Residual austenite enhanced impact-resistant high-titanium wear-resistant steel and production method thereof

Abstract

The invention belongs to a production method of high-strength hot continuous rolling steel, and particularly relates to retained austenite enhanced impact-resistant high-titanium wear-resistant steel and a production method thereof. In order to improve the impact resistance of the wear-resistant steel, the impact-resistant and wear-resistant steel is prepared through conventional continuous casting, hot rolling and non-heat treatment, and the impact-resistant and wear-resistant steel contains 0.30%-0.40% of C, 1.4%-1.8% of Si, 1.5%-2.5% of Mn, 0.40%-0.60% of Ti, 0.020%-0.050% of Nb, 0.015%-0.050% of Als, smaller than or equal to 0.020% of P, smaller than or equal to 0.010% of S, smaller than or equal to 0.0030% of N and the balance Fe and inevitable impurities. Micron-sized TiC hard particles in the steel can improve the wear resistance; the bainite isothermal process is simulated through the high-silicon component and slow cooling of the steel coil, a large amount of bainite with high dislocation density is formed, and meanwhile, a certain content of retained austenite is formed between bainite laths to improve the impact resistance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of production methods of high-strength hot-rolled steel, and particularly relates to a residual austenite reinforced impact-resistant high-titanium wear-resistant steel and a production method thereof. BACKGROUND

[0002] Commercial wear-resistant steel plates are generally prepared through forging, medium plate rolling or hot continuous rolling, and the strength and hardness of the steel are improved through quenching and tempering heat treatment. The microstructure thereof is martensite, which has high strength and hardness but low toughness and plasticity. Certain wear-resistant material application scenarios, such as crusher liner plates, require that the material has high hardness and toughness and plasticity, otherwise the liner plate material is prone to cracking under the impact and extrusion of ore, and cannot meet the service requirements. Therefore, it is urgent to develop a material that has wear-resistant performance and impact-resistant performance to meet the requirements of the impact and wear-resistant performance of the crusher liner plate.

[0003] At present, patent CN104451405A discloses an austenitic wear-resistant steel with impact and wear-resistant performance and a hot-rolled plate manufacturing method thereof. The composition of the steel is as follows: C: 0.81-0.99%, Si: ≤0.5%, Mn: 7.00-9.00%, P: ≤0.030%; S: ≤0.020%, Cr: 0.5-1.49%, Mo: 0.2-0.5%, V: 0.1-0.5%, Nb: 0.01-0.15%, B ≤0.0040%, and the rest is iron and inevitable impurities. Although the invention uses high-carbon and high-manganese components to prepare austenitic steel to improve the impact resistance, the alloy content is high, which is not suitable for continuous casting production, and the alloy cost is high.

[0004] On the other hand, CN115449702A discloses a preparation method of high-titanium wear-resistant steel. Waste steel, carbon additive, chromium iron and silicon iron are mixed and heated in an electric furnace, and after the molten steel is melted, manganese iron is added, the temperature is raised to 1622-1636℃, 0.08-0.10% of aluminum in terms of mass fraction of the molten steel in the furnace is added, and the chemical composition and mass fraction of the molten steel in the furnace are controlled to be 0.69-0.77% C, 1.68-1.85% Si, 2.22-2.48% Mn, 0.65-0.79% Cr, <0.035% S, <0.040% P, 0.03-0.06% Al, and the balance of Fe and inevitable impurities. Then, 0.8-1.0% of titanium iron in terms of mass fraction of the molten steel in the furnace is added, the molten steel is treated outside the furnace, and then cast into a casting. After heat treatment, high-titanium wear-resistant steel with high hardness, good strength and toughness, and excellent wear resistance is obtained. Although the invention uses high Ti content to improve the wear-resistant performance, it does not involve the improvement of the impact resistance, and the invention uses a casting process for preparation, which is limited in production process.

[0005] From the above, the prior art is to use high manganese or high silicon components, and to use high content of alloy, and at the same time, heat treatment is carried out in the production process to obtain austenite structure or residual austenite structure, so as to realize the effect of improving the impact resistance of wear-resistant steel. However, the cost is high, and the process is complex, which is not conducive to popularization. SUMMARY

[0006] In order to improve the impact resistance of wear-resistant steel, and reduce the cost and simplify the production process, the present application adopts lower alloy cost, and prepares the impact-resistant and wear-resistant steel through conventional continuous casting and hot rolling process without heat treatment.

