Production process of stainless steel with low-temperature impact resistance

Abstract

The invention discloses a production process of stainless steel with low-temperature impact resistance, which comprises the following steps: step 1, after tapping steel from an electric furnace or an intermediate frequency furnace and transferring to an AOD (Argon Oxygen Decarburization) refining furnace, removing primary smelting slag thoroughly, and entering a decarburization period; 2, slagging off after the decarburization period is finished, entering a pre-reduction period, adopting full silicon iron for pre-reduction, and slagging off until the residual slag amount is less than 200kg after the pre-reduction slag color is changed; 3, entering a reduction period, adding special-grade lime and special-grade fluorite for slagging, and adding an aluminum ingot for reduction; and 4, after the temperature is 1650-1700 DEG C, nitrogen is blown to the bottom of the steel ladle, so that the content of N in the molten steel is larger than 400 ppm, and a finished product is obtained. The method has the characteristics of improving the low-temperature impact performance of the stainless steel and improving the stability of production batches.

Description

Technical Field

[0001] The invention relates to a stainless steel production process, in particular to a stainless steel production process with low temperature impact resistance. Background Art

[0002] In modern manufacturing and engineering applications, stainless steel is widely used due to its excellent corrosion resistance, strength and aesthetics. For example, in oil and gas extraction, it is necessary to work in low temperature environments (such as polar regions or deep sea); in the aerospace industry, materials need to withstand extremely low temperatures and high impact forces, so stainless steel materials need to have good low-temperature impact resistance. However, for some stainless steels, such as martensitic stainless steel, the impact performance in low-temperature environments is insufficient, resulting in brittle fracture under extreme conditions, affecting the safety and reliability of the structure.

[0003] There are currently some methods to improve the low-temperature impact properties of stainless steel, such as changing the alloy composition, heat treatment, etc. However, the method of changing the alloy composition has little effect on improving the performance of the final product, and the improvement effect is not obvious; while the heat treatment method may affect the corrosion resistance or tensile properties of stainless steel, resulting in unstable mechanical properties of the finished product.

[0004] Therefore, the existing methods for improving the low-temperature impact properties of stainless steel have certain limitations and poor stability, resulting in large quality differences between production batches, affecting the continuity and stability of stainless steel production, and cannot meet actual requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a stainless steel production process with low temperature impact resistance. The present invention has the characteristics of improving the low temperature impact resistance of stainless steel and improving the stability of production batches.

[0006] The technical solution of the present invention is a production process of stainless steel with low temperature impact resistance, comprising the following steps:

[0007] Step 1: After the steel is tapped from the electric furnace or medium frequency furnace and transferred to the AOD refining furnace, the primary slag is scraped off and the decarburization period begins;

[0008] Step 2: After the decarburization period, the slag is removed and the pre-reduction period begins. Full ferrosilicon pre-reduction is adopted. After the pre-reduction slag changes color, the slag is removed until the remaining slag amount is less than 200kg.

[0009] Step 3: Entering the reduction period, adding special grade lime and special grade fluorite to make slag, and adding aluminum ingots for reduction;

[0010] Step 4: When the temperature reaches 1650-1700°C, nitrogen is blown from the bottom of the ladle to make the nitrogen content in the molten steel greater than 400ppm to obtain the finished product.

[0011] In the aforementioned low-temperature impact-resistant stainless steel production process, the temperature is controlled at 1680°C to 1720°C after pre-reduction.

[0012] In the aforementioned low-temperature impact-resistant stainless steel production process, the pre-reduction period of step 2 is greater than 10 minutes.

[0013] In the aforementioned low-temperature impact-resistant stainless steel production process, in step three, the amount of special-grade lime added is ≥20kg / T; the amount of special-grade fluorite added is ≥6kg / T, and the amount of aluminum ingot added is ≥1.5Kg / T.

[0014] In the aforementioned low-temperature impact-resistant stainless steel production process, in step three, the slag is white in color after reduction, and the reduction period is greater than 10 minutes.

[0015] In the aforementioned low temperature impact resistant stainless steel production process, in step 4, the initial nitrogen flow rate is 1-2m 3 / h, the final flow rate is 10-14m 3 / h, nitrogen blowing time>10min, total nitrogen increment>0.9m 3 .

