B1800HS热成形钢组织转变的JMatPro计算和试验研究

以B1800HS系试制热成形钢为例,探究了JMatPro软件计算热力学数据的可靠性。在计算所得的热成形钢TTT曲线上读取其奥氏体化温度、最小临界冷却速度以及相变温度范围,与采用热膨胀仪测试所得钢的CCT曲线结果进行了对比分析,研究了添加Mo、V合金元素对钢组织和性能的影响。结果显示,JMatPro软件计算的奥氏体化温度和临界冷却速度与试验结果吻合度较好,预测的组织转变温度范围有微小偏差,表明JMatPro软件对B1800HS热成形钢的热处理方案制订有较高的提供指导。此外通过性能测试,确定多元钼钒微合金化可使试验钢拥有更加优异的综合服役性能。     

Mechanical and fracture characterization of a bi-material steel plate

Fracture behavior of a hot-rolled bi-material plate consisting of a substrate (low carbon ferritic–pearlitic steel) and a clad layer (austenitic stainless steel), has been investigated. Micro-hardness and tensile properties measured from the clad down to the substrate showed an abrupt change adjacent to the interface, due to a coarse grained soft ferritic band near the interface. Flat bi-material tensile specimens were tested and two formulae were established to correlate the relative thickness of the bi-material components to the tensile properties of the bi-material system. Crack tip opening displacement (δ₅) based R-curves of thick bi-material SENB specimens with a deep crack (a₀/W=0.50), located in both the substrate and the clad, are found to be similar to the curve of the homogeneous substrate. Thinner SENB specimens with a shallow crack (a₀/W≤0.20) located in the clad material, showed higher fracture toughness than homogeneous clad CT specimens, because of the lower strength substrate and shallower crack size. Studying cross-sections machined out from SENB specimens revealed crack deviation into the underclad soft coarse grained region band due to the strength mis-matching nature of the bi-material system.     

Field-dependent neutron depolarization study of the ferrite formation in medium-carbon steels

Neutron depolarization experiments have been performed on the ferrite and pearlite phase transformations of the medium-carbon C60 and C35 steels. The interaction of the polarized neutron beam with the ferromagnetic ferrite grains gives information on the mean magnetization and the magnetic correlation length. From these parameters the ferrite fraction and the mean ferrite grain size are determined in situ as a function of time and temperature during the phase transformations. The applied magnetic field was varied periodically in order to record a full hysteresis curve of the magnetization, which gives essential information on the microstructure of the ferromagnetic ferrite grains. The field dependence of the mean particle size during the early stages of the pearlite formation is a strong indication of multi-domain behavior, which is absent in the austenite–ferrite transformation and at the end of the pearlite formation.     

一种抗旋转的全息水印算法

为了找到一种能够抵抗旋转攻击的安全的水印算法,综合分析了常见的水印算法后,发现离散小波变换、离散余弦变换、奇异值分解的变换域水印能够较好地满足抗旋转攻击的需求。对水印图像进行了双随机相位全息加密,通过密钥保障水印的安全性,把加密的水印嵌入到变换域中。设计了试验,研究了含有水印的图像在平移、缩放、旋转、中值滤波、高斯噪声、椒盐噪声和压缩攻击下提取水印质量的影响。实验结果表明,水印能够抵抗常见的几何攻击,特别是旋转攻击,对常见的噪声压缩攻击同样有很好的效果。基于变换域的全息水印算法具有很好的鲁棒性,能够抵抗常见的几何攻击,具有很好的安全性,没有密钥不能对水印进行检测和去除。     

西气东输工程用大口径X70输气管线用板卷的研制

宝山钢铁股份有限公司开发研制的针状铁素体型X70大口径输气管线用板卷钢已应用于西气东输管线工程.与贫珠光体(含有少量的珠光体)组织类型的X70管线钢相比,新开发的针状铁素体型X70管线钢板卷在具有高强度的同时,具有更高的低温冲击韧性、低的韧-脆转变温度以及高的抗动态撕裂能力.其优良的性能得益于具有与细小析出相交互作用的高密度位错的超低碳针状铁素体组织.     

考虑应力比和门槛值的海水腐蚀疲劳裂纹扩展预测模型

采用自行改造的海水腐蚀疲劳试验机,研究了3 Hz频率、不同应力比R(0.1、0.3、0.5)下,海洋工程用结构钢DH36Z35在空气和人造海水中疲劳裂纹扩展动力学行为.结果 表明:相同裂纹尖端应力场强度因子幅值△K下,空气和海水环境中都显示疲劳裂纹扩展速率随着应力比R的增加而增加的规律,在近门槛值区间1×10-7 mm...     

980 MPa先进高强钢材料在门槛加强梁上的辊压应用

目的为获得980 MPa级别不同先进高强钢材料在辊压零件上应用时的差异,研究典型980 MPa先进高强钢的辊压成形特性。方法采用调研和统计方法获得门槛辊压用材的主流强度与钢种,基于三点弯曲的实验方法,获得了980 MPa先进高强钢材料在指定角度和弯曲半径下的回弹特性,针对典型的门槛加强梁零件,采用CAE方法评估材料应用的可行性。结果门槛零件980 MPa级别所采用的主要先进刚强钢钢种为双相钢(DP)和马氏体钢(MS),在相对弯曲半径比R/t=2.5的情况下,980DP回弹角度最小,980QP次之,980MS最大;早期模具回弹补偿设计时对于90°圆角可给予11°~14°的回弹过弯角度;成形过程中有可能出现边波缺陷,需优化辊压成形变形过程。结论 980 MPa先进高强钢材料在应用于辊压零件时,应在设计阶段充分考虑材料回弹特性,同时变形过程应合理,避免产生边波等质量缺陷。     

Internal friction associated with dislocation relaxations in virgin martensite—I. Experiments

Four internal friction peaks were observed during heating of virgin lenticular martensite from 82 to 350 K. Investigations on the effect of alloying contents and test conditions on the internal friction peaks have shown that there are three internal friction peaks exhibiting relaxation features, and can be attributed to the dislocation relaxation processes. Two of them have been related to the generations of kink-pairs along non-screw and screw dislocations, and one is due to the interactions between non-screw dislocations and carbon atoms (for interpretation see Part II).