Free-cutting austenitic stainless steel with excellent cold working performance and preparation method thereof

Abstract

The invention belongs to the technical field of manufacturing of austenitic stainless steel, and discloses free-cutting austenitic stainless steel with excellent cold working performance and a preparation method of the free-cutting austenitic stainless steel. The stainless steel comprises the following components in percentage by weight: less than or equal to 0.15% of C, less than or equal to 1.00% of Si, less than or equal to 3.00% of Mn, less than or equal to 0.04% of P, more than or equal to 0.15% of S, 17.00%-19.00% of Cr, 8.00%-10.00% of Ni, 1.50%-1.80% of Cu, 0.20%-0.60% of Mo, less than or equal to 0.10% of N, more than or equal to 0.0080% of O, less than or equal to 2.5 ppm of H and the balance of iron and inevitable impurities. The preparation method comprises the following steps: smelting a steel material to obtain molten steel with target components, obtaining a continuous casting square billet by using a continuous casting machine, and carrying out rolling and solution treatment on the continuous casting square billet to obtain the stainless steel wire rod. According to the austenitic stainless steel wire rod, the room-temperature tensile strength can reach 580-600 MPa, the percentage elongation after fracture is 55.0%-60.0%, the percentage reduction of area is 65%-70%, the grain size rating is finer than 10, the turning performance is excellent, the stability of the cold machining performance of materials is improved, and the machining yield and efficiency of austenitic stainless steel are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of austenitic stainless steel production and manufacturing, and in particular relates to an austenitic stainless steel with excellent cold working performance and easy cutting and a preparation method thereof. Background Art

[0002] Stainless steel has a wide range of applications. It not only plays a huge role in aerospace, petrochemical and other fields, but also has a wide range of applications in transportation facilities, kitchen utensils, household appliances, construction supplies and other life fields. Free-cutting stainless steel refers to stainless steel that has a certain amount of one or more free-cutting elements such as sulfur, phosphorus, lead, calcium, selenium, tellurium, etc. added to the steel to improve its cutting properties. This type of steel is mainly used for processing on automatic cutting machine tools. With the automation, high speed and precision of cutting processing, the requirements for the turning properties of materials are getting higher and higher, and at the same time, high requirements are also placed on the cold processing deformation ability, so the material needs to have good plasticity. At present, this type of product is often used in precision parts for food machinery, office machinery, communication equipment and other equipment, and is also used in fine products such as watches, jewelry, and toys.

[0003] Since sulfides are soft at high temperatures, they are easily deformed and arranged in rows in the rolling direction during rolling, which makes the steel's resistance to lateral strain worse and increases the anisotropy. The elongated manganese sulfide will also significantly reduce the plasticity of stainless steel. Therefore, the uniform distribution of matrix sulfides is the key factor in improving the cold plasticity of such materials. Adjusting the composition and optimizing the process are the main research directions for improving the plasticity of free-cutting stainless steel. Ultimately, various performance indicators will reach advanced domestic and international levels, and some indicators will reach the international leading level, gradually replacing imported products. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an austenitic stainless steel with excellent cold working performance and a preparation method thereof. The steel and the preparation method thereof of the present invention can: 1) optimize the cooling system of the continuous casting process to make the sulfide of the free-cutting austenitic stainless steel uniformly distributed; 2) standardize and control the hydrogen content in molten steel to effectively improve the plasticity index of the free-cutting austenitic stainless steel; 3) improve the solid solution process system to reduce the heterogeneity of the austenitic stainless steel structure; 4) accurately control the smelting components to reduce the economic cost pressure.

[0005] The invention achieves spindle-shaped sulfides and uniformly distributed austenite structures evenly distributed inside and outside the matrix by precisely controlling the oxygen content in the components, reducing the hydrogen content in the molten steel and optimizing the continuous casting process, thereby significantly improving the plasticity and turning performance of the free-cutting austenitic stainless steel, wherein the room temperature tensile strength can reach 580-600 MPa, the elongation after fracture is 55.0%-60.0%, the cross-sectional shrinkage is 65%-70%, and the grain size rating is finer than grade 10. The addition of sulfur in the invention can not only improve the turning performance of the material, but also a large amount of sulfides are uniformly distributed in the matrix, which improves the uniformity of the room temperature structure, optimizes the stability of the mechanical properties of the material, and greatly improves the cold working yield and efficiency of the free-cutting austenitic stainless steel.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The invention provides an austenitic stainless steel with excellent cold working performance and easy cutting. The chemical composition of the stainless steel comprises, by weight percentage, C≤0.15%, Si≤1.00%, Mn≤3.00%, P≤0.04%, S≥0.15%, Cr: 17.00%-19.00%, Ni: 8.00-10.00%, Cu: 1.50%-1.80%, Mo: 0.20%-0.60%, N≤0.10%, O≥0.0080%, H≤2.5ppm, and the rest is iron and unavoidable impurities.

[0008] Preferably, the cold working performance good free cutting austenitic stainless steel comprises the following chemical components by weight percentage, C: 0.03% ~ 0.06%, Si: 0.20% ~ 0.50%, Mn: 2.00% ~ 2.50%, P ≤ 0.032%, S: 0.27% ~ 0.29%, Cr: 17.50% ~ 17.80%, Ni: 8.05 ~ 8.15%, Mo: 0.22% ~ 0.30%, Cu: 1.55% ~ 1.65%, N: 0.035% ~ 0.055%, O: 0.0080% ~ 0.0100%, H ≤ 2ppm, the rest is iron and unavoidable impurities

[0009] The present invention also provides a method for preparing the above-mentioned austenitic stainless steel with excellent cold working performance and easy cutting, comprising the steps of: electric arc furnace smelting → AOD furnace refining → LF furnace refining → continuous casting → rolling → solid solution, the steel material is sequentially subjected to electric arc furnace smelting, AOD furnace refining, and LF furnace refining to obtain molten steel with target composition, a continuous casting machine is used to complete the molten steel into continuous casting billets, and the continuous casting billets are subjected to rolling and solid solution processes to obtain the above-mentioned stainless steel wire rod.

