Method for controlling decarburized layer of steel for small-specification guide rail

Abstract

The invention particularly discloses a method for controlling a decarburized layer of steel for a small-specification guide rail. The method comprises the following steps: adding 0.15-0.20% of Cr into the steel during smelting in an LF (Ladle Furnace); combustion gas of a burner in the heating furnace is coke oven gas, blast furnace gas and air, and the coke oven gas, the blast furnace gas and the air respectively account for 50-60%, 20-30% and 10-20%; the temperature of a preheating section of a heating furnace is less than or equal to 750 DEG C, the temperature of a first heating section is 990-1010 DEG C, the temperature of a second heating section is 1005-1035 DEG C, and the temperature of a soaking section is 1005-1035 DEG C The air excess coefficient of the first heating section and the second heating section is 1.05-1.10, the air excess coefficient of the soaking section is 0.70-0.90, and the air-fuel ratio of the heating section and the soaking section is not larger than 1.3; the initial rolling temperature is 900-930 DEG C; the temperature of the rolled round steel on a cooling bed is 650-700 DEG C; and producing the high-grade high-quality round steel for the guide rail with a small-specification decarburized layer less than or equal to 0.8% D.

Description

Technical Field

[0001] The present invention belongs to the technical field of special steel smelting, and particularly relates to a method for controlling the decarburized layer of steel for Φ20-25mm small-sized guide rails in various mechanical equipment such as intelligent manufacturing industrial robots and intelligent machine tools. Background Art

[0002] Industrial robots and intelligent machine tools are the most important and commonly used equipment in intelligent manufacturing industry, and are known as the "mother machines". The guide rail is a key component of intelligent manufacturing industrial robots and intelligent machine tools, and its quality largely affects the normal operation of industrial robots and intelligent machine tools. As an important mechanical transmission device, the guide rail is widely used in various mechanical equipment such as intelligent manufacturing industrial robots and intelligent machine tools, and is widely favored for its excellent stiffness, high precision and reliability. The guide rail plays a guiding and supporting role for the moving components, guiding the components to move reciprocally in a certain direction. In a sense, the guide rail is a sliding bearing, which requires the guide rail to have high fatigue performance, extremely high precision, good impact resistance and processing performance, etc.

[0003] The materials for making the guide rail are mainly Japanese standard S55C and national standard material 55 steel, and its production process is: round steel cold rolling (3-4 passes) → annealing → phosphating, saponifying → cold drawing → surface induction hardening → surface tempering (surface hardness requirement 58-62HRC) → finished product shot peening → precision straightening → surface grinding (grinding 0.10mm) → cutting to size → finished product guide rail. The guide rail has high requirements for the decarburized layer. It is required that there is no decarburized layer after the guide rail is ground by 0.10mm. If there is a decarburized layer after grinding, it will cause soft spots on the surface of the guide rail, and its hardness cannot reach the technical requirement of 58-62HRC, which will greatly reduce the service life and fatigue life of the guide rail. Therefore, the guide rail has high requirements for the decarburized layer depth of the base material round steel, and generally requires that the decarburized layer depth of the base material round steel is not more than 0.80% of the diameter.

[0004] Production shows that when S55C and 55 steel are produced according to the conventional process, the decarburized layer depth of round steel with a diameter of more than Φ25mm can meet the decarburized layer requirement of 0.8%D, but when producing round steel with a diameter of Φ20-25mm, it is difficult for the decarburized layer to meet the 0.8%D requirement.

[0005] In order to meet the requirement that the decarburized layer depth of small-sized S55C and 55 round steel with a diameter of Φ20-25mm is not more than 0.8%D of the customer, it is urgent to develop a new composition control and hot rolling process for steel for guide rails. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for controlling the decarburized layer of steel for small-sized guide rails, so as to solve the problem that the decarburized layer depth of existing Φ20-25mm small-sized S55C and 55 round steel is greater than 0.8%D.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for controlling large-sized inclusions in medium-carbon alloy sulfur-containing steel. The method is to add 0.15 - 0.20% of Cr into the steel during LF furnace smelting; the heating process is to push the continuous casting billet into the heating furnace for heating. The heating furnace includes a preheating section, a first heating section, a second heating section, and a soaking section. The combustion gas of the burners in the heating furnace is coke oven gas + blast furnace gas + air, where the proportion of coke oven gas is 50 - 60%, the proportion of blast furnace gas is 20 - 30%, and the proportion of air is 10 - 20%; the heating parameters of the heating furnace are that the preheating section ≤ 750°C, the temperature of the first heating section is 990 - 1010°C, the temperature of the second heating section is 1005 - 1035°C, the temperature of the soaking section is 1005 - 1035°C, and the residual oxygen content ≤ 4%; the air excess coefficients of the first heating section and the second heating section of the heating furnace are 1.05 - 1.10, the air excess coefficient of the soaking section is 0.70 - 0.90, and the air-fuel ratio of the heating section and the soaking section is controlled to be not greater than 1.3; the rolling start temperature is controlled at 900 - 930°C; after rolling, water-cooling through water spraying is adopted, and the temperature of the round steel on the cooling bed is controlled at 650 - 700°C.

