Medium-thickness tempered steel plate superposition production method

Abstract

The invention belongs to the technical field of steel plate tempering processes, and particularly relates to a medium-thickness tempered steel plate stacking production method which adopts a ventilation partition plate to separate an upper steel plate layer and a lower steel plate layer, and it is guaranteed that the upper surfaces and the lower surfaces, adjacent to each other, of the two steel plates are evenly heated. According to the steel plate air cooling device, it is effectively guaranteed that all parts of the steel plates are evenly heated in the tempering process, it is guaranteed that each steel plate is evenly cooled in the air cooling process by limiting the stacking number of the steel plates and the thickness of the ventilation partition plates, deformation of the steel plates and instability of the structure performance are avoided, the qualified rate of steel is effectively increased, and the qualified rate of the high-strength steel performance is increased to 98.28% from 97.33%.

Description

Technical Field

[0001] The invention relates to the technical field of steel plate tempering technology, and relates to a method for superimposing tempered steel plates of medium and thick specifications. Background Art

[0002] Tempering is a heat treatment process in which the workpiece is heated to a temperature below Ac1 (the starting temperature of pearlite to austenite transformation during heating) after hardening, kept at a certain temperature for a certain period of time, and then cooled to room temperature. According to the tempering temperature range, it can be divided into low-temperature tempering (150-250℃), medium-temperature tempering (350-500℃) and high-temperature tempering (above 500-650℃). The heating temperature is low during tempering production. In order to ensure that the performance of the steel plate is qualified, a longer heating time in the furnace is required, resulting in low tempering production efficiency.

[0003] In the early stage, Laigang wide and thick plate heat treatment line completed the research and development of the superimposed tempering production mode for steel plates with a thickness of less than 20mm, and the steel plate performance was good. However, when the superimposed trial production of high-strength steel with a thickness of 30-60mm was carried out according to this idea, the performance qualification rate of the steel plate after tempering was low. The reasons are analyzed as follows:

[0004] 1. In order to improve production efficiency, the time in the furnace for two steel plates after being stacked is set to 1.5 times that of a single steel plate. Since both steel plates can only be heated on one side, the temperature uniformity of the steel plate section is poor, resulting in unstable performance.

[0005] 2. The time of stacked steel plates in the furnace is set to be twice that of a single steel plate, and the performance stability is improved, but the production efficiency is increased by less than 5%, and the efficiency improvement effect is not obvious. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for stacking and producing medium and thick tempered steel plates. The present invention uses a ventilation partition to separate the upper and lower layers of steel plates, thereby ensuring that the upper and lower surfaces adjacent to the two steel plates are evenly heated. Since the ventilation partition is provided with an air distribution channel, it is effectively ensured that the steel plates are evenly heated at all locations during the tempering process. In addition, by limiting the number of stacked steel plates and the thickness of the ventilation partition, it is ensured that each steel plate is evenly cooled during the air cooling process, thereby avoiding deformation of the steel plates and instability of the organizational properties, and effectively improving the qualified rate of steel materials.

[0007] The technical problem to be solved by the present invention is achieved by adopting the following technical solution: A method for stacking and producing medium and thick tempered steel plates, comprising the following steps:

[0008] S1. Steel loading: Place the steel plates of the lower layer on the furnace entry rollers, set ventilation baffles above the steel plates of the lower layer, and hoist the steel plates of the upper layer above the ventilation baffles;

[0009] The thickness of the steel plate is 30-60mm, and the thickness of the ventilation partition is 40-50mm;

[0010] The upper and lower surfaces of the ventilation baffle are arranged in parallel, and the ventilation baffle is provided with an air distribution channel;

[0011] S2, tempering treatment: use the furnace roller and the furnace bottom roller to send the stacked steel plates into the heat treatment furnace, close the furnace door for high temperature tempering, the tempering temperature is above 600℃;