[0010] Preferably, during the electric arc furnace smelting process, scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi) is selected as the steel material, and the steel tapping P is controlled to be ≤0.032%, more preferably P ≤0.028%, to obtain crude molten steel.

[0011] Preferably, the AOD furnace smelting process includes: adding crude steel smelted in an electric arc furnace to an AOD furnace and then adding cold lime, using top and bottom combined oxygen blowing to raise the temperature to 1650-1700°C to achieve decarburization, with a target C content of 0.02% to 0.04%; reducing by adding ferrosilicon and silicon-manganese alloy, and adding fluorite to improve the fluidity of the slag, controlling the slag basicity R at 1.6 to 1.8, and finally adding ferrosulphide alloy to the molten steel according to the target sulfur content of 0.27% to 0.29% and the ferrosulphide recovery rate, with a target tapping temperature of 1600 to 1630°C, and more preferably, blowing 15-20Nm 3 oxygen.

[0012] Preferably, the LF furnace refining process includes: after the AOD smelting molten steel arrives at the station, adjusting the Ar gas flow rate to 500-600m 3 / h, take samples and measure the temperature when the slag has fluidity, add alloys according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel, then soft blow argon gas from the bottom for ≥5min to make the inclusions fully float and effectively reduce the hydrogen content in the molten steel, and finally control the hanging bag temperature at 1530-1560℃. More preferably, the sufficient soft blowing time can control the hydrogen content in the molten steel to ≤2ppm.

[0013] Preferably, the continuous casting process improves the shape of the cast sulfide in the billet into a uniformly distributed spherical or quasi-spherical shape by controlling the cooling system. A more preferred continuous casting process includes: a target superheat of 30 to 50°C, a casting speed setting of 1.0 to 1.2 m / min, a crystallizer water flow setting of 90 to 93 m / min, and a casting speed setting of 1.0 to 1.2 m / min. 3 / h, the water flow rate of the full roller section is set at 4.3~4.6m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 More preferably, the target molten steel obtained by LF furnace refining is continuously casted by an arc-shaped progressive straightening continuous casting machine to obtain a continuously cast square billet.

[0014] Preferably, the rolling process of the free-cutting austenitic stainless steel wire rod needs to ensure that the starting rolling temperature is set to avoid cracking caused by cooling during the rolling process and to achieve the target hot-rolled wire rod structure requirements. The more preferred starting rolling temperature is set to 1280-1300°C, and the rough rolling adopts head water-avoiding rolling to obtain the hot-rolled wire rod. The rolling specifications can be a variety of common specifications.

[0015] Preferably, the solutionizing step is performed by rapidly heating the hot-rolled wire rod to 1020-1040°C at 900-950°C / h and keeping the temperature for 120-150 minutes, and then cooling the hot-rolled wire rod to room temperature at 1000-1050°C / h.

[0016] Preferably, the room temperature tensile strength of the wire rod of the austenitic stainless steel with excellent cold working performance and easy cutting can reach 580-600 MPa, the elongation after fracture is 55.0%-60.0%, the cross-sectional shrinkage is 65%-70%, and the grain size rating is finer than 10 grades.

[0017] Preferably, the cold working performance is better than the turning performance of the free-cutting austenitic stainless steel: the surface roughness of the sample after turning is ≤1.0μm, the turning chips are easy to break, of which "C"-shaped turning chips account for as high as 50% to 60%, and the main turning force is ≤100N.

[0018] The functions and design principles of each chemical component in the present invention are described below.

[0019] Carbon (C) and nitrogen (N): Carbon and nitrogen are main austenite-forming elements. As the carbon and nitrogen contents increase, the austenite content in stainless steel can be significantly increased. At the same time, the strength and hardness of austenitic stainless steel also increase accordingly. The carbon content of the present invention is controlled at ≤0.15%, and the nitrogen content is controlled at ≤0.10%.

[0020] Silicon (Si): Silicon is a strong deoxidizer, which reduces the oxygen content in steel and improves the inclusions in steel. However, higher silicon content will also reduce the cold working performance of stainless steel, and affect the plasticity and chloride ion corrosion resistance of stainless steel. Therefore, the silicon content of the present invention is controlled to ≤1.00%.

[0021] Manganese (Mn): Manganese is an austenite-forming element. In steel, manganese easily forms manganese sulfide with sulfur, which fully improves the hot brittleness of the material caused by the formation of a large amount of iron sulfide on the grain boundaries in high-sulfur free-cutting stainless steel. In addition, manganese sulfide inclusions can serve as a stress concentration source during cutting, reduce cutting force and effectively improve turning performance. Therefore, the manganese content of the present invention is controlled to ≤3.0%.

[0022] Phosphorus (P): Phosphorus is a harmful element in steel, which causes cold brittleness of steel. The phosphorus content of the present invention is controlled to be ≤0.04%.

