Cold-resistant medium-carbon sulfur-containing structural steel for small and micro motor rotating shaft and smelting method of cold-resistant medium-carbon sulfur-containing structural steel

Abstract

The invention discloses medium-carbon sulfur-containing structural steel for a cold-resistant small and micro motor rotating shaft and a smelting method, the alloy elements in the steel are controlled to comprise, by mass, 0.40-0.50% of C, 0.15-0.35% of Si, 0.50-1.0% of Mn, less than or equal to 0.005% of P, 0.025-0.045% of S, 0.006-0.008% of T.[ O] and the balance Fe and inevitable impurities, and the corresponding relation of Mn and S is limited so as to ensure the cutting performance and hardness control of a product. The steel can meet the performance requirements of the steel for the small and micro motor rotating shaft under the extremely cold working condition, is good in cold resistance, capable of avoiding cold brittleness failure in the extremely cold environment, long in fatigue life, durable, good in cutting performance, good in machining precision, high in surface smoothness, small in abrasion in the operation process, low in noise and capable of meeting the higher use requirements of products.

Description

Technical Field

[0001] The invention relates to a medium-carbon sulfur-containing structural steel and a smelting method, in particular to a medium-carbon sulfur-containing structural steel for small and micro motor shafts that can meet the requirements of extremely cold working conditions and a smelting method, belonging to the technical field of steel metallurgy. Background Art

[0002] With the high-quality development of my country's motor industry, the demand for small and micro motor shafts has increased. Most of these products have complex hole structures and rotate at high speeds during operation. They require materials with good processing accuracy, which can reduce the energy consumption and damage of the motor, reduce motor noise, and have a high fatigue life and durability. Especially when used in extremely cold environments, the product is required to have a low P content to avoid cold brittle failure. At present, the main material used for this type of product in China is No. 45 steel, but it has many problems such as high noise, poor cold resistance, and low fatigue life, which directly affects the promotion and application of the product in extremely cold international markets including Russia. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a medium-carbon sulfur-containing structural steel for small and micro motor shafts that can meet extremely cold working conditions and a smelting method thereof, thereby meeting the market demand.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0005] A medium-carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, wherein the mass percentages of various alloy elements are: C 0.40-0.50%, Si 0.15-0.35%, Mn 0.50-1.0%, P≤0.005%, S 0.025-0.045%, T.[O] 0.006-0.008%, and the rest is Fe and unavoidable impurities; the mass percentage relationship of Mn and S in the steel is preferably: wt[Mn]≤16.3×wt[S]+0.25.

[0006] When designing the composition, the C content in the steel is controlled at C 0.40-0.50%, which can meet the strength requirements of the product application, and ensure that the S content in the steel is S 0.025-0.045% to improve the cutting performance of the product and save costs when processing porous structures. More importantly, the product has good cutting performance and can withstand higher machining tool rotation speeds. The surface finish after processing is higher, and there is less wear and lower noise during operation.

[0007] On the basis of the design of S content, the applicant uses Ohnaka model to calculate the segregation of solute sulfur during the solidification process of small square billets. The calculation results show that MnS is formed in the mushy zone at the end of solidification. At this time, the corresponding S segregation index reaches 16.3, which verifies that S is an element that is very easy to segregate. On this basis, the total oxygen content and the content of Mn element in steel are designed: the technical means for optimizing the morphology of MnS in the mushy zone is to control the total oxygen content at the level of 60-80ppm, which can promote the cast MnS to be Class I block, rather than clustered Class II morphology; at the same time, it must be ensured that enough Mn elements are combined with S in the mushy zone to form MnS, and the remaining Mn exists in the form of solid solution Mn. The solid solution Mn content cannot be too high, otherwise it will increase the hardness of the product and affect the tool life during processing. Therefore, the present invention controls the content of Mn element to: wt[Mn]≤16.3×wt[S]+0.25.

[0008] A smelting method for medium-carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, the smelting method comprises the following control points: the production process adopts an all-scrap steel electric furnace EAF→LF ladle refining furnace steel liquid→small billet continuous casting smelting and casting; when the all-scrap steel electric furnace is tapped, the molten steel T is controlled to be 1650-1680°C, the molten steel oxygen activity is 0.04-0.06%, P≤0.003%, Al is added to the molten steel for deoxidation during tapping, and the mass of Al added per ton of steel is 0.3-0.35kg; in the LF stage, the mass fraction of CaO / SiO2 in the slag is controlled to be between 1.0-1.2, and the mass fraction of Al2O3 in the slag is controlled to be between 5-8%; before LF soft blowing, S wire is appropriately fed according to the mass fraction of S in the steel to ensure that the mass fraction of S in the molten steel before LF soft blowing satisfies: S=0.028-0.048%.

[0009] As a preferred embodiment, in the above-mentioned method for smelting medium-carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, in the LF soft blowing stage, it is best to control the soft blowing time to 8-10 minutes.

[0010] As a preferred embodiment, in the above-mentioned method for smelting medium-carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, when continuous casting of small square billets is adopted, the cross-sectional side length of the continuously cast small square billets is preferably controlled between 150mm and 200mm.

[0011] In the electric furnace smelting stage: when the all-scrap steel electric furnace is tapping, the molten steel T is controlled at 1650-1680℃, the molten steel oxygen activity is 0.04-0.06%, P≤0.003%, and Al is added to the molten steel for deoxidation during tapping, with the mass of Al added per ton of steel being 0.3-0.35kg.

