Manufacturing method of high-toughness rolled steel guide

Abstract

The invention discloses a manufacturing method of a high-toughness rolled steel guide and guard device, and relates to the technical field of metallurgy. The high-toughness steel rolling guide is based on a medium-carbon high-chromium-nickel 4Cr18Ni alloy, and comprises the following elements in percentage by weight: 0.35 to 0.45 percent of C, 17 to 19 percent of Cr, 0.8 to 1.2 percent of Ni, 0.5 to 1.0 percent of Si, 0.5 to 1.0 percent of Mn and the balance of Fe and inevitable impurities. On the basis, through the high-temperature normalizing-tempering heat treatment technology, the toughness of the guide and guard material is greatly improved, meanwhile, the hardness and the abrasion resistance of the guide and guard material are considered, compared with a conventional quenching or annealing technology, the heat treatment equipment and time cost are further reduced, and high production and application value is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for manufacturing a high-toughness steel rolling guide. Background Art

[0002] The rolling guide is a key component in the rolling production line, and its main function is to guide the rolled piece to enter and exit the roller smoothly. Since the rolling guide is in a high temperature, high pressure, high friction and high corrosion environment for a long time, traditional materials (such as ordinary alloy steel) are difficult to meet its performance requirements, resulting in a short life of the guide and frequent replacement, which increases production costs and maintenance intensity. Therefore, the development of a high-performance rolling guide material has important industrial production significance.

[0003] The prior art often uses high-carbon alloy steel as an improved steel material for manufacturing rolling mill guides, which increases the life of the guides. For example, the Chinese invention with the authorization announcement number CN102534426B discloses a rolling mill guide alloy, including 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 elements such as C and Cr, the alloy has excellent hardness and wear resistance, but the high C content will affect its toughness, causing the guide to crack and break when impacted by steel; the invention does not solve the problem of the toughness of the alloy, and adds an ultra-high proportion of Ni (mass fraction 4.5-5.5%) and other alloying elements, which greatly increases the cost of production.

[0004] A Chinese invention with authorization announcement number CN102864372B discloses a wear-resistant rolling mill guide and a method for manufacturing the same, manufacturing a guide alloy that does not undergo high-temperature heat treatment, and recycling scrap steel to reduce costs, achieving high wear resistance, toughness and mechanical strength; however, its formula is very complex, production quality is difficult to control, and relatively scarce rare earth elements are used.

[0005] In summary, medium-carbon guide steels with high toughness are still relatively rare in the prior art, and generally contain overly complex additives, which is not conducive to the simplicity of production and cost control. Summary of the invention

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

[0007] The purpose of the present invention is to disclose a method for manufacturing a high-toughness steel rolling guide, comprising the following steps:

[0008] (1) The metal raw materials are melted in an electric arc furnace and then poured into a preheated mold for casting;

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

[0010] (3) The normalized castings are subjected to tempering treatment and then air-cooled to room temperature;

[0011] (4) The tempered castings are machined to obtain the high-toughness rolling guide;

[0012] The metal raw materials, by mass, include the following elements: 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 balance is Fe and unavoidable impurities.

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

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

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

[0016] Further, the tempering treatment is high-temperature tempering, and its temperature is 650 - 700 °C.

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

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

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

[0020] Further, the melting temperature in the electric arc furnace is 1600 - 1650 °C.

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

[0022] The beneficial effects of the technical solution of the present invention are:

[0023] 1. In the manufacturing method of the high-toughness rolling guide described in the present invention, the application of medium-carbon high-alloy steel in the guide material is developed. Especially when a relatively low proportion of carbon and a relatively high proportion of nickel are added, a rolling guide with both high hardness and extremely high toughness is obtained through subsequent heat treatment means, and its service life can be increased by 2.5 to 4 times compared with traditional materials.

[0024] 2. In the manufacturing method of the high-toughness rolling guide described in the present invention, the heat treatment method of high-temperature normalizing plus tempering is adopted for 4Cr18Ni steel with simple composition and low cost, achieving an effect similar to quenching and high-temperature tempering (i.e., quenching plus high-temperature tempering), and greatly saving production time and equipment costs. Specific Embodiments

[0025] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and should be understood as an illustration of the technical solutions of the present invention rather than a limitation.

[0026] A manufacturing method of a high-toughness rolling guide provided by the present invention includes the following steps:

[0027] (1) The metal raw materials are melted 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 normalized castings are subjected to tempering treatment and then air-cooled to room temperature.

[0030] (4) The tempered castings are machined to obtain the high-toughness rolling guide.

[0031] The metal raw materials, by mass, include the following elements: 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 are Fe and inevitable impurities.