[0023] Sulfur (S): Sulfur is a harmful element for ordinary stainless steel, but as a typical free-cutting element, sulfur easily forms manganese sulfide inclusions with manganese (Mn) in steel. The morphology of such inclusions is the key to improving turning performance. The mechanism of action is that when the material is turned, a stress notch will form at the inclusion, reducing the cutting resistance. At the same time, manganese sulfide inclusions can also play a role in lubricating the tool. In addition, sulfide effectively improves the coarseness of austenitic stainless steel structure and improves the plastic toughness of austenitic stainless steel. Therefore, the sulfur content of the present invention is controlled to be ≥0.15%.

[0024] Chromium (Cr): Chromium is the main element in stainless steel. When the chromium content in the steel exceeds 10.5%, a passivation film will be formed on the surface, which hinders the further occurrence of oxidation reaction, thereby making the stainless steel have significant corrosion resistance. As the chromium content in the stainless steel increases, the pitting points of the stainless steel increase and the corrosion resistance improves. Therefore, the chromium content of the present invention is controlled at 17.00% to 19.00%.

[0025] Nickel (Ni): The main function of nickel is to form and stabilize austenite so that stainless steel has good strength, plasticity, toughness, low-temperature non-magnetic and other excellent properties. Increasing the nickel content is conducive to improving the cold working forming properties of austenitic stainless steel, but these properties can only be fully exerted when combined with chromium, so the nickel content of the present invention is controlled at 8.00% to 10.00%.

[0026] Copper (Cu): Copper can improve the corrosion resistance of stainless steel, improve the mechanical properties of stainless steel, and significantly improve the antibacterial effect of some stainless steels. Therefore, the copper content of the present invention is controlled at 1.50% to 1.80%.

[0027] Molybdenum (Mo): Mo is an important element in austenitic stainless steel. Its main function is to improve the corrosion resistance of austenitic stainless steel together with chromium, especially to improve the pitting corrosion resistance and crevice corrosion resistance. Therefore, the molybdenum content of the present invention is controlled at 0.20% to 0.60%.

[0028] Oxygen (O): Oxygen is mostly distributed in steel in the form of inclusions, and most steels require a lower inclusion level. Therefore, the oxygen content in stainless steel needs to be controlled at an extremely low level (≤20ppm). For free-cutting stainless steel, the higher the oxygen content, the more uniform the sulfide distribution and the better the morphology. Therefore, the oxygen content of the present invention is controlled at ≥0.0080%.

[0029] Hydrogen (H): Hydrogen is a harmful element in stainless steel. It mainly causes hydrogen embrittlement that destroys the crystal structure of steel, resulting in reduced plasticity of the material. On the other hand, hydrogen corrosion can destroy the metal passivation layer on the surface of stainless steel, causing corrosion to intensify. Therefore, the hydrogen content of the present invention is controlled to be ≤2.5ppm.

[0030] The free-cutting austenitic stainless steel with excellent cold working performance in the present invention is optimized through continuous casting process and oxygen content control, aiming to improve the uniformity of sulfide distribution inside and outside the free-cutting austenitic stainless steel, and adjusting the uniform distribution of matrix structure through heat treatment so that the material has excellent plasticity at room temperature. In addition, the sulfur content and manganese content are specified, and coarse austenite grains are pinned by manganese sulfide inclusions to effectively delay their deformation austenite recrystallization behavior, significantly improve the comprehensive mechanical properties and turning performance of the material, ensure the excellent cold working performance of the material, and have broad market application prospects.

[0031] Compared with the prior art, the cold working performance and easy-to-cut austenitic stainless steel of the present invention has the following significant beneficial effects:

[0032] 1. The austenitic stainless steel with excellent cold working performance and easy cutting designed and produced by the present invention has very excellent mechanical properties under room temperature, wherein the room temperature tensile strength is 580-600MPa, the elongation after fracture is 55.0%-60.0%, and the cross-sectional shrinkage is 65%-70%.

[0033] 2. The cold processing performance of the easy-to-cut austenitic stainless steel produced by the present invention has excellent turning performance, among which the surface roughness of the sample after turning is ≤1.0μm, the turning chips are easy to break, among which the "C" shaped turning chips account for as high as 50% to 60%, the main turning force is ≤100N, and the turning performance is equivalent to or even better than the Japanese standard SUS303Cu. The stability of the cold processing performance of the material has been improved, which greatly improves the processing yield and efficiency of austenitic stainless steel.

[0034] 3. The cold working performance of the easy-to-cut austenitic stainless steel designed and produced by the present invention is excellent and the transverse microstructure grain size is uniformly finer than grade 10.

[0035] The steel of the present invention has excellent performance, has broad market application prospects, and has a simple preparation method, and is suitable for large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a distribution diagram of stainless steel sulfides in Example 2 of the present invention.

[0037] Figure 2 This is a distribution diagram of stainless steel sulfides in comparative example 1 of the present invention.

[0038] Figure 3 This is the distribution diagram of sulfide in SUS303Cu stainless steel, a comparative example of the present invention.

[0039] Figure 4 This is a distribution diagram of stainless steel sulfides in comparative example 2 of the present invention.

[0040] Figure 5 This is the room temperature transverse microstructure distribution of the stainless steel of Example 2 of the present invention.

[0041] Figure 6 This is the room temperature lateral microstructure distribution of SUS303Cu stainless steel, a comparative example of the present invention.

[0042] Figure 7 This is a chip breaking morphology diagram of the stainless steel turning experiment according to Example 2 of the present invention.

