Composite cast steel roll and method for manufacturing the same

Abstract

The application discloses a kind of composite steel casting roll and preparation method thereof, belong to the field of roll manufacturing technology, including the main alloy element component of outer layer and its weight percentage content C:0.3-1.2%, Si:0.20-1.00%, Mn:0.50-2.00%, P≤0.05, S≤0.03, Cr:1.0-8.0%, Ni:0.10-1.0%, Mo:0.30-2.0%, V+W+Nb≤0.5%;The alloy element component of core and its weight percentage content C:0.5-1.5%, Si:0.50-1.50%, Mn:0.2-1.0%, P≤0.05, S≤0.03, Cr≤0.60%, Ni:0.2-1.0, Mo≤0.50%, V≤0.50%, batching, according to the above composition is smelted, pours outer layer and core, with high heat-resistant crack high fatigue resistance characteristics.

Description

Technical Field

[0001] This invention relates to the field of roll manufacturing technology, and in particular to a composite cast steel roll and its preparation method. Background Technology

[0002] Currently, the two-roll roughing mill stands of hot strip mills are made of conventional materials such as alloy steel and alloy forged steel. They have deep hot cracks after exiting the mill, high roll wear, and short on-machine cycle time. Therefore, materials with high resistance to hot cracking and high wear resistance are required. At the same time, since the two-roll mill stands have no support rolls, they are subjected to large reduction and high impact, which requires the roll neck to have high strength.

[0003] In particular, the working layer thickness of the two-roll roughing mill roll is as high as 80mm or even higher on one side, which is higher than that of the conventional hot continuous rolling mill working roll (thickness of about 50mm). How to ensure the quality of the bonding layer under the conditions of large impact and reduction in the roughing or medium plate rolling line, and how to ensure the stability within the working layer, requires special research on the casting process and heat treatment process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a composite cast steel roll and its preparation method, which can obtain a composite tool steel material with high resistance to hot cracking, improve the roll's resistance to hot cracking and thermal fatigue, and achieve better performance.

[0005] To solve the above-mentioned technical problems, the improved technical solution of the present invention is as follows:

[0006] On one hand, a composite cast steel roll includes an outer layer and a core. The composition and weight percentage of each alloying element in the outer layer are as follows: C: 0.3-1.2%, Si: 0.20-1.00%, Mn: 0.50-2.00%, P≤0.05%, S≤0.03%, Cr: 1.0-8.0%, Ni: 0.10-1.0%, Mo: 0.30-2.0%, V+W+Nb≤0.5%, with the remainder being Fe and unavoidable impurities.

[0007] The composition and weight percentage of each alloying element in the core are as follows: C: 0.5-1.5%, Si: 0.50-1.50%, Mn: 0.2-1.0%, P≤0.05%, S≤0.03%, Cr≤0.60%, Ni: 0.2-1.0%, Mo≤0.50%, V≤0.50%, with the remainder being Fe and unavoidable impurities.

[0008] A further improvement of the present invention is that the core composition C+(Si+P) / 3 is greater than or equal to the outer layer composition C+(Si+P) / 3.

[0009] On the other hand, a method for preparing the above-mentioned composite cast steel roll includes the following steps:

[0010] Step A: Raw materials such as scrap steel, ferrochrome, nickel plate, ferromolybdenum, and ferromanganese are batched and added to a smelting furnace. The alloy elements and their weight percentages for the outer layer and core are smelted at a temperature of 1500-1600℃. After the outer layer molten steel reaches the design requirements, the temperature is raised to 1600-1700℃ and then poured. The core molten steel is smelted at a temperature of 1450-1550℃. The core is poured at a temperature of 1500-1550℃ and then poured at a temperature of 1600-1650℃.

