Small size guide rail steel decarburization layer control method

Abstract

This invention specifically discloses a method for controlling the decarburization layer of steel used in small-size guide rails. The method involves adding 0.15-0.20% Cr to the steel during LF furnace smelting; the combustion gas in the burners of the heating furnace is coke oven gas + blast furnace gas + air, with coke oven gas, blast furnace gas, and air accounting for 50-60%, 20-30%, and 10-20% respectively; the temperature of the preheating section of the heating furnace is ≤750℃, the temperature of the first heating section is 990-1010℃, the temperature of the second heating section is 1005-1035℃, and the temperature of the soaking section is 1005-1035℃; the excess air coefficient in the first and second heating sections is 1.05-1.10, the excess air coefficient in the soaking section is 0.70-0.90, and the air-fuel ratio in the heating and soaking sections is not greater than 1.3; the initial rolling temperature is 900-930℃; and the temperature of the rolled round steel on the cooling bed is 650-700℃. Producing high-quality round steel for guide rails with a small-size decarburized layer ≤0.8%D.

Description

Technical Field

[0001] This invention belongs to the field of special steel smelting technology, specifically relating to a method for controlling the decarburization layer of steel used in small-diameter guide rails (Φ20-25mm) in various mechanical equipment such as intelligent manufacturing industrial robots and smart machine tools. Background Technology

[0002] Industrial robots and smart machine tools are among the most important and commonly used equipment in intelligent manufacturing, often referred to as "mother machines." Guide rails are key components of intelligent manufacturing industrial robots and smart machine tools, and their quality significantly impacts their normal operation. As an important mechanical transmission device, guide rails are widely used in various mechanical equipment such as intelligent manufacturing industrial robots and smart machine tools, favored for their excellent rigidity, high precision, and reliability. Guide rails guide and support moving components, directing their reciprocating motion in a specific direction. In a sense, guide rails are like sliding bearings, requiring them to possess high fatigue performance, extremely high precision, good impact resistance, and machinability.

[0003] The main materials used to manufacture guide rails are Japanese standard S55C and Chinese standard 55 steel. The production process is as follows: cold rolling of round steel (3-4 passes) → annealing → scaling and saponification → cold drawing → surface induction hardening → surface tempering (surface hardness requirement 58-62 HRC) → shot blasting of finished product → precision straightening → surface grinding (0.10mm grinding) → cutting into lengths → finished guide rail. Guide rails have high requirements for the decarburized layer. It is required that after grinding 0.10mm, there should be no decarburized layer. If a decarburized layer remains after grinding, it will cause soft spots on the guide rail surface, and its hardness will not reach the technical requirement of 58-62 HRC, significantly reducing the service life and fatigue life of the guide rail. Therefore, guide rails have high requirements for the depth of the decarburized layer of the base round steel, generally requiring the depth of the decarburized layer to be no greater than 0.80% of the diameter.

[0004] Production data shows that when S55C and 55 steel are produced using conventional processes, the decarburization layer depth of round steel with a diameter of 25mm or larger can meet the 0.8%D decarburization layer requirement. However, when producing round steel with a diameter of 20-25mm, it is difficult to meet the 0.8%D requirement for the decarburization layer.

[0005] To meet customers' requirements that the decarburization layer depth of small-sized S55C and 55 round steel (Φ20-25mm) should not exceed 0.8%D, it is urgent to develop a new steel composition control and hot rolling process for guide rails. Summary of the Invention

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

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for controlling large particle inclusions in medium-carbon alloy sulfur-containing steel, wherein the method involves adding 0.15-0.20% Cr to the steel during LF furnace smelting; the heating process involves pushing the continuously cast billet into a heating furnace for heating, the heating furnace comprising a preheating section, a first heating section, a second heating section, and a soaking section; the combustion gas in the burners of the heating furnace is coke oven gas + blast furnace gas + air, wherein coke oven gas accounts for 50-60%, blast furnace gas accounts for 20-30%, and air accounts for 10-20%; the heating parameters of the heating furnace are: preheating section ≤750℃, adding... The heating zone temperature is 990-1010℃, the heating zone temperature is 1005-1035℃, and the soaking zone temperature is 1005-1035℃, with residual oxygen content ≤4%. The excess air coefficient for the heating zone is 1.05-1.10, and the excess air coefficient for the soaking zone is 0.70-0.90. The air-fuel ratio for the heating and soaking zones is controlled to be no greater than 1.3. The initial rolling temperature is controlled at 900-930℃. After rolling, water cooling is adopted, and the temperature of the round steel on the cooling bed is controlled at 650-700℃.

[0009] Preferably, the burners in the heating furnace are flame-adjustable and flame-flat burners, with the flame-adjustable burner having an angle of 6 degrees with the continuous casting billet and the flame-flat burner having an angle of 0 degrees with the continuous casting billet.

[0010] Preferably, the upper and lower heating sections employ flame-adjusting burners, with 10 burners evenly distributed in an alternating pattern. The lower left and lower right of the heat-spreading section employ flame-adjusting burners, with 4 burners evenly distributed in an alternating pattern. The upper left and upper right of the heat-spreading section employ flat flame burners, with 18 burners evenly distributed in an alternating pattern.