[0007] To achieve the above application purposes, the technical scheme adopted by the present application is as follows: In a first aspect, the present application provides an impact-resistant high-titanium wear-resistant steel, which comprises the following chemical components in percentage by mass: C: 0.30-0.40%, Si: 1.4-1.8%, Mn: 1.5-2.5%, Ti: 0.40-0.60%, Nb: 0.020-0.050%, Als: 0.015-0.050%, P≤0.020%, S≤0.010%, N≤0.0030%, and the balance being Fe and unavoidable impurities.

[0008] Further, the microstructure of the high-titanium wear-resistant steel comprises 20-50% of bainite and residual austenite with a volume fraction of ≥10%.

[0009] Further, the high-titanium wear-resistant steel contains TiC hard particles with an average size of 1-10 μm.

[0010] Further, the high-titanium wear-resistant steel has a yield strength of ≥700 MPa, a tensile strength of ≥1000 MPa, an elongation of ≥12%, an impact energy at-20℃ of ≥80 J, and a hardness HB of ≥300.

[0011] In a second aspect, the present application provides a production method of the above-mentioned impact-resistant high-titanium wear-resistant steel, which comprises the following steps: sequentially carrying out converter smelting, LF refining, RH refining, continuous casting, slab heating, rolling, laminar cooling and slow cooling according to the set steel chemical composition.

[0012] Further, the steel is poured with high superheat during continuous casting, and the tundish superheat is 50-60℃.

[0013] Further, the secondary cooling water of continuous casting adopts strong cooling mode, and the cooling rate is ≥50℃ / min.

[0014] Further, the thickness of the steel casting blank after continuous casting is 200-250 mm.

[0015] Further, the steel temperature is ≥600℃ when the steel casting blank after continuous casting is hot sent and hot charged, and the steel temperature is ≤100℃ when the steel is cold charged after slow cooling.

[0016] Further, the slab heating is at a temperature of 1190-1230℃.

[0017] Further, the slab heating is at a time of 200-300 min.

[0018] Further, the slab is descaled after heating, and the temperature of the steel blank before descaling is ≥1180℃, and the water pressure of descaling is ≥20 MPa.

[0019] Further, the steel plate after descaling is subjected to two-stage rolling, and the cumulative compression ratio of the recrystallization zone rolling is ≥4, and the finish rolling temperature is ≥1050℃.

[0020] Further, the cumulative compression ratio of the non-recrystallization zone rolling is ≥4, and the finish rolling temperature is 850-900℃.

[0021] Further, the steel plate after rolling is subjected to front-stage cooling in laminar flow cooling, and the cooling rate is 10-20℃ / s, and the coiling temperature is 380-460℃.

[0022] Further, the steel plate is subjected to slow cooling after coiling, and the slow cooling time is ≥48 h, and the out-of-pit temperature is ≤160℃.

[0023] Beneficial effects: Compared with the prior art, the impact-resistant high-titanium wear-resistant steel has the following advantages: (1) The steel provided by the present application is micro-alloyed by low-cost Si, Ti and other elements, and the alloy cost is low.

[0024] (2) The bainite and residual austenite in the microstructure of the steel can improve the toughness and plasticity of the steel, and the residual austenite can generate TRIP effect during impact deformation to absorb impact energy. Experiments show that the volume fraction of bainite is 20-50%, and the volume fraction of residual austenite is ≥10%.

[0025] (3) The steel provided by the present application contains TiC hard particles with an average size of 1-10 μm, and the micron-level TiC hard particles can improve the wear resistance of the matrix and prolong the service life of the material.

[0026] (4) The yield strength of the steel provided by the present application is ≥700 MPa, the tensile strength is ≥1000 MPa, the elongation is ≥12%, the impact energy at-20℃ is ≥80 J, the hardness HB is ≥300, and the wear resistance reaches the level of commercial wear-resistant steel NM300.

