Preparation method of peritectic steel large forged circle

Abstract

The invention discloses a preparation method of a peritectic steel large forged circle, and relates to the technical field of forged circle manufacturing, and the preparation method comprises the following steps: S1, molten steel pouring; s2, the red mold enters a slow cooling pit for heat preservation; s3, digging out of the pit; step S4, surface cleaning; s5, steel ingot preheating; s6, forging and forming; and S7, heat treatment. The peritectic steel large forged circle manufactured through the manufacturing method of the peritectic steel large forged circle is few in surface crack, high in black skin yield and large in yield strength.

Description

Technical Field

[0001] The invention relates to the technical field of forged circle manufacturing, and in particular to a method for preparing a large forged circle of peritectic steel. Background Art

[0002] Peritectic steel is a special steel that forms a large number of peritectics on the surface of the steel. The peritectics are mainly composed of iron carbide and other elements. The chemical composition of peritectic steel is complex, and it contains a large amount of alloying elements, such as molybdenum, chromium, cobalt, tungsten, etc., to improve its strength, hardness and wear resistance. Peritectic steel has excellent properties such as high strength, high hardness, high wear resistance and high toughness. It is often used to manufacture high-strength and high-wear-resistant parts such as cutting tools, molds, and bearings. Peritectic steel large forging round is one of the common peritectic steel materials. It has a wide range of applications, a large market demand, and higher and higher performance requirements.

[0003] The surface of peritectic steel large forging round is prone to cracks during the forging process, mainly because the molten steel is overheated during the pouring process, which delays the solidification of the molten steel and reduces the thickness of the shell. At the same time, it causes the shell temperature to increase and move to the brittle zone of the steel, aggravating the crack tendency. In addition, the liquid level of the molten steel in the crystallizer fluctuates greatly, making the shell in the crystallizer unable to grow evenly, which is the cause of the formation of longitudinal cracks in the shell of the cast billet. The peritectic steel large forging round made by the existing conventional formula and process has more or less technical defects such as low black skin yield rate and the yield strength needs to be further improved.

[0004] In order to solve the above problems, a Chinese invention patent with application publication number CN117816916A discloses a crack-sensitive peritectic steel large forging round and a preparation method thereof, which is applied in the technical field of preparation of peritectic steel large forging round. The invention adopts high-basicity protective slag in the process of preparing crack-sensitive peritectic steel, so as to form a slag film with high thermal resistance on the wall of the crystallizer, reduce the heat conduction between the crystallizer and the billet shell, achieve the purpose of slow cooling of the crystallizer, ensure the uniform growth of the raw billet shell in the crystallizer, eliminate the cause of the formation of longitudinal cracks in the raw billet shell of the cast billet, and improve the flow field in the crystallizer, mainly by changing the heat flow ratio of the narrow and wide sides of the crystallizer, appropriately reducing the heat conductivity of the narrow side, so that the heat flow ratio of the narrow side to the wide side is 0.8-0.9, and the longitudinal crack index of the slab surface in this range can be minimized, and the superheat of the molten steel is greatly reduced, which can avoid the delay of molten steel solidification and the thinning of the billet shell thickness, while causing the billet shell temperature to increase and move to the brittle zone of the steel, thereby aggravating the crack tendency. However, the yield rate and yield strength of large forged black round skin of peritectic steel produced by this method still need to be further improved. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing large forged peritectic steel rounds with few surface cracks, high black skin yield and high yield strength. The preparation method is simple and easy to implement, has low dependence on equipment, consumes less energy, is suitable for continuous large-scale production, and has high promotion and application value.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a large forged circle of peritectic steel, comprising the following steps:

