Welding wire and maraging steel welding method

Abstract

The invention provides a welding wire and maraging steel welding method. The method comprises the steps that a to-be-welded material is subjected to solution treatment and cold treatment, and solution treatment, cold treatment and aging treatment; designing a welding groove of a material to be welded, wherein the welding groove comprises a V-shaped lock bottom butt joint groove and an I-shaped lock bottom butt joint groove; before welding, oxide layers in a welding groove and a nearby 30mm area are removed in a mechanical removal or polishing mode; the to-be-connected workpiece is assembled, wherein the local assembling clearance is not larger than x; setting welding process parameters according to the to-be-obtained front and back welding width conditions of a welding joint, setting a welding speed, a welding current and a fuse speed by gas shielded welding or setting an acceleration voltage, a welding beam current, a filament current and a rotating speed by electron beam welding; and according to the set welding process parameters, maraging steel wire filling welding is carried out under the inert gas shielding condition of gas shielded welding, or maraging steel electron beam welding is carried out under the vacuum condition.

Description

Technical Field

[0001] The present application belongs to the field of welding technology, and specifically relates to a welding method of a welding wire and maraging steel. Background Art

[0002] Relative technology does not propose welding under aging state, and the strength of welded joints after ordinary welding is relatively low. High-strength stainless steel is prone to cracks during melting welding. Although adjusting the composition of the welding wire has a certain restraining effect on the cracks, the improvement effect is poor. Summary of the invention

[0003] Purpose of the invention: The present invention can obtain higher weld strength by welding the base material under different welding methods and different heat treatment conditions, and performing two schemes after welding: solid solution + cold treatment + aging heat treatment, and no heat treatment. At the same time, the weld has certain toughness and plasticity.

[0004] The present application provides a welding method of a welding wire and maraging steel, the method comprising:

[0005] Step 1: subject the materials to be welded to solution treatment + cold treatment, solution treatment + cold treatment + aging treatment;

[0006] Step 2: Design the welding groove of the material to be welded, such as V-shaped bottom-locking butt groove and I-shaped bottom-locking butt groove;

[0007] Step 3: Before welding, remove the oxide layer in the welding groove and the surrounding 30mm area by mechanical removal or grinding, and wipe the welding groove and the surrounding area with alcohol or acetone;

[0008] Step 4, assemble the workpieces to be connected: make the local assembly gap no larger than △x, the value range of △x is 30%·δ or 0.5mm, δ is the wall thickness of the base material to be welded; when welding different thicknesses, δ is the smaller base material wall thickness, take the smaller value; the assembly misalignment is no larger than △y, the value range of △y is 20%·δ or 0.3mm, take the smaller value;

[0009] Step 5, setting welding process parameters: according to the weld width of the front and back sides of the welding joint to be obtained, the welding speed, welding current, and fuse speed of gas shielded welding are set, or the acceleration voltage, welding beam, filament current, and rotation speed of electron beam welding are set;

[0010] Step 6, implement welding: according to the set welding process parameters, implement the maraging steel wire welding under the protection of inert gas by gas shielded welding or implement the maraging steel electron beam welding under vacuum conditions.

[0011] Preferably, the method further comprises:

[0012] Step 7: Quality inspection: Perform non-destructive testing on the welded joints. Non-destructive testing methods include X-ray testing and penetration testing.

[0013] Preferably, the maraging steel material is Custom 465 high-performance, corrosion-resistant and high-strength stainless steel bar, and its main chemical components are: A: C≤0.02, Cr: 11.0-13.0, Ni: 9.0-11.50, Mo: 0.7-2.0.

[0014] Preferably, the welding method includes gas shielded welding and vacuum electron beam welding; the gas shielded welding includes tungsten inert gas welding, metal inert gas shielded welding and metal active gas shielded welding.

[0015] Preferably, the solution treatment process is: temperature 810°C to 1000°C, holding time 50 to 70 minutes, oil cooling or water cooling, so as to obtain a martensitic structure.

[0016] Preferably, the cold treatment process is: after solutionizing, keep at ≯-60°C for more than 8 hours and then return to room temperature, so that the remaining austenite in the steel continues to transform into martensite, thereby ensuring sufficient transformation of the austenite.

