High-hardness bainite cast steel and manufacturing method thereof

Abstract

The invention relates to the technical field of high-hardness cast steel, in particular to high-hardness bainite cast steel and a manufacturing method thereof. The alloy comprises the following chemical components in percentage by weight: 0.3%-0.6% of C, 1.5%-2.5% of Mn, 1.0%-2.0% of Si, 0.8%-1.5% of Cr, 0.03%-0.06% of Ti, 0.4%-1.0% of Cu, 0.002%-0.004% of B, Plt and the balance of Fe and inevitable impurities. 0.04%, Slt; 0.04%, and the balance being Fe and inevitable impurities. The manufacturing method specifically comprises the following steps: 1) smelting; (2) the pouring temperature is 1570 DEG C to 1610 DEG C; 3) unpacking and demolding at 480-520 DEG C; 4) charging at room temperature, heating to 860-900 DEG C, and keeping the temperature for more than 120 minutes; 5) air cooling to room temperature; and (6) tempering at 440-460 DEG C for 35-45 minutes, and cooling to room temperature along with the furnace. The bainite cast steel is low in cost, low in alloy content, easy to manufacture and excellent in performance, the hardness HRC is larger than or equal to 52, and the ballistic work at the temperature of minus 40 DEG C is not smaller than 30 J.

Description

Technical Field

[0001] The present invention relates to the technical field of high-hardness cast steel, and specifically to a high-hardness bainitic cast steel and a manufacturing method thereof. Background Art

[0002] With the rapid development of basic industries such as metallurgy, mining, electric power, building materials, coal, and petroleum, higher requirements have been put forward for the production and supply of wear-resistant materials. Developing new wear-resistant materials and their manufacturing processes to meet the needs of China's basic industries has always been a new topic that material researchers have been constantly concerned about. Currently, the widely used wear-resistant materials mainly include three categories: high manganese steel, white cast iron, and low alloy steel. High manganese steel is a traditional wear-resistant material. In China, during the 1950s and 1960s, high manganese steel was almost regarded as a universal wear-resistant material. In practical use, it was found that high manganese steel is wear-resistant only under the conditions of large impact, high stress, and hard abrasive. Moreover, its yield strength is low and it is easy to deform. Therefore, in many fields, it has gradually been replaced by other wear-resistant materials. The white cast iron structure contains more than 20% of high-hardness eutectic carbides and has excellent wear resistance; however, it has the disadvantages of a large amount of alloying elements, high production cost, and easy deformation and cracking during high-temperature heat treatment. Ordinary white cast iron and low alloy white cast iron also have the disadvantages of continuous carbide distribution, high brittleness, and easy spalling or even fracture during use. Low alloy steel is a promising type of wear-resistant material with good comprehensive properties, that is, good wear resistance and good strength and toughness matching. Foreign low alloy wear-resistant steels are mainly of the Cr, Mo series and contain a small amount of other alloying elements such as Ni, which have good wear resistance. However, the cost is relatively high and the casting difficulty is increased.

[0003] If the composition of traditional low alloy wear-resistant cast steel (including bainitic cast steel) is optimized to reduce the cost on the premise of ensuring performance, it will undoubtedly make bainitic wear-resistant cast steel have broad application prospects and objective economic and social benefits.

[0004] The Chinese patent document with the publication number CN103498092A discloses "a preparation method of wear-resistant cast steel", which adopts a high-carbon, high-alloy composition design, with extremely high cost and greatly increasing the difficulty of smelting, casting, and heat treatment. The Chinese patent document with the publication number CN103114247A discloses "a high-hardness and high-toughness wear-resistant steel", which belongs to high manganese steel. In addition to being difficult to produce, its wear resistance can only be exerted under high-impact conditions. The Chinese patent document with the publication number CN1557984A discloses "high-hardness and high-toughness wear-resistant steel", with a large addition of precious metals and still relatively high cost. Summary of the Invention

[0005] To overcome the deficiencies of the prior art, the present invention provides a high-hardness bainitic cast steel and its manufacturing method, which is a bainitic cast steel with low cost, low alloy content, easy to manufacture and excellent performance, with a hardness of HRC≥52 and an impact energy at -40°C of not less than 30J.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions:

[0007] A high-hardness bainitic cast steel is composed of chemical components with the following weight percentages:

[0008] C: 0.3% - 0.6%, Mn: 1.5% - 2.5%, Si: 1.0% - 2.0%, Cr: 0.8% - 1.5%, Ti: 0.03% - 0.06%, Cu: 0.4% - 1.0%, B: 0.002% - 0.004%, P < 0.04%, S < 0.04%, and the balance is Fe and unavoidable impurities.

