In early 2022, a fleet of heavy trucks loaded with 9Ni steel plates departed from the Shougang Jingtang Company to a downstream customer's construction site in Nantong, Jiangsu Province...

This historic moment meant that Shougang had filled the gap in the domestic market for 9Ni steel for extremely low-temperature vessels, and taken a key step into the market of high-end moderately thick plate products.

Fruits grown from a decade of accumulated strength

In the 21st century, the energy structure is changing, and natural gas, recognized as the cleanest fossil energy, has entered the golden age of rapid development. After being compressed and cooled to its freezing point (-161.5°C), natural gas is converted into liquefied natural gas (LNG) which is easy to store and transport, with high safety and less indirect investment. Accordingly, there is a surge in demand for cryogenic steel throughout the entire LNG industry chain, including such links as production, storage, transportation and application. 9Ni steel is favored for its high strength, excellent ultra-low temperature toughness and good weldability.

9Ni steel is known as the "diamond of steel" in the field of moderately thick plate products. It is widely used in the construction of cryogenic vessels for LNG storage, transportation and application due to its high nickel alloy content of up to 9% and its good toughness and high strength even at extremely low temperatures of -196°C. Due to the particularity of the service environment, in order to ensure good application performance and reliable safety at extremely low temperatures, impurities such as phosphorus, sulfur, nitrogen, hydrogen and oxygen in molten steel should be strictly controlled, so 9Ni is recognized by the iron and steel industry as the most difficult product to produce, as well as the most high-tech product in the field of moderately thick plate products.

As early as 2009, based on the nickel cryogenic steel project, Shougang officially started the R&D of 9Ni steel. At the beginning of the localization of 9Ni steel, the research group relied on its own strength to uncover the mystery of 9Ni steel step by step, and mastered the core production technology of 9Ni steel through a large number of laboratory studies and field simulation tests covering composition design, organizational morphology, strengthening-toughening mechanisms and industrial production technology. In 2014, Shougang carried out the industrial trial production of 9Ni steel on the Shouqin Company's 4,300 mm production line, and the technical review of the China Standardization Committee on Boilers and Pressure Vessels was passed, making Shouqin one of the few steel mills with 9Ni steel supply qualifications in China at that time. Soon after, according to the unified deployment of the Group, Shouqin began relocation preparations: the moderately thick plate production line was moved from Qinhuangdao to Caofeidian, and the market promotion of Shougang 9Ni steel products was suspended.

Adhering to the concept of "taking a market demand-oriented and user demand-driven approach", during the "dormant" period, the research group took the initiative to establish smooth communication channels with downstream users and accurately grasp the development direction of steel for cryogenic vessels. By conducting in-depth research, accumulating strength, constantly optimizing product performance and improving consumer application technology, the research group made full preparations for product promotion.

With the proposal of China's "Dual Carbon" Goals, the demand for LNG surged and the domestic 9Ni steel market continued to improve. All was ready except the right timing! Relying on its accumulated strength, Shougang Jingtang seized the opportunity to resolutely start the development of 9Ni steel for cryogenic containers.

The Institute of Wide and Thick Plates of the Shougang Research Institute of Technology pooled its superior forces and sent them to the production site. Chai Yuguo, the leader of the research group, led an R&D team to formulate whole-process technical solutions that covered steelmaking, rolling, heat treatment and other processes according to the key points and difficulties of 9Ni steel production on the basis of the preliminary technical reserves and changes in the tooling conditions of Jingtang's moderately thick plate production line in the second phase. Clear guidance was formed for the precise control of molten steel composition, internal and external quality control of steel billets, comprehensive performance control of steel plates, surface quality control, storage and transportation, anti-magnetization, quality inspection and other critical control points, thereby providing strong technical support for the industrial trial production of 9Ni steel.

New achievements after relocation

Due to the particularity of the service environment, the content of phosphorus, sulfur and other impurity elements has to be strictly controlled for 9Ni steel, and the content of nickel alloy must be as high as 9%. Under the interaction of multiple factors, 9Ni steel smelting is much more difficult than conventional converter smelting.

After receiving the task of 9Ni steel smelting, the Steel Rolling Department acted quickly to refine the technical solutions of each process. Technical professionals and post operators were organized to tackle key problems in critical control points such as extremely low phosphorus and low sulfur smelting of molten steel, process temperature control and slab continuous casting. The night before smelting, the Steel Rolling Department held a final preparation meeting before production, emphasized every detail from production organization and raw material preparation to operation key points and precautions, and defined the responsibilities of each post and person to make sure nothing was wrong. "9Ni steel represents the highest level of plate products. It's our honor to produce such high-end steel," said Hu Xiantang, Deputy Head of the Steel Rolling Department, in a sonorous voice, striking a strong chord with the participants. 

