Soft magnetic stainless steel wire rod with ultrahigh corrosion resistance, good machinability and excellent plasticity and toughness and preparation method of soft magnetic stainless steel wire rod

Abstract

The invention belongs to the technical field of soft magnetic stainless steel, and provides a soft magnetic stainless steel wire rod with ultrahigh corrosion resistance, good machinability and excellent plasticity and toughness and a preparation method of the soft magnetic stainless steel wire rod. The stainless steel wire rod comprises the following chemical components in percentage by mass: less than or equal to 0.020% of C, 1.20 to 2.00% of Si, less than or equal to 0.50% of Mn, 18.0 to 20.0% of Cr, less than or equal to 0.30% of Ni, 2.50 to 3.00% of Mo, less than or equal to 0.020% of N, less than 0.020% of P, 0.008 to 0.015% of S, 0.030 to 0.050% of Se, 0.20 to 0.30% of Nb and the balance of Fe and inevitable impurities. The material has ultrahigh corrosion resistance, excellent soft magnetic performance, good free-cutting performance and good plasticity and toughness, is suitable for subsequent drawing machining and turning machining, and has a wide market application prospect. And the preparation method provided by the invention is high in yield and suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of soft magnetic stainless steel, and relates to technical fields such as metal smelting, rolling, heat treatment, etc. Specifically, it relates to a soft magnetic stainless steel with excellent corrosion resistance, good machinability and excellent plastic toughness, and a preparation method thereof. Background Art

[0002] Soft magnetic stainless steel wire rods are used to process various solenoid valves for intelligent control. First, the material needs to be drawn in multiple passes, and the material needs to have good plastic toughness so as not to crack or break during the drawing process; then it needs to be processed into various complex shapes through grinding, turning and drilling, and the material needs to have good machinability; at the same time, soft magnetic stainless steel also needs to meet the usage requirements in liquid media, chlorides, chemical reagents and other harsh environments, and the corrosion resistance requirements of the material are also getting higher and higher.

[0003] However, there are contradictory problems among these properties. For example, increasing the sulfur content in the material to improve the turning performance often sacrifices the corrosion resistance; increasing the Cr and Mo content in the material to improve the corrosion resistance, but the increase in the Cr and Mo content will significantly reduce the plastic toughness of the material, which is not conducive to the subsequent drawing process of the material; Therefore, obtaining a soft magnetic stainless steel material with excellent corrosion resistance, good machinability and excellent plastic toughness is a difficult and painful problem in the industry, and it is also the fundamental reason for the gap between domestic and foreign soft magnetic stainless steel materials in China. Summary of the Invention

[0004] To solve the problems existing in the above-mentioned prior art, the present invention provides a soft magnetic stainless steel with excellent corrosion resistance, good machinability and excellent plastic toughness; it also provides a manufacturing method of the soft magnetic stainless steel. The preparation method of the stainless steel of the present invention is easy to operate and suitable for industrial mass production.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The invention provides a soft magnetic stainless steel with ultra-high corrosion resistance, good machinability and excellent plasticity and toughness. The chemical components of the wire rod include, by mass percentage, C≤0.020%, Si: 1.20-2.00%, Mn≤0.50%, Cr: 18.0-20.0%, Ni:≤0.30%, Mo: 2.50-3.00%, N≤0.020%, P<0.020%, S: 0.008-0.015%, Se: 0.030-0.050%, Nb: 0.20-0.30%, and the balance is Fe and unavoidable impurities. The invention improves the corrosion resistance of the material by reducing the contents of C and Mn and increasing the contents of Cr (≥18%) and Mo (≥2.5%), controls the contents of S: 0.008-0.015% and Se: 0.030-0.050% to optimize the turning performance while avoiding a significant decrease in the corrosion resistance; adds Nb content to refine the grain size of the material to improve the plasticity and toughness, thereby obtaining a soft magnetic stainless steel material with ultra-high corrosion resistance, good cutting performance, and excellent plasticity and toughness.

