Method for improving wheel grain size mixed crystal and surface decarburization, wheel

Abstract

The invention provides a method and a wheel for improving the grain size mixing and surface decarburization of a wheel, and belongs to the field of wheel steel rolling. The invention controls the chromium and manganese content of the wheel, Cr reduces the diffusion rate of carbon, forms a dense oxide film layer on the metal surface to inhibit the penetration of oxygen; Mn reacts with oxygen to generate a stable manganese oxide film, which prevents further decarburization. The continuous casting parameters are controlled so that the depth of the quenching layer of the ingot is 15mm-25mm, and the grains of the quenching layer are ≤100μm; the heating parameters are controlled, and the residual oxygen content in the furnace is controlled to 3%-5% to limit the sensitivity of decarburization. At the same time, the descaling pressure is adjusted to more than 120bar to avoid decarburization in the residual oxide scale area. The wheel expansion speed during rolling meets the formula V=0.12×(12-T / 120)×[1.7+2.5×C+0.6×(Si+Mn)+0.3×Cr], improves the cooling uniformity of the wheel, and the grain size difference is within the range of 2 levels.

Description

Technical Field

[0001] The invention belongs to the field of steel rolling, and in particular relates to a method for improving wheel grain size mixed crystal and surface decarburization, and a wheel. Background Art

[0002] Wheel decarburization is one of the main defects of rail surface quality, which directly leads to reduced wheel surface hardness and poor wear resistance, affecting product qualification rate. In order to minimize the depth of wheel surface decarburization layer, the inevitable defects of wheel surface decarburization layer control technology during production have become one of the research focuses.

[0003] The Chinese patent with the publication number CN 101857452 A published on October 13, 2010 discloses an anti-oxidation and decarburization coating during steel billet rolling and its preparation method. The raw materials of the anti-oxidation and decarburization coating are 20-60 parts of vanadium tailings, 0-40 parts of sintering agent, and 30-60 parts of binder. The anti-oxidation and decarburization coating of the steel billet is applied on the surface of the heavy rail steel specimen (the heavy rail steel specimen must be cleaned and degreased before application, and then the pretreatment liquid is applied to increase the adhesion between the coating and the steel billet. The pretreatment liquid is the binder in the anti-oxidation and decarburization coating). The anti-oxidation and decarburization performance of the anti-oxidation and decarburization coating on the steel billet is tested under the heat treatment condition of 1250℃ for 3 hours.

[0004] The Chinese patent with the publication number CN 105315821 A published on February 10, 2016 discloses an anti-decarbonization nano coating and its preparation method. The coating composition wt% is: 5-20% nano Al2O3, 50-80% diatomaceous earth, 2-10% graphite powder, 5-20% binder, 1-3% suspension dispersant, and the rest is solvent and impurities. The coating is applied to the surface of the workpiece to be treated, and the coating thickness is 0.1-1.0mm.

[0005] However, the above existing technologies all involve additional coating, which has the disadvantages of increasing the costs of raw materials, spraying equipment, operation and maintenance, occupying limited space in the factory, and being difficult to ensure the spraying effect on each surface of the ingot during actual operation. Summary of the invention

[0006] The object of the present invention is to provide a method for improving wheel grain size mixing and surface decarburization, a wheel, and a method for simply and effectively controlling the depth of the decarburization layer of wheel steel by controlling production process parameters, while preventing rolling grain size mixing. The obtained wheel meets the needs of such users due to its superior high-temperature grain size and decarburization performance, and increases product competitiveness.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for improving wheel grain size, mixed crystal and surface decarburization includes smelting, continuous casting, heating, descaling and rolling.

[0009] In the smelting, 0.20%-0.30% of Cr and 0.67%-1.0% of Mn are added to the wheel steel composition; Cr and Mn are commonly used micro-alloying elements. Cr can reduce the diffusion rate of carbon and form a dense oxide film on the metal surface to inhibit oxygen penetration. Mn can react with oxygen to form a stable manganese oxide film to prevent further decarburization.

[0010] The continuous casting controls the depth of the slab chilling layer to be 15mm-25mm, and the grain size of the chilling layer is ≤100μm. To achieve this control requirement, the superheat of the molten steel is controlled to be no higher than 25°C to control the depth of the chilling. The crystallizer flow is 4000-4500l / min, the pressure is 8.0-10bar, the billet straightening tonnage is 15t, the secondary water cooling pressure is 10-12.5bar, the cooling water temperature is 10-25°C, and the cooling intensity is 5500-6000kg / m 2 •s, to control the grain size of the quench layer.

