Hydrogen-induced cracking in a very-high-purity high-strength steel

It is shown that intergranular fracture along prior-austenite grain boundaries in a ultrahigh-strength quenched and tempered 4340-type steel is not suppressed by eliminating all segregated embrittling elements. This leaves open the question of how brittle intergranular cracks are nucleated in hydrogen in the absence of such impurities.     

特种高强度钢等厚冷压成球面工艺

球缺封头传统成形工艺无法满足某水下使用设备球形板形状、厚度、力学性能、重量等设计要求。通过开展特种高强度钢等厚冷压球面工艺研究，掌握了冷压成形中板厚变化规律、形状误差控制、消除冷作硬化及保证力学性能控制和成形压力控制四项主要关键技术，实现了特种高强度钢等厚球面冷压成形，满足了球形板设计要求。     

Oxidation limited life times of chromia forming ferritic steels

Long term, cyclic oxidation studies of three high – Cr, ferritic steels were carried out at 800°C and 900°C in air. It was found that with decreasing sample thickness the life time of the mentioned alloys decreases due to breakaway phenomena. This effect is caused by faster exhaustion of the chromium reservoir from the bulk alloy in case of thinner components. The observed life time limits can be predicted with reasonable accuracy by a theoretical model, using oxide growth rate parameters, initial alloy Cr content and critical Cr content required for protective chromia scale formation. In the calculation it has, however, to be taken into account that the oxidation rates of the steels increase with decreasing specimen thickness.     

连续酸洗过程控制模块的研究与应用

酸洗过程对产品质量、能源消耗、介质利用有着极为重要的影响。针对某1 740mm酸轧机组进行了连续酸洗功能模块架构,实现了设定计算、酸洗分析与控制、测量值处理等主要功能。同时,基于模块化理念,设计了实际数据处理模块、实际数据存档模块和产品数据生成模块,以实现酸轧过程控制的数据处理。实践证明,该酸洗过程控制模块具有良好的模型设定计算精度,可以显著提高高强汽车板的酸洗表面质量,有效保证酸洗工艺的稳定性,提高高强钢生产成材率。     

A novel approach of accurately evaluating residual stress and microstructure of welded electrical steels

In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten inert gas was used for the welding method. Residual stress was directly determined through deformation measurements and appropriate math calculations. Two methods were used: the magnetic, non-destructive method of Barkhausen noise and the semi-destructive method of X-ray diffraction. In order to evaluate the accuracy and reliability of the magnetic method applied, the steel samples were subjected to both compressive and tensile stresses and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. The results were then verified by the XRD method and were further evaluated by examining the microstructure and the mechanical properties of the as received and welded samples through scanning electron microscopy and hardness measurements, respectively. It was found that the deviation between the two methods was within acceptable limits, thus implying potential applicability of the MBN method in non-destructive testing of materials.     

Friction stir welding of duplex stainless steels

Duplex stainless steels are successful in a variety of applications such as the food industry, petrochemicals and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may change during fusion welding steps, and it can compromise the performance of these materials. Friction stir welding is a solid-state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. Superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat-affected zone. Consolidated friction stir welded joints with full penetration 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints, showing increased yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding grain refinement was observed in the welded joint, achieving grain sizes as small as 1 μm. This refinement was associated with the combination of microstructural restoration mechanisms in the dual-phase microstructure promoted by severe deformation associated with a high temperature during the welding process.     

含1.2%铝TRIP钢中残留奥氏体的EBSD研究

残留奥氏体的含量、颗粒尺寸与分布及其稳定性是相变诱导塑性（TRIP）钢获得优良使用性能的关键。马钢试制成功含1.2%铝的TRIP-600钢板,作者用场发射枪扫描电镜EBSD技术对该TRIP钢的残留奥氏体形态、分布与体积分数进行了实验研究。结果表明：实验钢中的奥氏体主要呈细小颗粒状、尺寸在几微米以下,弥散分布于铁素体晶界和晶粒内。EBSD与X-射线衍射测得实验钢板半厚度区的奥氏体体积分数分别为2%和11.4%。本文讨论了EBSD技术测定TRIP钢奥氏体分数引入误差的主要因素。采集图像的步长、试样分析区的选取及试样制备技术等是影响实验结果的重要因素。     

An effect of strength of railway axle steels on fatigue resistance under press fit

High-cycle fatigue tests with an evaluation of fatigue limit were carried out on large model components of bars with press fitted hubs of diameter 63/59 mm. Bars were made of three railway axle steels EA1N, EA4T and 34CrNiMo6 with considerable different strength from 586 MPa to 1041 MPa, respectively. Detection and measurement of crack growth under hubs by ultrasonic method was performed during the tests. In spite of the differences in strength and alloying of tested bars, differences in mean value of fatigue limit were not significant. This result was connected with specific damage mechanism and microcracks initiation under hubs with fretting effects. Short fatigue crack growth under hubs occurred at stress intensity factor range ΔK considerably bellow threshold value ΔK_th of long cracks. Simultaneous growth of main cracks from more than one point of surface circumferential area under hub was quite frequently observed.     

Effect of Varying Carbon Content and Shot Peening upon Fatigue Performance of Prealloyed Sintered Steels

The aim of the work was to find out how the modification of surface treatment and microstructures affect the fatigue characteristics of the considered sintered materials.Two different systems were prepared:as-sintered and shot peened prealloyed sintered(Astaloy CrL based)steels with addition of 0.5%and 0.7%C.Sintering was carried out in laboratory tube furnace in an atmosphere of pure gases 75%N2+25%H2.The sintering temperature was 1180-C and sintering time was 60 min.Heating and cooling rates were 10-C/min...     

高钢级管线钢的常规TMCP工艺与HTP工艺

介绍了常规TMCP工艺和HTP工艺在管线钢生产方面的发展历程和管线钢整体的化学成分设计情 况，对比分析了主要微合金元素Mo和Nb分别在常规TMCP工艺和HTP工艺中的作用，论述了常规TMCP工艺的机理，即通过奥氏体再结晶区粗轧来细化奥氏体组织和非再结晶区精轧来增加奥氏体内位错密度，提高铁素体的形核率细化相变后的组织，最后根据终轧厚度对钢板采用不同的冷却方式来获得良好性能。分析了HTP工艺与常规TMCP工艺的主要不同点,并指出HTP工艺经济效益优于TMCP工艺，已成为目前高强度管线钢生产的主要工艺。