Novel high-hardenability mining chain steel and preparation method thereof

Abstract

The invention relates to novel high-hardenability mine chain steel. The novel high-hardenability mine chain steel comprises the following chemical components in percentage by mass: 0.22 to 0.26 percent of C, 0.22 to 0.30 percent of Si, 1.52 to 1.60 percent of Mn, less than or equal to 0.011 percent of P, 0.008 to 0.025 percent of S, 0.47 to 0.53 percent of Ni, 1.21 to 1.31 percent of Cr, 0.40 to 0.48 percent of Mo and the balance of Fe and inevitable impurity elements. The whole technological process comprises the steps of burdening, KR molten iron pretreatment, converter or electric furnace smelting, LF refining (sulfide denaturation treatment), degassing, continuous casting, warm conveying to a heating furnace, heating, high-pressure water descaling, PSM rolling, slow cooling, annealing treatment and straightening. The diameter of the prepared chain steel ranges from 18 mm to 130 mm, the material Di value is controlled within the range of 250 mm to 280 mm, the martensite content of a core area after overall quenching reaches 90% or above, the core-surface hardness difference after quenching is controlled within 3 HRC, and the chain steel achieves high dimensional precision, high hardenability and high abrasion resistance at the same time; and various performance indexes of the chain are fully guaranteed, meanwhile, the smelting cost is low, and the market competitiveness of the product is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of special steel smelting, and specifically relates to a novel high-hardenability mining chain steel and a preparation method thereof. Background Art

[0002] Mining chains refer to chains used to transport minerals, personnel and equipment in coal mines, metal mines and other mines. Mining chains are usually made of high-strength alloy steel, which has the characteristics of high strength, high toughness and high wear resistance, and can withstand large loads and impact forces. Therefore, the requirements for mining chain steel are also extremely stringent. High strength and toughness require a reasonable component system and a reasonable heat treatment process, and high wear resistance is closely related to the composition of mining chain steel.

[0003] The production process of mining chain steel includes steelmaking, steel rolling, heat treatment and other links. In the steelmaking process, it is necessary to control the chemical composition and purity of the steel to ensure the quality of the steel. In the steel rolling process, it is necessary to use advanced steel rolling equipment and processes to ensure the dimensional accuracy and surface quality of the steel. In the heat treatment process, it is necessary to use appropriate heat treatment processes according to the chemical composition and use requirements of the steel to improve the strength and toughness of the steel. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a new type of high hardenability mining chain steel and a preparation method thereof in response to the above-mentioned prior art. Based on the existing mature mining chain steel, a new type of high hardenability mining chain steel is provided through reasonable component design. The diameter of the steel is in the range of 18 to 130 mm, and the steel has excellent flash weldability, so that the chain links manufactured downstream can fully meet the mining requirements.

[0005] The technical solution adopted by the present invention to solve the above problems is: a new type of high hardenability mining chain steel, the chemical composition of the chain steel is C: 0.22-0.26%, Si: 0.22-0.30%, Mn: 1.52-1.60%, P: ≤0.011%, S: 0.008-0.025%, Ni: 0.47-0.53%, Cr: 1.21-1.31%, Mo: 0.40-0.48%, and the balance is Fe and unavoidable impurity elements.

[0006] The chemical composition of the novel high hardenability mining chain steel of the present invention is determined as follows:

[0007] C: It is an essential element to ensure the strength and hardness of steel, but its plasticity and toughness are poorer and it is not conducive to the welding performance of steel. Considering the strength and toughness of the chain, welding performance, etc., the present invention controls the carbon content to 0.22-0.26%.

[0008] Si: Adding silicon as a reducing agent and deoxidizer during the steelmaking process is beneficial to the deoxidation of molten steel, thereby improving the purity of the material; silicon dissolves in ferrite in steel to increase the strength and hardness of the steel. Too high Si will increase the brittleness of the steel and reduce the weldability of flash welding and the performance of the weld. Taking all factors into consideration, the silicon content in the present invention is controlled to be 0.22-0.30%.

