Non-quenched and tempered steel for connecting rod, preparation method of non-quenched and tempered steel and vehicle connecting rod

Abstract

The invention relates to non-quenched and tempered steel for a connecting rod, a preparation method of the non-quenched and tempered steel and a vehicle connecting rod, in particular to the field of steel, and the non-quenched and tempered steel for the connecting rod comprises, by mass, 0.44%-0.47% of C, 0.65%-0.75% of Si, 1.15%-1.25% of Mn, smaller than or equal to 0.045% of P, 0.04%-0.07% of S, 0.15%-0.2% of V, 0.2%-0.25% of Cr, 0.1%-0.2% of Ni, smaller than or equal to 0.2% of Cu, 0.02%-0.04% of Nb, 0.014%-0.02% of N and the balance Fe and inevitable impurities. According to the non-quenched and tempered steel for the connecting rod, the grain size grade of the steel is optimized through the element composition of the steel and the synergistic effect of Ni, Nb and N, and the grain size of the obtained product is larger than or equal to 7.5 grade.

Description

Technical Field

[0001] The present invention relates to the field of steel, and specifically relates to a non-quenched and tempered steel for connecting rods, a preparation method thereof, and a vehicle connecting rod. Background Art

[0002] At present, the non-quenched and tempered steels for conventional connecting rods are mainly made of materials such as C70S6, 36MnVS4, 46MnVS5, etc. For example, CN106086288A discloses a manufacturing method of a 36MnVS4 fracture-split connecting rod steel. By selecting raw materials, the residual elements are controlled; by adopting a smelting method for controlling the phosphorus content, the phosphorus content is controlled within 0.020 - 0.030%, so that the reject rate after fracture splitting is not more than 3‰; by controlling the converter smelting, VD+LF secondary refining and argon protection casting steelmaking processes, the purity of the molten steel is ensured; by controlling the residual element chromium within 0.10 - 0.15%, nickel not more than 0.10%, molybdenum not more than 0.03%, and controlling the carbon equivalent within 1.18 - 1.27%, the hardness of the finished connecting rod is achieved.

[0003] CN117625905A discloses a forging heat treatment method and a connecting rod of a 46MnVS5 material. This method is to design a controlled cooling process and an initial forging temperature after connecting rod forging; the controlled cooling process after connecting rod forging is: first slowly cool to control the dispersed precipitation of V(CN) particles, so that the surface grain size increases and then rapidly cool, and control the initial forging temperature of the connecting rod between 1220 - 1260°C; the controlled cooling process is that the temperature entering the controlled cooling system is 900 - 950°C, air-cooled for 90 s to cool to 800 - 820°C, air-cooled for 180 s to cool to 680 - 700°C, air-cooled for 520 s to 420 - 440°C; air-cooled to 380 - 400°C and taken out of the controlled cooling system and packed in a box.

[0004] However, currently, the requirements for torque, fatigue strength, etc. of commercial vehicles are becoming increasingly strict, and the performance indicators for connecting rods are also getting higher and higher. The composition and microstructure design of the steel for connecting rods directly affect the final performance of the finished connecting rod, directly determine the indicators such as the strength and plasticity of the connecting rod, and further affect the requirements for the load capacity and lightweight of commercial vehicles. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a non-quenched and tempered steel for connecting rods, a preparation method thereof, and a vehicle connecting rod to solve the defect that the mechanical properties of the current 46MnVS5 series non-quenched and tempered steels are insufficient to meet high-performance use.

[0006] To achieve this purpose, the present invention adopts the following technical solutions:

[0007] In the first aspect, the present invention provides a non-quenched and tempered steel for connecting rods, which includes, by mass percentage:

[0008] C 0.44 - 0.47%, Si 0.65 - 0.75%, Mn 1.15 - 1.25%, P ≤ 0.045%, S 0.04 - 0.07%, V 0.15 - 0.2%, Cr 0.2 - 0.25%, Ni 0.1 - 0.2%, Cu ≤ 0.2%, Nb 0.02 - 0.04%, N 0.014 - 0.02%, and the balance is Fe and inevitable impurities.

[0009] The non - quenched and tempered steel for connecting rods provided by the present invention optimizes the grain size grade of the steel by utilizing the synergistic effect of Ni, Nb, and N on the elemental composition of the steel, making the grain size of the obtained product ≥ grade 7.5 and improving the mechanical properties of the product.