[0007] Step S1, molten steel pouring: a continuous casting machine is used for molten steel pouring, and protective slag is placed in a crystallizer, the thickness of the liquid slag layer is 9-12 mm, and the slag consumption is 0.4-0.45 kg per ton of steel; the molten steel comprises the following components by weight percentage: C: 0.08%-0.15%, Si: 0.1%-0.4%, Mn: 0.5%-0.7%, Cr: 0.8%-1.2%, Ni: 0.1%-0.3%, Ti: 0.1%-0.3%, Mo: 0.3-0.5%, Hf: 0.01%-0.03%, rare earth elements: 0.01%-0.03%, Te: 0.001%-0.003%, and the balance is Fe and unavoidable impurities;

[0008] Step S2, red-envelope demoulding and entering slow cooling pit for heat preservation: after the molten steel is poured, let it stand, measure the temperature of the middle part of the ingot mold during the standing period, when the temperature is 660-500℃, red-envelope steel is taken out and entered into slow cooling pit for heat preservation;

[0009] Step S3, exiting the pit: measuring the surface temperature of the steel ingot during the heat preservation period, when the temperature is ≤200°C, the steel ingot is exited from the pit for air cooling;

[0010] Step S4, surface cleaning: the steel ingot is naturally cooled to below 70°C after leaving the pit, and is ground with a grinding machine to remove surface defects, and the riser end is cleaned with a flame;

[0011] Step S5, preheating the steel ingot: performing programmed temperature preheating treatment on the steel ingot;

[0012] Step S6, forging: hoisting the preheated steel ingot to the forging machine to start forging;

[0013] Step S7, heat treatment: heat treatment is performed on the rough forged round product formed by forging, and then polishing treatment is performed to obtain a large forged round of peritectic steel.

[0014] Preferably, the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of (3-5):(0.8-1.2):(0.1-0.3).

[0015] Preferably, in step S1, the heat flow ratio between the narrow and wide sides of the crystallizer is 0.75-0.95, and the cold water inlet temperature is above 25°C.

[0016] Preferably, the protective slag in step S1 includes the following components in parts by weight: 3-5 parts of strontium oxide, 6-8 parts of titanium oxide, 1-3 parts of calcium fluoride, 2-4 parts of molybdenum oxide, 8-10 parts of sodium oxide, 1-3 parts of cesium oxide, 2-4 parts of gallium oxide, 1-3 parts of cobalt oxide, 3-5 parts of copper oxide, and 1-3 parts of boron oxide.

[0017] Preferably, the preheating treatment in step S5 is specifically as follows: heating from room temperature to 600-700°C at a heating rate of 1-3°C / min, keeping warm for 2-3h, then heating to 780-880°C at a heating rate of 3-6°C / min, keeping warm for 1-3h, then heating to 900-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.5-1.2h, and finally heating to 1210-1270°C at a rate of 10-12°C / min, keeping warm for 3-5h.

[0018] Preferably, the total forging ratio of the forging in step S6 is (3-5):1; the start forging temperature during the forging process is 1200-1250°C, and the final forging temperature is 760-860°C.

[0019] Preferably, the heat treatment in step S7 includes normalizing, annealing and tempering performed sequentially.

[0020] Preferably, the normalizing treatment is carried out at a temperature of 920-960°C for 1-2 hours, followed by cooling in air; the annealing treatment is carried out at a temperature of 550-650°C for 0.5-1.5 hours; the tempering treatment is a two-stage tempering treatment, the first stage tempering treatment is carried out at a temperature of 580-680°C for 1-2 hours, the second stage tempering treatment is carried out at a temperature of 200-250°C for 1-3 hours. DETAILED DESCRIPTION

[0021] The preferred embodiments of the present invention will be described in detail below.

