Heat treatment process for producing 1.2311 die steel thick plate by trolley furnace

Abstract

The invention discloses a heat treatment process for producing a 1.2311 die steel thick plate by a trolley furnace, which aims at industrial batch heat treatment of the 1.2311 die steel thick plate with the thickness of 150-260mm in the trolley furnace, the hardness difference of the produced steel plate at the same position in the same furnace is less than or equal to 15HB, the performance stability is good, and the industrial batch production requirement can be met. Through the optimized hearth design, cushion block design and steel loading mode design, the temperature uniformity of different areas of the steel plate is guaranteed; the heat preservation coefficients of steel plates in the same furnace are standardized, and the consistency of the heat preservation coefficients of the steel plates with different thicknesses in a target heat treatment temperature interval is ensured, so that the consistency of the performance of 1.2311 die steel thick plates produced in batches is ensured, the hardness difference of positions with the same thickness of the steel plates in the batch production process is smaller than or equal to 12 HB, and the hardness difference of positions with the same furnace is smaller than or equal to 15 HB; and aiming at the cooling characteristic of the large-thickness steel plate, a furnace cooling process is canceled, and the production efficiency is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgical processing, and relates to a heat treatment process for producing 1.2311 die steel thick plates by a car bottom furnace. BACKGROUND

[0002] In recent years, with the rapid development of the large-size plastic mold industry for automobiles, household appliances and the like, the demand for domestic large-section pre-hardened plastic mold steels is also increasing; and with the continuous improvement of the internal quality of 450mm-specification large-thickness continuous casting billets, the hardness uniformity and internal organization compactness of the 150-260mm high-quality 1.2311 die steel thick plates produced by using the section are greatly improved, and the quality stability is comparable to that of the steel plates produced by forging, thereby greatly improving the production efficiency. However, due to the high alloy content of the die steel and the long heat treatment time, the production efficiency of the 150-260mm 1.2311 die steel thick plates is low when a continuous annealing furnace is used, and it is unable to meet the production requirements, while the car bottom furnace production mode is flexible and can realize efficient heat treatment production of large-thickness die steels.

[0003] Chinese patent CN201410361032.4 provides a heat treatment process for producing high-quality die steels by a car bottom furnace, but in the patent, a profile steel is used as a spacer in the middle of the steel plate, which affects the air convection of the hearth, and the spacer height is 400mm, the charging efficiency is low, the difference between the steel plates in the same furnace is not required, and the temperature uniformity is compensated by slow cooling after the furnace, the production efficiency is low, and it is not suitable for the production of large-thickness die steel thick plates. At present, when the car bottom furnace is used for heat treatment tempering production of conventional varieties, the problems of non-standardization of the heating, holding process, temperature control range, thickness difference of the steel plates in the same furnace and the shape of the spacers between the steel plates seriously affect the cross-section hardness uniformity of the 150-260mm 1.2311 die steel thick plates, and it is unable to meet the strict requirements of the die steels on the heat treatment process. SUMMARY

[0004] The application aims to provide a heat treatment process for efficiently producing 1.2311 die steel thick plates by a car bottom furnace, and the hardness difference between the steel plates in the same position in the same furnace is required to be ≤15HB, the performance stability is good, and the industrial batch production requirements can be met.