[0012] S3, cooling after exiting the furnace: The heat-treated steel plate is removed as a whole by means of furnace bottom rollers and exiting furnace rollers for air cooling. The present invention adopts an air cooling method to cool the steel plate. Due to high-temperature tempering, the temperature of the steel plate exiting the furnace is higher than the demagnetization temperature of the magnet by 450 degrees. Therefore, the steel plates still need to be kept stacked together when air-cooled after exiting the furnace. Air cooling can form pearlite structure with a small inter-sheet spacing, which helps to improve the plasticity and toughness of the material. Compared with furnace cooling, the cooling speed is fast. However, the difference from furnace cooling, which can control the cooling speed of the steel plate and make the multi-layer stacked steel plates evenly cooled, is that when multiple layers of medium and thick plates are stacked together for air cooling, there is a problem that the steel plates in the middle cannot be evenly cooled. Therefore, the present invention limits the number of steel plates and the thickness of the ventilation baffles, which improves the tempering efficiency while ensuring the qualified and stable performance of the steel plates.

[0013] Preferably, in step S2, the total steel plate thickness is set to 1.5 times the thickness of a single steel plate, the heating coefficient is set to 2.2, and the steel plate in-furnace time = total steel plate thickness * 2.2 (min). The in-furnace time is determined according to the thickness of the steel plate to ensure uniform heating of the steel plate and stability of the performance of various parts of the steel plate. By increasing the in-furnace time of the steel plate, the impact resistance of the steel plate is improved.

[0014] Preferably, in step S3, the stacked steel plates are sent to the cooling bed for cooling by the furnace discharge rollers and the conveying rollers. The stacked steel plates are directly conveyed to the cooling bed for cooling by the furnace discharge rollers and the conveying rollers, which improves the cooling speed of the steel plates and ensures the flatness of the steel plates, so that the steel plates have a good plate shape.

[0015] Preferably, the present invention further includes step S4: after the steel plates are air-cooled to 300-500°C, the steel plates are hoisted and separated, stacked and slowly cooled, and the ventilation baffles are recycled. Since the temperature is too high to use a magnetic crane to hoist the steel plates, the steel plates need to be air-cooled to 300-500°C to separate the stacked steel plates. In order to reduce the site occupied by too many ventilation baffles, the cooled ventilation baffles are recycled.

[0016] Preferably, in step S1, during the heating process, the temperature of the heat treatment furnace is adjusted in real time according to the steel plate temperature calculated by the secondary calculation, and the furnace outlet temperature of the steel plate is controlled within ±10°C of the target temperature to ensure that the steel plate has a straight shape and uniform performance after heat treatment.

[0017] Preferably, in step S1, the ventilation baffle is made of the same material as the steel plate. The ventilation baffle is made of the same material as the steel plate, that is, the ventilation baffle has the same thermal conductivity as the steel plate, and can heat up and cool down synchronously with the steel plate, thereby ensuring the uniformity of temperature at various locations on the steel plate and the stability of performance at various locations on the steel plate.

[0018] Preferably, in step S1, the ventilation baffle is an integrated structure. The ventilation baffle is an integrated structure, which greatly improves the loading efficiency and ensures the stability of the steel plates when they are stacked together during the movement on the roller table, avoiding safety accidents caused by the steel plates falling, and effectively avoiding scratches on the surface of the steel plates.

[0019] Preferably, in step S1, the ventilation baffle comprises a vertical support bar arranged along the length direction of the heat treatment furnace and a plurality of transverse support bars arranged along the width direction of the heat treatment furnace, the transverse support bars are arranged at intervals along the length direction of the heat treatment furnace, and the transverse support bars are symmetrically arranged on both sides of the vertical support bar. Since the side walls of the heat treatment furnace are spaced apart along the length direction with heating devices such as radiation tubes or flamethrowers, the transverse support bars are symmetrically arranged on both sides of the vertical support bar, so that the temperature flow field of the steel plates on both sides of the vertical support bar is the same, thereby ensuring uniform heating of the steel plates.

