High-strength wear-resistant steel material, its heat treatment process and application in shield machine

Abstract

The application discloses a novel high-strength wear-resistant steel material and a heat treatment process and application thereof in a shield tunneling machine. The novel high-strength wear-resistant steel material comprises the following components in percentage by mass: C 0.65%-0.75%, Cr 6.50%-7.50%, V 1.70%-2.20%, Mo 2.00%-2.50%, Si 0.70%-1.20%, Mn 0.06%-0.50%, Ce 0.02%-0.03%, Ti 0.05%-0.08%, P≤0.03%, S≤0.03%, and the balance of Fe. The novel high-strength wear-resistant steel material is optimized by controlling and optimizing rare earth Ce elements and Ti elements, combined with spheroidizing annealing, high-temperature quenching and high-temperature tempering processes, so that the novel high-strength wear-resistant steel material has excellent mechanical properties, and exhibits a tensile strength of more than 2600 MPa while maintaining a hardness of more than 60HRC.

Description

Technical Field

[0001] This invention belongs to the field of steel material technology, specifically relating to a new type of high-strength wear-resistant steel material, its heat treatment process, and its application in tunnel boring machines. Background Technology

[0002] A tunnel boring machine (TBM) is a machine that breaks through rock underground to continuously excavate and advance tunnels. Currently, it plays a crucial role in the construction of large-scale tunnel projects. The cutterheads of the TBM are key to its smooth excavation. The cutterhead rings, in particular, are subjected to extreme wear and impact during operation. Therefore, research on cutterhead ring materials is fundamental to improving TBM efficiency. Currently, most cutterhead rings used in Chinese TBMs are made of H13 steel. H13 steel is the most widely used hot-work die steel, possessing good resistance to thermal fatigue and excellent wear resistance, as well as good toughness under medium-temperature conditions. However, while ensuring H13 steel reaches a high hardness of over 56 HRC, its toughness and tensile strength decrease, thus limiting its applicability in the TBM field. Therefore, developing a new TBM cutterhead ring material with a good balance of strength and toughness, along with high hardness, is particularly important.

[0003] Due to the complex working conditions of the cutterhead, a good cutterhead material should have a hardness of no less than 55 HRC and a tensile strength of no less than 2000 MPa. LD steel is a high-strength, high-toughness, and high-wear-resistant cold work die steel independently developed in my country. Its greatest characteristic is its high degree of austenitic alloying, significant solid solution strengthening and secondary hardening effects, achieving a hardness exceeding 60 HRC, while its wear resistance is superior to H13 steel. If, based on the high wear resistance and high hardness of LD steel, its mechanical properties can be improved to develop a material with a good balance of strength and toughness, capable of meeting the high impact, high load, and easy wear requirements of tunnel boring machine cutterheads, the service life of the cutterhead rings will be effectively extended, reducing the construction cost of tunnel engineering. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a novel high-strength wear-resistant steel material prepared using the aforementioned heat treatment process. This novel high-strength wear-resistant steel material, through the controlled optimization of rare earth elements Ce and Ti, combined with spheroidizing annealing, high-temperature quenching, and high-temperature tempering processes, possesses excellent mechanical properties, exhibiting a tensile strength exceeding 2600 MPa while maintaining a hardness above 60 HRC.

[0005] The second objective of this invention is to provide a heat treatment process for a novel high-strength wear-resistant steel material. This heat treatment process can effectively optimize the material's mechanical properties, adjust its microstructure, and improve the distribution and uniformity of carbides. Based on LD steel, a new type of steel has been developed that not only possesses high strength and a certain degree of toughness but also exhibits good wear resistance. This new steel contains a suitable ratio of alloying elements, and the added alloying elements are all abundant in domestic resources.

[0006] The third objective of this invention is to provide a novel high-strength wear-resistant steel material for use in tunnel boring machines.

[0007] The primary objective of this invention is achieved through the following technical solution:

[0008] A novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.65%-0.75%, Cr 6.50%-7.50%, V 1.70%-2.20%, Mo 2.00%-2.50%, Si 0.70%-1.20%, Mn 0.06%-0.50%, Ce 0.02%-0.03%, Ti 0.05%-0.08%, P≤0.03%, S≤0.03%, with the balance being Fe.

[0009] Preferably, the novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.65%, Cr 6.72%, V 1.90%, Mo 2.30%, Si 1.18%, Mn 0.06%, Ce 0.02%, Ti 0.08%, P 0.01%, S 0.01%, with the balance being Fe.

