An ultra-high strength duplex stainless steel wire and its preparation method

Abstract

The present invention discloses an ultra-high strength duplex stainless steel wire and a preparation method thereof. The steel wire contains the following components by mass percentage: C: 0.02% - 0.03%, Cr: 21.5% - 22.5%, Ni: 0.8% - 1.5%, Mn: 3.5% - 5.0%, Mo: 0.05% - 0.15%, N: 0.20% - 0.35%, P ≤ 0.009%, S ≤ 0.008%, Si: 0.45% - 0.60%, W: 0.08% - 0.20%, Ce: 0.05% - 0.15%, La: 0.05% - 0.15%, and the balance is Fe. The preparation method is as follows: The stainless steel wire rod is drawn into a stainless steel wire with a strain of 2.47 - 2.57 by using a unidirectional multi-pass cold drawing method. The stainless steel wire of the present invention has a tensile strength exceeding 2600 MPa at room temperature, an elongation rate greater than 3%, high strength and good corrosion resistance.

Description

Technical Field

[0001] The present invention relates to a stainless steel wire and a preparation method thereof, and particularly to an ultra-high strength duplex stainless steel wire and a preparation method thereof. Background Art

[0002] Stainless steel wire is a kind of metal wire with good corrosion resistance and high strength, and is widely used in the fields of marine engineering, medical treatment, transportation, etc. With the progress of science and technology and industrialization, the application fields of stainless steel wire are constantly expanding, especially in the high-tech fields. Currently, the most widely used is 304 austenitic stainless steel wire. Duplex stainless steel is a kind of stainless steel composed of austenite and ferrite phases, and has the advantages of both austenitic stainless steel and ferritic stainless steel. Due to the coexistence of the two phases, the strength of duplex stainless steel is higher than that of 304 stainless steel, and its yield strength has increased by nearly one time. Compared with 304 stainless steel, the Ni content in duplex stainless steel is lower, so the production cost of duplex stainless steel is lower. Therefore, duplex stainless steel wire is superior to 304 stainless steel wire in terms of mechanical properties and cost, and it has become a trend to use duplex stainless steel wire to replace 304 stainless steel wire.

[0003] Since duplex stainless steel contains ferrite phase, its plasticity and cold workability are lower than those of austenitic stainless steel, which makes it difficult to prepare duplex stainless steel wire by cold drawing. Currently, there are many studies on duplex stainless steel plates and tubes, but few studies on duplex stainless steel wire. Patent CN 103103457A discloses a manufacturing method of duplex stainless steel braided hose wire. In the process of obtaining the finished duplex stainless steel wire, this patent undergoes 4 times of solution treatment and changes the lubricant 4 times. Finally, the tensile strength of the steel wire is 810 MPa. Patent CN 105624580B discloses a duplex stainless steel wire and a preparation method thereof. By adding alloy elements such as Ce, the strength of the steel wire is improved, and the tensile strength of the final finished steel wire is about 1800 MPa. However, it still needs to undergo multiple high-temperature solution treatments during the drawing process. Multiple solution treatments and changing lubricants during the production process not only increase the production cost but also reduce the production efficiency. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide an ultra-high strength duplex stainless steel wire that can obtain high strength while simplifying the process;

[0005] The second object of the present invention is to provide a preparation method of the above ultra-high strength duplex stainless steel wire.

[0006] Technical solution: The ultra-high strength duplex stainless steel wire of the present invention comprises the following components by mass percentage: C: 0.02% - 0.03%, Cr: 21.5% - 22.5%, Ni: 0.8% - 1.5%, Mn: 3.5% - 5.0%, Mo: 0.05% - 0.15%, N: 0.20% - 0.35%, P ≤ 0.009%, S ≤ 0.008%, Si: 0.45% - 0.60%, W: 0.08% - 0.20%, Ce: 0.05% - 0.15%, La: 0.05% - 0.15%, and the balance is Fe.

[0007] The present invention adds Ce and La elements; Ce, La and S and O elements in steel have strong affinity, and have the functions of desulfurization, deoxidation and inclusion modification. The main harm of inclusions in steel is to reduce the corrosion resistance and plasticity of steel. Therefore, the addition of Ce and La rare earth elements can improve the cleanliness of steel, improve the drawability of steel, and facilitate drawing with larger deformation. Moreover, since the atomic radii of Ce and La are larger than that of Fe, they can provide solid solution strengthening effect on the solid solution in steel, making the grain refined, and improving the strength and plasticity of duplex stainless steel. The plasticity of the wire is improved, that is, the drawability of the wire is improved.

