Low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers and its manufacturing method

Abstract

The present invention relates to low-carbon, high-silicon, corrosion-resistant stainless steel for containers with strong toughness and a manufacturing method. The stainless steel comprises the following components by weight: C: 0.02% to 0.03%, Si: 1.7% to 3.2%, Mn: 0.8% to 0.93%, P ≤ 0.01%, S ≤ 0.001%, Cr: 15.3% to 17%, Ni: 2.3% to 3.2%, Mo: 1.5% to 2.1%, Ca: 0.00032% to 0.0021%, Als: 0.002% to 0.03%, with the remainder being Fe and unavoidable impurities. The volume content of ferrite is no more than 1%. The advantages of the stainless steel are: the steel plate has a simple and reasonable composition, and adopts a four-stage heating, staged rolling, and solution heat treatment method to ensure that the finished steel plate has a uniform grain size throughout the thickness, high strength and toughness, and excellent corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the field of stainless steel production, and in particular relates to low-carbon, high-silicon, strong and tough stainless steel for corrosion-resistant containers and a manufacturing method thereof. Background Art

[0002] Stainless steel is a general term for a type of steel that exhibits a certain degree of stability in both mildly corrosive media (such as air and water) and highly corrosive media (such as acids, alkalis, salts, and organic matter). It is typically manufactured by adding a certain amount of alloying elements, such as chromium (usually greater than 12%), to the steel. Stainless steel's corrosion resistance stems from the ability to automatically form a stable "passivation film" on its surface, typically composed primarily of Cr2O3. Since its invention in the early 20th century, stainless steel has been widely used for its excellent heat and corrosion resistance, oxidation resistance, ease of processing, and surface gloss.

[0003] With the development of the national economy, and the subsequent rapid growth in oil exploration and aerospace, the demand for high-strength stainless steel with high strength and hardness, good corrosion resistance, and easy processing and welding has increased rapidly. Currently, ferritic, austenitic, and martensitic stainless steels are widely used. However, while ferritic and austenitic stainless steels have good corrosion resistance, they also have low strength. Maraging stainless steels, on the other hand, have relatively poor corrosion resistance, plasticity, and weldability.

[0004] Therefore, in order to solve the problems of strength-toughness matching and corrosion resistance of stainless steel plates for full-thickness pressure vessels (thickness 40-100mm), it is urgent to develop a new type of corrosion-resistant stainless steel for containers, which is required to have excellent comprehensive performance, with strength and toughness better than conventional steel, and corrosion resistance similar to or even better, and the production cost is lower than that of ideal corrosion-resistant stainless steel plates for containers with the same performance materials made abroad.

[0005] Patent publication number CN114438408A discloses a low-cost, high-strength, heat-resistant, and corrosion-resistant stainless steel material and a method for producing precision parts using it. The material is composed of the following alloying elements by mass: C: 0-0.03%, O: 0-0.30%, Si: 1.0-2.0%, Mn: 0.2-0.8%, Cr: 12-16%, Ni: 5-10%, Cu: 0.5-2.5%, Mo: 0.5-2.0%, with the balance being Fe. This method combines aging heat treatment with ion nitriding, but this method is costly and unsuitable for large-scale production of components and corresponding steel plates.

[0006] Patent publication number: CN113522972A, discloses a production process for surface corrosion-resistant stainless steel composite plates, and provides a production process for surface corrosion-resistant stainless steel composite plates, which is divided into two parts: a stainless steel coating and a carbon steel base. The maximum thickness of the studied steel plate is only 24 mm, and no research has been conducted on large-thickness steel plates. Summary of the Invention

[0007] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a low-carbon, high-silicon, corrosion-resistant stainless steel for containers with strong toughness and a manufacturing method, so as to solve the problems of strength-toughness matching and corrosion resistance. The stainless steel for containers with a thickness of 40 to 100 mm has excellent comprehensive performance, and its strength and toughness are better than those of conventional steels, while its corrosion resistance is similar to or even better, and it can reduce production costs.

