Hot-rolled round steel for die gasket and preparation method of hot-rolled round steel

Abstract

The invention relates to the technical field of die steel, in particular to hot-rolled round steel for a die gasket and a preparation method of the hot-rolled round steel for the die gasket. 0.50 to 0.90 percent of Si; mn: 2.00 to 2.90%; p: less than or equal to 0.025%; s: less than or equal to 0.035%; 0.20% to 0.60% of Cr; 0.010% to 0.060% of Mo; 0.015% to 0.030% of Ti; b: 0.0008% to 0.0030% of the total weight of the 0.015% to 0.035% of Al; 0.004-0.008% of N, and the balance of iron and inevitable impurities. According to the die gasket hot-rolled round steel obtained through the preparation method, a rolled material does not need any heat treatment, the total cross-section structure of the rolled material is uniform, and metallographic structures of the near surface, the half radius and the center of the round steel are fine bainite structures; and the hardness distribution of the rolled material is uniform (29-35 HRC), the hardness dispersion difference is less than or equal to 2 HRC, and the requirements of the mold manufacturing industry on high quality and low cost of the material are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of die steel, in particular to a hot-rolled round steel for die gasket and a preparation method thereof. BACKGROUND

[0002] In the traditional production mode, there are mainly two kinds of die gasket steels. One kind needs to be quenched and tempered to obtain stable organization and hardness, but its production cycle is long and energy consumption is high, which does not meet the requirements of energy saving and cost reduction and efficiency improvement. The other kind is not quenched and tempered, but directly machined, but it mainly uses high alloy steel, which is high in cost, and the full section hardness deviation is large and the core hardness is low. The existing technology is difficult to produce green die gasket steel with high hardness uniformity and high purity, and cannot meet the high quality and low cost requirements of the die manufacturing industry on materials.

[0003] The existing technology about die steel is reported, such as patent CN100340691C discloses "a bainite large section plastic mold steel and its manufacturing method", the chemical composition is as follows (wt%): C 0.05~0.19%, Si 0.10~0.60%, Mn 1.0~1.65%, V 0.04~0.20%, Cr 1.0~1.70%, Mo 0.15~0.50%, <0.02% P, S <0.01%, Ni 0~0.50%, N <0.01%, Ti 0.005~0.025%, CaO ~0.0050%, Al 0.01~0.04%, the rest is Fe and inevitable impurities. After smelting, hot working, and then tempering at not higher than 600℃, the final hardness level reaches HRC28~33. The alloy composition design of the patent is high, it is a slab, and needs to be tempered, which is high in production cost.

[0004] Patent CN101230442A discloses "a low alloy non-quenched and tempered steel for plastic mold frame steel and its manufacturing method", which provides a low alloy non-quenched and tempered steel for plastic mold frame steel and its preparation method. The chemical composition of the low alloy non-quenched and tempered steel is as follows (wt%): C: 0.30-0.40, Si: 0.20-0.70, Mn: 1.00-1.50, P: ≤0.030, S: <0.025, Cr: 1.00-1.50, Mo: 0.10-0.30, Ni: 0.10-0.30, Ti: 0.010-0.030. The quenching and tempering process is omitted, the pre-hardened hardness is 24-29HRC, the alloy composition design is high, and annealing heat treatment is needed, which is high in production cost.

[0005] The die gasket steel needs to have high hardness uniformity, high purity, green low carbon, and has very high requirements for the design of raw materials, smelting process and rolling process. All domestic manufacturers are making efforts in this regard, and have been carrying out a lot of research and development work in the composition design, process optimization and other aspects of the die gasket steel, but the overall performance is not very satisfactory, and it is urgent to further research and develop high-quality, low-cost die gasket steel. SUMMARY

[0006] The present application aims at the above technical problems, overcomes the shortcomings of the prior art, and provides a hot-rolled round steel for die gasket and a preparation method thereof. The obtained die gasket hot-rolled round steel has a hardness that meets the requirements without any heat treatment. The Si and Mn contents are increased, the B content is added, the use of valuable alloys such as Cr, Ni, Mo and V is reduced, and the rolling material forms a uniform bainite structure. The rolling material can ensure the hardness and uniformity of the steel material without any heat treatment, has good product performance and cost advantage, and meets the demand of die gasket steel.

[0007] In a first aspect, the present application provides a hot-rolled round steel for die gasket, specifically comprising the following chemical components and mass percentages: C: 0.15-0.25%; Si: 0.50-0.90%; Mn: 2.00-2.90%; P: ≤0.025%; S: ≤0.035%; Cr: 0.20-0.60%; Mo: 0.010-0.060%; Ti: 0.015-0.030%; B: 0.0008-0.0030%; Al: 0.015-0.035%; N: 0.004-0.008%, and the rest is iron and unavoidable impurities.

[0008] Further, the hot-rolled round steel for die gasket comprises the following chemical components and mass percentages: C: 0.15-0.25%; Si: 0.50-0.80%; Mn: 2.00-2.80%; P: ≤0.020%; S: ≤0.030%; Cr: 0.20-0.50%; Mo: 0.010-0.060%; Ti: 0.015-0.030%; B: 0.0010-0.0030%; Al: 0.015-0.030%; N: 0.004-0.007%, and the rest is iron and unavoidable impurities.

