Manufacturing method for improving hardness uniformity of ultra-long single-rolling pre-hardening type plastic mold steel plate

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a manufacturing method for improving the hardness uniformity of a super-long single-rolling pre-hardening type plastic mold steel plate, which is characterized by comprising the following steps of: pouring a thick casting blank, rolling by a single-stand reciprocating rolling mill, balancing the temperature of the steel plate by laminar cooling equipment, stacking, insulating and slowly cooling high-temperature steel plates, and carrying out heat treatment and tempering treatment.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a manufacturing method for improving the hardness uniformity of an ultra-long single-rolled pre-hardened plastic mold steel plate. Background Art

[0002] With the rapid development of China's plastics industry in recent years, its market demand has also increased; while the plastics market is expanding, the terminal's quality requirements for plastic products are also getting higher and higher, and the demand and quality of plastic molds are increasingly higher, which has promoted the continuous development of plastic molds. At present, plastic molds are developing in the direction of high efficiency, high precision and long life. Despite this, my country's mold technology and mold life are still lagging behind those of some industrially developed countries. The mold materials and heat treatment of plastic molds are complex in structure, and the requirements for the plastic mold cavity size accuracy and surface roughness are very high. The requirements for the plastic mold cavity material are relatively harsh. Therefore, the correct selection of mold materials and their heat treatment methods are very important for improving mold quality and extending mold life.

[0003] With the increasing demand for plastic products, the original ingot production form is no longer satisfactory in the current market. Under the current efficient continuous casting production, more and more steel mills have adopted continuous casting billets to process mold steel. However, due to the thickness of the continuous casting billet and the rolling form of the rolling mill, the current billet thickness is limited, and most of the production is mold steel plates with specifications below 300mm, but the production efficiency has been greatly improved; in order to further reduce costs and improve production efficiency, it is necessary to tackle the problem of rolling length; but after the rolling mill steel plate reaches a certain length, the uniformity of hardness distribution in the length direction of the rolled steel plate is reduced due to the influence of rolling temperature, process control, etc.; hardness distribution uniformity is one of the important performance indicators of plastic mold steel plates. Poor hardness uniformity will cause jitter in the cutting process of the steel plate, reduce the quality of the cutting surface, cause stress anisotropy or local stress excessive concentration and other defects, poor hardness uniformity will increase the wear of the saw blade during the cutting process, increase production costs, and even cause saw blade breakage during processing, endangering the personal safety of processing personnel.

[0004] How to ensure the hardness uniformity of ultra-long single-rolling die steel plates through rolling process control and subsequent effective measures. The present invention combines the control characteristics of ultra-long steel plates rolled by a single-stand rolling mill and the balance of finished product quality to provide a reasonable control method. Summary of the invention

[0005] The purpose of the present invention is to provide a manufacturing method for improving the hardness uniformity of extra-long single-rolled pre-hardened plastic mold steel plates. The ingots of extra-long single-rolled plastic mold steel produced by a single-frame reciprocating rolling mill are subjected to heating, rolling, cooling, stacking, slitting, tempering and other operations, so that the overall hardness and uniformity of the steel plate with a length of up to 52m are excellent and stable, meeting the manufacturing and use requirements of users.

[0006] To achieve the above object, the technical solution of the present invention is: The length of the steel plate is 45m-52m and the thickness is 20mm-70mm after the 150mm thick ingot is rolled in a single-frame reciprocating mill and cooled by laminar flow. The production includes: 150mm thick ingot, rolling in a single-frame reciprocating mill, laminar cooling equipment to balance the temperature of the steel plate, high-temperature steel plate stacking insulation and slow cooling, heat treatment and tempering treatment, specifically: The smelting and wide slab continuous casting machine is used to cast 150mm thick ingots, with low segregation not exceeding B1.0 level, porosity not exceeding 1.0 level, and no internal or surface cracks; the internal quality of the ingot is balanced, and the organizational structure on the finished steel plate is also balanced. It is particularly important to control the internal quality balance of the 150mm thick ingot under low reduction ratio.