[0008] To achieve the above object, the present invention is implemented through the following technical solutions:

[0009] A low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers, comprising the following components by weight:

[0010] C: 0.02% ~ 0.03%, Si: 1.7% ~ 3.2%, Mn: 0.8% ~ 0.93%, P ≤ 0.01%, S ≤ 0.001%, Cr: 15.3% ~ 17%, Ni: 2.3% ~ 3.2%, Mo: 1.5% ~ 2.1%, Ca: 0.0021% ~ 0.0033%, Als: 0.002% ~ 0.03%, the rest are Fe and unavoidable impurities; among which, the volume content of ferrite is not higher than 1%.

[0011] Among them, the role of each chemical component:

[0012] Carbon often forms carbides with other alloying elements in steel, contributing to its strengthening properties. Carbon easily combines with alloying elements to form carbides, causing segregation within the steel and significantly reducing the toughness and ductility of the steel plate. This invention addresses this issue by adopting a low-carbon design. While maintaining the strength of the steel plate, the carbon content is controlled to 0.02% to 0.03%.

[0013] Si deoxidizes and desulfurizes steel and improves steel plate strength through solid solution strengthening. Si is also a key corrosion-resistant element. Adding Si to austenitic stainless steel improves its corrosion resistance in strongly oxidizing media. Furthermore, Si enhances the fluidity of molten steel. Si is an inexpensive alloying element. Adding an appropriate amount of Si to steel can increase the hardness and strength of ferrite, improve the elastic limit, yield strength, yield ratio, fatigue strength, and fatigue ratio, and improve resistance to localized corrosion. However, high Si content can negatively impact the impact toughness of the heat-affected zone (HAZ). Si reacts with Al in steel to form Si-Al compounds, reducing the content and volume fraction of aluminum-containing inclusions in the finished steel plate and improving the uniformity of the through-thickness microstructure. This enhances both strength and toughness while also improving wear resistance. However, high Si content can easily combine with the carbon and nitrogen content in the steel, negatively impacting the impact toughness of the HAZ. Therefore, the Si content is limited to 1.7% to 3.2%.

[0014] Mn is a commonly used desulfurizer in steel, but excessive Mn addition increases the number of MnS inclusions, increasing the probability of segregation in the steel, resulting in high-strength, low-toughness hard phases of martensite and bainite, which can reduce the weldability of the steel. Therefore, the Mn content should not be too high. Taking into account the strength, toughness, and weldability of the steel plate, the Mn content is set within the range of 0.8% to 0.93% during composition design.

[0015] S is a brittle element in steel and is also an element that is highly susceptible to segregation, so the lower its content, the better. Both elements also significantly impair the low-temperature toughness of steel. However, considering factors such as steelmaking operability, steelmaking costs, and meeting application requirements, the contents of P and S are controlled below 0.01% and 0.001%, respectively.

[0016] Cr forms various carbides with carbon in steel and dissolves in austenite, providing dispersion, grain refinement, and solid solution strengthening, positively impacting the strength and toughness of the steel. However, excessive addition of Cr can reduce toughness, increase brittleness, and increase production costs. Therefore, the Cr content is controlled within a range of 15.3% to 17%.

[0017] Ni expands the austenite region while also inhibiting the formation of ferrite in the steel. Combined with Cr, it ensures the steel plate has excellent resistance to oxidation and corrosion. Due to its high cost, the Ni content is limited to 2.3%-3.2%.

[0018] Mo increases the probability of austenite formation and refines the austenite structure, improving the strength and toughness of the steel plate. However, Mo negatively impacts the weldability of the steel plate and is a precious metal with a high cost. Therefore, the Mo content in this invention is controlled to 1.5% to 2.1%.

