CN102400064B - Austenitic stainless steel with stamping performance and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a kind of austenitic stainless steel, the weight percent distribution ratio of its chemical composition is: C≤0.03%, Si≤0.75%, Mn: 2.0-3.5%, Cr: 16-19%, Ni: 8.0-9.50% , Cu: 2.0-3.0%, Nb: 0.1-0.25%, N≤0.03%, Al≤0.005%, and the content of Nb, C, and N must meet: Nb-8(C+N)≥0, (C+ Nb)≤0.30%, the rest is Fe and unavoidable impurities. The manufacturing method includes: during the smelting process, the basicity of the slag is controlled at 1.5-2.5; under vacuum or non-vacuum conditions, ferrosilicon or silicon-manganese alloy with an aluminum content of less than 1.0wt% is used for deoxidation; Casting into steel ingot or billet under the condition of no oxidation protection; hot rolling and cold rolling; the heat treatment process of the material after cold rolling is rapid cooling at 1010-1070 ℃ to ensure that the metallographic structure is finer than 6.0 grade. The steel of the invention has the characteristics of excellent stamping performance, avoiding stamping cracking and intermediate annealing.

Description

Austenitic stainless steel with excellent stamping performance and manufacturing method thereof

technical field

The invention relates to an austenitic stainless steel, in particular to an austenitic stainless steel with excellent stamping performance, avoiding stamping cracking and intermediate annealing and a manufacturing method thereof.

Background technique

Austenitic stainless steel has good comprehensive mechanical properties, is convenient for machining, stamping and welding, and has excellent corrosion resistance and good heat resistance in oxidizing environments, so it is widely used in various processing fields, especially Especially in the field of deep drawing, it has advantages that other stainless steels cannot match.

However, some products of stainless steel cold-rolled products in kitchen equipment and utensils, thermos cups (pots), solar energy, precision electronics and other industries have high requirements for deep processing performance, surface quality, mechanical properties and intermediate annealing, and ordinary 304 generally cannot meet them. Processing requirements. For this reason, mature stainless steel enterprises at home and abroad have carried out targeted composition design and process improvement for the materials used for stamping products to ensure that their products can meet the needs of users. For example, CN1113661A improves its deep drawing performance by adding Cu content below 3% to 304 stainless steel; US5571343 controls the Md30 and ferrite content of the material by adding Cu to 304 stainless steel, and improves the stamping cracking problem of the material; JP2001081535A is based on 304 The content of Si and Al is added to reduce Md30 to improve the formability; JP07204791A improves the deep drawing performance of the material by controlling the relationship between C, N, Ni and other elements; CN1502716A also adjusts the ferrite content of the material to improve the formability The purpose of performance; CN1364944A is to improve the deep processing performance of its material by controlling the inclusion composition of the material, and it pays more attention to the influence of the material processing method on the performance.

Judging from the control methods of the above-mentioned patented materials, most of them are based on 304 stainless steel, adding elements such as Ni, Cu, Al or Mn to reduce the Md30 of the material to improve the formability. But still can not meet the stamping performance requirements.

Contents of the invention

The object of the present invention is to provide an austenitic stainless steel with excellent stamping performance, avoid stamping cracking and avoid annealing during stamping.

In order to achieve the above object, the austenitic stainless steel of the present invention has a weight percentage distribution ratio of its chemical composition: C≤0.03%, Si≤0.75%, Mn: 2.0-3.0%, Cr: 16-19%, Ni: 8.0 -9.50%, Cu: 2.0-3.0%, Nb: 0.1-0.25%, N≤0.03%, Al≤0.005%, and the content of Nb, C and N must meet: Nb-8(C+N)≥0, (C+Nb)≤0.30%, the rest is Fe and unavoidable impurities.

The present invention is based on 304 stainless steel, in addition to adding Cu and Mn elements to reduce Md30, it also reduces the C and N content of 304 stainless steel, and adds Nb element to minimize the negative impact of interstitial atoms in the material on the material formability, thereby To achieve the purpose of improving the formability of the material.

