Latest ArticlesIn this paper, the heat treatment schedule which is easy to generate yellow block of martensite is obtained through observing and analyzing the metallographic structure of samples of tube for 12Cr1MoVG boiler after different heat treatments. Moreover, the method for eliminating yellow block of martensite is obtained through exploring the heat treatment schedule, which provides technical reference for heat treatment production on site.
In the paper, the microstructures of BT-65MnRE steel at different cooling rates are observed with the metalloscope by determining its continuous cooling transformation (CCT) curves at different cooling rates. The results showed that the phase transition points of test steel BT-65MnRE, Ac1 was 707 ℃ and Ac3 was 764 ℃, the microstructure at room temperature was pearlite + proeutectoid ferrite when the cooling rate was 1~4 ℃/s, it was pearlite + bainite + martensite + a small number of ferrite when the cooling rate was 5~8 ℃/s, it was pearlite + martensite + a small number of ferrite when the cooling rate was 10~30 ℃/s and it was martensite when the cooling rate was greater than 40 ℃/s.
In the paper, the effects of different quenching and tempering temperatures on the microstructure and mechanical properties of chrome-molybdenum steel are studied. The results showed that the tensile strength, elongation and impact energy of test steel were not changed much with the tempering temperature increased. The yield strength was more sensitive to tempering temperature and it decreased with the temperature increased. The optimum quenching and tempering temperatures were 900~920 ℃ and 690~710 ℃ respectively for hardening and tempering C90 steel grade steel tube with this grade of steel.
After the heat treatment of normalizing + tempering, the hardness value of P22 high pressure boiler tube with specification of Φ325 mm × 10 mm exceeds the upper limit of standard due to thinner wall thickness and faster cooling rate. A new heat treatment process of "slow cooling after normalizing + air cooling + tempering" is proposed through experimental research. The P22 steel pipe is with the microstructure of ferrite + pearlite after heat treatment by controlling the cooling rate after normalizing, which is the key to ensure its good comprehensive mechanical properties.
In this paper, it is introduced the micro analysis of microstructure for Q345B high pressure fertilizer pipe with metalloscope aiming at the problem of its unqualified longitudinal impact property and found out its cause is the existence of a large number of Widmanstatten structure. The sample tube was treated with the heat treatment of normalizing process and the results showed that the Widmanstatten structure in steel could be eliminated by normalizing treatment as well as the longitudinal impact energy is greater than 120 J, reaching 3 times of the lower limit value of impact in standard GB 6479-2013.
The reasonable heat treatment process parameters are formulated in view of the problem that the time of full annealing for 1Cr5Mo seamless steel tube for high pressure fertilizer facility is longer and its mechanical properties cannot meet the standard requirements with normalizing and tempering process. Finally, the heat treatment process of isothermal annealing with heating temperature of 880 ℃ is adopted through trial and error so that the products with stable performances meeting the requirements of standard GB/6479—2013 are successfully produced with volume production.
In this paper, the continuous cooling transformation (CCT) curve of test steel is determined with FORMAS-TOR-F full automatic phase transformation instrument by taking low carbon medium manganese steel as the object of study. The results showed that the microstructure at room temperature was proeutectoid ferrite + pearlite when the cooling rate was 0.1~0.5 ℃/s; when the cooling rate was 1~2 ℃/s, there was granular bainite and the microstructure at room temperature was ferrite + pearlite + granular bainite; when the cooling rate was 5~10 ℃/s, the bainite gradually transformed to martensite, so the martensite increased continuously and it was the mixed microstructure of martensite + bainite at room temperature; when the cooling rate was greater than 10.0℃/s, it was martensite structure at room temperature, which provide references for formulating heat treatment process.
In this paper, the structure, working principle, characteristics and performances of silicon controlled rectifier are summarized as well as its advantage of controlling high power with low power for metallurgical hoisting crane is introduced through examples. It can control the 160 kW motor of main coil with milliampere current, it is with such functions superior to those of contactor as it can be turned on and off in microsecond, noncontacting operation, no spark and noises, high efficiency as well as low costs and failure rate.
With the continuous development of medium frequency power supply of thyristor technology, the medium frequency smelting furnace has become very important equipment in the field of casting and steelmaking at present. In this paper, the working principle and electrical faults easy to occur of medium frequency smelting furnace are analyzed and studied, the emphasis is to study the main common electrical faults of rectifier and inverter electric control systems as well as load circuit, which provide the references for relevant practitioners.
In this article, the composition of main machine system for tube gang saw and logic control process of sawing are introduced, the hydraulic operation scheme of clamping mechanism for control system of sawing for tube gang saw as well as the composition of hardware and design thought of software for sawing of main machine are mainly described.
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