As a well-known domestic shipbuilding enterprise, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. has long been committed to the construction and technological breakthrough of high value-added vessels. In recent years, with the increasing demands for larger and lighter ships, our company has accumulated rich experience in the application of high-strength marine steel and has developed a mature technological system.
High-strength steel features high yield strength, good toughness, and excellent weldability. In the construction of large bulk carriers, oil tankers and offshore engineering vessels, we widely adopt high-strength steel grades such as EH36 and EH40. Compared with conventional marine steel, high-strength steel can reduce hull structural weight by more than 20%, significantly lowering the ship's lightship weight at the same deadweight tonnage, thereby improving fuel economy and cargo carrying capacity.
However, the application of high-strength steel places higher demands on welding processes. Our technical team, targeting the hardenability tendency and hydrogen‑induced cracking sensitivity of high-strength steel, has formulated strict welding procedure specifications. Before welding, preheating measures are strictly implemented, with preheating temperature controlled between 80°C and 120°C and precisely adjusted according to plate thickness and carbon equivalent. Low‑hydrogen electrodes or flux‑cored wires are selected as welding consumables; they are dried at specified temperatures before use and stored in dedicated holding ovens. During welding, heat input is strictly controlled, and multi‑pass, multi‑layer welding processes are adopted to avoid grain coarsening in the heat‑affected zone. After welding, slow cooling is carried out in time, and hydrogen‑removal heat treatment is applied when necessary.
In the construction of a 48,000 DWT bulk carrier, our company applied EH36 high-strength steel on a large scale for the first time to build the longitudinal girders in the cargo hold area and the side shell framing. By optimising the welding sequence and adopting a double‑sided continuous fillet welding process, welding distortion was effectively controlled. At the same time, we introduced ultrasonic phased array inspection technology to perform 100% non‑destructive testing on high-strength steel welds, ensuring that every weld met quality requirements. After completion, the hull structural weight was reduced by about 450 tonnes compared with traditional designs, and the lightship weight index reached an advanced level among sister vessels.
In addition, our company attaches great importance to the cutting accuracy of high-strength steel. We have introduced high‑precision plasma cutting machines and fibre laser cutting machines, together with a CNC nesting system, to achieve precision cutting of high-strength steel plates. The cut edge quality is excellent, the heat‑affected zone is narrow, and subsequent grinding work is significantly reduced.
In the future, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. will continue to deepen its application technology of high-strength steel, integrating digital welding management systems and robotic automatic welding equipment to further improve construction quality and efficiency, providing shipowners with lighter, stronger, and more economical high-quality vessels.