Preparation method of low-residual-stress decoiling ship plate steel

Abstract

The invention discloses a preparation method of decoiling ship plate steel with low residual stress, which belongs to the technical field of steel rolling, and comprises the following steps: hot-rolled plates are stacked in a centralized manner after being offline, and are uniformly conveyed to a heat treatment workshop for tempering treatment; during tempering treatment, the temperature of the heat treatment furnace is controlled to be 620-640 DEG C, and batch continuous tempering is immediately carried out after the steel plate is put into a warehouse; the in-furnace time is adjusted according to the thickness of the steel plate, and the calculation basis of the in-furnace time is 2.5 min / mm + 10-30 min; the temperature difference between the head and the tail of the plate body is less than or equal to 20 DEG C, so that the tempering uniformity is ensured; and naturally cooling the tempered steel plate in the air. Through precise temperature control, dynamic in-furnace time calculation and swing heat preservation, the residual stress of the ship plate is remarkably reduced to be smaller than or equal to 100 MPa, the unevenness is smaller than or equal to 1 mm / m, and meanwhile high strength and high toughness are kept; the method is suitable for AH32 ship plates with the thickness smaller than or equal to 60 mm, and the cutting efficiency and the material utilization rate can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a method for preparing Kaiping ship plate steel with low residual stress, which is particularly suitable for low-stress processing of 32-level ship plates. Background Art

[0002] In the medium and heavy plate sector, shipbuilding plates occupy a large portion of the market, with Kaiping shipbuilding plates being a top priority. Kaiping shipbuilding plates have the advantages of high dimensional accuracy, good plate quality, high yield rate, and low production cost.

[0003] However, traditional hot-rolled shipbuilding plates are prone to residual stress during production, causing deformation when cut, seriously impacting processing efficiency and product quality. Residual stress is a stress that exists within the steel plate when no additional load is applied and remains balanced throughout the entire plate structure. The presence of residual stress has a critical impact on the plate's formability and product quality. Residual stress also affects the plate's dimensional stability. When the steel plate is cut, the residual stress within the plate is released, causing deformation, especially invisible plate defects—uneven stress within the plate's transverse direction. However, the plate's cross-sectional modulus is sufficient to resist buckling. Plates with invisible plate defects are straight in the absence of external tension. However, after being cut into strips, the stress is released, causing the plate to deform. Severe invisible plate defects can cause production delays, damage to processing equipment, and welding difficulties for shipyard customers. Existing annealing processes, such as those disclosed in CN116891979A and CN118792583A, can partially eliminate stress, but they suffer from a wide temperature range and insufficient plate shape control. Especially for 32-level ship plates with a thickness of ≤60mm, the existing process is difficult to balance the strength and residual stress elimination effect. Summary of the Invention

[0004] Technical problem to be solved: In response to the above problems, the present invention provides a method for preparing Kaiping ship plate steel with low residual stress, which combines the processes of precise temperature control, batch continuous tempering and swing insulation to significantly reduce residual stress and improve plate shape quality.

[0005] Technical solution: The method for preparing Kaiping ship plate steel with low residual stress according to the present invention comprises the following steps: Step 1: After the hot-rolled plates come off the production line, they are piled up and transported to the heat treatment workshop for tempering. Step 2: During tempering, the heat treatment furnace temperature is controlled at 620-640℃, and batch continuous tempering is carried out immediately after the steel plates arrive at the warehouse; Step 3: Adjust the furnace time according to the thickness of the steel plate. The calculation basis for the furnace time is: 2.5min / mm + 10-30min; Step 4: the steel plate is swung in the furnace for heat preservation, and the temperature difference between the head and tail of the plate body is less than or equal to 20 DEG C, so as to ensure the uniformity of tempering; Step 5: the steel plate is naturally cooled in air after tempering.

[0006] Preferably, the tempering treatment is suitable for AH32 grade ship plates with a thickness less than or equal to 60 mm.

[0007] Preferably, the heat preservation time of the tempering treatment can be extended according to requirements to preferentially ensure the casting temperature.

