A method for predicting the causes of surface hair cracks in bearing steel bars

Abstract

The present invention discloses a method for predicting the formation reasons of surface hair cracks of bearing steel bars, which relates to the technical field of steel production, and includes: First, establish a numerical simulation system; Second, establish a finite element rolling model; Third, input boundary conditions, material parameters, and process parameters into the numerical simulation system according to actual rolling conditions; Fourth, perform mesh division; Fifth, analyze the formation reasons of surface hair cracks of bearing steel bars. Through finite element numerical simulation, it is possible to analyze the possible hair crack defects and their causes that may occur in the rolled piece during the rolling process of bearing steel bars, optimize process parameters, improve the surface quality and production efficiency of the rolled piece, and reduce production costs.

Description

Technical Field

[0001] The present invention relates to the technical field of steel production, and in particular to a method for predicting causes of surface cracks on bearing steel bars. Background Art

[0002] Surface hairline defects are the most common surface defect in bearing steel bars. Removing these defects often requires significant manpower and resources, even severely impacting normal production and economic profitability. The railway, aviation, and aerospace industries place high demands on the quality integrity and reliability of bar products, leading to increasing attention to the identification and control of hairline defects. Bearing steel bars are produced using a hot rolling process and are widely used in industries such as machining, construction, and home appliances. The box-ellipse-round pass system commonly used in hot rolling is commonly used.

[0003] Hairline defects are one of the macroscopic defects on the surface of steel. They are usually manifested as hair-like fine lines on the surface of the steel. They are shallower and shorter than cracks and are scattered or clustered along the rolling direction. The presence of hairline defects on the steel surface can greatly affect the mechanical properties of the steel, especially fatigue strength. Hairline defects on the steel surface can greatly reduce the plasticity and toughness of the steel. In severe cases, they can even cause cracking, seriously shortening the service life of the material. In addition to promoting crack initiation, common hazards of hairline defects include triggering pseudo-cracks in non-destructive testing, forming unacceptable surface defects, and causing leakage and failure of sealing structures. By studying and summarizing the different manifestations of hairline defects, we can more accurately determine the cause of hairline defects and propose targeted preventive measures and inspection and evaluation methods, which will help improve product quality and reliability.

[0004] Currently, the main causes of surface striation are temperature stress during billet heating, pressure and limited width expansion during billet rolling, temperature and structural stress during cooling, and scale. Because so many factors influence the formation of striation, the influence of any one factor on the surface striation of bearing steel bars has not been specifically addressed. Therefore, to effectively analyze and predict the formation of surface striation in bearing steel, the influence of initial rolling temperature parameters was investigated, and other process parameters were standardized. Finite element numerical simulations of the rolling process of bearing steel bars were performed to characterize and analyze their effects on the surface striation of bearing steel bars. Summary of the Invention

[0005] The present invention addresses the above technical problems, overcomes the shortcomings of the prior art, and provides a method for predicting the causes of surface cracking on bearing steel bars, comprising:

[0006] 1. Establish a numerical simulation system and use CAD software to create the geometric models of the rolls and rolled products;

[0007] II. According to the material properties of the roll and the rolled piece in the pre-processor of MSC.Marc, set the interaction between components, set the analysis steps and loads; during the rolling process of bearing steel bars, set the properties of the rolled piece as plastic and the roll as rigid; then define the friction factor, select shear friction, and set the contact heat transfer between the roll and the rolled piece. Since the rolled piece and the roll show symmetric characteristics, 1 / 4 of the rolled piece and 1 / 2 of the roll can be selected as the research object, and a finite element rolling model is established based on this;

[0008] III. Input boundary conditions, material parameters, and process parameters into the numerical simulation system according to the actual rolling conditions; during the rolling process, due to the plastic deformation of the metal, the temperature of the rolled piece increases. The heat transfer coefficient of heat work is 0.9. The rolled piece will contact the roll during the rolling process, resulting in friction and heat generation. This part of the heat is evenly distributed to the contact surface between the rolled piece and the roll;

[0009] IV. Conduct mesh division, and use the default mesh type in the MSC.Marc finite element software for mesh division. The mesh type is an eight-node hexahedron;

[0010] V. According to different initial rolling temperature parameters, conduct finite element numerical simulation on the rolling process of bearing steel bars, obtain the stress and strain distribution laws, temperature field and rolling force distribution laws of bearing steel, and analyze the formation reasons of surface hair cracks on bearing steel bars.

[0011] The further limited technical solution of the present invention is:

[0012] For the method for predicting the formation reason of surface hair cracks on bearing steel bars described above, in step one, a billet with an initial cross-sectional size of 250mm×300mm is used, and five rolling mills are arranged alternately in a flat (H)-vertical (V) mode, and a box-ellipse-round pass system is adopted.

