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 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%.

The frequent quality defect of corner crack for casting blank of carbon structural steel with conventional composition design of medium carbon and low manganese seriously affects the hot charge rate of products. With the original equipment and working conditions, composition optimization design is carried out. The mechanical properties of products are ensured through replacing part of C with microalloying element Ti as well as replacing solution strengthening with fine-grain strengthening and precipitation strengthening. Meanwhile, the high temperature plasticity and corner crack of casting blank are improved through liquation of second phase particle for TiN with the high temperature of Ti microalloying to fix free nitrogen atom in liquid steel. The rate of corner crack for carbon structural steel Q235B with new composition design is controlled effectively through the evaluations of mass production and applications.

Phosphating and silane treatments are the common surface pretreatment technologies for cold rolled sheet. In this paper, the two conversion coating technologies are compared and analyzed from such aspects as the process flow, mechanism of film formation and evaluation methods as well as the morphologies of the two conversion coatings are compared and analyzed by scanning electron microscopy. Moreover, the influences of pretreatment technology on the surface roughness and peak density of cold rolled automobile steel DC04 are studied. The results showed that the surface conditioning and double washes after phosphating were omitted for silane treatment process compared with phosphating process as well as process flow was short and environmental; the mode of phosphate precipitation was adopted for film formation of phosphating, while covalent bond was adopted for film formation of silane treatment. Since the phosphating phase is crystal structure, so its phase composition and proportion could be evaluated by X-ray diffractometer. The phosphating film is composed of phosphate of 2~4 μm, while silane film is composed of finer round or irregular particles analyzed by scanning electron microscopy. After phosphating or silane treatment, the surface roughness of sample of cold rolled sheet DC04 remains unchanged, but peak density is increased slightly.

As a type of very important soft magnetic material, non-oriented silicon steel is widely used in such electrical equipment as motor and transformer. In recent years, with the continuous development of science and technology, the requirements of energy conservation and emission reduction are increasing so that the requirements for performances of iron core material are higher. As an important alloying method, the addition of rare earth elements has significant effects on the properties of non-oriented silicon steel and has been widely concerned. In this paper, the effects of rare earth elements on inclusions, texture and magnetic property of non-oriented silicon steel are summarized as well as the future development direction is proposed according to present research status.

During the process of manufacturing automobile rims by purchased 420CL steel of one wheel plant in the winter, there is welding deformation cracking at edge of the rims with remained “rolled round edge” of steel coils. The metallographic structure and microhardness of edges with and without cracking of rim are detected with metalloscope and microhardness tester respectively as well as the causes of cracking are analyzed. The values of microhardness of weld seam, coarse grain heat affected zone, fine grain heat affected zone and parent metal at edge of the rims with remained “rolled round edge” of steel coils are 217, 215, 223 and 150 respectively, while those without “rolled round edge” of steel coils are 222, 230, 235 and 220 respectively. The difference of microhardness for welding heat affected zone and parent metal at edge of the rim with cracking is about 70, this is the main cause for cracking of rim. After flash butt welding, the difference of material hardness for welding fine grain heat affected zone and without welding heat effect along edge of rim is too large so that the deformation coordination ability at edge of rim is destroyed and the stress concentration is generated at juncture to cause cracking.

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.

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.

In this paper, the continuous cooling transformation (CCT) curve of X80 pipeline steel researched and developed in laboratory is determined. The determination results showed that the ideal microstructure of X80 pipeline steel could be obtained when cooling rate was 5~30 ℃/s, which was granular bainite + ferrite bainite + a small quantity of martensite/austenite island; the microstructure transformation was basically completed when finish cooling temperature was 450 ℃. The determination of CCT curve could provide references for subsequent optimization of composition design, establishment of process parameters and control of microstructure.

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.