A rolling method of high-carbon microalloyed non-quenched and tempered steel for connecting rod

Abstract

The application relates to the technical field of steel metallurgy, and particularly discloses a rolling method of high-carbon micro-alloyed non-quenched and tempered steel for connecting rods, which comprises raw material heating, raw material rolling, bar control cooling and bar pit slow cooling; the chemical components of the raw material comprise C: 0.69-0.71%, Si: 0.17-0.23%, Mn: 0.55-0.59%, Cr: 0.12-0.16%, P: <0.020%, S: 0.060-0.070%, Ni: 0.050-0.060%, V: 0.035-0.045%, Cu: <=0.10%, Mo <=0.05% and Ti: <=0.010% in percentage of mass; the raw material is smelted into a continuous casting blank by using an electric furnace; the steel has high carbon and high sulfur; the continuous casting blank is prone to segregation and loose defects; the bar does not need to be heat treated and has high tensile strength, good toughness and brittleness.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods. Background Technology

[0002] Connecting rods are critical components in engines, transmitting the gas forces from the piston to the crankshaft, converting the piston's reciprocating motion into the crankshaft's rotational motion. Therefore, connecting rods require sufficient fatigue strength and stiffness. The application principles for engine connecting rod materials are reliability and low cost, demanding good comprehensive mechanical and technological properties. Traditionally, connecting rods are manufactured using medium-carbon steels and medium-carbon alloy structural steels such as 45, 40Cr, and 35CrMoA. To reduce production costs, microalloyed non-quenched and tempered steel has been developed for connecting rod production. Non-quenched and tempered steel, also known as non-quenched and tempered mechanical structural steel, is defined as: medium-carbon steel with the addition of trace alloying elements (V, Nb, Ti, and N, etc.) through controlled-temperature rolling and cooling, resulting in the dispersion of carbon (nitrogen) compounds as strengthening phases in ferrite and pearlite. This allows the steel to achieve the mechanical properties of ferritic structural steel and alloy structural steel after quenching and tempering without subsequent tempering treatment. In recent years, with the improvement of research and production technology of microalloyed non-quenched and tempered steel in my country, non-quenched and tempered steel has been widely used in the automotive industry, seamless steel pipes, automotive connecting rods, engine crankshafts, and other components. Therefore, it is necessary to design a rolling method for high-carbon microalloyed sulfur-containing free-machining non-quenched and tempered steel for connecting rods with a carbon content of about 0.7%. In order to obtain the required uniform and stable mechanical properties of the parts, it is necessary to control the cooling method and cooling rate of the microalloyed non-quenched and tempered steel after rolling. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods.

[0004] The technical solution adopted by this invention to solve its technical problem is: a rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods, comprising the following steps:

[0005] 1) After being weighed and measured, the continuously cast billet is loaded into the walking beam furnace for heating via the furnace feed roller conveyor;

[0006] 2) After the continuous casting billet exits the furnace, it enters a high-pressure water descaling device with a water pressure of 24MPa to remove the iron oxide scale on the surface of the continuous casting billet.

[0007] 3) The rolling temperature control range is 970~1070℃. The continuously cast billet enters the roughing mill, which has a total of 6 stands.

[0008] 4) The continuous casting billet after rough rolling enters the intermediate and finishing mill. The intermediate mill consists of 5 mills with a diameter of φ750mm, and the finishing mill consists of 4 mills with a diameter of φ550mm.

[0009] 5) After rolling, the bars are sequentially fed into water-cooled boxes 1#, 2#, 3#, 4#, 5#, and 6#.

[0010] 6) After the bar stock is cooled by the water cooling box, it enters the long-length cooling bed for further cooling. The temperature of the upper cooling bed is 660-680℃ and the temperature of the lower cooling bed is 340℃.