[0013] For the method for predicting the formation reason of surface hair cracks on bearing steel bars described above, in step two, the friction coefficient between the rolled piece and the roll is set to 0.7, and the equivalent heat transfer coefficient is 9.5kw / m 2 ·°C.

[0014] For the method for predicting the formation reason of surface hair cracks on bearing steel bars described above, in step three, set the roll temperature to 250°C and the ambient temperature to 25°C.

[0015] For the method for predicting the formation reason of surface hair cracks on bearing steel bars described above, in step three, the simulation experiment process parameters are as follows:

[0016] Pass 1: Roll gap 30mm, rolling linear speed 0.264m / s, elongation coefficient 1.13, roll diameter 950mm;

[0017] Pass 2: roll gap 30 mm, rolling linear speed 0.303 m / s, elongation coefficient 1.21, roll diameter 870 mm;

[0018] Pass 3: roll gap 30 mm, rolling linear speed 0.352 m / s, elongation coefficient 1.18, roll diameter 900 mm;

[0019] Pass 4: roll gap 25 mm, rolling linear speed 0.456 m / s, elongation coefficient 1.33, roll diameter 800 mm;

[0020] Pass 5: roll gap 25 mm, rolling linear speed 0.600 m / s, elongation coefficient 1.32, roll diameter 800 mm.

[0021] The method for predicting the formation cause of surface hair cracks of bearing steel bars as described above, step four, set the billet length to 3500 mm and divide it into 33600 units.

[0022] The beneficial effects of the present invention are: through finite element numerical simulation, the present invention can analyze the possible hair crack defects and their causes in the rolling process of bearing steel bars, optimize process parameters, improve the surface quality and production efficiency of the rolled pieces, and reduce production costs. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the rolling process;

[0024] Figure 2 It is a finite element model of rough continuous rolling of bars;

[0025] Figure 3 shows the surface condition of the rolled piece during rolling in five passes at 1050 five passes;

[0026] Figure 4 shows the surface condition of the rolled piece during rolling in five passes at 1075 five passes;

[0027] Figure 5 shows the surface condition of the rolled piece during rolling in five passes at 1100 five passes. Specific Embodiments

[0028] A method for predicting the formation cause of surface hair cracks of bearing steel bars provided in this embodiment, the rolling process is as Figure 1 , including:

[0029] I. Establish a numerical simulation system, use CAD software to establish the geometric models of the rolls and the rolled piece, for a billet with an initial cross-sectional size of 250 mm × 300 mm, five rolling mills are arranged alternately in the flat (H)-vertical (V) mode, and a box-ellipse-round pass system is adopted;

[0030] II. In the preprocessor of MSC.Marc, set the interactions between components, analysis steps, and loads according to the material properties of the roll and the rolled piece. During the rolling process of bearing steel bars, set the properties of the rolled piece as plastic and the roll as rigid. Then define the friction factor, select shear friction, and set the friction coefficient between the rolled piece and the roll to 0.7. When setting the contact heat transfer between the roll and the rolled piece, the equivalent heat transfer coefficient is 9.5 kw / m 2 ·℃. Due to the symmetric characteristics of the rolled piece and the roll, 1 / 4 of the rolled piece and 1 / 2 of the roll can be selected as the research object, and a finite element rolling model can be established accordingly, as shown in Figure 2 ;

[0031] III. Input boundary conditions, material parameters, and process parameters into the numerical simulation system according to the actual rolling conditions. Set the roll temperature to 250℃ and the ambient temperature to 25℃. During the rolling process, due to plastic deformation of the metal, the temperature of the rolled piece increases. The heat transfer coefficient of thermal work is 0.9. The rolled piece will come into contact with the roll during the rolling process, generating friction heat. This part of the heat is evenly distributed to the contact surface of the rolled piece and the roll. The specific simulation process parameters are shown in Table 1:

[0032] Table 1 Simulation experiment process parameters

[0033] Pass Roll gap / mm Rolling line speed m / s Elongation coefficient Roll diameter / mm 1 30 0.264 1.13 950 2 30 0.303 1.21 870 3 30 0.352 1.18 900 4 25 0.456 1.33 800 5 25 0.600 1.32 800 ;

[0035] IV. Conduct mesh generation. Use the default mesh type in the MSC.Marc finite element software for mesh generation. The mesh type is an eight-node hexahedron. Set the billet length to 3500 mm and divide it into 33600 elements;

[0036] V. According to different initial rolling temperature parameters, conduct finite element numerical simulation on the rolling process of bearing steel bars, obtain the stress, strain distribution laws, temperature field, and rolling force distribution laws of bearing steel, and analyze the formation reasons of surface hair cracks on bearing steel bars.

[0037] Specific application process:

[0038] The initial rolling temperature may be a key factor causing surface hair cracks on bearing steel bars. Therefore, different initial rolling temperature conditions are designed. When the designed initial rolling temperature is 1050 ℃, the surface conditions of the rolled piece after five passes of rolling are shown in Figures 3(a), (b), (c), (d), and (e). It can be seen from the figures that the billet can pass through the rolling of the existing pass smoothly. There are a small number of protrusions on the surface of the rolled piece at the end of the fifth pass.