[0011] The heating and heating temperature control are as follows: for the continuous casting billet after sawing, a high-temperature heating method is adopted, the furnace temperature in the preheating section is controlled within 1000-1100°C, and the heating time is 1.0-1.5h; entering the first heating section, the furnace temperature is gradually increased to 1250-1280°C at a heating rate of 6-8°C / min, and the heating time is 0.5-1.0h; entering the second heating section, the furnace temperature is gradually increased to 1280-1310°C at a heating rate of 4-5°C / min, and the heating time is 0.5-1.0h; entering the soaking section, the furnace temperature is controlled at 1230-1250°C, and the heating time is 1-2h.

[0012] Furthermore, the heating controls the calorific value and air-fuel ratio of each section of the annular heating furnace as follows:

[0013] Gas calorific value 2000<q≤2100 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.16-2.25, heating section 1 2.26-2.35, heating section 2 2.46-2.55, equalizing section 2.36-2.45;

[0014] Gas calorific value 2100<q≤2200 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.26-2.35, heating section 1 2.36-2.45, heating section 2 2.56-2.65, equalizing section 2.46-2.55;

[0015] Gas calorific value 2200<q≤2300 kcal / m 3, the air-fuel ratio is controlled as follows: preheating section 2.36-2.45, heating section 1 2.46-2.55, heating section 2 2.66-2.75, equalizing section 2.56-2.65;

[0016] Gas calorific value 2300<q≤2400 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.46-2.55, heating section 1 2.56-2.65, heating section 2 2.76-2.85, equalizing section 2.66-2.75;

[0017] Gas calorific value 2400<q≤2500 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.56-2.65, heating section 1 2.66-2.75, heating section 2 2.86-2.95, equalizing section 2.76-2.85;

[0018] Gas calorific value 2500<q≤2600 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.66-2.75, heating section 1 2.76-2.85, heating section 2 2.96-3.05, equalizing section 2.86-2.95;

[0019] Gas calorific value 2600<q≤2700 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.76-2.85, heating section 1 2.86-2.95, heating section 2 3.06-3.15, equalizing section 2.96-3.05;

[0020] By the above heating, the residual oxygen content in the furnace can be controlled at 3%-5%, thus limiting the sensitivity of decarburization.

[0021] The control of decarburization is mainly about the matching relationship between the heating value and atmosphere of the heating furnace, so that the oxygen is fully consumed and avoids oxidation with the billet. The reasonable heating value is to prevent the billet from forming too thick iron oxide scale, and the air-fuel ratio control is to completely consume the oxygen in the furnace to prevent excess oxygen from reacting with the billet to form iron oxide scale.

[0022] Only when heated to above 1200℃ in steel can it slowly dissolve into the solid solution. Before dissolving, it has the effect of preventing the growth of grains. In the initial stage of solidification of the ingot, that is, in the surface layer of the ingot, due to the fast solidification speed, the grains are uniform and small, not exceeding 90μm, and the microsegregation is also well controlled. Therefore, the present invention controls the furnace temperature of the preheating section within 1000-1100℃, and the heating time is 1.0-1.5h.

[0023] The descaling is carried out by high-pressure water after the billet is taken out of the furnace to ensure that the descaling equipment operates normally. At the same time, the high-pressure water descaling pressure is adjusted to above 120 bar to ensure that the surface oxide scale is cleaned and decarburization in the residual oxide scale area is avoided.

[0024] The forming process is carried out before the steel billet is rolled;

[0025] The rolling process is optimized by air cooling to control the wheel temperature during the rolling process, and the air cooling ensures that the surface of the steel billet is cooled by 2-5°C / s; the wheel rolling start temperature is 950-970°C; the wheel expansion speed meets the formula V=0.12×(12-T / 120)×[1.7+2.5×C+0.6×(Si+Mn)+0.3×Cr], wherein the wheel expansion speed V is in units of mm / s, and T is the start rolling temperature in units of °C; through the above rolling process, the cooling uniformity of the wheel is improved, and the grain size difference between the rim and the web of the steel billet is within a range of 2 levels.

[0026] The rolling temperature of the present invention is controlled at 950-970°C, which is matched with the rolling speed to mainly ensure the refinement and uniformity of the grains.