[0008] The present invention adds W element; W element can improve the hardness and wear resistance of steel. W is a metal with very high hardness and can form hard tungsten compounds with iron element. Adding an appropriate amount of W element in steel can improve the hardness and wear resistance of steel, making the service life of steel longer; moreover, it also improves the strength and toughness of steel, making steel have better tensile resistance and impact resistance.

[0009] The preparation method of the above-mentioned ultra-high strength duplex stainless steel wire comprises the following steps:

[0010] (1) Mix the raw materials of each element according to the proportion and carry out smelting, and cast the molten steel obtained by smelting to obtain a billet;

[0011] (2) Heat and forge the billet to obtain a forged billet, and subject the forged billet to hot rolling treatment to obtain a hot-rolled wire rod;

[0012] (3) Subject the hot-rolled wire rod to solution treatment, and then carry out multi-pass cold drawing. Control the first pass to use a smaller reduction ratio, the second to eighth passes to use a larger reduction ratio, and the ninth to the last pass to use a smaller reduction ratio; to obtain the above-mentioned ultra-high strength duplex stainless steel wire.

[0013] Among them, in step (3), the multi-pass cold drawing is unidirectional multi-pass cold drawing; preferably, a total of 11 passes of cold drawing are carried out; the total area reduction rate is greater than 90%.

[0014] In step (3), the surface reduction rate in the first pass is 7% - 9%, and the wire drawing speed is 3.0 m / min - 3.5 m / min. Since the diameter of the stainless steel wire rod may be uneven after rolling and there may still be scale on the surface that has not been removed. Therefore, the surface reduction rate in the first pass is relatively small. The main purposes are: to make the wire rod specifications uniform and to remove the possible scale on the surface. After the first pass of wire drawing, the surface of the wire is complete and shiny, and the size of the wire is uniform. If the surface reduction rate in the first pass is too large, due to the uneven wire rod specifications, the wire rod may be stressed unevenly during wire drawing, damaging the surface of the wire and affecting subsequent wire drawing.

[0015] In step (3), the surface reduction rates in the 2nd - 8th passes are 28% - 26%, 27% - 25%, 26% - 24%, 24% - 22%, 23% - 22%, 22% - 21%, 21% - 20% respectively, and the wire drawing speed is 2.0 m / min - 2.5 m / min. At this time, the strain is relatively low, the work hardening degree of the wire is not high, and the wire drawing speed is relatively fast. After wire drawing, the surface of the wire is complete and shiny, the size of the wire is uniform, and it is not easy to break.

[0016] In step (3), the surface reduction rates in the 9th - 11th passes are 19% - 18%, 19% - 17%, 17% - 16% respectively; the wire drawing speed is 1.0 m / min - 1.5 m / min. At this time, the strain is relatively high, the work hardening degree of the wire is high, and the wire drawing speed is relatively slow. After wire drawing, the surface of the finished wire is complete and shiny, and the specifications of the whole wire are uniform. If the surface reduction rate is relatively large, wire breakage is likely to occur during the final wire drawing process.

[0017] Among them, in step (3), before each pass of wire drawing, MoS2 is used for spraying and coating. MoS2 has good high-temperature resistance. Since the wire is likely to generate a relatively high temperature rise during wire drawing, MoS2 can maintain lubrication during wire drawing; it also has a friction reduction effect. Since the friction coefficient of MoS2 is relatively low, between 0.05 - 0.1, it can greatly reduce the frictional resistance of the friction device, play a role in protecting the surface of the wire, and improve the drawability of the wire.

[0018] Among them, in step (2), the hot forging temperature is 1100°C - 1200°C; the hot rolling temperature is 1000°C - 1100°C.

[0019] Among them, the ratio of the volume fractions of austenite and ferrite in the stainless steel wire is 1.3 - 1.5.

[0020] Among them, in step (1), the output power of smelting is 100 KW - 110 KW, and the furnace temperature is 1550°C - 1650°C.

