Selenium-tin complex high-performance free-cutting bar and method for manufacturing the same

Abstract

The application discloses a selenium-tin combined high-performance free-cutting bar and a manufacturing method thereof. The selenium-tin combined high-performance free-cutting bar comprises the following components: C: 0.30%-0.45%, Si: 0.10%-0.25%, Mn: 0.90%-1.15%, Cr: 0.05%-0.15%, Se: 0.10%-0.20%, S: 0.05%-0.15%, Sn: 0.01%-0.10%, O: 0.0040%-0.0060%, Mn / Se is greater than or equal to 4.5, and the rest is iron and inevitable impurities, and the percentage of the components is by weight. The application adds free-cutting elements selenium, tin and flow, combines with medium carbon, controls the distribution and form of beneficial inclusions in the steel, significantly improves the cutting performance and mechanical properties of the structural steel, and meets the requirements of improving the cutting performance of the high-carbon free-cutting steel for automobile structural parts, efficiently cleaning the cutting chips, and well matching the mechanical properties and the cutting performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-carbon free-cutting steel rod, and particularly relates to a selenium-tin combined high-performance free-cutting rod and a manufacturing method thereof. BACKGROUND

[0002] In recent years, with the rapid development of the automobile industry and the increasing global awareness of environmental protection, people have generally begun to explore free-cuting steel rod structural members with better cutting performance, better structural strength and more environmentally friendly. However, the existing high-performance cutting steel rod mainly contains lead, but does not meet the environmental protection requirements, and only relies on sulfur, which is prone to high-temperature sulfur embrittlement. Therefore, the present application provides a selenium-tin combined high-performance free-cutting rod and a manufacturing method thereof. Since selenium and sulfur belong to the same main group elements and have similar physical and chemical properties, they can replace part of the sulfur to achieve the effect of strengthening the cutting performance. Tin and lead belong to the same main group, have similar physical and chemical properties, have high boiling points and low vapor pressures, are not easy to volatilize and are non-toxic, and are an environmentally friendly free-cuting element. In the cutting process, it is easy to produce chip breaking, thereby improving the cutting performance of the steel.

[0003] CN117821833A discloses a production method of an ultrahigh-sulfur free-cutting steel rod, the rod containing C≤0.08%, Si≤0.05%, Mn=2.00%-2.80%, P=0.04%-0.09%, S=0.50%-0.70%, and the rest being Fe and unavoidable impurity elements; the rod has a tensile strength Rm of 400-540 MPa, a reduction of area of ≥45%, and an elongation of ≥22%, but belongs to the field of low-carbon steel, and the excessively high manganese and sulfur contents easily lead to an increase in the micro-cracks of the blank and serious segregation.

[0004] CN112063924A discloses a high-carbon selenium-tin-containing free-cutting steel and a production method thereof, the method adding free-cutting elements selenium and tin, combining high carbon, controlling the distribution and morphology of beneficial inclusions in the steel, and significantly improving the cutting performance and mechanical properties of the high-carbon structural steel to meet the requirements of the automobile structural member for improved cutting performance, efficient chip cleaning, and good cooperation between the mechanical properties and the cutting performance. However, the technology is for wire rods, not for rod materials, and there is an essential difference in the manufacturing process.

[0005] CN1540022A discloses a tin-containing free-cutting structural steel, the steel containing a high content of tin (0.09-0.25 wt%), containing a certain amount of Sn, and the cutting performance is improved to a certain extent, but the tin content of the steel cannot achieve the cutting performance effect of high-carbon free-cutting steel, and the cutting performance is unstable without the cooperation of selenium.

[0006] CN106978570 A discloses a free-cutting steel containing a high tin content and a preparation method, which solves the problem of excessive tin content causing excessive hot brittleness of the free-cutting steel by alloying the free-cutting steel with Mo, W and rare earth element La. To obtain good cutting performance, the steel contains a high amount of Sn, and a plurality of alloying elements with high content, which increases the cost and process complexity.

[0007] CN105088106 A discloses a tin-bismuth-containing composite free-cutting steel, which has good cutting performance, but has a large oxidation loss and evaporation of Bi during smelting, a low yield, high industrial production cost and great difficulty. SUMMARY

[0008] The present application provides a selenium-tin combined high-performance free-cutting bar and a manufacturing method thereof. The purpose is to replace lead and part of sulfur free-cutting steel bar products in the field of high carbon steel bars by using environmentally friendly selenium-tin combined free-cutting elements through smelting, rolling, heat treatment and other processes, to improve the cutting performance and mechanical properties of existing high carbon structural steel, and to meet the requirements of high carbon free-cutting steel in terms of cutting performance improvement, mechanical properties and good combination of cutting performance.

