High-hardness rare earth crane rail and production method thereof

Abstract

The invention discloses a high-hardness rare earth crane rail and a production method thereof. The high-hardness rare earth crane rail provided by the invention comprises the following chemical components in percentage by mass: 0.40 to 0.60 percent of C, 0.55 to 0.65 percent of Si, 1.10 to 1.25 percent of Mn, 0.70 to 0.80 percent of Cr, 0.11 to 0.15 percent of V, 0.03 to 0.05 percent of B, 0.02 to 0.05 percent of Ce and the balance of rare earth. The steel comprises, by weight, 0.020% or less of P, 0.025% or less of S, 0.004% or less of Al and the balance Fe and inevitable impurities. The performance of the provided high-hardness rare earth crane rail meets the conditions that the tensile strength Rm is larger than or equal to 1250 MPa, the tread hardness is larger than or equal to 400 HB, and the bearing strength and abrasion resistance of the crane rail can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the field of metallurgical materials, and in particular relates to a high-hardness rare earth crane rail and a production method thereof. Background Art

[0002] Crane rails are mainly used for cranes or load-bearing vehicles to transport load-bearing materials. The load-bearing weight is much greater than the load-bearing weight of railway transportation lines, so the strength and hardness requirements for crane rails are higher. Foreign countries generally use CR175 crane rails specified in the American standard ASTMA-759, and the rail strength grade is 880MPa. In recent years, some countries such as Brazil and the United States have gradually demanded high-strength CR175 crane rails, with a rail strength requirement of more than 1080MPa and a hardness requirement of 321 to 388HB. However, in order to increase the market share of crane rails, there is a need to further improve the bearing strength and wear resistance of the rails. Summary of the invention

[0003] The present invention aims to provide a method for producing a high-hardness rare earth crane rail, which adds alloy elements such as Cr, V, B and rare earth CE on the basis of C, Si and Mn rails to improve the performance of the rails, and can further increase the strength of the rails to more than 1250MPa, and the hardness of the rails to more than 400HB, thereby improving the bearing strength and wear resistance of the rails. The specific technical scheme is as follows.

[0004] In one aspect, the present invention provides a high-hardness rare earth crane rail, wherein the chemical composition is as follows by mass percentage: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, and the rest is Fe and unavoidable impurities; the performance of the high-hardness rare earth crane rail meets the following requirements: the tensile strength R m ≥1250MPa, tread hardness ≥400HB.

[0005] In some embodiments, the high-hardness rare earth crane rail has an elongation after fracture A of ≥10%.

[0006] In some embodiments, the high-hardness rare earth crane rail is produced according to the following process flow: molten iron pretreatment - converter smelting - LF refining - VD vacuum degassing - continuous casting - billet heating - rolling - rail straightening.

[0007] In some embodiments, in the molten iron pretreatment process, the sulfur content in the molten iron is controlled to be ≤ 0.02%.

[0008] In some embodiments, in the converter smelting process, the C content of the steel is controlled to be ≥0.08%, the steel tapping temperature is ≥1630°C, lime, silicon calcium barium and fluorite are added after steel tapping to modify the slag, the argon blowing effect is ensured during the steel tapping process, and the top slag is prevented from agglomerating when the molten steel is refined in place.

[0009] In some embodiments, in the LF refining process, high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome, ferroboron alloy and rare earth alloy are added, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595°C, so that the chemical composition weight percentage of the molten steel is as follows: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, and the rest is Fe and unavoidable impurities.

[0010] In some embodiments, in the VD vacuum degassing process, the deep vacuum degassing time is controlled to be ≥15 min, the soft blowing time after vacuum degassing is ≥18 min, and the argon flow rate is controlled during the soft blowing process to prevent the molten steel from rolling violently and causing slag rolling.

[0011] In some embodiments, in the continuous casting process, protective casting is adopted, low-aluminum protective slag is adopted, ultra-weak cooling water is adopted in the second cooling stage, the casting speed is operated at a constant throughout the whole process, and electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the ingot.

