A kind of martensitic wear-resistant steel and preparation method thereof

Abstract

The present invention relates to the technical field of metal casting, and specifically discloses a martensitic wear-resistant steel and a preparation method thereof. The martensitic wear-resistant steel provided by the present invention is composed of the following chemical components: C: 0.38% to 0.42%, Ti: 0.75% to 0.8%, Mo: 0.2% to 0.28%, V: 0.38% to 0.4%, Mn: 1.58% to 2%, Si: 0.084% to 0.1%, P < 0.015%, S < 0.002%, and the remainder is Fe and inevitable impurities; the martensitic wear-resistant steel provided by the present invention has carbon, manganese and silicon as main elements, and further controls the addition amount of titanium, molybdenum and vanadium elements, and compositely strengthens the elements, inhibits the growth of austenite crystals, refines martensitic crystals and improves the tempering stability of martensitic wear-resistant steel, thereby improving the strength and toughness of martensitic wear-resistant steel.

Description

Technical Field

[0001] The invention relates to the technical field of metal casting, and in particular to a martensitic wear-resistant steel and a preparation method thereof. Background Art

[0002] Wear-resistant steel mainly includes the following three categories: martensitic wear-resistant steel, austenitic wear-resistant steel and bainitic wear-resistant steel. Among them, austenitic wear-resistant steel is suitable for high impact load conditions, but difficult to machine and weld; bainitic wear-resistant steel has low uniformity of organizational properties, high carbon steel content and poor welding performance; martensitic wear-resistant steel is easy to mass produce due to its good weldability, formability and machinability. Therefore, martensitic wear-resistant steel has become the mainstream product in the wear-resistant steel market.

[0003] Traditionally, the hardness and toughness of martensitic wear-resistant steel are improved by adding a large amount of alloy elements, but this also leads to an increase in production costs. In addition, since the hardness and toughness of quenched martensite are relatively poor and there is quenching stress, complex heat treatment processes are usually required, such as multiple quenching and tempering cycles, which also leads to a long production process and increased process costs. In view of the above problems, it is of great significance to provide a martensitic wear-resistant steel with both high strength and high toughness and a preparation method thereof. Summary of the invention

[0004] In view of this, the present invention provides a martensitic wear-resistant steel and a preparation method thereof. The composite strengthening between the elements of the martensitic wear-resistant steel provided by the present invention improves the strength and toughness of the martensitic wear-resistant steel by inhibiting the growth of austenite crystals, refining martensitic crystals and improving the tempering stability of the martensitic wear-resistant steel.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] The first aspect of the present invention provides a martensitic wear-resistant steel, which is composed of the following chemical components, measured by mass percentage: C: 0.38%~0.42%, Ti: 0.75%~0.8%, Mo: 0.2%~0.28%, V: 0.38%~0.4%, Mn: 1.58%~2%, Si: 0.084%~0.1%, P<0.015%, S<0.002%, and the balance is Fe and unavoidable impurities.

[0007] Compared with the prior art, the martensitic wear-resistant steel provided by the present invention adopts a low-cost design, and trace amounts of titanium, molybdenum and vanadium are added to carbon, manganese and silicon elements, wherein titanium and vanadium can form fine carbides with carbon elements, which are pinned at the grain boundaries, and the two elements act synergistically to prevent the growth of austenite grains, thereby fully refining the martensitic structure, thereby effectively improving the strength of the martensitic wear-resistant steel and making it have excellent toughness, and the carbides formed by titanium, vanadium and carbon can also avoid the precipitation of harmful phases, thereby further improving the mechanical properties of the martensitic wear-resistant steel; the addition of molybdenum can increase the hardenability of the steel, so that it can better form a martensitic structure during the quenching process, thereby improving the hardness and wear resistance of the steel, and at the same time, molybdenum can also effectively eliminate residual stress by improving the tempering stability of the steel, thereby greatly improving the toughness of the martensitic wear-resistant steel.

[0008] The martensitic wear-resistant steel provided by the present invention has carbon, manganese and silicon as main elements, and further controls the addition amounts of titanium, molybdenum and vanadium elements to achieve composite strengthening between the elements, thereby inhibiting the growth of austenite crystals, refining martensite crystals and improving the tempering stability of the martensitic wear-resistant steel, thereby improving the strength and toughness of the martensitic wear-resistant steel; the present invention determines the type of element addition and the addition amount of each element, and adopts a low-cost design principle, so that the prepared martensitic wear-resistant steel has both high strength and excellent toughness, and has important practical value for actual production.

