高钢级管线钢显微组织的演变

随着管线钢强韧性的提高,其对应组织的演变为铁素体-珠光体型(X65级)、针状铁素体型(X80级)、粒状贝氏体-铁素体型(X100级)和下贝氏体型(X120级)组织.晶粒细化和弥散的第2相亦是提高管线钢强韧性的重要手段,通常通过钢的成分优化和提高控制轧制工艺的冷却速度改善管线钢的组织.     

Effect of hot deformation on phase transformation kinetics of 86CrMoV7 steel

The time–temperature–transformation (TTT) and continuous cooling transformation (CCT) diagrams of 86CrMoV7 steel with and without hot deformation were constructed by means of dilatometry, metallography and transmission electron microscopy (TEM). The results show that the pearlite and bainite transformations of 86CrMoV7 steel can be promoted and the microstructure can be refined by hot deformation. The undissolved carbides associated with hot deformation increase the inhomogeneity of carbon distribution in deformed austenite. The inhomogeneities of the austenite increase the number of nucleation sites for pearlite and bainite, and promote pearlite and bainite formation, which result in refinement of both the pearlite and bainite microstructures. In contrast, the undissolved carbides do not play a direct role on the pearlite and bainite transformation of 86CrMoV7 steel in the absence of hot deformation.     

氧氮液化装置故障原因分析与处理

介绍马钢YPON-3750/1710型液化装置运行过程中出现的膨胀机气侧流道进油、冷箱喷砂、膨胀量降低、膨胀机出口压力高的故障现象,分析了故障原因,阐述了采取的处理措施及效果。     

Effects of alloying elements and cooling rates on the high-strength pearlite steels

The effects of the alloying elements of Cr, Mn and the cooling rates after hot deformation on the microstructures and mechanical properties of pearlite steels were studied. Results show that increasing Cr and decreasing Mn significantly increase the eutectoid transformation temperature of steel. The grain sizes of prior austenite of the steels after hot deformation are ～12?µm. However, the high-Cr–low-Mn steel exhibits a finer interlamellar spacing and some better mechanical properties than that of the high-Mn–low-Cr steel. A full pearlite microstructure with an interlamellar spacing of 97?nm was obtained on the former steel, which exhibits a hardness of HRC49, a tensile strength of 1700?MPa and an elongation of 19%.     

球化退火温度对65Mn—N组织与性能的影响

为确定合适的65Mn—N钢球化退火温度,模拟工厂的等温退火工艺对65Mn—N钢进行退火处理,并对钢的组织与性能随退火温度的变化规律进行了研究。结果表明,将热轧态的试样在720℃保温9h,然后炉冷至550℃．最后空冷时,铜的组织为铁素体和分布较为均匀的球粒状Fe3C碳化物,钢的显微硬度较低。     

Effect of niobium in medium alloyed ductile cast irons

The present work studies the effect of niobium addition on the mechanical properties and microstructure of an as-cast 4·3%Ni alloyed ductile iron. The experimental iron was made from high purity raw materials in a laboratory induction furnace. Eight castings were produced with niobium content in the range 0–0·8%. Silicon and carbon content were fixed at 2·4 and 3·1% respectively for all the castings. A complete micro-structural characterisation was undertaken for all the as-cast alloys. Niobium was observed to be directly related to the formation of polygonal niobium carbides of the type NbC. Such carbides increased in size and amount as niobium content increased in the alloys. The amounts of pearlite and ferrite phases were not affected by the niobium content added in the present study. Neither nodule count nor nodularity was affected by such niobium addition. Mechanical properties such as hardness, tensile strength, yield strength and ductility were measured for the alloy; a small strengthening of the alloys was observed as the niobium amount increased. Such strengthening is explained in terms of NbC formation during solidification. IJCMR/372     

High strength low carbon hot rolled δ-ferritic steel: microstructure and mechanical properties

Abstract

The present study concerns the development of high strength low carbon hot rolled bainitic and martensitic δ transformation induced plasticity steels. Equilibrium and para-equilibrium phase evolution have been examined by carrying out thermodynamic calculation using MT-DATA software. Microanalysis demonstrates that both manganese and aluminium partition between liquid and solid phases. Isothermal treatment and tempering at 350°C for bainitic and martensitic microstructures respectively have yielded the best combination of strength and ductility. All the steels have exhibited the continuous yielding behaviour and favourable ratio of yield and tensile strength, which are desirable for formability. The annealed steel has yielded a high level of tensile strength with the static toughness value in between the conventional transformation induced plasticity assisted and dual phase steels.     

Change in carbon state by low-temperature aging in heavily drawn pearlitic steel wires

Atom probe tomography analysis of heavily drawn pearlitic steel wires was performed with and without low-temperature aging. In the as-drawn wire, the lamellar cementite hardly decomposed and remained in a sufficient amount. By contrast, almost homogeneous carbon atomic distribution of the concentration near the average carbon content was observed in the wire with maximum tensile strength aged at 150 °C for 30 min. In the 200 °C × 30 min aging, carbon atoms were enriched at the boundary (prior lamellar cementite) and the carbon concentration in the lamellar ferrite was lower. The change in carbon state was explained by the presence of the high number density of vacancies that was introduced by heavy drawing. These results indicate that cementite decomposition occurred during the thermal aging after, and not during, drawing. The mechanism of the change in strength by low-temperature aging was discussed.