[0012] In some embodiments, in the billet heating process, the total billet heating time is controlled to be ≥3 hours, wherein the temperature of the preheating section of the heating furnace is ≤800°C, the temperature of the first heating section is ≤1200°C, the temperature of the second heating section is 1150-1250°C, and the soaking section is 1150-1200°C.

[0013] In some embodiments, in the rolling process, the starting rolling temperature is controlled to be 1030°C to 1060°C, and the finishing rolling temperature is controlled to be 910°C to 930°C.

[0014] On the other hand, the present invention provides a method for producing a high-hardness rare earth crane rail, which includes the following process flow: molten iron pretreatment - converter smelting - LF refining - VD vacuum degassing - continuous casting - billet heating - rolling - rail straightening; wherein:

[0015] In the molten iron pretreatment process, the sulfur content in the molten iron is controlled to be ≤0.02%;

[0016] In the converter smelting process, the C content of the tapped steel is controlled to be ≥ 0.08%, the tapping temperature is ≥ 1630°C, lime, silicon calcium barium and fluorite are added after tapping to modify the slag, the argon blowing effect is ensured during the tapping process, and the top slag is prevented from agglomerating when the molten steel is refined in place;

[0017] In the LF refining process, high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome, ferroboron alloy and rare earth alloy are added, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595° C., so that the chemical composition weight percentage of the molten steel is as follows: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, and the rest is Fe and unavoidable impurities;

[0018] In the VD vacuum degassing process, the deep vacuum degassing time is controlled to be ≥15min, and the soft blowing time after vacuum degassing is ≥18min. During the soft blowing process, the argon flow rate is well controlled to prevent the molten steel from rolling violently and causing slag rolling.

[0019] In the continuous casting process, protective casting is adopted, low-aluminum protective slag is used, ultra-weak cooling water is used in the secondary cooling stage, the casting speed is kept constant throughout the process, and electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the ingot;

[0020] In the billet heating process, the total billet heating time is controlled to be ≥ 3 hours, wherein the preheating temperature of the heating furnace is ≤ 800°C, the first heating temperature is ≤ 1200°C, the second heating temperature is 1150-1250°C, and the soaking temperature is 1150-1200°C;

[0021] In the rolling process, the starting rolling temperature is controlled at 1030°C to 1060°C, and the final rolling temperature is controlled at 910°C to 930°C.

[0022] In some embodiments, in the LF refining process, the chemical composition of the molten steel is as follows by weight percentage: C: 0.51%, Si: 0.60%, Mn: 1.15%, P: 0.015%, S: 0.010%, Cr: 0.76%, V: 0.13%, B: 0.04%, Al: 0.003%, Ce: 0.03%, and the rest is Fe and unavoidable impurities. DETAILED DESCRIPTION

[0023] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0024] Example 1

[0025] This embodiment provides a method for producing a high-hardness rare earth crane rail, which includes the following process flow:

[0026] 1) Hot metal pretreatment: The sulfur content in hot metal is 0.014%;

[0027] 2) Converter smelting: Control the C content of steel to 0.09% and the tapping temperature to 1640°C. Add lime, silicon calcium barium and fluorite after tapping to modify the slag. Ensure the argon blowing effect during the tapping process. There is no lumping of top slag when the molten steel is refined in place.

[0028] 3) LF furnace refining: high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome, ferroboron alloy and rare earth alloy are added during LF refining, the slag basicity is controlled at 2.2, the heating time is 34 minutes, and the ex-situ temperature is 1591°C;

[0029] 4) VD vacuum degassing: Deep vacuum degassing time is 15 minutes, and soft blowing is performed for 18 minutes after vacuum degassing. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without exposure.

[0030] 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, and ultra-weak cooling water distribution in the secondary cooling section. The whole process is operated at a constant pulling speed of 0.55m / min. The electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0031] 6) Billet heating: The total heating time is 3 hours and 40 minutes. The heating time and heating temperature of each section are shown in Table 1 below.

