Effect of continuous annealing temperature on the microstructure and mechanical property of an aluminum killed steel

The continuous annealing process of a typical aluminum killed steel was investigated. A cold rolled sheet was annealed continuously at holding temperature ranging from 580 to 760 ℃. The microstructures were analyzed in detail based on contiuous cooling transformation（ CCT） curves that were simulated with JM artP ro softw are. The results show ed that recrystallization and perlitic transformations caused a diversity of microstructures and mechanical properties. In comparison with annealed steel that was produced from insufficient recrystallization,annealed steel produced from sufficient recrystallization had more isometric grains and exhibited low er strength and higher ductility. Higher annealing temperatures than A_1 provided steel with lamellar pearlite zones,large ferrite grains,low strength,and high ductility. The results are attributed to the property optimization of the steel.

胶凝材料与纤维种类对UHTCC性能的影响

对12组超高韧性水泥基复合材料(UHTCC)进行流动性、抗压强度、劈裂抗拉强度和抗弯强度试验,探讨胶凝材料与纤维种类对UHTCC性能的影响。结果表明,单掺2.0%镀铜钢纤维时,抗压强度和劈裂抗拉强度最佳;镀铜钢纤维掺量的增加,拉压比、抗弯试验峰值荷载以及韧度因子明显增大,抗弯性能与韧性能力得到提升;随着硅灰掺量、镀铜钢纤维掺量增大以及聚丙烯纤维的掺入,拌合物的流动性变差;当水泥掺量为胶凝材料质量的70%,粉煤灰与硅灰掺量皆为15%时,拌合物流动性良好,有利于纤维发挥增韧作用;当镀铜纤维与聚丙烯纤维组合时,较单掺镀铜钢纤维,抗压强度与劈裂抗拉强度显著提升,特别是抗弯强度试验峰值荷载明显增大。

关于低碳钢屈服延伸现象的研究现状

低碳钢因其优良的塑性常被用于家电和汽车面板。在低碳钢工业生产中,节能、高效的连续退火工艺取代能耗高、效率低的罩式退火工艺后,低碳钢在使用过程中遇到了严重的质量问题——因时效而产生的屈服延伸现象。屈服延伸现象是指低碳钢经人工时效或长时间的自然时效后,钢板表面在变形过程产生不均匀塑性变形而出现褶皱的现象,又称吕德斯带,该现象对钢板的表面质量和性能造成严重的损害。屈服延伸现象受碳氮含量、晶粒尺寸、合金元素、工艺参数和应变等因素影响,在明确屈服延伸现象发生的微观机理前提下,选择适当的成分和工艺参数能够在一定程度上减少或消除屈服延伸现象。关于屈服延伸的出现一般认为与晶体内间隙原子(碳原子和氮原子)的偏聚有关:经典理论认为屈服延伸现象是由于间隙原子在晶体内位错周围偏聚(也称柯氏气团),柯氏气团对位错的反复钉扎和解钉扎过程导致了屈服延伸;但是部分学者认为屈服延伸现象是偏聚在晶界上的间隙原子对位错运动的反复钉扎和解钉扎引起;也有部分学者认为是两者共同作用的结果。因此,关于出现屈服延伸现象的原因的争议在于间隙原子偏聚的位置,即偏聚于位错周围形成柯氏气团或偏聚于晶界。为了有效消除屈服延伸现象带来的危害,近些年来除研究屈服延伸现象发生的微观机理,即探究屈服延伸发生过程间隙原子偏聚的位置外,研究者们也探索了屈服延伸现象发生的微观力学行为。针对屈服延伸现象的研究引入了内耗、三维原子探针、聚焦离子束等先进技术手段,可实现对基体、晶界和位错等位置上各元素含量的表征,为进一步明确屈服延伸现象产生机制奠定基础;纳米压痕和扫描电镜原位拉伸等技术可用来研究屈服延伸发生过程的微观形变机理。其中采用纳米压痕技术研究屈服延伸现象时所得载荷-位移曲线上出现的晶界pop-in现象已被证实与屈服延伸现象存在联系,否定了较早认为初始pop-in现象与屈服延伸现象存在联系的观点。本文对屈服延伸的影响因素、机理和研究方法等方面进行了系统的综述,以期为低碳钢连续退火工业生产工艺中消除屈服延伸现象提供一定的线索,在降低生产成本、提高低碳钢表面成形质量方面有重要意义。

Comparative study on the corrosion behavior of low alloy steels in sulfuric acid solution

The corrosion behavior of a weathering steel SPA-C and two acid resistance steels（ S-TEN1 and ND）in sulfuric acid solution was investigated by using potentiodynamic polarization and weight loss measurement techniques. Both potentiodynamic polarization and weight loss measurement tests indicated that corrosion resistance of these three alloy steels was as follows： ND ~ S-TEN1 〉 SPA-C. Surface analysis of the corroded samples conducted after the immersion test indicated that two layers were formed on the substrates, with the outer layer comprising FeSO4. H20 and the inner layer mainly comprising iron oxides. The addition of Cu, Cr, and Sb refined the corrosion products and improved the adhesion ability between the rust layer and the substrate.

Secondary work embrittlement of cold-rolled 05CuPCrNi sheet at low temperature

Due to the rapid development of China＇ s rail transportation equipment manufacturing industry and related international distribution, important material suppliers such as Baoshan Iron ＆ Steel Co., Ltd. carries on investigating the stability of material under extremely cold conditions. In this study, mechanical properties and secondary work embrittlement of weathering steel 05CuPCrNi were tested at low temperature. Compared to the mechanical properties at room temperature, the yield and tensile strength increase slightly with decreasing temperature. However, the variation of elongation is not obvious. The experimental results also show that the secondary work embrittlement transition temperature of 05CuPCrNi is lower than - 60 ℃. These results provide the basis for the use of this train body material in extremely cold regions.