[0027] (5) The production method of the steel provided by the present application is simple, and the steel can be prepared by conventional continuous casting and rolling methods without heat treatment. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1Microstructure chart of high-titanium wear-resistant steel prepared for Example 1 of the present application; Figure 2 Microstructure chart of wear-resistant steel prepared for Comparative Example 2 of the present application; Figure 3 Graph of friction and wear test data results for the example and comparative example steels. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application more clear and explicit, the present application will be further described in detail below in combination with embodiments. Unless otherwise defined, all technical terms used herein have the same meanings as understood by those of ordinary skill in the art.

[0030] Various types of mining machinery such as ball mills, crushers, mine carriages, etc., in addition to requiring strong friction and wear resistance, also need to have certain impact and wear resistance to withstand the extrusion and impact of the ore. Traditional wear-resistant steels use martensite hardening to improve wear resistance, while the present application uses high-titanium micro-alloying to form a large number of micron-sized TiC hard particles in the matrix structure to improve the friction and wear resistance of the matrix. In addition, to improve the impact and wear resistance of the material, the present application uses a high-silicon composition system to simulate the bainite isothermal process through slow cooling of the steel coil in the bainite temperature range, forming a large amount of bainite structure with high dislocation density, and a certain amount of residual austenite between the bainite laths. This part of the residual austenite can form martensite structure through TRIP effect when the material is subjected to impact deformation, absorbing impact energy, and the hardened martensite structure can further enhance the wear resistance of the material.

[0031] Therefore, in one embodiment of the present application, an impact-resistant high-titanium wear-resistant steel is provided, which has a chemical composition comprising, by mass percent: C: 0.30-0.40%, Si: 1.4-1.8%, Mn: 1.5-2.5%, Ti: 0.40-0.60%, Nb: 0.020-0.050%, Als: 0.015-0.050%, P≤0.020%, S≤0.010%, N≤0.0030%, and the balance being Fe and unavoidable impurities.

[0032] The reasons for limiting the main alloying elements in the steel described in the present application are described below.

[0033] C in steel can combine with Ti to form TiC hard particles, the steel described in the application adds 0.40-0.60% of Ti, according to the ideal chemical formula, this part of Ti can occupy 0.10-0.15% of C, Ti and C at the end of the solidification of the billet form micron TiC hard particles through eutectic reaction, these particles can play a role in inhibiting the wear furrow and the wear scratch expansion in the service of the material in the wear-resistant scene, at the same time, the higher the C content, the higher the [Ti][C] concentration product, the higher the volume fraction of micron TiC. Secondly, C is the constituent element of bainite and martensite, and C can also improve the stability of austenite and promote the formation of residual austenite structure, therefore, in addition to the 0.10-0.15% of C occupied by Ti, about 0.20% of C needs to be added additionally to meet the nucleation of bainite transformation and residual austenite structure. Therefore, the C content in the application is limited to the range of 0.30-0.40%.

[0034] Because Ti and C can occur eutectic reaction at the end of solidification, micron TiC hard particles are formed, and TiC can also precipitate during rolling, cooling and coiling, forming nanoscale TiC particles of different sizes, this part of precipitated phase plays a role in precipitate strengthening, which can strengthen ferrite structure and reduce the hardness difference between ferrite and bainite, realizing the overall improvement of the hardness of the material matrix structure. Therefore, the Ti content in the application is limited to 0.40-0.60%.

[0035] Mn in steel plays a role in solid solution strengthening and improving toughness, at the same time, higher Mn content can improve the stability of residual austenite and increase the content of residual austenite. Therefore, the Mn content in the application is controlled in the range of 1.5-2.5%.

[0036] Si element in steel is also an important austenite stabilizing element, increasing Si content can improve the stability of residual austenite and increase the volume fraction of residual austenite, at the same time, Si can increase the phase transition temperature of steel and promote bainite transformation. However, Si content is easy to form red iron oxide scale, which affects the surface quality of the material. Therefore, the Si content in the application is limited to 1.4-1.8%.