[0008] Preferably, the mechanical properties of the steel plate after the tempering treatment meet the following requirements: Tensile strength: 490-630 MPa; Yield strength: greater than or equal to 355 MPa; Elongation after fracture: greater than or equal to 21 %; Unevenness index: less than or equal to 1 mm / m.

[0009] Preferably, the heat treatment furnace is divided into 24 symmetrically distributed temperature control zones, and the odd zones are upper zones and the even zones are lower zones, and the temperature of each zone is set to 620-640 DEG C.

[0010] Preferably, the residual stress of the steel plate after the tempering treatment is less than or equal to 100 MPa.

[0011] Compared with the prior art, the present application has at least the following beneficial effects: 1. The kaiping ship plate steel prepared in the present application is naturally cooled in air after casting, so that the tempering stress relief effect is ensured; while the original grade strength is maintained, the toughness of the steel plate is further enhanced by the tempering treatment; the internal stress is eliminated, the customer's transverse and longitudinal kaiping cutting plate material is not deformed, the continuous cutting of the material can be realized, the production efficiency is optimized, the utilization rate of the material is improved, and the machine damage caused by the warping, buckling and curling of the plate material is avoided. 2. The flatness of the kaiping ship plate steel is improved, the transverse and longitudinal stress of the steel plate during rolling is eliminated by tempering, the unevenness index data of the steel plate is significantly improved, the residual stress is reduced to less than or equal to 100 MPa, and the cutting deformation rate is reduced by more than 50 %; the unevenness index is improved to less than or equal to 1 mm / m, and the flatness stability of the plate is significantly enhanced; while the AH32 grade strength is maintained, the elongation after fracture is improved to greater than or equal to 21 %.

[0012] The present application also has other beneficial effects which are stated in the embodiment part of the specification, and will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The preparation process flowchart of the present application is shown in the figure; Figure 2 The tempering furnace temperature zone distribution schematic diagram of the present application is shown in the figure; Figure 3This is a comparison chart of the cutting deformation rates of Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0014] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the following Figure 1-Figure 3 The technical solutions of the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0015] like Figure 1 As shown, the present invention provides a method for preparing Kaiping ship plate steel with low residual stress, comprising the following steps: Step 1: After the hot-rolled plates come off the production line, they are piled up and transported to the heat treatment workshop for tempering, which can avoid stress accumulation caused by multiple handling; Step 2: During tempering, the heat treatment furnace temperature is controlled at 620-640℃. After the steel plates arrive at the warehouse, batch continuous tempering is carried out immediately. The heat treatment furnace is divided into 24 symmetrically distributed temperature control zones, with odd-numbered zones as the upper zone and even-numbered zones as the lower zone. The temperature of each zone is set at 620-640℃ (e.g. Figure 2 This tempering process is suitable for AH32 grade ship plates with a thickness of ≤60mm. The tempering furnace temperature is set at 620-640℃, which ensures stress relief efficiency and avoids grain coarsening. Step 3: Adjust the furnace time according to the thickness of the steel plate. The calculation basis for the furnace time is: 2.5min / mm + 10-30min; the holding time of the tempering treatment can be extended as needed to prioritize the tapping temperature; Step 4: The steel plate is swung in the furnace to keep warm. The temperature difference between the head and tail of the plate is ≤20℃ to ensure uniform tempering. Step 5: After tempering, the steel plate is cooled naturally in air.

[0016] The mechanical properties of the steel plate after tempering treatment using the method of the present invention meet the following requirements: tensile strength: 490-630MPa; yield strength ≥355MPa; elongation after fracture ≥21%; unevenness index ≤1mm / m; and residual stress of the steel plate after tempering treatment ≤100MPa.

[0017] Example 1: The above preparation method is used to produce Kaiping ship plate steel with grade AH32 and thickness of 24 mm. The tempering temperature is controlled at 630±10°C, the furnace time is 2.5 min / mm×24mm+20min=80min; and the cooling method is natural air cooling.

[0018] The performance test results of the Kai Pi ship plate steel prepared in Example 1 are: tensile strength 509.5 MPa, yield strength 389 MPa, elongation after fracture 31.5%, unevenness 0.4 mm / m.