[0019] Ca controls the morphology of sulfides in steel, suppressing the formation of MnS by forming CaS. To achieve this effect, the Ca content must be at least 0.0003%. Furthermore, if the Ca content exceeds 0.005%, the resulting CaS becomes excessively large, increasing brittleness and becoming a potential initiation point for fracture cracks. Therefore, the Ca content is limited to 0.0021% to 0.0033%.

[0020] Als is a deoxidizing element in steel. It can effectively refine grains by forming AlN in steel. The appropriate content is 0.002%-0.03%.

[0021] A method for manufacturing low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers, comprising the following processes: smelting - continuous casting - heating - rolling - heat treatment, wherein:

[0022] The heating method of the continuous casting billet is a four-stage heating method of preheating section - first heating section - second heating section - soaking section.

[0023] The preheating temperature is 875-920℃ and the heating time is 2.6-3.2h;

[0024] The temperature of the heating section is 1120-1260°C, wherein the temperature of the first heating section is 1120-1185°C, the heating time is 1.2-1.8h, and the temperature of the second heating section is 1200-1265°C, the heating time is 1-1.4h;

[0025] The temperature of the soaking section is 1186~1200℃, and the soaking time is not more than 1h.

[0026] The continuous casting process includes: a tundish molten steel casting temperature of 1505-1535° C., and adopts electromagnetic stirring or a continuous casting billet soft reduction process.

[0027] In the continuous casting billet soft reduction process, the soft reduction rate is controlled at 5% to 7%.

[0028] The rolling process: the continuous casting slab adopts two-stage controlled rolling;

[0029] The finishing rolling temperature of the first stage is 1035-1050℃, and the single-pass reduction rate is 10%-13%;

[0030] The second stage rolling temperature is 940-964°C, and a small deformation amount is used for rapid rolling, with a single-pass reduction rate of 4%-7%.

[0031] The heat treatment mentioned above: the steel plate is subjected to solution heat treatment after rolling;

[0032] The solution temperature is controlled at 1060-1150°C, the net holding time is 0.6-1.4 min / mm, and the steel is water-cooled to room temperature after being taken out of the furnace.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention is suitable for stainless steel used in containers for natural gas and crude oil transportation, petroleum refining, and acidic corrosive media. In terms of steel grade composition design, the steel plate composition is simple and reasonable. By rationally controlling the C and Si contents in the steel, the strength of the steel plate is guaranteed while the corrosion resistance is guaranteed. Ca is added to change the shape of inclusions in the steel, making the inclusions spherical and reducing their size. At the same time, to ensure that the steel plate has good strength and toughness, alloying elements Cr, Ni, and Mo are added to the steel to refine the grains, and precipitation strengthening is used to ensure that the steel plate has good comprehensive properties after solution heat treatment. The low-carbon, high-silicon stainless steel for corrosion-resistant containers with strong toughness has a tensile strength of 550-580 MPa, an impact absorption energy of 300-315 KV2 / J, and a hardness of not less than 140 HBW.

[0035] In terms of manufacturing process, the present invention adopts a four-stage heating, staged rolling and solution heat treatment method to ensure that the finished steel plate has a uniform grain size and high strength and toughness matching throughout the thickness direction while also having excellent corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a metallographic diagram of low-carbon, high-silicon steel for corrosion-resistant containers with strong toughness.

[0037] Figure 2 This is a metallographic diagram of inclusions in low-carbon, high-silicon steel for corrosion-resistant containers with strong toughness. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0039] Low carbon, high silicon, corrosion resistant stainless steel plate for containers with excellent strength and toughness, including the following components and their percentage weight:

[0040] C: 0.02% to 0.03%, Si: 1.7% to 3.2%, Mn: 0.8% to 0.93%, P ≤ 0.01%, S ≤ 0.001%, Cr: 15.3% to 17%, Ni: 2.3% to 3.2%, Mo: 1.5% to 2.1%, Ca: 0.0021% to 0.0033%, Als: 0.002% to 0.03%, and the rest are Fe and unavoidable impurities. Among them, the volume content of ferrite is not higher than 1%. Figure 1 The steel plate structure is austenite, the structure in the steel is uniform and pure (grain size and inclusions), and the corrosion resistance salt spray test results show that the steel plate has good corrosion resistance.