[0027] In the formula calculation, C, Si, Mn, Cr are the mass percentage contents of C, Si, Mn, Cr in the wheel steel, and the unit is %;

[0028] When calculating the above formula, just substitute the value before the unit into the formula.

[0029] The present invention provides a wheel, which is produced by adopting the above method for improving the grain size mixing and surface decarburization of the wheel.

[0030] The wheel includes the following components in mass percentage: C: 0.48-0.77%, Si: 0.15-1.10%, Mn: 0.67-1.0%, P: ≤0.015%, S: ≤0.010%, Cr: 0.20%-0.30%, and the remainder is Fe and unavoidable impurities.

[0031] The decarburization layer depth of the wheel is controlled in the range of 0.17 to 0.24 mm, wherein the decarburization layer depths of 90% of the wheels are ≤ 0.23 mm, and the average decarburization layer depth is 0.21 mm.

[0032] The wheels have grains generally finer than level 4, with a grain size difference of 2 levels.

[0033] Beneficial effects of the present invention: Compared with the prior art, the wheel steel of the present invention contains 0.20%-0.30% Cr and 0.67-1.0% Mn. Cr can reduce the diffusion rate of carbon and form a dense oxide film on the metal surface to inhibit oxygen penetration; Mn can react with oxygen to generate a stable manganese oxide film to prevent further decarburization. By controlling the continuous casting parameters, the depth of the slab chilling layer is controlled to be 15mm-25mm, and the grain size of the chilling layer is ≤100μm; by controlling the calorific value and air-fuel ratio of each section of the annular heating furnace and the heating parameters, the residual oxygen content in the furnace can be controlled to be 3%-5%, limiting the sensitivity of decarburization. At the same time, the descaling pressure is adjusted to above 120bar to ensure that the surface oxide scale is cleaned and decarburization in the residual oxide scale area is avoided. During the rolling stage, the wheel expansion speed meets the formula V=0.12×(12-T / 120)×[1.7+2.5×C+0.6×(Si+Mn)+0.3×Cr], the cooling uniformity of the wheel is improved, and the grain size difference is within the range of 2 levels. The present invention controls the production process parameters to simply and effectively control the depth of the wheel decarburization layer, and can also prevent the grain size of the rolling batch from mixing. The obtained wheel meets the needs of such users due to its superior high-temperature grain size and decarburization performance, and increases the product competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the rim microstructure diagram of the wheel after rolling in Example 1, and the white part is the depth of the decarburized layer. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1-Example 3

[0037] A method for improving wheel grain size, mixed crystal and surface decarburization, comprising smelting, continuous casting, heating, descaling and rolling; the produced wheel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0038] Comparative Example 1-Comparative Example 6

[0039] A wheel production method includes smelting, continuous casting, heating, descaling and rolling; the produced wheel includes the following components in mass percentage: as shown in Table 1, the balance not shown in Table 1 is Fe and unavoidable impurities.

[0040]

[0041] In the smelting, 0.20%-0.30% of Cr and 0.67%-1.0% of Mn are added to the wheel steel composition; Cr and Mn are commonly used micro-alloying elements. Cr can reduce the diffusion rate of carbon and form a dense oxide film on the metal surface to inhibit oxygen penetration. Mn can react with oxygen to form a stable manganese oxide film to prevent further decarburization. The contents of Mn and Cr in the steel of each embodiment and comparative example are shown in Table 1.

[0042] The continuous casting controls the depth of the slab chilling layer to be 15mm-25mm, and the grain size of the chilling layer is ≤100μm. To achieve this control requirement, the superheat of the molten steel is controlled to be no higher than 25°C to control the depth of the chilling. The crystallizer flow is 4000-4500l / min, the pressure is 8.0-10bar, the billet straightening tonnage is 15t, the secondary water cooling pressure is 10-12.5bar, the cooling water temperature is 10-25°C, and the cooling intensity is 5500-6000kg / m 2 •s, in order to control the grain size of the chill layer. The main parameters of continuous casting of steel in specific embodiments and comparative examples are shown in Table 2.

[0043]

[0044] The heating and heating temperature control are as follows: After the continuous casting billet is sawed, a high-temperature heating method is adopted, and the furnace temperature in the preheating section is controlled within 1000-1100°C, and the heating time is 1.0-1.5h; entering the first heating section, the furnace temperature is gradually increased to 1250-1280°C at a heating rate of 6-8°C / min, and the heating time is 0.5-1.0h; entering the second heating section, the furnace temperature is gradually increased to 1280-1310°C at a heating rate of 4-5°C / min, and the heating time is 0.5-1.0h; entering the soaking section, the furnace temperature is controlled at 1230-1250°C, and the heating time is 1-2h.