[0010] Preferably, the novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.66%, Cr 6.60%, V 1.91%, Mo 2.02%, Si 1.14%, Mn 0.12%, Ce 0.03%, Ti 0.07%, P 0.01%, S 0.01%, with the balance being Fe.

[0011] Preferably, the novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.71%, Cr 7.11%, V 2.10%, Mo 2.12%, Si 0.91%, Mn 0.08%, Ce 0.03%, Ti 0.06%, P 0.01%, S 0.01%, with the balance being Fe.

[0012] Preferably, the novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.66%, Cr 6.62%, V 2.05%, Mo 2.20%, Si 0.98%, Mn 0.08%, Ce 0.03%, Ti 0.07%, P 0.01%, S 0.01%, with the balance being Fe.

[0013] Preferably, the mechanical properties of the novel high-strength wear-resistant steel material are as follows: hardness > 60HRC, tensile strength ≥ 2600MPa, and impact absorption energy ≥ 75J.

[0014] The second objective of this invention is achieved through the following technical solution:

[0015] A heat treatment process for a novel high-strength wear-resistant steel material includes the following steps:

[0016] (1) Preparation of primary wear-resistant steel material: The raw materials are prepared according to the following mass percentages: C 0.65%-0.75%, Cr 6.50%-7.50%, V 1.70%-2.20%, Mo 2.00%-2.50%, Si 0.70%-1.20%, Mn 0.00%-0.50%, Ce 0.02%-0.03%, Ti 0.05%-0.08%, Fe balance; the above raw materials are smelted in an electric arc furnace at a tapping temperature of 1550-1600℃ and a casting temperature of 1480-1520℃; the castings are then forged to obtain the primary wear-resistant steel material.

[0017] (2) Annealing: Place the initial product of wear-resistant steel material described in step (1) in an annealing furnace, heat it from room temperature to 840℃-860℃ and hold it for 2-3 hours, then cool it in the furnace to 720℃-760℃ and hold it for 5-6 hours, then cool it in the furnace to below 500℃ and air cool it to room temperature.

[0018] (3) Quenching: Place the initial product of wear-resistant steel material after annealing in step (2) into a quenching furnace at a temperature of 1120-1150℃, keep it at the temperature for 0.5-1 hour, then take it out and oil quench it until it is cooled to below 200℃.

[0019] (4) Tempering: The initial product of wear-resistant steel material after quenching in step (3) is placed in a tempering furnace at a temperature of 520-550℃, kept at the temperature for 2-3 hours, and then air-cooled. The tempering is repeated 2-3 times to prepare a new type of high-strength wear-resistant steel material.

[0020] Preferably, in the forging process described in step (1), the initial forging temperature is 1080℃-1020℃ and the final forging temperature is ≥850℃.

[0021] Since metal raw materials cannot be 100% pure metals, the new high-strength wear-resistant steel materials prepared will contain impurities such as P and S.

[0022] The third objective of this invention is achieved through the following technical solution:

[0023] Application of a novel high-strength wear-resistant steel material in tunnel boring machines.

[0024] The reason for selecting the above alloying elements and their contents in this invention is that carbon (C) is a major element in steel materials. It often exists in the matrix as carbides formed by solid solution with the matrix. The addition of carbon is beneficial for alloy steel to obtain the M phase, improving the strength and hardness of the steel. Its content affects the microstructure and carbide precipitation of the steel material. Generally speaking, the carbon content in steel determines the hardness and strength of the material, but excessively high strength affects the toughness. Through numerous innovative experiments, this invention has determined that the most suitable carbon content for high-strength wear-resistant steel materials is 0.65%-0.75%.

[0025] Chromium (Cr) is one of the basic elements in wear-resistant materials. Its main function is to improve the hardenability of steel, significantly improve the strength, hardness and wear resistance of steel, form a series of continuous solid solutions in steel, cause changes in the isothermal transformation properties of steel, and increase the amount of eutectic and secondary carbides in steel. After many innovative experiments, the chromium content tested in this invention is in the range of 6.5-7.5%.

[0026] Vanadium (V), as an alloying element, is a key element in the formation of carbides in steel. It has a significant affinity for elements such as carbon (C) and oxygen (O) in steel, forming stable compounds. In addition, vanadium also has the ability to form carbides with other elements in steel (such as chromium (Cr), molybdenum (Mo), and manganese (Mn), effectively improving the strength and ductility of the steel. However, this alloying effect may adversely affect the impact toughness of the steel, requiring reasonable control of the vanadium (V) content. Through numerous innovative experiments, this invention has determined that the vanadium content is between 1.70% and 2.20%.

