A continuous rolling on-line quenching process method and a steel for engineering machinery

Abstract

The application relates to a continuous rolling on-line quenching process method and an engineering machinery steel. The continuous rolling on-line quenching process method adopts a 210mm*210mm continuous casting billet, a walking beam heating furnace, rough rolling, intermediate rolling, finish rolling and final rolling (KOCKS) processes, through a multi-pass strong water quenching process, the opening rolling temperature is controlled to be 950 DEG C to 1000 DEG C, the final rolling temperature is controlled to be 810 DEG C to 840 DEG C, and the temperature on the cooling bed is less than 400 DEG C, so that the steel organization transformation is completed, the hardness is improved, the plasticity and toughness are improved, the engineering machinery steel with excellent comprehensive mechanical properties is obtained, the engineering machinery steel satisfies the yield strength of more than 450MPa, the Brinell hardness at the center is greater than 220HB, and the surface hardness is 250HB to 280HB.

Description

TECHNICAL FIELD

[0001] The present application relates to a continuous rolling on-line quenching process method and a steel for engineering machinery, and belongs to the technical field of quenching. BACKGROUND

[0002] The piston rod of the engineering machinery is an axle part, mainly bearing axial load, and has high requirements on material strength and hardness. Most of the piston rods use non-adjusted steel, and the commonly used steel grade is medium carbon Mn-V (vanadium) micro-alloyed principle design to improve the strength of the steel. For example, 45 steel is added with V micro-alloying, and the steel produced on the basis of this design can meet the use requirements of the yield strength of 350 MPa grade steel for engineering machinery. However, the production cost of V micro-alloying is relatively high, and the mechanical properties cannot meet the requirements of high-strength piston rods. The yield strength of 450 MPa grade and above high-strength piston rods still use quenched and tempered steel. The high-strength piston rod requires that the Brinell hardness at the center is greater than 220 HB, the surface hardness is 250 HB-280 HB, and the yield strength reaches 450 MPa grade and above. At present, the high-strength piston rod uses 45 steel, which is used after normalizing + quenching and tempering heat treatment. The energy consumption in the heat treatment process is high, and the production cost is high. Under the background of "double carbon" emission reduction, the engineering machinery industry is a major energy consumption and emission source, and new energy is the main trend of future development of engineering machinery. As a raw material supplier, the steel plant actively responds and carries out process innovation. The present application adopts a strong water quenching process method in the rolling process to produce round steel for engineering machinery. SUMMARY

[0003] In order to solve the above problems, the present application discloses a continuous rolling on-line quenching process method and a steel for engineering machinery, and the specific technical scheme is as follows:

[0004] A continuous rolling on-line quenching process method, comprising the following steps:

[0005] Step 1: obtaining a continuous casting billet: obtaining a 210mm×210mm continuous casting billet;

[0006] Step 2: heating in a walking beam furnace: heating the 210mm×210mm continuous casting billet in a walking beam furnace, the heating temperature is controlled as follows: the heating section is 1020℃-1060℃, the soaking section is 1070℃-1100℃, and the total heating time is 2.5h-3.0h;

[0007] Step 3: circulating high-pressure water phosphorus removal: the high-pressure water phosphorus removal pressure is 180-190bar, and the opening rolling temperature is 950℃-1000℃;

[0008] Step 4: rough rolling: 6 rolling mills, and the rolled material size is 110mm×111mm;

[0009] Step 5: medium rolling: 4 rolling mills, and the rolled material size is 74mm×72mm;

[0010] Step 6: finish rolling: 2 rolling mills, the size of the rolled material is φ57.8mm;

[0011] Step 7: finish rolling: KOCKS reducing mill rolling, the size of the finished product after rolling is φ46mm, the size tolerance is allowed to deviate ±0.125mm, and the ovality is less than 0.25mm;

[0012] Step 8: multi-pass continuous strong water penetration: the water in 2#, 3#, 4# and 5# water tanks is penetrated during the rolling process, the positive flushing valve of the 2# water tank is opened by 20%, the reverse flushing valve is opened by 40%, the positive flushing valve of the 3# water tank is opened by 60%, the reverse flushing valve is opened by 100%, the positive flushing valve of the 4# and 5# water tanks is opened by 90%, and the reverse flushing valve is opened by 100%;

[0013] Step 9: the steel material is placed on the cooling bed with a temperature less than 400℃.