[0011] Step B: Using the principle of communicating vessels, pour the outer layer of molten steel by bottom pouring, filling the entire cavity until the overflow port is reached. After pouring, wait 1-10 minutes before pouring the core layer of molten steel. The amount of molten steel poured into the core layer is 2 / 5-5 / 6 of the amount of molten steel poured into the outer layer. Pour in stages, with an interval of 10-40 seconds between each pour, and pour the core layer of molten steel in 20-30 stages.

[0012] Step C: After the outer layer of molten steel has been replaced, the overflow channel is blocked with high-temperature cement, and the entire cavity is poured to fill the riser.

[0013] Step D: After the riser is filled, start pouring water from top to bottom 10-20 minutes later. After filling, sprinkle carbonized rice husks on the surface of the riser water.

[0014] Step E: After pouring, open the hot box 20-50 hours later, and then directly put it into a high-temperature furnace for normalizing treatment.

[0015] Step F: Roughly machine the blank, leaving a diameter allowance of 6-20 mm and a length allowance of ≥20 mm;

[0016] Step G: Perform final heat treatment on the product, and then refine it until the finished product is obtained.

[0017] A further improvement of the present invention is that the ladle used for pouring the outer layer and core molten steel in steps A and B is a bottom-leaf ladle, and the ladle with the riser is a flip ladle. Furthermore, the bottom funnel brick must be cleaned each time the bottom-leaf ladle is poured, and argon is blown on the outer layer molten steel for 1-5 minutes after it exits the furnace.

[0018] A further improvement of the present invention is that the pouring in step C is completed in 2-4 stages until the riser is filled.

[0019] A further improvement of the present invention is that the thickness of the carbonized rice husk in step D is ≥100mm.

[0020] A further improvement of the present invention is that, in step E, the normalizing temperature is 880-980℃, and the cooling method is to first blow air for 40-100 minutes until the temperature reaches 500-550℃ and then stop the air blowing, followed by air cooling for 60-240 minutes before loading the furnace for tempering, with a tempering temperature of 550-650℃.

[0021] A further improvement of the present invention is that the final heat treatment method in step G is a high-efficiency high-temperature heat treatment method, specifically high-temperature quenching + tempering, and the radial and axial temperature difference within 100mm of the working layer must be kept within 10℃.

[0022] A further improvement of the present invention is that, after heat treatment in step G, a structure of tempered sorbite + a small amount of tempered martensite + a small amount of carbides is obtained, and the content of other carbides is ≤1.0%.

[0023] The technological advancements achieved by this invention through the above-mentioned technical features are as follows:

[0024] This invention, through specialized material design, limits the main carbide-forming elements C, Mo, and Cr to ensure that the carbide content is ≤1.0%. At the same time, this invention yields a composite tool steel material with high resistance to hot cracking, achieving better performance in use. Attached Figure Description

[0025] To more clearly illustrate the operating principle and technical solution of this invention, the accompanying drawings required for the operating principle and technical application will be briefly introduced below. Obviously, the drawings described below are merely some examples of the invention's operation. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0026] Figure 1 These are metallographic diagrams of thermal crack resistant and fatigue resistant (composite tool steel) rolls;

[0027] Figure 2 It is a metallographic image of alloy cast steel;

[0028] Figure 3 This is a metallographic image of high-chromium steel;

[0029] Figure 4 This is a diagram of the roll surface of the heat-crack-resistant and fatigue-resistant rolling mill rolls.

[0030] Figure 5 This is a diagram of the alloy steel roller surface. Detailed Implementation

[0031] This invention proposes a composite cast steel roll, comprising an outer layer and a core. The alloying elements and their weight percentages in the outer layer are as follows: C: 0.3-1.2%, Si: 0.20-1.00%, Mn: 0.50-2.00%, P≤0.05%, S≤0.03%, Cr: 1.0-8.0%, Ni: 0.10-1.0%, Mo: 0.30-2.0%, V+W+Nb≤0.5%, with the remainder being Fe and unavoidable impurities. The alloying elements and their weight percentages in the core are as follows: C: 0.5-1.5%, Si: 0.50-1.50%, Mn: 0.2-1.0%, P≤0.05%, S≤0.03%, Cr≤0.60%, Ni: 0.2-1.0%, Mo≤0.50%, V≤0.50%, with the remainder being Fe and unavoidable impurities.