[0027] Molybdenum (Mo) is a carbide-forming element that can improve the hardenability and tempering resistance of materials. It can occupy the segregation sites of impurity elements such as P and S at the austenite grain boundaries, thereby improving the intergranular bonding force. Therefore, it can improve the unnotched impact performance of high-strength steel. After many innovative experiments, the molybdenum content tested in this invention ranges from 2.00% to 2.50%.

[0028] Silicon (Si), as a non-carbide-forming element, mainly exists in α-Fe and can play a role in solid solution strengthening. Silicon can significantly hinder martensite recovery during tempering and slow down the precipitation rate of cementite during tempering, but it tends to cause steel to exhibit a banded structure, affecting impact performance. After multiple innovative experiments, the silicon content tested in this invention ranges from 0.70% to 1.20%.

[0029] Cerium (Ce) is highly chemically reactive. In molten steel, it can react with low-melting-point metals such as lead and tin, as well as harmful impurities like oxygen and sulfur, to form high-melting-point inclusions, thus reducing their harmful effects on the steel. Simultaneously, Ce's relatively large atomic radius determines its trace solid solution concentration in steel and its unique alloying effect, which is beneficial for improving steel performance. Through numerous innovative experiments, this invention has determined that the Ce content is 0.02%-0.03%.

[0030] Titanium (Ti) is used to control grain size, playing a role in precipitation strengthening and grain refinement strengthening, thereby improving the strength and hardness of materials. In steel, it readily reacts with C to form TiC, which has the effect of refining austenite grains and martensite laths. After multiple innovative experiments, the titanium content tested in this invention is 0.05%-0.08%.

[0031] Compared with existing technologies, the novel high-strength wear-resistant steel material of this invention has the following advantages and beneficial effects:

[0032] (1) This invention improves the as-cast microstructure of steel by adding a small amount of Ce element, while refining the grains and altered non-metallic inclusions, improving their morphology and distribution, which can significantly improve the strength and hardness of the steel. Moreover, my country has abundant rare earth element resources, and rare earth (Ce) element is inexpensive, which has broad application prospects.

[0033] (2) This invention controls grain size by adding a small amount of Ti, thereby achieving precipitation strengthening and grain refinement strengthening, and improving the strength and hardness of the material. Compared with other microalloying elements, titanium (Ti) microalloying not only has cost and resource advantages, but also has the potential to further develop high-strength and high-toughness steel.

[0034] (3) After the above heat treatment, the present invention can achieve the following mechanical properties: hardness > 60HRC, tensile strength ≥ 2600MPa, and impact absorption energy ≥ 75J. Attached Figure Description

[0035] Figure 1 Metallographic image of spherical carbide particles formed after spheroidizing annealing of the novel high-strength wear-resistant steel material in Example 4;

[0036] Figure 2 SEM microstructure of the novel high-strength wear-resistant steel material in Example 4 after quenching. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0038] The chemical composition and smelting composition of Examples 1 to 4 of the present invention are shown in Table 1. The actual process parameters of Examples 1 to 4 of the present invention are shown in Table 2. The test results of the physical properties of Examples 1 to 4 of the present invention are shown in Table 3.

[0039] Please see Figure 1-2 . Figure 1 These are spherical carbide particles formed from the material in Embodiment 4 of this invention after spheroidizing annealing. Figure 1 It can be seen that the annealed carbides are fine and evenly distributed. Figure 2 This is a SEM microstructure image of the material after quenching in Example 4 of the present invention. It can be seen that there are fine carbide precipitates in the grains, which greatly helps to improve the mechanical properties of the material.

[0040] Table 1. Smelting composition, wt%

[0041]

[0042] Table 2 Actual process parameters of the present invention

[0043]

[0044] Table 3. Physical inspection results of the present invention

[0045]

[0046] Table 4 shows the performance parameters of H13 steel, the material used for the blade ring.

[0047]

[0048] Table 4 shows the performance parameters of H13 steel for the cutter ring. The references are: [1]. Wang Haoping, Zhang Mengqi, Mo Jiliang, et al. Research status of performance enhancement of cutter ring for shield / TBM. Materials Reports, 2022, 36(07): 49-57. [2]. Li Shihong, et al. Analysis of cutter ring material for shield machine. Rock Drilling Machinery and Pneumatic Tools, 2013(04): 34-41.