[0009] The second aspect of the present invention provides a method for preparing the above-mentioned martensitic wear-resistant steel, comprising the following steps:

[0010] S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are first smelted at 1600° C. to 1700° C. to obtain a first molten steel; Si, P and S are added to the first molten steel at 1400° C. to 1600° C. for a second smelting and casting to obtain a metal slab;

[0011] S2, keeping the metal sheet blank at 1280° C. to 1320° C., then performing transverse forging at 950° C. to 1000° C., controlling the final forging temperature to be 680° C. to 720° C., water-cooling the forged metal sheet blank to room temperature, and then freezing at -190° C. to -120° C. to obtain a forged steel ingot;

[0012] S3, annealing the forged steel ingot at 600° C. to 650° C., and water cooling to obtain a casting;

[0013] S4. Performing ultrasonic shot peening on the cross section of the casting to obtain martensitic wear-resistant steel.

[0014] Compared with the prior art, the preparation method of martensitic wear-resistant steel provided by the present invention firstly keeps the metal sheet blank at a specific temperature to make the metal sheet blank fully austenitized, and then performs transverse forging at a specific temperature to ensure that the original austenite is in a rod shape. Under the action of external force, the specific final forging temperature can also promote the austenite phase to deform into fine strip martensite, and it is not easy to coarsen and grow, thereby significantly improving the hardness of the martensitic wear-resistant steel and ensuring its excellent toughness. Water cooling accelerated cooling combined with ultra-low freezing treatment is conducive to the continued transformation of unstable residual austenite into martensite, thereby improving the strength of the martensitic wear-resistant steel; the specific annealing temperature can make the nano-scale (Ti, V) C precipitate uniformly, which is pinned at the grain boundary to hinder the growth of grains, and improve the martensitic wear-resistant steel by reducing the grain size. The hardness of martensitic wear-resistant steel can be improved, and the service life of martensitic wear-resistant steel can be improved by eliminating the residual stress of martensitic wear-resistant steel; the specific annealing temperature can reduce part of the martensite to austenite, and through water cooling treatment, the transformed austenite is formed into tempered martensite, which significantly improves the hardness and toughness of the martensitic wear-resistant steel and ensures its excellent wear resistance; after the above-mentioned annealing heat treatment, a martensitic wear-resistant steel containing a large amount of martensite and a small amount of residual austenite is initially formed, and the surface of the martensitic wear-resistant steel is elastically strained by ultrasonic shot peening, so that the grains on the surface of the steel become finer full martensite, and the dislocation within the grains is increased. The central layer of the steel is martensite and residual austenite, so that the prepared martensitic wear-resistant steel has excellent toughness on the basis of high strength.

[0015] The present invention reasonably designs the alloy composition of the martensitic wear-resistant steel and combines the processes of high-temperature heat preservation, transverse forging, annealing and ultrasonic shot peening, wherein each process step plays a role of composite strengthening, so that the prepared martensitic wear-resistant steel has both high strength and excellent toughness.

[0016] Preferably, in S1, Ti, Mo, V, Mn, Si, P and S are added in the form of single elements, and C and Fe are added in the form of alloys.

[0017] Preferably, in S1, the first smelting time is 2h~3h.

[0018] Preferably, in S1, the second smelting time is 1 h to 2 h.

[0019] Preferably, in S2, the metal sheet blank is a cuboid with a square cross section.

[0020] Further preferably, in S2, the cross-sectional area of ​​the metal sheet blank is (48 mm to 52 mm)×(48 mm to 52 mm).

[0021] Preferably, in S2, the insulation time is 1h~2h.

[0022] The optimal holding time is conducive to fully austenitizing the metal sheet and providing a good precursor for subsequent processes.

[0023] Preferably, in S2, the number of times of transverse forging is 4 to 5 times.

[0024] Further preferably, in S2, the condition of the transverse forging is: the ratio of the area of ​​the metal sheet blank before each forging to the area of ​​the metal sheet blank after forging is 100:(74~80).

[0025] The preferred transverse forging conditions are conducive to the formation of martensitic wear-resistant steel with a specific metallographic structure, thereby greatly improving the strength of the martensitic wear-resistant steel.

[0026] Preferably, in S2, the water cooling adopts water cooling with a flow rate of 40m / s~60m / s.

[0027] Further preferably, in S2, the temperature of water during water cooling is 22°C to 28°C.

[0028] Preferably, in S2, the freezing time is 8 min to 10 min.

