully replaced 3Cr2W8V steel, which lacks toughness and thermal fatigue resistance. However, mandrels made of H13 steel have poor strength and thermal stability at high temperatures, and are prone to defects such as nose collapse, pitting, and material loss during the piercing process of bearing steel, resulting in a shorter service life (≤60 pieces / mandrel) and higher operating costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a seamless bearing steel tube perforated mandrel material. By optimizing the alloy composition design of the mandrel material, its high-temperature strength, thermal stability, and thermal fatigue resistance are improved, thereby solving the problem of short service life of existing H13 steel mandrels.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a seamless bearing steel tube perforation mandrel material, the chemical composition and weight percentage of which are: C 0.35-0.42, Si 0.80-1.30, Mn 0.40-0.50, Cr 4.90-5.50, Ni 0.10-0.50, Mo 1.20-1.90, V 1.0-1.2, Al 0.8-1.2, W 1.5-2.0, Ti 0.05-0.50, Mg 0.001-0.005, with the balance being iron and unavoidable trace impurities.

[0006] Another aspect of the present invention provides a preparation method comprising the following steps: Step 1: Perform vacuum induction melting to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions. Step 2: The refined molten steel from the vacuum induction furnace in Step 1 is poured into the preheated electrode mold under vacuum to cast the consumable electrode. The pouring process must be smooth to prevent the entrapment of gas and slag. Finally, a round rod-shaped consumable electrode with uniform chemical composition and dense structure is cast. Step 3: Perform electroslag remelting to form a coarse axial columnar crystal alloy master ingot.

[0007] As a further improvement to the preparation method, the specific steps of vacuum induction melting in step one are as follows: Step 1: Load the calculated weight of high-purity raw materials into the water-cooled copper crucible of the vacuum induction furnace, close the furnace chamber, and evacuate to a high vacuum state to completely remove air. In steps one and two, the furnace charge is gradually melted by heating with an induction coil. Through vacuum and high temperature, carbon deoxidation occurs in the molten steel, and dissolved hydrogen and nitrogen in the molten steel are also removed. Step 13: After the molten steel in Step 12 reaches the predetermined temperature and has been vacuum refined for a period of time, high-purity metallic aluminum is added through the feeding hopper. After addition, the mixture is stirred to ensure a uniform reaction. Step 14: Add nickel-magnesium master alloy to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions.

[0008] As a further improvement to the preparation method, the specific method for adding the nickel-magnesium master alloy in step one of the four steps is as follows: first, high-purity argon gas is refilled into the vacuum furnace to a certain positive pressure, then the nickel-magnesium alloy is added, followed by rapid and thorough induction stirring to promote the reaction of magnesium with residual sulfur and oxygen in the steel. Inclusions react to form tiny spherical shapes. Spinel or MgS inclusions. The vacuum induction furnace is evacuated again for a short period of calming, causing the inclusions to float to the surface and homogenizing the molten steel.

[0009] As a further improvement to the preparation method, the specific method of electroslag remelting in step three is as follows: the electrode rod cast in the vacuum induction furnace is peeled off and installed on the electrode rod of the electroslag furnace. An arc-starting pad is placed in the crystallizer, and pre-melted calcium fluoride-based slag is added. The arc is started by energizing, and the solid slag material is melted to form a liquid slag pool with stable depth and temperature. The electrode end is heated and melted by the high-temperature slag, forming metal droplets that pass through the slag pool. The pure metal droplets converge below the slag pool to form a molten pool. Under strong water cooling, the metal solidifies sequentially from bottom to top to form a coarse axial columnar crystal alloy ingot.

