Heat treatment method suitable for Q690C round steel for tunnel embedded part

Abstract

The invention discloses a heat treatment method suitable for Q690C round steel for tunnel embedded parts, which comprises the following steps: 1) hot-rolled round steel is placed in an annealing furnace heated to 500 DEG C for furnace cooling, and the temperature of the hot-rolled round steel is greater than or equal to 450 DEG C when the hot-rolled round steel is placed in the annealing furnace; (2) the round steel is heated to 930-940 DEG C in a quenching furnace, heat preservation is conducted for 50-60 min for complete austenitizing, and then quenching is conducted; and (3) the round steel is placed in a tempering furnace to be heated to 650-660 DEG C, heat preservation is conducted for 100-120 minutes, and then air cooling or water cooling is conducted. The mechanical properties after heat treatment meet the following requirements: the yield strength is greater than or equal to 850MPa, the tensile strength is greater than or equal to 900MPa, the percentage elongation after fracture is greater than or equal to 14 percent, the KV2 at 0 DEG C is greater than or equal to 47J, and the technical requirements are met.

Description

Technical Field

[0001] The invention belongs to the field of material metallurgy, and in particular relates to a heat treatment method for Q690C round steel used for tunnel embedded parts. Background Art

[0002] In recent years, the controlled rolling and controlled cooling (TMCP) technology has been widely used in the production process of low-alloy high-strength steel, but it is difficult to control the production of high-strength steel of 690MPa and above, mainly because it cannot reduce the low-temperature impact toughness of the steel while ensuring high strength. In order to ensure the performance of steel and improve the yield rate of products, the traditional quenching + high-temperature tempering heat treatment process is still the current mainstream process for the production of high-strength and high-toughness steel of 690MPa and above.

[0003] In the quenching heat treatment process, the reasonable combination of quenching heating temperature and holding time will have a direct impact on the austenitization degree, grain size, and dissolution distribution state of alloy elements of the test steel, and thus determine the final mechanical properties. A low quenching temperature and a short holding time can easily lead to insufficient dissolution and uneven distribution of alloy elements, as well as incomplete austenitization; while a high quenching temperature and a long holding time can easily lead to serious coarsening of the grain size of the austenite part, serious grain growth, and the formation of a coarse martensitic structure, which weakens the strengthening effect between alloy elements. In addition, the grain size obtained after tempering is uneven, which reduces the plastic toughness of the material. Both tendencies will lead to poor mechanical properties.

[0004] During high-temperature tempering, the organization undergoes stage changes such as martensite decomposition, carbide formation and transformation, cementite aggregation and spheroidization, and α phase recovery recrystallization. During high-temperature tempering, sufficient thermal activation energy can rearrange the lath martensite with high dislocation density into a network and strip distribution, transforming it into equiaxed crystals with low dislocation density, minimum energy and good stability, forming a tempered troostite organization composed of fine-grained cementite and equiaxed ferrite.

[0005] Since the surface and core temperatures of hot-rolled round steel are inconsistent, the surface and core structures are different after hot rolling and cooling, which will cause great differences in the performance of the product. Summary of the invention

[0006] The object of the present invention is to provide a heat treatment method for Q690C round steel used for tunnel embedded parts, which makes the performance of Q690C meet the technical requirements through appropriate heat treatment process system and adjustment of quenching temperature + holding time and tempering temperature + holding time and correct cooling method. After heat treatment, the yield strength of Q690C round steel used for tunnel embedded parts is ≥850MPa, the tensile strength is ≥900MPa, the elongation after fracture is ≥14%, and the 0℃ KV2 is ≥47J.

[0007] The present invention provides a heat treatment method for Q690C round steel used for tunnel embedded parts, which comprises the following operations:

[0008] 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C;

[0009] 2) Heat the round steel in a quenching furnace to 930-940°C, keep it warm for 50-60 minutes to completely austenitize, and then quench it;

[0010] 3) Heat the round steel in a tempering furnace to 650-660°C, keep it warm for 100-120 minutes, and then air-cool or water-cool it.