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

[0012] Preferably, the continuously cast billet undergoes descaling with high-pressure water at 20-30 MPa after exiting the heating furnace.

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

[0014] A small amount of Cr is added during smelting. The heating furnace uses a mixture of coke oven gas, blast furnace gas, and air. By controlling different proportions, the residual oxygen content in the heating furnace is reduced, and the furnace pressure and air-fuel ratio are controlled to ensure a weakly reducing atmosphere inside the furnace. At the same time, the production of high-temperature steel is strictly controlled, the time of the continuously cast 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 round steel being at a high temperature on the cooling bed. In this way, the need to apply anti-oxidation coating to the billet to control the decarburization layer is eliminated, saving manufacturing costs. It is possible to produce small-sized guide rail round steel with a decarburization layer depth of no more than 0.8%D, which is Φ20-25mm, providing high-quality and high-performance steel products for the high-end manufacturing field. Detailed Implementation

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

[0016] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0017] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0018] The chemical composition requirements for the Φ20-25mm small-specification S55C and 55 steel guide rails in this invention are shown in Table 1.

[0019] Table 1 Chemical composition (wt%)

[0020] Brand 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] 0.17% Cr is added when smelting S55C, and 0.15% Cr is added when 55 steel is smelted. The steel is then continuously cast into 240mm×300mm continuous casting billets.

[0023] The steel is rolled into Φ25mm round bars. No high-temperature steel production is scheduled before or after the rolling process. 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 for 20%, and air for 20%. The charging rhythm follows the same pattern as the previous steel grades, with half a furnace empty and 48 empty steps in the heating furnace. A 240mm × 300mm ambient temperature continuous casting billet is then fed into the heating furnace. The burners in the heating furnace are both flame-adjustable and flat-flame burners. The angle between the flame-adjustable 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. Flame-adjustable burners are used at the top and bottom of the second heating section, with 10 burners evenly distributed in a staggered arrangement. Flame-adjustable burners are used at the lower left and lower right of the soaking section, with 4 burners evenly distributed in a staggered arrangement. Flat-flame burners are used at the upper left and upper right of the soaking section, also in a staggered arrangement. Eighteen burners were evenly distributed throughout the furnace. The heating time was 146 minutes. The preheating temperature was 720℃, the first heating temperature was 995℃, the second heating temperature was 1010℃, and the soaking temperature was 1020℃. The residual oxygen content of the entire furnace was 4%. The excess air coefficient in the heating section was controlled at 1.06, and the air-fuel ratio was 1.3. The excess air coefficient in the soaking section was 0.8, and the air-fuel ratio was 1.2. The furnace pressure was 9 Pa. After the 240mm×300mm continuous casting billets exited the furnace, they were descaled by 26MPa high-pressure water. The roughing mill inlet temperature was 910℃. After rolling through the PSM mill, the billets were water-cooled. The temperature of the round bars on the cooling bed was 680℃. They were then sheared, collected, and placed in a slow cooling chamber. Three samples from different bundles were randomly collected to test the decarburization layer depth. The results all met the requirement of ≤0.8%D. The specific test results are shown in Table 2.

[0024] Example 2:

[0025] When smelting S55C, 0.18% Cr is added, and 0.20% Cr is added to 55 steel. The steel is then continuously cast into 240mm×300mm continuous casting billets.

[0026] The steel is rolled into Φ21mm round bars. No high-temperature steel production is scheduled before or after the rolling process. 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 for 30%, and air for 10%. The steel loading rhythm follows the same pattern as the previous steel grades, with half a furnace empty and 48 empty steps in the heating furnace. A 240mm × 300mm ambient temperature continuous casting billet is then fed into the heating furnace. The burners in the heating furnace are both flame-adjustable and flat-flame burners. The angle between the flame-adjustable 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. Flame-adjustable burners are used at the top and bottom of the second heating section, with 10 burners evenly distributed in a staggered arrangement. Flame-adjustable burners are used at the lower left and lower right of the soaking section, with 4 burners evenly distributed in a staggered arrangement. Flat-flame burners are used at the upper left and upper right of the soaking section, also in a staggered arrangement. Eighteen burners were evenly distributed throughout the furnace. The heating time was 160 min. The preheating temperature was 750℃, the first heating temperature was 990℃, the second heating temperature was 1005℃, and the soaking temperature was 1015℃. The residual oxygen content of the entire furnace was 3%. The excess air coefficient in the heating section was controlled at 1.10, and the air-fuel ratio was 1.3. The excess air coefficient in the soaking section was 0.7, and the air-fuel ratio was 1.1. The furnace pressure was 7 Pa. After the 240mm×300mm continuous casting billets exited the furnace, they were descaled by 20MPa high-pressure water. The roughing mill inlet temperature was 900℃. After rolling through the PSM mill, the billets were water-cooled. The round steel was placed on the cooling bed at 700℃, sheared, collected, and placed in a slow cooling chamber. Three samples from different bundles were randomly collected to test the decarburization layer depth. The results all met the requirement of ≤0.8%D. The specific test results are shown in Table 2.