[0007] Furthermore, the chemical components of the above-mentioned stainless steel wire rod, calculated by mass percentage, include C: 0.010-0.020%, Si: 1.6-1.7%, Mn: 0.2-0.4%, Cr: 18.50-19.00%, Ni: 0.1-0.3%, Mo: 2.55-2.65%, N: 0.010-0.020%, P: 0.010-0.020%, S: 0.008-0.015%, Se: 0.030-0.050%, Nb: 0.20-0.30%, and the balance is Fe and unavoidable impurities.

[0008] The invention provides a method for preparing a soft magnetic stainless steel wire rod with ultra-high corrosion resistance, good machinability, excellent plasticity and toughness. The method comprises the following steps: subjecting a furnace charge to arc furnace smelting, AOD furnace refining, LF refining furnace refining, die casting, ingot blanking, primary heat treatment, rolling, secondary heat treatment and the like in sequence, so as to obtain a soft magnetic stainless steel wire rod with ultra-high corrosion resistance, good machinability, excellent plasticity and toughness. By adopting the preparation method, the comprehensive yield rate of the material is ≥85%.

[0009] Furthermore, in the electric arc furnace smelting process, the charge is melted and the molten steel is initially smelted by the electric arc furnace, and the P content is controlled to be ≤0.020% when the steel is tapped.

[0010] Furthermore, in the AOD furnace refining process, ferrosilicon, pure manganese, ferrochrome and ferromolybdenum are added to fine-tune the content of Si, Mn, Cr and Mo elements in the molten steel, so that the composition of the finished stainless steel wire rod meets the target mass percentage ratio requirements, and the carbon and nitrogen contents in the molten steel are removed to C≤0.015% and N≤0.010%.

[0011] Further, in the refining process of the LF refining furnace, ferroniobium is added to the furnace to adjust the Nb content in the molten steel to 0.20 - 0.30%. At the same time, sulfur wire and Se wire are fed in to control S and Se in the molten steel at S: 0.008 - 0.015%, Se: 0.030 - 0.050%. After soft blowing argon for stirring for more than 10 minutes, the molten steel is tapped.

[0012] Further, in the ingot casting process, a large-sized ingot mold is used for casting, and more preferably, a 17 - 20-inch ingot mold is used for casting. The ladle temperature is controlled at 1500 - 1530°C.

[0013] Further, in the ingot heating and blooming process, the ingot is loaded into a heating furnace, the heating temperature is 1100 - 1150°C, and the holding time is 1.5 - 2.5 hours.

[0014] Further, the bloomed billet is subjected to a primary heat treatment annealing process, the annealing temperature is 680 - 720°C, and the holding time is 4 - 6 hours.

[0015] Further, in the wire rod rolling process, the billet after blooming and annealing is loaded into a heating furnace, the heating temperature is 950 - 1000°C, the holding time is 1 - 2 hours, and the final rolling temperature is controlled ≤850°C during rolling. Further, the wire rod specification is φ5.5 - 30mm.

[0016] Further, after wire rod rolling, a secondary heat treatment is carried out. In the secondary heat treatment annealing process of the wire rod, the rolled wire rod is loaded into a bell-type annealing furnace for heating, the annealing temperature is controlled at 800 - 880°C, the holding time is more than 60 minutes, and more preferably the temperature is 780 - 860°C and the holding time ≥2 hours.

[0017] Generally speaking, compared with the prior art through the above technical solutions provided by the present invention, the following beneficial effects can be achieved:

[0018] (1) By adding ultra-high contents of Cr (≥18%) and Mo (≥2.5%) to the steel and using AOD smelting to control the contents of harmful elements C and P in the steel at ≤0.02% simultaneously, the present invention enables the material to have ultra-high corrosion resistance (salt spray test ≥1000 hours without rusting);

[0019] (2) By increasing ferrite-forming elements such as Si, Cr, Mo, Nb, etc. and decreasing austenite-forming elements such as C, N, Mn, Ni, etc., and adopting a suitable heat treatment process after rolling, the present invention enables the structure of the material to be a pure ferrite structure, thus having excellent soft magnetic properties (saturation magnetic induction intensity ≥1.5T, coercive force ≤250A / m);

