In the paper, the microstructure and mechanical properties of test steel are analyzed aiming at the additional technical requirements for impact property and grain size of hot rolled J55 steel grade casing based on the Technical Specification for Seamless Casing Procurement published by China National Petroleum Corporation as well as the steel grade design of microalloying of titanium for restraining abnormal growth of austenite structure and the scheme for cooperative control of hot continuous rolling temperature are proposed. The industrial production of J55 steel grade casing with the specification of Φ244.48 mm × 8.94 mm has been carried out, the results showed that the grain size, impact energy and tensile property could all meet the requirements of Technical Specification for Seamless Casing Procurement.

In the paper, the improvement and practical application of slag retaining with sliding plate and detecting technology of roughing slag with infrared ray for 120 t converter of Baotou Steel are introduced as well as they are compared with present common slag retaining ways and analyzed. The results showed that the success rate of slag retaining could reach over 99%, the quantity of roughing slag was controlled within 80 mm and average rephosphorization of molten steel could be controlled within 0.001% with the improvement so that the cleanliness of molten steel was improved to lay a good foundation for manufacturing steel grades with high added value and reducing production costs.

The characteristics of continuous casting process for round billet and distribution of carbon element in round billet are analyzed as well as the causes of carbon segregation are analyzed and discussed. The optimum measures are put forward from such two aspects as degree of superheat of molten steel and cooling regime of continuous casting combining with the technological characteristics and equipment condition of continuous casting for round billet. Moreover, the industrial test results showed that the carbon segregation in round billet with large section could be effectively improved when the current of mold electromagnetic stirring was controlled at around 300 A, degree of superheat of molten steel was controlled at around 25 ℃ and specific water flow was controlled at 0.20~0.22 L/kg.

The quenching and tempering process with the quenching temperature of 900 ℃ and tempering temperature of 670 ℃ is determined by taking the upgraded BT135VRE process parameters provided by laboratory as references, on-site adjustment and determining the reasonable on-site heat treatment process parameters combining with reality. The yield strength, tensile strength, elongation and metallographic structure of steel tube are tested as well as the results could meet the product requirements.

The problems of misrun on surface of three-section mandrel for large diameter continuous rolling mill and fracture at joint of bolt are solved through such measures as controlling the cooling effect of mandrel, adjusting the thickness of lubricating layer of graphite, reducing the coefficient of elongation for rolling ultra-thin-wall steel pipe with maximum diameter mandrel, designing the function of "mandrel avoidance" in servo system of continuous rolling mill and adding gasket unit at the joint of connecting rod and working section so that the service life of mandrel is significantly improved and the use cost of mandrel is reduced by about 8%.

In the production process of 12CrMoV pearlitic heat resistant steel carrier rod, there are such problems as poor weldability and great welding difficulty caused by using the v-groove electrode arc welding and horizontal fixed all position butt joint welding, such defects as incomplete penetration, slag inclusion and cracks are effectively avoided by standardizing the welding process and welding quality control to ensure the welding quality.

The axle steel with large bulging rate is designed and developed as well as the trial production and evaluation of seamless steel tube are carried out aiming at the problem of cracking in bulging area when produce axle with large bulging rate using seamless steel tube in a domestic axle manufacturing enterprise. The results showed that the elongation of seamless steel tube for axle produced with the designed and developed steel grade was 28%~31%, its longitudinal impact energy at-60 ℃ could reach 80 J as well as it was with good plasticity and low temperature impact toughness. With the batch use by users, there is not the cracking problem when it is bulging.

The alloy composition design based on V and Cr is carried out through analyzing the performance requirements and technological characteristics of seamless steel tube for hydraulic cylinder as well as the corresponding control measures of smelting, rolling and heat treatment technology are formulated so that the seamless steel tube with excellent comprehensive performance is successfully developed. The yield strength, tensile strength and longitudinal low-temperature impact value at-20 ℃ of trial-manufacture steel tube are more than 480 MPa, 650 MPa and 100 J respectively.

The load-bearing axle tube for low-temperature working condition is developed and offered to user on trial with the beneficial effects of rare earth in steel aiming at the problem that there are cracks on axle tube XCQ16-1 produced by Baotou Steel in process of forming at low temperature of -5 ℃. The results showed that the products could completely meet the manufacture requirements at low-temperature working condition of -5 ℃, there were no cracks on them in use procedure, they had passed fatigue test of axle and had been supplied in batch stably.

The rotary hearth furnace with gas of Φ180 mm plant unit in Steel Tube Co. of Baotou Steel is the most important equipment in the process of producing and rolling steel tube. In this paper, it is analyzed such defects as unstable calorific value of gas, inaccurate flow element measurement and deviated flow characteristic of valve for combustion control system of rotary hearth furnace with gas as well as adopted such reformation measures of its intelligent upgrade as upgrading the temperature control program, introducing strategy of autocorrection for coefficient of excess air, reserving automatic regulation interface of air fuel ratio, newly increasing automatic control of pressure in air main, automatic control software of furnace pressure, functions of automatic starting up and air-tight test, basic alarm of loop and interlock. Finally, the stable intelligent combustion system is realized.