[0019] Example 2: The Kai Pi ship plate steel with the brand AH32 and the thickness of 26 mm is produced by using the above preparation method, the tempering temperature is controlled at 630±10℃, the time in the furnace is 2.5 min / mm*26 mm+15 min =80 min, and the cooling mode is natural air cooling.

[0020] The performance test results of the Kai Pi ship plate steel prepared in Example 2 are: tensile strength 507.5 MPa, yield strength 391.5 MPa, elongation after fracture 29.5%, unevenness 0.6 mm / m.

[0021] Example 3: The Kai Pi ship plate steel with the brand AH32 and the thickness of 22 mm is produced by using the above preparation method, the tempering temperature is controlled at 630±10℃, the time in the furnace is 2.5 min / mm*22 mm+30 min =85 min, and the cooling mode is natural air cooling.

[0022] The performance test results of the Kai Pi ship plate steel prepared in Example 3 are: tensile strength 520 MPa, yield strength 410 MPa, elongation after fracture 28.25%, unevenness 0.5 mm / m.

[0023] In the comparative example 1, the same specification 24 mm ship plate steel is produced by using the traditional non-tempering process, and the deformation rate after cutting is 12%, and the unevenness is 3.2 mm / m; while the deformation rate of the ship plate steel prepared in the examples 1-3 of the present application is ≤3% (as shown in Table 1), and the unevenness is ≤1 mm / m, which indicates that the flatness of the Kai Pi ship plate steel of the present application is improved, the tempering eliminates the transverse and longitudinal stress in the steel plate during rolling, and the unevenness index data of the steel plate is significantly improved. Figure 3

[0024] The method of the present application is applied to a steel plant with an annual production of 100,000 tons of ship plate production line, and the feedback data shows that the cutting efficiency is improved by 30%, the material utilization rate is improved by 15%, and the equipment loss is reduced by 20%, which indicates that the method eliminates the internal stress, the customer transverse and longitudinal Kai Pi cutting plate does not deform, can continuously cut the blank, optimizes the production efficiency, improves the material utilization rate, and avoids the machine damage caused by the warping, buckling and buckling of the plate.

[0025] The above is the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principle of the present application, a number of improvements and refinements can be made, which should be considered as the protection scope of the present application.​

Claims

1. A method for preparing Kaiping ship plate steel with low residual stress, characterized in that: The following steps are involved: Step 1: After the hot-rolled plates come off the production line, they are piled up and transported to the heat treatment workshop for tempering. Step 2: During tempering, the heat treatment furnace temperature is controlled at 620-640℃, and batch continuous tempering is carried out immediately after the steel plates arrive at the warehouse; Step 3: Adjust the furnace time according to the thickness of the steel plate. The calculation basis for the furnace time is: 2.5min / mm + 10-30min; Step 4: The steel plate is swung in the furnace to keep warm. The temperature difference between the head and tail of the plate is ≤20℃ to ensure uniform tempering. Step 5: After tempering, the steel plate is cooled naturally in air.

2. The method for preparing Kaiping ship plate steel with low residual stress according to claim 1, characterized in that: The tempering treatment is applicable to AH32 grade ship plates with a thickness of ≤60 mm.

3. The method for preparing Kaiping ship plate steel with low residual stress according to claim 1, characterized in that: The holding time of the tempering treatment can be extended according to demand to give priority to ensuring the tapping temperature.

4. The method for preparing Kaiping ship plate steel with low residual stress according to claim 1, characterized in that: The mechanical properties of the steel plate after tempering treatment meet the following requirements: Tensile strength: 490-630MPa; Yield strength: ≥355MPa; Elongation after break: ≥21%; Roughness index ≤1mm / m.

5. The method for preparing Kaiping ship plate steel with low residual stress according to claim 1, characterized in that: The heat treatment furnace is divided into 24 symmetrically distributed temperature control zones, with odd-numbered zones being upper zones and even-numbered zones being lower zones. The temperature of each zone is set at 620-640°C.

6. The method for preparing Kaiping ship plate steel with low residual stress according to claim 1, characterized in that: The residual stress of the steel plate after tempering is ≤100 MPa.

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