The stability for liquid level of molten steel for crystallizer is an important factor affecting the quality of continuously cast bloom. In this paper, the control principle and limitations for liquid level of molten steel for crystallizer of Baotou Steel are studied. A new three-dimensional measurement method and stability control technology for it are researched and developed so that the operation process is optimized, its control level is improved, the inclusions in continuously cast bloom are reduced as well as the quality and performance of bloom are improved.

In the paper, it is investigated the corner crack defect of continuous casting sheet billet, analyzed its causes from the process, operations and devices. The uneven thermal stress and mechanical stress on solidified slab shell are improved through such a series of improvement measures as improving the quality of molten steel, adjusting the cooling water and secondary cooling water consumption of crystallizer as well as improving the on-line equipment performance and chamfered crystallizer so that its occurrence rate is reduced and the quality of continuous casting sheet billet is improved.

The Q690D steel is the microalloying low-alloy high-strength steel with the yield strength of 690 MPa grade developed by Baotou Steel. It is with excellent low-temperature toughness, mainly used for engineering and mining machinery as well as the delivery of steel plate is in quenched and tempered condition. In order to grasp its basic weldability, the welding and postweld heat treatment technologies are formulated reasonably to make the performances of its welded joint meet the use requirements of industrial and mineral products. In the paper, the sensitivity of welding cold cracks, welding and postweld heat treatment technologies as well as comprehensive mechanical properites of its welded joint are with experimental study and assessment.

Since the original emission system for blast furnace gas and coke oven gas of Baotou Steel was affected by such factors as the quality of ignition gas, climate and equipment, gas was directly emitted due to extinction of accompanying flame so as to cause the air pollutions even poisoning accidents. The emitted gas is burnt and emitted fully with the sufficiently large ignition and accompanying flame generated by the stimulation of step electric arc and reaction of catalyst to self-emitted gas through improving the emission tower of our company with the direct-fired ignition device. As a result, the stability of equipment operation is good, emission after ignition is safe and reliable as well as a lot of fuel gas cost and maintenance charge are saved.

In this paper, the microstructure and properties of hot rolled 600 MPa grade dual phase steel plate for automobile structure are compared with those of hot rolled pickling plate. The results show that both of the yield strength and tensile strength are improved after pickling, there is no great change for elongation as well as the performances of hot rolled pickling plate could meet the requirements of standard; due to the work hardening of plate caused by withdrawal and straightening process before pickling, the impact energy values of pickling plate are lower than those of hot rolled plate with a series of thermal shock tests; after the pickling process, the microstructure is a large number of polygonal ferrite and a small amount of martensite, the grain size is changed from grade 10.5 to grade 12.0 and grain becomes finer because of cold deformation.

The high-strength automobile carriage steel BT600XT is successfully developed with the 2 250 mm hot continuous rolling production line of Baotou Steel by adopting the alloy design scheme of low carbon, sulfur and phosphorus as well as adding microalloy elements, niobium and titanium. It is with excellent overall performance and cold roll forming performance as well as the strength and toughness match well, which could fully meet the user requirements.

In the paper, the microstructures and properties of hot rolled dual phase steel DP590 with two component systems are compared and analyzed. The results show that the differences of microstructures for experimental steels are not obvious; the strength of experimental steel with C-Si-Mn-Nb component system is higher than that of experimental steel with C-Si-Mn component system, the surpluses of its yield strength and tensile strength are moderate, 81 MPa and 103 MPa respectively as well as the impact toughness and comprehensive mechanical properties are better, which are favorable for stable batch production.

The YQ450NQR1 Z-type steel is cracking during the rolling process so that it is determined to be rejected. Its causes are found out and reasonable control measures are put forward by metallographic examination, detection analysis of inclusions and scanning electron microscope.

Since the demand of high-grade fasteners in the fastener industry is increased year by year, the ML35CrMo alloying cold heading steel wire rod is developed. In this paper, it is introduced the non-metallic inclusions, mechanical properties, cold heading and rockwell hardness of quenched and tempered finished wire rod could all meet the standard requirements through controlling such processes as converter smelting, refining, continuous casting and rolling for ML35CrMo cold heading steel as well as selecting heat treatment system for wire rod.

In the paper, the high temperature plasticity of 15MnNbV was tested with MMS-200 thermal simulated test machine. The results showed that the reduction of area of 15MnNbV at 900 ℃ was only 26%, temperature of round billet entering straightening segment was about 900 ℃ during continuous casting, with the stress of straightening roll, there was easily to be microcracks on the surface of round billet, especially the Ф430 mm round billet causing wall scale on outside surface of steel tube. The composition of 15MnNbV was adjusted through analyzing the influencing factors for high temperature plasticity of steel and characteristics of precipitation for niobium and vanadium in steel. After that, the reduction of area of 15MnNbV at 900 ℃ reached 88%, surface quality of round billet was improved and wall scale on outside surface of steel tube was eliminated.