[0010] In a second aspect, the present invention provides a preparation method of the non - quenched and tempered steel for connecting rods as described in the first aspect, and the preparation method includes:

[0011] Converting hot metal into continuous casting billets through converter steelmaking, LF refining, VD vacuum treatment, and continuous casting in sequence;

[0012] Rolling the continuous casting billets to obtain non - quenched and tempered steel for connecting rods.

[0013] As a preferred technical solution of the present invention, alloying is carried out during converter steelmaking.

[0014] Preferably, the alloys added during the alloying include: manganese - silicon master alloy, chromium master alloy, vanadium source, silicon - iron master alloy, and nickel source.

[0015] Preferably, the tapping temperature of the converter steelmaking is ≥ 1600 °C.

[0016] Preferably, the final carbon content of the converter steelmaking is 0.06 - 0.15% by mass percentage.

[0017] Preferably, the final phosphorus content of the converter steelmaking is ≤ 0.015% by mass percentage.

[0018] As a preferred technical solution of the present invention, slag - making materials and the first master alloy are added during LF refining.

[0019] Preferably, the slag - making materials include: lime, aluminum pellets, and silicon carbide.

[0020] Preferably, the addition amounts of the slag - making materials are: lime ≤ 100 kg / furnace, aluminum pellets 30 - 50 kg / furnace, and silicon carbide 20 - 30 kg / furnace.

[0021] Preferably, the first master alloy includes: ferroniobium.

[0022] Preferably, the holding time of white slag during LF refining is 300 - 330 min.

[0023] As a preferred technical solution of the present invention, a first covering agent and a second master alloy are added in the VD vacuum.

[0024] Preferably, the first covering agent includes: carbonized rice husk.

[0025] Preferably, the addition amount of the first covering agent is 12-25 kg / furnace.

[0026] Preferably, the second master alloy includes: manganese-nitrogen alloy and calcium-silicon alloy.

[0027] Preferably, the soft blowing time in the VD vacuum is 15-25 min.

[0028] As a preferred technical solution of the present invention, a second covering agent and a protective slag are added in the continuous casting.

[0029] Preferably, the second covering agent includes: carbonized rice husk.

[0030] Preferably, the addition amount of the second covering agent is 15-25 kg / furnace.

[0031] Preferably, the protective slag includes: F02 protective slag.

[0032] Preferably, the addition amount of the protective slag is 0.4-0.5 kg / t.

[0033] As a preferred technical solution of the present invention, the superheat degree of the molten steel in the continuous casting is ≤25°C.

[0034] Preferably, the drawing speed of the continuous casting is 0.8-1 m / min.

[0035] As a preferred technical solution of the present invention, mold stirring and final electromagnetic stirring are carried out in the continuous casting.

[0036] Preferably, the current of the mold stirring is 250-350 A.

[0037] Preferably, the frequency of the mold stirring is 2-4 Hz.

[0038] Preferably, the current of the final electromagnetic stirring is 90-110 A.

[0039] Preferably, the frequency of the final electromagnetic stirring is 11-13 Hz.

[0040] As a preferred technical solution of the present invention, the preheating temperature of the rolling is ≤900°C.

[0041] Preferably, the rolling starting temperature is 1060-1130°C.

[0042] Preferably, the finish rolling temperature of the rolling is 840 - 860 °C.

[0043] In a third aspect, the present invention provides a vehicle connecting rod, which is prepared by using the non-quenched and tempered steel for connecting rods as described in the first aspect or the non-quenched and tempered steel for connecting rods obtained by the preparation method as described in the second aspect.

[0044] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0045] For the non-quenched and tempered steel for connecting rods provided by the present invention, through the element composition of the steel, by utilizing the synergistic effect of Ni, Nb, and N, the grain size grade of the steel is optimized. Further, by designing the continuous casting process in the preparation process, such as the parameters of mold electromagnetic stirring and final electromagnetic stirring, and controlling the superheat of the molten steel, better uniformity is achieved, so that the tensile strength of the obtained steel product is ≥1020 MPa.

[0046] The present invention will be further described in detail below. However, the following examples are merely simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention is subject to the claims. Specific Embodiments

[0047] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, the typical but non-limiting embodiments of the present invention are as follows:

[0048] I. This embodiment provides a non-quenched and tempered steel for connecting rods, which includes, by mass percentage:

[0049] C 0.44 - 0.47%, Si 0.65 - 0.75%, Mn 1.15 - 1.25%, P ≤ 0.045%, S 0.04 - 0.07%, V 0.15 - 0.2%, Cr 0.2 - 0.25%, Ni 0.1 - 0.2%, Cu ≤ 0.2%, Nb 0.02 - 0.04%, N 0.014 - 0.02%, and the balance is Fe and unavoidable impurities.