[0011] 7) The bars are sawn into sections, collected and bundled, and then placed in the pit for slow cooling;

[0012] 8) After straightening, peeling, and flaw detection, the bars are packaged in a standardized manner;

[0013] The chemical composition of the unmodified steel bar, by mass percentage, includes: C: 0.69–0.71%, Si: 0.17–0.23%, Mn: 0.55–0.59%, Cr: 0.12–0.16%, P: <0.020%, S: 0.060–0.070%, Cu: ≤0.10%, Mo: ≤0.05%, Ti: ≤0.010%, V: 0.035–0.045%, Ni: 0.050–0.060%, with the remainder being iron and unavoidable impurity elements.

[0014] Specifically, the specifications of the continuously cast billet in step 1) are 260mm×3000mm. The temperature of the continuously cast billet in the preheating section of the walking beam furnace is 450~850℃, the temperature of the heating section is 1150~1210℃, and the temperature of the soaking section is 1160~1190℃.

[0015] Specifically, the roughing mill in step 3) is a high-rigidity short-stress-line mill, with alternating horizontal and vertical arrangement, and is sheared by a hydraulic shearing head after roughing.

[0016] Specifically, the rolling mills of the intermediate rolling mill and the finishing rolling mill in step 4) are both high-rigidity short-stress-line rolling mills, arranged alternately in horizontal and vertical configurations.

[0017] Specifically, in step 5), the No. 1 Venturi tube water-cooled tank is controlled at a water pressure of 2.63 MPa and a water flow rate of 180 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 820℃;

[0018] #2 Venturi tube water-cooled box: controlled water pressure 1.55MPa, water flow rate 170m³ / h 3 / h, the outlet water cooling box temperature is controlled at 780℃;

[0019] The No. 3 Venturi tube water-cooled box has a controlled water pressure of 1.45 MPa and a water flow rate of 150 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 700℃;

[0020] The No. 4 Venturi tube water-cooled box has a controlled water pressure of 0.90 MPa and a water flow rate of 140 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 680℃;

[0021] The No. 5 Venturi tube water-cooled box has a controlled water pressure of 0.48 MPa and a water flow rate of 80 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 650℃;

[0022] The No. 6 Venturi tube water-cooled box has a controlled water pressure of 0.42 MPa and a water flow rate of 80 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 610℃.

[0023] Specifically, in step 7), the temperature of the bar entering the slow cooling pit is 300°C, and the bar is fully slow cooled in the slow cooling pit for 24 hours, with the temperature of the bar exiting the pit being ≤100°C.

[0024] The present invention has the following beneficial effects:

[0025] The high-carbon microalloyed non-quenched and tempered steel rods produced by the rolling method designed in this invention have high tensile strength and good toughness and brittleness without heat treatment. The method uses low Si and low Mn, strictly controls the alloying elements Cr, Ni and Mo, and adds trace element V. After hot rolling, its microstructure is pearlite and a small amount of ferrite, with sufficient strength and hardness. After pyrolysis processing, there is no obvious plastic deformation, and the fracture surface exhibits brittle fracture characteristics. Attached Figure Description

[0026] Figure 1 This is a flow chart of the rolling process for high-carbon microalloyed non-quenched and tempered steel used in connecting rods.

[0027] In the diagram: 1-Heating furnace; 2-High-pressure water descaling; 3-Roughing mill; 4-Insulation cover; 5-Hydraulic shear; 6-Intermediate mill; 7-Flying shear one; 8-Finishing mill; 9-1# Venturi tube water-cooled box; 10-2# Venturi tube water-cooled box; 11-3# Venturi tube water-cooled box; 12-4# Venturi tube water-cooled box; 13-5# Venturi tube water-cooled box; 14-6# Venturi tube water-cooled box; 15-Flying shear two; 16-Cooling bed; 17-Sawing machine; 18-Beveling machine one; 19-Collection device; 20-Short-length cooling bed; 21-Beveling machine one; 22-Automatic bundling machine; 23-Collection platform. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, a rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods is described. The rolling process route is as follows: continuous casting billet is heated in heating furnace 1 - high-pressure water descaling 2 - roughing mill 3 - insulation cover 4 and hydraulic shear 5 - intermediate mill 6 - flying shear 1 7 - finishing mill 8 - 1# Venturi tube water cooling box 9 - 2# Venturi tube water cooling box 10 - 3# Venturi tube water cooling box 11 - 4# Venturi tube water cooling box 12 - 5# Venturi tube water cooling box 13 - 6# Venturi tube water cooling box 14 - flying shear 2 15 - multiple length cooling bed 16 - cooling - sawing machine 17 - sawing - fixed length cooling bed 20 - cooling - chamfering machine 1 18 and chamfering machine 2 21 - automatic bundling machine 22 - collection device 19 - slow cooling in pit - finishing - collection platform 23.