[0011] In some embodiments, the heat treatment method comprises the following operations:

[0012] 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C;

[0013] 2) Heat the round steel in a quenching furnace to 930°C, keep it warm for 60 minutes to completely austenitize, and then quench it;

[0014] 3) Heat the round steel in a tempering furnace to 650°C, keep it warm for 120 minutes, and then air cool it.

[0015] In some embodiments, the heat treatment method comprises the following operations:

[0016] 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C;

[0017] 2) Heat the round steel in a quenching furnace to 940°C, keep it warm for 50 minutes to completely austenitize, and then quench it;

[0018] 3) Heat the round steel in a tempering furnace to 660°C, keep it warm for 100 minutes, and then water cool it.

[0019] In some embodiments, the chemical composition of the Q690C round steel for tunnel embedded parts is calculated by mass percentage as follows: C: 0.14-0.16%, Mn: 1.65-1.75%, Si: 0.40-0.50%, Cr: 0.50-0.60%, Mo: 0.18-0.28%, Nb: 0.02-0.04%, V: 0.07-0.10%, Ti: 0.02-0.04%, Al: 0.020-0.040%, P: ≤0.018%, S: ≤0.005%, B: 0.0018-0.0025%, and the rest are iron and inevitable trace chemical elements.

[0020] In some embodiments, the mechanical properties of the Q690C round steel for tunnel embedded parts after heat treatment meet the following requirements: yield strength ≥850MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and 0°C KV2 ≥47J.

[0021] In some embodiments, the mechanical properties of the Q690C round steel for tunnel embedded parts after heat treatment meet the following requirements: yield strength ≥ 970 MPa, tensile strength ≥ 1010 MPa, elongation after fracture ≥ 16%, and 0°C KV2 ≥ 54 J.

[0022] In some embodiments, the Q690C round steel for tunnel embedded parts is produced according to the following process steps: steelmaking process: blast furnace molten iron - molten iron pretreatment - converter - refining outside the furnace - VD vacuum treatment - continuous casting; and steel rolling process: billet heating - high-pressure water dephosphorization - Ф850 billet opening machine - Ф700mm×3+Ф550mm×4 continuous rolling mill group rolling - sawing (sampling) - slow cooling in a slow cooling pit; wherein:

[0023] Steelmaking process parameters:

[0024] Converter end point C ≥ 0.08%, P ≤ 0.020%;

[0025] Ar blowing operation during the whole refining process;

[0026] VD deep vacuum time ≥13min; soft blowing time ≥15min;

[0027] Continuous casting superheat ≤ 30℃, casting speed controlled at 0.60~0.65m / min;

[0028] Steel rolling process parameters:

[0029] Heating time ≥ 4h, heating temperature 1150~1250℃;

[0030] The starting rolling temperature is ≤1050℃, and the final rolling temperature is ≤980℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a heat treatment process flow chart of Example 1.

[0032] Figure 2 This is a heat treatment process flow chart for Example 2. DETAILED DESCRIPTION

[0033] The present invention makes the performance of Q690C meet the technical requirements through appropriate heat treatment process system, adjustment of quenching temperature + holding time and tempering temperature + holding time and correct cooling method.

[0034] Specifically, the present invention provides a heat treatment method for Q690C round steel for tunnel embedded parts, which includes the following operations:

[0035] 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C;

[0036] 2) Heat the round steel in a quenching furnace to 930-940°C, keep it warm for 50-60 minutes to completely austenitize, and then quench it;

[0037] 3) Heat the round steel in a tempering furnace to 650-660°C, keep it warm for 100-120 minutes, and then air-cool or water-cool it.