Another object of the present invention is to provide a method for producing the above-mentioned austenitic stainless steel. The method includes:

During the smelting process, the basicity of the slag is controlled at 1.5-2.5. Under vacuum or non-vacuum conditions, ferrosilicon or silicon-manganese alloy with an aluminum content of less than 1.0% is used for deoxidation, and the fully calmed molten steel is poured under the condition of no oxidation protection. into ingots or billets;

The suitable hot rolling heating temperature of the present invention is controlled at 1200-1240°C; compared with SUS304, the cold rolling hardening degree of the present invention is smaller, and the maximum deformation rate of each pass can be close to or equal to 35%, so that under the same deformation rate condition, the Cold rolling pass;

The heat treatment process of the material after cold rolling is 1010-1070°C rapid cooling, such as water cooling or air cooling, to ensure that the metallographic structure is finer than 6.0 grade.

The above process can be produced on the equipment for producing SUS304 in the metallurgical plant.

Description of drawings

Fig. 1 is a comparison of the inclusion control effect between the steel of Example 1 of the present invention and the 18Cr-8Ni-0.009Al steel. Among them, 1a is the morphology of inclusions in 18Cr-8Ni-0.009Al steel; 1b is the morphology of inclusions in the steel of the present invention.

Fig. 2 is a comparison of the cold work hardening of the steel of Example 1 of the present invention and the SUS304 steel.

Detailed ways

The present invention will be described in more detail below.

In the present invention, unless otherwise specified, the content refers to the weight percentage content.

SUS304 is a metastable austenitic stainless steel. During cold deformation, this metastable austenite transforms into deformed martensite. Due to the formation of deformed martensite, the material has high strength and hardness, thus It will cause difficulty in re-deformation of the material, affect the deep drawing performance of the material, and in severe cases, it may cause the material to crack during the deformation process, or aging cracking after deformation. Md30 (°C) is one of the important indicators to characterize the degree of martensitic transformation (Formula 1). The lower the Md30 (°C), the less the amount of deformed martensite formed during cold deformation of the material, and the better the stamping performance of the material. The lower the tendency of the material to age crack after stamping.

Md30(°C)=551-462(C%+N%)-9.2Si%-8.1Mn%-13.7Cr%

-18.5Mo%-29(Ni%+Cu%)-68Nb%-1.42(γ-8.0)(1)

In the formula γ: material grain size

The inventors found that the stamping process of austenitic stainless steel is essentially the flow process of metal between dies, and this process is accompanied by deformation and hardening of the material, thereby affecting the formability. Deformation hardening is caused by the accumulation of dislocations hindering the passage of other dislocations. The annihilation, rearrangement and cross-slip of dislocations will reduce the degree of hardening of deformation. At the same time, the stacking fault energy of metal is relatively high, and metal flow is easier. Or the deformation is easier, thus increasing the elements that increase the metal stacking fault energy is beneficial to the forming of the material.

C: Carbon is an element that strongly stabilizes austenite and expands the austenite zone in stainless steel, and is also a material strengthening element. However, since the atomic radius of C is much smaller than that of metal Fe, Cr, Ni, Cu and other atoms, it belongs to interstitial atoms in metal materials, which is not conducive to the corrosion resistance and stamping performance of materials. Therefore, the carbon content of the present invention is limited to ≤0.03%. Preferably, C≤0.02%, more preferably 0.007-0.02%.

Si: Silicon is a deoxidizing element commonly used in the stainless steel smelting process. It is necessary to ensure that there is a certain amount of Si in the molten steel to fully deoxidize the molten steel. On the other hand, silicon reduces the stacking fault energy of the material, which is not conducive to the deformation of the material. Therefore, the range of silicon content is determined to be ≤0.75%. Preferably, the silicon content is 0.20-0.70%, more preferably 0.40-0.70%.