[0009] Mn: It is an element that improves the hardenability of steel, so that when the material is made into a chain and quenched, it can be fully hardened, and the martensite content in the core is greatly increased. After tempering, the chain has excellent comprehensive mechanical properties, and the increase in Mn content can greatly improve the wear resistance of the material. However, the increase in Mn content will lead to an increase in the carbon equivalent of the material, thereby affecting the welding performance. Therefore, the Mn content of the present invention is controlled to be 1.52-1.60%.

[0010] Ni: Ni is a non-carbide forming element. Ni exists in steel in the form of solid solution, which can significantly improve the hardenability of steel. Nickel can improve the strength of steel while maintaining good plasticity and toughness. Nickel has a high corrosion resistance to acids and alkalis, but Ni is a precious metal. Adding too much will increase the production cost of the material and reduce the market competitiveness of the product. The present invention controls its content to 0.47-0.53%.

[0011] Cr: It is a medium carbide-forming element. When heated, Cr dissolved in austenite strongly improves hardenability. Part of Cr in steel replaces iron to form alloy cementite, improving stability; part of Cr is dissolved in ferrite, playing a role of solid solution strengthening, improving the strength and hardness of ferrite. The present invention controls its content to 1.21-1.31%.

[0012] Mo: It exists in the solid solution and carbide of steel, has a solid solution strengthening effect, can improve the hardenability and tempering stability of steel, and can also refine the grains and improve the inhomogeneity of carbides, thereby improving the strength and toughness of steel. Mo is also a precious metal. Too high a content will increase the cost and reduce the market competitiveness of the product. In the present invention, the content of Mo is controlled at 0.40-0.48%.

[0013] P: is a harmful impurity element in steel, which is easy to form defects such as segregation and inclusion. As an impurity element, it will have an adverse effect on the toughness of steel (especially the toughness of the core) and the toughness of the flash welding heat affected zone, and its content should be reduced as much as possible. In the present invention, P is controlled to be ≤0.011%.

[0014] S: Traditionally, S is a harmful impurity in steel. Steel with a high sulfur content is prone to brittle cracking when subjected to pressure processing at high temperatures, which is usually called hot brittleness. However, the present invention adds enough Mn, and manganese can form high-melting-point MnS with sulfur, eliminating the harmful effects of sulfur. However, the increase in sulfur content reduces the high-temperature resilience of the material. During the welding process, the material has a small resilience during the final upset forging, and the two ends of the weld are more tightly combined, which is conducive to the stability of the weld quality. The present invention controls the S content to be 0.008-0.025%.

[0015] The technical solution of the present invention to solve another technical problem is a method for manufacturing the above-mentioned new type of high hardenability mining chain steel, the entire process flow is: batching → KR molten iron pretreatment → converter or electric furnace smelting → LF refining (sulfide modification treatment) → degassing → continuous casting → warm delivery to heating furnace → heating → high-pressure water descaling → PSM rolling → slow cooling → annealing → straightening.

[0016] The above process includes the following specific steps:

