经济型双相不锈钢2101中氮化物在基体中的平衡固溶度计算

为了解析出物对经济型双相不锈钢2101热塑性的影响机制,对比了相同工艺下2101和2205双相不锈钢在热变形过程中相界析出物产生的规律.结果表明:2101钢比2205钢的相界处更倾向于产生析出物,促使后续热变形过程中相界产生裂纹,进而影响材料的热塑性.根据热力学相关数据,通过Thermo-Calc和实验测试数据,推导出2101和2205双相不锈钢析出物Cr₂N的平衡固溶度公式,计算实验钢中析出物Cr₂N的全固溶温度,同时引入Wagner相互作用系数,考虑了Ni、Mn、Mo和Si对固溶度积公式的影响.发现2101双相不锈钢中Cr₂N的全固溶温度比2205钢高100℃左右,计算结果和实验结果吻合较好.实际生产过程中必须控制双相不锈钢热轧的终轧温度到全固溶温度以上,否则相界容易产生氮化物析出,影响材料热塑性.      

含Nb不锈钢中厚板中间裂纹分层原因分析及控制

针对含Nb不锈钢热轧中厚板出现的中间裂纹分层以及力学性能不合问题,通过金相观察、扫描电镜、相分析和力学性能检测等手段对中间裂纹分层以及力学性能不合原因进行研究。结果表明,Mo、Nb在凝固过程中偏析严重、形成σ相和Z相(CrNbN)是产生热轧中厚板中间裂纹分层以及力学性能不合的主要原因。通过降低Nb含量,优化热处理制度,降低钢液过热度,确定合理冷却制度,添加电磁搅拌工艺,可以有效地减小中间裂纹分层的发生并提高低温冲击韧性。     

节镍型不锈钢冷轧表面短条状缺陷分析

对发生在节镍型不锈钢冷轧2B表面短条状缺陷进行显微结构、能谱分析,并结合其冶炼—热轧—冷轧—贯制生产工艺,得出缺陷的实质是热轧过程中咬入的氧化铁皮经过冷轧后的表现形式.通过对不同加热温度的统计对比、材料的热塑性分析以及热轧板氧化铁皮结构的分析,得出加热温度过高会影响材料的热塑性,导致加热和轧制过程出现微裂纹,热轧完成后演变为咬入式氧化铁皮缺陷.控制抽钢温度在1 215℃以下可以有效降低缺陷发生率.     

热轧出炉温度对IF钢r值的影响

通过控制热轧出炉温度控制Ti处理IF钢中TiC和TiN等析出物的分解,对热轧析出物形态、晶粒大小、再结晶温度、冷轧退火后性能均有显著影响.通过对罩式炉退火IF钢的再加热温度与r-的相关性进行统计分析,结果表明:热轧的出炉温度与罩式炉退火IF钢r呈负相关,在α=0.05时更明显.     

卷取温度对微合金化含磷钢薄钢板组织和性能的影响

以低碳微合金化含磷钢为研究对象,通过分析热轧态和冷轧退火态的显微组织和力学性能以及退火再结晶动力学行为,研究了卷取温度(600、650、700℃)对微合金化含磷钢组织和性能的影响.研究结果表明,热轧卷取温度对微合金化含磷钢的显微组织和力学性能有显著的影响,随着热轧卷取温度从700℃降低到600℃,试验钢退火再结晶受到明显延迟,再结晶激活能明显提高;卷取温度对热轧态和退火态铁素体晶粒尺寸影响较小,但热轧态强度随着卷取温度降低而提高;随着卷取温度的降低,冷轧退火态的强度提高,且力学性能对退火温度的敏感性增加.     

高氮不锈钢热轧开裂原因分析及工艺改进

采用显微电镜、扫描电镜对高氮不锈钢热轧后钢板开裂处的金相组织进行了观察,分析了钢板热轧开裂的原因,并对轧制工艺参数进行了优化。结果表明:钢中较多的σ析出相是钢板热轧开裂的主要原因,提高终轧温度后显著降低了钢板的轧制开裂倾向。     

非对称热轧单面不锈钢-碳钢复合板生产工艺研究

釆用“电子束真空焊接制坯+热轧”的工艺在钢厂热连轧生产线上进行了“316L不锈钢+Q345C碳 钢”的单面不锈钢复合板热轧生产。采用非对称制坯及异步轧制的手段生产出了高品质单面不锈钢复合板,所生 产的不锈钢复合板界面剪切强度大于320 MPa、屈服强度大于370 MPa、抗拉强度大于520 MPa、断后伸长率大于 30%,各项指标均达到GB/T8165-2008的要求。不锈钢层和碳钢层结合度良好,复合界面平直,无明显缺陷,不锈 钢与碳钢之间实现了良好的冶金结合,结合率达100% 。     