[0009] In the above composition design of the high-hardness bainitic cast steel:

[0010] C: Carbon is one of the most important alloying elements in steel. Its main functions are to form solid solution structures and improve the strength of steel. For example, ferrite and austenite structures dissolve carbon elements; forming carbide structures can improve the hardness and wear resistance of steel. Therefore, in steel, the higher the carbon content, the higher the strength and hardness of the steel, but the plasticity and toughness will also decrease accordingly; conversely, the lower the carbon content, the higher the plasticity and toughness of the steel, and its strength and hardness will also decrease accordingly. To ensure that the wear-resistant steel has a high hardness, a certain carbon content must be ensured. If the carbon content is too high, the impact toughness will decrease sharply, reducing the wear-resistant performance; therefore, it is selected between 0.3% and 0.6%.

[0011] Mn: It lowers Ar3, expands the austenite phase region, and improves the hardenability of steel. Manganese has a significant strengthening effect on carbon steel; when the Mn content is too high, overheating is likely to occur. Manganese has the effect of promoting grain growth and will significantly reduce the corrosion resistance of steel, so it is selected between 1.5% and 2.5%.

[0012] Cr: It improves the bainite hardenability, strength and corrosion resistance, and inhibits the graphitization tendency of carbon. However, if the chromium content is too high, carbides are likely to precipitate, affecting the performance of the steel, so the content is controlled at 0.8% - 1.5%.

[0013] Si: It is a good solid solution strengthening element. While increasing the strength of steel, it also improves the cold working hardening performance of steel and inhibits the formation of carbides. Silicon can also improve the corrosion resistance of steel, but too high a content leads to an increase in brittleness. Therefore, 1.0 - 2.0% is selected.

[0014] Cu: Copper is an element that expands the austenite phase region, improves the hardenability of bainite, increases the fatigue strength of steel while enhancing its strength, and is beneficial for improving the wear resistance of steel. Moreover, copper can significantly improve the corrosion resistance of steel. However, if the copper content is too high, hot brittleness is likely to occur, so the content is controlled within 0.4% - 1.0%.

[0015] B: Trace amounts of B can strongly inhibit the nucleation of proeutectoid ferrite and is the most effective element for improving hardenability. Excessive amounts form compounds and increase brittleness. Therefore, B is controlled between 0.002% - 0.004%.

[0016] Ti: Titanium can refine the grain size, fix oxygen and nitrogen in steel, and has the ability of precipitation strengthening. However, excessive amounts form coarse liquid segregation TiN, deteriorating the properties of steel. Therefore, Ti is controlled between 0.03% - 0.06%.

[0017] P and S are harmful impurities, and the upper limit is set at 0.04%.

[0018] The manufacturing method of the above high-hardness bainitic cast steel specifically includes the following steps:

[0019] 1) Smelting.

[0020] 2) Pouring temperature: 1570 - 1610 °C.

[0021] 3) Unboxing and demoulding at 480 - 520 °C.

[0022] 4) Loading into the furnace at room temperature, heating to 860 - 900 °C, and holding for more than 120 minutes.

[0023] 5) Air cooling to room temperature.

[0024] 6) Tempering at 440 - 460 °C for 35 - 45 minutes and cooling to room temperature with the furnace.

[0025] Furthermore, in step 1), vacuum electric furnace smelting is used for smelting.

[0026] Furthermore, in step 2), the pouring temperature is 1590 - 1610 °C.

[0027] Furthermore, in step 3), unboxing and demoulding are carried out at 500 - 520 °C.

[0028] Furthermore, in step 4), heating is carried out to 880 - 900 °C and holding for 120 minutes.

[0029] Furthermore, in step 6), tempering is carried out at 450 - 460 °C for 40 minutes.