[0043] Figure 8 This is a chip breaking morphology diagram of the SUS303Cu stainless steel turning experiment in the comparative example of the present invention. DETAILED DESCRIPTION

[0044] In order to better clarify and understand the purpose, process scheme and advantages of the present invention, the technical scheme and implementation method of the present invention are further described clearly, completely and in detail through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to explaining and interpreting the present invention, and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0045] The experimental methods and conditions used in the embodiments of the present invention are conventional methods and conventional conditions unless otherwise specified. The materials, reagents or instruments used in the embodiments, unless otherwise specified, can be obtained from commercial sources or prepared by conventional methods. The reaction conditions embodied in the content of the invention of the present invention can achieve the reaction and obtain the product of the expected effect. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention.

[0046] Example 1

[0047] The composition and mass fraction of the austenitic stainless steel with excellent cold working performance and easy cutting performance in this embodiment are shown in Table 1;

[0048] In this embodiment, the austenitic stainless steel with excellent cold working performance and easy cutting is manufactured by the following method: electric arc furnace smelting → AOD refining → LF refining → continuous casting → rolling → solid solution, which is specifically as follows:

[0049] (1) Electric arc furnace smelting: The electric arc furnace melts scrap steel, and uses scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi). The target crude steel molten P is ≤ 0.028%, and the actual value is 0.024%;

[0050] (2) AOD refining: The crude steel smelted in the electric arc furnace is added to the AOD furnace, and then 1200 kg of cold lime is added. The temperature is raised to 1650-1700 ° C by top and bottom oxygen blowing to achieve decarburization. The target C content is 0.02%-0.04%, and the actual value is 0.036%. Silicon iron and silicon manganese alloy are added for reduction. At the same time, fluorite is added to improve the fluidity of the slag. The slag basicity is controlled at R 1.6-1.8, and the actual value is 1.67. Finally, according to the target sulfur content of 0.27%-0.29% and the ferrosulphide recovery rate (60%-70%), 350-400 kg of ferrosulphide alloy is added to the molten steel, and the actual ferrosulphide is 380 kg. The actual sulfur content is 0.281%. The target tapping temperature is 1600-1630 ° C, and the actual value is 1616 ° C. 15-20 Nm 3 Oxygen, actual value is 16Nm 3 .

[0051] (3) LF refining: After the above-mentioned AOD smelting molten steel arrives at the station, the Ar gas flow rate is adjusted to 500-600m 3 / h, when the slag becomes fluid, sampling and temperature measurement are carried out, and alloy is added according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel. Subsequently, argon is soft-blown at the bottom for ≥5min, the actual value is 6 minutes, so that the inclusions can fully float up, and finally the ladle temperature is controlled at 1530-1560℃, the actual value is 1535℃, the target H content is ≤2.5ppm, and the actual value is 1.9ppm.

[0052] (4) Continuous casting: The target molten steel obtained by LF refining is continuously cast using an arc progressive straightening continuous casting machine. The target superheat during the continuous casting process is 30-50°C, the actual value is 42°C, the casting speed setting value is 1.0-1.2 m / min, the actual value is 1.05-1.15 m / min, and the crystallizer water flow setting value is 90-93 m 3 / h, the actual value is 91m 3 / h, the water flow rate of the full roller section is set at 4.3~4.6m 3 / h, the actual value is 4.4m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 / h, the actual value is 4.0m 3 / h.

[0053] (5) Wire rod rolling: The continuous casting billet produced above is heated by a stepping furnace, wherein the starting rolling temperature setting value is 1280-1300°C, and the actual value is 1295°C. The rolling specifications can be various common specifications. The rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

[0054] (6) Heat treatment process: The austenitic stainless steel wire rod prepared as described above is subjected to solution treatment in an annular solution furnace, the hot-rolled wire rod is rapidly heated to 1025°C at 900°C / h and kept at this temperature for 130 min, and then cooled to room temperature at 1000°C / h.

[0055] The components of Example 1 meet the control requirements, as shown in Table 1, and the wire rod yield is 97.6%. After heat treatment, the wire rod has a room temperature tensile strength of 586MPa, an elongation after fracture of 56%, and a cross-sectional shrinkage of 66.0%. In the turning performance test, the surface roughness after turning is 0.97μm, the proportion of "C" chips is 58%, and the main cutting force is 91N. The main mechanical properties are shown in Table 2, and the turning performance evaluation is shown in Table 3.

[0056] Comparative Example 1

[0057] This comparative example is a method for preparing free-cutting austenitic stainless steel before continuous casting process optimization, and its composition and mass fraction are shown in Table 1:

[0058] The free-cutting austenitic stainless steel in this comparative example is manufactured by the following method: electric arc furnace smelting → AOD refining → LF refining → continuous casting → rolling → solid solution, as follows:

[0059] (1) Electric arc furnace smelting: The electric arc furnace melts scrap steel, and uses scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi). The target crude steel molten P is ≤ 0.028%, and the actual value is 0.0215%;

[0060] (2) AOD refining: The crude steel smelted in the electric arc furnace is added to the AOD furnace, and then 1200 kg of cold lime is added. The temperature is raised to 1650-1700 ° C by top and bottom oxygen blowing to achieve decarburization. The target C content is 0.02%-0.04%, and the actual value is 0.0312%. Silicon iron and silicon manganese alloy are added for reduction. At the same time, fluorite is added to improve the fluidity of the slag. The slag basicity is controlled at R 1.6-1.8, and the actual value is 1.63. Finally, according to the target sulfur content of 0.27%-0.29% and the ferrosulphide recovery rate (60%-70%), 350-400 kg of ferrosulphide alloy is added to the molten steel, and the actual ferrosulphide is 372 kg. The actual sulfur content is 0.274%. The target tapping temperature is 1600-1630 ° C, and the actual value is 1612 ° C. 15-20 Nm 3 Oxygen, actual value is 17Nm 3 .

