Development of Technology for Microstructure Control during On-line Heat Treatment Process for Hot-rolled Seamless Steel Pipe

In the conventional manufacturing process for the hot-rolled seamless steel pipe, the pipe as rolled was air-cooled down to the ambient temperature. And due to absence of proper on-line microstructure control of the pipe, properties had to be controlled depending on addition of much more alloy elements, and the subsequent heat treatment process. Described here in the paper were the progresses of development and application of the controlledcooling technique for the hot-rolled seamless steel pipe, and the applications of improvement and control of Histomorphology, microstructure refining and cooling route control. As for the currently-used microstructure control during the manufacturing process of hot-rolled seamless steel pipe， emphases of further research were proposed, focusing on the improvement of cast billet quality and fine grain homogenization. The new technological system of microstructure control for the whole manufacturing process was expected to be set up by means of taking the controlledcooling technique as the key, optimizing chemical composition, and comprehensively using the strengthening mechanism. Then the potential of the materials can be further tapped， and finally the overall improvement of product quality and reduction manufacture for the hot-rolled seamless steel pipe can be achieved.

Since the application of the hot-rolled seamless steel pipe to control the cooling process technology, the effect is remarkable: the temperature control precision after cooling is high, the cooling is uniform, and the steel pipe shape is good after cooling; effectively solving the low-rolling performance of the medium-thickness structural pipe, and relies on offline heat treatment The problem is to realize the process reduction production; the direct quenching function is used to realize the online organization control and direct quenching of related products, which provides an effective means for shortening the process flow and further developing high-performance, high value-added hot-rolled seamless steel pipe products. The successful development of this technology provides hot-rolled seamless steel tubes with component-saving and process reduction, as well as steel pipe products with higher quality requirements. It provides key technical means and production support in the development of organizational performance control and efficient production process. It is of great significance to realize the short-process green manufacturing process of hot-rolled seamless steel pipe in China.

In the traditional production process, the steel pipe is cooled to room temperature by air cooling after rolling deformation, and the coarsening of the crystal grains cannot be suppressed due to the lower cooling rate during the cooling process, so that it is easy to generate individual coarse structures in the tissue, resulting in the tissue. Uneven, deteriorating performance. After the post-rolling controlled cooling process, the higher cooling rate inhibits the abnormal coarseness of the structure, and finally the steel pipe structure is significantly thinner than the original air-cooling process, and the uniformity of the structure is significantly improved.

Based on the successful development of the control technology of circular section, the technology breakthrough and application of industrialized control cooling equipment in the field of hot-rolled seamless steel pipe has been realized, and effective technical means have been provided in the online regulation of product organization performance.