Mn: Manganese is one of the austenite-forming elements, which has the effect of stabilizing the austenite structure. At the same time, manganese is also a cheap element that reduces Md30 (°C) (Formula 1), but it is considered that it has an effect on the corrosion resistance of materials. Certain negative effects, the manganese content in the steel is determined as: 2.0-3.5%. Preferably, the manganese content is 2.5-3.5%, more preferably 2.7-3.45%.

Cr: Chromium is the most basic element of stainless steel, and is the basic element for stainless steel to obtain corrosion resistance. Simultaneously Cr is also the ferrite forming element in stainless steel, because the present invention requires lower C, N (strong austenite forming element) content, in order to keep the phase balance of material, the chromium content of the present invention is 16-19%. Preferably it is 16.1-18.8%, more preferably 16.5-18.6%.

Ni: Ni belongs to the formation of strong austenite, stable element, has higher stacking fault energy, and is the main alloy to improve the formability of materials, but because its expensive price limits its large addition, the nickel content of the present invention is 8.0- 9.0%. Preferably it is 8.05-9.0%, more preferably 8.06-8.7%.

Cu: Cu belongs to austenite forming and stabilizing elements, and has high stacking fault energy. It is the main alloy to improve the formability of materials, but too high Cu content affects the thermal processing performance of materials. The nickel content of the present invention is 2.0 -3.0%. Preferably it is 2.05-2.95%, more preferably 2.08-2.92%, most preferably 2.3-2.92%.

N: Nitrogen is a strong austenite forming element. Since N is an interstitial element and is not conducive to the formability of the material, the nitrogen content of the steel of the present invention is ≤0.03%. Preferably ≤0.02%, more preferably 0.005-0.015%.

Nb: Nb has a strong binding force with C and N in stainless steel, which reduces the harmful effects of C and N interstitial atoms in austenitic stainless steel, making the material "IF", and Nb refines the austenitic stainless steel Grain, reduce the Md30 (°C) of the material, the stacking fault energy of the solid solution Nb increases the material, which is beneficial to the interlayer flow of the material, but too high Nb improves the strength of the material and increases the production cost, so the Nb content of the present invention 0.1-0.25%. In order to ensure the effect of adding Nb, the contents of Nb, C and N must satisfy: Nb-8(C+N)≥0 and (C+Nb)≤0.30%. Preferably it is 0.15-0.25%.

Al: Al mainly exists in the form of Al ₂ O ₃ inclusions in stainless steel. Since such inclusions are brittle inclusions that cannot be deformed with the metal, they have relatively great harm to the formability of the material. In order to limit their harmful effects, the present invention stipulates Al≤0.005%, preferably 0.003-0.005%.

P: Phosphorus is a harmful element in stainless steel, and the phosphorus content in the steel should be kept as low as possible, but there is no economical and effective means for dephosphorization in stainless steel smelting, and the content of phosphorus in the steel of this invention is determined to be ≤0.03%.

S: Sulfur is also a harmful element in stainless steel. It is easy to form inclusions such as MnS in steel. At the same time, sulfur deteriorates the hot workability of steel and has a negative effect on the corrosion resistance of materials. Therefore, in the present invention, the sulfur content in the steel is ≤0.02%, preferably ≤0.005%.

The invention improves the deformation flow performance of the material by reducing the C and N content of the interstitial atoms of SUS304 stainless steel, increases the Cu content to improve the formability of the material, increases the Mn and Cu elements and reduces the Md30 (℃) of the material, and adds Nb to reduce the C and N gap The harm of atoms, the reduction of Md30(°C) of the material, the refinement of the crystal grains of the material, the increase of strength and the avoidance of stamping cracking of the material make the formability of the present invention be improved.

The grain size of the material after heat treatment not only affects Md30(°C) (Formula 1), but also improves the strength of the material to a certain extent and reduces the risk of stamping cracking.

When austenitic stainless steel is used as a stamping material, thin-gauge materials are used in most cases. Therefore, the stamping processing material not only has relatively high requirements on the formability of the material, but also has a certain impact on the level of inclusions that affect the stamping process of the material. Higher requirements, so the present invention also specifies the production process of the material.

