Development of Roll Quenching Machine for High-strength Carbon Medium and Heavy Plates
1 Project background
In order to improve the grade of medium and heavy plate products and the production capacity of heat treatment products, enrich the means of developing and producing new varieties of steel, broaden the types of medium and heavy plate products, meet the development needs of a series of high-grade carbon steel medium and heavy plate new products, and improve the new steel Core competitiveness. As the core equipment of Xingang’s new heat treatment line, the roller hardening machine for medium and heavy plates plays a key role in success or failure.
In fact, many domestic steel companies still insisted on the concept of introduction when the Xinsteel Corporation made the project decision. The reason was that there were still some concerns about the domestic independent intellectual property rights of the roller quencher equipment: Lingang 3200mm roller quencher mainly For the production of stainless steel plates, whether the domestic quenching equipment will be at risk for the carbon steel quenching process.
After careful inspection, it is believed that the domestic scientific research and technical strength in the quenching and cooling technology and process development of medium and thick plates is strong. Possess development capabilities. To this end, based on the domestic, independently integrated the first domestic modern heat treatment quenching line of 3800mm medium and heavy plates.
2 Technical parameters and main features
The effective quenching width of the roller quenching machine is 3800mm, and the length is about 25500mm. It is composed of a detection roller table, fixed frame, moving upper frame, conveying roller table, lifting mechanism, water spray cooling system, and rear purge device. The quenching cooling zone of the quenching machine consists of a high-pressure quenching zone and a low-pressure quenching zone. It is equipped with a quenching nozzle system with my country’s independent intellectual property rights and a first- and second-level quenching process automation system.
The quenching mode parameters can be selected according to the steel type and specifications to realize the automatic control of the process parameters such as roll gap, water volume, roll speed, and the quenching and cooling process. In addition, in order to meet the needs of Xingang’s thick plate products (thick plate length specifications up to 18000mm), the length of the low-pressure quenching zone designed for the roller quenching machine is about 20,000mm, with 4 quenching cooling sections, which is the current domestic
The roller quenching machine with the longest quenching zone can meet the quenching production needs of wide and thick plate products with a thickness of 6mm~100mm (maximum 120mm), a width of 1500mm~3600mm, and a length of 3000mm~18000mm.
2.1 Cooling technology for uniformity of thin-gauge and wide-width steel plates The shape control of the quenching process of medium-thick plates is a very important issue in the practical application of the quenching process of the roller quenching machine.
The shape of the plate after quenching is a direct manifestation of the uniformity of the cooling of the steel plate during the quenching process, and it is also a macroscopic manifestation of the comprehensive effect of the internal stress of the steel plate during the quenching process. Especially for extremely thin quenched steel plates, its sensitivity to quenching process parameters is extremely high, so it is extremely important to ensure the rationality and stability of each process parameter.
The hardness of the martensite layer after quenching of the steel plate is very high, which greatly increases the yield strength of the steel plate. If the plate shape after quenching is too poor, it is difficult to correct it. And the wider the width of the steel plate, the thinner the thickness, the more difficult it is to control the cooling uniformity in the width direction, and the more difficult it is to control the shape of the quenching process.
The higher the requirements for the cooling uniformity of quenching equipment, especially the uniformity of flow distribution in the width direction of the quenching water spray system and the control means of the width of the cooling uniformity, are key technical issues that must be fully considered in the design process.
Therefore, the domestically developed slit nozzle is adopted, and the flow zone control technology in the width direction of the steel plate is applied. That is, through effective control of the flow distribution of the quenching system. Through the high-precision and stable control technology of the cooling rate of the upper and lower surfaces, the width-wise temperature uniformity control of the extremely thin quenched steel plate is realized. 2.2 Hardened layer depth of thick steel plate after quenching.
For thick plates, the key to the quenching process is to ensure that a reasonable plate hardened layer depth is obtained. The depth of the hardened layer of the plate quenching depends on the hardenability of the steel, the cross-sectional size, the cooling characteristics of the quenching medium, and the cooling capacity of the quenching equipment.
Hardenability is a property of steel. On the premise that the quenching medium is determined, the cooling capacity of the quenching equipment is an important external condition for the quenching of the steel plate, which is reflected in the cooling rate of the quenching process of the steel plate.
The quenching process consists of the heat exchange process between the quenching medium and the surface of the quenched steel plate and the heat transfer process from the inside of the steel to the surface. The former is the process in which the quenching medium takes away heat from the surface of the steel plate and the heat diffuses outward in the medium; the latter is the process in which heat diffuses from the inside of the steel plate to the surface.
For this reason, based on the theoretical calculation of the temperature field and previous work experience, key process design parameters such as reasonable water volume parameters and roller drive motor speed are proposed.
3 Production of high-strength carbon steel quenched and tempered plate
The equipment started the first phase of the quenching process debugging in February 2009. As of April 2009, the quenching process has been debugged on steel plates with multiple specifications of 12mm to 50mm, such as 07MnNiMoVDR, XGQ690E, XGCF62, etc. During the development and debugging of the quenching process of Xingang’s high-grade quenched and tempered plates such as wear-resistant steel series, high-strength structural steel series, and pressure vessel steel, the roller quenching machine quenching process suitable for the characteristics of new steel products was successfully developed.