[0061] (3) LF refining: After the above-mentioned AOD smelting molten steel arrives at the station, the Ar gas flow rate is adjusted to 500-600m 3 / h, when the slag becomes fluid, sampling and temperature measurement are carried out, and alloy is added according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel. Subsequently, argon is soft-blown at the bottom for ≥5min, with an actual value of 6 minutes, to allow inclusions to fully float. Finally, the ladle temperature is controlled at 1530-1560℃, with an actual value of 1534℃. The target H content is ≤2.5ppm, and the actual value is 1.9ppm.

[0062] (4) Continuous casting: The target molten steel obtained by LF refining is continuously cast using an arc progressive straightening continuous casting machine. The target superheat during the continuous casting process is 30-50°C, the actual value is 42°C, the casting speed setting value is 1.0-1.2 m / min, the actual value is 1.05-1.15 m / min, and the crystallizer water flow setting value is 90-100 m 3 / h, the actual value is 95m 3 / h, the water flow rate of the full roller section is set at 3.1~3.7m 3 / h, the actual value is 3.4m 3 / h, the water flow rate of the clamping section is set at 2.9~3.2m 3 / h, the actual value is 3.0m 3 / h.

[0063] (5) Wire rod rolling: The continuous casting billet produced above is heated by a stepping furnace, wherein the starting rolling temperature setting value is 1280-1300°C, and the actual value is 1288°C. The rolling specifications can be various common specifications. The rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

[0064] (6) Heat treatment process: The austenitic stainless steel wire rod prepared as described above is subjected to solution treatment in an annular solution furnace, the hot-rolled wire rod is rapidly heated to 1027°C at 910°C / h and kept at this temperature for 128 min, and then cooled to room temperature at 1010°C / h.

[0065] The ingredients of comparative example 1 meet the control requirements, as shown in Table 1, and the wire rod yield is 97.6%. After heat treatment, the wire rod has a room temperature tensile strength of 611MPa, an elongation after fracture of 51%, and a cross-sectional shrinkage of 61.0%. In the turning performance test, the surface roughness after turning is 0.99μm, the proportion of "C" chips is 49%, and the main cutting force is 101N. The main mechanical properties are shown in Table 2, and the turning performance evaluation is shown in Table 3.

[0066] Comparative Example 2

[0067] This comparative example is a method for preparing free-cutting austenitic stainless steel without controlling the oxygen content, and its composition and mass fraction are shown in Table 1:

[0068] The free-cutting austenitic stainless steel in this comparative example is manufactured by the following method: electric arc furnace smelting → AOD refining → LF refining → continuous casting → rolling → solid solution, as follows:

[0069] (1) Electric arc furnace smelting: The electric arc furnace melts scrap steel, and uses scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi). The target crude steel molten P is ≤ 0.028%, and the actual value is 0.0221%;

[0070] (2) AOD refining: The crude steel smelted in the electric arc furnace is added to the AOD furnace, and then 1200 kg of cold lime is added. The temperature is raised to 1650-1700 ° C by top and bottom oxygen blowing to achieve decarburization. The target C content is 0.02%-0.04%, and the actual value is 0.0324%. Reduction is carried out by adding ferrosilicon and silicon-manganese alloy. At the same time, fluorite is added to improve the fluidity of the slag. The slag basicity R is controlled at 1.6-1.8, and the actual value is 1.67. Finally, according to the target sulfur content of 0.27%-0.29% and the ferrosulphide recovery rate (60%-70%), 350-400 kg of ferrosulphide alloy is added to the molten steel, and the actual ferrosulphide added is 391 kg. The actual sulfur content is 0.288%, the target steel tapping temperature is 1600-1630 ° C, and the actual value is 1612 ° C.

[0071] (3) LF refining: After the above-mentioned AOD smelting molten steel arrives at the station, the Ar gas flow rate is adjusted to 500-600m 3 / h, take samples and measure the temperature when the slag becomes fluid, add alloy according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel, then soft blow argon at the bottom for ≥5min, the actual value is 7 minutes, so that the inclusions can fully float, and finally control the temperature of the hanging bag at 1530-1560℃, the actual value is 1544℃, the target H content is ≤2.5ppm, the actual value is 1.6ppm.

[0072] (4) Continuous casting: The target molten steel obtained by LF refining is continuously cast using an arc progressive straightening continuous casting machine. The target superheat during the continuous casting process is 30-50°C, the actual value is 39°C, the casting speed setting value is 1.0-1.2m / min, the actual value is 1.05-1.10m / min, and the crystallizer water flow setting value is 90-93m 3 / h, the actual value is 91.5m 3 / h, the water flow setting value of the full roller section is 4.3-4.6m 3 / h, the actual value is 4.36m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 / h, the actual value is 4.05m 3 / h.

[0073] (5) Wire rod rolling: The continuous casting billet produced above is heated by a stepping furnace, wherein the starting rolling temperature setting value is 1280-1300°C, and the actual value is 1291°C. The rolling specifications can be various common specifications. The rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

[0074] (6) Heat treatment process: The austenitic stainless steel wire rod prepared as described above is subjected to solution treatment in an annular solution furnace, the hot-rolled wire rod is rapidly heated to 1027°C at 910°C / h and kept at this temperature for 128 min, and then cooled to room temperature at 1010°C / h.

