成形工艺对冷弯方管残余应力及焊接微观组织的影响

冷弯方管成形有"直接成方"和"圆成方"两种方式。为了研究成形工艺对于产品的不同影响,以规格为100mm×100mm×6mm,材料为Q235的两种成形工艺的方管为研究对象,采用钻孔法对方管各个部位的残余应力进行了测量,并观测了焊缝处的显微组织。研究结果表明,不同成形工艺对纵向残余应力的分布影响较大,焊缝处的残余应力最大。"圆成方"过程中施加较大的焊接压力使得其焊接热影响区宽度小于"直接成方"工艺条件下焊接热影响区的宽度,且抑制了奥氏体晶粒长大,冷却后获得较为细小均匀的晶粒。     

成形工艺对冷弯方管残余应力及焊接微观组织的影响简

 冷弯方管成形有“直接成方”和“圆成方”两种方式。为了研究成形工艺对于产品的不同影响,以规格为100mm×100mm×6mm,材料为Q235的两种成形工艺的方管为研究对象,采用钻孔法对方管各个部位的残余应力进行了测量,并观测了焊缝处的显微组织。研究结果表明,不同成形工艺对纵向残余应力的分布影响较大,焊缝处的残余应力最大。“圆成方”过程中施加较大的焊接压力使得其焊接热影响区宽度小于“直接成方”工艺条件下焊接热影响区的宽度,且抑制了奥氏体晶粒长大,冷却后获得较为细小均匀的晶粒。     

厚壁冷弯型钢残余应力分布的实验研究

冷作加工带来的冷加工残余应力的大小、沿截面分布状况、不同加工方式对残余应力的影响、残余应力自然时效情况以及如何高效低能去除残余应力等,对冷弯型钢产品能否应用到重大工程有至关重要的影响。尽管国内冷弯型钢厂生产冷弯方矩管、冷弯槽钢等冷弯产品已有不短的历史,但对产品的上述情况还不精确了解,导致长期供货中低端市场。为了探知以上问题,提高产品质量,合理使用产品,有效制定去除永久残余应力的消残制度,采用X-射线衍射法对国内某厂典型产品冷弯残余应力沿壁厚的分布情况进行了实验测量,获得了一些极其有价值的数据。     

激光选区熔化非实体支撑薄壁曲面特征变形规律研究

激光选区熔化（SLM）成形工艺正越来越广泛应用于航空航天装备复杂构件制造,该类零件具有众多薄壁类曲面特征,成形制造中残余应力较大、曲面特征变形问题突出,严重制约增材制造薄壁曲面构件的成形精度和质量。针对非实体支撑薄壁曲面特征激光选区熔化成形,通过模拟仿真研究了非实体支撑的工艺参数和几何特征对支撑连接情况的影响,基于此分析了非实体支撑下曲面特征的残余应力分布与变形规律。采用热弹塑性法对不同支撑成形激光功率和支撑结构下非实体支撑连接情况进行模拟仿真,以连接效果为目标优选支撑参数。应用优选支撑参数,基于固有应变模型对不同壁厚和成形高度的薄壁曲面特征的残余应力和变形分布进行模拟仿真、实验验证与讨论分析。结果表明,优选非实体支撑的薄壁曲面零件的局部变形得到明显改善,薄壁曲面零件残余应力分布主要受零件的Z向正应力影响,且随零件厚度增加而增加。     

机械加工对粉末冶金铍材表面残余应力的影响

铍具有低密度、弹性模量高的特性，常用于航天结构件。粉末冶金铍材在机械加工时，表面会产生残余应力，对铍结构件的尺寸稳定性和使用寿命造成直接影响。因此，使用X-ray衍射仪测量铍材表面残余应力，测量了粗车、精车、时效工艺下残余应力沿表面的分布情况；进一步研究了不同机加工艺对铍材表面残余应力影响。结果表明，机械加工时，粉末冶金铍材残余应力均表现为压应力；残余应力与加工线速度负相关，与进刀量正相关，时效处理可有效降低铍材表面残余应力，还能有效提高残余应力的均匀性。     

