On February 27, 2020, the data review, on-site review, type test, outsourcing test and type test report in the parts approved by the factory were all successfully completed, marking that Shougang Jingtang’s upgraded product, a plate of middling thickness, successfully passed the ship plate certification of eight countries. In so doing, Shougang Jingtang has further broadened its product market and given a major boost to Shougang’s brand in the vast ocean that is the international market.

Ship plate steel is one of Shougang Jingtang’s key expanded products in 2020. The expansion certification of specifications and delivery status involved eight classification societies. The certification level was extended to EH36 high-strength ship plate. The certification thickness was expanded from 50 to 100 mm, and the delivery status covered TMCP and normalizing, of which the specification certification of 60 to 100 mm in TMCP status was the ever first certification for the plate, so there was no previous certification experience from which to learn. It is more difficult to certificate brand-new products because these processes are more complex.

In the face of these challenges, the Manufacturing Department at Shougang Jingtang actively approached the classification societies of various countries to optimize and integrate the certification experimental projects of various countries, and conducted welding and CTOD experiments with 725 institutes in Luoyang for follow up processes such as sampling and processing in real-time, to ensuring the data’s authenticity and accuracy. Ma Guojin, a professional technician in the Plate Room of the Manufacturing Department, read thousands of pages of English ship’s classification rules of various classification societies, integrated 90% of experimental projects of eight countries’ classification societies, merged and summarized 10% of the special clauses, and prepared 1,528 pages of Chinese and English testing guidelines for ship plate certification. It was finally approved by experts from various classification societies at once.

Working together to overcome difficulties and optimize process design. According to the rules of the various classification societies, the yield strength should not have the effect of weakening the thickness, and with a premise being to guarantee the strength, the core position is required to have good aging impact performance. The aging impact performance test of the core sample of 100 mm steel plate at minus 40 °C must be qualified, and the minus 80 °C low temperature impact test must also be conducted. In the first round of trial production of 100 mm steel plate, the problem of low temperature impact toughness conflicting with aging performance was found.

He Yuanchun, the engineer in charge of the technical center took the lead in setting up a group to jointly overcoming these difficulties. With years of technical experience, through metallographic analysis, the group proposed a two-pronged set of solutions for performance optimization. On the one hand, the toughness structure can be improved by reducing the carbon content and optimizing the alloy composition. On the other hand, the controlled rolling and controlled cooling technologies can be used to match the strength with toughness by refining the grain crystal and optimizing the organization structure. After the second round of steel plate testing, the core’s strength and toughness had been significantly improved, demonstrating the advantages of technical support and on-site collaboration. The trial steel plate met the certification requirements.

Careful arrangements ensured accurate implementation. After taking on this task, the Steel Rolling Operation Department and the Plate Business Department immediately established a working group for ship plate certification, held many special meetings to assign work, and made careful arrangements for the various related issues. They also made an on-site work plan and assigned a designated person to take charge of each link.

Xie Cuihong and Pang Lipeng from the Production Technology Room of the Steel Rolling Operation Department conducted an investigation, which they combined with the actual situation to compile production organization plans and smelting operation points, and organized targeted training for the management and operation personnel of each post. Beginning on December 10, 2019 when ship plate series of steel smelted began, the operation head of each operation area remained on duty for 24 hours, tracked and constantly monitored the KR desulfurization, converter smelting, refining treatment, casting machine casting and other posts’ process coordination and operation conditions. Through the joint efforts of the employees of this department, a total of 12 furnaces of ship plate series of steel were smelted. All their components were qualified, and the quality of the casting billets met the rolling needs.

Xu Zangwen and Li Bo of the Production Technology Room of the Plate Business Department quantified the management of work including the billet entry, rolling, water cooling, stack cooling, flaw detection, heat treatment and line sampling according to the experts’ on-site review time, confirmed the time node and explained technological difficulties to the relevant staff and the person in charge of the relevant operation area ahead of time, so as to closely coordinate various processes. At 10:00 a.m. on December 17, 2019, the first E-class certified ship plate of 40 mm thickness was tapped on time. There were a total of 8 steel plates for trial rolling. Experts from the classification societies checked the first-level and second-level operation interfaces of heating, rolling, and water cooling on site, and were impressed by the precise technological control. The experts supervised and checked processes including the certified steel plate’s flaw detection, sampling and lineation and heat treatment, and the operators standardized the operation, precisely controlled, and completed all the on-site work within the specified time node. This too was praised by experts from the classification societies.

In order to ensure that the on-site certification was carried out smoothly, the Quality Inspection and Supervision Department had lost no time in making a special certification plan to ensure the progress of the ship plate certification. Zhu Qimao, the chief operation head of the Steel Rolling Analysis Center, integrated equipment resources and human resources, and transferred 4 key workers from the Phase 1 Steel Rolling Analysis Center to cooperate with the certification test. Due to the low carbon content of the certified E-class high-strength ship plates, he encountered difficulties in the corrosion of TMCP welding impact fusion line sample. Therefore, the Quality Inspection and Supervision Department had set up a research group on low carbon austenite grain size. In order to get a satisfactory experimental result, Sun Jing, a technician of the Quality Inspection and Supervision Department, carried out careful consultations and even voluntarily gave up her vacation time to make multiple sets of testing plans and repeatedly conducted austenite grain size testing over three consecutive weeks. After hundreds of tests, she was able to summarize accurate data relating to the heat treatment temperature and oxygenation time. She learnt that the complete austenite area can be obtained when an oxide layer of slightly ground samples is retained and a 15% hydrochloric acid etching solution is used. This provided reliable data support for the ship plate certification.

An NDT drop-weight welding test was required to verify the sample’s performance during the certification process. In the past, this work had been assigned to relevant research institutes, but the processing cost had reached as much as 300,000 yuan. The Sample Processing Center of Shougang Qinhuangdao Machinery quickly summoned 7 key workers with welding experience, including Yu Huizhi, to establish a welding research group. In order to master welding skills better and faster, they invited members of Shougang Liu Hong Studio to carry out unified training. The drop-weight welding testing technology was difficult and demanding, and some samples were only a little thicker than an individual hair. They studied and trained hard. Practice makes perfect. Carefully guided by professional teachers, the research group’s members quickly mastered welding skills, successfully processed 128 standard samples in only 45 days, and completed the welding of the drop-weight test independently. This laid the groundwork for the follow-up certification and experiments without outsourcing.

The successful completion of the certification process marks a new level for the production capacity and management of Jingtang’s wide and thick plates, opening a wider channel for Shougang’s ship plate products to expand its international market.