[0030] The high-hardness bainitic cast steel manufactured by the above manufacturing method has a hardness of HRC ≥ 52 and an impact energy at -40 °C of not less than 30 J.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. Based on the C-Mn-Si-Cr steel composition, a certain amount of Cu and trace amounts of B and Ti are added to the present invention. By using the ordinary casting process and the heat treatment process of traditional quenching + low-temperature tempering, bainitic cast steel with excellent properties such as a hardness of HRC≥52 and an impact energy of ≥30 J (V-notch, -40 °C) can be obtained. The composite addition of Cu-Cr-Si-B improves the hardenability of the steel, enabling wear-resistant castings to obtain bainite structure (carbide-free bainite) at a lower cooling rate (such as air cooling), ensuring that the steel has high toughness while having high strength, and endowing the cast steel with high wear resistance. It breaks through the traditional water toughening treatment of wear-resistant steel and the quenching process of bainite-martensite type wear-resistant steel, avoiding the generation of microcracks due to high stress during the rapid cooling process of castings and reducing wear resistance. Through tempering at 450 °C, the structure of the steel can be stabilized and stress can be eliminated, enabling copper elements to precipitate in the form of fine particles, improving the strength of the steel without significantly reducing its toughness. The copper precipitation phase can also improve the shock absorption performance of the steel and reduce the working noise of wear-resistant materials.

[0033] 2. The present invention has low cost and good wear resistance without adding precious metals such as Ni and Mo. The composite addition of Cu-Cr-Si-B inhibits the formation of cementite due to Cu and Si. Therefore, the microstructure of the steel is carbide-free bainite (bainitic ferrite + austenite). For the same reason, cementite is not formed during the tempering process, and C is enriched in the austenite, stabilizing the austenite. Only under a large impact and a certain amount of plastic deformation, through the TRIP effect, the strength and toughness of the steel, that is, wear resistance, are improved. Adding a trace amount of Ti can refine the grains and improve the strength and toughness of the steel. Therefore, the wear resistance of the steel of the present invention can be ensured without adding expensive metal elements such as Mo and Ni.

[0034] 3. The heat treatment process of the present invention is simple, and compared with the water toughening treatment of high manganese steel (1050 °C), the energy-saving effect is remarkable. Due to the composition design ensuring that the steel has extremely high hardenability and no large-sized insoluble carbides, the austenitizing temperature is relatively low. With Cu, the thermal conductivity of the steel can be improved, so the soaking time is relatively short, and energy can be significantly saved.

[0035] In summary, the present invention has low cost, low alloy content, is easy to manufacture and has excellent properties, with a hardness of HRC≥52 and an impact energy at -40 °C of not less than 30 J. Brief Description of the Drawings

[0036] Figure 1 is the bainite metallographic structure diagram of the present invention. Detailed Embodiments

[0037] The present invention discloses a high-hardness bainitic cast steel and a manufacturing method thereof. Those skilled in the art can draw on the content of this article and appropriately improve the process parameters to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The method and application of the present invention have been described through preferred embodiments, and those related can obviously make changes or appropriate modifications and combinations to the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0038] A high-hardness bainitic cast steel is composed of chemical components with the following weight percentages:

[0039] C: 0.3% - 0.6%, Mn: 1.5% - 2.5%, Si: 1.0% - 2.0%, Cr: 0.8% - 1.5%, Ti: 0.03% - 0.06%, Cu: 0.4% - 1.0%, B: 0.002% - 0.004%, P < 0.04%, S < 0.04%, and the balance is Fe and inevitable impurities.

[0040] The manufacturing method of the above high-hardness bainitic cast steel specifically includes the following steps:

[0041] 1) Vacuum electric furnace smelting.

[0042] 2) Pouring temperature: 1570 - 1610 °C.

[0043] 3) Unboxing and demolding at 480 - 520 °C.

[0044] 4) Loading into the furnace at room temperature, heating to 860 - 900 °C, and holding for more than 120 minutes.

[0045] 5) Air cooling to room temperature.

[0046] 6) Tempering at 440 - 460 °C for 35 - 45 minutes and cooling to room temperature with the furnace.

[0047] The high-hardness bainitic cast steel manufactured according to the above manufacturing method has high hardness and high toughness, with a Rockwell hardness HRC ≥ 52 and an impact energy at -40 °C of not less than 30 J.

[0048]

Example

[0049] The invention example is as follows: Smelt qualified molten steel with a vacuum electric furnace (one ton), and start casting when the molten steel temperature drops to 1590 ± 20 °C. Unbox and demold when the temperature drops to 500 ± 20 °C. Clean the surface of the casting when it drops to room temperature, and visually inspect the quality of the casting. Load it into the heating furnace, heat to 880 ± 20 °C, and hold for 120 ± 10 minutes. Air cool to room temperature. Put it into the furnace, temper at 450 ± 10 °C for 40 ± 5 minutes, and cool to room temperature with the furnace.