[0032] Optionally, the core composition C+(Si+P) / 3 is greater than or equal to the outer layer composition C+(Si+P) / 3.

[0033] A method for preparing a composite cast steel roll includes the following steps:

[0034] Step A: Raw materials such as scrap steel, ferrochrome, and nickel plates are batched and added to a smelting furnace. The alloying elements and their weight percentages for the outer and core layers are smelted at a temperature of 1500-1600℃. After the outer layer molten steel reaches the design requirements, the temperature is raised to 1600-1700℃ before pouring. The core molten steel is smelted at 1450-1550℃, poured at 1500-1550℃, and poured at 1600-1650℃ when the risers are applied.

[0035] Step B: Using the principle of communicating vessels, pour the outer layer of molten steel using a bottom pouring method, filling the entire cavity until the overflow port is reached. After pouring, wait 2-10 minutes before starting to pour the core layer of molten steel. The amount of molten steel poured into the core layer is 2 / 5 to 5 / 6 of the amount of molten steel poured into the outer layer. Pour in stages, with a 30-40 second interval between each pour, and pour the core layer of molten steel in 20-30 stages.

[0036] Step C: After the outer layer of molten steel has been replaced, the overflow channel is blocked with high-temperature cement, and the entire cavity is filled with molten steel, that is, the riser is filled.

[0037] Step D: After the riser is filled, start pouring water from top to bottom 10-20 minutes later. After filling, sprinkle carbonized rice husks on the surface of the riser water.

[0038] Step E: After pouring, open the hot box 20-50 hours later, and then directly load it into a high-temperature furnace for normalizing treatment.

[0039] The present invention further requires that in step F, the normalizing temperature is 880-980℃, the heating time is ≥20h, and the cooling method is to first blow air for 40-100min until the temperature is 500-550℃ and then stop the air blowing, air cool for 60-240min and then load it into the furnace for tempering, the tempering temperature is 550-650℃, and the tempering time is 20-60h.

[0040] Step F: Roughly machine the blank, leaving a diameter allowance of 6-20 mm and a length allowance of ≥20 mm.

[0041] Step G: Perform final heat treatment on the product, and then refine it until the finished product is obtained.

[0042] like Figure 1 The 500x electron microscope image shown shows a carbide content of ≤1%, and the microstructure consists of tempered sorbite + a small amount of martensite + carbides, presenting as granular carbides. Figure 2 It is a conventional alloy cast steel with a microstructure of tempered sorbite + carbides; Figure 3 It is a high-chromium steel with a microstructure of martensite and carbides, and a carbide content of ≥8%.

[0043] The present invention will be further described in detail below with reference to embodiments:

[0044] Example 1

[0045] Using scrap steel, ferrochrome, ferromanganese, ferromolybdenum, and nickel plates as raw materials, the outer layer and core steel are smelted separately in an electric furnace. The outer layer composition meets the design specifications: C 0.39, Si 0.69, Mn 0.69, P 0.04, S 0.02, Cr 6.39, Ni 0.23, Mo 0.83, V 0.09, with the balance being Fe. The core material is C 0.60, Si 0.75, Mn 0.96, P 0.045, S 0.03, Cr 0.36, Ni 0.51, Mo 0.09, V 0.03. After the composition meets the specifications, the molten steel is heated to 1690℃ and tapped. Argon is blown at 0.25 MPa for 1-2 minutes before casting. The core steel is cast 2.5 minutes after the outer layer is cast. The raw billet is hot-opened and transferred to a high-temperature furnace for heating at 930℃ for 21 hours. After heating, air is blown for 65 minutes until the roller body temperature reaches 500-530℃, then the air is stopped. After air cooling for 65 minutes, it is loaded into the furnace for tempering, and then unloaded from the furnace after tempering. The roughing roller body diameter margin is 8mm, and the roller body length margin is 32mm. The roller body is preheated to 500℃. After preheating, an ultra-fast heating furnace is used to raise the temperature to 960℃ within 5 minutes, and the holding time is 50 minutes. After heating, it is water-cooled for 120 minutes, followed by air cooling for 35 minutes. After air cooling, it is loaded into the furnace for tempering at 580℃ for 35 hours. After heat treatment, subsequent processing is carried out to produce the finished product.