[0017] The smelting raw materials are sequentially subjected to KR hot metal pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent the refining temperature from returning to P, a slag-stripping process is adopted after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag-stripping process is adopted again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is adopted. During the refining process, calcium elements are added to the molten steel by feeding Ca-Si wire into the molten steel to modify the sulfides in the steel. During the solidification process of the molten steel, the high-melting-point CaS particles formed in advance can inhibit the total amount and aggregation degree of MnS generated by the molten steel in this process, and modify part or all of the MnS into CaS, that is, forming a fine, single CaS phase or a composite phase with MnS. This reduces the amount of manganese sulfide inclusions generated, and compounds fine, non-deformable CaS or calcium aluminate particles in the matrix of residual manganese sulfide inclusions, so that the originally easy-to-form strip-shaped inclusions with a large aspect ratio are transformed into inclusions with a small aspect ratio and relatively dispersed distribution, making the sulfides fine and evenly distributed in the molten steel, which is more conducive to reducing the resilience of the material when welding the top to ensure the stability of the weld quality; after the molten steel is continuously cast, in order to improve production efficiency, the ingot can be warm-sent to the heating furnace, and the warm-sent temperature is 300-450℃; the preheating section temperature of the steel rolling is 650-800℃, the heating section temperature is 900-1050℃, the soaking section temperature is 1200-1270℃, and the furnace is kept warm for 6-8 hours; after high-pressure water descaling, rolling is carried out, the rough rolling temperature is ≥1020℃, and the final rolling temperature is ≥90 0℃, using PSM three-roller finishing mill. Compared with the traditional two-roller rolling mill, PSM rolling mill is equipped with three rolling rolls. The continuous casting billet is subjected to pressure in three directions and is in a three-way compressive stress state. This stress state is conducive to the deformation of the rolled piece and can make the metal more easily plastically deformed. The three rollers are distributed at a certain angle, which has a stronger clamping and restraining effect on the rolled piece during the rolling process, and can make the deformation of the rolled piece more uniform, thereby improving the dimensional accuracy of the product, strictly controlling the dimensional tolerance of the material, and the final product dimensional tolerance is controlled within the range of ±0.20mm. After rolling, it enters the pit and cools slowly, and the exit temperature is lower than 150℃. To prevent cracking, it is imperative to use a hot pit, and the material entry temperature must be ≥600℃; then annealing is carried out, the annealing temperature is 700-720℃, the insulation time is ≥6 hours, and the furnace is cooled.

[0018] Compared with the prior art, the advantages of the present invention are: (1) The present invention adopts a new composition design, greatly increases the Mn content, and effectively improves the wear resistance of the material. The friction and wear test of the material is better than that of traditional materials. The test results are shown in the attached Figure 1 (Sample #1 is the material of the present invention, and sample #2 is the traditional material).

[0019] (2) The Di value of the new composition system can reach 250-280mm, which is about 90% higher than the Di value of 130-150mm of traditional mining chain steel. The martensite content in the core area of ​​the material after overall quenching reaches more than 90%, and the hardness difference between the core and the surface after quenching is controlled within 3HRC, so that the comprehensive mechanical properties of the chain after quenching + tempering are better. See the attached for the martensite test in the core area after quenching. Figure 2 , full cross-section hardness distribution see attached Figure 3 The mechanical properties of the material of the present invention, the three properties of the chain and the fatigue life are shown in Table 1 and Table 2.

[0020] (3) For the first time, the smelting method of "twice slag removal + twice P removal treatment" was used to produce mining chain steel, which greatly reduced the P content of the material and improved the toughness of the chain core and welding heat affected zone.

[0021] (4) The PSM rolling mill is used for the production of mining chain steel. The dimensional tolerance control range of the raw materials is ±0.2mm. The high-precision material size is beneficial to the stability of the chain welding quality, avoiding welding inclusions and gas that cannot be removed due to excessive gaps in the welding joints. On the other hand, it improves the dimensional accuracy of the final chain product and avoids problems such as chain jamming and tooth skipping during use.

[0022] (5) The sulfide modification technology was first applied in the production of mining chain steel, making the sulfides in the steel fine and evenly distributed in the steel, improving the rebound force during chain welding upsetting and stabilizing the weld quality.

[0023] (6) The new ingredient system significantly reduces smelting costs and improves the market competitiveness of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a friction and wear test distribution diagram of the product of the present invention.

[0026] Figure 2 This is the friction and wear test distribution diagram of traditional products.

[0027] Figure 3 This is a schematic diagram of the quenching structure of the core area of ​​the product of the present invention after overall quenching, 100×.

[0028] Figure 4 This is a schematic diagram of the quenching structure of the core area of ​​the product of the present invention after overall quenching, 500×.