[0020] (3) Since the soft magnetic stainless steel needs to be subsequently processed into parts by turning, drilling and other operations, the material must have good easy-cutting performance. Therefore, the present invention adds an appropriate amount of S, Se and other elements to the steel to improve the cutting performance. In order to avoid excessive S content reducing the corrosion resistance of the material, the S content in the steel is controlled at 0.008-0.015%, and at the same time, an appropriate amount of Se element is added that does not reduce the corrosion resistance, and its content is controlled to 0.030-0.050%, so that the material has good turning performance while still ensuring excellent corrosion resistance;

[0021] (4) In the current field, ultra-pure ferritic stainless steel is prone to form coarse grain structure during hot working, which reduces the plastic toughness of the material and leads to brittle fracture, center cracking and other problems during the subsequent drawing process. The present invention increases the rolling reduction ratio by using large die-cast ingots to make blanks, and the cross-sectional area of ​​the original blank / the cross-sectional area of ​​the final product is ≥20. At the same time, 0.20-0.40% Nb is added to refine the grains, and ultra-low temperature rolling (final rolling temperature ≤850°C) is used to control the grain size of the material to be finer than level 4, thereby improving the plastic toughness of the material.

[0022] The material of the present invention has ultra-high corrosion resistance, excellent soft magnetic properties, good easy-cutting performance, and good plasticity and toughness, is suitable for subsequent drawing and turning, and has broad market application prospects. The preparation method provided by the present invention has a high yield rate and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attached Figure 1 It is a manufacturing process flow chart of the soft magnetic stainless steel wire rod of the present invention;

[0024] Attached Figure 2 is a metallographic structure diagram of a soft magnetic stainless steel wire rod according to Example 1 of the present invention;

[0025] Attached Figure 3 It is the hysteresis loop (soft magnetic performance data) measured for the soft magnetic stainless steel wire rod according to Example 1 of the present invention. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] Example 1

[0029] This embodiment provides a soft magnetic stainless steel wire rod having ultra-high corrosion resistance, good machinability, excellent plasticity and toughness, and a preparation method thereof. The composition of the soft magnetic stainless steel wire rod is shown in Table 1 below:

[0030] Table 1 Schematic table of the composition of the stainless steel wire rod of Example 1

[0031]

[0032] The preparation method of the soft magnetic stainless steel wire rod comprises the following steps: subjecting the charge to arc furnace smelting, AOD furnace refining, LF refining furnace refining, die casting, ingot blanking, primary heat treatment, rolling, secondary heat treatment and other processes in sequence to obtain a soft magnetic stainless steel wire rod with ultra-high corrosion resistance, good cutting performance, excellent plasticity and toughness, and by adopting the preparation method, the comprehensive yield rate of the material is ≥85%;

[0033] Among them, in the electric arc furnace smelting process, the charge is melted and the molten steel is initially smelted by the electric arc furnace, and the P content is controlled to be ≤0.020% when the steel is tapped;

[0034] In the AOD furnace refining process, ferrosilicon, pure manganese, ferrochrome and ferromolybdenum are added to fine-tune the content of Si, Mn, Cr and Mo elements in the molten steel, so that the composition of the finished stainless steel wire rod meets the target mass percentage ratio requirements, and the carbon and nitrogen contents in the molten steel are removed to C≤0.015% and N≤0.010%;

[0035] In the refining process of the LF furnace, ferroniobium is added to the furnace to adjust the Nb content in the molten steel to 0.20 - 0.30%. At the same time, sulfur wire and Se wire are fed in to control S and Se in the molten steel at S: 0.008 - 0.015%, Se: 0.030 - 0.050%. Then, soft blowing argon is used for stirring for more than 10 minutes before tapping the steel.

[0036] The chemical composition of the molten steel after LF refining is shown in Table 1. Using the chemical composition of Example 1 described in Table 1, the subsequent wire rod manufacturing process is as follows:

[0037] In the ingot casting process, the larger the ingot size, the greater the forging reduction ratio, which is beneficial to grain refinement. If the ingot size is too large, the time required for blooming is too long and the risk of cracking during one - fire blooming is very high. It is preferably to use a 17 - inch to 20 - inch ingot mold for casting. In this example, a 17 - inch ingot mold is used, and the ladle - hanging temperature is controlled at 1500 - 1530°C.