湿法喷丸处理YG8合金表面残余应力分析及对性能的影响

采用湿法喷丸工艺对YG8硬质合金进行表面处理,旨在提高材料的性能.通过X射线衍射法对不同喷射条件处理的合金表面残余应力及其深度分布进行了分析,并研究了残余应力对力学性能的影响.研究表明,湿法喷丸处理在硬质合金表层内产生残余压应力,喷射压力和喷射时间对残余应力及分布有显著影响,该应力及分布有利于材料性能的提高.应用该处理方法,在喷射压力为0.5MPa、喷射时间为2min的条件下,硬质合金的抗弯强度提高约11%,洛氏硬度为89.64HRA,磨损量减少36%.     

考虑残余应力的船舶强度校核分析方法

船舶进行结构设计时,通常是按照外载荷计算结构强度,并按照规范许用应力校核结构的安全性,并未考虑船舶各个构件在加工成形、焊接、装配等过程中产生的残余应力的影响.为此,对一艘VLCC油船在常见工况下加入大小不同残余应力的强度校核方法进行研究,得到各主要构件应力分布受残余应力影响的规律.结果表明,有必要在船体强度校核中考虑工艺残余应力的影响.     

大型H型钢水平矫直压下量的优化

在型钢矫直过程中,矫直机各矫直辊压下量直接影响型钢的残余应力及弯曲度,为了减少残余应力及弯曲度,达到国家标准,文章对矫直工艺开展了正交实验仿真,根据实验,得出各工作辊对型钢残余应力和弯曲度的影响,从而找出矫直型钢时压下量的最优方案。     

环形薄壁类粉末冶金零件压坯残余应力分析

针对环形薄壁类粉末冶金零件压坯的残余应力进行分析,采用修正的Drucker-Prager Cap弹塑性本构模型对金属粉末压坯压制、卸载和脱模过程进行数值模拟,同时考虑不同零件压坯几何参数(高径比和厚径比)以及压制工艺条件(摩擦条件和脱模角度)对压坯内残余应力的影响.研究结果表明,压坯脱模后的残余应力分布规律是压坯侧表面出现明显的压应力层,内部为拉应力区域,且越靠近压坯中心值越小.随着高径比和厚径比的增加,其残余应力逐渐减小;随着摩擦系数的增加,压坯表面的轴向残余压应力不断增大且压坯内部的拉应力也不断加大;适当增加脱模角度有利于压坯内应力释放而减小残余应力.通过正交模拟试验及方差分析可知,厚径比和脱模角度对金属粉末成形脱模后压坯残余应力影响更为显著.     

激光多点冲击Zr基非晶合金残余应力研究

为了实现非晶合金大面积均匀应力强化,采用有限元数值模拟方法研究了激光多点冲击诱导Zr基块体非晶合金的表面残余应力场,得到了不同工艺条件下表面残余应力分布规律。结果表明,经激光冲击强化处理后,非晶合金表面形成了一定深度的残余压应力,然而,残余压应力的大小和均匀性受激光多点冲击工艺参数(相邻光斑中心距、搭接率和冲击波峰值压力)的显著影响;相邻光斑中心距对激光冲击区域的残余压应力影响较小,而光斑之间区域的残余压应力随光斑中心距的减小发生显著变化,其值逐渐增大;相邻光斑搭接冲击时,随搭接率的增加,非晶合金表面形成的残余压应力增大,且均匀性得到提高,搭接率相同时,搭接冲击排数对残余压应力并无明显影响;冲击波峰值压力越大,非晶合金表面残余压应力越大,但应力分布越不均匀,而且冲击区域凹凸不平的微凹坑形貌越明显。     

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MS980 is one of advanced high-strength steels, which has a great potential for producing square tubes. Residual stress plays a significant role in determining roll-formed members?? behavior and strength. An experimental study on transverse residual stress of roll-formed shape with square section was conducted via X-ray diffraction method. The distribution of transverse residual stresses at different position in sections was measured and studied, and influence of cold-rolled-sheet and hot-rolled-sheet, different fillet radius, different processes, and different pickling time on circumferential residual stress distribution for square section was investigated. The experimental results show the transverse residual stresses are compressive stress in the corner portion and the tensile stress in the straight edge. Fillet radius, sheet, and process have a significant impact on the distribution of residual stress, but the conventional pickling hardly affects residual stress.     