[0017] Preferably, the aging treatment process is: temperature 470°C to 550°C for 4h to 5h, and then returning to room temperature, so as to precipitate intermetallic compounds, carbides or second phase particles dispersed in the matrix structure, thereby significantly improving the strength of the steel.

[0018] Preferably, the special welding wire for gas shielded welding comprises:

[0019] A welding wire, composition: C≤0.08, Cr:11.0~13.0, Ni:8.0~9.0, Mn:0.5~1.0, Si:1.0~2.0, Mo:1.0~3.0, Al≤1.0, Mn≤1.0, Ti≤1.0;

[0020] B welding wire, composition: C≤0.08, Cr:9.0~13.0, Ni:6.0~9.0, Mo:5.0~6.0, Co:9.0~12.0, Mn≤1.0, Si≤1.0.

[0021] This application has the following technical effects:

[0022] The present invention provides a welding wire and a maraging steel welding method, which uses different welding methods to weld ultra-high strength maraging steel under different heat treatment conditions. Heat treatment is performed again after welding so that the weld can obtain good mechanical properties. Workpiece welding can also be completed in the final aging treatment state without any heat treatment after welding. The welding efficiency is high and the post-welding processing allowance is small, which can effectively improve production efficiency and reduce production costs. At the same time, better weld quality is obtained.

[0023] The gas shielded welding process included in the present invention is economical and convenient to operate. At the same time, the vacuum electron beam welding in the present invention can solve the problems of deformation of welded parts and over-dimension of welded structures due to re-heat treatment after welding, which makes it difficult to re-heat treat the welded parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a Custom 465V type groove gas shielded welding provided in an embodiment of the present application;

[0025] Figure 2 It is a schematic diagram of Custom 465I groove vacuum electron beam welding provided in an embodiment of the present application;

[0026] Among them, 1 is the first specimen to be welded; 2 is the second specimen to be welded. DETAILED DESCRIPTION

[0027] The gas shielded welding of the present invention adopts a special welding wire, and its welding process is: solution treatment + cold treatment + aging treatment + welding, and no heat treatment is required after welding. At the same time, it can effectively solve welding cracks, effectively reduce the welding process flow of the workpiece and the deformation caused by welding, and obtain welds with quality that meets the design requirements and welded parts with better mechanical properties.

[0028] See also Figure 1 and Figure 2 , provides an ultra-high strength martensitic aging steel welding method and material, belonging to the field of aerospace machinery. It includes a welding method, a pre-welding heat treatment state, a special welding wire, etc. The present invention can obtain a higher weld strength by welding the base material under different welding methods and different heat treatment states, and performing two schemes after welding: solid solution + cold treatment + aging heat treatment, and no heat treatment. At the same time, the weld has certain toughness and plasticity. The present invention can re-heat treat after welding, so that the weld can obtain good mechanical properties. The workpiece welding can also be completed in the final aging treatment state, without any heat treatment after welding, with high welding efficiency and small post-welding processing allowance, which can effectively improve production efficiency and reduce production costs.

[0029] The technical solution of the present invention is: a welding method of welding wire and maraging steel, comprising the following steps:

[0030] Step 1: subject the materials to be welded to solution treatment + cold treatment, solution treatment + cold treatment + aging treatment;

[0031] Step 2: Design the welding groove of the material to be welded, such as V-shaped bottom-locking butt groove and I-shaped bottom-locking butt groove;

[0032] Step 3: Before welding, use mechanical removal or grinding to remove the oxide layer in the welding groove and the surrounding 30mm area, and wipe the welding groove and the surrounding area with alcohol or acetone.

[0033] Step 4: Assemble the workpieces to be welded. Make the local assembly gap no larger than △x, the value range of △x is 30%·δ or 0.5mm (δ is the wall thickness of the base material to be welded; when welding different thicknesses, δ is the smaller base material wall thickness), whichever is smaller; the assembly misalignment is no larger than △y, the value range of △y is 20%·δ or 0.3mm, whichever is smaller.

[0034] Step 5: Set welding process parameters. According to the desired weld width on both sides of the weld joint, set the welding speed, welding current, fuse speed, etc. for gas shielded welding or the acceleration voltage, welding beam, filament current, rotation speed, etc. for electron beam welding.

[0035] Step 6: Implement welding. According to the set welding process parameters, gas shielded welding is performed under inert gas protection conditions to implement maraging steel filler wire welding or electron beam welding is performed under vacuum conditions to implement maraging steel.