[0050] The specific steel grades of the five embodiments of the present invention are shown in Table 1, the heat treatment process parameters of the cast steel are shown in Table 2, and the performance indexes of the cast steel are shown in Table 3.

[0051] Table 1 Chemical composition (wt, %) of the embodiments of the present invention

[0052] Example C Mn Si Cr Cu B Ti P S Example 1 0.30 2.45 1.85 1.40 0.80 0.0027 0.04 0.03 0.02 Example 2 0.41 2.02 1.67 1.28 0.69 0.0037 0.03 0.02 0.03 Example 3 0.51 1.70 1.52 1.08 0.40 0.0030 0.03 0.03 0.03 Example 4 0.55 1.66 1.26 0.93 0.53 0.0031 0.03 0.03 0.02 Example 5 0.60 1.52 1.05 0.81 1.00 0.0035 0.03 0.02 0.02

[0053] Table 2 Heat treatment process parameters of the embodiments of the present invention

[0054] Example Casting temperature °C Demoulding temperature °C Heating temperature °C Insulation time mins Tempering temperature °C Insulation time mins Example 1 1580 490 870 115 455 36 Example 2 1610 490 860 125 440 38 Example 3 1570 520 865 130 445 35 Example 4 1590 480 900 110 450 45 Example 5 1605 495 875 120 460 40

[0055] Table 3 Mechanical property parameters of the embodiments of the present invention

[0056] Example HRC Impact energy ak (J) Casting crack Example 1 53 45 None Example 2 52 48 None Example 3 53 38 None Example 4 54 40 None Example 5 55 30 None

[0057] As Figure 1 shown, the present invention is carbide-free bainite, a high-strength and high-toughness steel structure. As shown in Table 3, the present invention is a bainite cast steel with a hardness of HRC≥52, an impact energy of ≥30 J (V-notch, -40 °C), and excellent non-forging crack performance.

[0058] The present invention has low cost, has good wear resistance without adding precious metals such as Ni and Mo. Due to the addition of a relatively high amount of Cu in the present invention, the fluidity of the molten steel is good and it is easy to cast. Moreover, Cu increases the strength of the steel during tempering, ensuring the performance of the steel after heat treatment. The heat treatment process of the present invention is simple, and compared with the water toughening treatment (1050 °C) of high manganese steel, the energy-saving effect is remarkable. The present invention has a high hardness (HRC≥52) and high toughness (impact energy greater than 30 J at -40 °C).

[0059] The above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A high-hardness bainitic cast steel, characterized in that, Composed of chemical components with the following weight percentages as follows: C: 0.3% - 0.6%, Mn: 1.5% - 2.5%, Si: 1.0% - 2.0%, Cr: 0.8% - 1.5%, Ti: 0.03% - 0.06%, Cu: 0.4% - 1.0%, B: 0.002% - 0.004%, P < 0.04%, S < 0.04%, and the balance is Fe and unavoidable impurities.

2. A high-hardness bainitic cast steel according to claim 1, characterized in that the hardness of the high-hardness bainitic cast steel HRC ≥ 52.

3. A high-hardness bainitic cast steel according to claim 1, characterized in that the impact energy of the high-hardness bainitic cast steel at -40°C is not less than 30 J.

4. A manufacturing method of a high-hardness bainitic cast steel as described in any one of claims 1-3, characterized in that, The manufacturing method specifically includes the following steps: 1) Smelting; 2) Pouring temperature 1570 - 1610°C; 3) Unboxing and demolding at 480 - 520°C; 4) Loading into the furnace at room temperature, heating to 860 - 900°C, and holding for more than 120 minutes; 5) Air cooling to room temperature; 6) Tempering at 440 - 460°C for 35 - 45 minutes and cooling to room temperature with the furnace.

5. A manufacturing method of a high-hardness bainitic cast steel according to claim 4, characterized in that in step 1), vacuum electric furnace smelting is adopted for smelting.

6. A manufacturing method of a high-hardness bainitic cast steel according to claim 4, characterized in that in step 2), the pouring temperature is 1590 - 1610°C.

7. A manufacturing method of a high-hardness bainitic cast steel according to claim 4, characterized in that in step 3), unboxing and demolding at 500 - 520°C.

8. A manufacturing method of a high-hardness bainitic cast steel according to claim 4, characterized in that in step 4), heating to 880 - 900°C and holding for 120 minutes.

9. A manufacturing method of a high-hardness bainitic cast steel according to claim 4, characterized in that in step 6), tempering at 450 - 460°C for 40 minutes.

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