[0009] Preferably, this invention achieves high-performance and low-cost hot-rolled round steel for mold gaskets by appropriately adding boron (B), increasing Si and Mn, appropriately reducing Cr and Mo, and omitting V, Ni, and other metallic elements, thus integrating the subtle relationships and effects between the elements. It should be noted that Cr (chromium) significantly improves hardenability stability, strengthens ferrite through solid solution strengthening, and enhances corrosion resistance and oxidation resistance. Mo (molybdenum) atoms can dissolve in ferrite (iron matrix). Due to its different atomic size compared to iron, it causes lattice distortion, thereby hindering dislocation movement. This effectively improves the strength of the steel, i.e., "solid solution strengthening." Molybdenum also effectively improves the hardenability stability of steel, but its cost is relatively high. Si (Si) strengthens ferrite through solid solution strengthening, significantly improving the strength and hardness of steel, and enhancing its oxidation resistance at high temperatures; therefore, the Si content is appropriately increased. Mn (manganese) dissolves in ferrite, increasing strength and hardness. Significantly increasing the hardenability of steel (second only to molybdenum), enabling even larger cross-section parts to be hardened, and creating conditions for bainite formation, thus increasing the Mn content to partially replace the role of Mo. With the addition of Cr and Mo, hardenability stability is greatly improved. Furthermore, the addition of trace amounts of N, Ti, and Al, along with residual free N, forms fine, dispersed TiN and AlN strong nitrides pinned to the grain boundaries, hindering dislocations and significantly improving the strength, hardness, and wear resistance of round steel. Then, the addition of trace amounts of B effectively avoids the formation of harmful boron nitride compounds, fully utilizing the role of B segregation at grain boundaries. The very small size of B atoms and their strong segregation at grain boundaries reduce atomic mobility in high-energy regions of the grain boundaries, thereby hindering the diffusion of C and Fe required for ferrite growth, greatly reducing the nucleation rate of ferrite at grain boundaries, and delaying phase transformation, thus significantly reducing the critical cooling rate, expanding the cooling range, and greatly improving hardenability, fully replacing the hardenability effects of noble metals such as Cr, Mo, V, and Ni.

[0010] In a second aspect, the present invention also provides a method for preparing hot-rolled round steel for mold gaskets as described in any of the embodiments in the first aspect. The specific process includes electric furnace smelting, LF refining, continuous casting, rolling and post-rolling cooling. Specifically, the LF refining adopts LF ladle furnace desulfurization treatment, aluminum deoxidation, alloy material and aluminum wire are fed for alloying, vacuum degassing circulation is adopted, vacuum degree ≤1 mbar, argon gas blowing and stirring are used to remove harmful inclusions in the steel.

[0011] Furthermore, the electric furnace smelting specifically involves charging alloy materials and auxiliary materials into an electric furnace for melting, blowing oxygen to decarburize, sampling and analyzing the content of alloy elements, and adjusting the target values.

[0012] Furthermore, in the rolling process, the billet heating temperature is 1000℃~1220℃, the holding time is 3.5h~6.5h, and the billet is rolled after exiting the furnace, with an initial rolling temperature of 1050℃~1100℃ and a final rolling temperature of 880℃~950℃.

[0013] Furthermore, the post-rolling cooling specifically includes uniform cooling on an upper cooling bed after rolling, followed by slow cooling in a pit after the lower cooling bed.

[0014] The beneficial effects of this invention are: (1) The hot-rolled round steel for mold gaskets prepared by the method of the present invention does not require any heat treatment and the hardness can meet the requirements; the microstructure of the whole cross section of the rolled material is uniform, and the microstructure near the surface, half radius and the core of the round steel are all fine bainite microstructure; the hardness distribution of the rolled material is uniform (29-35HRC) and the hardness difference is ≤2HRC, which meets the high quality and low cost requirements of the mold manufacturing industry. (2) The present invention adds B content and appropriately increases Si and Mn content, greatly reducing the use of precious alloys such as Mo, Ni, Cr and V, and ensuring that the rolled material forms a uniform bainitic structure. It has good product performance and cost advantages, can effectively reduce costs, and meet the needs of steel for mold gaskets such as automotive battery housings. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the hardness and metallographic detection locations of the hot-rolled round steel for the mold gasket in a specific embodiment of the present invention (circles represent hardness, and triangles represent metallographic features). Figure 2 This is a near-surface metallographic image of the hot-rolled round steel for the mold gasket in a specific embodiment of the present invention; Figure 3 This is a metallographic diagram of the hot-rolled round steel at half the radius of the mold gasket in a specific embodiment of the present invention; Figure 4 This is a metallographic diagram of the core of the hot-rolled round steel die pad in a specific embodiment of the present invention. Detailed Implementation