[0007] The 150mm thick ingot is slowly heated in the heating furnace at 300℃-600℃ on the surface, with a heating coefficient of 0.8-1.0min / mm and an even heating temperature of 1200℃-1250℃; hot charging of the ingot reduces cracking or abnormal loss of high-carbon and high-alloy steel, and slow heating ensures a balanced ingot temperature, reducing quality loss and increased energy consumption caused by rapid heating and high-temperature heating.

[0008] The thick ingot after heating is roughly treated and then rolled with a single-frame reciprocating mill without temperature control. The single-frame reciprocating mill has a high yield rate of steel produced and a strong ability to control the reduction rate. The rolling without temperature control and the large reduction in the first few passes improve the penetration of the rolling force into the core of the steel plate, balance the surface and core structures, and have a low overall manufacturing cost; the single-pass reduction rate of the first three passes of rolling is >15%-21%, and each pass is descaled with high-pressure water. The last pass of rolling is a leveling pass, and the total number of rolling passes does not exceed 9. The final rolling temperature is 900℃-1050℃, and the total length of the rolled steel plate is 45m-52m; the high-pressure water in the previous passes removes the surface oxide scale due to the high temperature adhesion of Cr, and also reduces the surface temperature, improves the surface quality and rolling penetration, and the last pass of leveling can improve the flatness of the steel plate and improve the yield rate.

[0009] The ultra-long steel plate is cooled by laminar dispersed water outlet. The temperature difference between the head and tail of the laminar flow is within 50℃. The upper cooling bed temperature of the steel plate is 700℃-780℃, and the lower cooling bed temperature is 330℃-390℃. The stacking of the steel plates off the line is neat at the head and tail. The steel plates are covered with insulation cotton or insulation felt at the head and tail to keep them warm, or other insulation and slow cooling measures are taken to slowly cool the steel plates to 150℃-200℃ before cutting them according to the specified length. Laminar cooling balances the temperature of the steel plates and reduces the amount of high-temperature iron oxide scale generated. The high-temperature stacking of the steel plates off the line is slowly cooled for self-annealing treatment to reduce internal stress. After the steel plate is cut, it is put into the heat treatment furnace for tempering within 24 hours. After tempering, the single ingot is rolled into 45m-52m steel plates, and the hardness difference of each sub-plate of the same specification is less than 2HRC; after tempering, the structure and hardness are further balanced.

[0010] The principle of the present invention is: a 150mm thick ingot is subjected to controlled rolling by a single-frame reciprocating rolling mill to obtain a steel plate with a length of 52m, and the process and technological measures such as large-pressure rolling without temperature control, laminar cooling, high-temperature steel plate stacking, stacking insulation and slow cooling, heat treatment and tempering treatment are used to achieve balanced cooling of the super-long steel plate, good plate shape and acceptable performance differences of the same plate.

[0011] The beneficial effects of the present invention are: The 150mm thick single-roll reciprocating rolling mill produces plastic mold steel plates with a length of up to 52m. It uses processes and technological measures such as large-pressure rolling without temperature control, laminar cooling, high-temperature steel plate stacking, insulation and slow cooling, heat treatment and tempering treatment to achieve balanced hardness of 150mm ingot super-long single-rolled steel plates, improve the production efficiency of plastic mold steel, reduce manufacturing costs, and at the same time, the products also meet the manufacturing and use requirements of users. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The composition and low multiple of the ingot in each embodiment of the present invention.

[0013] Figure 2 This is a process control data table for each embodiment of the present invention.

[0014] Figure 3 It is the Rockwell hardness of each sub-plate in the embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following is combined with Figure 1-3 The specific implementation modes of the present invention are further described in detail.

[0016] The present invention rolls 150mm ingot into steel plates with a length of 45m-52m on a single-roll reciprocating rolling mill, adopts uncontrolled high-pressure rolling, laminar cooling, high-temperature steel plate stacking, heat preservation and slow cooling, heat treatment and tempering treatment and other processes and process measures to produce plastic mold steel plates with a hardness of 29-33HRC, and lists the implemented processes and finished steel plate performance.

