Impact-resistant high-manganese wear-resistant steel and preparation method thereof

Abstract

The invention belongs to the technical field of high-manganese steel, and discloses impact-resistant high-manganese wear-resistant steel and a preparation method thereof. The impact-resistant high-manganese wear-resistant steel comprises the following chemical components in percentage by weight: 0.95 to 1.25 percent of C, 0.05 to 0.15 percent of Si, 13 to 15 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.07 to 0.12 percent of Als, 0.3 to 0.8 percent of Cr and the balance of Fe and inevitable impurities. The segregation degree of the high-manganese wear-resistant steel is greatly improved, the structure uniformity is remarkably improved, the microstructure of the high-manganese wear-resistant steel shows an austenite structure with the area fraction as high as 99% or above, a small amount of carbides can be distributed in grains or on grain boundaries of austenite, the area proportion of the carbides in the microstructure is smaller than or equal to 1%, and the carbides are small in size; therefore, the toughness, the wear resistance and the impact resistance of the high-manganese wear-resistant steel disclosed by the invention are remarkably enhanced, and the service life is excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of high manganese steel, and particularly relates to an impact-resistant high manganese wear-resistant steel and a preparation method thereof. Background Art

[0002] When in the as-cast state, the microstructure of high manganese steel usually consists of austenite, carbide and pearlite, and sometimes contains a small amount of phosphide eutectic. When the amount of carbide is large, it often appears in a network form at the grain boundaries. This microstructure significantly reduces the toughness and plasticity of high manganese steel. Therefore, solution treatment is required, heating to 1050-1100 °C and holding to eliminate the as-cast structure to obtain single-phase austenite, improving the microstructure and properties of high manganese steel, so that it can be widely used in various engineering fields.

[0003] However, due to the high alloy content of high manganese steel, serious segregation is likely to occur. During the heating and cooling processes, more carbides are likely to appear near the austenite grain boundaries, resulting in a weakened work-hardening effect brought by dislocation movement, a reduced transformation amount of ε-martensite and deformation twins during the deformation process under impact load, and also a decrease in toughness. The wear resistance and impact resistance are not good. During subsequent use, under a large impact, a crack source is easily formed, and there is a risk of cracking. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an impact-resistant high manganese wear-resistant steel and a preparation method thereof in view of the deficiencies of the existing technology, which can effectively optimize the segregation quality of high manganese steel, reduce the amount of carbide precipitation, improve the uniformity of microstructure and properties, enhance the toughness, wear resistance and impact resistance of high manganese steel, and have excellent service life.

[0005] To solve the technical problems proposed by the present invention, the present invention provides an impact-resistant high manganese wear-resistant steel, and its chemical composition in terms of weight percentage includes: C: 0.95-1.25%, Si: 0.05-0.15%, Mn: 13-15%, P≤0.020%, S≤0.010%, Als: 0.07-0.12%, Cr: 0.3-0.8, and the balance is Fe and inevitable impurities.

[0006] Preferably, the chemical composition of the impact-resistant high manganese wear-resistant steel in terms of weight percentage includes: C: 1.0-1.15%, Si: 0.07-0.10%, Mn: 13.5-14.5%, P≤0.020%, S≤0.010%, Als: 0.08-0.10%, Cr: 0.35-0.65, and the balance is Fe and inevitable impurities.

[0007] In the above scheme, the main microstructure of the impact-resistant high manganese wear-resistant steel is austenite, and its area ratio is ≥99%, and the grain size is 20-30 μm.

[0008] In the above solution, a small amount of carbides may be distributed inside or at the grain boundaries of the austenite, and the area ratio thereof in the microstructure is ≤1%, and the size is ≤0.2 μm.

[0009] In the above solution, the yield strength of the impact-resistant high manganese wear-resistant steel is 350 - 650 MPa, the tensile strength is 900 - 1250 MPa, the elongation is 32 - 49%, the impact energy at -40 °C is 160 - 305 J, the Brinell hardness is 190 - 305 HBW, and the wear resistance under large impacts is better than that of traditional low-alloy wear-resistant steels.

[0010] The present invention also provides a preparation method for an impact-resistant high manganese wear-resistant steel, adopting a process route of smelting, continuous casting, direct charging, heating, rough rolling, finish rolling, cooling, coiling, and transverse cutting, including the following steps:

[0011] 1) Continuous casting: After the molten steel is smelted, continuous casting is carried out, and the superheat of the molten steel in the tundish is controlled at 5 - 20 °C;

[0012] 2) Heating: The cast slab enters the heating furnace for heating, the furnace inlet temperature is greater than 550 °C, the total heating time in the heating furnace is 180 - 220 min, wherein the heating temperature in the high-temperature section is 1160 - 1210 °C, and the heating time in the high-temperature section is ≥90 min;

[0013] 3) Rough rolling: 1 + 7 passes of rolling are adopted, the sum of the reduction ratios of the first three passes of R1 and R2 is greater than 60%, the rough rolling finishing temperature is 1040 - 1070 °C, and after rough rolling, a heat preservation cover is used to reduce the temperature drop of the intermediate slab;

[0014] 4) Finish rolling: The finish rolling starting temperature is 1030 - 1060 °C, and the finish rolling finishing temperature is 920 - 960 °C;

[0015] 5) Cooling and coiling: Immediately cool to the coiling temperature for coiling to achieve on-line solution treatment and obtain a fine austenite structure.