[0022] A method for preparing a large peritectic steel forging circle comprises the following steps:

[0023] Step S1, molten steel pouring: a continuous casting machine is used for molten steel pouring, and protective slag is placed in a crystallizer, the thickness of the liquid slag layer is 9-12 mm, and the slag consumption is 0.4-0.45 kg per ton of steel; the molten steel comprises the following components by weight percentage: C: 0.08%-0.15%, Si: 0.1%-0.4%, Mn: 0.5%-0.7%, Cr: 0.8%-1.2%, Ni: 0.1%-0.3%, Ti: 0.1%-0.3%, Mo: 0.3-0.5%, Hf: 0.01%-0.03%, rare earth elements: 0.01%-0.03%, Te: 0.001%-0.003%, and the balance is Fe and unavoidable impurities;

[0024] Step S2, red-envelope demoulding and entering slow cooling pit for heat preservation: after the molten steel is poured, let it stand, measure the temperature of the middle part of the ingot mold during the standing period, when the temperature is 660-500℃, red-envelope steel is taken out and entered into slow cooling pit for heat preservation;

[0025] Step S3, exiting the pit: measuring the surface temperature of the steel ingot during the insulation period, when the temperature is ≤200°C, the steel ingot is exited from the pit for air cooling;

[0026] Step S4, surface cleaning: the steel ingot is naturally cooled to below 70°C after leaving the pit, and is ground with a grinding machine to remove surface defects, and the riser end is cleaned with a flame;

[0027] Step S5, preheating the steel ingot: performing programmed temperature preheating treatment on the steel ingot;

[0028] Step S6, forging: hoisting the preheated steel ingot to the forging machine to start forging;

[0029] Step S7, heat treatment: heat treatment is performed on the rough forged round product formed by forging, and then polishing treatment is performed to obtain a large forged round of peritectic steel.

[0030] Preferably, the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of (3-5):(0.8-1.2):(0.1-0.3).

[0031] Preferably, in step S1, the heat flow ratio between the narrow and wide sides of the crystallizer is 0.75-0.95, and the cold water inlet temperature is above 25°C.

[0032] Preferably, the protective slag in step S1 includes the following components in parts by weight: 3-5 parts of strontium oxide, 6-8 parts of titanium oxide, 1-3 parts of calcium fluoride, 2-4 parts of molybdenum oxide, 8-10 parts of sodium oxide, 1-3 parts of cesium oxide, 2-4 parts of gallium oxide, 1-3 parts of cobalt oxide, 3-5 parts of copper oxide, and 1-3 parts of boron oxide.

[0033] Preferably, the preheating treatment in step S5 is specifically as follows: heating from room temperature to 600-700°C at a heating rate of 1-3°C / min, keeping warm for 2-3h, then heating to 780-880°C at a heating rate of 3-6°C / min, keeping warm for 1-3h, then heating to 900-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.5-1.2h, and finally heating to 1210-1270°C at a rate of 10-12°C / min, keeping warm for 3-5h.

[0034] Preferably, the total forging ratio of the forging in step S6 is (3-5):1; the start forging temperature during the forging process is 1200-1250°C, and the final forging temperature is 760-860°C.

[0035] Preferably, the heat treatment in step S7 includes normalizing, annealing and tempering performed sequentially.

[0036] Preferably, the normalizing treatment is carried out at a temperature of 920-960°C for 1-2 hours, followed by cooling in air; the annealing treatment is carried out at a temperature of 550-650°C for 0.5-1.5 hours; the tempering treatment is a two-stage tempering treatment, the first stage tempering treatment is carried out at a temperature of 580-680°C for 1-2 hours, the second stage tempering treatment is carried out at a temperature of 200-250°C for 1-3 hours.

[0037] Due to the application of the above technical scheme, the patent of the present invention has the following advantages compared with the prior art: the present invention gives the product the advantages of fewer surface cracks, high black skin yield rate and high yield strength through the reasonable design of molten steel composition formula, protective slag composition formula, preheating temperature gradient, forging process and heat treatment process. The preparation method involved in the present invention is simple and easy to operate, has low dependence on equipment, low energy consumption, is suitable for continuous large-scale production, and has high promotion and application value.