[0029] By limiting the water flow rate and freezing time, it is beneficial to convert the unstable residual austenite in the metal sheet after forging into martensite, further improving the hardness and toughness of the martensitic wear-resistant steel.

[0030] Preferably, in S3, the annealing time is 10 min to 20 min.

[0031] The optimal annealing time is beneficial to further improve the hardness of the martensitic wear-resistant steel.

[0032] Preferably, in S4, the shot used in the ultrasonic shot peening treatment is tungsten carbon steel.

[0033] Preferably, in S4, the shot peening diameter of the ultrasonic shot peening is 2 mm to 3 mm.

[0034] Preferably, in S4, the ultrasonic frequency of the ultrasonic shot peening treatment is 15kHz~25kHz.

[0035] Preferably, in S4, the processing time of each cross section during the ultrasonic shot peening is 20 min to 30 min. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] In order to better illustrate the present invention, further examples are given below.

[0038] Example 1

[0039] The present embodiment provides a martensitic wear-resistant steel, which is composed of the following chemical components, measured by mass percentage: C: 0.38%, Ti: 0.8%, Mo: 0.2%, V: 0.4%, Mn: 2%, Si: 0.1%, P: 0.005%, S: 0.001%, and the balance is Fe and unavoidable impurities;

[0040] This embodiment provides a method for preparing the above-mentioned martensitic wear-resistant steel, comprising the following steps:

[0041] S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are smelted at 1700° C. for 2 h to obtain a first molten steel; Si, P and S are added to the first molten steel at 1400° C. and smelted for 1 h to cast a rectangular metal slab with a cross-sectional area of ​​48 mm×48 mm;

[0042] S2, keeping the metal sheet blank at 1320° C. for 1 hour, and then performing transverse forging at 1000° C. for 4 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area ratio of the metal sheet blank after forging is 100:74, and the final forging temperature is controlled to be 680° C.; cooling the metal sheet blank after the 4 forging to room temperature with water at a flow rate of 40 m / s, and then freezing at -120° C. for 8 minutes to obtain a forged steel ingot;

[0043] S3, annealing the forged steel ingot at 650° C. for 20 min, and water cooling to obtain a casting;

[0044] S4. Perform ultrasonic shot peening on the two cross-sectional surfaces of the casting to obtain the martensitic wear-resistant steel; wherein the ultrasonic shot peening uses tungsten carbon steel with a diameter of 2 mm, sets the ultrasonic frequency to 15 kHz, and the treatment time for each cross-sectional surface is 20 minutes.

[0045] Example 2

[0046] The present embodiment provides a martensitic wear-resistant steel, which is composed of the following chemical components by mass percentage: C: 0.42%, Ti: 0.75%, Mo: 0.28%, V: 0.38%, Mn: 1.58%, Si: 0.084%, P: 0.01%, S: 0.001%, and the balance is Fe and unavoidable impurities;

[0047] This embodiment provides a method for preparing the above-mentioned martensitic wear-resistant steel, comprising the following steps:

[0048] S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are smelted at 1600° C. for 3 hours to obtain a first molten steel; Si, P and S are added to the first molten steel at 1600° C. and smelted for 2 hours to cast a rectangular metal slab with a cross-sectional area of ​​52 mm×52 mm;

[0049] S2, keeping the metal sheet blank at 1280°C for 2h, and then performing transverse forging at 950°C for 5 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area of ​​the metal sheet blank after forging is 100:80, and the final forging temperature is controlled to be 720°C; cooling the metal sheet blank after the 5 forging to room temperature with water at a flow rate of 60m / s, and then freezing at -190°C for 10min to obtain a forged steel ingot;

[0050] S3, annealing the forged steel ingot at 600° C. for 10 min, and water cooling to obtain a casting;

[0051] S4. Perform ultrasonic shot peening on the two cross-sectional surfaces of the casting to obtain the martensitic wear-resistant steel; wherein the ultrasonic shot peening uses tungsten carbon steel with a diameter of 3 mm, sets the ultrasonic frequency to 25 kHz, and the treatment time for each cross-sectional surface is 30 minutes.