On the day of formal smelting, from steelmaking to refining to slab continuous casting, along with the running track of molten steel, the production personnel performed their respective duties and paid close attention to changes in the molten steel temperature, composition and other process parameters to ensure smooth smelting. Through careful operation and reasonable control, the production personnel gave full play to the capacity of the equipment. Next to the steelmaking platform, Wang Dong, a model worker of Shougang and technical expert of the Jingtang Company with 30 years of experience in steelmaking, attentively watched the slagging of the converter, his face flushed by the flashing fire. From time to time, he used the intercom to remind an assistant to adjust the operation: "Five hundred ore, lower the lance..." Thanks to meticulous preparations and solid technical skills, the whole smelting process was carried out in an orderly and controlled manner. At the moment when the tundish car drove out slowly and the crystallizer was capped, Department Head Wang Guolian breathed a sigh of relief, overwhelmed with joy. 

During the continuous casting process in seven furnaces, the average phosphorus content was 10.2 ppm, the average sulfur content was 4.7 ppm and the total amount of nitrogen, hydrogen, oxygen, phosphorus and sulfur was less than 50 ppm!

Astonishing parallels can often be found in history. The three converters in the second phase of the Jingtang Company were the backbone of Shougang, producing ten million tons of steel annually in a brave and pioneering way. Once responsible for Shougang's glory, they have been relocated from the former Shougang No. 2 Steelmaking Plant to Caofeidian hundreds of kilometers away to protect the capital's environment. They embody the ardent hopes of the older generation of steelmakers. From the mountains to the seaside, from increasing output to creating high-end products, they have made new achievements in the process of developing 9Ni steel against the backdrop of fast-changing times! This scene is the true portrayal of Shougang responding to the call of the state, taking the overall situation into consideration and conforming to the trend of the times.

A high-end variety made with superior craftsmanship

"Jingtang's Moderately Thick Plate Business Division adheres to the production of high-end varieties represented by 9Ni to seize the market with high-end and efficient products, and achieve high efficiency. Relying on technical support and driven by innovation, we will accelerate the promotion of green manufacturing to help the low-carbon and high-efficiency development of the industry", said Tian Shiping, Head of the Moderately Thick Plate Business Division. 

9Ni steel has a long production process and involves more processes than ordinary quenched and tempered steel, such as billet blooming, billet grinding, painting and remanence control. Meanwhile, with a large proportion of ultimate thin gauges, it has the highest manufacturing capacity requirements among all moderately thick plate products. Zhang Xuefeng, Chief Engineer of the Moderately Thick Plate Business Division, proposed, "We must take 9Ni steel production as an opportunity to quickly improve our ability in process planning, channel line control and process control in the whole process of steel rolling, develop a production process suitable for our production line and finally improve its manufacturing capacity".

To ensure smooth delivery according to the contract, the Moderately Thick Plate Business Division set up a special research team along with the Manufacturing Department, Technology Center, Steel Rolling Operation Department, Quality Inspection Department, Sales Management Department and other departments and specialties, and formulated special technical solutions based on the characteristics of 9Ni steel, such as its long production process and large proportion of ultimate thin gauges.

High-quality products require the control of every process and a standard, efficient and collaborative manufacturing system. For each steel billet and plate, a detailed tracking ledger was established to master the production information of the whole process. Led by SPC, the control of key product characteristics was strengthened; accurate control was achieved through process parameters; and the stability of temperature control, size control and other indicators was ensured. In the billet cleaning process, professionals checked the surface quality piece by piece, and guided the billet operation on site. For the rolling process, production planning and scheduling were optimized, and scale removal and thickness accuracy control were strengthened. The heat treatment process was equipped with special tooling, a separate steel plate movement path was developed and a separate palletizing site was created. Through continuous optimization, refinement and solidification, the operation key points of the whole production process of 9Ni steel with Shougang characteristics were finally formed.

For 9Ni steel, remanence is a unique inspection indicator related to the normal use of steel plates. The research team measured the production line environment and equipment remanence, recorded nearly 1,000 data entries, formulated the production logistics plan of 9Ni steel control remanence, provided special tools and made full preparations for production. In the heat treatment process, every time a steel plate moved to a new link, professionals measured its remanence change in detail and determined the control points. Finally, the remanence of 9Ni steel was 100% qualified. In order to ensure on-time delivery according to the contract, an innovation were made to the production organization mode: 9Ni steel production was realized in two furnaces at the same time, thereby doubling the production capacity.