[0032] Table 1: Heating time and temperature for each stage

[0033] Preheating section Heating 1 stage Heating 2 stages Heat soaking section Heating time 50min 1h 1h 50min temperature 655℃ 1002℃ 1205℃ 1186℃

[0034] 7) Rolling: The ingot is rolled into rails by a universal rolling mill, with the starting rolling temperature at 1045°C and the final rolling temperature at 921°C.

[0035] 8) Straightening: The rails are pre-bent and cooled on a cooling bed, and then straightened in a straightening machine. The straightened rails are inspected for surface and straightness. No damage is found on the surface and the straightness test meets the standard requirements.

[0036] 9) Ultrasonic flaw detection: The rails are subjected to ultrasonic flaw detection along their entire length, with detection carried out on the overhang, rail waist, rail bottom, rail bottom corner and other parts. No internal defects are found along the entire length of the rails.

[0037] After inspection, the chemical composition of the high hardness rare earth crane rails is as follows by weight: C: 0.51%, Si: 0.60%, Mn: 1.15%, P: 0.015%, S: 0.010%, Cr: 0.76%, V: 0.13%, B: 0.04%, Al: 0.003%, Ce: 0.03%, and the rest is Fe and unavoidable impurities.

[0038] The mechanical properties of the rails are as follows: tensile strength: 1255MPa, elongation after fracture A: 10.5%, tread hardness: 412HB.

[0039] Comparative Example 1

[0040] This comparative example provides a production method for a common crane rail, which includes the following process flow:

[0041] 1) Hot metal pretreatment: The sulfur content in hot metal is 0.013%;

[0042] 2) Converter smelting: Control the C content of steel to 0.09% and the tapping temperature to 1640°C. Add lime, silicon calcium barium and fluorite after tapping to modify the slag. Ensure the argon blowing effect during the tapping process. There is no lumping of top slag when the molten steel is refined in place.

[0043] 3) LF furnace refining: high carbon ferromanganese, low aluminum ferrosilicon and high carbon ferrochrome are added during LF refining, the slag basicity is controlled at 2.2, the heating time is 30 minutes, and the ex-situ temperature is 1593°C;

[0044] 4) VD vacuum degassing: Deep vacuum degassing time is 15 minutes, and soft blowing is performed for 18 minutes after vacuum degassing. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without exposure.

[0045] 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, and ultra-weak cooling water distribution in the secondary cooling section. The whole process is operated at a constant pulling speed of 0.55m / min. The electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0046] 6) Billet heating: The total heating time is 3 hours and 40 minutes. The heating time and heating temperature of each section are shown in Table 2 below.

[0047] Table 2: Heating time and temperature for each stage

[0048] Preheating section Heating 1 stage Heating 2 stages Heat soaking section Heating time 50min 1h 1h 50min temperature 655℃ 1002℃ 1205℃ 1186℃

[0049] 7) Rolling: The ingot is rolled into rails by a universal rolling mill, with the starting rolling temperature at 1045°C and the final rolling temperature at 921°C.

[0050] 8) Straightening: The rails are pre-bent and cooled on a cooling bed, and then straightened in a straightening machine. The straightened rails are inspected for surface and straightness. No damage is found on the surface and the straightness test meets the standard requirements.

[0051] 9) Ultrasonic flaw detection: The rails are subjected to ultrasonic flaw detection along their entire length, with detection carried out on the overhang, rail waist, rail bottom, rail bottom corner and other parts. No internal defects are found along the entire length of the rails.

[0052] After inspection, the chemical composition of the high-hardness rare earth crane rails is as follows by weight: C: 0.52%, Si: 0.64%, Mn: 1.13%, P: 0.014%, S: 0.011%, Cr: 0.73%, V: 0.15%, Al: 0.003%, and the rest is Fe and unavoidable impurities.

[0053] The mechanical properties of the rails are as follows: tensile strength: 985MPa, elongation after fracture A: 11%, tread hardness: 304HB.