[0038] In the ingot heating and blooming process, the ingot is loaded into the heating furnace, the heating temperature is 1100 - 1150°C, and the holding time is 1.5 - 2.5 hours. In this example, the heating temperature is 1140°C and the holding time is 2.0 hours. After blooming, the billet is subjected to a primary annealing treatment, the annealing temperature is 680 - 720°C, and the holding time is 4 - 6 hours. In this example, the annealing temperature is 720°C and the holding time is 6 hours.

[0039] In the wire rod rolling (specification φ5.5 - 30mm) process, the billet after blooming and annealing is loaded into the heating furnace, the heating temperature is 950 - 1000°C, the holding time is 1 - 2 hours, and the final rolling temperature is controlled ≤850°C. In this example, the heating temperature is 980°C, the holding time is 1.5 hours, and the final rolling temperature is controlled at 800 - 820°C.

[0040] The rolled wire rod is loaded into a bell - type annealing furnace for secondary annealing heat treatment. The annealing temperature is controlled at 800 - 880°C, and the holding time is more than 60 minutes. In this example, the annealing temperature is 860°C and the holding time is 2 hours.

[0041] The soft magnetic stainless steel obtained in this example has excellent corrosion resistance, good machinability, and excellent plastic toughness. It does not rust after 1000h of salt spray testing, has excellent cutting performance, the surface finish roughness after turning is ≤1.0μm, the tool wear is small, and the magnetic properties are excellent, with saturation magnetic induction intensity Bs>1.50T and coercivity<250A / m. Grain size detection: 6 - 7 grades on the outside and 4 - 5 grades on the inside. Tensile property test: tensile strength 530MPa, elongation after fracture 35%, reduction of area 72%, and the plastic toughness of the material is excellent.

[0042] Among them, the salt spray test method is GB / T10125 - 2021 Artificial Atmosphere Corrosion Tests + Salt Spray Tests;

[0043] The magnetic property test method is the measurement method for DC magnetic properties of soft magnetic materials in GB / T 13012-2008;

[0044] The crystal grain size detection method is the method for determining the average grain size of metals in GB / T 6394-2017;

[0045] The tensile property test method is the test method for tensile properties of metallic materials - Part 1: Test at room temperature in GB / T 228.1-2021;

[0046] The evaluation of turning performance is to detect the surface roughness and the tool wear condition after turning the specimen. The roughness detection method is the nominal characteristics of product geometric technical specifications (GPS) - surface texture: profile method - contact (stylus) instruments in GB / T 6062-2009.

[0047] Examples 2 - 6

[0048] Based on Example 1, by changing the component ratio and process parameters of the stainless steel material, the corresponding soft magnetic stainless steel wire rods are obtained. The components of the soft magnetic stainless steel wire rods are shown in Table 2 below:

[0049] Table 2 Schematic table of the components of the stainless steel wire rods in each example

[0050]

[0051] The process parameters of the preparation method of the soft magnetic stainless steel wire rods are shown in Table 3 below:

[0052] Table 3 Schematic table of the preparation process parameters of the stainless steel wire rods in each example

[0053]

[0054] In Examples 2 - 6, the corresponding soft magnetic stainless steels with excellent corrosion resistance, good machinability, and excellent plasticity and toughness are prepared. The properties of the soft magnetic stainless steels are basically equivalent to those of Example 1. Among them, the soft magnetic stainless steels in Examples 5 and 6 perform more excellently.

[0055] Comparative Examples 1 - 4

[0056] Meanwhile, based on Example 1, by changing the formula and production process of the stainless steel, as comparative examples, they are compared with Example 1 to further reflect the advantageous effects of the present invention.

