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I. Introduction to S355J2: S355J2 is a low-alloy high-strength steel. Its governing standard is the European standard EN10025; it can meet the inspection requirements of grades Z-15, Z-25, Z-35, as well as grades I, II, and III. The extended grades of S355J2 are S355J2, S355J2-Z35, and S355J2+N-Z35. S355J2-Z35 adds requirements for the properties in the thickness direction of the steel plate to those of S355J2, that is, the Z-direction properties. S355J2+N-Z35 is a heat treatment process that enhances Z-directional properties and involves normalizing rolling (or normalization). II. Chemical composition of S355J2: C: 0.15–0.18%, Si: 0.30–0.50%, Mn: 1.30–1.50%, P≤0.015%, S≤0.004%, Cr≤0.30%, Ni≤0.50%, Mo≤0.10%, Cu≤0.30%, V≤0.15%, Nb≤0.05%, Ti≤0.05%; the remainder is Fe and unavoidable impurities. Use a thickness of: 125-150mm. III. Analysis of the mechanical properties of S355J2: Yield strength Rp0.2 ≥ 275 MPa; tensile strength Rm: 450–600 MPa; elongation A ≥ 18%; impact energy at -20°C KV2 ≥ 47 J; reduction in area on the tension test specimen in the thickness direction Z ≥ 35%. The steel plates produced have excellent internal quality, high density, and stable properties. The meaning of S355J2-Z35: J2 specifies a shock test at -20 degrees, while Z35 refers to the Z-direction properties of the steel plate. The meaning of S355J2+N-Z35: J2 indicates a requirement for impact resistance at -20 degrees; N means that the steel has been rolled in a normalized condition, though normalization is not strictly necessary – it’s just a way of naming the steel grade according to standards. Z35 refers to the Z-direction mechanical properties of the steel plate. The meaning of S355k2+N: K2 requires a shock at -20 degrees, J2 also requires a shock at -20 degrees; N means it is equivalent to normalizing through rolling, but normalizing is not strictly necessary. IV. Production process of S355J2 steel plates The production method includes steelmaking, heating, rolling, and normalizing processes ； The steel rolling process employs shape-controlled rolling technology. In the steel rolling process, the starting temperature for rolling ingots is 1000–1050 ； In the first stage, a low-speed high-reduction rolling process is employed; the temperature during rolling is between 950 and 1000 degrees, the rolling speed is 1.6 to 2.0 m/s, the reduction per pass is 15 to 20%, and the cumulative reduction is 40 to 45%, all of which ensure sufficient deformation of the steel ingot. The starting rolling temperature in Stage 1 is 910–930, while the final rolling temperature is ≤870. 1. The steelmaking process involves a combined melting technique using an electric furnace and an LF furnace. During the VD vacuum treatment, the vacuum level is maintained at ≤66 Pa, with a vacuum retention time of 20–25 minutes; after the vacuum is released, the steel ingot is formed. 2. Heating process: The ingot is heated in a soaking furnace, with a maximum heating temperature of 1270°C and a temperature in the soaking zone of 1250–1260°C, to ensure uniform heating throughout the ingot. 3. Normalizing process: The steel plate is normalized in a bottom-type furnace. The normalizing temperature for the steel plate is 880–910°C, with a holding time of 1.8–2.2 minutes per mm, thereby yielding the desired S355J2+N-Z35 steel plate. 4. The product standard for S355J2 steel plates refers to EN10025-2 ； The standard for product performance testing methods refers to EN10025. V. Application areas of S355J2: S355J2 is a structural steel specified in European standards, and it is primarily used in the manufacturing of large machinery, as base frames for equipment, in large welded steel structures, in construction, and in bridge construction. With the continuous development of the economy and the increasing demand for larger-scale equipment, the need for ultra-thick structural steel plates is rising. The technical requirements for such steel plates are becoming more stringent, and their added value is relatively high; in particular, the production of ultra-thick steel plates presents considerable challenges. The production of ultra-thick steel plates is achieved by using ingots in the rolling process, which ensures a uniform grain distribution, eliminates defects such as pores and porosity within the steel plates, provides a good balance between strength and impact toughness, and yields better properties in the thickness direction, making it suitable for mass production.