[0020] Preferably, in step S1, the ventilation baffle is cut from a whole steel plate. The ventilation baffle is directly prepared by cutting from a whole steel plate, which effectively ensures the flatness of the ventilation baffle.

[0021] Preferably, in the step S1, the ventilation baffle is in the shape of a Chinese character "W" or a Chinese character "I".

[0022] Compared with the prior art, the beneficial effects of the present invention are: the method for superimposing medium and thick tempered steel plates of the present invention not only improves production efficiency, but also improves the performance qualification rate. When a single steel plate is loaded into a furnace for production, the single furnace output is up to 230 tons / shift. When the ventilation baffle of the present invention is superimposed for production, the single furnace output is up to 298 tons / shift, and the production efficiency is improved by about 29.6%.

[0023] In addition, since the flatness of the upper and lower surfaces of the ventilation baffles is the same, the ventilation baffles and the steel plates are tightly fitted together, and the ventilation baffles have the same thermal conductivity efficiency at all locations, the flatness of the steel plates after tempering heating is effectively guaranteed, and by limiting the number of steel plates to two and the thickness of the baffles to 40-50mm, the center and edge positions of the upper and lower steel plates are guaranteed to maintain a basically consistent cooling rate during air cooling, thereby avoiding deformation caused by uneven cooling of the steel plates, ensuring the uniformity of temperature at all locations of the steel plates and the stability of performance at all locations of the steel plates, and the qualified rate of high-strength steel performance is increased from 97.33% to 98.28%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the production method of the present invention;

[0025] Figure 2 It is a structural schematic diagram of a production device corresponding to the production method of the present invention;

[0026] Figure 3 Schematic diagram of the stacking method of steel plates in the present invention

[0027] Figure 4 This is a schematic diagram of the structure of the ventilation baffle described in Example 1 of the present invention;

[0028] In the figure, 1 steel plate, 2 ventilation baffle, 3 air distribution channel;

[0029] 100 entry rollers, 200 heat treatment furnaces, 300 furnace bottom rollers, 400 exit rollers. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings.

[0031] Example 1

[0032] like Figure 1 , Figure 2 and Figure 3 As shown, a method for stacking and producing medium-thickness tempered steel plates comprises the following steps:

[0033] S1. Steel loading: placing the steel plate 1 of the lower layer on the furnace entry roller 100 , setting a ventilation baffle 2 above the steel plate 1 of the lower layer, and hoisting the steel plate 1 of the upper layer above the ventilation baffle 2 .

[0034] The thickness of the steel plate 1 is 30-60 mm, and the thickness of the ventilation baffle 2 is 40-50 mm.

[0035] The upper and lower surfaces of the ventilation baffle 2 are arranged in parallel, and the ventilation baffle 2 is provided with an air distribution channel 3. The air distribution channels 3 are arranged at intervals along the length direction of the heat treatment furnace 200, and the axial direction of the air distribution channel 3 is parallel to the width direction of the heat treatment furnace 200.

[0036] S2. Tempering treatment: The stacked steel plates 1 are fed into the heat treatment furnace 200 by the inlet rollers 100 and the bottom rollers 300, the furnace door is closed for high-temperature tempering, and the tempering temperature is above 600 °C.

[0037] S3. Furnace discharging and cooling: The heat-treated steel plates 1 are integrally removed by the bottom rollers 300 and the outlet rollers 400 for air cooling.

[0038] In step S2, the total thickness of the steel plates is set according to 1.5 times the thickness of a single steel plate, the heating coefficient is set to 2.2, and the residence time of the steel plates in the furnace = total thickness of the steel plates × 2.2 (min).

[0039] In step S3, the stacked steel plates 1 are sent to the cooling bed for cooling through the outlet rollers 400 and the conveying roller table.

[0040] The method for producing the medium and heavy gauge tempered steel plates by stacking further includes step S4: When the steel plates 1 are air-cooled to 300 - 500 °C, the steel plates 1 are hoisted and separated, stacked for slow cooling, and the ventilation partition plates 2 are recycled.