The manufacturing process of the austenitic stainless steel with excellent stamping performance of the present invention: during the smelting process, the basicity of the slag is controlled at 1.5-2.5, and under vacuum or non-vacuum conditions, ferrosilicon or silicon-manganese with an aluminum content of less than 1.0% is used The alloy is deoxidized, and the molten steel that has been sufficiently calmed is cast into a steel ingot or a billet under the condition of no oxidation protection. The suitable hot rolling heating temperature of the present invention is controlled at 1200-1240°C; compared with SUS304, the cold rolling hardening degree of the present invention is small, and the pass deformation The rate can be close to 35%, so that under the same deformation rate, the number of cold rolling passes can be reduced; after cold rolling, the heat treatment process of this material is 1010-1070 ℃ rapid cooling to ensure that a finer metallographic structure than grade 6.0 can be obtained . This material can be produced with equipment for producing SUS304 in metallurgical plants.

The present invention will be further described below in conjunction with embodiment.

Table 1 is the comparison between the typical composition (%) of the material of the present invention and the typical composition (%) and Md30 (° C.) of related patents. It can be seen from Table 1 that except for JP08295980A which improves the bulging ability, the Md30(°C) of most patented products is lower than that of the conventional SUS304, and all have achieved the goal of improving the stamping performance of the material, but the Md30(°C) of the present invention is controlled to - 47°C is the lowest among several materials. Under the same deformation conditions, the ability of this material to continue cold deformation is relatively strong.

Table 1 Typical composition of patented materials, Md30 (°C) comparison

The chemical composition of table 2 embodiment of the present invention and Md30 (℃) control result

Table 2 lists the composition control of the material embodiment of the present invention and the calculated Md30 (°C). It can be seen that with the change of composition, Md30 (°C) changes in the range of -20°C to -75°C, which is lower than that of conventional SUS304 around 15°C level.

Test Example 1: Mechanical Properties

Carry out tensile test according to GB/T 228-2002 method, measure the yield strength, tensile strength, yield ratio, elongation of the steel of the embodiment of the present invention and SUS304 steel, its result is shown in Table 3.

Test example 2: according to GB/T 4340.1 (Vickers hardness) method, measure the hardness of the steel of the embodiment of the present invention and SUS304 steel, its result is shown in Table 3.

Test example 3: IE (cupping value)

According to the GB4156 experimental method, the experimental materials are all 0.5mm products, and the IE of the steel in the embodiment of the present invention and the SUS304 steel is measured, and the results are shown in Table 3.

Test Example 4: LDR (Limited Drawing Ratio)

According to the test method of GB/T15825.3, the test materials are all 0.5mm products, and the LDR of the steel in the embodiment of the present invention and the SUS304 steel is measured, and the results are shown in Table 3.

Test Example 5: Tissue

After the LDR experiment, the average martensite content (area percentage) was detected by a ferrite analyzer, and the results are shown in Table 3.

Table 3 Comparison of Typical Formability of the Embodiments of the Present Invention

Table 3 has listed the contrast of the typical formability index of the embodiment of the present invention and conventional SUS304, and the intensity of the material of the present invention, hardness are obviously lower than conventional SUS304, and reflect the LDR of material drawing performance index, the martensite after cold deformation of material. The volume content is obviously better than that of SUS304, and the IE reflecting the bulging performance index of the material is not as good as that of conventional SUS304. Table 2 and Table 3 fully show that the material of the present invention has excellent stamping performance, can avoid stamping cracking, and can avoid the excellent performance of stamping intermediate annealing.

Test Example 6: Composition and Morphology of Inclusions

The control effect of the inclusions in the steel of the embodiment of the present invention measured by transmission electron microscopy and the comparison of conventional SUS304 are shown in Figure 1 and Table 4 and Table 5, wherein Figure 1a is the morphology of inclusions in 18Cr-8Ni-0.009Al steel; Figure 1b It is the morphology of inclusions in the steel of Example 1 of the present invention; Table 4 is the composition of inclusions in 18Cr-8Ni-0.009Al steel; Table 5 is the composition of inclusions in the steel of Example 1 of the present invention.