[0038] In some embodiments, the chemical composition percentage requirements of Q690C round steel for tunnel embedded parts involved in the present invention are: C: 0.14-0.16%, Mn: 1.65-1.75%, Si: 0.40-0.50%, Cr: 0.50-0.60%, Mo: 0.18-0.28%, Nb: 0.02-0.04%, V: 0.07-0.10%, Ti: 0.02-0.04%, Al: 0.020-0.040%, P: ≤0.018%, S: ≤0.005%, B: 0.0018-0.0025%, and the rest are iron and inevitable trace chemical elements.

[0039] The main chemical components of the present invention are limited by the following reasons:

[0040] C: C is the most effective element for improving the strength of steel. As the C content increases, the tensile strength and yield strength of steel increase, but the elongation and impact toughness decrease, the corrosion resistance also decreases, and the welding heat affected zone of the steel will also be hardened, resulting in the generation of welding cold cracks. In order to ensure that the round steel obtains good comprehensive performance, the C content of the steel of the present invention is designed to be 0.14-0.16%.

[0041] Mn: Mn is an important strengthening element with low composition. With the increase of manganese content, the strength of steel is significantly improved, the processing performance of steel is improved, and the tough-brittle transition temperature hardly changes. However, if the manganese content is too high, it will inhibit the transformation of ferrite, affect the yield strength of steel, and be unfavorable for the control of yield strength ratio. The Mn element content of the steel of the present invention is designed to be 1.65-1.75%.

[0042] Cr: Cr can improve the strength, hardness and atmospheric corrosion resistance of steel. When added with other alloying elements, the effect is more significant. Chromium can slow down the decomposition rate of austenite, significantly improve the hardenability of steel, and have a secondary hardening effect, but it also increases the temper brittleness tendency of steel. However, when the chromium content is too high, the toughness of the base material and the heat-affected zone will be reduced. The Cr element content of the steel of the present invention is designed to be 0.50-0.60%.

[0043] Mo: Mo element can improve the uniformity of corrosion and inhibit local corrosion. In addition, Mo is also the most effective element for improving the high temperature strength of steel plates. Generally, the higher its content, the higher its high temperature strength, but the cost of Mo element is high, and excessive Mo element may cause the welding performance to decline. The Mo element content of the steel of the present invention is designed to be 0.18-0.28%.

[0044] Nb: Nb is dissolved in austenite during rolling and precipitates niobium carbonitride particles induced by deformation, which significantly increases the austenite non-recrystallization temperature, refines the austenite grains and then refines the grains of ferrite, etc., and improves the strength. Nb dissolved in austenite can also improve hardenability. The carbide Nb particles precipitated during quenching or precipitated as a second phase with V and Mo, which improves the high temperature strength. Therefore, the Nb element content in the steel of the present invention is designed to be 0.02-0.04%.

[0045] Si: Si can improve the corrosion resistance of steel and is often added to stainless steel, low alloy steel, and corrosion-resistant alloys to improve the corrosion resistance of these alloys, so that they have the properties of resistance to chloride stress corrosion cracking, pitting corrosion, hot concentrated nitric acid corrosion, oxidation resistance, and seawater corrosion resistance. Studies have shown that in a hot and humid atmospheric environment, Si can significantly improve the atmospheric corrosion resistance of carbon steel and low alloy steel. In addition, Si can also improve the corrosion resistance of low alloy steel in the splash zone of seawater. The Si element content in the steel of the present invention is designed to be 0.40-0.50%.

[0046] P, S: P and S are impurity elements in steel. P has a certain effect on improving corrosion resistance, but P is an element that is easy to segregate. It will cause serious segregation in some parts of the steel, reduce plasticity and toughness, and have a negative impact on low temperature toughness.

[0047] The sulfur element is easy to segregate and enrich in steel, and is an element harmful to corrosion resistance. The steel of the present invention strictly controls the sulfur and phosphorus content levels in terms of metallurgical quality, that is, P: ≤0.018%, S: ≤0.005% to meet the requirements of steel grade for purity, impact toughness, welding performance and corrosion resistance.