[0050] In the present invention, the C element in the non-quenched and tempered steel for connecting rods is 0.44 - 0.47% by mass percentage. For example, it can be 0.44%, 0.442%, 0.444%, 0.446%, 0.448%, 0.45%, 0.452%, 0.454%, 0.456%, 0.458%, 0.46%, 0.462%, 0.464%, 0.466%, 0.468% or 0.47, etc., but is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0051] In the present invention, the Si element in the non-quenched and tempered steel for connecting rods is 0.65 - 0.75% by mass percentage. For example, it can be 0.65%, 0.66%, 0.67%, 0.68%, 0.69%, 0.7%, 0.71%, 0.72%, 0.73%, 0.74% or 0.75%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0052] In the present invention, the Mn element in the non-quenched and tempered steel for connecting rods is 1.15 - 1.25% by mass percentage. For example, it can be 1.15%, 1.16%, 1.17%, 1.18%, 1.19%, 1.2%, 1.21%, 1.22%, 1.23%, 1.24% or 1.25%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0053] In the present invention, the P element in the non-quenched and tempered steel for connecting rods is ≤0.045% by mass percentage. For example, it can be 0.045%, 0.04%, 0.035%, 0.03%, 0.025%, 0.02%, 0.015%, 0.01%, 0.005% or 0.001%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0054] In the present invention, the S element in the non-quenched and tempered steel for connecting rods is 0.04 - 0.07% by mass percentage. For example, it can be 0.04%, 0.042%, 0.044%, 0.046%, 0.048%, 0.05%, 0.052%, 0.054%, 0.056%, 0.058%, 0.06%, 0.062%, 0.064%, 0.066%, 0.068% or 0.07%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0055] In the present invention, the V element in the non-quenched and tempered steel for connecting rods is 0.15 - 0.2% by mass percentage. For example, it can be 0.15%, 0.155%, 0.16%, 0.165%, 0.17%, 0.175%, 0.18%, 0.185%, 0.19%, 0.195% or 0.2%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0056] In the present invention, the content of Cr element in the non-quenched and tempered steel for connecting rod is 0.2-0.25% by mass percentage. For example, it can be 0.2%, 0.205%, 0.21%, 0.215%, 0.22%, 0.225%, 0.23%, 0.235%, 0.24%, 0.245% or 0.25%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0057] In the present invention, the content of Ni element in the non-quenched and tempered steel for connecting rod is 0.1-0.2% by mass percentage. For example, it can be 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19% or 0.2%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0058] In the present invention, the content of Cu element in the non-quenched and tempered steel for connecting rod is ≤0.2% by mass percentage. For example, it can be 0.2%, 0.18%, 0.16%, 0.14%, 0.12%, 0.1%, 0.08%, 0.06%, 0.04%, 0.02%, 0.01% or 0.001%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0059] In the present invention, the content of Nb element in the non-quenched and tempered steel for connecting rod is 0.02-0.04% by mass percentage. For example, it can be 0.02%, 0.022%, 0.024%, 0.026%, 0.028%, 0.03%, 0.032%, 0.034%, 0.036%, 0.038% or 0.04%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0060] In the present invention, the content of N element in the non-quenched and tempered steel for connecting rod is 0.014-0.02% by mass percentage. For example, it can be 0.014%, 0.0145%, 0.015%, 0.0155%, 0.016%, 0.0165%, 0.017%, 0.0175%, 0.018%, 0.0185%, 0.019%, 0.0195% or 0.02%, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0061] II. This embodiment provides a preparation method of non-quenched and tempered steel for connecting rod. The preparation method includes:

[0062] The molten iron is successively subjected to converter steelmaking, LF refining, VD vacuum and continuous casting to obtain a continuous casting billet;

[0063] The continuous casting billet is rolled to obtain non-quenched and tempered steel for connecting rod.