[0036] Step 7: Quality inspection: Perform non-destructive testing on the welded joints. Non-destructive testing methods include X-ray testing and penetration testing.

[0037] Furthermore, the maraging steel material is Custom 465 high-performance, corrosion-resistant and high-strength stainless steel bar, and its main chemical composition is: A: C≤0.02, Cr:11.0~13.0, Ni:9.0~11.50, Mo:0.7~2.0. ;

[0038] Furthermore, the welding method includes gas shielded welding (argon tungsten arc welding, metal inert gas shielded welding, metal active gas shielded welding) and vacuum electron beam welding.

[0039] Furthermore, the solution treatment process is as follows: temperature 810°C to 1000°C, holding time 50 to 70 minutes, oil cooling or water cooling, so as to obtain the martensitic structure.

[0040] Furthermore, the cold treatment process is: after solutionizing, keep at ≯-60°C for more than 8 hours and then return to room temperature, so that the remaining austenite in the steel continues to transform into martensite, ensuring sufficient transformation of the austenite.

[0041] Furthermore, the aging treatment process is: temperature 470°C to 550°C for 4h to 5h, and then returning to room temperature, so as to precipitate intermetallic compounds, carbides or second phase particles dispersed in the matrix structure, thereby significantly improving the strength of the steel.

[0042] Furthermore, the composition of the special welding wire for gas shielded welding is:

[0043] A: C≤0.08, Cr:11.0~13.0, Ni:8.0~9.0, Mn:0.5~1.0, Si:1.0~2.0, Mo:1.0~3.0, Al≤1.0, Mn≤1.0, Ti≤1.0.

[0044] B: C≤0.08, Cr:9.0~13.0, Ni:6.0~9.0, Mo:5.0~6.0, Co: 9.0~12.0, Mn≤1.0, Si≤1.0.

[0045] To improve the purity of welding wire, both A and B welding wires are smelted by vacuum induction + vacuum arc remelting, which reduces the gas content and S, P, Si content of welding wire, reduces and disperses the inclusions in welding wire, thereby controlling the solidification segregation of weld and the low melting point liquid film between crystals, thereby improving the weld's resistance to thermal cracking. It is also beneficial to maintain the plasticity and toughness of the weld. After the alloy is smelted, it is poured into ingots, and after the surface is cleaned, it is forged into billets, and then the billets are rolled into wire rods. The wire rods are finally made after drawing. of welding wire.

[0046] Added elements in welding wire A: Cr is an essential alloying element in precipitation hardening stainless steel. As the main corrosion resistant element, it can also reduce the Ms point of steel and improve the hardenability of steel. The trace amount of Mo added to the alloy can promote the passivation of Cr, hinder the nucleation of small holes, and promote the passivation of the pitting corrosion zone, thereby effectively reducing the effect of Cr content on the corrosion resistance of the steel. Ni and Mn elements have austenitizing effect, which makes the weld tend to form austenite, thereby increasing the toughness of the steel. Al is usually added to steel as a deoxidizer and is a ferrite forming element. Al plays a major role in aging strengthening in martensitic aging stainless steel. At the same time, adding Al can form a dense oxide film A12O3 on the surface of steel, which improves the oxidation resistance of stainless steel. In order to improve the weld structure and mechanical properties of the weld, B welding wire decides to add Mo and Co elements to the welding wire. Mo element can prevent the precipitation phase from precipitating along the original austenite grain boundary, while Co element can make the precipitation phase finer, which is beneficial to improve the plastic toughness of the weld. In order to improve the purity of welding wire, welding wire A and B are smelted by vacuum induction + vacuum arc remelting, which reduces the gas content and S, P, Si content of welding wire, reduces and disperses the inclusions in welding wire, thereby controlling the solidification segregation of weld and the low melting point liquid film between crystals, thereby improving the weld's resistance to thermal cracking. At the same time, it is also beneficial to maintain the plastic toughness of the weld.

[0047] Furthermore, the welding process includes: tack welding and welding. Tungsten-grade argon arc welding is used for tack welding, and the tack welding spot should not exceed 75% of the width of the base weld (first layer); to avoid thermal cracks during welding, the heat input should be controlled during gas shielded welding, and welding should be performed with a smaller welding current. The interlayer temperature is controlled at about 150°C.