[0048] V: V has strong bonding ability with C, O and N, and forms extremely stable compounds with them, thus refining the grains, reducing the thermal sensitivity and temper brittleness of steel. It can significantly improve the welding performance of ordinary low alloy steel. The V content in the steel of the present invention is designed to be 0.07-0.10%.

[0049] B: The main function of B in steel is to increase the hardenability of steel, thereby saving relatively rare and precious metals. Boron has a strong affinity with nitrogen and oxygen. Adding 0.007% B to boiling steel can eliminate the aging phenomenon of steel. The designed content of B element in the steel of the present invention is 0.0018-0.0025%.

[0050] Al: Al has a strong affinity with O and N, and is a deoxidizing and nitrogen fixing agent during steelmaking. Aluminum can strongly reduce the austenite phase region in steel, refine the intrinsic grain size of steel, reduce the notch sensitivity of steel, reduce and eliminate the aging phenomenon of steel, especially reduce the toughness-brittleness transition temperature of steel, and improve the low-temperature toughness of steel. However, when the solid-solution Al content in steel exceeds a certain value, the austenite grains tend to grow and coarsen. The Al element content of the steel of the present invention is designed to be 0.020-0.040%.

[0051] In some embodiments, the Q690C round steel for tunnel embedded parts of the present invention is produced according to the following process: the steelmaking process is: blast furnace molten iron - molten iron pretreatment - converter - refining outside the furnace - VD vacuum treatment - continuous casting. The steel rolling process is: heating of the ingot - high-pressure water dephosphorization - Ф850 ingot opening machine - Ф700mm×3+Ф550mm×4 continuous rolling mill group rolling - sawing (sampling) - slow cooling in the cooling pit - inspection - grinding - bundling - storage - delivery; wherein:

[0052] Steelmaking process parameters:

[0053] Converter end point C ≥ 0.08%, P ≤ 0.020%;

[0054] Ar blowing operation during the whole refining process;

[0055] VD deep vacuum time ≥13min; soft blowing time ≥15min;

[0056] Continuous casting superheat ≤ 30℃, casting speed controlled at 0.60~0.65m / min;

[0057] Steel rolling process parameters:

[0058] Heating time ≥ 4h, heating temperature 1150~1250℃;

[0059] The starting rolling temperature is ≤1050℃, and the final rolling temperature is ≤980℃.

[0060] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0061] Example 1

[0062] 1) Place the hot-rolled Q690C round steel (chemical composition of which is shown in Table 1 below) for tunnel embedded parts in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel in the annealing furnace is ≥450°C;

[0063] 2) Heat the round steel in a quenching furnace to 930°C, keep it warm for 60 minutes to completely austenitize, and then quench it;

[0064] 3) Heat the round steel in a tempering furnace to 650°C, keep warm for 120 minutes, and then air cool. Figure 1 shown.

[0065] Example 2

[0066] 1) Place the hot-rolled Q690C round steel (chemical composition of which is shown in Table 1 below) for tunnel embedded parts in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel in the annealing furnace is ≥450°C;

[0067] 2) Heat the round steel in a quenching furnace to 940°C, keep it warm for 50 minutes to completely austenitize, and then quench it;

[0068] 3) Heat the round steel in a tempering furnace to 660°C, keep it warm for 100 minutes, and then water cool it. Figure 2 shown.

[0069] The mechanical properties of the Q690C round steel for tunnel embedded parts after heat treatment in Example 1 and Example 2 were tested, and the results are shown in Table 2 below.

[0070] Table 1: Chemical composition and weight percentage of round steel in each embodiment

[0071] Example C Si Mn P S Mo Ti Cr Nb V B Al 1 0.15 0.44 1.68 0.014 0.004 0.22 0.03 0.57 0.03 0.08 0.0018 0.025 2 0.16 0.42 1.68 0.012 0.003 0.23 0.03 0.56 0.04 0.08 0.0019 0.027

[0072] Table 2: Mechanical properties of round steel after heat treatment in each embodiment

[0073] Example <![CDATA[R p0.2 / MPa]]> <![CDATA[R m / MPa]]> A / ％ 0℃ impact energy 1 890 926 16 57 2 970 1018 17 54

[0074] It can be seen from the test results in Table 2 that the performance test results of the round steel treated by the heat treatment methods of Examples 1 and 2 all meet the technical requirements.