[0045] Furthermore, the heating controls the calorific value and air-fuel ratio of each section of the annular heating furnace as follows:

[0046] Gas calorific value 2000<q≤2100 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.16-2.25, heating section 1 2.26-2.35, heating section 2 2.46-2.55, equalizing section 2.36-2.45;

[0047] Gas calorific value 2100<q≤2200 kcal / m 3, the air-fuel ratio is controlled as follows: preheating section 2.26-2.35, heating section 1 2.36-2.45, heating section 2 2.56-2.65, equalizing section 2.46-2.55;

[0048] Gas calorific value 2200<q≤2300 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.36-2.45, heating section 1 2.46-2.55, heating section 2 2.66-2.75, equalizing section 2.56-2.65;

[0049] Gas calorific value 2300<q≤2400 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.46-2.55, heating section 1 2.56-2.65, heating section 2 2.76-2.85, equalizing section 2.66-2.75;

[0050] Gas calorific value 2400<q≤2500 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.56-2.65, heating section 1 2.66-2.75, heating section 2 2.86-2.95, equalizing section 2.76-2.85;

[0051] Gas calorific value 2500<q≤2600 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.66-2.75, heating section 1 2.76-2.85, heating section 2 2.96-3.05, equalizing section 2.86-2.95;

[0052] Gas calorific value 2600<q≤2700 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.76-2.85, heating section 1 2.86-2.95, heating section 2 3.06-3.15, equalizing section 2.96-3.05;

[0053] By the above heating, the residual oxygen content in the furnace can be controlled at 3%-5%, thus limiting the sensitivity of decarburization.

[0054] The main heating parameters, calorific value and air-fuel ratio of the embodiment and the comparative example are shown in Table 3.

[0055]

[0056] Table 3

[0057]

[0058] The descaling is carried out by high-pressure water after the billet is taken out of the furnace to ensure that the descaling equipment operates normally. At the same time, the high-pressure water descaling pressure is adjusted to above 120 bar to ensure that the surface oxide scale is cleaned and decarburization in the residual oxide scale area is avoided.

[0059] The rolling process is optimized by air cooling to control the wheel temperature during the rolling process, and the air cooling ensures that the surface of the steel billet is cooled by 2-5°C / s; the wheel rolling start temperature is 950-970°C; the wheel expansion speed complies with the formula V=0.12×(12-T / 120)×[1.7+2.5×C+0.6×(Si+Mn)+0.3×Cr], T is the start rolling temperature, unit is °C; through the above rolling process, the cooling uniformity of the wheel is improved, and the grain size difference is within 2 levels.

[0060] The main control parameters of the wheel blank rolling process of each embodiment and comparative example are shown in Table 4.

[0061]

[0062] The steel produced in the above embodiments and comparative examples was tested for wheel decarburization and grain size, and the results are shown in Table 5. The test was carried out according to GB / T 6394.

[0063]

[0064] The wheel is composed of three parts: a rim, a spoke plate and a hub. The rim is quenched during heat treatment, and the spoke plate and the hub are in a normalized state. The normalized state can only improve a limited amount of rolled grains, so the present invention improves the toughness of the wheel spoke plate by controlling the rolled grains.

[0065] In Comparative Example 1, due to insufficient Mn and Cr elements, the decarburization layer is deep, reaching 0.56 mm. During the continuous casting process, due to high superheat and insufficient secondary water cooling intensity, the grain size difference is large and the toughness index is poor.

[0066] In comparative example 2, during the heating process of the steel billet, the soaking temperature was high, resulting in a deeper decarburized layer.

[0067] In comparative example 3, the secondary water cooling intensity was too high during the continuous casting process, resulting in uneven solidification process inside the steel billet, large grain size difference, and coarse grains. In the heating process of the steel billet, the parameters were improperly controlled, resulting in a deep decarburization layer.

[0068] Comparative Example 4: During the continuous casting process, due to high superheat and insufficient secondary water cooling strength, the billet chill layer is shallow, resulting in large grain size differences and coarse grains. During the heating process of the billet, the heating section temperature time is long, the air-fuel ratio is high during the heat treatment, and the excess oxygen reacts with the billet, resulting in a deeper decarburization layer.