[0048] Furthermore, the welding process is specifically as follows:

[0049] (1) Welding is performed using tungsten-grade argon arc welding, V-lock bottom butt groove, welding wire A, and solid solution + cold treatment state, and cold treatment + aging heat treatment is performed after welding.

[0050] (2) Welding is performed using tungsten-grade argon arc welding, V-lock bottom butt groove, welding wire B, and solid solution state. After welding, solid solution treatment + cold treatment + aging heat treatment are performed.

[0051] (3) Welding is performed using tungsten-grade argon arc welding, V-lock bottom butt groove, welding wire B, solid solution + cold treatment + aging heat treatment, and no heat treatment is performed after welding.

[0052] (4) Vacuum electron beam welding, I-type lock bottom butt groove, solid solution state + cold treatment are used for welding, and solid solution treatment + cold treatment + aging heat treatment are performed after welding.

[0053] (5) Vacuum electron beam welding, I-type lock bottom butt groove, solid solution + cold treatment + aging state are used for welding, and no heat treatment is performed after welding.

[0054] The present invention provides a welding wire and a maraging steel welding method, which uses different welding methods to weld ultra-high strength maraging steel under different heat treatment conditions. Heat treatment is performed again after welding so that the weld can obtain good mechanical properties. The workpiece welding can also be completed in the final aging treatment state without any heat treatment after welding. The welding efficiency is high and the post-welding processing allowance is small, which can effectively improve production efficiency and reduce production costs. At the same time, better weld quality is obtained. The gas shielded welding process included in the present invention is economical and convenient to operate. At the same time, the vacuum electron beam welding in the present invention can solve the problems of deformation of welded parts and over-dimension of welding structures caused by re-heat treatment after welding, and difficulty in re-heat treatment.

[0055] The key point of this technology lies in a welding method of welding wire and maraging steel, which mainly includes the composition of the welding wire, the welding method, the heat treatment state of the materials to be welded during welding such as: solid solution, solid solution + cold treatment, solid solution + cold treatment + aging treatment, re-heat treatment after welding or partial heat treatment or no heat treatment, etc.

[0056] In other embodiments of the present application, a method and material for welding ultra-high strength maraging steel are provided, and special welding wire A and gas shielded welding method are used for welding; ultra-high strength maraging steel is welded by tungsten grade argon arc welding, V-lock bottom butt groove, welding wire A, solid solution + cold treatment state, and cold treatment + aging heat treatment is performed after welding. The obtained welded joint has high strength and toughness, beautiful weld shape, and very good welding processability, including the following steps:

[0057] When the ultra-high strength maraging steel is Custom465, the chemical composition and mass percentage of its special welding wire are as follows: C≤0.08, Cr:11.0~13.0, Ni:8.0~9.0, Mn:0.5~1.0, Si:1.0~2.0, Mo:1.0~3.0, Al≤1.0, Mn≤1.0, Ti≤1.0;

[0058] The gas shielded welding is tungsten inert gas welding, metal inert gas shielded welding, metal active gas shielded welding;

[0059] The heat treatment process is: solution treatment: temperature 810°C to 1000°C, holding time 50 to 70 minutes, oil cooling or water cooling;

[0060] Cold treatment: After solution treatment, keep at ≯-60℃ for more than 8h, and then return to room temperature;

[0061] Aging treatment: temperature 470℃~550℃ for 4h~5h, then return to room temperature.

[0062] The welding is carried out in a solid solution + cold treatment state, and cold treatment + aging heat treatment is carried out after welding.

[0063] For the specific implementation plan of welding Custom 465 ultra-high strength maraging steel, please refer to the attached Figure 1 , the specific method is as follows:

[0064] 1. Before welding, mechanical removal or grinding should be used to remove the oxide layer in the welding groove and the surrounding 30mm area; alcohol or acetone should be used to wipe the oil and moisture in the welding groove and the surrounding area before welding, and the welding should be completed within 4 hours after wiping;

[0065] 2. Carry out solution treatment + cold treatment on the welded parts 1 and 2;

[0066] 3. Press Figure 1 Assemble the weldments 1 and 2 as shown, and perform evenly spaced 3-point positioning welding as shown in 3. When welding, pay attention to welding both sides in five layers in sequence, and clean each layer of welds between layers. The welding parameters are shown in Table 1.