[0049] Comparing the values ​​in Tables 3 and 4, it can be seen that the novel high-strength wear-resistant steel material prepared by this invention has a hardness > 60 HRC, tensile strength > 2600 MPa, and impact absorption energy ≥ 75 J, which is far superior to H13 steel. The novel high-strength wear-resistant steel material prepared by this invention meets the requirements of tunnel boring machines for steel materials.

[0050] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A novel high-strength wear-resistant steel material, characterized in that, The composition includes the following percentages by mass: C 0.65%-0.75%, Cr 6.50%-7.50%, V 1.70%-2.20%, Mo 2.00%-2.50%, Si 0.70%-1.20%, Mn 0.06%-0.50%, Ce 0.02%-0.03%, Ti 0.05%-0.08%, P≤0.03%, S≤0.03%, balance Fe; The mechanical properties of the new high-strength wear-resistant steel material are as follows: hardness > 60HRC, tensile strength ≥ 2600MPa, and impact absorption energy ≥ 75J.

2. The novel high-strength wear-resistant steel material according to claim 1, characterized in that, The novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.65%, Cr 6.72%, V 1.90%, Mo 2.30%, Si 1.18%, Mn 0.06%, Ce 0.02%, Ti 0.08%, P 0.01%, S 0.01%, with the balance being Fe.

3. The novel high-strength wear-resistant steel material according to claim 1, characterized in that, The novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.66%, Cr 6.60%, V 1.91%, Mo 2.02%, Si 1.14%, Mn 0.12%, Ce 0.03%, Ti 0.07%, P 0.01%, S 0.01%, with the balance being Fe.

4. The novel high-strength wear-resistant steel material according to claim 1, characterized in that, The novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.71%, Cr 7.11%, V 2.10%, Mo 2.12%, Si 0.91%, Mn 0.08%, Ce 0.03%, Ti 0.06%, P 0.01%, S 0.01%, with the balance being Fe.

5. The novel high-strength wear-resistant steel material according to claim 1, characterized in that, The novel high-strength wear-resistant steel material comprises the following components by mass percentage: C 0.66%, Cr 6.62%, V 2.05%, Mo 2.20%, Si 0.98%, Mn 0.08%, Ce 0.03%, Ti 0.07%, P 0.01%, S 0.01%, with the balance being Fe.

6. A heat treatment process for a novel high-strength wear-resistant steel material according to any one of claims 1 to 5, characterized in that, Includes the following steps, (1) Preparation of primary wear-resistant steel material: The raw materials are prepared according to the following mass percentages: C 0.65%-0.75%, Cr 6.50%-7.50%, V 1.70%-2.20%, Mo 2.00%-2.50%, Si 0.70%-1.20%, Mn 0.00%-0.50%, Ce 0.02%-0.03%, Ti 0.05%-0.08%, Fe balance; The above raw materials are smelted in an electric arc furnace, the tapping temperature is 1550-1600℃, and the casting temperature is 1480-1520℃; The castings are then forged to obtain the primary wear-resistant steel material. (2) Annealing: Place the initial product of wear-resistant steel material described in step (1) in an annealing furnace, heat it from room temperature to 840℃-860℃ and hold it for 2-3 hours, then cool it in the furnace to 720℃-760℃ and hold it for 5-6 hours, then cool it in the furnace to below 500℃ and air cool it to room temperature. (3) Quenching: Place the initial product of wear-resistant steel material after annealing in step (2) into a quenching furnace at a temperature of 1120-1150℃, keep it at the temperature for 0.5-1 hour, then take it out and oil quench it until it is cooled to below 200℃. (4) Tempering: The initial product of wear-resistant steel material after quenching in step (3) is placed in a tempering furnace at a temperature of 520-550℃, kept at the temperature for 2-3 hours, and then air-cooled. The tempering is repeated 2-3 times to prepare a new type of high-strength wear-resistant steel material.

7. The heat treatment process for the novel high-strength wear-resistant steel material according to claim 6, characterized in that, In the forging process described in step (1), the initial forging temperature is 1080℃-1020℃, and the final forging temperature is ≥850℃.

8. The application of a novel high-strength wear-resistant steel material according to any one of claims 1 to 5 in a tunnel boring machine.

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