[0016] The aforementioned low-temperature impact-resistant stainless steel production process also includes step five, performing slag pulling operation before tapping, and after tapping, the thickness of the ladle slag layer is 200 to 300 mm.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention can prevent the primary smelting slag from contaminating the molten steel and reduce the difficulty of subsequent smelting by scraping off the primary smelting slag. During the pre-reduction period, the slag is scraped off until the remaining slag is less than 200kg, which can effectively reduce the generation of inclusions in the molten steel and improve the purity of the molten steel. The slag pulling operation is performed before tapping, so that the thickness of the ladle slag layer is 200-300mm, which is more conducive to the floating of inclusions and the rapid addition of alloys. Nitrogen is blown from the bottom of the ladle to control the flow rate of nitrogen and the N content in the molten steel, thereby improving the low-temperature impact performance of stainless steel and having stable performance.

[0019] The present invention improves the production process as above, reduces material cost, reduces the ferrite content of finished products, and effectively improves the low-temperature impact performance of stainless steel, so that the stainless steel can reach >88KV at a temperature of -20°C. 2 / J, even up to 166KV 2 / J, hardness requirement after annealing is ≤295HBW, quality is stable after multiple tests, and a good and stable production process is in place to improve the mechanical properties of the finished product. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0021] Embodiment 1:

[0022] A production process of stainless steel with low temperature impact resistance, taking 25 tons of molten steel as an example, martensitic stainless steel 431 stainless steel comprises the following steps:

[0023] Step 1: After the steel is tapped from the electric furnace or medium frequency furnace and transferred to the AOD refining furnace, the primary slag is scraped off and the decarburization period begins. The primary slag is scraped off to prevent it from contaminating the molten steel and reduce the difficulty of subsequent smelting.

[0024] Step 2: After the decarburization period, the slag is removed and the pre-reduction period begins. All-ferrosilicon pre-reduction is used. After the pre-reduction, the temperature is controlled at 1700°C. After the pre-reduction slag changes color, the slag is removed until the remaining slag reaches 150kg. The pre-reduction period is 15 minutes.

[0025] Step 3: Enter the reduction period, add 20kg / T of molten steel special grade lime and 6kg / T of molten steel special grade fluorite to make slag, add 1.5kg / T of molten steel aluminum ingot to reduce, the slag color is white after reduction, and the reduction period is 30min.

[0026] Step 4: When the temperature reaches 1680℃, blow nitrogen from the bottom of the ladle, and the initial nitrogen flow rate is 1.13m 3 / h, the final flow rate is 11.08m 3 / h, the total nitrogen increment is 0.966m 3 The nitrogen blowing time is 11 minutes, and strong stirring and weak stirring are combined to make the nitrogen content in the molten steel 403ppm, and the finished product is obtained;

[0027] Step 5: Before tapping, slag pulling operation is performed. Part of the final slag is removed according to the slag conditions. After tapping, the thickness of the ladle slag layer is 200mm.

[0028] Embodiment 2:

[0029] This embodiment is basically the same as embodiment 1, except that in step 4, the initial nitrogen flow rate is 1.75m 3 / h, the final flow rate is 12.73m 3 / h, the total nitrogen increment is 1.09m 3 The nitrogen blowing time is 15 minutes, and strong stirring and weak stirring are combined to make the nitrogen content in the molten steel 423ppm.

[0030] Embodiment 3:

[0031] This embodiment is basically the same as embodiment 1, except that the amount of molten steel is 25.7 tons, and in step 4, the initial nitrogen flow rate is 1.716m3 / h, the final flow rate is 12.86m 3 / h, the total nitrogen increment is 1.24m 3 The nitrogen blowing time is 17.5 minutes, and strong stirring and weak stirring are combined to make the nitrogen content in the molten steel 440ppm.

[0032] Embodiment 4:

[0033] This embodiment is basically the same as embodiment 3, except that in step 4, the initial nitrogen flow rate is 1.868m 3 / h, the final flow rate is 12.33m 3 / h, the total nitrogen increment is 1.05m 3 The nitrogen blowing time was 17 minutes, and strong stirring and weak stirring were combined to make the nitrogen content in the molten steel 414ppm.