[0064] Among them, the non-quenched and tempered steel for the connecting rod comprises, by mass percentage: C 0.44 - 0.47%, Si 0.65 - 0.75%, Mn 1.15 - 1.25%, P ≤ 0.045%, S 0.04 - 0.07%, V 0.15 - 0.2%, Cr 0.2 - 0.25%, Ni 0.1 - 0.2%, Cu ≤ 0.2%, Nb 0.02 - 0.04%, N 0.014 - 0.02%, and the balance is Fe and unavoidable impurities.

[0065] Among them, alloying is carried out during the converter steelmaking.

[0066] Among them, the alloys added during the alloying include: ferromanganese-silicon master alloy, chromium master alloy, vanadium source, ferrosilicon master alloy and nickel source.

[0067] In the present invention, the ferromanganese-silicon master alloy used can be selected as ferromanganese-silicon alloy, the chromium master alloy can be selected as high-carbon ferrochrome, the vanadium source can be selected as flake vanadium, the ferrosilicon master alloy can be selected as ferrosilicon, and the nickel source can be selected as nickel plate or nickel powder, etc.

[0068] Among them, the tapping temperature of the converter steelmaking is ≥ 1600 °C, for example, it can be 1600 °C, 1620 °C, 1640 °C, 1660 °C, 1680 °C, 1700 °C, 1720 °C, 1740 °C, 1760 °C, 1780 °C or 1800 °C, etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0069] Among them, the final carbon content of the converter steelmaking is 0.06 - 0.15% by mass percentage, for example, it can be 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14% or 0.15%, etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0070] Among them, the final phosphorus content of the converter steelmaking is ≤ 0.015% by mass percentage, for example, it can be 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, etc., but not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0071] Among them, slag-making materials and a first master alloy are added during the LF refining.

[0072] Among them, the slag-making materials include: lime, aluminum pellets and silicon carbide.

[0073] Among them, the addition amount of the slag-making material includes: lime ≤ 100 kg / furnace, for example, it can be 100 kg / furnace, 90 kg / furnace, 80 kg / furnace, 70 kg / furnace, 60 kg / furnace, 50 kg / furnace, 40 kg / furnace, 30 kg / furnace, 20 kg / furnace or 10 kg / furnace, etc.; aluminum pellets 30 - 50 kg / furnace, for example, it can be 30 kg / furnace, 32 kg / furnace, 34 kg / furnace, 36 kg / furnace, 38 kg / furnace, 40 kg / furnace, 42 kg / furnace, 44 kg / furnace, 46 kg / furnace, 48 kg / furnace or 50 kg / furnace, etc.; silicon carbide 20 - 30 kg / furnace, for example, it can be 20 kg / furnace, 21 kg / furnace, 22 kg / furnace, 23 kg / furnace, 24 kg / furnace, 25 kg / furnace, 26 kg / furnace, 27 kg / furnace, 28 kg / furnace, 29 kg / furnace or 30 kg / furnace, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0074] Among them, the first master alloy includes: ferroniobium.

[0075] Among them, the holding time of the white slag in the LF refining is 300 - 330 min, for example, it can be 300 min, 302 min, 304 min, 306 min, 308 min, 310 min, 312 min, 314 min, 316 min, 318 min, 320 min, 322 min, 324 min, 326 min, 328 min or 330 min, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0076] Among them, a first covering agent and a second master alloy are added in the VD vacuum.

[0077] Among them, the first covering agent includes: carbonized rice husk.

[0078] Among them, the addition amount of the first covering agent is 12 - 25 kg / furnace, for example, it can be 12 kg / furnace, 13 kg / furnace, 14 kg / furnace, 15 kg / furnace, 16 kg / furnace, 17 kg / furnace, 18 kg / furnace, 19 kg / furnace, 20 kg / furnace, 21 kg / furnace, 22 kg / furnace, 23 kg / furnace, 24 kg / furnace or 25 kg / furnace, etc. However, it is not limited to the listed values, and other unlisted values within this range also meet the requirements.

[0079] Among them, the second master alloy includes: manganese-nitrogen alloy and calcium-silicon alloy.

[0080] Among them, the time for soft blowing in VD vacuum is 15 - 25 min. For example, it can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min or 25 min, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0081] Among them, a second covering agent and a flux are added during continuous casting.

[0082] Among them, the second covering agent includes: carbonized rice husk.

[0083] Among them, the addition amount of the second covering agent is 15 - 25 kg / furnace. For example, it can be 15 kg / furnace, 16 kg / furnace, 17 kg / furnace, 18 kg / furnace, 19 kg / furnace, 20 kg / furnace, 21 kg / furnace, 22 kg / furnace, 23 kg / furnace, 24 kg / furnace or 25 kg / furnace, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0084] Among them, the flux includes: F02 flux.

