Niobium-chromium-molybdenum-containing steel plate and production method thereof

Abstract

The invention discloses a steel plate containing niobium, chromium and molybdenum and a production method thereof. The steel plate comprises the following chemical components in percentage by weight: 0.06 to 0.17 percent of C, 0.15 to 0.60 percent of Si, 0.20 to 0.70 percent of Mn, 0.40 to 12.0 percent of Cr, 0.40 to 1.20 percent of Mo, 0.014 to 0.110 percent of Nb, less than or equal to 0.05 percent of Ni and the balance of Fe and inevitable impurities. The production method comprises the procedures of smelting, rolling and heat treatment, the niobium-iron alloy is added in the smelting procedure, and the niobium-iron alloy is added before the vacuum procedure. According to the steel plate, traditional Ni and other alloy elements are replaced with Nb microalloying, one-time quenching procedure is omitted in the heat treatment link of the steel plate with the plate thickness larger than or equal to 60 mm, compared with a traditional method, the production cost is further reduced, and the steel plate has good strength, plasticity and toughness, excellent internal and external quality and wide applicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a niobium-containing chromium-molybdenum steel plate and a production method thereof. Background Art

[0002] In the current domestic container steel field, with the continuous increase of the steel plate thickness and the continuous tightening of the technical requirements of the owners, as a low-alloy steel, chromium-molybdenum steel, due to only containing limited Cr and Mo elements, according to the current composition design level, the performance, especially the performance of the steel plate core, has reached a bottleneck. Although some enterprises have tried to improve the performance of the steel plate by adding Ni element to the steel or increasing the primary quenching process, practice has proved that new breakthroughs still cannot be achieved. At the same time, due to the limitation of the niobium element content in the American standard, it has brought great troubles to domestic steel plate manufacturing enterprises. According to the latest research results, domestic mainstream container steel production enterprises still do not use niobium alloying in chromium-molybdenum steel. Based on the above background, considering the huge market application and development potential of niobium in this type of steel, the present invention starts from the national standard chromium-molybdenum steel, aims at the current composition and performance mismatch problem of this steel, adds a certain amount of niobium element to the steel, realizes a breakthrough upgrade of chromium-molybdenum steel, thus solves the application problem of niobium in the domestic chromium-molybdenum steel field, and also provides theoretical support for the niobium alloying of foreign related grades. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a niobium-containing chromium-molybdenum steel plate with excellent comprehensive internal and external properties and a production method thereof. The steel plate produced by this method has good strength and toughness matching, and can meet the manufacturing and use requirements of various medium and high temperature, high pressure pressure vessels and affiliated pipelines and pipe fittings.

[0004] To solve the above technical problem, the technical solution adopted by the present invention is: a niobium-containing chromium-molybdenum steel plate, the chemical composition and weight percentage content of the steel plate are: C: 0.06 - 0.17%, Si: 0.15 - 0.60%, Mn: 0.20 - 0.70%, Cr: 0.40 - 12.0%, Mo: 0.40 - 1.20%, Nb: 0.014 - 0.110%, Ni ≤ 0.05%, and the balance is Fe and unavoidable impurities.

[0005] The thickness of the niobium-containing chromium-molybdenum steel plate of the present invention is 6 - 250 mm.

[0006] The yield strength of the niobium-containing chromium-molybdenum steel plate of the present invention is ≥ 240 MPa, the tensile strength is 410 - 820 MPa, the elongation is ≥ 25%, and the single value of the -55 °C Kv8 impact energy is > 54 J.

[0007] For the niobium-containing chromium-molybdenum steel plate of the present invention, all types of coarse and fine inclusions of A, B, C, D, and Ds are ≤ 0.5 grade, and the grain size is ≥ 6 grade.

[0008] Another object of the present invention is to provide a production method of a niobium-chromium-molybdenum steel plate, the production method including smelting, rolling and heat treatment processes. Ferro-niobium alloy is added in the smelting process, and the ferro-niobium alloy is added before the vacuum process.

[0009] In the rolling process of the present invention: the blank used for the steel plate is a continuous casting billet, an ingot or an electroslag ingot. The heating temperature of the blank is 1180 - 1350 °C, the starting rolling temperature in the first stage is 1140 - 1300 °C, and the starting rolling temperature in the second stage is 780 - 820 °C.