[0057] The components of the soft magnetic stainless steel wire rods in Comparative Examples 1 - 4 are shown in Table 4 below:

[0058] Table 4 Schematic table of the components of the stainless steel wire rods in Example 1 and Comparative Examples 1 - 4

[0059]

[0060] The performance of the stainless steel in each comparative example was tested, and the test results and effects are shown in Table 5 below:

[0061] Table 5 Summary of the performance test of the stainless steel wire rods in Example 1 and Comparative Examples 1-4

[0062]

[0063]

[0064] Based on the steps of the preparation method in Example 1, the specific process parameters and implementation effect tests of each comparative example are shown in Table 6 below:

[0065] Table 6 Summary of the production process and effect test of the stainless steel wire rods in Example 1 and Comparative Examples 1-4

[0066]

[0067]

[0068] The above-described embodiments are only the preferred solutions of the present invention, and do not impose any form of limitation on the present invention. There are other variations and modifications without exceeding the technical solutions described in the claims.

Claims

1. A soft magnetic stainless steel wire rod with both ultra-high corrosion resistance, good machinability, and excellent plastic toughness, characterized in that, The chemical components of the wire rod, by mass percentage, include: C ≤ 0.020%, Si: 1.20 - 2.00%, Mn ≤ 0.50%, Cr: 18.0 - 20.0%, Ni: ≤ 0.30%, Mo: 2.50 - 3.00%, N ≤ 0.020%, P < 0.020%, S: 0.008 - 0.015%, Se: 0.030 - 0.050%, Nb: 0.20 - 0.30%, and the balance is Fe and unavoidable impurities.

2. The soft magnetic stainless steel wire rod with excellent corrosion resistance, good machinability and excellent plastic toughness according to claim 1, characterized in that The chemical components of the wire rod, by mass percentage, include: C: 0.010 - 0.020%, Si: 1.6 - 1.7%, Mn: 0.2 - 0.4%, Cr: 18.50 - 19.00%, Ni: 0.1 - 0.3%, Mo: 2.55 - 2.65%, N: 0.010 - 0.020%, P: 0.010 - 0.020%, S: 0.008 - 0.015%, Se: 0.030 - 0.050%, Nb: 0.20 - 0.30%, and the balance is Fe and unavoidable impurities.

3. A method for preparing a soft magnetic stainless steel having both ultra-high corrosion resistance, good machinability, and excellent plastic toughness as described in claim 1 or 2, characterized in that, The preparation method includes processing the furnace charge through the processes of electric arc furnace smelting, AOD furnace refining, LF refining furnace refining, ingot casting, ingot blooming, primary heat treatment, rolling, and secondary heat treatment in sequence to obtain a soft magnetic stainless steel wire rod with excellent ultra-high corrosion resistance, good machinability, and excellent plastic toughness.

4. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability, and excellent plastic toughness according to claim 3, characterized in that In the LF refining furnace refining process, ferroniobium is added, and S wire and Se wire are fed to control the components in the molten steel as: S: 0.008 - 0.015%, Se: 0.030 - 0.050%, Nb: 0.20 - 0.30%.

5. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability, and excellent plastic toughness according to claim 3, characterized in that, In the ingot casting process, a 17 - 20-inch ingot mold is used for casting.

6. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability and excellent plastic toughness according to claim 3, characterized in that, In the ingot blooming process, the ingot is loaded into a heating furnace, the heating temperature is 1100 - 1150 °C, and the holding time is 1.5 - 2.5 hours.

7. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability and excellent plastic toughness according to claim 3, characterized in that, The annealing temperature of the primary heat treatment is 680 - 720 °C, and the holding time is 4 - 6 hours.

8. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability, and excellent plastic toughness according to claim 3, characterized in that In the rolling process, the billet after blooming and annealing is loaded into a heating furnace, the heating temperature is 950 - 1000 °C, the holding time is 1 - 2 hours, and the final rolling temperature is controlled ≤ 850 °C during rolling.

9. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability and excellent plastic toughness according to claim 3, characterized in that, The rolled wire rod has a specification of φ5.5 - 30 mm.

10. The preparation method of a soft magnetic stainless steel with both ultra-high corrosion resistance, good machinability and excellent plastic toughness according to claim 3, characterized in that, The annealing temperature of the secondary heat treatment is 800 - 880 °C, and the time is controlled to be more than 60 min.

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