[0009] Preferably, the burners in the heating furnace adopt flame-adjusting and flat-flame burners. The angle between the flame-adjusting burner in the heating furnace and the continuous casting billet is 6 degrees, and the angle between the flat-flame burner and the continuous casting billet is 0 degree.

[0010] Preferably, the upper and lower parts of the second heating section adopt flame-adjusting burners, and 10 burners are evenly distributed respectively in a staggered arrangement; the lower left and lower right of the soaking section adopt flame-adjusting burners, and 4 burners are evenly distributed respectively in a staggered arrangement; the upper left and upper right of the soaking section adopt flat-flame burners, and 18 burners are evenly distributed respectively in a staggered arrangement.

[0011] Preferably, in the heating process, the in-furnace heating time is controlled at 130 - 160 min, and the furnace pressure of the heating furnace is controlled at 7 - 9 Pa.

[0012] Preferably, after the continuous casting billet exits the heating furnace, it undergoes descaling with high-pressure water of 20 - 30 MPa.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] During smelting, a small amount of Cr is added. The heating furnace uses a mixed gas of coke oven gas + blast furnace gas + air. By controlling different ratios, the residual oxygen content in the heating furnace is reduced, the furnace pressure and air-fuel ratio are controlled to ensure that the atmosphere in the furnace is a weakly reducing atmosphere. At the same time, the production with high-temperature steel is strictly controlled, the residence time of the continuous casting billet in the furnace is controlled, the heating furnace is heated at a low temperature, and water cooling is adopted after rolling to avoid the temperature of the round steel on the cooling bed being in a high-temperature state. In this way, the application of anti-oxidation coating on the casting billet to control the decarburized layer is eliminated, the manufacturing cost is saved, and round steel for guide rails with a small specification of Φ20 - 25mm and a decarburized layer depth not greater than 0.8%D can be produced, providing high-quality and high-performance steel products for the high-end manufacturing field. Specific Embodiments

[0015] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below through examples.

[0016] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0017] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0018] In the embodiments of the present invention, the range of chemical composition requirements for small-sized S55C and 55 steel for guide rails with a specification of Φ20 - 25mm is shown in Table 1.

[0019] Table 1 Chemical Composition (wt%)

[0020] Grade C Si Mn P S Cr Ni Mo Cu S55C 0.54～0.58 0.15～0.30 0.60～0.90 ≤0.025 ≤0.020 ≤0.20 ≤0.20 ≤0.08 ≤0.15 55 0.52～0.60 0.17～0.37 0.50～0.80 ≤0.025 ≤0.020 ≤0.20 ≤0.20 ≤0.08 ≤0.15

[0021] Example 1:

[0022] When smelting S55C, 0.17% of Cr is added, and when smelting 55 steel, 0.15% of Cr is added. The continuous casting billet is drawn into a continuous casting billet of 240mm × 300mm.

[0023] Rolled into round steel with a diameter of Φ25mm. During rolling, high-temperature steel production is not arranged before and after. The combustion gas in the heating furnace is coke oven gas + blast furnace gas + air, with the coke oven gas accounting for 60%, the blast furnace gas accounting for 20%, and the air accounting for 20%. The steel loading rhythm is the same as that of the previous steel type with a half-empty furnace. The heating furnace has 48 empty steps. The 240mm×300mm normal-temperature continuous casting billet is sent into the heating furnace. The burners in the heating furnace adopt flame-adjusting and flat-flame burners. The angle between the flame-adjusting burner in the heating furnace and the continuous casting billet is 6 degrees, and the angle between the flat-flame burner and the continuous casting billet is 0 degrees. The upper and lower parts of the heating section II adopt flame-adjusting burners, and 10 burners are evenly distributed respectively in a staggered arrangement. The lower left and lower right of the soaking section adopt flame-adjusting burners, and 4 burners are evenly distributed respectively in a staggered arrangement. The upper left and upper right of the soaking section adopt flat-flame burners, and 18 burners are evenly distributed respectively in a staggered arrangement; the heating time in the furnace is 146min, the temperature in the preheating section is 720℃, the temperature in the heating section I is 995℃, the temperature in the heating section II is 1010℃, the temperature in the soaking section is 1020℃, the residual oxygen content of the whole furnace is 4%, the air excess coefficient in the heating section is controlled at 1.06, the air-fuel ratio is 1.3, the air excess coefficient in the soaking section is 0.8, the air-fuel ratio is 1.2, the furnace pressure of the heating furnace is 9Pa. After the 240mm×300mm continuous casting billet leaves the furnace, it is descaled by high-pressure water of 26MPa. The rough rolling inlet temperature is 910℃. After rolling through the PSM rolling mill, it is water-cooled by passing through water. The temperature of the round steel on the cooling bed is 680℃, and then it is sheared, collected, and sent into the slow-cooling chamber. Samples of 3 different bundles are randomly collected to detect the decarburized layer depth, and the results all meet the requirement of ≤0.8%D. The specific detection results are shown in Table 2.