[0038] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0039] Example 1

[0040] A method for preparing a large peritectic steel forging circle comprises the following steps:

[0041] Step S1, molten steel pouring: a continuous casting machine is used for molten steel pouring, and protective slag is placed in a crystallizer, the thickness of the liquid slag layer is 9 mm, and the slag consumption is 0.4 kg per ton of steel; the molten steel includes the following components in weight percentage: C: 0.08%, Si: 0.1%, Mn: 0.5%, Cr: 0.8, Ni: 0.1, Ti: 0.1%, Mo: 0.3, Hf: 0.01, rare earth elements: 0.01%, Te: 0.001%, and the balance is Fe and unavoidable impurities;

[0042] Step S2, red-envelope demoulding and entering slow cooling pit for heat preservation: after the molten steel is poured, let it stand, measure the temperature of the middle part of the ingot mold during the standing period, and when the temperature is 660°C, red-envelope steel is taken out and placed in slow cooling pit for heat preservation;

[0043] Step S3, exiting the pit: measuring the surface temperature of the steel ingot during the insulation period, when the temperature is ≤200°C, the steel ingot is exited from the pit for air cooling;

[0044] Step S4, surface cleaning: the steel ingot is naturally cooled to below 70°C after leaving the pit, and is ground with a grinding machine to remove surface defects, and the riser end is cleaned with a flame;

[0045] Step S5, preheating the steel ingot: performing programmed temperature preheating treatment on the steel ingot;

[0046] Step S6, forging: hoisting the preheated steel ingot to the forging machine to start forging;

[0047] Step S7, heat treatment: heat treatment is performed on the rough forged round product formed by forging, and then polishing treatment is performed to obtain a large forged round of peritectic steel.

[0048] The rare earth elements are Ce, Nd and Er mixed in a mass ratio of 3:0.8:0.1.

[0049] In step S1, the heat flow ratio between the narrow and wide sides of the crystallizer is 0.75, and the cold water inlet temperature is above 25°C.

[0050] The protective slag in step S1 includes the following components in parts by weight: 3 parts of strontium oxide, 6 parts of titanium oxide, 1 part of calcium fluoride, 2 parts of molybdenum oxide, 8 parts of sodium oxide, 1 part of cesium oxide, 2 parts of gallium oxide, 1 part of cobalt oxide, 3 parts of copper oxide, and 1 part of boron oxide.

[0051] The preheating treatment in step S5 is specifically as follows: heating from room temperature to 600°C at a heating rate of 1°C / min, keeping warm for 2 hours, then heating to 780°C at a heating rate of 3°C / min, keeping warm for 1 hour, then heating to 900°C at a heating rate of 8°C / min, keeping warm for 0.5 hours, and finally heating to 1210°C at a rate of 10°C / min, keeping warm for 3 hours.

[0052] The total forging ratio of the forging in step S6 is 3:1; the starting forging temperature during the forging process is 1200°C and the final forging temperature is 760°C.

[0053] The heat treatment in step S7 includes normalizing, annealing and tempering in sequence. The normalizing temperature is 920°C for 1 hour, followed by cooling in air; the annealing temperature is 550°C for 0.5 hour; the tempering is a two-stage tempering treatment, the first stage tempering temperature is 580°C for 1 hour, and the second stage tempering temperature is 200°C for 1 hour.

[0054] Example 2

[0055] A method for preparing a large forged round of peritectic steel, which is basically the same as Example 1, except that the molten steel includes the following components in percentage by weight: C: 0.1%, Si: 0.2%, Mn: 0.55%, Cr: 0.9%, Ni: 0.15%, Ti: 0.15%, Mo: 0.35%, Hf: 0.015%, rare earth elements: 0.015%, Te: 0.0015%, and the balance is Fe and inevitable impurities; the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of 3.5:0.9:0.15; the protective slag includes the following components in parts by weight: 3.5 parts of strontium oxide, 6.5 parts of titanium oxide, 1.5 parts of calcium fluoride, 2.5 parts of molybdenum oxide, 8.5 parts of sodium oxide, 1.5 parts of cesium oxide, 2.5 parts of gallium oxide, 1.5 parts of cobalt oxide, 3.5 parts of copper oxide, and 1.5 parts of boron oxide.