[0046] Example 2

[0047] Using scrap steel, ferrochrome, ferromanganese, ferromolybdenum, and nickel plates as raw materials, the outer layer and core steel are smelted separately in an electric furnace. The outer layer composition meets the design specifications: C 0.41, Si 0.71, Mn 0.72, P 0.045, S 0.03, Cr 5.43, Ni 0.53, Mo 0.93, V 0.06, with the balance being Fe. The core material is C 0.71, Si 0.78, Mn 0.99, P 0.05, S 0.029, Cr 0.39, Ni 0.56, Mo 0.05, V 0.06. After the composition meets the specifications, the molten steel is heated to 1680℃ and tapped. Argon is blown at 0.23 MPa for 1.5 minutes before casting. The core steel is cast 1.5 minutes after the outer layer is cast. The raw billet is hot-opened and transferred to a high-temperature furnace for heating at 950℃ for 21 hours. After heating, air is blown for 72 minutes until the roller body temperature reaches 515-520℃, then the air is stopped. After air cooling for 65 minutes, it is loaded into the furnace for tempering, and then unloaded from the furnace after tempering. The roughing roller body diameter margin is 8mm, and the roller body length margin is 35mm. The roller body is preheated to 510℃. After preheating, it is heated in an ultra-fast heating furnace to reach 930℃ within 6 minutes and held at that temperature for 45 minutes. After heating, it is water-cooled for 115 minutes, followed by air cooling for 39 minutes. After air cooling, it is loaded into the furnace for tempering at 560℃ for 39 hours. After heat treatment, subsequent processing is carried out to produce the finished product.

[0048] Example 3

[0049] Using scrap steel, ferrochrome, ferromanganese, ferromolybdenum, and nickel plates as raw materials, the outer layer and core steel are smelted separately in an electric furnace. The outer layer composition meets the design specifications: C 0.49, Si 0.75, Mn 0.78, P 0.043, S 0.028, Cr 5.49, Ni 0.56, Mo 0.73, V 0.13, with the balance being Fe. The core material is C 0.76, Si 0.79, Mn 0.89, P 0.045, S 0.029, Cr 0.29, Ni 0.36, Mo 0.05, V 0.06. After the composition meets the specifications, the molten steel is heated to 1675℃ and tapped. Argon is blown at 0.21 MPa for 1.8 minutes before casting. The core steel is cast 1.9 minutes after the outer layer is cast. The raw billet is hot-opened and transferred to a high-temperature furnace for heating at 940℃ for 31 hours. After heating, air is blown for 79 minutes until the roll body temperature reaches 510-515℃, then the air is stopped. After air cooling for 63 minutes, it is loaded into the furnace for tempering, and then unloaded from the furnace after tempering. The roughing roll body diameter margin is 9mm, and the roll body length margin is 32mm. The roll body is preheated to 530℃. After preheating, it is heated in an ultra-fast heating furnace to reach 960℃ within 6 minutes and held at that temperature for 49 minutes. After heating, it is water-cooled for 119 minutes, followed by air cooling for 41 minutes. After air cooling, it is loaded into the furnace for tempering at 550℃ for 41 hours. After heat treatment, subsequent processing is carried out to produce the finished product.