[0034] Embodiment 5:

[0035] This embodiment is basically the same as embodiment 3, except that in step 4, the initial nitrogen flow rate is 1.012m 3 / h, the final flow rate is 13.59m 3 / h, the total nitrogen increment is 1.263m 3 The nitrogen blowing time was 14.5 min, and strong stirring and weak stirring were combined to make the nitrogen content in the molten steel 449 ppm.

[0036] Comparative Example 1:

[0037] This comparative example is basically the same as Example 1, except that there is no nitrogen blowing operation at the bottom of the ladle in step 4.

[0038] Comparative Example 2:

[0039] This comparative example is basically the same as Example 1, except that in step 4, the initial nitrogen flow rate is 1.262m 3 / h, the final flow rate is 4.265m 3 / h, the total nitrogen increment is 0.287m 3 The nitrogen blowing time is 4 minutes, and strong stirring and weak stirring are combined to make the nitrogen content in the molten steel reach 150ppm.

[0040] The mechanical properties and hardness of the stainless steel obtained in different embodiments and comparative examples are shown in Table 1:

[0041]

[0042] As can be seen from the above, multiple measurements were performed on Examples 1-5 and Comparative Examples 1-2 in the same range. The impact of Example 1 at -20°C was 130KV and 2 / J and 120KV2 / J, Example 2 at -20℃ impact is 101KV 2 / J and 103KV 2 / J, Example 3 at -20℃ impact is 130KV 2 / J, 112KV 2 / J and 166KV 2 / J, Example 4 at -20℃ impact is 101KV 2 / J, 88KV 2 / J and 104KV 2 / J, Example 5 at -20℃ impact is 129KV 2 / J, 158KV 2 / J and 159KV 2 / J; while the comparative example 1 at -20℃ impact is 16KV 2 / J, 31KV 2 / J and 26KV 2 / J, comparative example 2 at -20℃ impact is 21KV 2 / J, 26KV 2 / J and 22KV 2 / J.

[0043] It can be seen from the above that the low-temperature impact performance of the stainless steel prepared in the present application is greatly improved.

[0044] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A process for producing stainless steel with low temperature impact resistance, characterized in that: The following steps are involved: Step 1: After the steel is tapped from the electric furnace or medium frequency furnace and transferred to the AOD refining furnace, the primary slag is removed and the decarburization period begins; Step 2: After the decarburization period, the slag is removed and the pre-reduction period begins. Full ferrosilicon pre-reduction is adopted. After the pre-reduction slag changes color, the slag is removed until the remaining slag amount is less than 200kg. Step 3: Entering the reduction period, adding special grade lime and special grade fluorite to make slag, and adding aluminum ingots for reduction; Step 4: When the temperature reaches 1650-1700°C, nitrogen is blown from the bottom of the ladle to make the nitrogen content in the molten steel greater than 400ppm to obtain the finished product.

2. The process for producing stainless steel with low temperature impact resistance according to claim 1, characterized in that: After pre-reduction, the temperature is controlled at 1680°C to 1720°C.

3. The production process of stainless steel with low temperature impact resistance according to claim 1, characterized in that: The pre-reduction period of step 2 is > 10 minutes.

4. The process for producing stainless steel with low temperature impact resistance according to claim 1, characterized in that: In step 3, the amount of special grade lime added is ≥20kg / T; the amount of special grade fluorite added is ≥6kg / T, and the amount of aluminum ingot added is ≥1.5Kg / T.

5. The production process of stainless steel with low temperature impact resistance according to claim 1, characterized in that: In step 3, the residue is white after reduction, and the reduction period is greater than 10 minutes.

6. The production process of stainless steel with low temperature impact resistance according to claim 1, characterized in that: In step 4, the initial nitrogen flow rate is 1-2m 3 / h, the final flow rate is 10-14m 3 / h, nitrogen blowing time>10min, total nitrogen increment>0.9m 3 .

7. The production process of stainless steel with low temperature impact resistance according to claim 1, characterized in that: The method also includes step five, performing slag pulling operation before steel tapping, and after steel tapping, the thickness of the ladle slag layer is 200 to 300 mm.

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