The changes of morphology, component and size for non-metallic inclusions in smelting process are studied with metalloscope and scanning electron microscope-energy spectrum analysis by sampling in each link of technological process of heavy rail. The results showed that the non-metallic inclusions in smelting process were spherical and their main components were CaO-SiO₂-MgO-Al₂O₃ as well as the proportion of content for each component was changed regularly with technological links, sizes were decreased gradually and quantity was reduced with the advance of technological process. The main source of inclusions in rail could be judged according to the change laws of components for inclusions in each process of smelting process for heavy rail. It could be inferred that the large size inclusions in heavy rail steel are compound inclusions composed of deoxidation product that is not upfloated combining with foreign inclusions during continuous casting process by analyzing the scanning electron microscope-energy spectrum detection results for large size inclusions in heavy rail.

In the paper, the design thought and development of Φ73 mm pass series for FQM (Fine Quality Mill)-Φ100 mm mandrel pipe mill with six stands are mainly introduced. When design this series of pass of mandrel pipe mill, the “distribution method of coefficient of elongation on top of pass” is adopted so that the applications of development technology of minimum pass series of mandrel pipe mill with retained mandrel are realized. The industrial results showed that the wall thickness accuracy of seamless steel pipe produced by the pass of mandrel pipe mill designed with this technology is within±8% as well as the internal and external surface qualities of steel pipe are good.

The trace amount of refining grain elements are added into carbon manganese steel as well as the heat treatment method of quenching and tempering is applied in production based on the standard. The mass production results showed that the mechanical properties could meet requirements and toughness was good. After the heat treatment of quenching and tempering, the yield strength of steel tube is not less than 500 MPa, tensile strength is not less than 620 MPa, longitudinal elongation is not less than 20%, average longitudinal impact value at -20 ℃ is not less than 180 J and the performances could meet customer's requirements; carbon equivalent is controlled below 0.44 to ensure the subsequent weldability.

The pipeline steel is mainly used for transportation of oil and natural gas as well as the acid service condition means that there are such acidic mediums as H₂S,CO₂ and H⁺ in application environment, so pipeline steel in acid service condition is the pipeline steel with resistance to hydrogen induced corrosion cracking. In the paper, the development and industrial production of X46MS hot rolled coil are mainly introduced. The development includes chemical components, hot rolling process and production technology process as well as the performance tests include pulling, bending, impact, hardness, metallography, non-metallic inclusions and hydrogen induced cracking (HIC). The test results showed that the chemical components and process design of X46MS hot rolled coil in acid service condition were reasonable as well as it was with pure steel, well-closed formation and excellent mechanical properties, especially the resistance to hydrogen induced cracking.

In this paper, the chemical composition and production process are designed according to the technical requirements of cold rolled 980 MPa martensitic steel as well as the study of its annealing process in laboratory is carried out with pilot-scale test platform. The study results showed that the yield strength was 750~940 MPa, tensile strength reached over 1 020 MPa and elongation was over 10% for the products of cold rolled 980 MPa martensitic steel produced with the same chemical composition and rolling process through adjusting the slow cooling temperature of annealing, which could meet technical requirements. The effect laws of slow cooling temperature on microstructure and properties of cold rolled 980 MPa martensitic steel are clear and definite as well as the soaking temperature is determined to be 800 ℃,slow cooling rate is determined to be 3 ℃/s, rapid cooling rate is determined to be 45 ℃/s and the optimum slow cooling temperature is determined to be 680 ℃ when rapid cooling temperature is 280 ℃ with the composition system combining with the microstructure and mechanical properties of finished products.

The static continuous cooling transformation (CCT) curves of N80 grade steel for ERW oil casing with and without Mo are determined by Formaster-F full automatic phase transformation meter as well as the microstructures of the two types of steel at different cooling rates are observed with optical microscope. The results showed that the critical points of test steels of N80 grade steel for ERW oil casing, Ac₁ and Ac₃ were basically not affected by Mo element as well as the critical cooling rate for test steel 1 and 2 to start generating martensitic structure was 8 ℃/s. The interval range of cooling rate for bainite transformation of the test steels is expanded due to addition of Mo element and their microstructures are refined.

The causes of cracks are analyzed through the observation with metalloscope and scanning electron microscopy aiming at the problem that product quality is affected by the microcracks on surfaces of web and flange of Q420NHB weathering resistant H-shaped steel. The results showed that the surface defects of flange were caused by the subcracks and intercrystalline cracks on inner arc of ingot blank, while the surface defects of web were caused by the pressfit of scale on surface of ingot blank during rolling process. The surface quality of weathering resistant H-shaped steel is effectively improved through optimizing the cooling process of crystallizer and rolling technology during continuous casting process.

The Φ7.3 mm wire rod without drawing for high-speed wire rod is rolled successfully by reasonable roll pass and guide designs as well as optimization of control process aiming at the individual requirements of it in market combining with the characteristics of the fifth-generation Morgan high-speed wire rod mill. As a result, the usage requirements of users could be satisfied very well and product mix of the fifth-generation Morgan high-speed wire rod mill is widened, which could provide the references for developing like products subsequently as well as a brand new market is exploited and the green production in the whole process of industry is realized.

The phase transformation law is analyzed through determining the transformation kinetics curve of supercooled austenite for U71Mn steel. The effects of cooling rate and finish cooling temperature on microstructure and hardness are studied with the thermal simulation tests of sectional type cooling strengthening based on the heat treatment process of rails on site. The results showed that the critical cooling rate of perlitic transformation for U71Mn steel was 7 ℃/s and temperature range allowing perlitic transformation was 500~600 ℃. The reasonable process parameters of sectional type cooling for U71Mn steel were that the starting cooling temperature was 850 ℃, cooling rates was 6~12 ℃/s and finish cooling temperature was 570 ℃. The perlite structrure could be obtained with this process parameter and it could meet the hardness requirements of rails.

The causes for lower qualified rate of transverse low temperature impact toughness at -20 ℃ of SM490YB hot-rolled H beam for offshore oil platform are analyzed with such instrument and equipment as the optical microscope, scanning electron microscope and energy spectrometer. The results showed that the poorer low temperature impact toughness of test steel was caused by large Al₂O₃ inclusion, harder bainite structure, coarse grain and banded structure in the steel. The transverse low temperature impact toughness at -20 ℃ of test steel is improved obviously and qualified rate of impact at -20 ℃ is increased from 80% to 100% by reducing carbon content of test steel as well as optimizing smelting and rolling processes so that the grain size and inclusions of test steel are refined as well as types of microstructure are optimized.