The development and trial production of high corrosion-resistant products with Zn-Al-Mg coating for photovoltaic applications are carried out after transform Zn-Al-Mg production line of Baotou Steel. The microstructure of coating for Zn-Al-Mg products is analyzed, neutral salt spray test and surface defects of the products with Zn-Al-Mg coating are analyzed, controlled and studied. The analysis results showed that the microstructure of the coating was composed of Zn-rich phase, ternary eutectic phase of Zn/MgZn₂/Al and binary eutectic phase of Zn/MgZn₂ as well as the elements of Al and Mg were with uniform distribution in the coating; the neutral salt spray test results showed that the products with Zn-Al-Mg coating manufactured by Baotou Steel were with good corrosion resistance, processability, formability and self-healing ability of notch. The trial production results showed that the process control of Zn-Al-Mg production line of Baotou Steel was stable, stable batch productions of products with Zn-Al-Mg coating were realized, qualified rate of products reached 95.33% and yield reached 97.84% so that all performances could meet the technical requirements.

The chemical compositions of wire rod for large heat input welding are designed, its continuous cooling transformation (CCT) curves are determined, key control parameters of smelting process are established and industrial trial production is carried out with twice-heating production by analyzing the influences of chemical elements on welding performances of wire rod. The results indicated that the Ti content needed to be controlled over 0.15% in order to increase the input quantity of welding energy; the non-metallic inclusion of TiN in steel was controlled effectively in smelting process to ensure the pouring in continuous casting process is trouble-free; the optimum cooling rate was controlled at around 1 ℃/s, microstructure obtained was ferrite+pearlite+a small amount of bainite; the performance examination results of wire rod could fully meet the requirements of technical agreement and its welding performances were good, there were no welding cold cracks after drawing by user.

The timely pipeline dredging for long distance slurry pipeline could effectively ensure the safe operations of high pressure pipeline system. For the long distance high pressure slurry pipeline with the inner diameter of Φ212.75 mm, such 5 positioning tube cleaners of 3 types as the soft tube cleaners of Φ205 mm and Φ209 mm, soft descaling tube cleaners of Φ205 mm and Φ209 mm as well as four cup tube cleaners of Φ212 mm are adopted for descaling inside pipelines. For the slurry pipeline before dredging, the water discharge was 230.45 m³/h and outlet pressure of main pump was 1 150.7 kPa, while after dredging, the water discharge was 303.13 m³/h and outlet pressure of main pump was 1 115.2 kPa under the same condition of transporting slurry so that the flow of pipeline is increased by 31.54% and outlet pressure of main pump is reduced by 3.09%. The transportation capacity of pipeline could be effectively improved and outlet pressure of main pump could be reduced with the successful applications of dredging for slurry pipeline on site, which could be as important references for descaling long distance slurry pipeline.

The continuous cooling transformation (CCT) curves of Q1100D steel in cooling process are obtained through the thermal simulation of welding process with Gleeble-3800 testing machine. The microstructure and properties of welded joints under different heat inputs are tested with such methods as the Y-slit welding cold crack test, metallographic analysis and mechanical performance test. The results showed that the ultra high strength steel Q1100D for lifting arm of heavy machinery of Baotou Steel was with better cold check resistance. It could be welded without preheating at room temperature with the condition of a little heat input; with the condition of greater heat input, cold cracks are not observed on the surface and cross section, which indicates that Q1100D steel plate is with good cold check resistance. The evaluation results of comprehensive mechanical and structure properties of the joint indicate that the Q1100D steel plate with thickness of 14 mm is with optimum mechanical properties (tensile, bending and impact) of welded joint under heat input of 1.05 kJ/mm.

The hardness of hardened layer for rails after quenching is with hardness gradient and it is difficult to accurately calculate the threshold value ΔK_th of fatigue crack growth for rails. In the paper, the detection of threshold value ΔK_th is carried out through software optimization based on the fatigue crack growth software. The threshold values ΔK_th of U75V and U71Mn quenched rails with different stress ratios are obtained by national standard method and actual measurement method respectively. As a result, the threshold values ΔK_th of quenched rails obtained by actual measurement method are more accurate through comparative analysis of data.

