Problems in the development of heat-resistant steel materials in china

Compared with industrialized countries, problems in the development of heat-resistant steel materials in China
(1) The cleanliness and uniformity of steel materials need to be greatly improved. Impurities and inclusions in steel materials do great harm to its plasticity, fatigue fracture performance and surface quality, while the inhomogeneous distribution of impurities, inclusions and two-phase and even matrix structures in steel seriously affects the homogeneity and isotropy of steel properties. Therefore, it is very important to significantly reduce the content of impurity elements in steel, strictly control the size of inclusions, control and improve the shape and distribution of inclusions and large particle carbides or desalted substances, and improve and improve the homogeneity of microstructure in steel to improve the properties of steel materials. At present, the national iron and steel production enterprises have put forward quite strict requirements for steel impurities. The total content of O, H, N, S, P, H is required to be no more than 100ppm, and the level is even controlled to 50ppm. For steels that need higher cold workability and higher surface quality, strict requirements are also put forward for carbon content in steel. For high strength or ultra-high strength steels whose fatigue life is required to be greater than the 7th power of 10, it is required to control the size of inclusions and carbides in the steel to be no greater than 4um

(2) The proportion of long steel sections and flat steel materials needs to be adjusted. The current consumption of iron and steel materials in China is construction steel, accounting for about 50% of the total consumption of steel, while the construction steel is mainly long sections with bars and wires. In addition, the production technology of long sections is simpler than that of flat sections. As a result, the production capacity of iron and steel enterprises in China for long sections continues to increase while the production capacity of flat sections is relatively insufficient. At present, the imported steel in China is mainly flat materials. However, with the development of the national economy, especially the implementation of the strategy of building a world manufacturing power, machinery, automobiles, ships, household appliances, transportation and other industries will gradually become the industries with fast growth in steel consumption (automobile manufacturing industry is the main user of steel materials in industrial developed countries), and the demand for high-quality flat materials will increase rapidly. Therefore, it is necessary to reasonably adjust the production proportion of long sections and flat sections of iron and steel materials in China. In this process, it is necessary to deeply study and solve the special technical problems in the production of flat materials, such as the control of surface quality, the guarantee of transverse performance, and the isotropy of super thick plates and large size modules.
(3) The proportion of alloy steel needs to be increased. The reasonable addition of alloy elements has a significant impact on the properties of steel materials. However, due to the production pattern dominated by construction steel and the resource constraints of some alloy elements, the proportion of alloy steel in the production of steel materials in China is significantly lower than that in the industrial developed countries. For example, the proportion of microalloyed steel in the industrial developed countries has reached about 15% while that in China is only 3%~5%, As a result, many high performance and high quality steel products cannot be produced (for example, X80~X100 steel products have been produced and used in industrial developed countries, while X65~X70 is still the mainstream product in China). Therefore, it is very important to appropriately increase the production proportion of alloy steel in China. In view of resource constraints, we can first consider increasing the production proportion of microalloyed steel.
(4) The internal and surface quality of steel should be improved urgently. High added value steel products all require high steel internal quality and surface quality, and there is an obvious gap in this regard in China.
In a word, due to the obvious gap between China's steel materials and the international level, it not only restricts the production of high value-added steel products, but also obviously restricts the healthy and sustainable development of the follow-up processing industry and even the entire industrial chain. For example, the low surface quality of stainless steel produced in China in the past has obviously affected the corrosion resistance and decoration of stainless steel. In the 1960s and 1970s, a large number of ultra-low carbon stainless steels were produced abroad and the problem of intergranular corrosion was basically solved. In recent years, China has only produced stainless steel according to international standards, and the qualified rate of intergranular corrosion resistance has reached 98%. However, the qualified rate of intergranular corrosion resistance of ICr18Ni9Ti steel produced by individual steel plants is only 85%~90%. 1 The main reason is that the chemical composition of steel fluctuates greatly, and the solution temperature is too high, resulting in coarse grains. In the past, the formability and polishing of cold-rolled stainless steel plates in China were poor. Recently, with the progress of stainless steel production equipment and technology in China, the quality of stainless steel has been greatly improved.