[0016] Preferably, the furnace inlet temperature of the cast slab is 580 - 790 °C, and the heating time in the high-temperature section is 90 - 110 min.

[0017] Preferably, the sum of the reduction ratios of the first three passes of rough rolling R1 and R2 is 62 - 74%.

[0018] In the above solution, during the whole process of rough rolling, rapid cooling is adopted for the first 3 - 4 m of the head, with a cooling rate of 10 - 20 °C / s, and normal air cooling is adopted for the remaining parts.

[0019] In the above solution, the cooling rate in step 5) is 100 - 180 °C / s.

[0020] In the above solution, the coiling temperature is 20 - 50 °C.

[0021] The design key points of the present invention in terms of chemical composition are as follows:

[0022] 1) When the carbon content is relatively low, the work hardening effect is not strong, which is not beneficial to the service life and application effect. When the carbon content is high, carbide precipitation cannot be avoided in the water toughening treatment state, deteriorating the properties of the steel and increasing the degree of continuous casting segregation. Considering comprehensively, the C weight percentage is preferably 0.95 - 1.25%;

[0023] 2) Silicon is a good deoxidizer. Adding a certain amount of silicon when deoxidizing with aluminum can significantly improve the deoxidizing ability of aluminum, which is beneficial to the steel purity. The affinity of silicon with oxygen is stronger than that of iron. During welding, low melting point silicates are easily generated, increasing the fluidity of the slag and the molten metal, causing splashing phenomena and affecting the weld quality, which is not conducive to the application of high manganese steel. Considering comprehensively, the Si weight percentage is preferably 0.05 - 0.15%;

[0024] 3) Manganese dissolves in ferrite and austenite, expanding the austenite region. When the manganese content is relatively high, the steel can form a single austenite at room temperature, having good toughness. When impacted, the surface will be strengthened due to deformation and have high wear resistance. However, when the manganese content is too low, a single austenite structure cannot be formed. Considering comprehensively, the Mn weight percentage is preferably 13 - 15%;

[0025] 4) Aluminum element is one of the important alloying elements in high manganese steel. It can significantly improve the mechanical properties, wear resistance, welding properties and hot working properties of high manganese steel, and expand the application range of high manganese steel. When the addition amount of aluminum in high manganese steel is too much, the fluidity of the molten steel decreases significantly, the nozzle brick is easily blocked, and it will also coarsen the grains of the steel, deteriorating the mechanical properties of high manganese steel and the wear resistance also decreases accordingly. Considering comprehensively, Als is 0.07 - 0.12%;

[0026] 5) Cr can form hard phases of chromium compounds. After appropriately increasing the carbon, manganese and chromium contents, the initial hardness after water toughening treatment is high, and the work hardening rate also increases significantly, making the high toughness austenite matrix distributed with dispersed carbide hard particles, thus improving the hardening effect and strengthening the wear resistance. Chromium can improve the corrosion resistance and hardness, extending its service life in harsh environments. However, chromium forms a continuous solid solution with iron, narrowing the austenite phase region, increasing the tendency of temper brittleness, easily forming dendritic segregation, reducing plasticity, and the Cr-containing carbides are difficult to dissolve, increasing the difficulty of water toughening treatment and reducing the effect. Considering comprehensively, Cr is 0.3 - 0.8%;

[0027] 6) P is prone to segregation, which reduces the welding performance, decreases the impact toughness, and may also cause defects such as cracking. S is prone to form plastic sulfides, which cause the steel plate to delaminate and are likely to result in opening defects during the rolling process, affecting production safety. Sulfur and manganese combine to form manganese sulfide and enter the slag. Therefore, the lower the contents of P and S, the better. Considering comprehensively, the P and S contents of the steel are P ≤ 0.020% and S ≤ 0.010%.

[0028] The design key points of the preparation method of the present invention are as follows:

[0029] 1) Based on the characteristic that the thermal conductivity of high manganese steel (about 12 - 15 W / (m·K)) is lower than that of traditional steel, the superheat of the continuous casting tundish is controlled within the range of 5 - 20 °C. If the temperature is too high, a large temperature gradient will be generated during the cooling of the casting, resulting in large thermal stress and prone to defects such as longitudinal cracks and segregation. Higher central segregation will greatly deteriorate the impact toughness. If the temperature is too low, the fluidity of the molten steel will be poor, and defects such as insufficient pouring and cold shut are likely to occur. These parts are also prone to crack during the subsequent cooling process.