[0067] Table 1

[0068]

[0069] 4. Cold treatment + aging heat treatment after welding;

[0070] 5. The mechanical properties of welds of welded parts are σb ≥ 1190MPa, σS ≥ 1156MPa, δ5% ≥ 11%, Aku ≥ 44.2J.

[0071] The mechanical properties of Custom 465 base material are σb≥1740MPa, σS≥1703MPa, δ5%≥7%, and Aku≥32.8J.

[0072] In other embodiments of the present application, a method and material for welding ultra-high strength maraging steel is provided, and special welding wire B and gas shielded welding method are used for welding; ultra-high strength maraging steel is welded by tungsten-grade argon arc welding, V-lock bottom butt groove, welding wire A, and solid solution state, and solid solution treatment + cold treatment + aging heat treatment are performed after welding. Its welding process parameters are consistent with those in Example 1. The mechanical properties of the weld of the welded part are σb≥1387MPa, σS≥1375MPa, δ5%≥8.5%, and Aku≥21.7J.

[0073] In other embodiments of the present application, a method and material for welding ultra-high strength maraging steel is provided, and special welding wire B and gas shielded welding method are used for welding; ultra-high strength maraging steel is welded by tungsten grade argon arc welding, V-lock bottom butt groove, welding wire A, solid solution + cold treatment + aging heat treatment state, and no heat treatment is performed after welding. Its welding process parameters are consistent with those in Example 1. The mechanical properties of the weld of the welded part are σb≥886MPa, σS≥758MPa, δ5%≥11%, and Aku≥150J.

[0074] In other embodiments of the present application, a method and material for welding ultra-high strength maraging steel is provided. The ultra-high strength maraging steel is welded by vacuum electron beam welding. The welding is performed in the state of solid solution + cold treatment in the I-type lock bottom butt groove, and solid solution treatment + cold treatment + aging heat treatment is performed after welding. The obtained welded joint has high strength and toughness, beautiful weld shape, and very good welding processability, including the following steps:

[0075] When the ultra-high strength maraging steel is Custom 465, the welding method is vacuum electron beam welding;

[0076] The heat treatment process is: solution treatment: temperature 810°C to 1000°C, holding time 50 to 70 minutes, oil cooling or water cooling;

[0077] Cold treatment: After solution treatment, keep at ≯-60℃ for more than 8h, and then return to room temperature;

[0078] Aging treatment: temperature 470℃~550℃ for 4h~5h, then return to room temperature.

[0079] The welding is carried out in a solid solution + cold treatment state, and solid solution treatment + cold treatment + aging heat treatment are performed after welding.

[0080] For the specific implementation plan of welding Custom 465 ultra-high strength maraging steel, please refer to the attached Figure 2 , the specific method is as follows:

[0081] 1. Before welding, mechanical removal or grinding should be used to remove the oxide layer in the welding groove and the surrounding 30mm area; alcohol or acetone should be used to wipe the oil and moisture in the welding groove and the surrounding area before welding, and the welding should be completed within 4 hours after wiping;

[0082] 2. Carry out solution treatment + cold treatment on the welded parts 1 and 2;

[0083] 3. Press Figure 1Assemble the weldments 1 and 2 as shown, and perform evenly spaced three-point tack welding as shown in 3. Tungsten-grade argon arc welding is used for tack welding, and the maximum acceleration voltage of 85kV is used for electron beam welding to increase the beam penetration ability, improve the welding speed, and reduce the heat input. The welding parameters are shown in Table 2.

[0084] Table 2

[0085]

[0086] 4. Solution treatment + cold treatment + aging heat treatment after welding;

[0087] 5. The mechanical properties of welds of welded parts are σb ≥ 1460MPa, σS ≥ 1375MPa, δ5% ≥ 2.6%, Aku ≥ 12.1J.

[0088] In other embodiments of the present application, a method and material for welding ultra-high strength maraging steel is provided. The ultra-high strength maraging steel is welded by vacuum electron beam welding; the I-type lock bottom butt groove is welded in a solid solution + cold treatment + aging heat treatment state, and no heat treatment is performed after welding. The welding process parameters are consistent with those in Example 1. The mechanical properties of the weld of the welded part are σb ≥ 885 MPa, σS ≥ 820 MPa, δ5% ≥ 11%, and Aku ≥ 70.2 J.