[0024] Example 2:

[0025] When smelting S55C, 0.18% of Cr is added, and when smelting 55 steel, 0.20% of Cr is added. The continuous casting billet is drawn into a 240mm×300mm continuous casting billet.

[0026] Rolled into round steel with a diameter of Φ21mm. During rolling, high-temperature steel production is not arranged before and after. The combustion gas in the heating furnace is coke oven gas + blast furnace gas + air, with coke oven gas accounting for 60%, blast furnace gas accounting for 30%, and air accounting for 10%. The steel loading rhythm is the same as that of the previous steel grade with a half-empty furnace, and the heating furnace has 48 empty steps. A 240mm×300mm normal-temperature continuous casting billet is sent into the heating furnace. The burners in the heating furnace adopt flame-adjusting and flat-flame burners. The angle between the flame-adjusting burner in the heating furnace and the continuous casting billet is 6 degrees, and the angle between the flat-flame burner and the continuous casting billet is 0 degrees. The upper and lower parts of the second heating section adopt flame-adjusting burners, and 10 burners are evenly distributed respectively in a staggered arrangement. The lower left and lower right of the soaking section adopt flame-adjusting burners, and 4 burners are evenly distributed respectively in a staggered arrangement. The upper left and upper right of the soaking section adopt flat-flame burners, and 18 burners are evenly distributed respectively in a staggered arrangement; the heating time in the furnace is 160min, the temperature in the preheating section is 750℃, the temperature in the first heating section is 990℃, the temperature in the second heating section is 1005℃, the temperature in the soaking section is 1015℃, the residual oxygen content of the whole furnace is 3%, the air excess coefficient in the heating section is controlled at 1.10, the air-fuel ratio is 1.3, the air excess coefficient in the soaking section is 0.7, the air-fuel ratio is 1.1, the furnace pressure of the heating furnace is 7Pa. After the 240mm×300mm continuous casting billet leaves the furnace, it is descaled with 20MPa high-pressure water. The rough rolling inlet temperature is 900℃. After rolling through the PSM rolling mill, it is water-cooled by passing through water. The temperature of the round steel on the cooling bed is 700℃, and then it is sheared, collected, and sent into the slow-cooling chamber. Samples of 3 different bundles are randomly collected to detect the decarburized layer depth, and the results all meet the requirement of ≤0.8%D. The specific detection results are shown in Table 2.

[0027] Example 3:

[0028] When smelting S55C, 0.19% of Cr is added, and when smelting 55 steel, 0.16% of Cr is added. The continuous casting billet is drawn into a 240mm×300mm continuous casting billet.