Inclusion composition of table 418Cr-8Ni-0.009Al steel

elements Wt% At% OK 33.65 48.24 MgK 14.13 13.33 AlK 36.82 31.29 SiK 00.59 00.49 CaK 02.40 01.37 TiK 00.80 00.38 CrK 03.58 01.58 MnK 04.24 01.77 FeK 03.79 01.56 Matrix Correction ZAF

Table 5 Composition of steel inclusions of the present invention

elements Wt% At% OK 15.11 33.62 MgK 02.60 03.81 AlK 04.15 05.47 SiK 08.42 10.67 SK 00.10 00.11 CaK 05.23 04.65 TiK 00.82 00.61 CrK 13.53 09.27 MnK 01.80 01.17 FeK 44.30 28.24 K 03.93 02.38 Matrix Correction ZAF

Where XK represents element X, Wt%: represents weight %, At%: represents atomic %, ZAF: correction factor for quantitative analysis.

From the comparison of Fig. 1 and Table 4 and Table 5, it can be seen that the inclusion control of the material of the present invention is more conducive to the stamping of the material.

Test Example 7: Strength under Different Cold Rolling Deformation Ratio Conditions

The strength comparison between the steel of Example 1 of the present invention and conventional SUS304 under different cold rolling deformation ratios is shown in Fig. 2 .

It can be seen from the figure that since the material of the present invention has a lower Md30 (°C), the strength of the material after cold rolling is obviously lower than that of SUS304, and it has better stamping performance than SUS304.

Claims (15)

1. An austenitic stainless steel, the weight percentage of its chemical composition is: C≤0.03%, Si≤0.75%, Mn: 2.0-3.5%, Cr: 16-19%, Ni: 8.0-9.50%, Cu: 2.0-3.0%, Nb: 0.1-0.25%, N≤0.03%, Al≤0.005%, and the content of Nb, C and N must meet: Nb-8(C+N)≥0, (C+Nb )≤0.30%, the rest is Fe and unavoidable impurities; Md30≤-20℃; The steel is manufactured by a method comprising the steps of: include: During the smelting process, the basicity of the slag is controlled at 1.5-2.5. Under vacuum or non-vacuum conditions, ferrosilicon or silicon-manganese alloy with an aluminum content of less than 1.0wt% is used for deoxidation. Pouring into ingots or billets; hot rolling and cold rolling; The heat treatment process of the material after cold rolling is rapid cooling at 1010-1070°C to ensure a finer metallographic structure than grade 6.0. 2. The austenitic stainless steel according to claim 1, characterized in that C≤0.02%. 3. The austenitic stainless steel according to claim 1, characterized in that C: 0.007-0.02%. 4. The austenitic stainless steel according to claim 1, characterized in that Si: 0.20-0.70%. 5. The austenitic stainless steel according to claim 1, characterized in that Mn: 2.5-3.45%. 6. The austenitic stainless steel according to claim 1, characterized in that Al: 0.003-0.005%. 7. The austenitic stainless steel according to claim 1, characterized in that Cr: 16.1-18.8%. 8. The austenitic stainless steel according to claim 1, wherein Ni: 8.05-9.0%. 9. The austenitic stainless steel according to claim 1, characterized in that Cu: 2.05-2.95%. 10. The austenitic stainless steel according to claim 1, wherein Nb: 0.15-0.25%. 11. The austenitic stainless steel according to claim 1, characterized in that N: 0.005-0.02%. 12. The austenitic stainless steel according to claim 1, characterized in that P≤0.03% and S≤0.02%. 13. The austenitic stainless steel according to claim 1, wherein the rapid cooling is water cooling or air cooling. 14. The austenitic stainless steel according to claim 1, characterized in that the suitable heating temperature in hot rolling is controlled at 1200-1240°C. 15. The austenitic stainless steel according to claim 1, characterized in that the maximum deformation rate of each pass in cold rolling is 35%.