[0021] Among them, the diameter of the hot-rolled wire rod is 5.5 mm to 7.0 mm, the specification of the finished stainless steel wire is 1.6 mm to 2.0 mm, and the drawing strain is 2.47 to 2.57.

[0022] Among them, the wire drawing die preferably uses a polycrystalline die; it has good wear resistance and long service life. The service life of the polycrystalline die is about 30 to 50 times that of the cemented carbide die, so there is no need to frequently stop the machine to replace the die during the wire drawing process.

[0023] Beneficial effects: Compared with the prior art, the present invention has achieved the following remarkable effects: (1) The present invention improves the composition of the steel wire, controls the first pass to have a smaller area reduction rate, the second to eighth passes to have a larger area reduction rate, and the ninth to eleventh passes to have a smaller area reduction rate, so that the present invention can obtain a steel wire with high tensile strength without repeated drawing and annealing processes; (2) The duplex stainless steel wire prepared by the present invention has high N and Mn contents, and contains W, and the tensile strength of the steel wire is high, exceeding 2600 MPa; the elongation is greater than 3%; (3) The duplex stainless steel wire prepared by the present invention has a low Ni content, and contains rare earth elements Ce and La, and the steel wire has low cost and high purity. Description of the Drawings

[0024] Figure 1 is the engineering stress-strain curve of the duplex stainless steel wire rod and the finished product in Example 1;

[0025] Figure 2 is the microstructural morphology of the duplex stainless steel wire rod and the finished product in Example 1;

[0026] Figure 3 is the tensile strength diagram of the duplex stainless steel wire in the examples and the comparative examples. Detailed Description

[0027] The present invention will be further described in detail below.

[0028] Example 1

[0029] A method for preparing an ultra-high strength duplex stainless steel wire, comprising the following components by mass percentage: C: 0.03%, Cr: 22.5%, Ni: 0.8%, Mn: 5.0%, Mo: 0.15%, N: 0.35%, P: 0.006%, S: 0.005%, Si: 0.45%, W: 0.20%, Ce: 0.15%, La: 0.15%, and the balance is Fe. The components of the above stainless steel wire are mixed in proportion and melted in an intermediate frequency induction furnace, and the molten steel obtained by melting is cast to obtain a casting blank; the casting blank is heated and forged to obtain a forged blank, and the forged blank is hot-rolled to obtain a hot-rolled wire rod; the unidirectional multi-pass cold drawing method is adopted, and before each pass of drawing, MoS2 spraying and film coating are required.

[0030] The specific process is as follows:

[0031] (1) After weighing the wire rod components according to the mass ratio, heat and dry them. Add the pretreated raw materials into an intermediate frequency induction furnace for melting. The output power is 110KW and the furnace temperature is 1600°C. Add calcium-silicon-manganese accounting for 0.3% of the total weight of the molten steel for deoxidation. After deoxidation, add pure Ce, pure La, and pure W into the molten steel according to the mass ratio, and then cast the molten steel obtained by melting to obtain a casting blank;

[0032] (2) Heat and forge the casting blank to obtain a forged blank, with the hot forging temperature being 1200°C; subject the forged blank to hot rolling treatment to obtain a hot rolled wire rod, with the hot rolling temperature being 1100°C, and the final diameter of the hot rolled wire rod being 6.5mm;

[0033] (3) Solution-treat the hot rolled wire rod at 1200°C for 1.5h. After solution treatment, pickle the wire rod with a dilute sulfuric acid solution with a volume fraction of 8%. The engineering stress-strain curve of the wire rod is as shown in Figure 1 shown, and the microstructure is as shown in Figure 2 (a) in. Then perform cold drawing for 11 passes, with the wire drawing die being a polycrystalline die.

[0034] 1) Before wire drawing, first use a rolling end machine to roll the head of the wire rod, spray and coat the wire with a MoS2 spray. After waiting for the spray to dry, perform the first pass of wire drawing, with the wire drawing speed being 3m / min. After the first pass of wire drawing, the cross-sectional reduction rate of the wire is 9%. Since the thickness of the wire rod may be uneven after rolling of the stainless steel wire rod and there may still be scale on the surface that has not been removed. Therefore, the cross-sectional reduction rate of the first pass of wire drawing is small. The main purpose is to make the wire rod specifications uniform and remove the possible scale on the surface.