[0052] Example 3

[0053] The present embodiment provides a martensitic wear-resistant steel, which is composed of the following chemical components by mass percentage: C: 0.4%, Ti: 0.77%, Mo: 0.25%, V: 0.39%, Mn: 1.62%, Si: 0.092%, P: 0.006%, S: 0.0018%, and the balance is Fe and unavoidable impurities;

[0054] This embodiment provides a method for preparing the above-mentioned martensitic wear-resistant steel, comprising the following steps:

[0055] S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are smelted at 1660° C. for 2.5 hours to obtain a first molten steel; Si, P and S are added to the first molten steel at 1500° C. and smelted for 1.5 hours to cast a rectangular metal slab with a cross-sectional area of ​​50 mm×50 mm;

[0056] S2, keeping the metal sheet blank at 1300° C. for 1.5 h, and then performing transverse forging at 980° C. for 5 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area ratio of the metal sheet blank after forging is 100:78, and the final forging temperature is controlled to be 700° C.; cooling the metal sheet blank after the 5 forging to room temperature with water at a flow rate of 50 m / s, and then freezing at -170° C. for 9 min to obtain a forged steel ingot;

[0057] S3, annealing the forged steel ingot at 620° C. for 15 min, and water cooling to obtain a casting;

[0058] S4. Perform ultrasonic shot peening on the two cross-sectional surfaces of the casting to obtain the martensitic wear-resistant steel; wherein the ultrasonic shot peening uses tungsten carbon steel with a diameter of 3 mm, sets the ultrasonic frequency to 20 kHz, and the processing time for each cross-sectional surface is 25 minutes.

[0059] Comparative Example 1

[0060] This comparative example provides a wear-resistant steel, which is different from Example 1 in that: Ti is replaced by an equal amount of Cr, and specifically consists of the following chemical composition: C: 0.38%, Cr: 0.8%, Mo: 0.2%, V: 0.4%, Mn: 2%, Si: 0.1%, P: 0.005%, S: 0.001%, and the balance is Fe and unavoidable impurities;

[0061] The other operations are the same as those in Example 1.

[0062] Comparative Example 2

[0063] This comparative example provides a wear-resistant steel, which is different from Example 1 in that: Mo is replaced by an equal amount of Ti, and specifically consists of the following chemical composition: C: 0.38%, Ti: 1.0%, V: 0.4%, Mn: 2%, Si: 0.1%, P: 0.005%, S: 0.001%, and the balance is Fe and unavoidable impurities;

[0064] The other operations are the same as those in Example 1.

[0065] Comparative Example 3

[0066] This comparative example provides a wear-resistant steel, which is different from Example 1 in that V is replaced by an equal amount of Mo, and specifically consists of the following chemical composition: C: 0.38%, Ti: 0.8%, Mo: 0.6%, Mn: 2%, Si: 0.1%, P: 0.005%, S: 0.001%, and the balance is Fe and unavoidable impurities;

[0067] The other operations are the same as those in Example 1.

[0068] Comparative Example 4

[0069] This comparative example provides a wear-resistant steel, which is different from Example 1 in that:

[0070] S2, keeping the metal sheet blank at 1320° C. for 1 hour, and then performing transverse forging at 1000° C. for 4 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area ratio of the metal sheet blank after forging is 100:74, and the final forging temperature is controlled to be 750° C.; cooling the metal sheet blank after the 4 forging to room temperature with water at a flow rate of 40 m / s, and then freezing at -120° C. for 8 minutes, to obtain a forged steel ingot;

[0071] The other components and operations were the same as in Example 1.

[0072] Comparative Example 5

[0073] This comparative example provides a wear-resistant steel, which is different from Example 1 in that:

[0074] S2, keeping the metal sheet blank at 1320° C. for 1 hour, and then performing transverse forging at 1000° C. for 4 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area ratio of the metal sheet blank after forging is 100:74, and the final forging temperature is controlled to be 650° C.; cooling the metal sheet blank after the 4 forging to room temperature with water at a flow rate of 40 m / s, and then freezing at -120° C. for 8 minutes to obtain a forged steel ingot;

[0075] The other components and operations were the same as in Example 1.

[0076] Comparative Example 6

[0077] This comparative example provides a wear-resistant steel, which is different from Example 1 in that:

[0078] S3, annealing the forged steel ingot at 680° C. for 20 min, and water cooling to obtain a casting;

[0079] The other components and operations were the same as in Example 1.

[0080] Comparative Example 7

[0081] This comparative example provides a wear-resistant steel, which is different from Example 1 in that:

[0082] S3, annealing the forged steel ingot at 580° C. for 20 min, and water cooling to obtain a casting;

[0083] The other components and operations were the same as in Example 1.