[0027] Example 3:

[0028] 0.19% Cr is added during the smelting of S55C, and 0.16% Cr is added to 55 steel. The steel is then continuously cast into 240mm×300mm continuous casting billets.

[0029] The steel is rolled into Φ20mm round bars. No high-temperature steel production is scheduled before or after the rolling process. 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 for 30%, and air for 20%. The charging rhythm follows the same pattern as the previous steel grades, with half a furnace empty and 48 empty steps in the heating furnace. A 240mm × 300mm ambient temperature continuous casting billet is then fed into the heating furnace. The burners in the heating furnace are both flame-adjustable and flat-flame burners. The angle between the flame-adjustable 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. Flame-adjustable burners are used at the top and bottom of the second heating section, with 10 burners evenly distributed in a staggered arrangement. Flame-adjustable burners are used at the lower left and lower right of the soaking section, with 4 burners evenly distributed in a staggered arrangement. Flat-flame burners are used at the upper left and upper right of the soaking section, also in a staggered arrangement. Eighteen burners were evenly distributed throughout the furnace. The heating time was 130 min. The preheating temperature was 710℃, the first heating temperature was 1010℃, the second heating temperature was 1025℃, and the soaking temperature was 1035℃. The residual oxygen content of the entire furnace was 4%. The excess air coefficient in the heating section was controlled at 1.05, and the air-fuel ratio was 1.3. The excess air coefficient in the soaking section was 0.9, and the air-fuel ratio was 1.2. The furnace pressure was 8 Pa. After the 240mm×300mm continuous casting billet exited the furnace, it was descaled by 30MPa high-pressure water. The roughing mill inlet temperature was 930℃. After rolling through the PSM mill, it was water-cooled. The round steel was placed on the cooling bed at 650℃, sheared, collected, and placed in a slow cooling chamber. Three samples from different bundles were randomly collected to test the decarburization layer depth. The results all met the requirement of ≤0.8%D. The specific test results are shown in Table 2.

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

[0031]

[0032] As can be seen from the above embodiments, the key innovations of the present invention are the addition of a small amount of Cr during the smelting of S55C and 55 steel for small-sized guide rails (Φ20-25mm), the setting of different burner types in the heating furnace, the types and proportions of combustion gases, and the layout of the burners inside the furnace. Combined with strict heating control and water cooling during rolling, the problem of excessive decarburization layer in S55C and 55 steel for small-sized guide rails (Φ20-25mm) using conventional processes is solved, resulting in the production of high-grade, high-quality round steel for guide rails with a decarburization layer ≤0.8%D for Φ20-25mm specifications.

[0033] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling the decarburization layer of steel used in small-size guide rails, characterized in that: The small-sized guide rails are made of Φ20-25mm small-sized S55C and 55 round steel. The method involves adding 0.15-0.20% Cr to the steel during LF furnace smelting. The heating process involves pushing the continuously cast billet into the heating furnace, which includes a preheating section, a first heating section, a second heating section, and a soaking section. The combustion gas in the burners of the heating furnace is coke oven gas + blast furnace gas + air, with coke oven gas accounting for 50-60%, blast furnace gas for 20-30%, and air for 10-20%. The heating parameters are: preheating section temperature ≤750℃, first heating section temperature 990-1010℃, second heating section temperature 1005-1035℃, soaking section temperature 1005-1035℃, residual oxygen content ≤4%. The excess air coefficient in the first and second heating sections is 1.05-1.10, and the excess air coefficient in the soaking section is 0.70-0. The air-fuel ratio in the heating and soaking sections is controlled to be no greater than 1.3; the initial rolling temperature is controlled at 900-930℃; after rolling, water cooling is adopted, and the temperature of the round steel on the cooling bed is controlled at 650-700℃; the burners in the heating furnace are flame-adjusting burners and flat flame burners, with the angle between the flame-adjusting burners and the continuous casting billet being 6 degrees and the angle between the flat flame burners and the continuous casting billet being 0 degrees; flame-adjusting burners are used at the top and bottom of the second heating section, with 10 burners evenly distributed in a staggered arrangement; flame-adjusting burners are used at the lower left and lower right of the soaking section, with 4 burners evenly distributed in a staggered arrangement; flat flame burners are used at the upper left and upper right of the soaking section, with 18 burners evenly distributed in a staggered arrangement; the heating time in the furnace is controlled at 130-160 minutes, and the furnace pressure is controlled at 7-9 Pa.

2. The method for controlling the decarburization layer of steel for small-size guide rails according to claim 1, characterized in that, After exiting the heating furnace, the continuously cast billet undergoes descaling with high-pressure water at 20-30 MPa.

3. The method for controlling the decarburization layer of steel for small-size guide rails according to claim 1, characterized in that, The continuous casting adopts an integral intermediate tank. The intermediate tank is cleaned and purged with argon gas before casting begins. The argon blowing time is ≥2 minutes. The casting process is protected throughout and casting begins outside the tank.

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