[0035] 2) Before the 2nd to 8th passes of wire drawing, first use a rolling end machine to roll the head of the wire rod, spray and coat the wire with a MoS2 spray. After waiting for the spray to dry, perform wire drawing. The cross-sectional reduction rates after each pass of wire drawing are 27%, 26%, 24%, 23%, 22%, 21%, 21% respectively, and the wire drawing speed is 2.5m / min. At this time, the strain is low, the work hardening degree of the wire is not high, and the wire drawing speed is fast.

[0036] 3) Before the 9th to 11th passes of wire drawing, first use a rolling end machine to roll the head of the wire rod, spray and coat the wire with a MoS2 spray. After waiting for the spray to dry, perform wire drawing. The cross-sectional reduction rates after each pass of wire drawing are 19%, 18%, 16% respectively, and the wire drawing speed is 1.5m / min. At this time, the strain is large, and the work hardening degree of the wire increases with the increase of the strain. Therefore, the larger the strain, the smaller the cross-sectional reduction rate should be.

[0037] After the above preparation process, we obtained the finished product of duplex stainless steel wire with a diameter of 1.8 mm, a strain of 2.57, a tensile strength of 2656 MPa, and an elongation of 3.2%. The engineering stress-strain curve of the wire is as shown in Figure 1 shown. The microstructure is as shown in Figure 2 (b) in. The microstructure of the wire rod consists of austenite and ferrite grains, and the structure of the finished wire is fibrous.

[0038] Example 2

[0039] The preparation process is the same as that of the duplex stainless steel wire in Example 1, except that its chemical composition is by mass percentage: C: 0.02%, Cr: 21.5%, Ni: 1.5%, Mn: 3.5%, Mo: 0.05%, N: 0.25%, P: 0.009%, S: 0.008%, Si: 0.45%, W: 0.15%, Ce: 0.15%, La: 0.05%, and the balance is Fe.

[0040] Example 3

[0041] The preparation process is the same as that of the duplex stainless steel wire in Example 1, except that its chemical composition is by mass percentage: C: 0.03%, Cr: 22.0%, Ni: 1.0%, Mn: 4.0%, Mo: 0.15%, N: 0.30%, P: 0.006%, S: 0.005%, Si: 0.45%, W: 0.10%, Ce: 0.05%, La: 0.15%, and the balance is Fe.

[0042] Example 4

[0043] The preparation process is the same as that of the duplex stainless steel wire in Example 1, except that its chemical composition is by mass percentage: C: 0.03%, Cr: 22.5%, Ni: 0.8%, Mn: 4.5%, Mo: 0.15%, N: 0.25%, P: 0.006%, S: 0.005%, Si: 0.45%, W: 0.10%, Ce: 0.10%, La: 0.10%, and the balance is Fe. The diameter of the wire rod is 5.5 mm, and the diameter of the finished wire is 1.6 mm, with a strain of 2.47.

[0044] Example 5

[0045] The preparation process is the same as that of the duplex stainless steel wire in Example 1, except that its chemical composition is by mass percentage: C: 0.03%, Cr: 22.5%, Ni: 0.8%, Mn: 4.5%, Mo: 0.15%, N: 0.25%, P: 0.006%, S: 0.005%, Si: 0.45%, W: 0.08%, Ce: 0.05%, La: 0.05%, and the balance is Fe.

[0046] In step (1), the output power of smelting is 100 KW, and the furnace temperature is 1550 °C.

[0047] In step (2), the hot forging temperature is 1100 °C; the hot rolling temperature is 1000 °C.

[0048] The reduction of area in the first pass is 7%, and the reduction of area in the 2nd - 8th passes is 28%, 27%, 24%, 24%, 23%, 22%, 21%, and the reduction of area in the 9th - 11th passes is 19%, 19%, 17%; the wire drawing speed in the first pass is 3.5 m / min, the wire drawing speed in the 2nd - 8th passes is 2.5 m / min, and the wire drawing speed in the 9th - 11th passes is 1.0 m / min.

[0049] The diameter of the hot - rolled wire rod is 7.0 mm, the specification of the finished stainless - steel wire is 2.0 mm, and the drawing strain is 2.51. The ratio of the volume fractions of austenite and ferrite in the stainless - steel wire is 1.5.

