High-strength medium-chromium ferritic stainless steel

Abstract

The invention discloses high-strength medium-chromium ferritic stainless steel which comprises the following chemical components in percentage by weight: less than or equal to 0.02% of C, less than or equal to 0.2% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.04% of P, less than or equal to 0.01% of S, 18.0-20.0% of Cr, 0.4-0.6% of Cu, 0.4-0.6% of Nb, less than or equal to 0.02% of N, 0.3-0.5% of W and the balance of Fe and inevitable impurity elements. The product obtained through component design has high strength and excellent plasticity in performance, and can meet the high-end requirements of the product industry.

Description

Technical Field

[0001] The present invention relates to the steel smelting process, and particularly to a high-strength medium-chromium ferritic stainless steel. Background Art

[0002] Medium-chromium ferritic stainless steel (the weight percentage content of Cr is about 18-20%) is a newly emerging steel type in recent years. This type of steel improves the corrosion resistance of the material by reducing the carbon and nitrogen content, and improves the cold working and welding properties of the material by adding microalloying elements (such as niobium, titanium, vanadium, etc.) that stabilize carbon and nitrogen. These trace elements can also improve the surface quality of the material after cold working, such as reducing the degree of wrinkling after cold forming of the material. This steel type has corrosion resistance basically equivalent to that of conventional 304 austenitic stainless steel and excellent cold forming properties, and has low cost, and can be widely used in industries such as electrical appliances, products, automobiles, elevators, etc.

[0003] At present, companies such as Nisshin Steel in Japan have mass-produced this type of steel, and the grades include SUS430J1L, etc. This type of steel is mainly used to replace austenitic stainless steel with higher prices and low-chromium ferritic stainless steel with poor corrosion resistance, and has been applied in multiple industries, with a large market demand. There are also domestic steel enterprises producing this type of steel and starting to apply it in various industries, such as: household appliance parts, products, interior and exterior automotive trim parts, and also used for heat exchanger parts, etc. It can be seen that this type of steel is widely used at home and abroad, and has good market prospects.

[0004] Table 1 lists the chemical compositions of previous patents on medium-chromium ferritic stainless steel. It can be seen from Table 1 that: in the chemical composition design, carbon and nitrogen are controlled at a relatively low level in most patents, and contain a certain amount of elements such as niobium, titanium, vanadium, and aluminum that stabilize carbon and nitrogen. Some patents also add a certain amount of nickel and copper. Such chemical composition designs are all to improve the corrosion resistance and cold working plasticity of the material. However, for industries such as household appliances and products, there is still a high-end demand for high strength, and it is hoped to improve the material strength without losing corrosion resistance and plasticity, with the aim of saving materials and reducing costs. This requires steel enterprises to continuously develop new stainless steel materials.

[0005] Table 1. Unit (wt, %) Summary of the Invention

[0006] The purpose of the present invention is to provide a high-strength medium-chromium ferritic stainless steel.

[0007] The technical solution for achieving the purpose of the present invention is: a high-strength medium-chromium ferritic stainless steel, and the weight percentages of its chemical components are as follows: C: ≤0.02, Si: ≤0.2, Mn: ≤0.2, P: ≤0.04, S: ≤0.01, Cr: 18.0 - 20.0, Cu: 0.4 - 0.6, Nb: 0.4 - 0.6, N: ≤0.02, W: 0.3 - 0.5, The balance is Fe and inevitable impurity elements.

[0008] In the composition design of the present invention: Carbon: To ensure excellent plasticity of the material, it should be as little as possible, preferably controlled below 0.02%.

[0009] Silicon: To ensure excellent plasticity of the material, it should be as little as possible, preferably controlled below 0.2%.

[0010] Manganese: To ensure the plasticity and corrosion resistance of the material, it should be as little as possible, preferably controlled below 0.2%.

[0011] Phosphorus and sulfur: Considering hot plasticity and corrosion resistance, these two elements should be as low as possible, and P≤0.04% and S≤0.01% should be controlled.

[0012] Chromium: An important element to ensure corrosion resistance. When it is less than 18%, the corrosion resistance is poor and cannot meet the use requirements. However, when it exceeds 20%, it will increase the production difficulty and material cost. It is preferably controlled at 18 - 20%.