In this paper, the products of 685 and Armox 500T, armor plate BTP500 are selected to compare and analyze. The results showed that the microstructure of armor plate BTP500 produced by Baotou Steel was tempered martensite, original austenite grain was fine, average grain size was 10.5 μm and grain size was uniform. The average hardness of BTP500 steel plate (HBW) is 291~296, which is about 30 higher than that of 685 steel plate. The mechanical performance indexes could fully reach the levels of Armox 500T protective plate, average low-temperature impact absorbing energy at -40 ℃ is 51.6 J, which is higher than that of Armox 500T. The BTP500 steel plate is still with good bullet proof property in the case that it is thinner, which provides the ideal protective material for lightweight of armored vehicles.

The drawing speed of welding wire is seriously affected and fracture of welding wire is easy to happen due to high nitrogen content of the ER70S-6 welding wire steel so that user requirements cannot be met. In order to reduce the nitrogen content in steel, the technological process of converter steelmaking is studied systematically as well as the factors influencing nitrogen content in steel and control measures are discussed. In the paper, the dissolution mechanisms of nitrogen in steel are analyzed by thermodynamics, restricted links of nitrogen removal are analyzed and studied by dynamics as well as the influences of sulfur content in molten iron in furnace, slag charge in top of converter, times of spot blowing for converter and maintenance of tap hole of converter on nitrogen content and corresponding measures for controlling nitrogen content in the technological process of steelmaking are studied based on the thermodynamic analysis and dynamic mechanical analysis.

The contents of calcium oxide, silicon dioxide, magnesium oxide, phosphorus and sulfur in metallurgical lime are determined by means of fusion sample preparation-X-ray fluorescent spectrometry. The optimum experimental conditions are determined by analyzing the influences of such factors as fusing agent, release agent, dilution ratio, melting time and temperature on the determination results. Meanwhile, the calibration curves of each element are drawn with standard samples and self-made standard samples with appropriate contents as well as the correlation coefficients are all over 0.999. The experimental samples are determined with test methods. The results showed that the measured and theoretical values of each element could meet the requirements of tolerances as well as relative standard deviations of each element in precision experiment were all less than 5%, which was with higher accuracy and precision. The operation of loss on ignition is not needed for preparing fusion samples in this method so that the experimental processes are greatly simplified and work efficiency is effectively improved, which is with certain promotional and application values.

The main causes for strength fluctuation are determined to be abnormal microstructure and length differences of furnace area in the two continuous annealing production lines by analyzing the causes aiming at the problems of great strength fluctuation and low qualified rate for HC500LA steel with small batch trial production of Rare Earth Steel Plate Plant. The abnormal microstructure and strength fluctuation caused by incomplete recrystallization are reduced by optimizing the compositions. The design of differentiated annealing temperature and speed of steel strip for the two continuous annealing production lines is carried out so that the strength fluctuation of steel strip is significantly improved and qualification rate of performances is increased from 87.8% to 98.2%.

In the paper, the representational capacity of modified Johnson-Cook (m-JC) constitutive model on the high temperature rheological behavior of 304 austenitic stainless steel is studied. The material constants of constitutive model are calculated with the data of experimental true stress-strain for isothermal compression test at different temperatures, strains and strain rates so that the m-JC constitutive model of 304 austenitic stainless steel is established. The applicability of the model is evaluated by comparing the correlation coefficient, average relative error and mean square error of predicted results. The results showed that the average absolute relative error between the predicted results and experimental results of m-JC model was 6.77%, correlation coefficient was 0.987 as well as mean square error was 11.2 MPa so that the m-JC constitutive model could more accurately describe the rheological behavior of 304 austenitic stainless steel.