[0056] Example 3

[0057] A method for preparing a large forged round of peritectic steel, which is basically the same as Example 1, except that the molten steel includes the following components in percentage by weight: C: 0.13%, Si: 0.25%, Mn: 0.6%, Cr: 1%, Ni: 0.2%, Ti: 0.2%, Mo: 0.4%, Hf: 0.02%, rare earth elements: 0.02%, Te: 0.002%, and the balance is Fe and inevitable impurities; the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of 4:1:0.2; the protective slag includes the following components in parts by weight: 4 parts of strontium oxide, 7 parts of titanium oxide, 2 parts of calcium fluoride, 3 parts of molybdenum oxide, 9 parts of sodium oxide, 2 parts of cesium oxide, 3 parts of gallium oxide, 2 parts of cobalt oxide, 4 parts of copper oxide, and 2 parts of boron oxide.

[0058] Example 4

[0059] A method for preparing a large forged round of peritectic steel, which is basically the same as Example 1, except that the molten steel includes the following components in percentage by weight: C: 0.14%, Si: 0.35%, Mn: 0.65%, Cr: 1.1%, Ni: 0.25%, Ti: 0.25%, Mo: 0.45%, Hf: 0.025%, rare earth elements: 0.025%, Te: 0.0025%, and the balance is Fe and inevitable impurities; the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of 4.5:1.1:0.25; the protective slag includes the following components in parts by weight: 4.5 parts of strontium oxide, 7.5 parts of titanium oxide, 2.5 parts of calcium fluoride, 3.5 parts of molybdenum oxide, 9.5 parts of sodium oxide, 2.5 parts of cesium oxide, 3.5 parts of gallium oxide, 2.5 parts of cobalt oxide, 4.5 parts of copper oxide, and 2.5 parts of boron oxide.

[0060] Example 5

[0061] A method for preparing a large forged round of peritectic steel, which is basically the same as Example 1, except that the molten steel includes the following components in percentage by weight: C: 0.15%, Si: 0.4%, Mn: 0.7%, Cr: 1.2%, Ni: 0.3%, Ti: 0.3%, Mo: 0.5%, Hf: 0.03%, rare earth elements: 0.03%, Te: 0.003%, and the balance is Fe and inevitable impurities; the rare earth elements are Ce, Nd, and Er mixed in a mass ratio of 5:1.2:0.3; the protective slag includes the following components in parts by weight: 5 parts of strontium oxide, 8 parts of titanium oxide, 3 parts of calcium fluoride, 4 parts of molybdenum oxide, 10 parts of sodium oxide, 3 parts of cesium oxide, 4 parts of gallium oxide, 3 parts of cobalt oxide, 5 parts of copper oxide, and 3 parts of boron oxide.

[0062] Comparative Example 1

[0063] A method for preparing a large forged circle of peritectic steel is basically the same as that of Example 1, except that Te, rare earth elements and strontium oxide are not added.

[0064] Comparative Example 2

[0065] A method for preparing a large forged circle of peritectic steel is basically the same as that of Example 1, except that Mo, Hf, cesium oxide and calcium fluoride are not added.

[0066] In order to further illustrate the beneficial technical effects of each product, relevant performance tests were conducted on each product. The test methods refer to the current national standards or conventional methods in this field. The test results are shown in Table 1.

[0067] Table 1

[0068] project Yield Strength Black leather yield rate unit MPa ％ Example 1 923 94.2 Example 2 930 95.0 Example 3 935 95.6 Example 4 946 96.6 Example 5 955 97.2 Comparative Example 1 900 89.0 Comparative Example 2 892 91.7

[0069] It can be seen from Table 1 that the peritectic steel large forged rounds produced by the preparation method of the peritectic steel large forged rounds in the embodiment of the present invention have higher yield strength and black skin yield rate, and the combined use of Te, rare earth elements, strontium oxide, Mo, Hf, cesium oxide and calcium fluoride is beneficial to improving the above properties.