Residual stresses in rails due to roll straightening

The knowledge of residual stresses in rails due to roll straightening has become increasingly important for the evaluation of the fatigue behaviour of rails. The residual stresses are induced both by the bending process and the roll contact leading to a very complicated distribution especially near those parts of the surface where the roll contact had taken place. So far, no clear picture has emerged with respect to the residual stress field, either from experiments or from simulations. This study intends to clarify the residual stress distribution by simulation with a fully three-dimensional model taking into account both the bending and contact process. This work shows that especially in those areas where the roll contact happens compressive residual longitudinal stresses appear on the surface. Furthermore, a very steep gradient of the residual longitudinal stress distribution near the surface is observed which is reported also in very recent X-ray and neutron diffraction experimental investigations.     

局部感应加热对高强钢方管二次辊压成形的影响

本文通过对高强钢方管角部进行局部感应加热,提高其弯角区域的成形性能,降低其变形抗力,由此在不影响非变形区域组织性能的前提下,获得所需方管的截面尺寸和组织性能.在热辊压过程中,坯料在没有模具限制的方管角部外侧邻近区域发生堆积,且随着加热温度上升,角部外侧金属堆积更明显.同时,在方管内角表层出现显微裂纹恶化,裂纹以树枝状生长.热辊压成形后的残余温度会产生一个自回火过程,能够明显降低残余应力,且随着温度的升高,残余应力降低的幅度变大.当加热温度在650℃以上时,自回火对残余应力的影响大于宏观裂纹的扩展能力,起主导作用,且压扁过程中压下量超过方管对角线长度2/3时也不会产生裂纹.      

用发展的Sachs法研究模拟轧辊中的残余应力

对不同辊型，尺寸，材料与加工处理方法的模拟冷轧辊进行了内剥层试验研究，求出了原辊和打中心孔或扩孔后辊内残余应力分布曲线，提出了虚拟打孔法和虚拟剥层法，解决了实心辊中心和空心辊内表层的残余应力的精确测量问题，丰富了Ｓａｃｈｓ内剥层法的内容，机械法打中心孔，热处理前打中心孔，空心辊表淬前改变温度场的方法可降低残余应力值，后者降低残余应力的效果尤为显著。     

Temperature and thermal stresses in work rolls during the hot rolling of strip

In this paper the solution of the unsteady, three-dimensional heat transfer in work rolls was derived by using Bessel functions and the δ-function and expressed by an infinite series. In this manner other problems of heat transfer in solid cylinders and hollow cylinders can also be calculated. The temperature profile of the work roll due to the distribution of the temperature in the axial direction can cause unregular pressure distribution between work roll and backup roll and can influence the quality of strip. Therefore, the thermal crowns must be considered at various moments during rolling. The thermal crown can be determined by using the FE-Method or others. The reason for the fire-cracking in the roll surface can be determined as the thermal shock load in the contact zone, in which the sharp compressive stresses lead to local plastic deformation. The local plastic deformations are followed by residual deformations. Therefore, residual tensile stresses occur in the cooling zone. On each revolution, the surface undergoes plastic strain in compression and in tension. The result is thermal fatigue. The fine network of cracks in the roll surface can result in a sharp stress concentration which is dangerous for the rolls loaded with a bending moment. The maximum tensile stresses due to the temperature distribution occur in the roll core, which usually do not lead to damages of the rolls.     