[0013] Copper: A small amount of copper can improve the cold working plasticity of the material, but when there is more, it will instead reduce the plasticity and increase the material cost. Generally, it is preferably controlled at 0.4 - 0.6% which is more ideal.

[0014] Niobium: Adding a certain amount of trace element niobium can play a role in stabilizing carbon and nitrogen in the material, refine the structure, and can improve strength and plasticity, etc. However, when there is too much, it is instead unfavorable to the plasticity of the material and increases the material cost. The ideal range is 0.4 - 0.6%.

[0015] Nitrogen: To ensure excellent plasticity of the material, it should be as little as possible, preferably controlled below 0.02%.

[0016] Tungsten: In the composition design of the present invention, an appropriate amount of tungsten element is creatively selected. It is found that on the basis of not significantly losing the plasticity and corrosion resistance of the material, the strength can be significantly improved to meet the high requirements of high - end users for strength. However, when there is too much, it has an adverse effect on the plasticity of the material and increases the material cost. Through comprehensive analysis of the chemical composition system and characteristics of various properties of this alloy, the ideal range of tungsten is 0.3 - 0.5%.

[0017] The products designed with the components of the present invention have high strength and excellent plasticity in performance, and can meet the high-end requirements of the product industry. Detailed implementation manners

[0018] The following is a detailed description of the preferred embodiments of a manufacturing method of a high-strength medium-chromium ferritic stainless steel according to the present invention: Example 1

[0019] A high-strength medium-chromium ferritic stainless steel has the following weight percentages of chemical components: C: 0.009, Si: 0.05, Mn: 0.11, P: 0.031, S: 0.01, Cr: 18.6, Cu: 0.47, Nb: 0.45, N: 0.010, W: 0.33, The balance is Fe and inevitable impurity elements.

[0020] The manufacturing method of the high-strength medium-chromium ferritic stainless steel includes the following steps: 1) Steelmaking and casting: The foregoing chemical component ratio adopts electric furnace - AOD - VOD steelmaking; 2) Hot rolling: The initial hot rolling temperature is 1230 °C, and the final temperature is 900 °C; 3) Annealing and pickling: The annealing temperature is 10100 °C, and pickling is carried out after annealing; 4) Cold rolling: The cold rolling reduction rate is 90%; 5) Bright annealing: The bright annealing temperature is 1010 °C.

[0021] The weight percentages of the chemical components (unit: %, the balance is Fe and inevitable impurity elements) of Examples 1 - 5 and Comparative Examples 1 - 2 of the high-strength medium-chromium ferritic stainless steel according to the present invention are shown in Table 2: Table 2:

[0022] The mechanical properties, corrosion resistance and surface quality of Examples 1 - 5 and Comparative Examples 1 - 2 of the present invention are shown in Table 3 Table 3:

[0023] As can be seen from Table 3, under the same process conditions, the chemical compositions of Invention Examples 1-5 all meet the requirements of this patent. The elongation rates are all above 30%, the yield strengths are all above 400 MPa, and the tensile strengths are all above 600 MPa. The elongation rate is higher than 31%, higher than the lower limit of 30% agreed upon in the industry. The product has a combination of high strength and excellent plasticity, and can meet the high-end requirements of the product industry. Moreover, the stainless steels of Invention Examples 1-5 of the present invention have excellent corrosion resistance and can meet the high-end requirements of the product industry. From Invention Example 1 to 5, as the tungsten content increases, the strength gradually increases, and the plasticity changes little. At the same time, the tungsten content of Comparative Example 1 is lower than the scope of this invention patent, and its strength is lower, indicating that the strength of the material is poor when the tungsten content is low; the tungsten content of Comparative Example 2 is higher than the scope of this invention patent, and its elongation rate is low, and the corresponding plasticity is low. It can be seen that the plasticity of the material is poor when the tungsten content is too high and cannot meet the high-end requirements of the product industry.

[0024] The process described in the embodiments of the present invention is a conventional process flow, which is not an innovation of the present invention and will not be elaborated here.

[0025] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A high-strength medium-chromium ferritic stainless steel, characterized in that: The weight percentages of its chemical components are as follows: C：≤0.02， Si: ≤0.2, Mn: ≤0.2, P：≤0.04， S：≤0.01， Cr：18.0～20.0， Cu: 0.4~0.6, Nb: 0.4~0.6, N：≤0.02， W：0.3～0.5， The rest is Fe and inevitable impurity elements.

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