[0010] The beneficial effects of this invention are that, due to the presence of high-temperature resistant Mo, W, and V elements, along with the introduction of appropriate amounts of Al and Mg elements, the high-temperature strength, thermal stability, thermal fatigue resistance, and durability of the hot-piercing mandrel material for bearing steel tubes are improved. The hot-piercing mandrels for bearing steel tubes prepared using this material extend the time before the mandrel collapses, increasing the lifespan of the hot-pierced GCr15 steel tube mandrels from 60 pieces / mandrel for H13 material to 80-100 pieces / mandrel. The preparation method utilizes a dual process of vacuum induction melting and electroslag remelting, achieving high purity and dense microstructure in the molten steel. Precise control of forging and heat treatment further ensures the uniformity of the mandrel's mechanical properties. Detailed Implementation

[0011] The present invention will be further described in detail below with reference to the given embodiments.

[0012] The seamless bearing steel tube perforation mandrel in this embodiment is made of the following material, and the improvement principle is as follows: C: 0.35-0.42 (weight percentage, the same below). C is a carbide-forming element, which can improve hardness and wear resistance, and form carbides to enhance the strength of steel. If the C is too low, the material is too soft; if it is too high, it is not conducive to oxidation and nitriding heat treatment, as oxygen reacts with carbon first, which is not conducive to the formation of oxide scale.

[0013] Si: 0.80-1.30. It can improve strength and oxidation resistance, and is beneficial for forming a well-adhesive oxide scale on the metal surface, but too high a content will reduce the strength at high temperatures.

[0014] Mn: 0.40-0.50. It can improve hardenability and strength, but too high a content will reduce thermal conductivity and make it prone to cracking.

[0015] Cr: 4.90-5.50. It can impart high hardenability, oxidation resistance and corrosion resistance, and form chromium carbides to enhance wear resistance and high-temperature strength. However, excessive content will reduce thermal conductivity and reduce oxidation ability.

[0016] Ni: 0.10-0.50. It can improve toughness and hardenability, and enhance resistance to thermal fatigue, but excessively high levels will reduce thermal conductivity and decrease oxidation resistance.

[0017] Mo: 1.20-1.90. It can improve high-temperature strength, resistance to temper softening and hardenability; refine grains and reduce temper brittleness; form molybdenum carbides to enhance wear resistance and thermal stability, thereby improving the service life of the mandrel.

[0018] V: 1.0-1.2. It can form high-hardness vanadium carbides, significantly improving wear resistance and refining grains; it inhibits grain growth at high temperatures, improves thermal fatigue performance, and reduces deformation and cracking of the mandrel during use.

[0019] Al: 0.8-1.2. It can refine grains, control the temperature at which grain coarsening begins, and improve the machinability and high-temperature strength of steel.

[0020] W: 1.5-2.0. This improves red hardness and wear resistance; it forms tungsten carbides to enhance high-temperature strength, thereby increasing the service life of the mandrel.

[0021] Ti: 0.05-0.20. It can form stable carbides, which work synergistically with V and Mo carbides to optimize carbide distribution, reduce local wear, and enhance high-temperature hardness and wear resistance; it also refines grains, improves strength, toughness and thermal fatigue resistance, and delays crack propagation.

[0022] Mg: 0.001-0.005. Magnesium is a strong deoxidizer and desulfurizer, which can purify molten steel. It reacts with oxygen and sulfur in steel to form MgO and MgS, reducing harmful inclusions (such as FeO and MnS). The generated MgO-MgS composite inclusions have high melting points and small sizes, making them easy to float and remove, thus improving the hot plasticity and thermal fatigue properties of steel. Trace amounts of magnesium can promote the formation of a dense oxide film, delaying high-temperature oxidation; improve carbide defects in steel; magnesium can transform long, strip-shaped MnS inclusions into fine, dispersed spherical MgS, reducing anisotropy. Hard MgO-MgS composite inclusions can improve wear resistance (especially under high-temperature friction conditions) and can control the size, distribution, and morphology of carbides, thereby improving fatigue life.