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

[0033] The guiding device metal raw material of the present invention reduces the carbon content on the basis of conventional high-chromium cast iron guiding device materials, and significantly increases the content of Ni element, which is increased from generally less than 0.6% to 0.8-1.2%, in order to enhance the toughness, corrosion resistance and hardenability of the guiding device. The present invention also adopts the method of normalizing-tempering at high temperature to heat-treat the guiding device casting. Normalizing is the heat treatment method with the simplest equipment and operation and lower cost. However, it is generally considered that the hardness of high-chromium steel by normalizing treatment is significantly lower than that by quenching, and quenching treatment also has its limitations. Exceeding its optimal quenching temperature will instead cause the hardness of the steel to drop sharply. However, the inventor finds that normalizing the medium-carbon high-chromium steel at a temperature slightly higher than the conventional quenching temperature (for high-chromium steel, the conventional quenching temperature is 950-1050°C) can make the steel reach a hardness and wear resistance close to that of quenching, and save the quenching medium. This may be because at high temperatures where a large amount of eutectic carbides dissolve, the carbides will precipitate and coarsen along the grain boundaries during quenching, but fine and dispersed secondary carbides will be formed during normalizing. It should be noted that the "high temperature" in "normalizing at high temperature" does not merely refer to temperature generally, but describes that normalizing is carried out at a temperature not lower than the quenching temperature that the medium-carbon high-alloy steel should adopt by the conventional method.

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

[0035] Preferably, during the heating-up process of the high-temperature normalizing treatment, the heating-up rate is 40-80°C / h when the temperature is below 600°C, and the heating-up rate is 80-130°C / h when the temperature is above 600°C. Since the thermal conductivity of high-alloy steel varies significantly at low and high temperatures, it is preferred to increase the heating-up rate in stages.

[0036] Furthermore, the tempering treatment belongs to high-temperature tempering, and its temperature is 650-700°C.

[0037] The "high-temperature tempering" is a well-known term, which generally refers to heating the steel to 500-650°C after quenching to completely eliminate internal stress. Since high-temperature normalizing can obtain steel with a hardness close to that of quenching, in order to fully achieve the goal of improving the toughness of the guiding device steel, the present invention preferably adopts the method of high-temperature tempering. In addition to transforming martensite into tempered sorbite to improve toughness, it can also control the amount of retained austenite to avoid deformation of the steel during processing and use. Due to the high alloy content, the temperature range of high-temperature tempering in the present invention is higher than that of general steel.

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

[0039] Preferably, during the heating-up process of the tempering treatment, the heating-up rate is 40-70°C / h when the temperature is below 500°C, and the heating-up rate is 70-100°C when the temperature is above 500°C. The reason for heating up in stages is as described above.

[0040] Optionally, by mass, the metal raw material further includes Mo: 0.2 - 0.5% or W: 0.3 - 0.7%. The metal raw material may include a small amount of components Mo or W to weaken the second type of temper brittleness during tempering and cooling; however, since the guide is mainly used in the high-temperature environment of red-hot steel, the influence of temper brittleness is small. Therefore, adding inhibitory elements is not necessary considering the cost.

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

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

[0043] The following is specifically described in conjunction with embodiments. The experimental methods are all conventional methods unless otherwise specified, and the raw materials are all of conventional sources without difference unless otherwise specified.

[0044] Example 1

[0045] (1) Prepare raw materials according to the following element ratios: C: 0.45%, Cr: 19%, Ni: 1.2%, Si: 1.0%, Mn: 1.0%, and the balance is Fe; among them, the elements except Fe are crushed and mixed in the form of ferroalloys.

[0046] (2) Put the raw materials into an electric arc furnace and melt at 1650 °C.

[0047] (3) Pour the molten steel after melting into a mold preheated to 900 °C to obtain a casting.

[0048] (4) Perform high-temperature normalizing on the casting: heat up to 600 °C at a rate of 80 °C / h, then heat up to 1100 °C at a rate of 120 °C / h, hold for 2 h, and then air-cool to room temperature.

[0049] (5) Perform tempering on the casting: heat up to 500 °C at a rate of 70 °C / h, then heat up to 700 °C at a rate of 100 °C / h, hold for 3 h, and then air-cool to room temperature.

[0050] (6) Perform machining on the casting that has undergone normalizing and tempering to obtain the required rolling guide.

[0051] Example 2

[0052] (1) Prepare raw materials according to the following element ratios: C: 0.4%, Cr: 18%, Ni: 1.0%, Si: 0.8%, Mn: 0.6%, and the balance is Fe; among them, the elements except Fe are crushed and mixed in the form of ferroalloys.