[0009] The present application realizes the technical effect by a certain proportion of manganese, selenium, tin and oxygen, especially by replacing part of sulfur with selenium and lead with tin, combined with steelmaking and rolling processes. The selenium manganese and manganese sulfide and their oxide inclusions are formed, the inclusions are spindle-shaped or spherical, and are dispersedly distributed, which significantly improves the cutting performance of the bar, solves the problem of poor cutting performance of the bar caused by the elongation of the manganese sulfide inclusions in the existing selenium-tin combined high-performance free-cutting bar, protects the cutting tool with tin and improves the surface quality of the bar with sulfur. The stable addition of selenium and tin is realized in a short time in vacuum to avoid being oxidized. The control of oxygen is to form a certain amount of oxide for the adsorption and nucleation of manganese sulfide and manganese sulfide, and to adjust the morphology of inclusions to spherical and spindle-shaped. The slow cooling of the continuous casting billet reduces the crack tendency of the continuous casting billet.

[0010] The present application significantly improves the cutting performance and mechanical properties of structural steel by adding free-cutting elements selenium, tin and flow, combined with medium carbon, controlling the distribution and morphology of beneficial inclusions in steel, and meets the requirements of high carbon free-cutting steel for automobile structural parts in terms of cutting performance improvement, efficient cutting chip cleaning, good combination of mechanical properties and cutting performance.

[0011] According to one aspect of the present application, there is provided a selenium-tin combined high-performance free-cutting bar, characterized in that the composition of the selenium-tin combined high-performance free-cutting bar is as follows: C: 0.30%-0.45%, Si: 0.10%-0.25%, Mn: 0.90%-1.15%, Cr: 0.05%-0.15%, Se: 0.10%-0.20%, S: 0.05%-0.15%, Sn: 0.01%-0.10%, O: 0.0040%-0.0060%, Mn / Se≥4.5, and the balance is iron and inevitable impurities, in terms of percentage by weight.

[0012] The selection of the amount of each element (percentage by weight) and the role thereof are described as follows:

[0013] C: Carbon is the most basic matrix strengthening element of steel materials. The free-cutting structural steel in the present application has relatively high strength, and the addition of carbon elements guarantees good mechanical properties. When the carbon content is lower than 0.30%, the strength index of the bar cannot be guaranteed; when the carbon content is higher than 0.45%, the cutting performance is severely reduced. Therefore, the carbon content in the present application is controlled within the range of 0.30%-0.45%.

[0014] Si: Silicon is a good deoxidizer in the present application and also provides certain strength. When the silicon content is lower than 0.10%, the deoxidation effect is not good; when the silicon content is higher than 0.25%, the toughness is reduced. Therefore, the silicon content in the present application is controlled within the range of 0.10%-0.25%.

[0015] Mn: Mn and Se are important elements of Mn-Se inclusions in the present application, which are beneficial to improving the free-cutting performance. When the manganese content is lower than 0.90%, manganese sulfide and manganese selenide are easily elongated; when the manganese content is higher than 1.15%, the cutting performance is reduced. Therefore, the manganese content in the present application is controlled within the range of 0.90%-1.15%.

[0016] Cr: Chromium is a strength-improving element, and the role of chromium in the present application is to improve the strength and hardness. When the chromium content is lower than 0.05%, the improvement effect is not obvious; when the chromium content is higher than 0.15%, the cutting performance is reduced. Therefore, the chromium content in the present application is controlled within the range of 0.05%-0.15%.

[0017] Se: Selenium is an effective free-cutting element, which can form manganese selenide with manganese, change the morphology and distribution of inclusions, and cooperate with tin to significantly improve the cutting performance and chip morphology of the free-cutting steel. When the selenium content is lower than 0.10%, the above-mentioned effect cannot be achieved; when the selenium content exceeds 0.20%, the grain boundary segregation of tin cannot be prevented, and the smelting cost is increased. Therefore, the selenium content in the present application is controlled within the range of 0.10%-0.20%.

[0018] S: Sulfur is an easy cutting element, and appropriate addition and formation of compounds with manganese and selenium can significantly improve the easy cutting performance. When the sulfur content is lower than 0.05%, the compounds that help the cutting performance cannot be well formed with manganese and selenium. When the sulfur content is higher than 0.15%, the hot workability of the steel is reduced. Therefore, the sulfur content in the application is controlled in the range of 0.05% to 0.15%.