[0037] In the deformed austenite, solid solution Nb or Nb(CN) can play a role in dragging the austenite grain boundary, inhibiting the grain boundary expansion, thereby playing a role in refining the deformed austenite, and further refining the finished product structure, at the same time, Nb can inhibit the nucleation of pearlite and cementite and promote bainite transformation. As can be seen above, adding Nb is beneficial to obtain bainite and residual austenite structure, at the same time, refine the grain size of the above structure and improve the stability of residual austenite. Therefore, the application requires adding 0.020-0.050% of Nb.

[0038] The Al element in the steel can play the role of refining grains and deoxidation, and can reduce the number of oxide inclusions in the steel. P, S and N are common impurity elements in the steel, among which, the high content of P can easily reduce the cold brittleness of the material, the high content of S can easily lead to the increase of the sulfide inclusion level of the material, and N can easily combine with Ti to form liquid-precipitated TiN inclusions, thereby affecting the toughness of the material. For the Ti content of 0.40-0.60%, the N content is controlled to be less than 30 ppm, so as to reduce the TiN nucleation rate. Therefore, the content of Als, P, S and N is limited to the range of 0.015-0.050%, ≤0.020%, ≤0.010% and ≤0.0030% respectively.

[0039] In another embodiment of the present application, a production method of the above-mentioned impact-resistant high-titanium wear-resistant steel is provided, which comprises the following steps: sequentially performing converter smelting, LF refining, RH refining, continuous casting, slab heating, rolling, laminar cooling and slow cooling according to the set steel chemical composition.

[0040] In the following, the reasons for the production process limitation are described in combination with the requirements for the microstructure and performance control of the steel according to the present application.

[0041] As mentioned above, the present application mainly improves the wear resistance by forming micron-level TiC hard particles through eutectic reaction at the solidification end. Since the precipitation amount of TiC is controlled by the [Ti][C] concentration product, a higher solidification temperature, i.e. a higher tundish superheat, is beneficial to increase the solid solubility product of [Ti][C], and is beneficial to precipitate more micron TiC. At the same time, a higher solidification cooling rate is also beneficial to the nucleation of TiC. Therefore, the present application requires that the tundish superheat is controlled in the range of 50-60℃, the secondary cooling water adopts a strong cooling mode, and the cooling rate is controlled at a higher level of ≥50℃ / min.

[0042] Since a large amount of micron-level TiC is formed during the solidification of the billet, and a higher C and Si element is added in the steel, the hardenability of the steel is greatly improved. Therefore, the billet is required to be hot charged or slowly cooled to near room temperature before being charged into the furnace. This is to avoid the fracture of the billet during the transportation process due to the brittleness of the billet after solidification. The specific provisions are as follows: the billet temperature is ≥600℃ when hot charging, and the billet temperature is ≤100℃ when slowly cooling and then cold charging.

[0043] The slab heating temperature and the furnace time are also limited in the present application, which are 1190-1230℃ and 200-300 min respectively. Firstly, the present application adopts lower slab heating temperature and shorter furnace time, which is mainly to avoid the re-dissolution of micron TiC formed during solidification. Meanwhile, a large amount of Si is also added in the steel, which is easy to form Fe2SiO4 olivine phase during the slab heating process. The melting point of this substance is relatively low, which is about 1180℃. Therefore, the heating temperature is limited to above 1190℃ in the present application, so as to ensure that the slab temperature is relatively high when the slab is discharged for descaling, and the Fe2SiO4 on the surface of the slab is still in liquid phase, which can be removed together with the surface oxide scale. If the heating temperature is too low, the Fe2SiO4 will be solidified when the slab is descaled, and it will act as an adhesive on the tortuous interface between the oxide scale and the steel substrate, which will lead to incomplete descaling of the slab, and red oxide scale will be left on the surface of the slab.

[0044] The rolling adopts two-stage deformation, wherein the first stage rolling, i.e. austenite recrystallization deformation, requires to ensure a certain deformation amount, to avoid the occurrence of coarse austenite structure or mixed crystal structure, and the deformation temperature is required to be higher than the critical recrystallization temperature, which is generally about 950℃. Therefore, the present application requires that the rolling compression ratio in the austenite recrystallization zone is ≥4, and the finish rolling temperature is ≥1050℃.