2205双相不锈钢热轧裂边成因分析与改善

论述了2205双相不锈钢热轧裂边问题与精炼炉添加高铅萤石有关,过量的铅元素残留于钢液中,导致钢坯热塑性恶化而产生热轧裂边缺陷,通过管控精炼炉所添加萤石中的铅含量,2205双相不锈钢热轧裂边问题得到有效解决。     

不锈钢热轧浊环水处理工艺设计

介绍宝钢集团上海五钢不锈钢长型材热轧工程浊循环水处理的工艺设计,探讨了采用化学除油工艺、自动反清洗过滤器等技术和设备处理不锈钢热轧浊环水的技术特点.     

影响超纯铁素体不锈钢钢包自开率的因素研究及改进措施

太钢南区在生产超纯铁素体不锈钢过程中出现自开率低问题,严重影响了铸坯成材率和生产顺行,针对该问题采取现场调研和数据分析,通过对炼钢过程时间、出钢温度、钢液流动性的研究,厘清了 自开率低主要原因:过程时间过长、出钢温度高、引流剂与工艺匹配性存在问题,通过采取优化钢包调度和钢种计划安排、控制出钢温度和优化引流剂产品性能,有效解决了超纯铁素体不锈钢钢包自开率低的问题.     

大尺寸钨镧块烧结分层机理探究

通过对大尺寸钨镧块进行4种不同工艺的烧结试验,对各个烧结坯料进行轧制处理,利用超声探伤仪、金相显微镜、SEM、EDS、ICP-AES等设备对烧结和轧制后钨镧块的密度、探伤、晶粒、弥散相、镧含量、杂质含量进行详细研究,探究大尺寸钨镧烧结层机理,并得出的结论为:升温速率快时钨镧块会出现烧结分层、整体密度低、轧制易开裂的现象;分层主要有3层:芯部层、中间层和外部层。平均晶粒尺寸、弥散相颗粒大小为中间层>芯部层>外部层。密度为外部层>中间层>芯部层。La含量为中间层>外部层>芯部层。出现该种现象的主要原因为升温速率快、内外温差大,通过减慢升温速率可以解决该问题。     

Delamination Buckling and Growth in Rings under Pressure

A delaminated composite ring under external pressure is studied to understand the effect of curvature on delamination buckling and growth. Examples with differing crack lengths and delamination locations were considered. In all cases, the delamination surfaces come in contact rather early in the loading history, no matter what the initial imperfections are assumed to be. Furthermore, the delaminated part never becomes separated from the main ring. The modes of buckling given by standard linear stability analysis do not play any role in the behavior. Strain energy release rates were computed with the objective of predicting possible crack growth. Because of the contact, total energy release rate is dominated by the shear mode. Because the critical values of energy release rates are generally much higher in the shear mode than in the opening mode, one may conclude that shells tend to be more delamination tolerant than plates in which the opening modes tend to dominate.     

Delamination Effect on Flutter of Homogeneous Laminated Plates

The effect of delamination on the flutter boundary of two‐dimensional laminated plates are investigated theoretically. Linear‐plate theory and qusai‐steady aerodynamic theory are employed. A simple beam‐plate‐theory model is developed to predict the flutter boundaries of delaminated homogeneous plates with simply supported ends. The effects of delamination position, size, and thickness on the flutter boundary are studied in detail. The results reveal that the presence of a delamination degraded the stiffness and the natural frequencies of the plate and thereby decreases the flutter boundary of the plate. However, for certain geometries the flutter boundaries were raised due to the flutter coalescence modes of the plate altered by the presence of a delamination in the plate.     

Stability Analysis of Composite Plates with Through-the-Width Delamination

In this paper, the compressive bucking and postbuckling behavior of composite laminates with through-the-width delamination are investigated. The analytical method is based on the first-order shear deformation theory, and its formulation is developed on the basis of the Rayleigh-Ritz approximation technique by the implementation of the polynomial series, which has been used for the first time in the case of the mixed mode of buckling. Both local buckling of the delaminated sublaminate and global buckling of the whole plate are investigated. Also, the contact among sublaminates is taken into account. The three-dimensional finite-element analysis is performed by using ANSYS5.4 general-purpose commercial software just to compare the finite-element method results with those obtained by the analytical model. It is noted that the significance and contribution of the current paper lies in the fact that for a rather complicated problem, very good results are obtained by using a fairly small number of degrees of freedom through the application of complete polynomial series.     