[0014] Further, steps 4 to 7 form a continuous rolling line, four water tanks are continuously penetrated on the continuous rolling line, and the water tanks are arranged along the rolling line direction, each water tank is arranged with water valves from front to back, 1, 2, 3, 4, 5 and 6, 7, wherein 1, 2, 3, 4 and 5 are positive flushing valves, and 6 and 7 are reverse flushing valves, the positive flushing is sprayed along the vertical direction of the steel material, and the reverse flushing is sprayed at an angle of 45° along the opposite direction of rolling.

[0015] Further, the 2# water tank is opened with 1, 2, 3, 4, 5 and 6 water valves, the positive flushing valve is opened by 20%, and the reverse flushing valve is opened by 40%, the rolling temperature of the KOCKS reducing mill is controlled at 810-840℃, the deformation strengthening and grain refinement are realized, and the hardenability is further improved.

[0016] Further, the 3# water tank is opened with 1, 2, 3, 4, 5 and 6 water valves, the water volume of the positive flushing valve is 60%, and the water volume of the reverse flushing valve is 100%, the temperature of the steel material after water penetration is controlled to be less than or equal to 650℃, the ferrite precipitation is inhibited, and the pearlite structure is strengthened.

[0017] Further, the 4# and 5# water tanks are opened with 1, 2, 3, 4, 5, 6 and 7 water valves, the positive flushing valve is opened by 90%, and the reverse flushing valve is opened by 100%, the temperature of the cooling bed is controlled to be less than 400℃, the red temperature of the cooling bed is less than 550℃, the martensite structure is obtained through instantaneous quenching after water penetration, and the sorbite structure is obtained through the recovery and tempering of the steel material.

[0018] The application also simultaneously applies the engineering machinery steel prepared by the continuous rolling and online quenching process method.

[0019] Further, the engineering machinery steel has the chemical composition percentage of C: 0.45%-0.49%, Si: 0.20%-0.30%, Mn: 0.65%-0.75%, Al: 0.015%-0.035%, Cr: 0.05%-0.10%, P≤0.030%, S≤0.030%, and the rest is Fe and inevitable impurities.

[0020] Further, the engineering machinery steel has the Brinell hardness of 225-230 HB at the center, the surface Brinell hardness of 256-260 HB, and the yield strength of 465-478 MPa.

[0021] Further, the engineering machinery steel has the water layer depth of 7-8 mm, the water layer ratio of 55%-60%, the water layer structure of sorbite + a small amount of pearlite, and the matrix structure of pearlite + a small amount of ferrite.

[0022] The principle of the application is:

[0023] Controlled rolling and controlled cooling is a common organization and performance control method in steel metallurgy rolling production, and is mostly applied to some ferrite-pearlite type and bainite type non-adjustable steel, by controlling the rolling temperature and the cooling speed of the cooling bed, the content of bainite or ferrite precipitation in the steel metallographic structure is controlled, the mechanical properties meeting the user's requirements are realized, and the application adopts the continuous multi-pass strong water penetration mode in the continuous rolling process, the temperature of the steel on the cooling bed is controlled to be less than 400 DEG C, the super-fast cooling makes the supercooled austenite structure instantaneously transform into martensite, the sorbite is transformed by the self-tempering mode of the steel, the pearlite structure is strengthened, and the ferrite precipitation is inhibited, and finally the strengthening purpose is achieved.

[0024] The application has the beneficial effects:

[0025] The application adopts a continuous rolling online quenching process method, the engineering machinery steel produced can meet the use requirements of the high-strength piston rod with the yield strength of 450 MPa or above, the heat treatment process is cancelled, the energy is saved, the cost is reduced, and the market competitiveness is improved.

[0026] The comprehensive performance of the engineering machinery steel produced by the process method of the application can reach the actual level after heat treatment, the downstream heat treatment process is cancelled, the energy is saved, the cost is reduced, and the application can be popularized to other types of production, such as wind power anchor bolts, shaft structural parts, etc.

[0027] The steel produced by the continuous rolling online quenching process method has the Brinell hardness of 225-230 HB at the center, the surface hardness of 256-260 HB, meets the use requirements of the high-strength piston rod, and can be used for the production of the engineering machinery steel with the yield strength of 450 MPa or above.

[0028] The round steel produced by the process has high size precision and straight shape. Attached Figure Description

[0029] Fig. 1 These are photographs of the water-penetrating layer structure of the product of this invention.