[0029] Figure 5 This is a full-section hardness distribution diagram of the product of the present invention after overall quenching. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in more detail in conjunction with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred implementation methods of the present invention and cannot impose any limitation on the scope of the present invention.

[0031] Example 1

[0032] The diameter of the new high hardenability mining chain steel involved in this embodiment is 34 mm, and its chemical composition is as follows by mass percentage: C: 0.24%, Si: 0.25%, Mn: 1.55%, P: ≤0.008%, S: 0.018%, Ni: 0.51%, Cr: 1.25%, Mo: 0.44%, and the remainder is Fe and unavoidable impurity elements.

[0033] The manufacturing process of the chain steel is to sequentially subject the smelting raw materials to KR molten iron pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent the P return during refining temperature rise, a slag removal process is adopted after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag removal process is adopted again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is adopted to make the sulfide become fine and evenly distributed in the molten steel, which is more conducive to reducing the rebound force of the material when welding the top to ensure the stability of the weld quality. After the molten steel is continuously cast, To improve production efficiency, the ingot can be warm-sent to the heating furnace at a temperature of 382-420°C; the preheating section temperature of the steel rolling is 693-780°C, the heating section temperature is 985-1021°C, the soaking section temperature is 1223-1252°C, and it is kept warm for 6.5 hours before being taken out of the furnace; after descaling with high-pressure water, it is rolled at a rough rolling temperature of 1032°C and a final rolling temperature of 922°C. The PSM three-roller finishing mill is used to strictly control the dimensional tolerance of the material, and the final product dimensional tolerance is controlled within the range of 34±0.18mm. After rolling, the material is put into the pit for slow cooling. In order to prevent cracking, a hot pit is used, and the material entering the pit temperature is 621°C; then annealing is carried out at a temperature of 710°C, a holding time of 7 hours, and furnace cooling.

[0034] The chain steel produced by the above manufacturing process has high strength, high processing accuracy and excellent flash welding performance.

[0035] Example 2

[0036] The diameter of the new high hardenability mining chain steel involved in this embodiment is 56 mm, and its chemical composition is as follows by mass percentage: C: 0.24%, Si: 0.23%, Mn: 1.53%, P: ≤0.009%, S: 0.020%, Ni: 0.50%, Cr: 1.25%, Mo: 0.42%, and the remainder is Fe and unavoidable impurity elements.

[0037] The manufacturing process of the chain steel is to sequentially subject the smelting raw materials to KR molten iron pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain ingots that meet the chemical composition requirements. In order to prevent P from returning during refining temperature increase, a slag stripping process is used after the converter is tapped to remove the slag on the surface of the molten steel. After the molten steel is transferred to the refining furnace, lime (main component CaO) is added to the surface of the molten steel again for further P removal. After the slag stripping process is used again, refining and degassing are carried out. During refining, a sulfide modification treatment technology is used to make the sulfide become fine and evenly distributed in the molten steel, which is more conducive to reducing the rebound force of the material when welding the top to ensure the stability of the weld quality. After the molten steel is continuously cast, To improve production efficiency, the ingot can be warm-sent to the heating furnace at a temperature of 385-424°C; the preheating section temperature of the steel rolling is 695-781°C, the heating section temperature is 988-1023°C, the soaking section temperature is 1221-1250°C, and it is kept warm for 7 hours before being taken out of the furnace; it is rolled after descaling with high-pressure water, the rough rolling temperature is 1035°C, the final rolling temperature is 928°C, and the PSM three-roll finishing mill is used to strictly control the dimensional tolerance of the material. The final dimensional tolerance of the finished product is controlled within the range of 56±0.16mm. After rolling, it is put into the pit for slow cooling. To prevent cracking, a hot pit is used, and the material entering the pit temperature is 629°C; then annealing is carried out, the annealing temperature is 710°C, the holding time is 7 hours, and the furnace is cooled.