[0030] A rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods, wherein the chemical composition by mass percentage comprises: C: 0.69–0.71%, Si: 0.17–0.23%, Mn: 0.55–0.59%, Cr: 0.12–0.16%, P: <0.020%, S: 0.060–0.070%, Cu: ≤0.10%, Mo: ≤0.05%, Ti: ≤0.010%; and also contains V: 0.035–0.045%, Ni: 0.050–0.060%.

[0031] The main steps are as follows:

[0032] Step 1: The continuous casting billet has a size of 260mm×3000mm. After weighing and length measurement, it is loaded into the walking beam furnace via the furnace feed roller conveyor. The preheating section temperature is 450~850℃, the heating section temperature is 1150~1210℃, and the soaking section temperature is 1160~1190℃.

[0033] Step 2: After the continuous casting billet exits the furnace, it enters a high-pressure water descaling device with a water pressure of 24 MPa to remove the iron oxide scale from the surface of the continuous casting billet.

[0034] Step 3: The rolling temperature is controlled within the range of 970 to 1070℃. The continuously cast billet enters the roughing mill. The roughing mill has a total of 6 stands. The mill type is a high-rigidity short stress line mill, which is arranged alternately in horizontal and vertical configurations. After roughing, it is sheared by a hydraulic shear head.

[0035] Step 4: The continuously cast billet after rough rolling enters the intermediate and finishing mill. The intermediate mill consists of 5 stands with a diameter of... The rolling mill consists of four stands with a diameter of [missing information]. The rolling mill consists of a high-rigidity, short-stress-line rolling mill, arranged in alternating horizontal and vertical configurations.

[0036] Step 5: After rolling, the bar enters the No. 1 Venturi tube water cooling box with a water pressure of 2.63MPa, a water flow rate of 180m3 / h, and the temperature at the outlet of the water cooling box is controlled at 820℃.

[0037] Step 6: The bar stock enters the No. 2 Venturi tube water-cooled box from the No. 1 Venturi tube water-cooled box. The water pressure is 1.55MPa, the water flow rate is 170m3 / h, and the temperature of the water-cooled box is controlled at 780℃.

[0038] Step 7: The bar stock enters the No. 3 Venturi tube water-cooled box from the No. 2 Venturi tube water-cooled box. The water pressure is 1.45MPa, the water flow rate is 150m3 / h, and the temperature of the water-cooled box is controlled at 700℃.

[0039] Step 8: The bar stock enters the No. 4 Venturi tube water-cooled box from the No. 3 Venturi tube water-cooled box. The water pressure is 0.90MPa, the water flow rate is 140m3 / h, and the temperature of the water-cooled box is controlled at 680℃.

[0040] Step 9: The bar stock enters the No. 5 Venturi tube water-cooled box from the No. 4 Venturi tube water-cooled box. The water pressure is 0.48MPa, the water flow rate is 80m3 / h, and the temperature of the water-cooled box is controlled at 650℃.

[0041] Step 10: The bar stock enters the No. 6 Venturi tube water-cooled box from the No. 5 Venturi tube water-cooled box. The water pressure is 0.42MPa, the water flow rate is 80m3 / h, and the temperature of the water-cooled box is controlled at 610℃.

[0042] Step 11: After the bar stock is cooled by the water tank, it enters the long-length cooling bed for further cooling. The upper cooling bed temperature is 660-680℃, and the lower cooling bed temperature is 340℃.

[0043] Step 12: The bar stock is sawn into sections, collected and bundled, and then placed in a pit for slow cooling at a temperature of 300℃.