[0023] Therefore, the chemical composition and weight percentage of the mandrel material in this embodiment are as follows: C 0.35-0.42, Si 0.80-1.30, Mn 0.40-0.50, Cr 4.90-5.50, Ni 0.10-0.50, Mo 1.20-1.90, V 1.0-1.2, Al 0.8-1.2, W 1.5-2.0, Ti 0.05-0.50, Mg 0.001-0.005, with the balance being iron and unavoidable trace impurities. During the piercing process, the material enhances high-temperature hardness through the carbide phase formed by Cr and Mo, improves thermal stability through W, and inhibits grain boundary oxidation through the combined effect of Al and Mg. This effectively resists alternating hot and cold shocks from 25℃ to 1000℃, solving the problem of insufficient high-temperature strength in traditional H13 steel mandrels and extending their service life.

[0024] Further steps include the following: Step one involves vacuum induction melting to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions; the carbon deoxidation and gas removal processes of vacuum induction melting lay the foundation for the high toughness of the subsequent mandrel.

[0025] Step two involves casting the refined molten steel from the vacuum induction furnace in step one into a preheated electrode mold under vacuum to produce a consumable electrode. The casting process must be smooth to prevent the entrapment of gas and slag, ultimately resulting in a cylindrical consumable electrode with uniform chemical composition and dense structure. The vacuum casting process avoids air pollution and improves the density of the consumable electrode.

[0026] Step 3 involves electroslag remelting to form a coarse axial columnar crystal alloy master ingot. The electroslag remelting process, through slag pool purification and directional solidification, allows for better control of the inclusion level in the alloy master ingot and improves the axial grain boundary strength.

[0027] Furthermore, the specific steps of vacuum induction melting in step one are as follows: Step 1: Load the calculated weight of high-purity raw material into the water-cooled copper crucible of the vacuum induction furnace, close the furnace chamber, and evacuate to a high vacuum state to completely remove air; ensure that there is no oxidation during the melting process of the raw material.

[0028] In steps one and two, the furnace charge is gradually melted by heating with an induction coil. Through vacuum and high temperature, carbon deoxidation occurs in the molten steel, and dissolved hydrogen and nitrogen in the molten steel are also removed. The melting temperature and holding time promote the full escape of gases.

[0029] Step 1 and Step 3: After the molten steel in Step 1 and Step 2 reaches the predetermined temperature and has been vacuum refined for a period of time, high-purity metallic aluminum is added through the feeding hopper. After addition, it is thoroughly stirred to make it uniform. The amount of aluminum added is controlled at 0.8% to 1.2% of the weight of the molten steel, and the stirring time is ≥5 minutes to achieve the final deoxidation of the molten steel.

[0030] Step 14: Add a nickel-magnesium master alloy to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions; the amount of nickel-magnesium alloy added is such that the Mg content in the molten steel reaches 0.001%–0.005%, forming… Smaller inclusions effectively improve the fluidity of molten steel.

[0031] Furthermore, the specific method for adding the nickel-magnesium master alloy in step one of the above steps is as follows: first, high-purity argon gas is refilled into the vacuum furnace to a positive pressure of less than 10 kPa, then the nickel-magnesium alloy is added. After addition, the mixture is induction stirred at a stirring speed of 300 r / min for less than 5 minutes to promote the reaction of magnesium with residual sulfur and oxygen in the steel. Inclusions react to form tiny spherical shapes. Spinel or MgS inclusions. The vacuum induction furnace is then evacuated again and the mixture is calmed, causing the inclusions to float to the surface and significantly improving the purity of the molten steel.

[0032] Furthermore, the specific method of electroslag remelting in step three is as follows: the electrode rod cast in the vacuum induction furnace is surface-peeled to Ra1.6μm, installed on the electrode rod of the electroslag furnace, a pure iron arc-starting pad is placed in the crystallizer, and then... Pre-melted slag When an electric arc is ignited, the solid slag material is melted to form a liquid slag pool. Metal droplets formed at the end of the electrode pass through the slag pool. The pure metal droplets converge below the slag pool to form a molten pool. Under the strong water cooling effect of the crystallizer, the molten metal solidifies sequentially from bottom to top, forming a large-diameter axial columnar crystal alloy ingot. The direction of its columnar crystals is consistent with the direction of the working stress of the top, which effectively improves the fatigue resistance.

