A method for manufacturing a high-toughness rolling guide

Abstract

The application discloses a manufacturing method of high-toughness steel guide, and relates to the technical field of metallurgy.The high-toughness steel guide is based on a 4Cr18Ni alloy of medium-carbon high-chromium nickel, and the element composition of the 4Cr18Ni alloy comprises C: 0.35-0.45%, Cr: 17-19%, Ni: 0.8-1.2%, Si: 0.5-1.0%, Mn: 0.5-1.0%, and the rest is Fe and inevitable impurities.Based on the element composition, the high-toughness steel guide is subjected to high-temperature normalizing-tempering heat treatment technology, so that the toughness of the guide material is greatly improved, the hardness and wear resistance of the guide material are considered, compared with a conventional quenching or annealing process, the heat treatment equipment and time cost are reduced, and the high-toughness steel guide has high production application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a manufacturing method of high-toughness rolling guide. BACKGROUND

[0002] The rolling guide is a key component of the rolling production line, which mainly guides the rolling piece to enter and exit the roller. Since the rolling guide is in a high-temperature, high-pressure, high-friction and high-corrosion environment for a long time, the traditional material (such as ordinary alloy steel) cannot meet the performance requirements, resulting in short service life of the guide, frequent replacement, and increased production cost and maintenance intensity. Therefore, it is of great industrial production significance to develop a high-performance rolling guide material.

[0003] The prior art often uses high-carbon alloy steel as improved steel for manufacturing the rolling guide, which improves the service life of the guide. For example, a rolling mill guide alloy disclosed in a Chinese patent (CN102534426B) contains 1.15-1.25% by mass of C, 12.5-13.5% by mass of Cr, and iron and a high proportion of other alloying elements. Due to the high proportion of C, Cr and other elements, the hardness and wear resistance of the alloy are excellent, but the high C content affects the toughness, resulting in cracking and fracture of the guide when it is impacted by the steel; the invention does not solve the toughness problem of the alloy, and adds a very high proportion of Ni (4.5-5.5% by mass) and other alloying elements, greatly increasing the production cost.

[0004] A Chinese patent (CN102864372B) discloses a wear-resistant rolling mill guide and a manufacturing method thereof, which manufactures a guide alloy without high-temperature heat treatment, and recycles waste steel to reduce cost, achieving high wear resistance, toughness and mechanical strength; but the formula is very complex, the production quality is difficult to control, and rare earth elements are used.

[0005] In summary, medium-carbon guide steel with high toughness is still rare in the prior art, and generally contains too complex additive components, which is not conducive to the simplicity of production and cost control. SUMMARY

[0006] The present application aims to provide a manufacturing method of high-toughness rolling guide, which is based on medium-carbon high-chromium alloy steel 4Cr18, adds a high proportion of nickel and other alloying elements, and combines high-temperature normalizing and tempering heat treatment technology to achieve extremely high toughness and wear resistance, and also simplifies the production.

[0007] The present application aims to provide a manufacturing method of high-toughness rolling guide, which is based on medium-carbon high-chromium alloy steel 4Cr18, adds a high proportion of nickel and other alloying elements, and combines high-temperature normalizing and tempering heat treatment technology to achieve extremely high toughness and wear resistance, and also simplifies the production.

[0008] (1) the metal raw material is smelted in an electric arc furnace, and then poured into a preheated mold for casting;

[0009] (2) the castings obtained by casting are subjected to high-temperature normalizing treatment, and then air-cooled to room temperature;

[0010] (3) the castings after normalizing are subjected to tempering treatment, and then air-cooled to room temperature;

[0011] (4) the castings after tempering are subjected to mechanical processing to obtain the high-toughness rolled steel guide and guard;

[0012] The metal raw material comprises the following elements by mass: C: 0.35-0.45%, Cr: 17-19%, Ni: 0.8-1.2%, Si: 0.5-1.0%, Mn: 0.5-1.0%, and the rest is Fe and inevitable impurities.

[0013] Further, the temperature of the high-temperature normalizing treatment is 1000-1100℃.

[0014] Preferably, the holding time of the high-temperature normalizing treatment is 1.5-2h.