[0050] Example 6

[0051] In step (1), the output power of smelting is 110 KW, and the furnace temperature is 1650 °C.

[0052] In step (2), the hot forging temperature is 1200 °C; the hot rolling temperature is 1100 °C.

[0053] The reduction of area in the first pass is 8%, and the reduction of area in the 2nd - 8th passes is 26%, 25%, 26%, 22%, 22%, 21%, 20%, and the reduction of area in the 9th - 11th passes is 18%, 17%, 16%; the wire drawing speed in the first pass is 3.2 m / min, the wire drawing speed in the 2nd - 8th passes is 2.0 m / min, and the wire drawing speed in the 9th - 11th passes is 1.3 m / min.

[0054] The diameter of the hot - rolled wire rod is 5.5 mm, the specification of the finished stainless - steel wire is 1.6 mm, and the drawing strain is 2.47. The ratio of the volume fractions of austenite and ferrite in the stainless - steel wire is 1.4.

[0055] Comparative Example 1

[0056] Duplex stainless - steel wire disclosed in Patent CN 105624580B.

[0057] Comparative Example 2

[0058] Duplex stainless - steel braided hose wire disclosed in Patent CN 103103457A.

[0059] Comparative Example 3

[0060] Compared with Example 1, the difference is that the area reduction rate in the first pass is 20%; after the first pass of wire drawing, scratches appear on the surface of the wire.

[0061] Comparative Example 4

[0062] Compared with Example 1, the difference is that the wire drawing speed in the first pass is 4.5 m / min; after the first pass of wire drawing, scratches appear on the surface of the wire.

[0063] Comparative Example 5

[0064] Compared with Example 1, the difference is that the area reduction rates in the 2nd - 8th passes are 31%, 28%, 27%, 25%, 24%, 24%, 22%; the wire breaks during the wire drawing process in the 6th pass.

[0065] Comparative Example 6

[0066] Compared with Example 1, the difference is that the wire drawing speeds in the 2nd - 8th passes are 3.5 m / min; the wire breaks during the wire drawing process in the 7th pass.

[0067] Comparative Example 7

[0068] Compared with Example 1, the difference is that the area reduction rates in the 9th - 11th passes are 23%, 21%, 19%; the wire breaks during the wire drawing process in the 9th pass.

[0069] Comparative Example 8

[0070] Compared with Example 1, the difference is that the wire drawing speeds in the 9th - 11th passes are 3.0 m / min; the wire breaks during the wire drawing process in the 9th pass.

[0071] Comparative Example 9

[0072] Compared with Example 1, the difference is that MoS2 lubricant is not used; the surface of the wire is severely damaged after wire drawing, cracks and scratches appear on the surface, and the wire breaks during the wire drawing process in the 4th pass.

[0073] Comparative Example 10

[0074] Based on Example 1, different from Example 1, rare earth elements Ce and La are not added. The strength and elongation of the obtained wire are shown in Table 2.

[0075] Comparative Example 11

[0076] Based on Example 1, different from Example 1, W element is not added. The strength and elongation of the obtained wire are shown in Table 2.

[0077] The duplex stainless steel wires prepared in Examples 1 - 6 of the present invention and the wires of Comparative Examples 1 - 11 were subjected to mechanical property tests and comparisons, and the results are shown in Tables 1 and 2 below.

[0078] Table 1 Mechanical properties of duplex stainless steel wires in the examples

[0079]

[0080] Table 2 Mechanical properties of duplex stainless steel wires in the comparative examples

[0081]

[0082] From Table 1, Table 2 and Figure 3 it can be seen that the strength of the stainless steel wire of the present invention exceeds 2600 MPa, and the highest strength is 2656 MPa. At the same time, an elongation rate of 3.2% is maintained. During the drawing process, too fast a drawing rate, too large a reduction in area, and not using MoS2 lubricant will all damage the surface of the wire, reduce the drawability of the wire, and increase the wire breakage rate. By adding rare earth elements Ce, La and metal element W, the strength of the wire can be improved.