[0054] Comparative Example 2

[0055] This comparative example provides a method for producing a rare earth crane rail, which includes the following process flow:

[0056] 1) Hot metal pretreatment: The sulfur content in hot metal is 0.013%;

[0057] 2) Converter smelting: Control the C content of steel to 0.08%, the tapping temperature to 1640°C, add lime, silicon calcium barium and fluorite after tapping, modify the slag, ensure the argon blowing effect during the tapping process, and there is no lumping phenomenon on the top slag when the molten steel is refined in place;

[0058] 3) LF furnace refining: high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome and rare earth alloy are added during LF refining, the slag basicity is controlled at 2.2, the heating time is 32 minutes, and the ex-situ temperature is 1590°C;

[0059] 4) VD vacuum degassing: Deep vacuum degassing time is 15 minutes, and soft blowing is performed for 18 minutes after vacuum degassing. During the soft blowing process, the argon flow rate is stable, and the molten steel creeps without exposure.

[0060] 5) Continuous casting: The continuous casting process adopts protective casting, low-aluminum protective slag, and ultra-weak cooling water distribution in the secondary cooling section. The whole process is operated at a constant pulling speed of 0.55m / min. The electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the casting.

[0061] 6) Billet heating: The total heating time is 3 hours and 40 minutes. The heating time and heating temperature of each section are shown in Table 3 below.

[0062] Table 3: Heating time and temperature for each stage

[0063] Preheating section Heating 1 stage Heating 2 stages Heat soaking section Heating time 50min 1h 1h 50min temperature 655℃ 1002℃ 1205℃ 1186℃

[0064] 7) Rolling: The ingot is rolled into rails by a universal rolling mill, with the starting rolling temperature at 1045°C and the final rolling temperature at 921°C.

[0065] 8) Straightening: The rails are pre-bent and cooled on a cooling bed, and then straightened in a straightening machine. The straightened rails are inspected for surface and straightness. No damage is found on the surface and the straightness test meets the standard requirements.

[0066] 9) Ultrasonic flaw detection: The rails are subjected to ultrasonic flaw detection along their entire length, with detection carried out on the overhang, rail waist, rail bottom, rail bottom corner and other parts. No internal defects are found along the entire length of the rails.

[0067] After inspection, the chemical composition of the high hardness rare earth crane rails is as follows by weight: C: 0.50%, Si: 0.62%, Mn: 1.17%, P: 0.015%, S: 0.009%, Cr: 0.72%, V: 0.15%, Al: 0.004%, Ce: 0.03%, and the rest is Fe and unavoidable impurities.

[0068] The mechanical properties of the rails are as follows: tensile strength: 1184MPa, elongation after fracture A: 9%, tread hardness: 367HB.

[0069] By comparing Comparative Example 1 with Comparative Example 2, it can be seen that Example 1 adopts the composition range and process system of the present invention, and the mechanical properties of the rails are higher than those of the crane rails of Comparative Example 1 and Comparative Example 2, and the wear resistance and bearing capacity are better.

[0070] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-hardness rare earth crane rail, characterized in that: The chemical composition of the high-hardness rare earth crane rail is calculated by mass percentage as follows: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, the rest is Fe and unavoidable impurities; The performance of the high-hardness rare earth crane rail meets the following requirements: tensile strength R m ≥1250MPa, tread hardness ≥400HB.

2. The high-hardness rare earth crane rail according to claim 1, characterized in that: The elongation after fracture A of the high-hardness rare earth crane rail is ≥10%.

3. The high-hardness rare earth crane rail according to claim 1 or 2, characterized in that: The high-hardness rare earth crane rail is produced according to the following process flow: molten iron pretreatment - converter smelting - LF refining - VD vacuum degassing - continuous casting - billet heating - rolling - rail straightening.