[0075] The specific components of comparative example 2 are shown in Table 1, and the wire rod yield is 96.3%. After heat treatment, the wire rod has a room temperature tensile strength of 623MPa, an elongation after fracture of 50%, and a cross-sectional shrinkage of 61%. In the turning performance test, the surface roughness after turning is 1.12μm, the proportion of "C" chips is 41%, and the main cutting force is 110N. The main mechanical properties are shown in Table 2, and the turning performance evaluation is shown in Table 3.

[0076] Example 2

[0077] The composition and mass fraction of the austenitic stainless steel with excellent cold working performance and easy cutting performance in this embodiment are shown in Table 1;

[0078] In this embodiment, the austenitic stainless steel with excellent cold working performance and easy cutting is manufactured by the following method: electric arc furnace smelting → AOD refining → LF refining → continuous casting → rolling → solid solution, which is specifically as follows:

[0079] (1) Electric arc furnace smelting: The electric arc furnace melts scrap steel, and uses scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi). The target crude steel molten P is ≤ 0.028%, and the actual value is 0.025%;

[0080] (2) AOD refining: The crude steel smelted in the electric arc furnace is added to the AOD furnace, and then 1200 kg of cold lime is added. The temperature is raised to 1650-1700 ° C by top and bottom oxygen blowing to achieve decarburization. The target C content is 0.02%-0.04%, and the actual value is 0.033%. Silicon iron and silicon manganese alloy are added for reduction. At the same time, fluorite is added to improve the fluidity of the slag. The slag basicity is controlled at R 1.6-1.8, and the actual value is 1.62. Finally, according to the target sulfur content of 0.27%-0.29% and the ferrosulphide recovery rate (60%-70%), 350-400 kg of ferrosulphide alloy is added to the molten steel, and the actual ferrosulphide is 370 kg. The actual sulfur content is 0.279%. The target tapping temperature is 1600-1630 ° C, and the actual value is 1621 ° C. 15-20 Nm 3 Oxygen, actual value is 18Nm 3 .

[0081] (3) LF refining: After the above-mentioned AOD smelting molten steel arrives at the station, the Ar gas flow rate is adjusted to 500-600m 3 / h, when the slag becomes fluid, sampling and temperature measurement are carried out, and alloy is added according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel. Subsequently, argon is softly blown from the bottom for ≥5min, and the actual value is 7 minutes, so that the inclusions can float up fully. Finally, the temperature of the hanging bag is controlled at 1530-1560℃, and the actual value is 1539℃. The target H content is ≤2.5ppm, and the actual value is 1.8ppm.

[0082] (4) Continuous casting: The target molten steel obtained by LF refining is continuously cast using an arc progressive straightening continuous casting machine. The target superheat during the continuous casting process is 30-50°C, the actual value is 44°C, the casting speed setting value is 1.0-1.2 m / min, the actual value is 1.01-1.11 m / min, and the crystallizer water flow setting value is 90-93 m 3 / h, the actual value is 92.5m 3 / h, the water flow rate of the full roller section is set at 4.3~4.6m 3 / h, the actual value is 4.5m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 / h, the actual value is 4.1m 3 / h.

[0083] (5) Wire rod rolling: The continuous casting billet produced above is heated by a stepping furnace, wherein the starting rolling temperature setting value is 1280-1300°C, and the actual value is 1293°C. The rolling specifications can be various common specifications. The rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

[0084] (6) Heat treatment process: The austenitic stainless steel wire rod prepared as described above is subjected to solution treatment in an annular solution furnace, the hot-rolled wire rod is rapidly heated to 1030°C at 900°C / h and kept at this temperature for 140 min, and then cooled to room temperature at 1000°C / h.

[0085] The components of Example 2 meet the control requirements, as shown in Table 1, and the wire rod yield is 97.8%. After heat treatment, the wire rod has a room temperature tensile strength of 591 MPa, an elongation after fracture of 57%, and a cross-sectional shrinkage of 68.0%. In the turning performance test, the surface roughness after turning is 0.91 μm, the proportion of "C" chips is 56%, and the main cutting force is 87 N. The main mechanical properties are shown in Table 2, and the turning performance evaluation is shown in Table 3.

[0086] Take Nippon Steel SUS303Cu as a comparative example, the specific composition is shown in Table 1, and relevant performance tests are carried out. Figures 1 to 6 The internal sulfide distribution, room temperature tensile properties and turning properties of the stainless steel of Example 2 of the present invention and the comparative example SUS303Cu are compared and explained. Figure 1 The distribution diagram of stainless steel sulfide in Example 2 is attached. Figure 2The distribution diagram of sulfide of SUS303Cu stainless steel is shown in Table 1. Figure 1 and Figure 2 Comparing the sulfide distribution, it can be seen that the sulfide distribution of Example 2 is more uniform and dispersed, and the sulfide distribution of SUS303Cu has a local segregation phenomenon.

[0087] Attached Figure 3 The lateral structure distribution of the stainless steel in Example 2 is shown in the figure. It can be observed from the figure that the room temperature structure of Example 2 is uniform and fine, and there is no coarse austenite structure. Its grain size rating is finer than level 10, which helps to improve the comprehensive mechanical properties of the material. Figure 4 This is the lateral microstructure distribution of the comparative example SUS303Cu stainless steel. It can be observed from the figure that the grain size rating of the comparative example SUS303Cu is finer than level 10.