热成形温度对高强钢方管组织及性能的影响

为了克服传统辊弯工艺和设备对室温下高强钢的影响,提出弯角局部感应加热辊压成形工艺制备高强钢方管,并通过单向拉伸试验、断口形貌观察、微观组织扫描电镜观察和X射线衍射分析研究热辊压成形温度对高强钢方管弯角处组织及力学性能的影响.结果表明,随着温度的升高,弯角力学性能得到明显的改善,断口形貌由室温下解理断裂逐渐过渡为韧性断裂,弯角处微观组织由板条状贝氏体向粒状贝氏体发展且多边形铁素体晶粒开始长大,方管外表面周向和纵向残余应力都明显降低且分布更加合理.综合实验分析,高强钢方管热辊压成形工艺的最佳温度为650℃.      

低压等离子喷涂耐高温涂层残余应力检测及分析

采用低压等离子工艺制备耐高温可磨耗涂层,通过光学显微镜观察了耐高温涂层的显微结构,采用逐层法与曲率法相结合的检测技术,对不同厚度涂层残余应力进行检测,形成了涂层厚度与残余应力分布及趋势图,运用热处理技术控制和消除涂层内部残余的涂层应力。结果表明,低压等离子喷涂的耐高温涂层表面残余应力随着涂层厚度的增加而增大,当涂层厚度达到0.6mm左右极限时,涂层会发生自然开裂,采用热处理的工艺方法可以减少涂层内的热应力导致的涂层残余应力。     

Numerical Simulation of Continuous Tension Leveling Process of Thin Strip Steel and Its Application

 Cold rolled thin strip steel of high flatness quality undergoes multistage deformation during tension leveling. Thus, the parameters of set up and manipulating are more difficult. With the aid of FE code MSCMARC, the tension leveling process of thin strip steel was numerically simulated. Concentrating on the influence of the roll intermeshes in 2# anti cambering on the distribution and magnitude of residual stresses in leveled strip steel, several experiments were done with the tension leveler based on the results from the simulation. It was found from the simulation that the magnitude of longitudinal residual stresses in the cross section of the leveled strip steel regularly presents obvious interdependence with the roll intermeshes in 2# anti cambering. In addition, there is a steady zone as the longitudinal residual stresses of the surface layers in leveled strip steel vary with the roll intermeshes of 2# anti cambering, which is of importance in the manipulation of tension levelers. It was also found that the distribution of strains and stresses across the width of strip steel is uneven during leveling or after removing the tension loaded upon the strip, from which it was found that 3D simulation could not be replaced by 2D analysis because 2D analysis in this case cannot represent the physical behavior of strip steel deformation during tension leveling.     

Modeling of microstructure and residual stress in cast iron calender rolls

A comprehensive mathematical model based on the commercial finite-element (FE) code ABAQUS has been developed to predict the evolution of temperature, microstructure, and residual stresses in cast iron castings. The thermal component of the model, applied in stage one of the analysis, is capable of simulating the formation of microstructure over a broad range of cooling conditions, including the formation of columnar white iron as well as equiaxed gray iron. To test the model, it has been evaluated against thermocouple and microstructural data collected from a reduced-scale calender roll test casting. The model has been demonstrated to be able to predict the transition from columnar white iron to equiaxed gray iron which occurs approximately 20 mm below the outside surface of the roll test casting. In addition, the model is shown to be able to satisfactorily reproduce the evolution of temperature recorded from thermocouples embedded at various locations in the test casting. An elastic-plastic stress analysis, applied in the second stage of the analysis, was performed using the temperature history and the volume fraction of white and gray iron obtained with the thermal/microstructural model. The results were verified against residual stress measurements made at various locations along the outer-diameter (OD) surface of the roll. The elastic-plastic model accounts for the temperature-dependent plastic behavior of white and gray iron and the thermal dilatational behavior of white and gray iron, including volumetric expansion due to austenite decomposition and dilatational anisotropy in columnar white iron. The results of the mathematical analysis demonstrate that the residual stress distribution in full-scale calender thermorolls cannot be deduced simply from knowledge of the microstructural distribution and basic dilatometric considerations, as is currently the practice in industry.