[0015] Preferably, in the heating process of the high-temperature normalizing treatment, the heating rate is 40-80℃ / h below 600℃, and the heating rate is 80-130℃ / h above 600℃.

[0016] Further, the tempering treatment belongs to high-temperature tempering, and the temperature is 650-700℃.

[0017] Preferably, the holding time of the tempering treatment is 2-3h.

[0018] Preferably, in the heating process of the tempering treatment, the heating rate is 40-70℃ / h below 500℃, and the heating rate is 70-100℃ above 500℃.

[0019] Optionally, the metal raw material further comprises Mo: 0.2-0.5% or W: 0.3-0.7% by mass.

[0020] Further, the smelting temperature in the electric arc furnace is 1600-1650℃.

[0021] Further, the temperature of the preheated mold is 800-900℃.

[0022] The technical scheme of the present application has the following beneficial effects:

[0023] 1. The manufacturing method of the high-toughness rolling guide and guard according to the application, the application of medium-carbon high-alloy steel in the guide and guard material is developed, especially in the case of adding lower proportion of carbon and higher proportion of nickel, the rolling guide and guard with high toughness and hardness is still obtained through subsequent heat treatment, and the service life thereof can be increased by 2.5-4 times compared with the traditional material.

[0024] 2. The manufacturing method of the high-toughness rolling guide and guard according to the application, the heat treatment mode of high-temperature normalizing plus tempering is adopted, the effect similar to quenching plus high-temperature tempering is achieved for the 4Cr18Ni type steel with simple composition and low cost, and the production time and equipment cost are greatly saved. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, purposes and effects realized by the application easy to understand, the technical solutions of the application are further described below in combination with specific embodiments. Obviously, the described embodiments are only part of the implementation manners of the application, and should be understood as the description but not the limitation of the technical solutions of the application.

[0026] The manufacturing method of the high-toughness rolling guide and guard according to the application comprises the following steps:

[0027] (1) the metal raw material is smelted in an electric arc furnace and then poured into a preheated mold for casting;

[0028] (2) the castings obtained by casting are subjected to high-temperature normalizing treatment and then air-cooled to room temperature;

[0029] (3) the castings after normalizing are subjected to tempering treatment and then air-cooled to room temperature;

[0030] (4) the castings after tempering are subjected to mechanical processing to obtain the high-toughness rolling guide and guard;

[0031] The metal raw material comprises the following elements by mass: C: 0.35-0.45%, Cr: 17-19%, Ni: 0.8-1.2%, Si: 0.5-1.0%, Mn: 0.5-1.0%, and the rest is Fe and inevitable impurities.

[0032] Further, the temperature of the high-temperature normalizing treatment is 1000-1100℃.

[0033] The guide metal material of the present application reduces the carbon content and significantly increases the content of Ni element, which is generally less than 0.6% to 0.8-1.2%, in order to enhance the toughness, corrosion resistance and hardenability of the guide. The guide castings are heat treated by high temperature normalizing and tempering. The normalizing is the simplest and lowest cost heat treatment method, but it is generally considered that the hardness of high chromium steel treated by normalizing is significantly lower than that treated by quenching, and the quenching treatment also has its limitations, and the hardness of the steel will decrease sharply when the quenching temperature exceeds the optimal quenching temperature. However, the inventors found that the steel can reach the hardness and wear resistance close to quenching when the medium carbon high chromium steel is normalized at a temperature slightly higher than the conventional quenching temperature (the conventional quenching temperature of high chromium steel is 950-1050℃), and the quenching medium is saved. This may be because at a high temperature at which eutectic carbide dissolves a lot, the carbide will precipitate and coarsen along the grain boundary during quenching, but fine secondary carbide will be formed during normalizing. It is worth noting that the "high temperature" in "high temperature normalizing" is not a general description of temperature, but describes that the normalizing is carried out at a temperature not lower than the quenching temperature of the medium carbon high alloy steel under conventional method.

[0034] Preferably, the holding time of the high temperature normalizing treatment is 1.5-2h.