[0069] Comparative Example 5: During the continuous casting process, the secondary water cooling pressure is high, resulting in uneven solidification process inside the billet and large differences in grain size. During the heating process of the billet, the heating temperature is high for a period of time, resulting in a deep decarburization layer.

[0070] Comparative Example 6: The billet rolling temperature is high. During the rolling process, the billet is plastically deformed, and the billet is further heated. The γ-α phase transformation will bring about a great change in the microstructure, and the grains are uneven. The mechanical properties of the steel are reduced.

[0071] The underlined data above do not meet the requirements of the present invention.

[0072] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for improving wheel grain size mixing and surface decarburization, characterized in that: The method for improving wheel grain size, mixed crystal and surface decarburization comprises smelting, continuous casting, heating, descaling and rolling; In the rolling, the wheel rolling start temperature is 950-970°C; the wheel expansion speed meets the formula V=0.12×(12-T / 120)×[1.7+2.5×C+0.6×(Si+Mn)+0.3×Cr], wherein the wheel expansion speed V is in units of mm / s, T is the rolling start temperature, in units of °C; C, Si, Mn, Cr are the mass percentage contents of C, Si, Mn, Cr in the wheel steel, in units of %; In the smelting, 0.20%-0.30% by mass of Cr element and 0.67%-1.0% by mass of Mn element are added to the wheel steel composition; The continuous casting control requires that the superheat of the molten steel is not higher than 25°C, the crystallizer flow is 4000-4500l / min, the pressure is 8.0-10bar, the secondary water cooling pressure is 10-12.5bar, the cooling water temperature is 10-25°C, and the cooling intensity is 5500-6000kg / (m 2 •s); The heating, the preheating section furnace temperature is controlled within 1000-1100°C, the heating time is 1.0-1.5h; entering the first heating section, the furnace temperature is increased to 1250-1280°C, the heating time is 0.5-1.0h; entering the second heating section, the furnace temperature is increased to 1280-1310°C, the heating time is 0.5-1.0h; entering the soaking section, the furnace temperature is controlled at 1230-1250°C, the heating time is 1-2h; The heating controls the calorific value and air-fuel ratio of each section of the annular heating furnace as follows: Gas calorific value 2000<q≤2100 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.16-2.25, heating section 1 2.26-2.35, heating section 2 2.46-2.55, equalizing section 2.36-2.45; Gas calorific value 2100<q≤2200 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.26-2.35, heating section 1 2.36-2.45, heating section 2 2.56-2.65, equalizing section 2.46-2.55; Gas calorific value 2200<q≤2300 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.36-2.45, heating section 1 2.46-2.55, heating section 2 2.66-2.75, equalizing section 2.56-2.65; Gas calorific value 2300<q≤2400 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.46-2.55, heating section 1 2.56-2.65, heating section 2 2.76-2.85, equalizing section 2.66-2.75; Gas calorific value 2400<q≤2500 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.56-2.65, heating section 1 2.66-2.75, heating section 2 2.86-2.95, equalizing section 2.76-2.85; Gas calorific value 2500<q≤2600 kcal / m 3 , the air-fuel ratio is controlled as follows: preheating section 2.66-2.75, heating section 1 2.76-2.85, heating section 2 2.96-3.05, equalizing section 2.86-2.95; Gas calorific value 2600<q≤2700 kcal / m 3 The air-fuel ratio is controlled as follows: preheating section 2.76-2.85, heating section 1 2.86-2.95, heating section 2 3.06-3.15, and equalizing section 2.96-3.

05.

2. The method for improving wheel grain size, mixed crystal and surface decarburization according to claim 1, characterized in that: During the heating, the residual oxygen content in the furnace is controlled at 3%-5%.

3. The method for improving wheel grain size, mixed crystal and surface decarburization according to claim 1, characterized in that: For the descaling, the pressure of high-pressure water descaling is adjusted to above 120 bar.

4. A wheel produced by the method for improving wheel grain size mixing and surface decarburization as described in any one of claims 1 to 3, wherein the wheel comprises the following components in mass percentage: C: 0.48-0.77%, Si: 0.15-1.10%, Mn: 0.67-1.0%, P: ≤0.015%, S: ≤0.010%, Cr: 0.20%-0.30%, and the remainder is Fe and unavoidable impurities.

5. The wheel according to claim 4, characterized in that For the wheel, the decarburized layer depth is controlled within the range of 0.17 to 0.24 mm; the grains are finer than level 4, and the grain size difference is within the range of 2 levels.

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