[0012] Since the application requirement of the product requires low-temperature application, an upper limit is given to the P content, which shall not be higher than 50ppm. When using a traditional molten iron converter, it is very difficult to control the P content. Therefore, the present invention adopts all-scrap steel electric furnace smelting, and the P content in the scrap steel is basically at the level of 0.015%. The effect of oxygen blowing to remove P in the electric furnace stage is good, and the P content at the end of the electric furnace can reach 30ppm. The subsequent alloying process increases slightly, and the final product can reach 50ppm, meeting the low-temperature performance requirements.

[0013] Since the electric furnace uses oxygen blowing to remove P, the oxygen activity in the molten steel at the end of the electric furnace is relatively high, which can reach 500ppm. At this time, a certain amount of Al is added. After calculation, the mass of Al added per ton of steel is 0.3-0.35kg, which can appropriately remove the total oxygen content and match other elements such as Mn and Si for alloying, so as to control the final total oxygen content in the steel to meet the standard.

[0014] In the refining process: entering the LF stage, control the mass fraction of CaO / SiO2 in the slag between 1.0-1.2, and the mass fraction of Al2O3 in the slag between 5-8%; before LF soft blowing, feed S line appropriately according to the mass fraction of S in the steel to ensure that the mass fraction of S in the molten steel before LF soft blowing meets the following requirements: S = 0.028 ~ 0.048%; in the LF soft blowing stage, control the soft blowing time = 8-10min.

[0015] The purpose of this operation is to control the composition of the slag and the kinetic conditions of the slag reaction, so that the total amount of inclusions in the molten steel can be stably controlled to reach the control target of the final total oxygen content of 80ppm. At the same time, after S alloying, the mixing effect of the S element in the steel is guaranteed. According to the thermodynamic calculation of the desulfurization of molten steel and the adsorption effect of slag on inclusions, the main inclusion in the steel with proper Al deoxidation is still Al2O3. The basicity of the slag is controlled to be low and the activity of Al2O3 in the slag is low, which can control the number of inclusions in the final steel to be large and dispersed. At the same time, the low basicity of the slag is also conducive to ensuring the recovery rate of the S element and can stably maintain the S content in the steel.

[0016] Finally, small square billets and small rectangular billets are used for continuous casting, and the cross-sectional length of the continuous casting small square billets is between 150mm and 200mm. The small square billets can effectively control the segregation ratio of elements such as S and Mn, thereby ensuring that the size of the cast MnS will not be too large, and the MnS in the final product will not be too long after rolling extension, avoiding the anisotropy of the product or poor mechanical properties.

[0017] Beneficial effect: Compared with the prior art, the present invention specially designs the composition and smelting method of medium-carbon sulfur-containing structural steel for small and micro motor shafts suitable for extremely cold working conditions, controls the content of various alloy elements in the steel, and controls the deoxidation system, Mn-S element relationship, and slag composition to achieve morphological control of MnS inclusions and extremely low phosphorus cold resistance requirements, and ensures the cutting performance and hardness control of the product, which can meet the performance requirements of steel for small and micro motor shafts under extremely cold working conditions. It not only has good cold resistance, can avoid cold brittle failure in extremely cold environments, high fatigue life, long-lasting durability, and the product has good cutting performance, good processing accuracy, high surface finish, small wear and low noise during operation, which can meet higher product use requirements. DETAILED DESCRIPTION

[0018] Example 1: Molten steel smelting composition wt%:

[0019] C You Mn P S T.[O] 0.43 0.28 0.73 0.0045 0.031 0.0072

[0020] Smelting process control: adopt all-scrap steel electric furnace EAF → LF ladle refining furnace molten steel → small square billet continuous casting smelting and casting.

[0021]

[0022] Finished product application:

[0023]

[0024] Example 2: Molten steel smelting composition wt%:

[0025] C You Mn P S T.[O] 0.48 0.35 0.94 0.0047 0.035 0.0065

[0026] Smelting process control: adopt all-scrap steel electric furnace EAF → LF ladle refining furnace molten steel → small square billet continuous casting smelting and casting.

[0027]

[0028] Finished product application:

[0029]

[0030] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A medium carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, characterized in that: The mass percentages of various alloying elements are: C 0.40-0.50%, Si 0.15-0.35%, Mn 0.50-1.0%, P≤0.005%, S 0.025-0.045%, T.[O]0.006-0.008%, and the rest are Fe and unavoidable impurities; the mass percentage relationship of Mn and S in steel is: wt[Mn]≤16.3×wt[S]+0.

25.

2. A method for smelting medium-carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts, characterized in that: The production process adopts the method of all-scrap steel electric furnace EAF → LF ladle refining furnace molten steel → small billet continuous casting and smelting; when tapping steel from the all-scrap steel electric furnace, the molten steel T is controlled to be 1650-1680℃, the molten steel oxygen activity is 0.04-0.06%, P≤0.003%, Al is added to the molten steel for deoxidation during tapping, and the mass of Al added to a ton of steel is 0.3-0.35kg; in the LF stage, the mass fraction of CaO / SiO2 in the slag is controlled to be between 1.0-1.2, and the mass fraction of Al2O3 in the slag is controlled to be between 5-8%; before LF soft blowing, according to the mass fraction of S in the steel, S line is appropriately fed to ensure that the mass fraction of S in the molten steel before LF soft blowing meets the following requirements: S=0.028~0.048%.

3. The smelting method of the medium carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts according to claim 2 is characterized in that: During the LF soft blowing stage, the soft blowing time is controlled to be 8-10 minutes.

4. The smelting method of the medium carbon sulfur-containing structural steel for cold-resistant small and micro motor shafts according to claim 2 is characterized in that: The cross-sectional side length of the continuous casting small square billet is between 150mm and 200mm.

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