[0035] Preferably, the heating rate is 40-80℃ / h below 600℃ and 80-130℃ / h above 600℃ during the heating process of the high temperature normalizing treatment. Since the thermal conductivity of high alloy steel is significantly different at low and high temperatures, the heating rate is preferably increased in stages.

[0036] Further, the tempering treatment belongs to high temperature tempering, and the temperature is 650-700℃.

[0037] The "high temperature tempering" is a known term, which generally refers to heating the steel to 500-650℃ after quenching to completely eliminate internal stress. Since the high temperature normalizing can obtain steel with hardness close to quenching, in order to fully achieve the goal of improving the toughness of the guide steel, the present application preferably uses high temperature tempering, which not only converts martensite to tempered sorbite to improve toughness, but also controls the amount of residual austenite to avoid deformation of the steel during processing and use. Due to the high alloy content, the temperature range of the high temperature tempering of the present application is higher than that of general steel.

[0038] Preferably, the holding time of the tempering treatment is 2-3h.

[0039] Preferably, the heating rate is 40-70℃ / h below 500℃ and 70-100℃ above 500℃ during the heating process of the tempering treatment. The reason for the staged heating is as described above.

[0040] Optionally, the metal raw material further comprises Mo: 0.2-0.5% or W: 0.3-0.7% by mass. The metal raw material can comprise a small amount of component Mo or W to weaken the second type of temper brittleness during tempering cooling; but since the guide is mainly used in the high-temperature environment of red steel, the influence of temper brittleness is small, and therefore it is not necessary to add the inhibiting element for cost consideration.

[0041] Further, the temperature of the smelting in the electric arc furnace is 1600-1650°C.

[0042] Further, the temperature of the preheated mold is 800-900°C.

[0043] The following will be specifically described with examples. The experimental methods are conventional methods unless otherwise specified, and the raw materials are conventional sources without distinction unless otherwise specified.

[0044] Example 1

[0045] (1) The raw materials are configured according to the following element ratio: C: 0.45%, Cr: 19%, Ni: 1.2%, Si: 1.0%, Mn: 1.0%, and the balance is Fe; wherein the elements other than Fe are mixed in the form of iron alloy powder.

[0046] (2) The raw materials are placed in an electric arc furnace and smelted at 1650°C.

[0047] (3) The molten steel after smelting is cast into a mold preheated to 900°C to obtain a casting.

[0048] (4) The casting is subjected to high-temperature normalizing: the temperature is raised to 600°C at a rate of 80°C / h, then the temperature is raised to 1100°C at a rate of 120°C / h, and the temperature is maintained for 2h, and then air-cooled to room temperature.

[0049] (5) The casting is tempered: the temperature is raised to 500°C at a rate of 70°C / h, then the temperature is raised to 700°C at a rate of 100°C / h, and the temperature is maintained for 3h, and then air-cooled to room temperature.

[0050] (6) The casting subjected to normalizing and tempering is machined to obtain the required rolled steel guide.

[0051] Example 2

[0052] (1) The raw materials are configured according to the following element ratio: C: 0.4%, Cr: 18%, Ni: 1.0%, Si: 0.8%, Mn: 0.6%, and the balance is Fe; wherein the elements other than Fe are mixed in the form of iron alloy powder.

[0053] (2) The raw materials are placed in an electric arc furnace and smelted at 1625°C.

[0054] (3) The molten steel after smelting is cast into a mold preheated to 850°C to obtain a casting.

[0055] (4) The casting is subjected to high-temperature normalizing: heating at a rate of 70°C / h to 600°C, then heating at a rate of 100°C / h to 1050°C, holding for 1.75 h, and then air cooling to room temperature.

[0056] (5) The casting is subjected to tempering: heating at a rate of 50°C / h to 500°C, then heating at a rate of 80°C / h to 675°C, holding for 2.5 h, and then air cooling to room temperature.

[0057] (6) The casting subjected to normalizing and tempering is machined to obtain a desired rolling guide.

[0058] Example 3

[0059] (1) The raw materials are prepared according to the following element ratio: C: 0.35%, Cr: 17%, Ni: 0.8%, Si: 0.5%, Mn: 0.5%, and the balance being Fe; and the elements other than Fe are mixed in the form of iron alloy powder.