[0010] In the heat treatment process of the present invention: the quenching temperature of the steel plate is 850 - 1060 °C, and the tempering temperature is 660 - 800 °C.

[0011] In the heat treatment process of the present invention: for steel plates with a thickness of ≥60 mm, one quenching process is reduced.

[0012] The design concept of the present invention is as follows: Nb is a strong carbide and nitride forming element, and mainly exists in the form of carbides and nitrides in Nb-containing steel, and can form carbides, nitrides or carbonitride composite compounds with very high stability. The main functions of niobium in steel are as follows: (1) For undissolved niobium, in the process of rolling the steel plate, in order to reduce the rolling mill resistance, generally a higher heating temperature is adopted. The amount of undissolved niobium is very small and the size is relatively large (greater than 1000 nm), which has little effect on precipitation strengthening and grain refinement; (2) For dissolved niobium, the niobium dissolved in the steel at high temperature interacts with the dislocations in the austenite, preventing the austenite grains from recrystallizing and increasing the austenite recrystallization temperature; (3) For niobium that precipitates to form carbides, nitrides or carbonitrides, these compounds are fine and dispersed. When they precipitate below 900 °C during the rolling process, they inhibit recrystallization and prevent grain growth together with the dissolved niobium, and play a role in precipitation strengthening when they precipitate dispersedly at low temperature. In short, the added Nb element in the present invention can significantly enhance the hardenability of the steel, improve the controlled rolling effect of the steel, and thus improve the strength, plasticity and low-temperature impact toughness of the steel. Based on the above mechanism analysis, in order to balance the production cost and the performance of the steel plate, the content of the added Nb element takes into account both economy and applicability. Since the level of the controlled rolling temperature in the second stage will greatly affect the grain refinement effect of niobium, thus affecting the subsequent heat treatment effect and the final performance of the steel plate. In order to balance the recovery rate of niobium and ensure the maximization of the role of niobium in the steel, the present invention optimizes the adaptability of the smelting, rolling and heat treatment processes of the steel plate. In terms of beneficial effects: the present invention uses Nb microalloying to replace traditional alloying elements such as Ni, and reduces one quenching process for steel plates with a thickness of ≥60 mm, further reducing the production cost, having wide applicability and being worthy of popularization.

[0013] The beneficial effects of adopting the above technical solutions are as follows: 1. The steel plate of the present invention has good strength and plasticity, with a yield strength ≥ 240 MPa, a tensile strength of 410 - 820 MPa, and an elongation ≥ 25%. 2. It has excellent low-temperature impact toughness, and the single value of the Kv8 impact energy at -55°C > 54 J. 3. The steel plates obtained by the present invention can be widely used in the manufacture of various medium-high temperature and high-pressure pressure vessels and their attached pipelines and pipe fittings. Specific Embodiments

[0014] The following will further explain and illustrate the present invention in combination with specific embodiments. However, such explanations and illustrations should not unduly limit the technical solutions of the present invention. Example 1

[0015] The thickness of the niobium-chromium-molybdenum steel plate in this example is 6 mm, and it is composed of the following components by weight percentage: C: 0.06%, Si: 0.15%, Mn: 0.20%, Cr: 0.40%, Mo: 0.40%, Nb: 0.014%, Ni: 0.001%, and the balance is Fe and unavoidable impurities.

[0016] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling, and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting billet. The heating temperature of the blank is 1180°C, the starting rolling temperature in the first stage is 1140°C, and the starting rolling temperature in the second stage is 780°C.

[0017] 3) Heat treatment process: The quenching temperature of the steel plate is 1060°C, and the tempering temperature is 800°C.

[0018] After the heat treatment of the steel plate, samples are taken for inspection. The obtained mechanical property inspection results (all at the mid-thickness of the plate) and the grain size and inclusion analysis results (all at the mid-thickness of the plate) are shown in Table 1 and Table 2 respectively. Example 2

[0019] The thickness of the niobium-chromium-molybdenum steel plate in this example is 22 mm, and it is composed of the following components by weight percentage: C: 0.09%, Si: 0.18%, Mn: 0.25%, Cr: 0.48%, Mo: 0.42%, Nb: 0.016%, Ni: 0.002%, and the balance is Fe and unavoidable impurities.

[0020] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling, and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting billet. The heating temperature of the blank is 1220 °C, the rolling start temperature in the first stage is 1180 °C, and the rolling start temperature in the second stage is 790 °C.