4. The high-hardness rare earth crane rail according to claim 3, characterized in that: In the molten iron pretreatment process, the sulfur content in the molten iron is controlled to be ≤0.02%; In the converter smelting process, the C content of the tapped steel is controlled to be ≥ 0.08%, the tapping temperature is ≥ 1630°C, lime, silicon calcium barium and fluorite are added after tapping to modify the slag, the argon blowing effect is ensured during the tapping process, and the top slag is prevented from agglomerating when the molten steel is refined in place; In the LF refining process, high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome, ferroboron alloy and rare earth alloy are added, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595° C., so that the chemical composition weight percentage of the molten steel is as follows: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, and the rest is Fe and unavoidable impurities; In the VD vacuum degassing process, the deep vacuum degassing time is controlled to be ≥15min, and the soft blowing time after vacuum degassing is ≥18min. During the soft blowing process, the argon flow rate is well controlled to prevent the molten steel from rolling violently and causing slag rolling. In the continuous casting process, protective casting is adopted, low-aluminum protective slag is used, ultra-weak cooling water is used in the secondary cooling stage, the casting speed is kept constant throughout the process, and electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the ingot; In the billet heating process, the total billet heating time is controlled to be ≥ 3 hours, wherein the preheating temperature of the heating furnace is ≤ 800°C, the first heating temperature is ≤ 1200°C, the second heating temperature is 1150-1250°C, and the soaking temperature is 1150-1200°C; In the rolling process, the starting rolling temperature is controlled at 1030°C to 1060°C, and the final rolling temperature is controlled at 910°C to 930°C.

5. The method for producing a high-hardness rare earth crane rail according to any one of claims 1 to 4, characterized in that: The production method includes the following process flow: molten iron pretreatment - converter smelting - LF refining - VD vacuum degassing - continuous casting - billet heating - rolling - rail straightening; wherein: In the molten iron pretreatment process, the sulfur content in the molten iron is controlled to be ≤0.02%; In the converter smelting process, the C content of the tapped steel is controlled to be ≥ 0.08%, the tapping temperature is ≥ 1630°C, lime, silicon calcium barium and fluorite are added after tapping to modify the slag, the argon blowing effect is ensured during the tapping process, and the top slag is prevented from agglomerating when the molten steel is refined in place; In the LF refining process, high carbon ferromanganese, low aluminum ferrosilicon, high carbon ferrochrome, ferroboron alloy and rare earth alloy are added, the slag basicity is controlled to be ≥2.0, and the off-site temperature is 1585-1595° C., so that the chemical composition weight percentage of the molten steel is as follows: C: 0.40-0.60%, Si: 0.55-0.65%, Mn: 1.10-1.25%, Cr: 0.70-0.80%, V: 0.11-0.15%, B: 0.03-0.05%, Ce: 0.02-0.05%; P≤0.020%, S≤0.025%, Al≤0.004%, and the rest is Fe and unavoidable impurities; In the VD vacuum degassing process, the deep vacuum degassing time is controlled to be ≥15min, and the soft blowing time after vacuum degassing is ≥18min. During the soft blowing process, the argon flow rate is well controlled to prevent the molten steel from rolling violently and causing slag rolling. In the continuous casting process, protective casting is adopted, low-aluminum protective slag is used, ultra-weak cooling water is used in the secondary cooling stage, the casting speed is kept constant throughout the process, and electromagnetic stirring and light pressure of the casting machine are turned on to ensure the quality of the ingot; In the billet heating process, the total billet heating time is controlled to be ≥ 3 hours, wherein the preheating temperature of the heating furnace is ≤ 800°C, the first heating temperature is ≤ 1200°C, the second heating temperature is 1150-1250°C, and the soaking temperature is 1150-1200°C; In the rolling process, the starting rolling temperature is controlled at 1030°C to 1060°C, and the final rolling temperature is controlled at 910°C to 930°C.

6. The production method according to claim 5, characterized in that In the LF refining process, the chemical composition of the molten steel is as follows by weight percentage: C: 0.51%, Si: 0.60%, Mn: 1.15%, P: 0.015%, S: 0.010%, Cr: 0.76%, V: 0.13%, B: 0.04%, Al: 0.003%, Ce: 0.03%, and the rest is Fe and unavoidable impurities.