In this paper, it is introduced the CCT curve of 700 MPa grade high strength steel is measured with the Formastor-F full automatic phase change instrument and its microstructures at various cooling rates of 0.5~118 ℃/s are analyzed. The results showed that the transformation product was ferrite and pearlite when the cooling rate of test steel was 0.5 ℃/s; bainite structure began to form when the cooling rate was more than 1 ℃/s; bainite structure began to increase and perlite structure began to reduce with the cooling rate gradually increased; pearlite structure disappeared as well as the structure was ferrite and bainite when the cooling rate was 10 ℃/s; transformation products were mainly bainite when the cooling rate increased to 118 ℃/s. The analysis on the CCT curve and microstructure of 700 MPa grade high strength steel provide the theoretical basis for formulating heat treatment technology in actual production processes.

The phase transition temperature and static CCT curve at critical point of 800 MPa grade steel for hydropower project with low susceptivity to weld cracking are determined with phase change instrument Formast-F and the dilatation method combing with metallographic method as well as the effects of cooling rate on microstructure are studied. The results showed that the phase transition temperatures of test steel, Ac₁ was 675 ℃, Ac₃ was 875 ℃, Ar₁ was 615 ℃ and Ar₃ was 739 ℃; when the cooling rate was less than 0.25 ℃/s, the transformation products were ferrite (F) + pearlite (P) + a small amount of bainite (B); when the cooling rate was 0.25~1 ℃/s, the transformation products were ferrite (F)+ bainite (B); when the cooling rate was 1~5 ℃/s, the transformation product was bainite (B); when the cooling rate was 5~20 ℃/s, the transformation products were bainite (B)+ martensite (M); when the cooling rate was greater than 20 ℃/s, the transformation product was martensite (M).

In this paper, the industrial experiments of different heat treatment processes for X65Q seamless steel tube with medium thick wall are carried out as well as its microstructure and properties are tested and analyzed. The test results showed that the martensite content of X65Q seamless steel tube with specification of Ф406.4 mm×26.19 mm was gradually reduced from inner wall to center after quench with 3 300 m³/h inner and outer spraying as well as the microstructure of its internal surface was tempered sorbite+bainite, microstructure of its outer surface was bainite; after quenching, its grain size reached grade 8.5, transverse impact value at 0 ℃ reached over 200 J and yield strength reached over 500 MPa with tempering of 630 ℃ so that the strength and toughness of material matched well, which could meet the requirements of API 5L standard.

In the paper, it is discussed the research progress and protection measures of corrosion for rail at home and abroad, elaborated the mechanism of corrosion failure in service process of rail lines as well as listed the chemical composition, performance parameters and industrial applications of new materials for corrosion resistant rails currently researched and developed such as the corrosion resistant rails of India and Wuhan Iron and Steel (Group) Co.. The development direction of production technology for corrosion resistant rail is proposed combining with the research and development ideas of new materials for corrosion resistant rail as well as the effects of resisting corrosion for other steels. The countermeasures taken in the research and development of corrosion protection for rail of Baotou Steel are mainly introduced as well as the future research direction of this field is expected.

In order to improve product quality and strengthen quality monitoring of high speed rail, the chemical composition of U71Mn rail is optimized, Mn content in steel is reduced and rolling process is controlled as well as the trial productions are carried out for such whole series of sections as 60 N, 60 kg/m, 50 kg/m, QU120, QU100 and QU80 of U71Mn. The results showed that the tensile strength was reduced by 7.2 MPa and mean value reached 950 MPa, tread hardness (HB) was reduced by 2.8 and mean value reached 269.2 as well as elongation is basically unchanged by comparing the performances of U71Mn rail with those before optimization. Moreover, the ideal perlite structure is obtained, performances of rail could all meet the standard requirements and is with enough margin so that the effects are better.

The effect of residual stress for rail on its fatigue performance is great. In this paper, the influences of different residual stress values on fatigue crack growth rate for U75V heat-treated rail are studied with tempering test and metallographic analysis method. The influences of different tempering times on the residual tension of rail are analyzed with the tempering test. It is concluded that the residual stress gradually decreases with increase of tempering time; the crack growth path at tip of fatigue crack is analyzed by testing the metallographic structure of rail treated with tempering process and observing the metallographic structure of rail with different tempering times, the influences of different tempering times on fatigue crack growth rate are analyzed according to the mode and length of crack growth; the residual stress and fatigue crack growth rate of rail can be effectively reduced so that the anti-fatigue performance of rail can be improved through tempering process control.

In the article, it is introduced the rail is deformed violently in rolling process and internal compactness is changed greatly due to the cross section size of ingot blank increases when rolling 60 kg/m rail using ingot blank with the cross section of 320 mm×415 mm instead of that with the cross section of 280 mm×380 mm in the production of rail. In order to ensure the product quality in rolling process, the roller of each rolling mill is adjusted to ensure stable as rolled state. After rolling the finished products, the macrostructure, microstructure, grain size and impact performance of rail are tested and analyzed with such equipment as the optical microscope, scanning electron microscope and impact testing apparatus. The results showed that the compression ratio of ingot blank was increased by rolling rail with large size ingot blank so that such mechanical properties as grain size and impact of rail could be improved.

Such elements that could refine grain as V, Nb, Ti, Al and rare earth (RE) are added into the medium carbon steel as well as the stable compound formed by N, C and elements that could refine grain is used to refine the austenite grain and increase the strength and toughness of non-quenched and tempered steel. The stable compound formed by N, C, V, Nb, Ti and Al are observed with metallographic microscope and transmission electron microscope so that the non-quenched and tempered ferrite-pearlite steel is successfully developed. Its yield strength is greater than 550 MPa, tensile strength is greater than 780 MPa, hardness (HB) is not less than 210, elongation is greater than 18%, reduction of area is greater than 45% and impact value of V-notch at room temperature is greater than 50 J. Compared with common non-quenched and tempered steel, the non-quenched and tempered steel F28MnSiVTiRE is with such advantages as high strength and toughness and free cutting so that it could be used for machining such components as vehicle crankshaft and engine connecting rod.

In the process of rolling wire rods with Φ5.5 mm and Φ6.5 mm in Long Products Plant, the accident of piling-up of steel is easily to happen at the water cooling section after finishing rolling so that the rhythm of production and output are affected. Its true causes are found out through analyzing its phenomena, morphology and microstructure of its samples with the scanning electron microscope so that the probability of repetitive accidents and its times of piling-up of steel at water cooling section after finishing rolling are reduced. After the rectify and reform, the ratio of piling-up of steel is reduced to 0.013%, cumulative failure time is reduced to 35.8 hours and rejection rate is reduced to 0.027%.

The phase transition law of continuous cooling for SWRCH35KM test steel is tested with Gleeble-1500 thermal simulated test machine. The phase transition law of spheroidization of pearlite after final rolling is studied by the thermal simulation test of online spheroidization. There are transformations of ferrite and pearlite at different cooling rates as well as the characteristics of microstructure for ferrite change with the increase of cooling rates. When the cooling rate is below 2 ℃/s, the metallographic structure of SWRCH35KM test steel is ferrite and pearlite. With the cooling rate gradually increases, the acicular ferrite along with Widmanstatten structure appear continuously in the metallographic structure. Meanwhile, the ferrite is more refined than before and its volume fraction is also gradually reduced. Based on the phase transition law of microstructure and with thermal simulation test data of SWRCH35KM test steel, rolling and cooling will be strictly controlled in industrial production in order to obtain ideal metallographic structure, especially the controlled cooling mode of Stelmor cooling line to ensure to obtain fine ferrite and spheroidized pearlite.