[0045] The austenite non-recrystallization zone deformation can promote the flattening of austenite, and provide enough nucleation points for subsequent phase transformation, so as to promote the refinement of the structure of the finished steel. Therefore, the present application requires that the cumulative compression ratio is ≥4. The finish rolling temperature is generally required to be higher than the phase transformation temperature A3, so as to avoid rolling in the two-phase zone, thereby leading to mixed crystal. Meanwhile, the adoption of higher finish rolling temperature is also beneficial to the deformation-induced precipitation of TiC, and the adoption of higher finish rolling temperature is also beneficial to the improvement of the stability of the undercooled austenite, and the improvement of the volume fraction of residual austenite in the finished structure. However, too high finish rolling temperature will also lead to coarse structure, and reduce the toughness and plasticity of the material. The present application limits the finish rolling temperature in the second stage rolling to the range of 850-900℃.

[0046] The phase transformation occurs during the laminar cooling and coiling process, in order to obtain bainite structure. The present application limits the coiling temperature to the range of 380-460℃, which is in the bainite transformation zone, and adopts a suitable cooling rate of 10-20℃ / s. If the cooling rate is too low, pearlite structure will be produced, and since the pearlite occupies a high content of C element, it will lead to the difficulty of the formation of subsequent residual austenite. Meanwhile, since the bainite transformation mechanism is between shear type and diffusion type phase transformation, the bainite transformation requires a long holding time. Therefore, the present application simulates the bainite isothermal process through slow cooling after the coiling of the steel coil, and realizes the transformation of residual austenite through a long time of slow cooling. Therefore, the present application requires that the slow cooling time of the steel coil is ≥48 h, and the slow cooling temperature is lower than 160℃, at which temperature all the phase transformation processes are completely.

[0047] Specific examples will be listed below to explain the scheme of the present invention. Those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0048] Preparation of test example wear-resistant steel Table 1 shows the compositions of the examples and comparative examples of the present invention, Table 2 shows the production process parameters of the examples and comparative examples of the present invention, and Table 3 shows the mechanical properties and microstructural indicators of the steels of the examples and comparative examples of the present invention. In Table 3, F, B, RA, and P represent ferrite, bainite, retained austenite, and pearlite, respectively. Figure 1 、 2 The microstructures of the steels of Example 1 and Comparative Example 2 are shown in FIG. Figure 3 The relative wear resistance of the embodiment and comparative example steels and the commercial wear-resistant steel NM300 is the experimental result measured on a friction and wear testing machine. The experimental parameters are load 170N, revolution 1000, and speed 245 r / min.

[0049] The high-titanium wear-resistant steels described in Examples 1 to 3 of the present invention are subjected to continuous casting, slab heating, rolling, laminar cooling, coiling, and slow cooling to produce finished steel plates having a yield strength ≥ 700 MPa, a tensile strength ≥ 1000 MPa, an elongation ≥ 12%, an impact energy ≥ 120 J at -20°C, and a hardness HB ≥ 300. The microstructure consists of ferrite, bainite, and retained austenite.

[0050] The chemical composition of the steels in Comparative Examples 1 and 2 meets the requirements of the present invention. However, during the smelting process of the steel in Comparative Example 1, the tundish superheat was too low, at 35°C, which is lower than the requirement of 50-60°C. The secondary cooling water cooling rate was too low, at 42°C / min, which is lower than the requirement of ≥50°C. The furnace discharge temperature during slab heating was too high, at 1253°C, which is higher than the required value of 1190-1230°C. These process fluctuations resulted in a decrease in the content of micronized TiC hard phase nucleated through eutectic reaction during the smelting process and an increase in the content of micronized TiC dissolved back during slab heating. These two factors together resulted in a decrease in the micronized TiC content in the finished steel, resulting in lower friction and wear properties of the finished steel than those of commercial NM300 steel (see [1]). Figure 3 ).

[0051] The cooling rate of the steel of Comparative Example 2 is low at 5°C / s during the laminar cooling, which is lower than the required value of 10-20°C / s, and the coiling temperature is high at 643°C, which is higher than the required value of 380-460°C. The above process fluctuation results in a large amount of pearlite structure in the finished steel, and no bainite and residual austenite structure. In comparison, the pearlite structure has greater brittleness and lower dislocation density, so the strength of the steel of Comparative Example 2 is low at 864 MPa, the impact energy is low at 45 J, and the hardness HB is low at 228.