[0019] Sn: Tin is an easy cutting element, and appropriate addition and combined action with selenium can significantly improve the easy cutting performance. When the tin content is lower than 0.01%, the tin cannot form organic cooperation with selenium, and a brittle zone is formed in the cutting process. When the sulfur content is higher than 0.10%, the hot workability of the steel is reduced. Therefore, the tin content in the application is controlled in the range of 0.01% to 0.10%.

[0020] O: In the application, the acid-base environment is provided for selenium-tin cooperation. When the oxygen content is lower than 0.0040%, the selenium compound cannot form a dispersed distribution, and the form is difficult to control. When the oxygen content is higher than 0.0060%, the inclusion form is no longer obviously improved. Therefore, the oxygen content in the application is controlled in the range of 0.0040% to 0.0060%.

[0021] According to another aspect of the application, a manufacturing method of a selenium-tin cooperation high-performance easy cutting bar is provided, and the manufacturing method comprises the following steps: converter smelting, LF refining, VD vacuum degassing, continuous casting, and slab heating-rolling-post-rolling slow cooling. The specific steps of the slab heating-rolling-post-rolling slow cooling are as follows: the slab is heated to 600-610 DEG C for 1-1.5 h to prevent the increase of internal stress of the slab and the generation of cracks, the temperature is increased to 1180-1200 DEG C for 2-3 h, rolling is performed, slow cooling is performed in a 640-650 DEG C slow cooling pit for 10-12 h after rolling, and then normalizing is performed to 20-30 DEG C, so that the selenium-tin cooperation high-performance easy cutting bar is obtained.

[0022] Further, the specific steps of the converter smelting are as follows: the converter molten iron is not desulfurized and dephosphorized, and the total oxygen content of the molten steel is controlled in the range of 185-200 ppm.

[0023] Further, the specific steps of the LF refining are as follows: refining slag and submerged arc slag are first added, silicon iron is then added to perform slag surface deoxidization on the molten steel, weak argon blowing is performed, white slag treatment is performed, and then selenium-manganese alloy is added to the molten steel to perform alloying; the alloying refining time is controlled, and the oxygen content is ensured to be controlled in the range of 40-60 ppm.

[0024] Further, the specific steps of the VD vacuum degassing are as follows: the vacuum is passed for 5-8 min, the time is not too long to prevent the complete floating of oxides, tin particles are added, and the selenium content is appropriately supplemented with selenium-manganese alloy to adjust the selenium-tin composition.

[0025] Furthermore, the specific steps of the continuous casting are as follows: large square billets are used for continuous casting, and the cross-sectional dimensions of the billets are not less than 280mm×380mm. Medium carbon protective slag is used for protective casting during the continuous casting process. The tundish temperature is controlled at 1580~1595℃, the continuous casting speed is controlled at 0.60~0.70m / min, the secondary cooling water is weakly cooled, and the continuous casting billets are annealed to room temperature in a slow cooling pit at 800~810℃ after leaving the line.

[0026] Furthermore, the initial rolling temperature is 1120–1140°C, and the final rolling temperature is 925–940°C.

[0027] Furthermore, the Se content in the selenium-manganese alloy is 10% to 30%.

[0028] Furthermore, the selenium-tin composite high-performance free-cutting rod is spherical or spindle-shaped.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The technical solution of this invention achieves the technical effect by using a certain ratio of manganese, selenium, tin, and oxygen, especially by replacing part of the sulfur with selenium and replacing lead with tin, in conjunction with steelmaking and rolling processes. This forms manganese selenide, manganese sulfide, and their oxide composite inclusions, resulting in a spindle-shaped or spherical inclusion with a diffuse distribution, significantly improving the cutting performance of the bar stock. Tin protects the cutting tool and, in conjunction with sulfur, improves the surface quality of the bar stock. A short-time vacuum process ensures the stable addition of selenium and tin elements, preventing excessive oxidation. Controlling the oxygen position is to form certain oxides for manganese sulfide and manganese selenide to adsorb and nucleate, adjusting the inclusion morphology towards spherical and spindle shapes. Slow cooling of the continuously cast billet reduces the tendency for cracking.