[0030] 2) The sum of the reduction ratios of the first three passes of rough rolling R1 and R2 is greater than 60%. By rolling with a large reduction ratio, the dendritic segregation in the as-cast structure is effectively broken, element segregation (such as the segregation of Mn and C) is reduced, and the tissue uniformity is improved. The final rolling temperature RT2 of rough rolling is controlled at 1040 - 1070 °C. When RT2 is lower than 1040 °C, the reduction of area will decrease significantly. When it is above 1040 °C, the reduction of area is as high as more than 60%. Combining with the actual production, adopting this process can give full play to the good plasticity at high temperature, refine the grains, improve the strength and toughness, enhance the impact resistance, and reduce the cracking risk.

[0031] 3) During the rough rolling process, dynamic cooling control is increased. Through the head rapid cooling technology, the temperature difference between the head and the tail is further reduced, and the segregation risk is lowered. The head 3 - 4 m is rapidly cooled with a cooling rate of 10 - 20 °C / s to reduce the high-temperature residence time, avoid grain coarsening, and reduce the rolling opening risk caused by segregation, which affects production and equipment safety. The middle and tail parts are cooled by normal air cooling to avoid stress concentration and cracks caused by too fast cooling and improve the impact performance.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] Through precise optimization of chemical components, key elements such as Al and Cr were added in appropriate amounts, and a series of control measures such as casting with low superheat, hot rolling under high pressure, and online water toughening treatment were adopted. The content of inclusions in the steel was effectively reduced, the original austenite grains were significantly refined, the segregation degree was greatly reduced, and the cracking tendency was effectively suppressed. Thus, a high manganese wear-resistant steel with high original strength and excellent impact resistance was successfully prepared. Through practical verification, the segregation degree of this high manganese wear-resistant steel has been greatly improved, and the tissue uniformity in the thickness direction has been significantly enhanced. The precipitation amount and size of its network carbide have been greatly optimized, and the precipitation of micron-sized carbide has been completely avoided. At the microscopic level, its microstructure shows an austenite structure with an area fraction of 99% or more (including 100%), which significantly enhances its ability to withstand large impacts, has excellent fatigue resistance, and can fully meet the needs of downstream users in various harsh application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a microstructural diagram of the impact-resistant high manganese wear-resistant steel of Example 1.

[0035] Figure 2 It is a microstructural diagram of the high manganese steel of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0036] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with examples. However, the content of the present invention is not limited to the following examples.

[0037] Examples 1-10

[0038] The chemical components and weight percentage contents of the steel in Examples 1-10 and Comparative Examples 1-2 are shown in Table 1.

[0039] Table 1

[0040]

[0041] The preparation method of the steel in Examples 1-10 includes the following steps:

[0042] 1) Continuous casting: After the molten steel is smelted, continuous casting is carried out, and the superheat of the molten steel in the tundish is controlled at 5-20°C;

[0043] 2) Heating: The cast slab enters the heating furnace for heating. The furnace inlet temperature is greater than 550°C, and the total heating time in the heating furnace is 180-220 min, where the heating temperature in the high-temperature section is 1160-1210°C, and the heating time in the high-temperature section ≥90 min;

[0044] 3) Rough rolling: 1 (R1) + 7 (R2) passes of rolling are adopted. The sum of the reduction ratios in the first three passes of R1 and R2 is greater than 60%. The rough rolling finishing temperature is 1040 - 1070 °C. After rough rolling, the intermediate billet is covered with a heat preservation cover to reduce the temperature drop of the intermediate billet. During the whole process of rough rolling, rapid cooling is adopted within the range of 3 meters at the head, with a cooling rate of 10 - 20 °C / s, and normal air cooling is adopted for the rest of the parts.

[0045] 4) Finish rolling: The finish rolling starting temperature is 1030 - 1060 °C, and the finish rolling finishing temperature is 920 - 960 °C.

[0046] 5) Cooling and coiling: It is immediately cooled at a cooling rate of 100 - 180 °C / s to the coiling temperature of 20 - 50 °C for coiling, realizing online solution treatment to obtain a fine austenite structure.

[0047] For Comparative Examples 1 - 2 and Examples 1 - 10, the same technological process is adopted, but the specific parameter values are different. See the following table for details.

[0048] Table 2 Continuous casting and heating parameters

[0049]

[0050] Table 3 Rough rolling, finish rolling, cooling and coiling parameters

[0051]

[0052] According to the national standards of GB / T228 and GB / T231, the performances of Examples 1 - 10 and Comparative Examples 1 - 2 are tested as shown in Table 4.

