Heat treatment method for 800 MPa hydroelectric steel with specification of more than 100 mm

Abstract

The invention discloses a heat treatment method of 800 MPa hydroelectric steel with the specification of more than 100 mm, the heat treatment process comprises quenching and tempering, the quenching temperature is 880-890 DEG C, and the thickness coefficient of the quenching time is not more than 2.0 min / mm; the tempering temperature ranges from 600 DEG C to 640 DEG C, and the temperature coefficient of the tempering time ranges from 2.2 min / mm to 2.5 min / mm. By means of the heat treatment process, it can be guaranteed that the impact energy of the near surface of the extra-thick steel plate with the thickness larger than 100 mm is uniform and stable, and the problem that the surface impact energy is not stable in a conventional process is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and in particular relates to a heat treatment method for 800 MPa hydroelectric steel with a specification of more than 100 mm. Background Art

[0002] The production of hydropower steel with a specification of 800 MPa above 100 mm is difficult, especially the impact near the surface, which is difficult to control. The main reason is that during the quenching + tempering process of the extra-thick hydropower steel, due to the limitation of physical properties, the cooling rate of the surface and 1 / 2 of the thickness of the steel plate is quite different. There are two main problems with the conventional practice. First, it is difficult for the conventional heat treatment process to take into account the impact stability problem caused by the growth of the grain size during the near-surface quenching and heating. Second, in order to improve the near-surface impact toughness, more precious elements Ni are added to improve the surface impact, which results in high production costs and weak market competitiveness of the products.

[0003] Therefore, the present invention provides a heat treatment method for 800 MPa hydroelectric steel with a specification of more than 100 mm to solve the above-mentioned problems. Summary of the invention

[0004] Technical problem solved: In response to the above technical problem, the present invention provides a heat treatment method for 800 MPa hydropower steel with a specification of more than 100 mm, which can effectively solve the shortcomings of the above method.

[0005] Technical solution: A heat treatment method for 800MPa hydropower steel with a specification of more than 100mm, the heat treatment process includes quenching and tempering, the quenching temperature is 880-890℃, and the thickness coefficient of the quenching time does not exceed 2.0 minutes / mm; the tempering temperature is 600-640℃, and the temperature coefficient of the tempering time is 2.2-2.5 minutes / mm.

[0006] Preferably, the chemical composition and weight percentage of the hydropower steel are C 0.07-0.09%, Si 0.10-0.20%, Mn 1.0-1.20%, Al 0.020-0.060%, Nb 0.010-0.025%, Ti 0.008-0.015%, P≤0.012%, S≤0.003%, N≤0.0050%, Cr 0.30-0.40%, Ni 0.70-1.05%, Cu 0.30-0.40%, Mo 0.47-0.55%, and the rest are iron and unavoidable impurity elements; carbon equivalent Ceq=[C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15]≤0.54%.

[0007] Preferably, the slab thickness for producing hydropower steel is 320 mm.

[0008] Preferably, the specific process of quenching is as follows: after the steel plate is surface shot blasted to remove surface iron oxide, it is transferred through a roller conveyor and enters a radiation tube heating non-oxidation roller hearth furnace for quenching. The quenching furnace is set at a temperature of 880-890°C. The total time from entering the quenching furnace to exiting the quenching furnace is controlled to be no more than 2.0 minutes / mm. The surface temperature of the steel plate after exiting the quenching furnace is not less than 875°C. Then, high-pressure water is sprayed on the surface of the steel plate to quickly cool the temperature of the steel plate to below 50°C.

[0009] Preferably, the specific process of tempering is: the steel plate is cooled to room temperature after quenching, and then tempered in a radiation tube heated non-oxidation roller hearth furnace, the tempering temperature is set to 600-640 ° C, the total time from entering the tempering furnace to exiting the tempering furnace is controlled at 2.0-2.5 minutes / mm, and the steel plate is naturally cooled to room temperature in the air after exiting the furnace.

[0010] Beneficial effect: The technical solution adopted by the present invention adds less precious alloy element Ni in the composition design, optimizes and controls the quenching process parameters, strictly controls the quenching temperature and the quenching heating time, effectively inhibits the surface grain growth, and thus significantly improves the surface impact energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a metallographic structure photograph of the steel plate surface in Example 1 of the present invention; Figure 2 This is a metallographic structure photograph of the steel plate at 1 / 4 of Example 1 of the present invention; Figure 3 This is a metallographic structure photograph of the core of the steel plate of Example 1 of the present invention. DETAILED DESCRIPTION