[0089] The above embodiments can all obtain higher weld strength. The present invention mainly includes the composition of welding wire, the heat treatment state of the materials to be welded during welding, such as: solid solution + cold treatment or solid solution + cold treatment + aging treatment, no heat treatment after welding, welding method, etc. Welding is performed in the solid solution + cold treatment state, and aging treatment is performed after welding. In summary, the technical scheme is reasonable and feasible, especially using gas shielded welding + welding wire A to weld in the solid solution treatment + cold treatment state, and cold treatment + aging heat treatment is performed after welding, using gas shielded welding + welding wire B to weld in the solid solution treatment state, and solid solution treatment + cold treatment + aging treatment is performed after welding, and using electron beam welding in the solid solution + cold treatment state, and solid solution + cold treatment + aging treatment is performed again after welding, all of which can obtain high-quality weld joint strength.

Claims

1. A welding method for welding a welding wire and maraging steel, characterized in that: The method comprises: Step 1: subject the materials to be welded to solution treatment + cold treatment, solution treatment + cold treatment + aging treatment; Step 2: Design the welding groove of the material to be welded, such as V-shaped bottom-locking butt groove and I-shaped bottom-locking butt groove; Step 3: Before welding, remove the oxide layer in the welding groove and the surrounding 30mm area by mechanical removal or grinding, and wipe the welding groove and the surrounding area with alcohol or acetone; Step 4, assemble the workpieces to be connected: make the local assembly gap no larger than △x, the value range of △x is 30%·δ or 0.5mm, δ is the wall thickness of the base material to be welded; when welding different thicknesses, δ is the smaller base material wall thickness, take the smaller value; the assembly misalignment is no larger than △y, the value range of △y is 20%·δ or 0.3mm, take the smaller value; Step 5, setting welding process parameters: according to the weld width of the front and back sides of the welding joint to be obtained, the welding speed, welding current, and fuse speed of gas shielded welding are set, or the acceleration voltage, welding beam, filament current, and rotation speed of electron beam welding are set; Step 6, implement welding: according to the set welding process parameters, implement the maraging steel wire welding under the protection of inert gas by gas shielded welding or implement the maraging steel electron beam welding under vacuum conditions.

2. The method according to claim 1, characterized in that: The method further comprises: Step 7: Quality inspection: Perform non-destructive testing on the welded joints. Non-destructive testing methods include X-ray testing and penetration testing.

3. The method according to claim 1, characterized in that The maraging steel material is Custom 465 high-performance, corrosion-resistant and high-strength stainless steel bar, and its main chemical components are: A: C≤0.02, Cr: 11.0-13.0, Ni: 9.0-11.50, Mo: 0.7-2.

0.

4. The method according to claim 1, characterized in that: The welding methods include gas shielded welding and vacuum electron beam welding; the gas shielded welding includes tungsten inert gas welding, metal inert gas shielded welding and metal active gas shielded welding.

5. The method according to claim 1, characterized in that The solution treatment process is as follows: temperature 810° C. to 1000° C., holding time 50 to 70 minutes, oil cooling or water cooling, so as to obtain a martensitic structure.

6. The method according to claim 1, characterized in that The cold treatment process is: after solutionizing, the temperature is kept at ≯-60°C for more than 8 hours, and then restored to room temperature, so that the remaining austenite in the steel continues to transform into martensite, ensuring sufficient transformation of the austenite.

7. The method according to claim 1, characterized in that The aging treatment process is: temperature 470°C to 550°C for 4h to 5h, and then returning to room temperature to precipitate intermetallic compounds, carbides or second phase particles dispersed in the matrix structure, thereby significantly improving the strength of the steel.

8. The method according to claim 1, characterized in that The special welding wire for gas shielded welding includes: A welding wire, composition: C≤0.08, Cr:11.0~13.0, Ni:8.0~9.0, Mn:0.5~1.0, Si:1.0~2.0, Mo:1.0~3.0, Al≤1.0, Mn≤1.0, Ti≤1.0; B welding wire, composition: C≤0.08, Cr:9.0~13.0, Ni:6.0~9.0, Mo:5.0~6.0, Co:9.0~12.0, Mn≤1.0, Si≤1.0.

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