[0050] Example 4

[0051] Using scrap steel, ferrochrome, ferromanganese, ferromolybdenum, and nickel plates as raw materials, the outer layer and core steel are smelted separately in an electric furnace. The outer layer composition meets the design specifications: C 0.29, Si 0.71, Mn 0.70, P 0.03, S 0.022, Cr 4.49, Ni 0.36, Mo 0.61, V 0.07, with the balance being Fe. The core material is C 0.81, Si 0.59, Mn 0.71, P 0.035, S 0.028, Cr 0.21, Ni 0.26, Mo 0.06, V 0.08. After the composition meets the specifications, the molten steel is heated to 1673℃ and tapped. Argon is blown at 0.20 MPa for 1.7 minutes before casting. The core steel is cast 1.3 minutes after the outer layer is cast. The raw billet is hot-opened and transferred to a high-temperature furnace for heating at 930℃ for 29 hours. After heating, air is blown for 85 minutes until the roller body temperature reaches 505-510℃, then the air is stopped. After air cooling for 61 minutes, it is loaded into the furnace for tempering, and then unloaded from the furnace after tempering. The roughing roller body diameter margin is 7mm, and the roller body length margin is 35mm. The roller body is preheated to 525℃. After preheating, an ultra-fast heating furnace is used to raise the temperature to 925℃ within 6 minutes, and the holding time is 45 minutes. After heating, water cooling is performed for 111 minutes, followed by air cooling for 40 minutes. After air cooling, it is loaded into the furnace for tempering at 560℃ for 39 hours. After heat treatment, subsequent processing is carried out to produce the finished product.

[0052] Example 5

[0053] Using scrap steel, ferrochrome, ferromanganese, ferromolybdenum, and nickel plates as raw materials, the outer layer and core steel are smelted separately in an electric furnace. The outer layer composition meets the design specifications: C 0.23, Si 0.65, Mn 0.65, P 0.035, S 0.028, Cr 4.89, Ni 0.86, Mo 0.81, V 0.09, with the balance being Fe. The core material is C 0.71, Si 0.53, Mn 0.63, P 0.038, S 0.022, Cr 0.21, Ni 0.36, Mo 0.09, V 0.07. After the composition meets the specifications, the molten steel is heated to 1679℃ and tapped. Argon is blown at 0.23 MPa for 1.8 minutes before casting. The core steel is cast 1.4 minutes after the outer layer is cast. The raw billet is hot-opened and transferred to a high-temperature furnace for heating at 935℃ for 28 hours. After heating, air is blown for 86 minutes until the roll body temperature reaches 509-517℃, then the air is stopped. After air cooling for 63 minutes, it is loaded into the furnace for tempering, and then unloaded from the furnace after tempering. The roughing roll body diameter margin is 8mm, and the roll body length margin is 39mm. The roll body is preheated to 529℃. After preheating, an ultra-fast heating furnace is used to raise the temperature to 921℃ within 6 minutes, and the holding time is 48 minutes. After heating, it is water-cooled for 113 minutes, followed by air cooling for 13 minutes. After air cooling, it is loaded into the furnace for tempering at 550℃ for 36 hours. After heat treatment, subsequent processing is carried out to produce the finished product.

[0054] Example 6

[0055] Example 6 is a control example, using conventional alloy cast steel.

[0056] Implementation 7

[0057] Example 7 is a control example, using high-chromium steel rolls.

[0058] The tensile mechanical properties of the samples from Examples 1 to 7 were tested in accordance with the national standard GB / T 1503-2008. The test results are shown in Table 1.

[0059] Table 1. Results of tensile mechanical properties test of the products in the examples.

[0060]

[0061]

[0062] By comparing thermal crack resistant and fatigue resistant work rolls with alloy steel and high chromium steel, it is shown that the thermal crack resistant and fatigue resistant work rolls have significantly higher thermal crack resistance than alloy steel and high chromium steel products, and the neck strength is significantly higher than that of products with high chromium steel and other ductile iron as the neck material.

[0063] Actual rolling results show that the product is resistant to thermal cracking and fatigue. Figure 4 The roller service life is more than twice that of alloy steel, and the roller surface is smooth, while alloy steel ( Figure 5 Severe thermal cracking occurred after the machine was removed from the machine.