[0070] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a large forged circle of peritectic steel, characterized in that: The steps include: Step S1, molten steel pouring: a continuous casting machine is used for molten steel pouring, and protective slag is placed in a crystallizer, the thickness of the liquid slag layer is 9-12 mm, and the slag consumption is 0.4-0.45 kg per ton of steel; the molten steel comprises the following components by weight percentage: C: 0.08%-0.15%, Si: 0.1%-0.4%, Mn: 0.5%-0.7%, Cr: 0.8%-1.2%, Ni: 0.1%-0.3%, Ti: 0.1%-0.3%, Mo: 0.3-0.5%, Hf: 0.01%-0.03%, rare earth elements: 0.01%-0.03%, Te: 0.001%-0.003%, and the balance is Fe and unavoidable impurities; Step S2, red-envelope demoulding and entering slow cooling pit for heat preservation: after the molten steel is poured, let it stand, measure the temperature of the middle part of the ingot mold during the standing period, when the temperature is 660-500℃, red-envelope steel is taken out and entered into slow cooling pit for heat preservation; Step S3, exiting the pit: measuring the surface temperature of the steel ingot during the heat preservation period, when the temperature is ≤200°C, the steel ingot is exited from the pit for air cooling; Step S4, surface cleaning: the steel ingot is naturally cooled to below 70°C after leaving the pit, and is ground with a grinding machine to remove surface defects, and the riser end is cleaned with a flame; Step S5, preheating the steel ingot: performing programmed temperature preheating treatment on the steel ingot; Step S6, forging: hoisting the preheated steel ingot to the forging machine to start forging; Step S7, heat treatment: heat treatment is performed on the rough forged round product formed by forging, and then polishing treatment is performed to obtain a large forged round of peritectic steel.

2. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: The rare earth elements are Ce, Nd and Er mixed in a mass ratio of (3-5):(0.8-1.2):(0.1-0.3).

3. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: In step S1, the heat flow ratio between the narrow and wide sides of the crystallizer is 0.75-0.95, and the cold water inlet temperature is above 25°C.

4. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: The protective slag in step S1 includes the following components in parts by weight: 3-5 parts of strontium oxide, 6-8 parts of titanium oxide, 1-3 parts of calcium fluoride, 2-4 parts of molybdenum oxide, 8-10 parts of sodium oxide, 1-3 parts of cesium oxide, 2-4 parts of gallium oxide, 1-3 parts of cobalt oxide, 3-5 parts of copper oxide, and 1-3 parts of boron oxide.

5. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: The preheating treatment in step S5 is specifically as follows: heating from room temperature to 600-700°C at a heating rate of 1-3°C / min, keeping warm for 2-3h, then heating to 780-880°C at a heating rate of 3-6°C / min, keeping warm for 1-3h, then heating to 900-1050°C at a heating rate of 8-10°C / min, keeping warm for 0.5-1.2h, and finally heating to 1210-1270°C at a rate of 10-12°C / min, keeping warm for 3-5h.

6. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: The total forging ratio of the forging in step S6 is (3-5):1; the starting forging temperature during the forging process is 1200-1250°C, and the final forging temperature is 760-860°C.

7. The method for preparing a large peritectic steel forging circle according to claim 1, characterized in that: The heat treatment in step S7 includes normalizing, annealing and tempering performed in sequence.

8. The method for preparing a large peritectic steel forging circle according to claim 7, characterized in that: The normalizing treatment is performed at a temperature of 920-960° C. for 1-2 hours, followed by cooling in air.

9. The method for preparing a large peritectic steel forging circle according to claim 7, characterized in that: The annealing temperature is 550-650° C., and the annealing time is 0.5-1.5 h.

10. The method for preparing a large peritectic steel forging circle according to claim 7, characterized in that: The tempering treatment is a two-stage tempering treatment, the temperature of the first stage tempering treatment is 580-680°C, the insulation time is 1-2h, and the temperature of the second stage tempering treatment is 200-250°C, the insulation time is 1-3h.