[0085] Among them, the addition amount of the flux is 0.4 - 0.5 kg / t. For example, it can be 0.4 kg / t, 0.41 kg / t, 0.42 kg / t, 0.43 kg / t, 0.44 kg / t, 0.45 kg / t, 0.46 kg / t, 0.47 kg / t, 0.48 kg / t, 0.49 kg / t or 0.5 kg / t, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0086] Among them, the superheat of the molten steel during continuous casting is ≤25°C. For example, it can be 25°C, 24°C, 23°C, 22°C, 21°C, 20°C, 19°C, 18°C, 17°C, 16°C or 15°C, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0087] Among them, the casting speed during continuous casting is 0.8 - 1 m / min. For example, it can be 0.8 m / min, 0.82 m / min, 0.84 m / min, 0.86 m / min, 0.88 m / min, 0.9 m / min, 0.92 m / min, 0.94 m / min, 096 m / min, 0.98 m / min or 1 m / min, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0088] Among them, mold stirring and final electromagnetic stirring are carried out during continuous casting.

[0089] Among them, the current of the crystallizer stirring is 250 - 350A. For example, it can be 250A, 260A, 270A, 280A, 290A, 300A, 310A, 320A, 330A, 340A or 350A, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0090] Among them, the frequency of the crystallizer stirring is 2 - 4Hz. For example, it can be 2Hz, 2.2Hz, 2.4Hz, 2.6Hz, 2.8Hz, 3Hz, 3.2Hz, 3.4Hz, 3.6Hz, 3.8Hz or 4Hz, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0091] Among them, the current of the end electromagnetic stirring is 90 - 110A. For example, it can be 90A, 92A, 94A, 96A, 98A, 100A, 102A, 104A, 106A, 108A or 110A, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0092] Among them, the frequency of the end electromagnetic stirring is 11 - 13Hz. For example, it can be 11Hz, 11.2Hz, 11.4Hz, 11.6Hz, 11.8Hz, 12Hz, 12.2Hz, 12.4Hz, 12.6Hz, 12.8Hz or 13Hz, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0093] Among them, the preheating temperature of the rolling is ≤900°C. For example, it can be 900°C, 850°C, 800°C, 750°C, 700°C, 650°C, 600°C, 550°C or 500°C, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0094] Among them, the starting rolling temperature of the rolling is 1060 - 1130°C. For example, it can be 1060°C, 1065°C, 1070°C, 1075°C, 1080°C, 1085°C, 1090°C, 1095°C, 1100°C, 1105°C, 1110°C, 1115°C, 1120°C, 1125°C or 1130°C, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0095] Among them, the finishing rolling temperature of the rolling is 840 - 860°C. For example, it can be 840°C, 845°C, 850°C, 855°C or 860°C, etc., but not limited to the listed values. Other unlisted values within this range also meet the requirements.

[0096] III. This embodiment provides a vehicle connecting rod, which is prepared by using a non-quenched and tempered steel for connecting rods or a non-quenched and tempered steel obtained by its preparation method.

[0097] IV. In order to illustrate the excellent mechanical properties of the non-quenched and tempered steel for connecting rods provided by the present invention, the following practical examples are used for illustration, specifically as follows:

[0098] Example 1

[0099] This embodiment provides a non-quenched and tempered steel for connecting rods, which includes, by mass percentage:

[0100] C 0.45%, Si 0.7%, Mn 1.2%, P 0.005%, S 0.055%, V 0.18%, Cr 0.22%, Ni 0.15%, Cu 0.1%, Nb 0.03%, N 0.017%, and the balance is Fe and unavoidable impurities.