Claims

1. A composite steel cast roll comprising an outer layer and a core, characterized in that, The alloy element composition and its weight percentage of the outer layer are C: 0.3-1.2%, Si: 0.20-1.00%, Mn: 0.50-2.00%, P≤0.05, S≤0.03, Cr: 1.0-8.0%, Ni: 0.10-1.0%, Mo: 0.30-2.0%, V+W+Nb≤0.5%, and the rest is Fe and inevitable impurities; The alloy element composition and its weight percentage of the core are C: 0.5-1.5%, Si: 0.50-1.50%, Mn: 0.2-1.0%, P≤0.05, S≤0.03, Cr≤0.60%, Ni: 0.2-1.0, Mo≤0.50%, V≤0.50%, and the rest is Fe and inevitable impurities; The core composition C+ (Si+P) / 3≥ the outer layer composition C+ (Si+P) / 3; The structure is tempered sorbite + a small amount of tempered martensite + a small amount of carbide, and the carbide content is ≤1.0%.

2. A method of making a composite steel roll as claimed in claim 1, characterised in that, The method comprises the following steps: Step A: using scrap steel, ferrochrome, nickel plate, ferromolybdenum, and manganese iron raw materials for batching, adding into a smelting furnace, and smelting according to the alloy element composition and its weight percentage of the outer layer and the core, the smelting temperature is 1500-1600℃, the outer layer liquid steel reaches the design requirement, and then the temperature is raised to 1600-1700℃, and then the furnace is tapped and poured; the core molten steel smelting temperature is 1450-1550℃, the pouring core molten steel tapping temperature is 1500-1550℃, and the point riser tapping temperature is 1600-1650℃; Step B: using the principle of communicating vessels, the outer layer molten steel is poured in a bottom pouring manner to fill the entire cavity until reaching the overflow port, after pouring is completed, the core molten steel is poured after 1-10 minutes, the core molten steel quantity is 2 / 5-5 / 6 of the outer layer molten steel quantity, and the core molten steel is poured in multiple times with an interval of 10-40 seconds each time, and the core molten steel quantity is poured in 20-30 times; Step C: after the outer layer molten steel is replaced, the overflow groove is blocked with high-temperature cement, and the entire cavity is continuously poured to fill the riser; Step D: after the riser is filled, the riser is poured from top to bottom after 10-20 minutes, and carbonized rice husk is scattered on the upper surface of the filled riser; Step E: after pouring is completed, the box is opened after 20-50 hours, and the opened box is directly loaded into a high-temperature furnace for normalizing treatment; the normalizing temperature is 880-980℃, the cooling method is first blowing for 40-100 minutes until the temperature is 500-550℃, then stopping blowing, and then air cooling for 60-240 minutes before loading into the furnace for tempering; the tempering temperature is 550-650℃; Step F: rough machining is performed on the blank, the diameter direction allowance is 6-20mm, and the length direction allowance is ≥20mm; Step G: the product is finally heat treated, and then fine machining is performed until the finished product is obtained; The final heat treatment method adopts a high-efficiency high-temperature heat treatment method, and the specific heat treatment method is high-temperature quenching + tempering, and the radial and axial temperature differences within the working layer of 100mm need to be ensured to be within 10℃.

3. A method of manufacturing a composite steel roll according to claim 2, wherein The ladle for pouring the outer layer and the core steel in steps A and B is a bottom pouring ladle, the ladle for pouring the riser is a turning ladle, and the bottom funnel bricks are blown clean each time the bottom pouring ladle is poured.

4. The method for preparing a composite cast steel roll according to claim 2, characterized in that, The pouring in step C is completed in 2-4 times until the riser is filled.

5. The method for preparing a composite cast steel roll according to claim 2, characterized in that, The carbide rice husk thickness in step D is ≥100 mm.

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