[0084] Comparative Example 8

[0085] This comparative example provides a wear-resistant steel, the chemical composition of which is the same as that of Example 1, except that the ultrasonic shot peening process is omitted. The specific preparation method includes the following steps:

[0086] S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are smelted at 1700° C. for 2 h to obtain a first molten steel; Si, P and S are added to the first molten steel at 1400° C. and smelted for 1 h to cast a rectangular metal slab with a cross-sectional area of ​​48 mm×48 mm;

[0087] S2, keeping the metal sheet blank at 1320° C. for 1 hour, and then performing transverse forging at 1000° C. for 4 times, wherein the area ratio of the metal sheet blank before each transverse forging to the area ratio of the metal sheet blank after forging is 100:74, and the final forging temperature is controlled to be 680° C.; cooling the metal sheet blank after the 4 forging to room temperature with water at a flow rate of 40 m / s, and then freezing at -120° C. for 8 minutes to obtain a forged steel ingot;

[0088] S3. Annealing the forged steel ingot at 650° C. for 20 min to obtain wear-resistant steel.

[0089] The hardness, tensile strength, impact toughness value, yield strength, elongation and strength-ductility product of the wear-resistant steels prepared in Examples 1-3 and Comparative Examples 1-8 were tested, wherein the elongation, yield strength and tensile strength were tested according to GB / T10120-2013; the hardness of the wear-resistant steel was tested using a VexusMHV-1000Z Vickers hardness tester; according to GB / T229-2007, the impact energy of the sample was measured using a JBS-500B digital display impact testing machine;

[0090] Impact toughness = impact energy (J) / area (cm 2 );

[0091] Strength-ductility product = tensile strength × elongation. See Table 1 for specific test results:

[0092] Table 1

[0093]

[0094] It can be seen from Table 1 that the martensitic wear-resistant steel provided by the present invention has excellent strength and toughness, its hardness can reach 495HV, its tensile strength is as high as 1756MPa, and its strength-ductility product is 33.6GPa·%; it can also be seen from the comparative examples of the present invention that no matter whether the elements, element amounts or process parameters are changed, the steel prepared in the comparative examples is lower than the martensitic wear-resistant steel provided by the embodiments of the present invention in terms of performance parameters such as hardness or toughness.

[0095] The present invention reasonably designs the alloy composition of the martensitic wear-resistant steel and combines the processes of high-temperature heat preservation, transverse forging, annealing and ultrasonic shot peening, wherein each process step plays a role of composite strengthening, so that the prepared martensitic wear-resistant steel has both high strength and excellent toughness.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing martensitic wear-resistant steel, characterized in that: The martensitic wear-resistant steel is composed of the following chemical components by mass percentage: C: 0.38%-0.42%, Ti: 0.75%-0.8%, Mo: 0.2%-0.28%, V: 0.38%-0.4%, Mn: 1.58%-2%, Si: 0.084%-0.1%, P < 0.015%, S < 0.002%, and the balance is Fe and unavoidable impurities; The preparation method of the martensitic wear-resistant steel comprises the following steps: S1. In an inert atmosphere, C, Fe, Ti, V, Mo and Mn are first smelted at 1600° C. to 1700° C. to obtain a first molten steel; Si, P and S are added to the first molten steel at 1400° C. to 1600° C. for a second smelting and casting to obtain a metal slab; S2, keeping the metal sheet blank at 1280° C. to 1320° C., then performing transverse forging at 950° C. to 1000° C., controlling the final forging temperature to be 680° C. to 720° C., water-cooling the forged metal sheet blank to room temperature, and then freezing at -190° C. to -120° C. to obtain a forged steel ingot; S3, annealing the forged steel ingot at 600° C. to 650° C., and water cooling to obtain a casting; S4. Performing ultrasonic shot peening on the cross section of the casting to obtain martensitic wear-resistant steel.

2. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S1, the first smelting time is 2h~3h; and / or In S1, the second smelting time is 1h~2h.

3. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S2, the insulation time is 1h~2h.

4. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S2, the transverse forging is performed 4 to 5 times.

5. The method for preparing martensitic wear-resistant steel according to claim 4, characterized in that: In S2, the condition of the transverse forging is: the ratio of the area of ​​the metal sheet blank before each forging to the area of ​​the metal sheet blank after each forging is 100:(74-80).

6. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S2, the freezing time is 8 min to 10 min.

7. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S3, the annealing time is 10 min to 20 min.

8. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S4, the diameter of the shot peening in the ultrasonic shot peening treatment is 2 mm to 3 mm.

9. The method for preparing martensitic wear-resistant steel according to claim 1, characterized in that: In S4, the ultrasonic frequency of the ultrasonic shot peening treatment is 15kHz~25kHz; and / or In S4, the processing time of each cross section during the ultrasonic shot peening is 20 minutes to 30 minutes.

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