[0021] 3) Heat treatment process: The quenching temperature of the steel plate is 850 °C, and the tempering temperature is 735 °C.

[0022] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at half of the plate thickness) and the grain size and inclusion analysis results (all at half of the plate thickness) are shown in Table 1 and Table 2 respectively. Example 3

[0023] The niobium-chromium-molybdenum steel plate in this example has a thickness of 63 mm and is composed of the following components by weight percentage: C: 0.12%, Si: 0.27%, Mn: 0.44%, Cr: 0.70%, Mo: 0.55%, Nb: 0.020%, Ni: 0.005%, and the balance is Fe and unavoidable impurities.

[0024] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting billet. The heating temperature of the blank is 1250 °C, the rolling start temperature in the first stage is 1200 °C, and the rolling start temperature in the second stage is 800 °C.

[0025] 3) Heat treatment process: The steel plate reduces one quenching process. The quenching temperature of the steel plate is 875 °C, and the tempering temperature is 720 °C.

[0026] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at half of the plate thickness) and the grain size and inclusion analysis results (all at half of the plate thickness) are shown in Table 1 and Table 2 respectively. Example 4

[0027] The niobium-chromium-molybdenum steel plate in this example has a thickness of 88 mm and is composed of the following components by weight percentage: C: 0.14%, Si: 0.38%, Mn: 0.50%, Cr: 1.12%, Mo: 0.64%, Nb: 0.026%, Ni: 0.008%, and the balance is Fe and unavoidable impurities.

[0028] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The billet used for the steel plate is a continuous casting billet, the billet heating temperature is 1295 °C, the starting rolling temperature in the first stage is 1250 °C, and the starting rolling temperature in the second stage is 810 °C; 3) Heat treatment process: The steel plate reduces one quenching process, the quenching temperature of the steel plate is 890 °C, and the tempering temperature is 705 °C.

[0029] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at 1 / 2 of the plate thickness) and the grain size and inclusion analysis results (all at 1 / 2 of the plate thickness) are shown in Table 1 and Table 2 respectively. Example 5

[0030] The niobium-chromium-molybdenum steel plate in this example has a thickness of 130 mm and is composed of the following components by weight percentage: C: 0.15%, Si: 0.46%, Mn: 0.58%, Cr: 2.54%, Mo: 0.84%, Nb: 0.036%, Ni: 0.01%, and the balance is Fe and unavoidable impurities.

[0031] The production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The billet used for the steel plate is a continuous casting billet, the billet heating temperature is 1305 °C, the starting rolling temperature in the first stage is 1283 °C, and the starting rolling temperature in the second stage is 815 °C; 3) Heat treatment process: The steel plate reduces one quenching process, the quenching temperature of the steel plate is 905 °C, and the tempering temperature is 680 °C.

[0032] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at 1 / 2 of the plate thickness) and the grain size and inclusion analysis results (all at 1 / 2 of the plate thickness) are shown in Table 1 and Table 2 respectively. Example 6

[0033] The niobium-chromium-molybdenum steel plate in this example has a thickness of 193 mm and is composed of the following components by weight percentage: C: 0.16%, Si: 0.52%, Mn: 0.63%, Cr: 5.20%, Mo: 1.05%, Nb: 0.060%, Ni: 0.03%, and the balance is Fe and unavoidable impurities.

[0034] The production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting billet. The heating temperature of the blank is 1330 °C, the starting rolling temperature in the first stage is 1300 °C, and the starting rolling temperature in the second stage is 820 °C; 3) Heat treatment process: The steel plate reduces one quenching process. The quenching temperature of the steel plate is 970 °C, and the tempering temperature is 675 °C.

[0035] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at the mid-thickness of the plate) and the grain size and inclusion analysis results (all at the mid-thickness of the plate) are shown in Table 1 and Table 2 respectively. Example 7

[0036] The niobium-chromium-molybdenum steel plate in this example has a thickness of 220 mm and is composed of the following components by weight percentage: C: 0.16%, Si: 0.58%, Mn: 0.66%, Cr: 9.10%, Mo: 1.12%, Nb: 0.094%, Ni: 0.04%, and the balance is Fe and unavoidable impurities.