[0041] The production process of low-carbon, high-silicon, corrosion-resistant stainless steel plates for containers with excellent strength and toughness is smelting-continuous casting-heating-rolling-heat treatment. The specific steps are as follows:

[0042] 1) The steel is smelted using processes such as primary furnace smelting and VOD vacuum treatment. A continuous casting process is used, with controlled casting temperatures. The tundish molten steel pouring temperature is ≤1535°C. Low-temperature casting is preferred to refine the original as-cast structure. To control centerline segregation and porosity in the continuous casting slab, electromagnetic stirring or soft reduction of the continuous casting slab is used, with the soft reduction rate controlled at 5% to 7%.

[0043] 2) The continuous casting billet adopts a four-stage heating method, namely preheating section - first heating section - second heating section - soaking section.

[0044] The preheating temperature is 875-920°C, and the heating time is 2.6-3.2h.

[0045] The temperature of the heating section is 1120-1260°C, with the temperature of one heating section being between 1120-1185°C. The heating time and soaking time are 1.2-1.8 hours, so as to refine the coarse precipitates in the continuous casting billet and ensure the austenitization process of the steel plate.

[0046] The temperature of the second heating section is between 1200 and 1265°C, and the heating time is 1 to 1.4 hours. The heating temperature is guaranteed not to be higher than 1265°C to avoid the re-dissolution of fine precipitates in the continuous casting billet and excessive growth of grains.

[0047] The temperature of the soaking section shall not be lower than 1186°C and the soaking time shall not exceed 1h.

[0048] 3) The rolling process of the continuous casting billet adopts a two-stage controlled rolling process.

[0049] The finishing rolling temperature in the first stage is ≥1035℃. In this stage, large deformation is adopted for rapid rolling, and the single-pass reduction rate is 10-13% to ensure that the recrystallization process near the surface of the steel plate is complete.

[0050] The second stage rolling temperature is ≤964℃. In this stage, small deformation is adopted for rapid rolling, and the single-pass reduction rate is 4% to 7% to ensure the stability of the microstructure of the steel plate near the surface.

[0051] After rolling, the steel plates undergo a solution heat treatment process. The solution temperature is controlled at 1060-1150°C, with a net holding time of 0.6-1.4 min / mm. After exiting the furnace, the steel plates are water-cooled to room temperature. This reduces the formation of mixed crystals along the thickness of the steel plates and further ensures the uniformity of the grains within the steel plates.

[0052] Table 1 shows the chemical composition of the example steel, Table 2 shows the continuous casting and heating process parameters of the example steel, Table 3 shows the rolling and heat treatment parameters of the example steel, Table 4 shows the mechanical properties of the example steel plate, Table 5 shows the grain size and non-metallic inclusion test results, and Table 6 shows the salt spray test results of the corrosion resistance of the steel plate.

[0053] Table 1 Chemical composition of the examples (wt%)

[0054]

[0055] Table 2 Continuous casting process parameters of example steel

[0056]

[0057]

[0058] Table 3 Continuous casting slab heating process parameters

[0059]

[0060] Table 4 Rolling and heat treatment process parameters of the example steel

[0061]

[0062] Table 5 Mechanical properties of steel plates in the examples

[0063]

[0064]

[0065] Table 6 Grain size and non-metallic inclusion test results

[0066]

[0067] Table 7 Steel plate corrosion resistance salt spray test

[0068]

[0069] The present invention is suitable for stainless steel used in containers for natural gas and crude oil transportation, petroleum refining, and acidic corrosive media. In terms of steel grade composition design, the steel plate composition is simple and reasonable. By rationally controlling the C and Si contents in the steel, the strength of the steel plate is guaranteed while the corrosion resistance is guaranteed. Ca is added to change the shape of inclusions in the steel, making the inclusions spherical and reducing their size. At the same time, to ensure that the steel plate has good strength and toughness, alloying elements Cr, Ni, and Mo are added to the steel to refine the grains, and precipitation strengthening is used to ensure that the steel plate has good comprehensive properties after solution heat treatment. The low-carbon, high-silicon stainless steel for corrosion-resistant containers with strong toughness has a tensile strength of 550-580 MPa, an impact absorption energy of 300-315 KV2 / J, and a hardness of not less than 140 HBW.