[0031] (2) The technical solution of the present invention adds free-cutting elements selenium, tin and ferrous oxide, and combines them with medium carbon to control the distribution and morphology of beneficial inclusions in steel, thereby significantly improving the cutting performance and mechanical properties of structural steel, and satisfying the requirements of improved cutting performance, efficient chip removal and good combination of mechanical and cutting performance of high carbon free-cutting steel for automotive structural parts.

[0032] (3) The cutting performance index of the selenium-tin composite high-performance free-cutting bar obtained by the technical solution of the present invention is as follows: under the cutting conditions of f=0.08mm / r and rotation speed of 800 r / min, the proportion of C-type chips is 78% to 85%; the tensile strength is 600 to 690MPa, the yield strength is 400 to 470MPa, and the elongation after fracture is 12.0% to 13.8%, with good combination of mechanical properties and cutting performance. Attached Figure Description

[0033] Figure 1 This is a diagram showing the inclusion morphology of the selenium-tin composite high-performance free-cutting bar prepared in Example 13 of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0035] The present invention provides a high-performance free-machining bar stock with selenium-tin alloy composition in the specific embodiments section. The chemical composition of the high-performance free-machining bar stock with selenium-tin alloy composition is as follows: C: 0.30%~0.45%, Si: 0.10%~0.25%, Mn: 0.90%~1.15%, Cr: 0.05%~0.15%, Se: 0.10%~0.20%, S: 0.05%~0.15%, Sn: 0.01%~0.10%, O: 0.0040%~0.0060%, Mn / Se ≥ 4.5, with the balance being iron and unavoidable impurities, on a weight percentage basis.

[0036] The present invention provides a method for manufacturing a selenium-tin composite high-performance free-machining bar in the specific embodiments section, the method comprising the following steps:

[0037] (1) Converter smelting: The molten iron in the converter is not desulfurized or dephosphorized, and the total oxygen content of the steel is controlled at 185-200 ppm;

[0038] (2) LF refining: First, add refining slag and submerged arc slag, then add ferrosilicon to deoxidize the molten steel surface, weakly blow argon, and after white slag treatment, add selenium manganese alloy (self-made intermediate alloy with Se content of 10% to 30%) to the molten steel for alloying; control the alloying refining time and ensure that the oxygen content is controlled at 40 to 60 ppm.

[0039] (3) Vacuum degassing (VD): Vacuum for 5-8 minutes, the time should not be too long to prevent the oxides from floating completely. At the same time, add tin particles and supplement selenium-manganese alloy according to the selenium content to adjust the selenium-tin composition. The addition of selenium-tin elements in this process can make the spheroidization effect of manganese selenide inclusions better and improve the cutting performance;

[0040] (4) Continuous casting: Large square billet continuous casting is adopted, and the cross-sectional dimensions of the billet are not less than 280mm×380mm. Medium carbon protective slag is used for protection during the continuous casting process. The tundish temperature is controlled at 1580~1595℃, the continuous casting speed is controlled at 0.60~0.70m / min, the secondary cooling water is weakly cooled, and the continuous casting billet is annealed to room temperature in an 800℃ slow cooling pit after leaving the line.

[0041] (5) Heating, rolling and slow cooling of billet: When the billet is heated to 600℃, it is held for 1 hour to prevent the internal stress of the billet from increasing and causing cracks. Then it is held at 1200℃ for 2-3 hours. The initial rolling temperature is 1120-1140℃ and the final rolling temperature is 925-940℃. After rolling, it is placed in a slow cooling pit at 650℃ for 12 hours and then normalized to room temperature to obtain high-performance free-cutting bar material with selenium-tin combination.

[0042] Example

[0043] The chemical composition of the selenium-tin composite high-performance free-cutting bar stock described in the embodiments and comparative examples of this invention is shown in Table 1. The process parameters of the selenium-tin composite high-performance free-cutting bar stock are shown in Table 2. The cross-sectional dimensions of the cast billet are not less than 280mm × 380mm. The mechanical properties, elongation after fracture, and C-chip ratio of the selenium-tin composite high-performance free-cutting bar stock are shown in Table 3. The inclusion morphology of the selenium-tin composite high-performance free-cutting bar stock prepared in Example 13 is shown in Table 3. Figure 1 As shown, the inclusions are spherical or spindle-shaped and diffusely distributed, effectively solving the problem of manganese sulfide being elongated.

[0044] Table 1 shows the chemical composition of the selenium-tin composite high-performance free-cutting rods described in the embodiments and comparative examples of the present invention.

[0045] .

[0046] Table 2 shows the process parameters of the selenium-tin composite high-performance free-cutting rods described in the embodiments and comparative examples of the present invention.