[0053] (2) Put the raw materials into an electric arc furnace and melt 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: heated to 600 °C at a rate of 70 °C / h, then heated to 1050 °C at a rate of 100 °C / h, held for 1.75 h, and then air-cooled to room temperature.

[0056] (5) The casting is tempered: heated to 500 °C at a rate of 50 °C / h, then heated to 675 °C at a rate of 80 °C / h, held for 2.5 h, and then air-cooled to room temperature.

[0057] (6) The casting that has been normalized and tempered is machined to obtain the required rolling mill guard.

[0058] Example 3

[0059] (1) Raw materials are configured according to the following element ratios: C: 0.35%, Cr: 17%, Ni: 0.8%, Si: 0.5%, Mn: 0.5%, and the balance is Fe; the elements except Fe are crushed and mixed in the form of ferroalloys.

[0060] (2) The raw materials are put into 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: heated to 600 °C at a rate of 50 °C / h, then heated to 1000 °C at a rate of 80 °C / h, held for 1.5 h, and then air-cooled to room temperature.

[0063] (5) The casting is tempered: heated to 500 °C at a rate of 40 °C / h, then heated to 650 °C at a rate of 70 °C / h, held for 2 h, and then air-cooled to room temperature.

[0064] (6) The casting that has been normalized and tempered is machined to obtain the required rolling mill guard.

[0065] Example 4

[0066] The only difference between this example and Example 1 is that 0.4% of 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 mill guards obtained in each example and comparative example are tested, including their hardness, tensile strength, and impact toughness. The test results are shown in Table 1.

[0070] Table 1 Mechanical properties of rolling guides

[0071]

[0072] According to the above test results, the hardness of the rolling guide of the present invention reaches above 54 HRC, and the toughness is greatly improved compared with similar alloys (generally below 20 J / cm 2 ). Moreover, normalizing is used to replace quenching or annealing, greatly simplifying the heat treatment operation method. It can also be seen from the above table that the hardness and tensile strength of the guide material have a great relationship with the normalizing temperature, and increase steeply within the range of 900-1000 °C, while the impact toughness has little relationship with the normalizing temperature, and the room temperature impact toughness increases with the addition of a small amount of Mo.

[0073] In addition, the service lives of the rolling guides obtained in each example and comparative example in a high-impact production environment were also tested. The average steel passing amounts of the rolling guides obtained in Examples 1-4 and Comparative Example 1 were: 3724 t, 3469 t, 3045 t, 3740 t, and 2170 t, respectively.

[0074] Obviously, the above examples are only for clear illustration and not a limitation of the implementation mode. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description, and the obvious changes or modifications derived therefrom should still be regarded as the protection scope of the present invention.

Claims

1. A manufacturing method of a high-toughness rolling guide, characterized in that It includes the following steps: The metal raw material is melted in an electric arc furnace and then poured into a preheated mold for casting; The castings obtained by casting are subjected to normalizing treatment at high temperature and then air-cooled to room temperature; The normalized castings are subjected to tempering treatment and then air-cooled to room temperature; The tempered castings are machined to obtain the high-toughness rolling guide; The metal raw material, by mass, includes the following elements: 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 manufacturing method of the high-toughness rolling guide according to claim 1, characterized in that, The temperature of the high-temperature normalizing treatment is 1000 - 1100°C.

3. The manufacturing method of the high-toughness rolling guide according to claim 2, characterized in that, The holding time of the high-temperature normalizing treatment is 1.5 - 2 h.

4. The manufacturing method of the high-toughness rolling guide according to claim 2, characterized in that, During the heating process of the high-temperature normalizing treatment, the heating rate is 40 - 80°C / h below 600°C and 80 - 130°C / h above 600°C.

5. The manufacturing method of the high-toughness rolling guide according to claim 1, characterized in that, The tempering treatment is high-temperature tempering, and its temperature is 650 - 700°C.

6. The manufacturing method of the high-toughness rolling guide according to claim 5, characterized in that, The holding time of the tempering treatment is 2 - 3 h.

7. The manufacturing method of the high-toughness rolling guide according to claim 5, characterized in that, During the heating process of the tempering treatment, the heating rate is 40 - 70°C / h below 500°C and 70 - 100°C / h above 500°C.

8. The manufacturing method of the high-toughness rolling guide according to claim 5, characterized in that, The metal raw material, by mass, further includes Mo: 0.2 - 0.5% or W: 0.3 - 0.7%.

9. The manufacturing method of the high-toughness rolling guide according to claim 1, characterized in that The melting temperature in the electric arc furnace is 1600 - 1650°C.

10. The manufacturing method of the high-toughness rolling guide according to claim 1, characterized in that, The temperature of the preheated mold is 800 - 900°C.

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