[0101] The preparation process is as follows:

[0102] The molten iron is successively subjected to converter steelmaking, LF refining, VD vacuum and continuous casting to obtain a continuous casting billet;

[0103] The continuous casting billet is rolled to obtain a non-quenched and tempered steel for connecting rods;

[0104] Alloying is carried out in the converter steelmaking, and the added alloys are ferromanganese-silicon alloy, high-carbon ferrochrome, flake vanadium, ferrosilicon and nickel plate; the tapping temperature of the converter steelmaking is 1600°C, the end point carbon is 0.1% by mass percentage, and the end point phosphorus is 0.005% by mass percentage;

[0105] In the LF refining, slag-making materials and a first intermediate alloy are added. The addition amounts of the slag-making materials include: 50 kg / furnace of lime, 40 kg / furnace of aluminum pellets, and 25 kg / furnace of silicon carbide; the first intermediate alloy includes ferrocolumbium; the holding time of the white slag is 315 min;

[0106] In the VD vacuum, a first covering agent and a second intermediate alloy are added. The first covering agent is carbonized rice husk, and the addition amount is 20 kg / furnace; the second intermediate alloy is manganese-nitrogen alloy and calcium-silicon alloy, and the soft blowing time is 20 min;

[0107] In the continuous casting, a second covering agent and a protective slag are added; the second covering agent is carbonized rice husk, and the addition amount is 20 kg / furnace; the protective slag is F02 protective slag, and the addition amount is 0.45 kg / t; the superheat of the molten steel in the continuous casting is 25°C, and the drawing speed is 0.9 m / min; in the continuous casting, mold stirring and final electromagnetic stirring are carried out; the current of the mold stirring is 300 A, and the frequency is 3 Hz; the current of the final electromagnetic stirring is 100 A, and the frequency is 12 Hz;

[0108] The preheating temperature of the rolling is 900 °C, the starting rolling temperature is 1100 °C, and the finishing rolling temperature is 850 °C.

[0109] Example 2

[0110] This example provides a non-quenched and tempered steel for connecting rods, which, in terms of mass percentage, includes:

[0111] C 0.47%, Si 0.75%, Mn 1.15%, P 0.015%, S 0.04%, V 0.2%, Cr 0.25%, Ni 0.2%, Cu 0.15%, Nb 0.04%, N 0.02%, and the balance is Fe and inevitable impurities.

[0112] The preparation process is as follows:

[0113] The molten iron is successively subjected to converter steelmaking, LF refining, VD vacuum, and continuous casting to obtain a continuous casting billet;

[0114] The continuous casting billet is rolled to obtain a non-quenched and tempered steel for connecting rods;

[0115] In the converter steelmaking, alloying is carried out, and the added alloys are ferromanganese-silicon alloy, high-carbon ferrochrome, flake vanadium, ferrosilicon, and nickel plate; the tapping temperature of the converter steelmaking is 1800 °C, the end point carbon is 0.15% in terms of mass percentage, and the end point phosphorus is 0.015% in terms of mass percentage;

[0116] In the LF refining, slag-making materials and a first intermediate alloy are added. The addition amount of the slag-making materials is 80 kg / ladle of lime, 50 kg / ladle of aluminum pellets, and 20 kg / ladle of silicon carbide; the first intermediate alloy is ferroniobium; the holding time of the white slag is 330 min;

[0117] In the VD vacuum, a first covering agent and a second intermediate alloy are added. The first covering agent is carbonized rice husk, and the addition amount is 25 kg / ladle; the second intermediate alloys are manganese-nitrogen alloy and calcium-silicon alloy, and the soft blowing time is 15 min;

[0118] In the continuous casting, a second covering agent and a mold powder are added; the second covering agent is carbonized rice husk, and the addition amount is 15 kg / ladle; the mold powder is F02 mold powder, and the addition amount is 0.5 kg / t; the superheat of the molten steel in the continuous casting is 22 °C, and the casting speed is 1 m / min; mold stirring and final electromagnetic stirring are carried out in the continuous casting; the current of the mold stirring is 350 A, and the frequency is 2 Hz; the current of the final electromagnetic stirring is 110 A, and the frequency is 13 Hz;

[0119] The preheating temperature of the rolling is 800 °C, the starting rolling temperature is 1130 °C, and the finishing rolling temperature is 840 °C.

[0120] Example 3

[0121] This embodiment provides a non - quenched and tempered steel for connecting rods. The non - quenched and tempered steel for connecting rods, by mass percentage, includes:

[0122] C 0.44%, Si 0.65%, Mn 1.25%, P 0.045%, S 0.07%, V 0.15%, Cr 0.2%, Ni 0.1%, Cu 0.2%, Nb 0.02%, N 0.014%, and the balance is Fe and unavoidable impurities.