[0088] Attached Figure 5 Chip breaking morphology of stainless steel turning experiment in Example 2, attached Figure 6 This is the chip breaking morphology of the comparative SUS303Cu stainless steel turning experiment. Figure 5 and Figure 6 Comparing the chip breaking morphology images of the turning experiments, it can be seen that the proportion of "C"-shaped chips in both is relatively high, indicating that the chips are easy to clean during turning.

[0089] Example 3

[0090] The composition and mass fraction of the austenitic stainless steel with excellent cold working performance and easy cutting performance in this embodiment are shown in Table 1;

[0091] In this embodiment, the austenitic stainless steel with excellent cold working performance and easy cutting is manufactured by the following method: electric arc furnace smelting → AOD refining → LF refining → continuous casting → rolling → solid solution, which is specifically as follows:

[0092] (1) Electric arc furnace smelting: The electric arc furnace melts scrap steel, and uses scrap stainless steel with low P and low five harmful elements (Pb, Sn, As, Sb, Bi). The target crude steel molten P is ≤ 0.028%, and the actual value is 0.027%;

[0093] (2) AOD refining: The crude steel smelted in the electric arc furnace is added to the AOD furnace, and then 1200 kg of cold lime is added. The temperature is raised to 1650-1700 ° C by top and bottom oxygen blowing to achieve decarburization. The target C content is 0.02%-0.04%, and the actual value is 0.038%. Silicon iron and silicon manganese alloy are added for reduction. At the same time, fluorite is added to improve the fluidity of the slag. The slag basicity is controlled at R 1.6-1.8, and the actual value is 1.74. Finally, according to the target sulfur content of 0.27%-0.29% and the ferrosulphide recovery rate (60%-70%), 350-400 kg of ferrosulphide alloy is added to the molten steel. The actual ferrosulphide is 378 kg, and the actual sulfur content is 0.284%. The target tapping temperature is 1600-1630 ° C, and the actual value is 1627 ° C. 15-20 Nm 3 Oxygen, actual value is 19Nm 3 .

[0094] (3) LF refining: After the above-mentioned AOD smelting molten steel arrives at the station, the Ar gas flow rate is adjusted to 500-600m 3 / h, when the slag becomes fluid, sampling and temperature measurement are carried out, and alloy is added according to the sample results to slightly adjust the composition of the molten steel to obtain the target molten steel. Subsequently, argon is soft-blown at the bottom for ≥5min, with an actual value of 8 minutes, to allow the inclusions to float fully. Finally, the ladle temperature is controlled at 1530-1560℃, with an actual value of 1544℃. The target H content is ≤2.5ppm, and the actual value is 1.7ppm.

[0095] (4) Continuous casting: The target molten steel obtained by LF refining is continuously cast using an arc progressive straightening continuous casting machine. The target superheat during the continuous casting process is 30-50°C, the actual value is 45°C, the casting speed setting value is 1.0-1.2 m / min, the actual value is 1.07-1.17 m / min, and the crystallizer water flow setting value is 90-93 m 3 / h, the actual value is 92.8m 3 / h, the water flow rate of the full roller section is set at 4.3~4.6m 3 / h, the actual value is 4.33m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 / h, the actual value is 4.15m 3 / h.

[0096] (5) Wire rod rolling: The continuous casting billet produced above is heated by a stepping furnace, wherein the starting rolling temperature setting value is 1280-1300°C, and the actual value is 1297°C. The rolling specifications can be various common specifications. The rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

[0097] (6) Heat treatment process: The austenitic stainless steel wire rod prepared as described above is subjected to solution treatment in an annular solution furnace, the hot-rolled wire rod is rapidly heated to 1045°C at 900°C / h and kept at this temperature for 140 min, and then cooled to room temperature at 1000°C / h.

[0098] The components of Example 3 meet the control requirements, as shown in Table 1, and the wire rod yield is 97.8%. After heat treatment, the wire rod has a room temperature tensile strength of 595MPa, an elongation after fracture of 58%, and a cross-sectional shrinkage of 69.0%. In the turning performance test, the surface roughness after turning is 0.88μm, the proportion of "C" chips is 54%, and the main cutting force is 79N. The main mechanical properties are shown in Table 2, and the turning performance evaluation is shown in Table 3.

[0099] Table 1 shows the composition (wt%) of the austenitic stainless steel with excellent cold working performance and easy cutting prepared in each embodiment and comparative example.

[0100]

[0101] Table 2 shows the room temperature tensile properties of the austenitic stainless steel with excellent cold working performance and easy cutting prepared in each embodiment and comparative example.

[0102]

[0103]

[0104] Table 3 shows the turning test results of austenitic stainless steel with excellent cold working performance and easy cutting prepared in each embodiment and comparative example

[0105]

[0106] Through the above performance test results, combined with the attached Figures 1 to 8It can be found that the cold working performance of the austenitic stainless steel produced by the present invention is good and easy to cut. The internal sulfidation distribution at room temperature is more dispersed, the uniformity of the organization distribution is good, and the plasticity is excellent. At the same time, the stability of the subsequent cold working performance is guaranteed. The stability is reflected in: 1) The tensile strength of Examples 1 to 3 produced by the process required by the present invention is stable at 580 to 600 MPa, the elongation is 55.0% to 60.0%, and the cross-sectional shrinkage is 65.0% to 70.0%. There is no obvious deviation from the data; 2) The transverse organization grain size rating of Examples 1 to 3 is uniformly finer than 10 levels, and there is no mixed crystal and coarse crystal phenomenon; 3) The cold working yield rate of Examples 1 to 3 is 98%, and there is no wire breakage during material processing. The comparative example and Nippon Steel SUS303Cu processing process have a wire breakage rate of 3-5%. The cold working performance excellent and easy-to-cut austenitic stainless steel wire rod produced by the present invention was subjected to a comprehensive evaluation test on turning performance, and the surface roughness, turning force, and C-shaped chip proportion of the samples after turning were compared. The results showed that the surface roughness, chip performance, and main turning force of the stainless steel of Examples 1-3 after turning were better than those of Japanese standard SUS303Cu and the control example, so the comprehensive turning performance was greatly improved.