Claims

1. An ultra-high strength duplex stainless steel wire, characterized in that, It contains the following components by mass percentage: C: 0.02% - 0.03%, Cr: 21.5% - 22.5%, Ni: 0.8% - 1.5%, Mn: 3.5% - 5.0%, Mo: 0.05% - 0.15%, N: 0.20% - 0.35%, P ≤ 0.009%, S ≤ 0.008%, Si: 0.45% - 0.60%, W: 0.08% - 0.20%, Ce: 0.05% - 0.15%, La: 0.05% - 0.15%, and the balance is Fe; The preparation method of the ultra-high strength duplex stainless steel wire described above includes the following steps: (1) Mix the raw materials of each element in proportion and add them to an intermediate frequency induction furnace for melting, and cast the molten steel obtained by melting to obtain a casting blank; (2) Heat and forge the casting blank to obtain a forging blank, and subject the forging blank to hot rolling treatment to obtain a hot rolled wire rod; (3) Subject the hot rolled wire rod to solution treatment, and then perform multi-pass cold drawing. Control the first pass to use a smaller reduction ratio, the second to eighth passes to use a larger reduction ratio, and the ninth to the last pass to use a smaller reduction ratio; to obtain the ultra-high strength duplex stainless steel wire; In step (3), before each pass of drawing, spray and coat with MoS2; a total of 11 passes of cold drawing are performed; the area reduction rate of the first pass is 7% - 9%, and the drawing speed is 3.0 m / min - 3.5 m / min; the area reduction rates of the second to eighth passes are 28% - 26%, 27% - 25%, 26% - 24%, 24 - 22%, 23% - 22%, 22% - 21%, 21% - 20% respectively, and the drawing speeds are all 2.0 m / min - 2.5 m / min; the area reduction rates of the ninth to eleventh passes are 19% - 18%, 19% - 17%, 17% - 16% respectively; the drawing speeds are all 1.0 m / min - 1.5 m / min.

2. The preparation method of the ultra-high strength duplex stainless steel wire according to claim 1, characterized in that, It includes the following steps: (1) Mix the raw materials of each element in proportion and add them to an intermediate frequency induction furnace for melting, and cast the molten steel obtained by melting to obtain a casting blank; (2) Heat and forge the casting blank to obtain a forging blank, and subject the forging blank to hot rolling treatment to obtain a hot rolled wire rod; (3) Subject the hot rolled wire rod to solution treatment, and then perform multi-pass cold drawing. Control the first pass to use a smaller reduction ratio, the second to eighth passes to use a larger reduction ratio, and the ninth to the last pass to use a smaller reduction ratio; to obtain the ultra-high strength duplex stainless steel wire; In step (3), before each pass of wire drawing, MoS2 is used for spraying and film coating; a total of 11 passes of cold wire drawing are carried out; the reduction of area in the first pass is 7% - 9%, and the wire drawing speed is 3.0 m / min - 3.5 m / min; the reduction of area in the 2nd - 8th passes are 28% - 26%, 27% - 25%, 26% - 24%, 24% - 22%, 23% - 22%, 22% - 21%, 21% - 20% respectively, and the wire drawing speed is 2.0 m / min - 2.5 m / min for all; the reduction of area in the 9th - 11th passes are 19% - 18%, 19% - 17%, 17% - 16% respectively; the wire drawing speed is 1.0 m / min - 1.5 m / min for all.

3. The preparation method of the ultra-high strength duplex stainless steel wire according to claim 2, characterized in that, In step (2), the temperature for hot forging is 1100 °C - 1200 °C; the hot rolling temperature is 1000 °C - 1100 °C.

4. The preparation method of the ultra-high strength duplex stainless steel wire according to claim 2, characterized in that, The ratio of the volume fractions of austenite and ferrite in the stainless steel wire is 1.3 - 1.

5.

5. The method for preparing an ultra-high strength duplex stainless steel wire according to claim 2, characterized in that, In step (1), the output power for melting is 100 KW - 110 KW, and the furnace temperature is 1550 °C - 1650 °C.

6. The preparation method of the ultra-high strength duplex stainless steel wire according to claim 2, wherein, The diameter of the hot - rolled wire rod is 5.5 mm - 7.0 mm, the specification of the finished stainless steel wire is 1.6 mm - 2.0 mm, and the drawing strain is 2.47 - 2.57.

Images