[0016] The method for preparing hot-rolled round steel for mold spacers provided by the present invention comprises the following steps: (1) Electric furnace smelting, LF refining, and continuous casting: alloy materials and auxiliary materials are charged into the electric furnace and melted. Oxygen is blown to decarburize. The alloy element content is sampled and analyzed and the target value is adjusted. LF ladle furnace desulfurization treatment is adopted. After adding aluminum shot for deoxidation, alloy materials and aluminum wire are fed for alloying. Vacuum degassing circulation is adopted with a vacuum degree of 0.86 mbar. Argon gas is blown to stir. After removing harmful inclusions in the steel, it is continuously cast into square billets. The chemical composition of Examples 1-3 and Comparative Examples 1-3 is shown in Table 1. (2) Rolling: The billet is heated to 1080℃~1200℃ and held for 4.5h. After the billet is taken out of the furnace, it is rolled. The initial rolling temperature is 1050℃~1080℃ and the final rolling temperature is 900℃~930℃. (3) Cooling after rolling: After rolling, the upper cooling bed is used for uniform cooling, and after the lower cooling bed, the roll is placed in the pit for slow cooling; (4) The rolled material can meet the delivery requirements without heat treatment.

[0017] The hardness and metallographic testing locations in Examples 1-3 are as follows: Figure 1 As shown. The metallographic structures near the surface, at half the radius, and in the core of Examples 1-3 are as follows. Figures 2-4 As shown in Table 2, the hardness distributions of Examples 1-3 and Comparative Examples 1-2 are shown in Table 2.

[0018] Table 1 Chemical composition of Examples 1-3 and Comparative Examples 1-2

[0019] Table 2. Hardness distribution / HRC of Examples 1-3 and Comparative Examples 1-2 As shown in Tables 1 and 2, the amount of Mo, Ni, and Cr precious alloys used in Examples 1-3 of the present invention is greatly reduced compared with Comparative Examples 1-2, which effectively reduces the cost of use; the hardness distribution of the rolled materials in Comparative Examples 1-3 is uniform (29-35HRC), and the hardness dispersion is ≤2HRC, which is much smaller than that in Comparative Examples 1-2.

[0020] The hot-rolled round steel for mold gaskets obtained by this invention requires no heat treatment to achieve the required hardness. The rolled material exhibits uniform microstructure across its entire cross-section, with fine bainitic microstructure near the surface, at half the radius, and in the core. The hardness distribution is uniform (29-35 HRC), with a hardness variation ≤2 HRC. By increasing the boron (B) content and appropriately raising the Si and Mn content, the use of precious alloys such as Mo, Ni, and Cr is significantly reduced, effectively lowering costs. This results in excellent product performance and cost advantages, meeting the needs of mold gaskets for automotive battery casings and other applications. Calculations show that each ton of steel from this invention is 800 yuan more profitable than other ordinary steels.

[0021] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A hot-rolled round steel bar for mold gaskets, characterized in that, It includes the following chemical components and mass percentages: C: 0.15~0.25%; Si: 0.50~0.90%; Mn: 2.00~2.90%; P: ≤0.025%; S: ≤0.035%; Cr: 0.20~0.60%; Mo: 0.010~0.060%; Ti: 0.015~0.030%; B: 0.0008~0.0030%; Al: 0.015~0.035%; N: 0.004~0.008%, with the remainder being iron and unavoidable impurities.

2. The hot-rolled round steel for mold gaskets according to claim 1, characterized in that, Includes the following chemical components and their mass percentages: C: 0.15~0.25%; Si: 0.50~0.80%; Mn: 2.00~2.80%; P: ≤0.020%; S: ≤0.030%; Cr: 0.20~0.50%; Mo: 0.010~0.060%; Ti: 0.015~0.030%; B: 0.0010~0.0030%; Al: 0.015~0.030%; N: 0.004~0.007%, with the remainder being iron and unavoidable impurities.

3. The method for preparing hot-rolled round steel for mold gaskets as described in claim 1 or 2, characterized in that, The process includes electric furnace smelting, LF refining, continuous casting, rolling, and post-rolling cooling. LF refining specifically involves LF ladle furnace desulfurization treatment, followed by aluminum deoxidation, then alloying with alloy materials and aluminum wire. Vacuum degassing circulation with a vacuum degree ≤1 mbar is used, along with argon blowing and stirring to remove harmful inclusions from the steel.

4. The method for preparing hot-rolled round steel for mold gaskets according to claim 3, characterized in that, The electric furnace smelting process specifically involves loading alloy materials and auxiliary materials into an electric furnace for melting, blowing oxygen to decarburize, sampling and analyzing the content of alloy elements, and adjusting the target values.

5. The method for preparing hot-rolled round steel for mold gaskets according to claim 3, characterized in that, In the rolling process, the billet is heated to 1000℃~1220℃ and held for 3.5h~6.5h. After the billet is taken out of the furnace, it is rolled with an initial rolling temperature of 1050℃~1100℃ and a final rolling temperature of 880℃~950℃.

6. The method for preparing hot-rolled round steel for mold gaskets according to claim 3, characterized in that, The post-rolling cooling specifically includes uniform cooling on an upper cooling bed after rolling, followed by slow cooling in a pit after the lower cooling bed.

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