[0060] (2) The raw materials are placed in an electric arc furnace and smelted at 1600°C.

[0061] (3) The molten steel after smelting is cast into a mold preheated to 800°C to obtain a casting.

[0062] (4) The casting is subjected to high-temperature normalizing: heating at a rate of 50°C / h to 600°C, then heating at a rate of 80°C / h to 1000°C, holding for 1.5 h, and then air cooling to room temperature.

[0063] (5) The casting is subjected to tempering: heating at a rate of 40°C / h to 500°C, then heating at a rate of 70°C / h to 650°C, holding for 2 h, and then air cooling to room temperature.

[0064] (6) The casting subjected to normalizing and tempering is machined to obtain a desired rolling guide.

[0065] Example 4

[0066] The only difference between this example and Example 1 is that 0.4% Mo is added to the raw materials.

[0067] Comparative Example 1

[0068] The only difference between this comparative example and Example 1 is that the holding temperature of normalizing is reduced to 900°C.

[0069] The mechanical properties of the rolling guides obtained in each example and comparative example, including hardness, tensile strength, and impact toughness, are tested. The test results are shown in Table 1.

[0070] Table 1 Mechanical properties of the rolling guide

[0071]

[0072] According to the above test results, the hardness of the rolling guide reaches 54HRC or above, and the toughness is greatly improved compared with similar alloys (generally 20J / cm 2 From the above table, it can be seen that the hardness and tensile strength of the guide material are greatly related to the normalizing temperature, and increase sharply within 900-1000℃, while the impact toughness is not greatly related to the normalizing temperature, and the room temperature impact toughness is increased by adding a small amount of Mo.

[0073] In addition, the service life of the rolling guide obtained from each example and the comparative example in a high-impact production environment is tested, and the average steel passing amount of the rolling guide obtained from examples 1-4 and comparative example 1 is 3724t, 3469t, 3045t, 3740t and 2170t, respectively.

[0074] Obviously, the above examples are only examples for clearly illustrating, but not limitation to the embodiments. Other different forms of changes or variations can be made by those skilled in the art on the basis of the above description, and the obvious changes or variations derived therefrom should be considered as the protection scope of the present application.

Claims

1. A method of manufacturing a high toughness mill guide and guard, characterized by, The method comprises the following steps: melting the metal raw material in an electric arc furnace and then pouring into a preheated mold for casting; the castings obtained by casting are subjected to high-temperature normalizing treatment and then air-cooled to room temperature; wherein, in the heating process of the high-temperature normalizing treatment, the heating rate is 40-80 ℃ / h below 600 ℃ and 80-130 ℃ / h above 600 ℃; the temperature of the high-temperature normalizing treatment is 1000-1100 ℃; the castings after normalizing are subjected to tempering treatment and then air-cooled to room temperature; wherein, in the heating process of the tempering treatment, the heating rate is 40-70 ℃ / h below 500 ℃ and 70-100 ℃ above 500 ℃; the tempering treatment belongs to high-temperature tempering, and the temperature is 650-700 ℃; the castings after tempering are subjected to mechanical processing to obtain the high-toughness rolled steel guide and guard; the metal raw material comprises the following elements by mass: C: 0.35-0.45%, Cr: 17-19%, Ni: 0.8-1.2%, Si: 0.5-1.0%, Mn: 0.5-1.0%, and the rest is Fe and inevitable impurities.

2. The method of claim 1, wherein The holding time of the high-temperature normalizing treatment is 1.5-2 h.

3. The method of claim 1, wherein the high toughness guide and guard for rolled steel is characterized by, The holding time of the tempering treatment is 2-3 h.

4. The method of claim 1, wherein The metal raw material further comprises Mo: 0.2-0.5% or W: 0.3-0.7% by mass.

5. The method of claim 1, wherein the high toughness guide and guard for rolled steel is characterized by The temperature of the melting in the electric arc furnace is 1600-1650 ℃.

6. The method of claim 1, wherein The temperature of the preheated mold is 800-900 ℃.

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