[0037] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling, and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting billet. The heating temperature of the blank is 1340 °C, the starting rolling temperature in the first stage is 1295 °C, and the starting rolling temperature in the second stage is 818 °C; 3) Heat treatment process: The steel plate reduces one quenching process. The quenching temperature of the steel plate is 940 °C, and the tempering temperature is 665 °C.

[0038] After the heat treatment of the steel plate, samples are taken for inspection. The mechanical property inspection results (all at the mid-thickness of the plate) and the grain size and inclusion analysis results (all at the mid-thickness of the plate) are shown in Table 1 and Table 2 respectively. Example 8

[0039] The niobium-chromium-molybdenum steel plate in this example has a thickness of 250 mm and is composed of the following components by weight percentage: C: 0.17%, Si: 0.60%, Mn: 0.70%, Cr: 12.0%, Mo: 1.20%, Nb: 0.110%, Ni: 0.05%, and the balance is Fe and unavoidable impurities.

[0040] A production method of a niobium-chromium-molybdenum steel plate in this example includes smelting, rolling, and heat treatment processes. The ferro-niobium alloy is added before the vacuum process. The specific control processes are as follows: 1) Smelting process: Add ferro-niobium alloy, and the ferro-niobium alloy is added before the vacuum process; 2) Rolling process: The blank used for the steel plate is a continuous casting blank. The heating temperature of the blank is 1350 °C, the starting rolling temperature in the first stage is 1300 °C, and the starting rolling temperature in the second stage is 820 °C; 3) Heat treatment process: The steel plate reduces one quenching process. The quenching temperature of the steel plate is 920 °C, and the tempering temperature is 660 °C.

[0041] After the heat treatment of the steel plate, samples are taken for inspection. The obtained mechanical property inspection results (all at the mid-thickness of the plate) and the grain size and inclusion analysis results (all at 1 / of the plate thickness) are shown in Table 1 and Table 2 respectively.

[0042] Table 1 Mechanical properties of the steel plates in each embodiment

[0043] Table 2 Detection results of inclusions and grain size of the steel plates in each embodiment

[0044] The above are only the preferred embodiments of the present invention, and the scope of the rights of the present invention cannot be limited thereby. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall fall within the scope covered by the present invention.

Claims

1. A niobium-chromium-molybdenum steel plate, characterized in that: The chemical composition and weight percentage of the steel plate are: C: 0.06-0.17%, Si: 0.15-0.60%, Mn: 0.20-0.70%, Cr: 0.40-12.0%, Mo: 0.40-1.20%, Nb: 0.014-0.110%, Ni≤0.05%, and the balance is Fe and unavoidable impurities.

2. The niobium-chromium-molybdenum steel plate according to claim 1, characterized in that: The thickness of the niobium-chromium-molybdenum-containing steel plate is 6-250 mm.

3. A niobium-chromium-molybdenum-containing steel plate according to claim 1 or 2, characterized in that: The niobium-chromium-molybdenum-containing steel plate has a yield strength of ≥240MPa, a tensile strength of 410-820MPa, an elongation of ≥25%, and a -55°C Kv8 impact energy single value of >54J.

4. A niobium-chromium-molybdenum-containing steel plate according to claim 1 or 2, characterized in that: The coarse and fine inclusions of the niobium-chromium-molybdenum-containing steel plates A, B, C, D, and Ds are all ≤0.5 level, and the grain size is ≥6 level.

5. A method for producing a niobium-chromium-molybdenum steel plate according to any one of claims 1 to 4, characterized in that: The production method comprises smelting, rolling and heat treatment processes, wherein ferroniobium alloy is added in the smelting process and the ferroniobium alloy is added before the vacuum process.

6. The method for producing a niobium-chromium-molybdenum steel plate according to claim 5, characterized in that: The rolling process: the billet used for the steel plate is a continuous casting billet or a steel ingot or an electroslag ingot, the billet heating temperature is 1180-1350°C, the first stage rolling temperature is 1140-1300°C, and the second stage rolling temperature is 780-820°C.

7. The heat treatment method of a niobium-chromium-molybdenum steel plate according to claim 5, characterized in that: The heat treatment process: the quenching temperature of the steel plate is 850-1060°C, and the tempering temperature is 660-800°C.

8. The heat treatment method of a niobium-chromium-molybdenum-containing steel plate according to claim 5, characterized in that: The heat treatment process: for steel plates with a thickness ≥ 60 mm, one quenching process can be reduced.

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