[0107] In summary, the present invention obtains dispersed sulfides in the material matrix by precisely controlling the oxygen content and hydrogen content and optimizing the continuous casting process. The evenly distributed and dispersed sulfides effectively pin the original austenite grain boundaries, refine the room temperature structure, optimize the uniformity of the structure, and avoid hydrogen embrittlement caused by excessive hydrogen content. After turning, the surface roughness of the parts is low, the chip breaking effect is good, and the turning force is low. Excellent turning performance. The cold processing performance and easy-to-cut austenitic stainless steel manufactured by the composition and process designed by the present invention can effectively solve the unstable cold processing performance of austenitic stainless steel and no broken wire after processing, ensuring smooth cold processing of this series of materials while improving processing efficiency.

[0108] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. An austenitic stainless steel with excellent cold working performance and easy cutting, characterized in that: The chemical composition, by weight percentage, includes C≤0.15%, Si≤1.00%, Mn≤3.00%, P≤0.04%, S≥0.15%, Cr: 17.00%~19.00%, Ni: 8.00%~10.00%, Cu: 1.50%~1.80%, Mo: 0.20%~0.60%, N≤0.10%, O≥0.0080%, H≤2.5ppm, and the rest is iron and unavoidable impurities.

2. The austenitic stainless steel with excellent cold working performance and easy cutting as claimed in claim 1, characterized in that: The chemical composition, by weight percentage, includes C: 0.03% ~ 0.06%, Si: 0.2% ~ 0.5%, Mn: 2.00% ~ 2.50%, P ≤ 0.032%, S: 0.27% ~ 0.29%, Cr: 17.50% ~ 17.80%, Ni: 8.05 ~ 8.15%, Mo: 0.22% ~ 0.30%, Cu: 1.55 ~ 1.65%, N: 0.035% ~ 0.055%, O: 0.0080% ~ 0.0100%, H ≤ 2ppm, and the rest is iron and unavoidable impurities.

3. A method for preparing the austenitic stainless steel with excellent cold working performance and easy cutting according to claim 1 or 2, comprising the following steps: Electric arc furnace smelting, AOD furnace smelting, LF furnace refining, continuous casting, rolling and solutionizing.

4. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: Scrap stainless steel with low phosphorus content and low five harmful elements is added to an electric arc furnace for smelting, and the phosphorus content of the steel is controlled to be less than or equal to 0.032% to obtain crude molten steel.

5. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: The AOD furnace smelting process includes: adding crude steel smelted in an electric arc furnace into the AOD furnace and then adding cold lime, using top and bottom combined oxygen blowing to increase the temperature for decarburization, with a target C content of 0.02% to 0.04%; reducing by adding ferrosilicon and silicon-manganese alloy, and adding fluorite to improve the fluidity of the slag, controlling the slag basicity R at 1.6 to 1.8, and finally adding ferrosulphide alloy to the molten steel according to the target sulfur content of 0.27% to 0.29% and the ferrosulphide recovery rate, with a target tapping temperature of 1600 to 1630°C, and blowing 15-20Nm 3 oxygen.

6. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: The LF furnace refining process includes: After the AOD smelting molten steel arrives at the station, adjust the Ar gas flow rate to 500-600m 3 / h, take samples and measure the temperature when the slag becomes fluid, add alloy according to the sampling results to slightly adjust the composition of the molten steel to obtain the target molten steel, then softly blow argon at the bottom for ≥5min to make the inclusions fully float and effectively reduce the hydrogen content in the molten steel, finally control the ladle temperature at 1530-1560℃.

7. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: The continuous casting process includes: target superheat 30 ~ 50 ℃, casting speed setting value 1.0 ~ 1.2m / min, crystallizer water flow setting value 90 ~ 93m 3 / h, the water flow rate of the full roller section is set at 4.3~4.6m 3 / h, the water flow rate of the clamping section is set at 3.9~4.2m 3 / h.

8. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: Rolling includes: The starting rolling temperature of the continuous casting slab is set at 1280-1300°C, and the rough rolling adopts head water-avoiding rolling to obtain hot-rolled wire rod.

9. The method for preparing austenitic stainless steel with excellent cold working performance and easy cutting according to claim 3, characterized in that: Solid solution includes: The hot rolled wire rod is rapidly heated to 1020-1040°C at 900-950°C / h and kept at this temperature for 120-150 minutes, and then water cooled to room temperature at 1000-1050°C / h.

10. The austenitic stainless steel with excellent cold working performance and easy cutting according to claim 1 or 2, or the austenitic stainless steel with excellent cold working performance and easy cutting prepared by the preparation method according to claims 3 to 9, characterized in that: The room temperature tensile strength of the austenitic stainless steel wire rod can reach 580-600 MPa, the elongation after fracture is 55.0%-60.0%, the cross-sectional shrinkage is 65%-70%, and the grain size rating is finer than 10 grades.

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