[0038] The chain steel produced by the above manufacturing process has high strength, high processing accuracy and excellent flash welding performance.

[0039] Table 1 Mechanical properties of materials

[0040] Yield strength MPa ≥ 980 Tensile strength MPa ≥ 1180 Elongation%≥10 Shrinkage%≥50 Impact energy J≥60 1187 1261 12.5 60 94 1182 1255 12.5 61 94

[0041] Table 2 Three chain properties and fatigue life

[0042] Breaking load KN≥1450 Maximum elongation under test load % ≤ 1.6 Elongation at break%≥12 Fatigue life ≥ 30,000 times 1772 1.5 28 76430 1697 1.5 27 75899

[0043] Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that various modifications and variations are possible for those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A new type of high hardenability mining chain steel, characterized by: The chemical composition of the fastener steel is, by mass percentage, C: 0.38-0.45%, Si: 0.22-0.30%, Mn: 1.52-1.60%, P: ≤0.011%, S: 0.008-0.025%, Ni: 0.55-0.65%, Cr: 1.21-1.31%, Mo: 0.50-0.58%, and the remainder is Fe and unavoidable impurity elements.

2. The novel high hardenability mining chain steel according to claim 1 is characterized in that: The diameter of the chain steel is 18-130 mm, the Di value of the material is controlled within the range of 250-280 mm, the martensite content of the core area after overall quenching reaches more than 90%, and the hardness difference between the core and the surface after quenching is controlled within 3HRC.

3. The novel high hardenability mining chain steel according to claim 1 is characterized in that: The mechanical properties of the quenched and tempered steel meet the following requirements: yield strength ≥980MPa, tensile strength ≥1180Mpa, elongation ≥10%, shrinkage ≥50%, impact energy ≥60J, breaking load ≥1450KN, maximum elongation under test load ≤1.6%, breaking elongation ≥12%, and fatigue life ≥30,000 times.

4. A method for preparing the novel high hardenability mining chain steel as claimed in claim 1, characterized in that: The method comprises the following steps: 1) The smelting raw materials are sequentially subjected to KR molten iron pretreatment, converter or electric furnace smelting, LF refining, RH or VD degassing and continuous casting to obtain a casting billet that meets the chemical composition requirements; 2) The temperature of the preheating section of the rolled steel is 650-800℃, the temperature of the heating section is 900-1050℃, the temperature of the soaking section is 1200-1270℃, and the steel is kept warm for 6-8 hours before being taken out of the furnace; 3) After descaling with high-pressure water, rolling is carried out, the rough rolling temperature is ≥1020℃, the final rolling temperature is ≥900℃, and the final product size tolerance is controlled within the range of ±0.20mm; 4) After rolling, the steel is slowly cooled in the pit, and the exit temperature is lower than 150°C; 5) Annealing treatment is then carried out at a temperature of 700-720°C, with a holding time of ≥6 hours and furnace cooling.

5. The method for preparing a novel high hardenability mining chain steel according to claim 4, characterized in that: After continuous casting, the molten steel is warm-transferred to a heating furnace at a temperature of 300-450°C.

6. The method for preparing a novel high hardenability mining chain steel according to claim 4, characterized in that: In order to prevent the refining temperature from returning to P, the slag removal process is used to remove the slag on the surface of the molten steel after the converter is tapped. After the molten steel is transferred to the refining furnace, lime is added to the surface of the molten steel again for further P removal. After the slag removal process is used again, refining and degassing are carried out.

7. The method for preparing a novel high hardenability mining chain steel according to claim 4, characterized in that: During the refining process, calcium is added to the molten steel by feeding Ca-Si wire into the molten steel to denature the sulfides in the steel.

8. The method for preparing a novel high hardenability mining chain steel according to claim 4, characterized in that The rolling process uses a three-roller finishing mill. The three rolls are distributed at a certain angle. The continuous casting billet is subjected to pressure in three directions and is in a three-way compressive stress state, thereby controlling the dimensional accuracy.

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