[0017] All technical and scientific terms used in this specification have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure belongs. In this specification, "Rockwell hardness (HRC)" is used as an indicator of the hardness value of steel. Rockwell hardness (HRC) is measured using GB / T 230.1-2018 "Rockwell hardness test for metallic materials Part 1: Experimental method". Example

[0018] The following three embodiments are used for comparative description. The steel plates of the three embodiments are prepared by the following steps: (1). According to Figure 1 The composition and low magnification shown are used to smelt the molten steel, refine it, vacuum treat it, and cast it into 150mm thick ingots on a slab continuous casting machine. The low magnification of the ingots is tested after it comes off the production line. (2) The billet is hot loaded into the heating furnace at a temperature of 300℃-600℃. After entering the furnace, it is slowly heated with a heating coefficient of 0.8-1.0min / mm in the furnace. The target temperature of the soaking section is 1200℃-1250℃. After rough descaling, the billet enters the single-stand reciprocating rolling mill with a rolling temperature of 1000℃-1100℃. The reduction rate of each of the first three rolling passes is >15%-21%, and high-pressure water is used for descaling in each pass. The last rolling pass is a leveling pass, and the total number of rolling passes is 5-9; the final rolling temperature is 900℃- 1050℃, the total length of the rolled steel plate is 45m-52m; the steel plate is cooled by laminar dispersed water, the temperature difference between the head and tail of the laminar flow is within 50℃, the upper cooling bed temperature of the steel plate is 700℃-780℃, and the lower cooling bed temperature is 330℃-390℃; the head and tail of the offline steel plate stack are neatly covered with insulation cotton or insulation felt for insulation, and slowly cooled for 18-30 hours until 150℃-200℃ cutting; heat treatment 550-620℃ tempering treatment, heating coefficient 2.5-4.5min / mm, Figure 2 To control the data of process technology; (3). Figure 3 Examples 1-3 are given to test the Rockwell hardness HRC of each sub-plate of the same specification cut from a single ingot rolled into 45m-52m steel plates.

[0019] The steel plates of the above-mentioned embodiments 1-3 have highly uniform cross-sectional hardness of each sub-plate in the length direction and each sub-plate in the thickness direction, and the products all meet the requirements of flaw detection and fully meet the production requirements of plastic mold steel plates.

Claims

1. A method for improving the uniformity of hardness of an ultra-long single-rolled pre-hardened plastic mold steel plate, characterized in that: It includes pouring thick ingots, rolling with a single-stand reciprocating mill, equalizing the temperature of steel plates with laminar cooling equipment, heat preservation and slow cooling of high-temperature steel plates, and heat treatment and tempering treatment, specifically: Step 1: Casting thick ingot: Cast 150mm thick ingot, macrosegregation does not exceed B1.0 level, porosity does not exceed 1.0 level, no internal or surface cracks, 150mm thick ingot surface is slowly heated in a heating furnace at 300℃-600℃, heating coefficient is 0.8-1.0min / mm, and soaking temperature is 1200℃-1250℃; Step 2, rolling with a single-stand reciprocating mill: the heated thick ingot is roughly treated and rolled with a single-stand reciprocating mill without temperature control, the first three passes have a single pass reduction rate of >15%-21%, each pass is descaled with high-pressure water, the last rolling pass is a leveling pass, the total number of rolling passes is 5-9, the final rolling temperature is 900℃-1050℃, the total length of the rolled steel plate is 45m-52m, and the thickness is 20mm-70mm; Step 3: Laminar cooling equipment balances the temperature of the steel plate: The ultra-long steel plate is cooled by laminar dispersed water when it leaves the rolling mill, and the temperature difference between the head and tail of the laminar flow is within 50°C; Step 4: Insulation and slow cooling of high-temperature steel plate stacking: The upper cooling bed temperature of the steel plate returns to 700℃-780℃, and the lower cooling bed temperature is 330℃-390℃. The head and tail of the offline steel plate are neatly stacked, and the head and tail of the steel plate are covered with insulation cotton or insulation felt for insulation, or other insulation and slow cooling measures are taken to slowly cool the steel plate to 150℃-200℃ before cutting it according to the specified length; Step 5: Heat treatment and tempering: After the steel plate is cut, it is put into the heat treatment furnace for tempering within 24 hours. After tempering, the single ingot is rolled into a 45m-52m steel plate. The hardness difference of each sub-plate of the same specification cut is less than 2HRC.

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