[0005] The technical scheme of the application is as follows: A heat treatment process for producing 1.2311 die steel thick plates by a car bottom furnace, comprising the following key process steps: 1) tempering: in the 450-600℃ heat treatment holding process, the temperature difference of the hearth is less than ±5℃; the hot air in the furnace is circularly circulated in the clockwise and counterclockwise directions along the width direction at regular intervals, the interval time is 10-15min; the distance between the air outlets on both sides of the hearth and the edge of the steel plate is 150-250mm; 2) Steel loading: the steel plates are loaded into the furnace in a stacked manner, each steel plate is separated by a cylindrical hollow spacer, the distance between the steel plates in the vertical direction is 150-300 mm, the steel plates are stacked in the width direction and are kept at equal intervals close to the air outlets on both sides of the furnace; the lowermost steel plate is 400 mm away from the furnace bottom, and the uppermost steel plate is ≥300 mm away from the furnace top; 3) Temperature rising: according to the thickness specification of the produced steel plate, the steel plate is heated to a target holding temperature of 540-580℃ at a temperature rising rate of 30-60℃ / h, and 1-2 holding steps are set at 450-520℃ during the temperature rising process, and each step is held for 60-150 min; 4) Holding: when the furnace temperature reaches the set target temperature, the holding time is started, the holding time is designed according to the thickness of the steel plate, the thickness difference of the steel plate in each furnace is <20 mm, and the holding coefficient of each steel plate is required to be in the range of 3.5-4.0 min / mm; 5) Discharge: after the steel plate is held, it is directly discharged and air-cooled on the rack, and hardness detection is performed when the steel plate is cooled to <50℃.

[0006] The present application has the following advantages: 1) The optimized furnace design, spacer and steel loading method design ensure the uniformity of the temperature of different regions of the steel plate; 2) The holding coefficient of the steel plate in the same furnace is specified to ensure the consistency of the holding coefficient of steel plates of different thicknesses in the target heat treatment temperature range, thereby ensuring the consistency of the performance of the batch-produced 1.2311 die steel thick plate, and the hardness difference of the same thickness position of the same steel plate during batch production is ≤12 HB, and the hardness difference of the same position of the steel plates in the same furnace is ≤15 HB; 3) According to the cooling characteristics of the thick steel plate, the furnace cooling process is cancelled, and the production efficiency is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 It is a schematic diagram of the loading structure; the steel plates are separated by spacers.

[0008] Figure 2 It is an enlarged perspective view of the shape of the spacer in the steel grade. DETAILED DESCRIPTION

[0009] The content of the present application will be further illustrated below in combination with examples. Example 1

[0010] The heat treatment process of the 1.2311 die steel thick plate produced by the trolley furnace includes the following process steps: 1) tempering: target temperature 570±5℃, hot air in the furnace is clockwise and counterclockwise circulation along the width direction, change direction every 15 min to ensure that each steel plate is heated evenly; the distance between the air outlet on both sides of the hearth and the edge of the steel plate is 150~250mm, which ensures that the hot air effectively enters the upper and lower surfaces between the steel plates to achieve overall heating; 2) loading: the thickness of the loaded steel plate is 190~200mm, the grade is 1.2311, each steel plate is separated by a cylindrical hollow pad, the pad height between the steel plates is 200mm, and the distance between the pad and the air outlet on both sides of the hearth is 170~200mm; the distance between the lowermost steel plate and the furnace bottom is 400mm, and the distance between the uppermost steel plate and the furnace top is 600mm; 3) heating: heating to 520±5℃ at a rate of 45℃ / s, holding for 120min, and then heating to the target temperature of 570±5℃ at a rate of 30℃ / s; 4) holding: holding for 750min after the target temperature of 570±5℃ is reached in each zone of the hearth; 5) unloading: after the holding is completed, the steel plate is directly unloaded from the furnace and air cooled on the rack, the steel plate is cooled to 25~40℃ for hardness testing, and the hardness testing results are shown in Table 1.