[0053] Table 4 Performance test results

[0054]

[0055]

[0056] Figure 1 It is the microstructure diagram of the impact-resistant high manganese wear-resistant steel of Example 1. Its main microstructure is austenite, and its area ratio is ≥99.6%. The grain size is 20 - 30 μm. There are very few carbides precipitated at the grain boundaries, and the area ratio is ≤0.4%. The size of the precipitated phase is at the nanometer level, with a size ≤0.2 μm. The segregation quality is excellent. The Mn content in the normal part is at the same level as that in the central part, and there is almost no segregation. The microstructures of other examples also all meet the requirements that the austenite area ratio is ≥99% and the carbide area ratio is ≤1%. Figure 2 It is the microstructure diagram of the high manganese steel of Comparative Example 1. The microstructure is austenite structure and a large amount of carbide precipitation, and the segregation degree is serious. The carbides in the central part are significantly precipitated along the grain boundaries, resulting in a significant decline in the performance of the steel, especially the impact resistance.

[0057] The above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here, and thus the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An impact-resistant high manganese wear-resistant steel, characterized in that: Its chemical composition includes, by weight percentage, C: 0.95-1.25%, Si: 0.05-0.15%, Mn: 13-15%, P≤0.020%, S≤0.010%, Als: 0.07-0.12%, Cr: 0.3-0.8, and the balance is Fe and unavoidable impurities.

2. The impact-resistant high manganese wear-resistant steel according to claim 1, characterized in that: The chemical composition of the impact-resistant high manganese wear-resistant steel includes, by weight percentage, C: 1.0-1.15%, Si: 0.07-0.10%, Mn: 13.5-14.5%, P≤0.020%, S≤0.010%, Als: 0.08-0.10%, Cr: 0.35-0.65, and the balance is Fe and unavoidable impurities.

3. The impact-resistant high manganese wear-resistant steel according to claim 1, characterized in that: The main microstructure of the impact-resistant high-manganese wear-resistant steel is austenite, with an area ratio of ≥99% and a grain size of 20 to 30 μm.

4. The impact-resistant high manganese wear-resistant steel according to claim 1, characterized in that: A small amount of carbides are distributed inside the austenite grains or on the grain boundaries, with an area ratio of ≤1% in the microstructure and a size of ≤0.2 μm.

5. The impact-resistant high manganese wear-resistant steel according to claim 1, characterized in that: The impact-resistant high manganese wear-resistant steel has a yield strength of 350-650 MPa, a tensile strength of 900-1250 MPa, an elongation of 32-49%, an impact energy of 160-305 J at -40°C, and a Brinell hardness of 190-305 HBW. The wear resistance under large impact is better than that of traditional low-alloy wear-resistant steel.

6. A method for preparing the impact-resistant high manganese wear-resistant steel according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Continuous casting: Continuous casting after molten steel smelting, controlling the superheat of molten steel in the tundish to 5-20℃; 2) Heating: The ingot enters the heating furnace for heating. The furnace temperature is greater than 550°C. The total heating time in the heating furnace is 180-220 minutes, of which the heating temperature in the high temperature section is 1160-1210°C, and the heating time in the high temperature section is ≥90 minutes; 3) Rough rolling: 1+7 ​​passes are adopted, the sum of the reduction rates of the first three passes of rough rolling R1 and R2 is greater than 60%, and the final rolling temperature of rough rolling is 1040-1070°C; after the rough rolling, a heat preservation cover is used to reduce the cooling of the intermediate billet; 4) Finishing rolling: the starting temperature of finishing rolling is 1030-1060°C, and the final rolling temperature of finishing rolling is 920-960°C; 5) Cooling and coiling: Immediately cool to the coiling temperature for coiling to achieve online solid solution and obtain fine austenite structure.

7. The method for preparing impact-resistant high manganese wear-resistant steel according to claim 6, characterized in that: The furnace temperature of the casting billet is 580-790° C., and the heating time in the high temperature section is 90-110 minutes.

8. The method for preparing impact-resistant high manganese wear-resistant steel according to claim 6, characterized in that: The sum of the reduction ratios of the first three passes of the rough rolling R1 and R2 is 62-74%.

9. The method for preparing impact-resistant high manganese wear-resistant steel according to claim 6, characterized in that: During the entire rough rolling process, rapid cooling is adopted for the head 3 to 4 meters at a cooling rate of 10 to 20°C / s, and normal air cooling is adopted for the remaining parts.

10. The method for preparing impact-resistant high manganese wear-resistant steel according to claim 6, characterized in that: The cooling rate of step 5) is 100-180°C / s; the coiling temperature is 20-50°C.

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