Delamination Characteristics around Hole in Laminates with Softening Strip

Graphite/epoxy laminates with and without a softening strip around a hole were investigated. The softening strip is a portion of the graphite critical ply, which is replaced by a glass/epoxy composite. Analysis was conducted with finite element methods: The in‐plane stress distribution was found using a planform two‐dimensional model and interlaminar stress distributions around a hole were obtained from a through‐thickness quasi‐three‐dimensional model. The variation of strain‐energy release rate for a delamination occurring at the critical interface was investigated. The finite element results indicate that the inplane and interlaminar stress distributions, as well as the strain‐energy release rates, are significantly reduced for laminates with a softening strip.     

Delamination Analysis for Laminated Composites. I: Fundamentals

Analytical models for the delamination of a class of composite laminates are developed. Two approaches are used in deriving the governing equations. The first approach follows a refined engineering bending theory that stems from the premise that the statically equivalent stresses obtained from classical theory can be used to estimate the strains ignored in the classical theory. The second follows a modified Donnell approach in which the stresses obtained from the classical engineering theory are improved by adding a series of corrections. These corrections are determined by satisfying the stress equilibrium and compatibility conditions of two‐dimensional elasticity theory. A comparison of the derived governing equations is provided in order to assess the consistency and accuracy of the engineering approach. The deformation modes associated with each model are identified. Interlaminar stresses predicted by the developed models for a quasi‐isotropic double cracked‐lap‐shear laminate are compared with finite‐element results.     

Delamination Analysis for Laminated Composites. II: Numerical Verification

A validation of the delamination analysis models developed in a companion paper is provided through comparisons of predictions with finite‐element and elasticity solutions. The models are applied to the analysis of composite compression specimens reinforced with end tabs. An elasticity solution for the gage section of the specimens is developed. A comparison of the characteristic roots shows that the predictions of the models include the material and geometric parameters that control the behavior, and the roots corresponding to the basic stretching and bending modes are accurately predicted. The stress distribution at the interface between tabs and specimen is in good agreement with a finite‐element simulation. The interlaminar shear and peel stresses show an exponential increase with a maximum intensity at the free edges of the tabs. The behavior of previously tested specimens is explained; and practical guidelines for specimen design are provided to avoid unwanted extraneous modes of failure. The influence of the deformation modes associated with each model is investigated. An assessment of the accuracy and level of complexity is presented.     

Nonlinear Fracture Analysis of Delamination Crack Jumps in Laminated Composites

As part of the quest to add the infraply scale to high-fidelity simulations of damage evolution in composites, a model of the phenomenon of delamination jumping across transverse plies is formulated by using nonlinear cohesive fracture models in the augmented finite element method (A-FEM). The nonlinearity of the fracture process zone and the interaction between multiple cracks combines to determine the details of how the delamination jump occurs. Simulations reveal that the jumping process starts with the triggering of a sequence of kinking cracks branching from the propagating delamination crack into the transverse plies. The first few kinking cracks arrest within the transverse plies just above the further interface because of the crack-retarding effects of the nonlinear process zone and the effects of material heterogeneity. Eventually, one kinking crack reaches the interface and initiates a new delamination crack, a step that is accompanied by a significant load spike. The competition between delamination and kinking cracks shows global-local coupling: kinking cracks are triggered when the local stress satisfies a critical condition, but a kinking crack does not reach the second interface and initiate the new delamination crack until the global energy release rate reaches the kinking crack toughness. This suggests that the jumping process is controlled more by deterministic load and geometrical factors than by stochastic flaw populations.     

Delamination Fracture Related to Tempering in a High-Strength Low-Alloy Steel

The delamination or splitting of mechanical test specimens of rolled steel plate is a phenomenon that has been studied for many years. In the present study, splitting during fracture of tensile and Charpy V-notch (CVN) test specimens is examined in a high-strength low-alloy plate steel. It is shown that delamination did not occur in test specimens from plate in the as-rolled condition, but was severe in material tempered in the temperature range 500 °C to 650 °C. Minor splitting was seen after heating to 200 °C, 400 °C, and 700 °C. Samples that had been triple quenched and tempered to produce a fine equiaxed grain size also did not exhibit splitting. Microstructural and preferred orientation studies are presented and are discussed as they relate to the splitting phenomenon. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating were responsible for the delamination.