8 mm has been the minimum thickness of quenched plates since heat treatment came into operation. Before formal production, 8 mm wear-resistant steel was used to explore the related water-cooling parameters, and the plate was in good shape. However, in formal production, since the composition of 9Ni steel is different from that of wear-resistant steel, and the steel plates vary in strength, edge waves appeared in the plates after quenching, so all the parameters of the quenching machine were adjusted and measured in the heat treatment operation area. Wang Kun, a professional engineer in the production technology room, optimized the water quantity of the quenching machine and the roll gap during quenching, which effectively ensured the smooth quenching and production of 8 mm 9Ni steel.

Finally, the mechanical properties, surface quality, remanence and other indicators of the steel plates fully met the customer's requirements. Shougang Jingtang achieved the batch supply of 9Ni steel, a new variety added to Shougang Jingtang's high-end moderately thick plate product portfolio!

"Only by constantly developing high-end products can we promote the self-upgrading of our production line to manufacture high-quality products in pursuit of perfection. In the future, we will strive to make breakthroughs in more fields and constantly improve the core competitiveness of Jingtang's moderately thick plates," said Yan Zhiping, a technical expert at Shougang, confident about the prospects of developing the market for Jingtang's moderately thick plates. 

Formidable strength from concerted efforts

At the start of the project, Zhou Deguang, a first-class scientist at Shougang, personally took charge of coordinating, organizing and formulating a promotion plan integrating trial production, certification and supply, arranged the schedule backwards and clarified the nodes and post responsibilities. A joint working group composed of Jingtang's Manufacturing Department, Technology Center, Steel Rolling Department, Moderately Thick Plate Business Division, Quality Supervision Department and Sales Management Department, with all members performing their own duties, keeping pace with each other and cooperating efficiently, solved a series of difficult problems in a short time, such as extremely low phosphorus smelting in converters, quality control of continuously cast billets, steel plate surface quality control, thin gauge plate shape, steel plate remanence control and accurate shipment. This paved the way for the mass production of 9Ni steel.

9Ni steel needs to experience a long cycle from trial production to classification society certification, and then to mass production and supply. Yu Wenfei, as a 9Ni steel variety specialist in the thick plate room of the Manufacturing Department, was responsible for designing the billet shape, scheduling production, organizing certification and receiving classification society inspection. At every link, he was busy working.

Compared with general steel, the most important feature of 9Ni steel is that it is "cold". The impact toughness and drop hammer tests are carried out at -196°C, and the performance testing is very complex. Before each performance test, Zhao Defu of the Quality Supervision Department communicated with multiple departments to contact liquid nitrogen suppliers. During the tests, whether in winter or summer, tester Zhou Yongjiang wore thick leather pants and sat next to the air-conditioned testing machine for one or two hours, silently completing the last quality checks amid the heavy poundings of metal.

It takes a lot of hard work to wash out the sand and find the glittering gold. After a complex production process, stacks of finished steel plates were neatly placed, ready for shipment. Zhou Jian and others from the Sales Management Department specially formulated a shipment organization plan. They meticulosity organized and implemented every step, from arranging vehicles, laying sleepers under vehicles, on-site loading and tarpaulin covering to dynamic tracking along the way and on-site unloading. This ensured that the achievements of countless people's hard work could be delivered to the user's construction site intact, displaying the image of Shougang as large modern iron and steel enterprise.

Marketing is an important link of bringing products to market. The Beijing Shougang Marketing Center attached great importance to 9Ni steel after its successful development. The Guangzhou Branch, Shanghai Branch, Tianjin Branch and Shandong Branch each showed their strength, actively contacted downstream users and received inquiries in a continuous stream.

Thanks to these diligent workers who have devoted themselves to intense and orderly work with great enthusiasm in their ordinary posts, and acted as paving stones on the road to promoting Shougang's cryogenic steel, the first industrial trial production of Shougang 9Ni steel has been successful, and the finished products have excellent quality. The 9Ni steel has passed the certification of classification societies in China, the United States, Norway, the United Kingdom, Japan and other countries, and achieved a continuous supply.

A long journey can be covered only by taking one step at a time, rivers and seas are formed by the confluence of small streams. Shougang's progress in the development of 9Ni steel marks a good start in the Group entering the cryogenic steel market. In its development of cryogenic steel, Shougang has always adhered to the goal of continuously improving the product quality, expanding the application scope and providing users with all-round technical services.