[0075] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A heat treatment method for Q690C round steel for tunnel embedded parts, characterized in that: The heat treatment method comprises the following operations: 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C; 2) Heat the round steel in a quenching furnace to 930-940°C, keep it warm for 50-60 minutes to completely austenitize, and then quench it; 3) Heat the round steel in a tempering furnace to 650-660°C, keep it warm for 100-120 minutes, and then air-cool or water-cool it.

2. The heat treatment method according to claim 1, characterized in that The heat treatment method comprises the following operations: 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C; 2) Heat the round steel in a quenching furnace to 930°C, keep it warm for 60 minutes to completely austenitize, and then quench it; 3) Heat the round steel in a tempering furnace to 650°C, keep it warm for 120 minutes, and then air cool it.

3. The heat treatment method according to claim 1, characterized in that: The heat treatment method comprises the following operations: 1) Place the hot-rolled round steel in an annealing furnace heated to 500°C for furnace cooling. The temperature of the hot-rolled round steel when placed in the annealing furnace is ≥450°C; 2) Heat the round steel in a quenching furnace to 940°C, keep it warm for 50 minutes to completely austenitize, and then quench it; 3) Heat the round steel in a tempering furnace to 660°C, keep it warm for 100 minutes, and then water cool it.

4. The heat treatment method according to any one of claims 1 to 3, characterized in that: The chemical composition of the Q690C round steel for tunnel embedded parts is calculated by mass percentage as follows: C: 0.14-0.16%, Mn: 1.65-1.75%, Si: 0.40-0.50%, Cr: 0.50-0.60%, Mo: 0.18-0.28%, Nb: 0.02-0.04%, V: 0.07-0.10%, Ti: 0.02-0.04%, Al: 0.020-0.040%, P: ≤0.018%, S: ≤0.005%, B: 0.0018-0.0025%, and the rest are iron and inevitable trace chemical elements.

5. The heat treatment method according to any one of claims 1 to 4, characterized in that: The mechanical properties of the Q690C round steel used for the tunnel embedded parts after heat treatment meet the following requirements: yield strength ≥850MPa, tensile strength ≥900MPa, elongation after fracture ≥14%, and 0°C KV2 ≥47J.

6. The heat treatment method according to claim 5, characterized in that: The mechanical properties of the Q690C round steel used for the tunnel embedded parts after heat treatment meet the following requirements: yield strength ≥970MPa, tensile strength ≥1010MPa, elongation after fracture ≥16%, and 0°C KV2 ≥54J.

7. The heat treatment method according to any one of claims 1 to 6, characterized in that: The Q690C round steel for tunnel embedded parts is produced according to the following process steps: steelmaking process: blast furnace molten iron - molten iron pretreatment - converter - refining outside the furnace - VD vacuum treatment - continuous casting; and steel rolling process: heating of ingot - high-pressure water dephosphorization - Ф850 ingot opening machine - rolling of Ф700mm×3+Ф550mm×4 continuous rolling mill - sawing (sampling) - slow cooling in slow cooling pit; wherein: Steelmaking process parameters: Converter end point C ≥ 0.08%, P ≤ 0.020%; Ar blowing operation during the whole refining process; VD deep vacuum time ≥13min; soft blowing time ≥15min; Continuous casting superheat ≤30℃, casting speed controlled at 0.60~0.65m / min; Steel rolling process parameters: Heating time ≥ 4h, heating temperature 1150~1250℃; The starting rolling temperature is ≤1050℃, and the final rolling temperature is ≤980℃.

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