[0123] The preparation process is as follows:

[0124] The molten iron is successively subjected to converter steelmaking, LF refining, VD vacuum treatment, and continuous casting to obtain a continuous casting billet;

[0125] The continuous casting billet is rolled to obtain the non - quenched and tempered steel for connecting rods;

[0126] Alloying is carried out during the converter steelmaking. The added alloys are ferromanganese - silicon alloy, high - carbon ferrochrome, flake vanadium, ferrosilicon, and nickel plate. The tapping temperature of the converter steelmaking is 1700 °C, the final carbon content is 0.06% by mass percentage, and the final phosphorus content is 0.045% by mass percentage;

[0127] In the LF refining, slag - making materials and the first intermediate alloy are added. The addition amount of the slag - making materials is 20 kg / lot of lime, 30 kg / lot of aluminum pellets, and 30 kg / lot of silicon carbide. The first intermediate alloy is ferro - niobium. The holding time of the white slag is 300 min;

[0128] In the VD vacuum treatment, a first covering agent and a second intermediate alloy are added. The first covering agent is carbonized rice husk, and the addition amount is 12 kg / lot. The second intermediate alloys are manganese - nitrogen alloy and calcium - silicon alloy, and the soft blowing time is 25 min;

[0129] In the continuous casting, a second covering agent and a protective slag are added. The second covering agent is carbonized rice husk, and the addition amount is 25 kg / lot. The protective slag is F02 protective slag, and the addition amount is 0.4 kg / t. The superheat of the molten steel in the continuous casting is 20 °C, and the drawing speed is 0.8 m / min. In the continuous casting, mold stirring and final electromagnetic stirring are carried out. The current of the mold stirring is 250 A, and the frequency is 4 Hz. The current of the final electromagnetic stirring is 90 A, and the frequency is 11 Hz;

[0130] The pre - heating temperature of the rolling is 700 °C, the starting rolling temperature is 1060 °C, and the final rolling temperature is 860 °C.

[0131] Comparative Example 1

[0132] The difference from Example 1 is only that the Nb element in the non - quenched and tempered steel is 0.01% by mass percentage.

[0133] Comparative Example 2

[0134] The difference from Example 1 is only that the Nb element in the non - quenched and tempered steel is 0.05% by mass percentage.

[0135] Comparative Example 3

[0136] The difference from Example 1 is only that the Ni element in the non - quenched and tempered steel is 0.05% by mass percentage.

[0137] Comparative Example 4

[0138] The difference from Example 1 is only that the Ni element in the non - quenched and tempered steel is 0.25% by mass percentage.

[0139] Comparative Example 5

[0140] The difference from Example 1 is only that the N element in the non - quenched and tempered steel is 0.01% by mass percentage.

[0141] Comparative Example 6

[0142] The difference from Example 1 is only that the N element in the non - quenched and tempered steel is 0.03% by mass percentage.

[0143] Example 4

[0144] The difference from Example 1 is only that mold stirring is not adopted in continuous casting.

[0145] Example 5

[0146] The difference from Example 1 is only that final electromagnetic stirring is not adopted in continuous casting.

[0147] Example 6

[0148] The difference from Example 1 is only that the superheat degree of the molten steel in continuous casting is 30℃.

[0149] Example 7

[0150] The difference from Example 1 is only that the current of mold stirring in continuous casting is 200A.

[0151] Example 8

[0152] The difference from Example 1 is only that the current of mold stirring in continuous casting is 400A.

[0153] Example 9

[0154] The difference from Example 1 is only that the frequency of mold stirring is 1Hz.

[0155] Example 10

[0156] It is only different from Example 1 in that the frequency of the mold stirring is 5 Hz.

[0157] Example 11

[0158] It is only different from Example 1 in that the current of the final electromagnetic stirring is 80 A.

[0159] Example 12

[0160] It is only different from Example 1 in that the current of the final electromagnetic stirring is 200 A.

[0161] Example 13

[0162] It is only different from Example 1 in that the frequency of the final electromagnetic stirring is 8 Hz.

[0163] Example 14

[0164] It is only different from Example 1 in that the frequency of the final electromagnetic stirring is 15 Hz.

[0165] The mechanical properties of the steel obtained from the above examples and comparative examples were tested according to the national standard GB / T 228.1-2021, and the grain size grade was determined according to GB / T 6394-2017. The results are shown in Table 1 below.

[0166] Table 1

[0167]

[0168]

[0169] As can be seen from Table 1, for the non-quenched and tempered steel for connecting rods provided by the present invention, by adjusting the elemental composition of the steel and utilizing the synergistic effect of Ni, Nb, and N, the grain size grade of the steel is optimized. Further, by designing the continuous casting process such as the mold electromagnetic stirring and the final electromagnetic stirring parameters during the preparation process and controlling the superheat of the molten steel, better uniformity is achieved, such that the tensile strength of the obtained steel is ≥1020 MPa.