[0011] Table 1 hardness results of steel plate in Example 1 . Example 2

[0012] The heat treatment process for producing 1.2311 mold steel thick plate in a trolley furnace includes the following process steps: 1) tempering target temperature 563±5℃, hot air in the furnace is clockwise and counterclockwise circulation along the width direction, change direction every 15 min to ensure that each steel plate is heated evenly; the distance between the air outlet on both sides of the hearth and the edge of the steel plate is 150~250mm, which ensures that the hot air effectively enters the upper and lower surfaces between the steel plates to achieve overall heating; 2) loading: the thickness of the loaded steel plate is 246~260mm, the grade is 1.2311, each steel plate is separated by a cylindrical hollow pad, the pad height between the steel plates is 250mm, and the distance between the pad and the air outlet on both sides of the hearth is 180~210mm; the distance between the lowermost steel plate and the furnace bottom is 400mm, and the distance between the uppermost steel plate and the furnace top is 340mm; 3) heating: heating to 520±5℃ at a rate of 40℃ / s, holding for 120min, and then heating to the target temperature of 563±5℃ at a rate of 30℃ / s; 4) holding: holding for 960min after the target temperature of 563±5℃ is reached in each zone of the hearth; 5) unloading: after the holding is completed, the steel plate is directly unloaded from the furnace and air cooled on the rack, the steel plate is cooled to 25~45℃ for hardness testing, and the hardness testing results are shown in Table 2.

[0013] Table 2 Hardness results of steel plates in Example 2 . Example 3

[0014] The heat treatment process for producing 1.2311 die steel thick plates in a hearth furnace includes the following process steps: 1) Tempering: the target temperature is 575±5℃, the hot air in the furnace is circulated clockwise and counterclockwise along the width direction, and the direction is changed every 15 minutes to ensure uniform heating of each steel plate; the distance between the air outlets on both sides of the furnace and the edge of the steel plate is 150~250mm, which ensures that the hot air effectively enters the upper and lower surfaces between the steel plates to achieve overall heating; 2) Loading: the thickness of the loaded steel plates is 160~175mm, the grade is 1.2311, and each steel plate is separated by a cylindrical hollow pad, the height of the pad between the steel plates is 170mm, and the distance between the pad and the air outlets on both sides of the furnace is maintained at 180~230mm; the distance between the lowermost steel plate and the furnace bottom is 400mm, and the distance between the uppermost steel plate and the furnace top is 340mm; 3) Heating: heating at 50℃ / s to 470±5℃, holding for 60min, then heating at 40℃ / s to 520℃, holding for 60min, and finally heating at 30℃ / s to the target temperature of 575±5℃; 4) Holding: holding for 630min after the furnace reaches the target temperature of 575±5℃; 5) Discharging: after the holding is completed, the steel plates are directly discharged from the furnace and air-cooled on the rack, and the hardness detection is performed when the steel plates are cooled to 25~40℃, and the hardness detection results are shown in Table 3.

[0015] Table 3 Hardness results of steel plates in Example 3 .

Claims

1. A heat treatment process for producing 1.2311 die steel thick plates using a bogie hearth furnace, characterized in that... The key process steps include the following: 1) Tempering: During the heat treatment and holding process at 450~600℃, the temperature difference in the furnace is less than ±5℃; the hot air in the furnace is circulated in a clockwise and counterclockwise direction along the width at regular intervals, with a reversal time interval of 10~15min; the distance between the air outlets on both sides of the furnace and the edge of the steel plate is 150~250mm. 2) Steel loading: Steel plates are loaded into the furnace in a stacked manner, with each steel plate separated by cylindrical hollow spacers. The steel plates are spaced 150~300mm apart in the vertical direction and stacked neatly in the width direction, maintaining a nearly equal distance from the air outlets on both sides of the furnace. The bottom layer of steel plates is 400mm from the furnace bottom, and the top layer of steel plates is ≥300mm from the furnace top. 3) Heating: Based on the thickness specifications of the steel plate being produced, a heating rate of 30~60℃ / h is designed to heat the steel plate to the target holding temperature of 540~580℃. During the heating process, 1~2 holding steps are set at 450~520℃, and each step is held for 60~150 minutes. 4) Heat preservation: When the furnace temperature reaches the set target temperature, the timer starts to perform heat preservation. The heat preservation time is designed according to the thickness of the steel plate entering the furnace. The thickness difference of the heat-treated steel plate in each furnace is <20mm, and the heat preservation coefficient of each steel plate is required to be in the range of 3.5~4.0min / mm. 5) Unloading: After the steel plate has finished heat preservation, it is directly unloaded from the furnace and air-cooled on the platform. The hardness is tested when the steel plate is cooled to <50℃.

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