[0030] Fig. 2 This is a photograph of the matrix structure of the product of this invention. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] High-strength piston rods for engineering machinery require a Brinell hardness greater than 220 HB at the center and a surface hardness of 250 HB to 280 HB. Steel produced by traditional rolling processes has a Brinell hardness of 180 HB to 190 HB and a microstructure of ferrite + pearlite, requiring normalizing and tempering heat treatment to meet usage requirements. Downstream users experience high energy consumption and production costs during heat treatment. To address energy conservation, reduce production costs, and enhance market competitiveness, this invention employs a continuous rolling online quenching process. The rolling process involves continuous high-intensity water quenching and self-tempering to obtain a sorbite + pearlite + small amount of ferrite microstructure, enabling the steel to achieve the Brinell hardness required for high-strength piston rods. The mechanical properties also reach the levels required after heat treatment. This process can meet the production needs of engineering machinery steel with a yield strength of 450 MPa.

[0033] This invention employs a 210mm×210mm continuously cast billet, a walking beam furnace, and roughing, intermediate rolling, finishing, and final rolling (KOCKS) processes. Through a multi-pass high-intensity water quenching process, the initial rolling temperature is controlled at 950℃~1000℃, the final rolling temperature at 810℃~840℃, and the upper cooling bed temperature at <400℃. This process completes the transformation of the steel's microstructure, improves hardness and ductility, and yields excellent comprehensive mechanical properties.

[0034] The chemical composition of steel for engineering machinery, by mass percentage, is as follows: C: 0.45%–0.49%, Si: 0.20%–0.30%, Mn: 0.65%–0.75%, Al: 0.015%–0.035%, Cr: 0.05%–0.10%, P≤0.030%, S≤0.030%, with the remainder being Fe and unavoidable impurities.

[0035] The continuous rolling online quenching process is as follows: obtaining a continuously cast billet, heating in a walking beam furnace, descaling with circulating high-pressure water, rough rolling, intermediate rolling, finish rolling, and final rolling (KOCKS), followed by multiple passes of continuous high-intensity water quenching.

[0036] The 210mm×210mm continuous casting billet is heated in a walking beam furnace. The heating temperature is controlled as follows: heating section 1020℃~1060℃, soaking section 1070℃~1100℃, initial rolling temperature 950℃~1000℃, high-pressure water descaling pressure 180~190bar, rolling is carried out on an 18-stand continuous rolling mill + KOCKS sizing and reducing mill, and four water tanks provide strong water penetration.

[0037] Four water tanks are arranged along the rolling direction on the continuous rolling line. Water tank #2 is arranged after finishing rolling, and water tanks #3, #4, and #5 are arranged after final rolling (KOCKS). Water is continuously pumped through the four water tanks. The water tanks are equipped with seven water valves from front to back: 1, 2, 3, 4, 5, 6, and 7. Valves #1, #2, #3, #4, and #5 are for forward spraying, spraying vertically along the steel. Valves #6 and #7 are for reverse spraying, spraying at a 45° angle in the opposite direction of rolling. The phase change temperature is controlled by adjusting the water volume using different water valves in the four water tanks. The opening parameters of the water tank valves are shown in Table 1.

[0038] Table 1

[0039]

[0040] Six water valves are opened in water tank #2: five forward flushing valves have a water volume of 20% and one reverse flushing valve has a water volume of 40%. The rolling temperature of the KOCKS sizing and reducing mill is controlled at 810℃~840℃, which strengthens the deformation, refines the grains, and further improves hardenability.

[0041] Six water valves are opened in water tank #3: five forward flushes with 60% water flow and one backflush with 100% water flow, controlling the temperature to ≤650℃, inhibiting ferrite precipitation and strengthening pearlite structure.

[0042] Seven water valves were opened in water tanks #4 and #5. Five valves were used for forward flushing at 90% capacity, and two valves were used for reverse flushing at 100% and 50% capacity, respectively. The temperature of the upper cooling bed was controlled to be <400℃ and the temperature of the red-hot temperature to be <550℃. After water immersion, the steel was instantly quenched and cooled to obtain a martensitic structure. The steel was then subjected to self-tempering through temperature recovery to obtain a sorbitic structure.

[0043] The engineering machinery steel produced by this continuous rolling online quenching process has a Brinell hardness of 225-230 HB at the center, a surface hardness of 256-260 HB, and a yield strength of 465-478 MPa, which fully meets the requirements for high-strength applications.

[0044] The microstructure of the engineering machinery steel produced by this continuous rolling online quenching process is as follows: the water-penetrating layer consists of sorbite with a small amount of pearlite, and the matrix consists of pearlite with a small amount of ferrite. Microstructure photographs are shown below. Figs. 1-2 As shown.