[0012] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments: Hydropower steel is prepared according to the following composition and weight percentage: C 0.07-0.09%, Si 0.10-0.20%, Mn 1.0-1.20%, Al 0.020-0.060%, Nb 0.010-0.025%, Ti 0.008-0.015%, P≤0.012%, S≤0.003%, N≤0.0050%, Cr 0.30-0.40%, Ni 0.70-1.05%, Cu 0.30-0.40%, Mo 0.47-0.55%, and the rest are iron and unavoidable impurity elements; carbon equivalent Ceq=[C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15]≤0.54%, and the slab thickness is 320mm. The specific weight percentages are shown in Table 1 below: Table 1 Melting Composition of Smelting Furnaces in Example 1-3

[0013] The specific process of quenching is as follows: after the steel plate is shot blasted to remove the surface iron oxide, it is transferred through a roller conveyor and enters a radiation tube heating non-oxidation roller hearth furnace for quenching. The quenching furnace is set at 880-890°C, and the total time from entering the quenching furnace to exiting the quenching furnace is controlled to be no more than 2.0 minutes / mm. The surface temperature of the steel plate after exiting the quenching furnace is not less than 875°C, and then high-pressure water is sprayed on the surface of the steel plate to quickly cool the temperature of the steel plate to below 50°C. The specific process of tempering is as follows: the steel plate is cooled to room temperature after quenching, and then tempered in a radiation tube heating non-oxidation roller hearth furnace. The tempering temperature is set at 600-640°C, and the total time from entering the tempering furnace to exiting the tempering furnace is controlled to be 2.0-2.5 minutes / mm. After the steel plate is removed from the furnace, it is naturally cooled to room temperature in the air.

[0014] The quenching temperature, quenching time, tempering temperature and tempering time and process parameters for preparing hydroelectric steel in Example 1-3 are shown in Table 2 below: Table 2 Process parameters for preparing hydroelectric steel in Example 1-3

[0015] The results are as follows Figure 1-Figure 3 As shown, it is shown that the impact energy of the extra-thick hydropower steel produced by the method of the present invention is very stable in the entire thickness section, and the impact energy at -40 ℃ can be stabilized at more than 100 J. The grain size near the surface is relatively uniformly controlled at about 30 μm, the grain size of 1 / 4 and 1 / 2 of the thickness is controlled at about 20 μm, and the grain size of the entire section is relatively uniform.

[0016] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A heat treatment method for 800 MPa hydroelectric steel with a thickness of 100 mm or more, characterized in that: The heat treatment process includes quenching and tempering. The quenching temperature is 880-890°C, and the thickness coefficient of the quenching time does not exceed 2.0 minutes / mm; the tempering temperature is 600-640°C, and the temperature coefficient of the tempering time is 2.2-2.5 minutes / mm.

2. The heat treatment method for 800MPa hydroelectric steel with a thickness of 100mm or more according to claim 1, characterized in that: The chemical composition and weight percentage of the hydropower steel are C 0.07-0.09%, Si 0.10-0.20%, Mn 1.0-1.20%, Al 0.020-0.060%, Nb 0.010-0.025%, Ti 0.008-0.015%, P≤0.012%, S≤0.003%, N≤0.0050%, Cr 0.30-0.40%, Ni 0.70-1.05%, Cu 0.30-0.40%, Mo 0.47-0.55%, and the rest are iron and unavoidable impurity elements; carbon equivalent Ceq=[C+Mn / 6+(Cr+Mo+V) / 5+(Cu+Ni) / 15]≤0.54%.

3. The heat treatment method for 800 MPa hydroelectric steel with a thickness of 100 mm or more according to claim 1, characterized in that: The slab thickness for producing hydropower steel is 320 mm.

4. The heat treatment method of a 800MPa hydroelectric steel with a thickness of 100 mm or more according to claim 1, characterized in that: The specific process of quenching is as follows: after the steel plate is shot blasted to remove surface iron oxide, it is transferred through a roller conveyor and enters a radiation tube heated oxidation-free roller hearth furnace for quenching. The quenching furnace is set at a temperature of 880-890°C. The total time from entering the quenching furnace to exiting the quenching furnace is controlled to be no more than 2.0 minutes / mm. The surface temperature of the steel plate after exiting the quenching furnace is not less than 875°C. Then, high-pressure water is used to spray the surface of the steel plate to quickly cool the temperature of the steel plate to below 50°C.

5. The heat treatment method of a hydroelectric steel with a thickness of 800 MPa and a thickness of 100 mm or more according to claim 1, characterized in that: The specific process of tempering is as follows: the steel plate is cooled to room temperature after quenching, and then subjected to tempering heat treatment in a radiation tube heated non-oxidizing roller hearth furnace, the tempering temperature is set at 600-640°C, and the total time from entering the tempering furnace to exiting the tempering furnace is controlled at 2.0-2.5 minutes / mm. After exiting the furnace, the steel plate is naturally cooled to room temperature in the air.

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