[0044] Step 13: The bar stock is allowed to cool slowly in the slow cooling pit for 24 hours, and the temperature after exiting the pit is ≤100℃.

[0045] Step 14: After straightening, peeling, and flaw detection, the bars are packaged in a standardized manner.

[0046] Table 1. Main performance test results

[0047]

[0048] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0049] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods, characterized in that, Includes the following steps: 1) After being weighed and measured, the continuously cast billet is loaded into the walking beam furnace for heating via the furnace feed roller conveyor; 2) After the continuous casting billet exits the furnace, it enters a high-pressure water descaling device with a water pressure of 24MPa to remove the iron oxide scale on the surface of the continuous casting billet. 3) The rolling temperature control range is 970~1070℃. The continuously cast billet enters the roughing mill, which has a total of 6 stands. 4) The continuous casting billet after rough rolling enters the intermediate and finishing mill. The intermediate mill consists of 5 mills with a diameter of φ750mm, and the finishing mill consists of 4 mills with a diameter of φ550mm. 5) After rolling, the bars are sequentially fed into the No. 1, No. 2, No. 3, No. 4, No. 5, and No. 6 Venturi tube water-cooling boxes for water cooling. The No. 1 Venturi tube water-cooled box has a controlled water pressure of 2.63 MPa and a water flow rate of 180 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 820℃; #2 Venturi tube water-cooled box: controlled water pressure 1.55MPa, water flow rate 170m³ / h 3 / h, the outlet water cooling box temperature is controlled at 780℃; The No. 3 Venturi tube water-cooled box has a controlled water pressure of 1.45 MPa and a water flow rate of 150 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 700℃; The No. 4 Venturi tube water-cooled box has a controlled water pressure of 0.90 MPa and a water flow rate of 140 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 680℃; The No. 5 Venturi tube water-cooled box has a controlled water pressure of 0.48 MPa and a water flow rate of 80 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 650℃; The No. 6 Venturi tube water-cooled box has a controlled water pressure of 0.42 MPa and a water flow rate of 80 m³ / h. 3 / h, the outlet water cooling box temperature is controlled at 610℃; 6) After the bar stock is cooled by the water cooling box, it enters the long-length cooling bed for further cooling. The temperature of the upper cooling bed is 660-680℃ and the temperature of the lower cooling bed is 340℃. 7) The bars are sawn into sections, collected and bundled, and then placed in the pit for slow cooling; 8) After straightening, peeling, and flaw detection, the bars are packaged in a standardized manner; The chemical composition of the unmodified steel bar, by mass percentage, includes: C: 0.69–0.71%, Si: 0.17–0.23%, Mn: 0.55–0.59%, Cr: 0.12–0.16%, P: <0.020%, S: 0.060–0.070%, Cu: ≤0.10%, Mo: ≤0.05%, Ti: ≤0.010%, V: 0.035–0.045%, Ni: 0.050–0.060%, with the remainder being iron and unavoidable impurity elements.

2. The rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods according to claim 1, characterized in that, The specifications of the continuously cast billet in step 1) are 260mm×3000mm. The temperature of the continuously cast billet in the preheating section of the walking beam furnace is 450~850℃, the temperature of the heating section is 1150~1210℃, and the temperature of the soaking section is 1160~1190℃.

3. The rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods according to claim 1, characterized in that, The roughing mill in step 3) is a high-rigidity short-stress-line mill, with alternating horizontal and vertical arrangement, and is sheared by a hydraulic shearing head after roughing.

4. The rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods according to claim 1, characterized in that, In step 4), both the intermediate and finishing mills are high-rigidity short-stress-line mills, arranged alternately in a horizontal-vertical configuration.

5. The rolling method for high-carbon microalloyed non-quenched and tempered steel for connecting rods according to claim 1, characterized in that, In step 7), the temperature of the bar entering the slow cooling pit is 300°C, and the bar is fully slow cooled in the slow cooling pit for 24 hours, with the temperature of the bar exiting the pit ≤100°C.

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