[0045] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A continuous rolling online quenching process, characterized in that, Includes the following steps: Step 1: Obtaining the continuous casting billet: Obtain a 210mm×210mm continuous casting billet; Step 2: Heating in a walking beam furnace: Heating the 210mm×210mm continuous casting billet in a walking beam furnace. Heating temperature control: 1020℃~1060℃ in the heating section, 1070℃~1100℃ in the soaking section, and a total heating time of 2.5h~3.0h. Step 3: High-pressure water descaling: The high-pressure water descaling pressure is 180-190 bar, and the initial rolling temperature is 950℃-1000℃; Step 4: Rough rolling: 6-stand rolling mill, the rolled material size is 110mm×111mm; Step 5: Intermediate rolling: 4 rolling mills, the rolled material size is 74mm×72mm; Step 6: Finishing rolling: 2 stands, the rolled material size is φ57.8mm; Step 7: Final rolling: Rolled on a KOCKS reducing mill, the finished product size is φ46mm, the allowable dimensional deviation is ±0.125mm, and the ovality is <0.25mm; Step 8: Multi-pass continuous high-intensity water purging: After finishing rolling, water tank #2 is arranged; after final rolling, water tanks #3, #4, and #5 are arranged. During the rolling process, water tanks #2, #3, #4, and #5 are opened for water purging. The positive flush valve of water tank #2 is opened to 20%, and the negative flush valve is opened to 40%. The positive flush valve of water tank #3 is opened to 60%, and the negative flush valve is opened to 100%. The positive flush valves of water tanks #4 and #5 are opened to 90%, and the negative flush valves are opened to 100%. Step 9: Cooling on a cooling bed: The temperature of the steel on the cooling bed is less than 400℃; the steel for engineering machinery is obtained, with the following chemical composition by mass percentage: C: 0.45%~0.49%, Si: 0.20%~0.30%, Mn: 0.65%~0.75%, Al: 0.015%~0.035%, Cr: 0.05%~0.10%, P≤0.030%, S≤0.030%, with the remainder being Fe and unavoidable impurities. The depth of the water-penetrating layer is 7mm~8mm, and the water-penetrating layer accounts for 55%~60%. The microstructure of the water-penetrating layer is sorbite + a small amount of pearlite, and the matrix microstructure is pearlite + a small amount of ferrite.

2. The continuous rolling online quenching process method according to claim 1, characterized in that, Steps 4 to 7 constitute a continuous rolling line. Four water tanks on the continuous rolling line continuously carry water. The water tanks are arranged along the rolling line direction. Each water tank has water valves numbered 1, 2, 3, 4, 5, 6, and 7 arranged from front to back. Among them, 1, 2, 3, 4, and 5 are positive flushing water valves, and 6 and 7 are negative flushing water valves. Positive flushing sprays water perpendicular to the steel and negative flushing sprays water at a 45° angle in the opposite direction of rolling.

3. The continuous rolling online quenching process method according to claim 1, characterized in that, The No. 2 water tank has valves 1, 2, 3, 4, 5, and 6 open. The positive flush valve is opened to 20% and the negative flush valve is opened to 40%. The rolling temperature of the KOCKS fixed-sizing and reducing mill is controlled at 810℃~840℃, which strengthens the deformation, refines the grains, and further improves hardenability.

4. The continuous rolling online quenching process method according to claim 1, characterized in that, The No. 3 water tank has valves 1, 2, 3, 4, 5, and 6 open. The water flow rate of the forward flush valve is 60%, and the water flow rate of the back flush valve is 100%. After water is applied, the temperature of the steel is controlled to be ≤650℃, which inhibits ferrite precipitation and strengthens the pearlite structure.

5. The continuous rolling online quenching process method according to claim 1, characterized in that, The water valves 1, 2, 3, 4, 5, 6, and 7 of the No. 4 and No. 5 water tanks are opened to 90% for the positive flushing valve and 100% for the back flushing valve, controlling the upper cooling bed temperature to be <400℃ and the upper cooling bed red-hot temperature to be <550℃. After water immersion, the steel is instantly quenched and cooled to obtain a martensitic structure, and then a sorbitic structure is obtained through self-tempering by the recovery heating of the steel.

6. Steel for engineering machinery produced by the continuous rolling online quenching process according to any one of claims 1 to 5.

7. The steel for engineering machinery according to claim 6, characterized in that, The Brinell hardness at the center of the steel used in engineering machinery is 225-230 HB, the surface Brinell hardness is 256-260 HB, and the yield strength is 465-478 MPa.

Images