[0047] .

[0048] Table 3 shows the mechanical properties, elongation after fracture, and C-chip ratio of the selenium-tin composite high-performance free-cutting bar stock described in the embodiments and comparative examples of the present invention.

[0049]

[0050] This invention achieves its technical effects through the above-mentioned technical solution, using a specific ratio of manganese, selenium, tin, and oxygen, particularly by replacing part of the sulfur with selenium and lead with tin, in conjunction with steelmaking and rolling processes. It forms composite inclusions of manganese selenide, manganese sulfide, and their oxides, resulting in spindle-shaped or spherical inclusions with a diffuse distribution, significantly improving the cutting performance of bars. Tin protects the cutting tools and, in conjunction with sulfur, enhances the surface quality of the bars. A short-duration vacuum process ensures the stable addition of selenium and tin, preventing excessive oxidation. Controlling the oxygen sites is crucial for forming certain oxides that provide nuclei for manganese sulfide and manganese selenide adsorption, thus adjusting the inclusion morphology towards spherical and spindle shapes. Slow cooling of continuously cast billets reduces their tendency to crack. The selenium-tin composite high-performance free-machining bar obtained by the technical solution of this invention has the following cutting performance indicators: under cutting conditions of f=0.08 mm / r and rotation speed of 800 r / min, the proportion of C-shaped chips is 78% to 85%; the tensile strength is 600 to 690 MPa; the yield strength is 400 to 470 MPa; and the elongation after fracture is 12.0% to 13.8%, showing a good balance between mechanical properties and cutting performance.

[0051] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A high-performance free-machining bar stock with selenium-tin alloy, characterized in that, The composition of the selenium-tin composite high-performance free-cutting bar stock is as follows: C: 0.30%–0.45%, Si: 0.10%–0.25%, Mn: 0.90%–1.15%, Cr: 0.05%–0.15%, Se: 0.10%–0.20%, S: 0.05%–0.15%, Sn: 0.01%–0.10%, O: 0.0040%–0.0060%, Mn / Se ≥ 4.5, with the balance being iron and unavoidable impurities, by weight percentage. The manufacturing method of the selenium-tin compound high-performance free-cutting bar includes the following steps: converter smelting, LF refining, VD vacuum degassing, continuous casting, billet heating-rolling-slow cooling after rolling. The specific steps of billet heating-rolling-slow cooling after rolling are as follows: heating the billet to 600~610℃ and holding it for 1~1.5h to prevent the increase of internal stress and cracks in the billet, raising the temperature to 1180~1200℃ and holding it for 2~3h, rolling, and then slow cooling in a 640~650℃ slow cooling pit for 10~12h, and then normalizing to 20~30℃ to obtain the selenium-tin compound high-performance free-cutting bar. The specific steps of the converter smelting are as follows: the molten iron in the converter is not desulfurized or dephosphorized, and the total oxygen content of the tapped steel is controlled at 185-200 ppm. The specific steps of the LF refining are as follows: first, add refining slag and submerged arc slag, then add ferrosilicon to deoxidize the molten steel surface, weakly blow argon, treat with white slag, and then add selenium manganese alloy to the molten steel for alloying; control the alloying refining time and ensure that the oxygen content is controlled at 40-60 ppm. The specific steps of the VD vacuum degassing are as follows: pass through vacuum for 5 to 8 minutes, the time should not be too long to prevent the oxides from floating completely, add tin particles at the same time, and supplement selenium-manganese alloy appropriately according to the selenium content to adjust the selenium-tin composition.

2. The selenium-tin composite high-performance free-machining bar according to claim 1, characterized in that, The specific steps of the continuous casting are as follows: large square billets are used for continuous casting, and the cross-sectional dimensions of the billets are not less than 280mm×380mm. Medium carbon protective slag is used for protective casting during the continuous casting process. The tundish temperature is controlled at 1580~1595℃, the continuous casting speed is controlled at 0.60~0.70m / min, the secondary cooling water is weakly cooled, and the continuous casting billets are annealed to room temperature in a slow cooling pit at 800~810℃ after leaving the line.

3. The selenium-tin composite high-performance free-machining bar according to claim 1, characterized in that, The initial rolling temperature is 1120–1140°C, and the final rolling temperature is 925–940°C.

4. The selenium-tin composite high-performance free-machining bar stock according to claim 1, characterized in that, The selenium-manganese alloy contains 10% to 30% Se.

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