Claims

1. A low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers, characterized in that: The following ingredients are included by weight percentage: C: 0.02%~0.03%, Si: 1.7%~3.2%, Mn: 0.8%~0.93%, P≤0.01%, S≤0.001%, Cr: 15.3%~17%, Ni: 2.3%~3.2%, Mo: 1.5%~2.1%, Ca: 0.0021%~0.0033%, Als: 0.002%~0.03%, the rest are Fe and unavoidable impurities; among which, the volume content of ferrite is not higher than 1%; The method for manufacturing the corrosion-resistant stainless steel for low-carbon, high-silicon and strong toughness containers includes the following processes: smelting - continuous casting - heating - rolling - heat treatment, wherein: 1) The soft reduction rate in the soft reduction process of continuous casting billets is controlled at 5%~7%; 2) Heating: The continuous casting billet adopts a four-stage heating method of preheating section - first heating section - second heating section - soaking section; The preheating temperature is 875~920℃, and the heating time is 2.6~3.2h; The temperature of the heating section is 1120~1260℃, of which the temperature of the first heating section is 1120~1185℃, the heating time is 1.2~1.8h, and the temperature of the second heating section is 1200~1265℃, the heating time is 1~1.4h; The soaking section temperature is 1186~1200℃, and the soaking time is no more than 1h; 3) Rolling: The continuous casting slab adopts two-stage controlled rolling; The finishing rolling temperature of the first stage is 1035~1050℃, and the single-pass reduction rate is 10%~13%; The second stage rolling temperature is 940~964℃, with small deformation for rapid rolling and single pass reduction of 4%~7%; 4) Heat treatment: The rolled steel plate is subjected to solution heat treatment; The solution temperature is controlled at 1060~1150℃, the net holding time is 0.6~1.4min / mm, and the steel is water-cooled to room temperature after being taken out of the furnace.

2. A method for manufacturing a low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers as claimed in claim 1, characterized in that: The process includes the following: smelting - continuous casting - heating - rolling - heat treatment, among which: 1) The soft reduction rate in the soft reduction process of continuous casting billets is controlled at 5%~7%; 2) Heating: The continuous casting billet adopts a four-stage heating method of preheating section - first heating section - second heating section - soaking section; The preheating temperature is 875~920℃, and the heating time is 2.6~3.2h; The temperature of the heating section is 1120~1260℃, of which the temperature of the first heating section is 1120~1185℃, the heating time is 1.2~1.8h, and the temperature of the second heating section is 1200~1265℃, the heating time is 1~1.4h; The soaking section temperature is 1186~1200℃, and the soaking time is no more than 1h; 3) Rolling: The continuous casting slab adopts two-stage controlled rolling; The finishing rolling temperature of the first stage is 1035~1050℃, and the single-pass reduction rate is 10%~13%; The second stage rolling temperature is 940~964℃, with small deformation for rapid rolling and single pass reduction of 4%~7%; 4) Heat treatment: The rolled steel plate is subjected to solution heat treatment; The solution temperature is controlled at 1060~1150℃, the net holding time is 0.6~1.4min / mm, and the steel is water-cooled to room temperature after being taken out of the furnace.

3. The method for manufacturing a low-carbon, high-silicon, strong and tough corrosion-resistant stainless steel for containers according to claim 2, characterized in that: The continuous casting process includes: a tundish molten steel casting temperature of 1505-1535°C, and adopts electromagnetic stirring or a continuous casting billet soft reduction process.

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