[0029] Rolled into round steel with a diameter of Φ20mm. During rolling, high-temperature steel production is not arranged before and after. The combustion gas in the heating furnace is coke oven gas + blast furnace gas + air, with coke oven gas accounting for 50%, blast furnace gas accounting for 30%, and air accounting for 20%. The steel charging rhythm is the same as that of the previous steel grade with a half-empty furnace. The heating furnace has 48 empty steps. A 240mm×300mm normal-temperature continuous casting billet is sent into the heating furnace. The burners in the heating furnace adopt flame-adjusting and flat-flame burners. The angle between the flame-adjusting burner in the heating furnace and the continuous casting billet is 6 degrees, and the angle between the flat-flame burner and the continuous casting billet is 0 degrees. The upper and lower parts of the second heating section adopt flame-adjusting burners, and 10 burners are evenly distributed respectively in a staggered arrangement. The lower left and lower right of the soaking section adopt flame-adjusting burners, and 4 burners are evenly distributed respectively in a staggered arrangement. The upper left and upper right of the soaking section adopt flat-flame burners, and 18 burners are evenly distributed respectively in a staggered arrangement; the heating time in the furnace is 130min, the temperature of the preheating section is 710℃, the temperature of the first heating section is 1010℃, the temperature of the second heating section is 1025℃, the temperature of the soaking section is 1035℃, the residual oxygen content of the whole furnace is 4%, the air excess coefficient of the heating section is controlled at 1.05, the air-fuel ratio is 1.3, the air excess coefficient of the soaking section is 0.9, the air-fuel ratio is 1.2, the furnace pressure of the heating furnace is 8Pa. After the 240mm×300mm continuous casting billet leaves the furnace, it is descaled by high-pressure water of 30MPa. The rough rolling inlet temperature is 930℃. After rolling through the PSM rolling mill, it is cooled by water through the water box. The temperature of the round steel on the cooling bed is 650℃, and then it is sheared, collected, and sent into the slow-cooling room. Samples of 3 different bundles are randomly collected to detect the decarburized layer depth, and the results all meet the requirement of ≤0.8%D. The specific detection results are shown in Table 2.

[0030] Table 2 Inspection Results of Decarburized Layer in Examples

[0031]

[0032] As can be seen from the above examples, when using the method of the present invention, a small amount of Cr is added during the smelting of S55C and 55 steel for small-sized guide rails with a diameter of Φ20-25mm. Different burner types, combustion gas types and proportions are set in the heating furnace, and the burner layout in the furnace is the key basic innovation point. At the same time, with strict heating control and rolling water-through cooling, the problem of excessive decarburized layer of S55C and 55 steel for small-sized guide rails with a diameter of Φ20-25mm in the conventional process is solved, and high-quality round steel for guide rails with a decarburized layer of ≤0.8%D for Φ20-25mm specifications is produced.

[0033] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for controlling the decarburization layer of small-size guide rail steel, characterized in that: The method comprises the following steps: adding 0.15-0.20% of Cr to steel during LF furnace smelting; the heating process comprises pushing the continuous casting billet into a heating furnace for heating; the heating furnace comprises a preheating section, a first heating section, a second heating section and a soaking section; the combustion gas of the burner in the heating furnace is coke oven gas + blast furnace gas + air, wherein the coke oven gas accounts for 50-60%, the blast furnace gas accounts for 20-30%, and the air accounts for 10-20%; the heating parameters of the heating furnace are that the preheating section temperature is ≤750°C, the first heating section temperature is 990-1 010℃, the temperature of the second heating stage is 1005-1035℃, the temperature of the soaking section is 1005-1035℃, and the residual oxygen content is ≤4%; the air excess coefficient of the first and second heating stages of the heating furnace is 1.05-1.10, the air excess coefficient of the soaking section is 0.70-0.90, and the air-fuel ratio of the heating section and the soaking section is controlled at not more than 1.3; the starting temperature of the rolling process is controlled at 900-930℃; after rolling, water cooling is adopted, and the temperature of the round steel upper cooling bed is controlled at 650-700℃.

2. The method for controlling the decarburization layer of small-size guide rail steel according to claim 1, characterized in that: The burners in the heating furnace are flame-adjusting burners and flat-flame burners. The angle between the flame-adjusting burners and the continuous casting billet is 6 degrees, and the angle between the flat-flame burners and the continuous casting billet is 0 degrees.

3. The method for controlling the decarburization layer of small-size guide rail steel according to claim 2, characterized in that: Flame-adjusting burners are used above and below the second heating section, and 10 burners are evenly distributed in a staggered arrangement. Flame-adjusting burners are used on the lower left and lower right of the equalizing section, and 4 burners are evenly distributed in a staggered arrangement. Flat flame burners are used on the upper left and upper right of the equalizing section, and 18 burners are evenly distributed in a staggered arrangement.

4. The method for controlling the decarburization layer of small-size guide rail steel according to claim 1, characterized in that: In the heating process, the heating time in the furnace is controlled at 130-160 minutes, and the furnace pressure of the heating furnace is controlled at 7-9Pa.

5. The method for controlling the decarburization layer of small-size guide rail steel according to claim 1, characterized in that: The continuous casting billet is descaled by high pressure water of 20-30 MPa after exiting the heating furnace.

6. The method for controlling the decarburization layer of small-size guide rail steel according to claim 1, characterized in that: The continuous casting adopts an integral tundish, which is cleaned and emptied by filling with argon before pouring. The argon blowing time is ≥ 2 minutes, and the casting is protected throughout the whole process. The pouring is started outside the tank.

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