[0052] The Si content in the steel of Comparative Example 3 is low at 0.55%, which is lower than the required value of 1.4-1.8%. The Si content of 0.55% cannot promote the formation of residual austenite, and in addition, the slow cooling time after coiling of the steel coil is short and the out-of-pit temperature is high, which results in insufficient isothermal time of the steel in the bainite temperature range, and finally results in the structure of the finished steel being 76% ferrite plus 28% bainite, the bainite content is reduced, and no residual austenite structure is formed. Under the combined action of the two, the strength and low-temperature impact performance of the steel of Comparative Example 3 are low.

[0053] The Ti content in the steel of Comparative Example 4 is low at 0.15%, which is lower than the required value of 0.40-0.60%, which results in insufficient [Ti][C] concentration product in the molten steel, and insufficient micron TiC cannot be formed, so the wear resistance of the steel of Comparative Example 4 is low, and the wear resistance index is lower than NM300 (see Figure 3 ).

[0054] Table 1 Chemical composition of the examples and comparative examples / % Table 2 Production process of the examples and comparative examples Table 2 (continued) Table 3 Structure and properties of the examples and comparative examples .

Claims

1. Impact-resistant high-titanium wear-resistant steel, characterized by: The chemical composition, by mass percentage, includes: C: 0.30-0.40%, Si: 1.4-1.8%, Mn: 1.5-2.5%, Ti: 0.40-0.60%, Nb: 0.020-0.050%, Als: 0.015-0.050%, P≤0.020%, S≤0.010%, N≤0.0030%, and the balance is Fe and unavoidable impurities.

2. The impact-resistant high-titanium wear-resistant steel according to claim 1, characterized in that: The microstructure of the high-titanium wear-resistant steel includes bainite with a volume fraction of 20-50% and retained austenite with a volume fraction of ≥10%; the high-titanium wear-resistant steel contains TiC hard particles with an average size of 1-10 μm.

3. The method for producing impact-resistant high-titanium wear-resistant steel according to claim 1 or 2, characterized in that: The following steps are involved: According to the set chemical composition of the steel, converter smelting, LF refining, RH refining, continuous casting, slab heating, rolling, laminar cooling and slow cooling can be carried out in sequence.

4. The method for producing impact-resistant high-titanium wear-resistant steel according to claim 3, characterized in that: The steel is poured at a high superheat during continuous casting, with the superheat of the tundish being 50-60°C.

5. The method for producing impact-resistant high-titanium wear-resistant steel according to claim 3 or 4, characterized in that: The secondary cooling water of continuous casting adopts strong cooling mode, and the cooling rate is ≥50℃ / min.

6. The method for producing impact-resistant high-titanium wear-resistant steel according to any one of claims 3 to 5, characterized in that: After continuous casting, the steel temperature during hot delivery and hot charging of the steel ingot shall be ≥600℃, and the steel temperature during cold charging after slow cooling shall be ≤100℃.

7. The method for producing impact-resistant high-titanium wear-resistant steel according to any one of claims 3 to 6, characterized in that: After heating, the slab temperature out of the furnace is 1190-1230℃, and the time in the furnace is 200-300 minutes.

8. The method for producing impact-resistant high-titanium wear-resistant steel according to any one of claims 3 to 7, characterized in that: The steel plate after descaling is rolled in two stages, with the cumulative rolling reduction ratio of the recrystallization zone being ≥4 and the final rolling temperature being ≥1050°C, and the cumulative rolling reduction ratio of the non-recrystallization zone being ≥4 and the final rolling temperature being 850-900°C.

9. The method for producing impact-resistant high-titanium wear-resistant steel according to any one of claims 3 to 8, characterized in that: The laminar cooling of the rolled steel plate adopts front-stage cooling, the cooling rate is 10-20℃ / s, and the coiling temperature is 380-460℃.

10. The method for producing impact-resistant high-titanium wear-resistant steel according to any one of claims 3 to 9, characterized in that: After coiling, the steel plate is slowly cooled, the slow cooling time is ≥48 h, and the pit temperature is ≤160℃.

Images