[0039] In the modeling, mainly analyze the influence of rolling temperature on the surface hair cracks of bearing steel bars. Further design the initial rolling temperature to be 1075 When the temperature is [specific temperature], the surface conditions of the rolled piece after five passes of rolling are shown in Figures 4(a), (b), (c), (d), and (e). It can be seen from the figures that the billet can pass through the rolling of the existing pass smoothly. A small amount of protrusions appear on the surface of the rolled piece at the second pass, and warping occurs at the end of the rolled piece. After the fourth pass of rolling, the protrusion phenomenon on the surface of the rolled piece becomes more serious. Obvious ears appear at the roll gap of the third and fifth passes of the rolled piece, which has seriously affected the product quality of the bar.

[0040] The initial rolling temperature is further designed to be 1100 When the temperature is [specific temperature], the surface conditions of the rolled piece after five passes of rolling are shown in Figures 5(a), (b), (c), (d), and (e). It can be seen from the figures that the billet can pass through the rolling of the existing pass smoothly. A small amount of protrusions appear on the surface of the rolled piece at the third pass, and a large number of protrusions appear on the surface of the rolled piece at the fourth pass. Obvious ears appear at the roll gap of the fifth pass, which has seriously affected the product quality of the bar. Surface defects are the most important factors affecting product quality in bar production. Therefore, the surface quality should be strictly controlled during bar rolling.

[0041] In addition to the above embodiments, the present invention can also have other implementation manners. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A method for predicting the cause of surface hair cracks in bearing steel bars, characterized in that: Including:

1. Establish a numerical simulation system, and use CAD software to establish the geometric models of the roll and the rolled piece.

2. In the pre-processor of MSC.Marc, according to the material properties of the roll and the rolled piece, set the interaction between components, set the analysis steps and loads; during the rolling process of bearing steel bars, set the property of the rolled piece as plastic and the roll as rigid; then define the friction factor, select shear friction, and set the contact heat transfer between the roll and the rolled piece. Due to the symmetric characteristics of the rolled piece and the roll, select 1 / 4 of the rolled piece and 1 / 2 of the roll as the research object, and establish a finite element rolling model accordingly.

3. Input the boundary conditions, material parameters, and process parameters into the numerical simulation system according to the actual rolling conditions; during the rolling process, due to the plastic deformation of the metal, the temperature of the rolled piece increases, and the heat transfer coefficient of thermal work is 0.

9. The rolled piece will contact the roll during the rolling process, thus generating heat due to friction. Divide this part of the heat evenly between the contact surfaces of the rolled piece and the roll.

4. Conduct mesh generation, and use the default mesh type in MSC.Marc finite element software for mesh generation. The mesh type is eight-node hexahedron.

5. According to different initial rolling temperature parameters, conduct finite element numerical simulation on the rolling process of bearing steel bars, obtain the stress and strain distribution laws, temperature field and rolling force distribution laws of bearing steel, and analyze the formation reasons of surface hair cracks on bearing steel bars.

2. The method for predicting the formation cause of surface hair cracks of bearing steel bars according to claim 1, wherein: In step 1, a billet with an initial cross-sectional size of 250mm×300mm is used, and five rolling mills are arranged alternately in the flat (H)-vertical (V) mode, adopting a box-ellipse-round pass system.

3. A method for predicting the cause of surface hair cracks in bearing steel bars according to claim 1, characterized in that: In Step 2, the friction coefficient between the rolled piece and the roll is set to 0.7, and the equivalent heat transfer coefficient is 9.5 kw / m 2 ·°C.

4. A method for predicting the cause of surface hairline formation in bearing steel bars according to claim 1, characterized in that: In step 3, set the roll temperature to 250°C and the ambient temperature to 25°C.

5. A method for predicting the cause of surface hair cracks in bearing steel bars according to claim 1, characterized in that: In step 3, the simulation experiment process parameters are as follows: Pass 1: Roll gap 30mm, rolling linear speed 0.264m / s, elongation coefficient 1.13, roll diameter 950mm; Pass 2: Roll gap 30mm, rolling linear speed 0.303m / s, elongation coefficient 1.21, roll diameter 870mm; Pass 3: Roll gap 30mm, rolling linear speed 0.352m / s, elongation coefficient 1.18, roll diameter 900mm; Pass 4: Roll gap 25mm, rolling linear speed 0.456m / s, elongation coefficient 1.33, roll diameter 800mm; Pass 5: Roll gap 25mm, rolling linear speed 0.600m / s, elongation coefficient 1.32, roll diameter 800mm.

6. A method for predicting the cause of surface hair cracks in bearing steel bars according to claim 1, characterized in that: In step 4, set the billet length to 3500mm and divide it into 33600 elements.

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