[0170] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0171] In addition, it should be noted that, in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0172] In addition, any combination can be made among various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should equally be regarded as the content disclosed by the present invention.

Claims

1. A non-quenched and tempered steel for connecting rods, characterized in that, The non-quenched and tempered steel for connecting rod comprises, by mass percentage: C 0.44 - 0.47%, Si 0.65 - 0.75%, Mn 1.15 - 1.25%, P ≤ 0.045%, S 0.04 - 0.07%, V 0.15 - 0.2%, Cr 0.2 - 0.25%, Ni 0.1 - 0.2%, Cu ≤ 0.2%, Nb 0.02 - 0.04%, N 0.014 - 0.02%, and the balance is Fe and inevitable impurities.

2. A preparation method of non-quenched and tempered steel for connecting rods as described in claim 1, characterized in that, The preparation method comprises: Converting molten iron into steel in a converter, followed by LF refining, VD vacuum treatment, and continuous casting to obtain a continuous casting billet; Rolling the continuous casting billet to obtain the non-quenched and tempered steel for connecting rod.

3. The preparation method according to claim 2, wherein Alloying is carried out during the converter steelmaking; Preferably, the alloys added during the alloying include: ferromanganese-silicon master alloy, chromium master alloy, vanadium source, ferrosilicon master alloy, and nickel source; Preferably, the tapping temperature of the converter steelmaking is ≥ 1600 °C; Preferably, the final carbon content of the converter steelmaking is 0.06 - 0.15% by mass percentage; Preferably, the final phosphorus content of the converter steelmaking is ≤ 0.015% by mass percentage.

4. The preparation method according to claim 2 or 3, characterized in that, Slag-making materials and a first master alloy are added during the LF refining; Preferably, the slag-making materials include: lime, aluminum pellets, and silicon carbide; Preferably, the addition amounts of the slag-making materials are: lime ≤ 100 kg / furnace, aluminum pellets 30 - 50 kg / furnace, and silicon carbide 20 - 30 kg / furnace; Preferably, the first master alloy includes: ferroniobium; Preferably, the holding time of the white slag during the LF refining is 300 - 330 min.

5. The preparation method according to any one of claims 3-4, characterized in that, A first covering agent and a second master alloy are added during the VD vacuum treatment; Preferably, the first covering agent includes: carbonized rice husk; Preferably, the addition amount of the first covering agent is 12 - 25 kg / furnace; Preferably, the second master alloy includes: manganese-nitrogen alloy and calcium-silicon alloy; Preferably, the soft blowing time during the VD vacuum treatment is 15 - 25 min.

6. The preparation method according to any one of claims 3-5, characterized in that, A second covering agent and a mold powder are added during the continuous casting; Preferably, the second covering agent includes: carbonized rice husk; Preferably, the addition amount of the second covering agent is 15 - 25 kg / furnace; Preferably, the mold powder includes: F02 mold powder; Preferably, the addition amount of the mold powder is 0.4 - 0.5 kg / t.

7. The preparation method according to any one of claims 3-6, characterized in that, The superheat degree of the molten steel during the continuous casting is ≤ 25 °C; Preferably, the casting speed of the continuous casting is 0.8 - 1 m / min.

8. The preparation method according to any one of claims 3 to 7, characterized in that, Mold stirring and final electromagnetic stirring are carried out during the continuous casting; Preferably, the current of the mold stirring is 250 - 350 A; Preferably, the frequency of the mold stirring is 2 - 4 Hz; Preferably, the current of the final electromagnetic stirring is 90 - 110 A; Preferably, the frequency of the final electromagnetic stirring is 11 - 13 Hz.

9. The preparation method according to any one of claims 3-8, characterized in that, The preheating temperature of the rolling is ≤ 900 °C; Preferably, the starting rolling temperature of the rolling is 1060 - 1130 °C; Preferably, the finishing rolling temperature of the rolling is 840 - 860 °C.

10. A vehicle connecting rod, characterized in that, The vehicle connecting rod is prepared by using the non-quenched and tempered steel for connecting rods described in Claim 1 or the non-quenched and tempered steel for connecting rods obtained by the preparation method described in any one of Claims 2-9.

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