[0041] In step S1, during the heating process, the furnace temperature of the heat treatment furnace 200 is adjusted in real time according to the temperature of the steel plates 1 calculated at the secondary level, and the outlet temperature of the steel plates 1 is controlled within ±10 °C of the target temperature. The target temperature is set according to the production requirements and will not be elaborated here.

[0042] In this embodiment, in step S1, the ventilation partition plates 2 are made of the same material as the steel plates 1.

[0043] Specifically, as Figure 4 shown, the upper and lower surfaces of the ventilation partition plate 2 are parallel to each other. The ventilation partition plate 2 includes a vertical support bar 21 arranged along the length direction of the heat treatment furnace 200 and a plurality of horizontal support bars 22 arranged along the width direction of the heat treatment furnace 200. The horizontal support bars 22 are arranged at intervals along the length direction of the heat treatment furnace 200, and the horizontal support bars 22 are symmetrically arranged on both sides of the vertical support bar 21. An air distribution channel 3 is formed between two adjacent horizontal support bars 22. To ensure the support effect and the uniformity of heat conduction, the widths of the vertical support bar 21 and the horizontal support bars 22 are at least 150 mm.

[0044] The ventilation partition plate 2 is of an integral structure and is cut from a whole steel plate. In this embodiment, the ventilation partition plate 2 is in a king-shaped form.

[0045] Taking the steel grade Q550D as an example, this embodiment has counted the properties of six groups of steel plates after high-temperature tempering, as shown in Table 1 below:

[0046] Table 1

[0047]

[0048]

[0049] The performance standards required for steel grade Q550D are: impact>33J, average>47J; yield strength 550-720MPa; tensile strength 670-830MPa; elongation ≥16%. As shown in Table 1, the performance of the steel plates after high temperature tempering in this embodiment meets the standard requirements, and the performance indicators of each group are stable.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that in step S1, two layers of steel plates 1 are arranged from bottom to top, and two adjacent layers of steel plates 1 are in contact with each other and are directly stacked together.

[0052] This comparative example takes the steel grade Q550D as an example, and statistics the properties of six groups of steel plates after high temperature tempering, as shown in Table 2 below:

[0053] Table 2

[0054]

[0055]

[0056] The performance standards required for steel grade Q550D are: impact>33J, average>47J; yield strength of 550-720MPa; tensile strength of 670-830MPa; elongation ≥16%. As shown in Table 2, although the average value of the performance of the steel plate after high temperature tempering in the manner of comparative example 1 meets the standard requirements, the yield strength of group 3 is lower than the standard range, and the impact test of group 2 is lower than the standard value of 33J, that is, the overall performance of the steel plate is unstable, the qualified rate is low, and it cannot meet normal production requirements.

[0057] Comparative Example 2

[0058] The difference from Example 1 is that in step S1, three layers of steel plates 1 are arranged from bottom to top, and a ventilation partition 2 is arranged between two adjacent layers of steel plates 1. The plate shape comparison is shown in Table 3.

[0059] Table 3

[0060] Plate shape (visual) Example 1 normal Comparative Example 2 abnormal

[0061] After comparison, it was found that when three layers of steel plates 1 were stacked and prepared, the use of ventilation baffles 2 would lead to abnormal plate shape, and the defects in the plate shape could be clearly found by visual inspection. After analysis, it was found that the temperature in the heat treatment furnace 200 was uniform. Due to the presence of the ventilation baffles 2, the stacking method of two layers of steel plates 1 and three layers of steel plates 1 did not affect the uniform heating of the steel plates 1. However, when the steel plates 1 were air-cooled in a stacked manner, since the steel plates 1 were medium and thick plates and retained a lot of heat, the middle steel plate 1 was in a relatively high temperature environment and could not directly contact the cold air. The cooling rate of the middle steel plate 1 in the three-layer steel plate 1 was significantly lower than the cooling rate of the steel plates 1 on the upper and lower sides, especially the cooling rate at the center of the middle steel plate 1 was lower than the cooling rate at the edge, which led to deformation of the steel plate 1.