After quenching, the measured sheet properties (including surface and thickness direction hardness and uniformity) and flatness, and other indicators have reached or exceeded the national standard and the physical level produced by similar imported equipment.
In particular, it is necessary to point out that the successful development of the roller quenching machine project is the quenching process for thin sheets with a thickness of 6mm~10mm, which has important symbolic significance both at home and abroad. The reason lies in the quenching process of low-alloy high-strength steel sheets with a thickness of 6mm~10mm. Due to the thin thickness of the plate, the plate has extremely high requirements on the uniformity of quenching and cooling during the quenching process.
The plate shape control of the quenching process is very difficult. It belongs to the ultimate process technology of plate quenching production. It has extremely high process difficulty and is a recognized key technical problem in the heat treatment production process of low-alloy high-strength thin plates. According to the investigation, similar imported equipment equipped by domestic enterprises can actually only achieve the production of specifications above 12mm thickness.
Due to the difficult quenching process of thin-gauge low-alloy high-strength steel sheet products, the supply price of high-strength thin-gauge sheet products is very high. At present, only one or two foreign manufacturers such as Sweden can achieve continuous and stable production and supply in the world.
They are in a monopoly position and have considerable market prospects. The quenching process of thin-gauge wear-resistant steel sheet products developed by Xingang Company has a good shape after quenching, and can smoothly achieve continuous and stable production of the quenching process for low-alloy high-strength steel sheets with a thickness of 6mm~10mm.
After quenching, the measured properties of the plate (including surface and thickness direction hardness and uniformity) and flatness are all up to or better than the national standard and the physical level of similar imported products, and it has high market competitiveness at home and abroad. It provides key technological support for enterprises to meet the serialized supply requirements of low-alloy high-strength steel sheet product specifications, and at the same time lays a solid equipment foundation for the development of high-grade serialized heat treatment products of Xingang Company.
4 Main innovations
During the implementation of the 3800mm roller quenching machine project, we achieved the following domestic bests of similar equipment projects:
(1) Realizing the continuous and stable production of the domestic thinnest (6mm thick) low-alloy high-strength steel sheet quenching process. The quenching process of low-alloy high-strength steel sheets is the ultimate process technology of sheet quenching, and similar imported equipment actually only achieves the production of specifications above 12mm thickness. For the quenching process of 6mm~10mm thickness plates, due to the thin plate thickness, it is difficult to control the plate shape during the quenching process.
The plate shape control after quenching is recognized as a key technical problem. Xingang’s 3800mm roller quenching machine successfully realized the continuous and stable production of the quenching process of low-alloy high-strength steel plates with a thickness of 6mm~10mm. Major technological breakthroughs have significant engineering demonstration significance.
(2) The quenching process debugging cycle is the shortest. From the completion of the equipment installation to the completion of the quenching process commissioning and commissioning of high-grade sheet products such as pressure vessels, low-alloy wear-resistant steel, and high-strength structural steel series, the actual effective commissioning time is only about 45 days.
(3) The amount of plates used for quenching process debugging is the least. After the equipment is installed, the quenching process debugging of high-grade carbon steel plates such as the new steel pressure vessel, low-alloy wear-resistant steel, and high-strength structural steel series will be completed. For the specifications above 16mm thickness, 1 to 2 commissioning boards are used to complete the quenching process debugging; although the quenching process for thin gauges below 16mm thickness is very difficult, on average only 6 to 8 commissioning boards are required to complete the quenching process commissioning. After quenching The plate shape is good.
(4) The project has the shortest implementation cycle and the fastest effect. According to the implementation cycle of similar domestic projects, imported equipment from abroad usually requires an 18-month cycle. However, it took less than 11 months for this project from contract signing to heat load test run and trial production, and the first batch of contract board products was delivered, setting a record for the fastest production of similar equipment in China. Under the severe economic situation of iron and steel enterprises, it has created economic benefits for enterprises as soon as possible, which is invaluable.
In fact, the biggest significance of the 3800mm roller quenching machine project of the thick plate heat treatment project is to completely eliminate domestic steel companies’ doubts about domestic roller quenching equipment and to contribute to the promotion and application of major domestic key process equipment. A demonstration project for the construction of a high-level modern heat treatment line for medium and heavy plates.
At present, the equipment and process debugging of the 3800mm roller quenching machine for the heat treatment project of Xingang’s thick plate have been successfully completed. The official delivery of the new steel to production and use indicates that the level of my country’s wide and heavy plate heat treatment and quenching process equipment has reached a new stage.
This shows that my country’s wide and heavy plate heat treatment line quenching machine equipment development capacity and quenching process technology development level has reached the international advanced level, laying a solid foundation for domestic steel companies to achieve high-grade, high-value-added medium and heavy plate production with lower equipment costs.
(Source: Heat Treatment)