[0033] This invention solves the technical problems of insufficient high-temperature strength and poor thermal stability of traditional H13 steel mandrels by optimizing the alloy composition design of the piercing mandrel material for seamless bearing steel pipes (C-Si-Mn-Cr-Ni-Mo-WV-Al-Ti-Mg composite system), combining a dual smelting process of vacuum induction melting and electroslag remelting with precision forging heat treatment technology. This increases the service life of the mandrel during the piercing process of bearing steel from ≤60 pieces / piece to 80-100 pieces / piece, significantly improving the production efficiency and product quality stability of seamless steel pipes.

[0034] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A perforated mandrel material for seamless bearing steel tubes, characterized in that: The chemical composition and weight percentage of the material are as follows: C 0.35-0.42, Si 0.80-1.30, Mn 0.40-0.50, Cr 4.90-5.50, Ni 0.10-0.50, Mo 1.20-1.90, V 1.0-1.2, Al 0.8-1.2, W 1.5-2.0, Ti 0.05-0.50, Mg 0.001-0.005, with the balance being iron and unavoidable trace impurities.

2. A method for preparing the perforated mandrel material as described in claim 1, characterized in that: Includes the following steps: Step 1: Perform vacuum induction melting to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions. Step 2: The refined molten steel from the vacuum induction furnace in Step 1 is poured into the preheated electrode mold under vacuum to cast the consumable electrode. The pouring process must be smooth to prevent the entrapment of gas and slag. Finally, a round rod-shaped consumable electrode with uniform chemical composition and dense structure is cast. Step 3: Perform electroslag remelting to form a coarse axial columnar crystal alloy master ingot.

3. The preparation method according to claim 2, characterized in that: The specific steps of vacuum induction melting in step one are as follows: Step 1: Load the calculated weight of high-purity raw materials into the water-cooled copper crucible of the vacuum induction furnace, close the furnace chamber, and evacuate to a high vacuum state to completely remove air. In steps one and two, the furnace charge is gradually melted by heating with an induction coil. Through vacuum and high temperature, carbon deoxidation occurs in the molten steel, and dissolved hydrogen and nitrogen in the molten steel are also removed. Step 13: After the molten steel in Step 12 reaches the predetermined temperature and has been vacuum refined for a period of time, high-purity metallic aluminum is added through the feeding hopper. After addition, the mixture is stirred to ensure a uniform reaction. Step 14: Add nickel-magnesium master alloy to obtain pure molten steel after removing hydrogen and nitrogen and converting inclusions.

4. The preparation method according to claim 3, characterized in that: The specific method for adding the nickel-magnesium master alloy in step one is as follows: First, high-purity argon gas is refilled into the vacuum furnace to a certain positive pressure, then the nickel-magnesium alloy is added. After addition, rapid and thorough induction stirring is performed to promote the reaction of magnesium with residual sulfur and oxygen in the steel. Inclusions react to form tiny spherical shapes. Spinel or MgS inclusions.

5. The vacuum induction furnace is evacuated again for a short period of calming, which causes inclusions to float to the surface and homogenizes the molten steel.

6. The preparation method according to any one of claims 2 to 4, characterized in that: The specific method of electroslag remelting in step three is as follows: the electrode rod cast in the vacuum induction furnace is peeled off and installed on the electrode rod of the electroslag furnace. An arc-starting pad is placed in the crystallizer, and pre-melted calcium fluoride-based slag is added. The arc is started by energizing and melting the solid slag material to form a liquid slag pool with stable depth and temperature. The electrode end is heated and melted by the high-temperature slag, forming metal droplets that pass through the slag pool. The pure metal droplets converge below the slag pool to form a molten pool. Under strong water cooling, the metal solidifies sequentially from bottom to top to form a coarse axial columnar crystal alloy ingot.