[0062] By stacking two layers of steel plates 1, the air cooling speeds of the upper and lower layers of steel plates 1 are basically the same by controlling the thickness of the ventilation partition 2, and the air cooling speeds at the center and edge positions of the same steel plate 1 are also basically the same, thereby effectively ensuring a good plate shape of the steel plate. Therefore, in order to ensure the tempering quality of medium and thick plates and to achieve the purpose of improving the heat treatment efficiency, the present invention can only use the method of stacking two layers of medium and thick plates for high-temperature tempering when air cooling is used.

Claims

1. A method for producing medium and thick tempered steel plates by stacking, characterized in that: The following steps are involved: S1, steel loading: placing the steel plate (1) of the lower layer on the furnace entry roller (100), arranging a ventilation baffle (2) above the steel plate (1) of the lower layer, and hoisting the steel plate (1) of the upper layer above the ventilation baffle (2); The thickness of the steel plate (1) is 30-60 mm, and the thickness of the ventilation baffle (2) is 40-50 mm; The upper and lower surfaces of the ventilation baffle (2) are arranged in parallel, and the ventilation baffle (2) is provided with an air distribution channel (3); S2, tempering treatment: using the furnace entry roller (100) and the furnace bottom roller (300) to feed the stacked steel plates (1) into the heat treatment furnace (200), closing the furnace door to perform high temperature tempering, the tempering temperature being above 600°C; S3, furnace cooling: the heat-treated steel plate (1) is removed as a whole by using the furnace bottom rollers (300) and furnace discharge rollers (400) for air cooling.

2. The method for superimposing and producing medium and thick tempered steel plates according to claim 1, characterized in that: In step S2, the total steel plate thickness is set to 1.5 times the thickness of a single steel plate, the heating coefficient is set to 2.2, and the steel plate in-furnace time = total steel plate thickness * 2.2 (min).

3. The method for producing medium and thick tempered steel plates according to claim 1, characterized in that: In step S3, the stacked steel plates (1) are sent to a cooling bed via the furnace discharge rollers (400) and the conveying rollers for cooling.

4. The method for superimposing and producing medium and thick tempered steel plates according to claim 1 or 3, characterized in that: The method further comprises step S4: after the steel plate (1) is air-cooled to 300-500° C., the steel plate (1) is hoisted and separated, stacked and slowly cooled, and the ventilation partition (2) is recycled.

5. The method for producing medium and thick tempered steel plates according to claim 1, characterized in that: In step S1, during the heating process, the furnace temperature of the heat treatment furnace (200) is adjusted in real time according to the temperature of the steel plate (1) calculated at the second level, and the furnace exit temperature of the steel plate (1) is controlled within ±10°C of the target temperature.

6. The method for superimposing and producing medium and thick tempered steel plates according to claim 1, characterized in that: In step S1, the ventilation baffle (2) and the steel plate (1) are made of the same material.

7. The method for producing medium and thick tempered steel plates according to claim 1, characterized in that: In step S1, the ventilation baffle (2) is an integrated structure.

8. The method for superimposing and producing medium and thick tempered steel plates according to claim 1 or 7, characterized in that: The ventilation baffle (2) comprises a vertical support bar (21) arranged along the length direction of the heat treatment furnace (200) and a plurality of transverse support bars (22) arranged along the width direction of the heat treatment furnace (200), wherein the transverse support bars (22) are arranged at intervals along the length direction of the heat treatment furnace (200), and the transverse support bars (22) are symmetrically arranged on both sides of the vertical support bar (21).

9. The method for superimposing and producing medium and thick tempered steel plates according to claim 1 or 7, characterized in that: In step S1, the ventilation baffle (2) is cut from a whole steel plate.

10. The method for superimposing and producing medium and thick tempered steel plates according to claim 1 or 7, characterized in that: In step S1, the ventilation baffle (2) is in the shape of a Chinese character "W" or a Chinese character "I".

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