白点的判据方法研究

最近几年,由于诸多原因,有时在盘环件低倍检验试样面上发现白点裂纹,低倍断口与力学性能检验结果均正常.取试样复验,低倍白点裂纹及断口白亮斑时有时无,裂纹性质难以确认.采用调质断口、缓慢拉伸、金相及蚀坑四种方法对疑白点裂纹的判定方法进行了研究.结果表明虽然调质断口法能判定白点,但是确认率不高;缓慢拉伸法不仅能判定白点,而且还能表明材料的原始状态且准确性较高;金相法是判定白点缺陷的一种简便方法;蚀坑法能反映白点断裂的晶体学取向关系,是研究白点判据的一种辅助手段.     

铁素体钢中白点缺陷的检验分析

 通过金相显微镜、扫描电镜等分析方法对铁素体钢低倍检验后发现的疑似白点缺陷进行了分析判断,发现疑似白点缺陷在金相显微镜下呈锯齿状裂纹,为白点裂纹形貌特征。通过对低倍试样上断口的检验发现,低碳铁素体钢宏观断口处分布有银灰色圆形斑点,为白点缺陷特征,铁素体不锈钢宏观断口无明显白点特征,但铁素体不锈钢的疑似白点显微断口有沿晶断裂和以夹杂物为裂纹源的解理断裂两种,都具有氢脆断口特征,由此判断,两种铁素体钢中缺陷均为白点缺陷。铁素体不锈钢中的白点缺陷与常见白点断口上的浮云状、波纹状、解理羽毛、显微疏松等形貌特征有所不同,而且不同铁素体不锈钢试样上的白点缺陷断口形貌也不同,一处为沿晶断裂,一处为以夹杂物为裂纹源的解理断裂。     

车轮低倍白点的确认

白点是破坏性极大的低倍缺陷。作为钢中的显微裂纹,白点可能成为疲劳裂纹源,降低钢的强度。为此,正确判断白点是车轮低倍生产检验中非常关键的一环。     

65Mn环件断裂的失效分析

65Mn环件装配后发生崩裂,采用断口分析、化学成分分析、金相分析及低倍分析等方法进行了失效分析。结果表明,环件中存在白点,白点在装配应力和内部氢压的作用下发生滞后扩展,当白点裂纹长大到临界尺寸时,裂纹尖端的应力强度因子达到断裂韧性,从而发生崩裂。     

低碳低合金钢板白点缺陷的检验和研究

应用超声波探伤，低倍，宏观断口，金相和扫描电镜检验方法，对低碳合金钢板中白点缺陷进行了检验和研究。详细介绍了钢板中白点缺陷的宏观特征和遭到同特征和微观貌及消除措施。     

钢中白点及其形成机理

白点是热轧钢坯和大型锻件中比较常见的低倍缺陷。白点的破坏性极大，作为钢中的显微裂纹，可能成为疲劳裂纹源，降低钢的强度。为此，研究了钢中白点的形成机理，找出消除白点的根本措施。     

钢中白点特征及形成机理的研究

白点是钢中比较常见的低倍缺陷。白点作为钢中的显微裂纹,很可能成为疲劳裂纹源,降低钢的强度。为此,探讨了钢中白点的特征和形成机理,提出了消除白点的根本措施,以改进其机械性能,提高产品质量。     

车轮钢中的白点(一)

研究了车轮钢中白点形成的机理以及白点对断口形貌的影响.结果表明,氢和空位聚集导致鼓泡形核和长大,随着鼓泡内氢气压力的升高,裂纹从鼓泡核壁形核、扩展导致白点形成.白点的断口为准解理,和氢致滞后开裂断口相同,含白点试样的断口形貌依赖于断裂方式和试样厚度.钢中的白点除了产生二次裂纹和局部准解理断面外,对各种断口形貌均没有明显的影响.     

40CrMo大截面锻材内裂探讨

对42CrMo大截面锻材的低倍检验,发现锻材的中心裂纹其实是白点,经采用去氢退火工艺后,白点消除,锻材探伤合格率、成材率明显提高。有电弧炉单炼,钢锭锻造由Φ250以睛的钢材时,去氢退火应是保证钢材内部质量的有效手段。     

车轮轮毂用钢开裂分析

主要对本钢产的车轮轮毂用钢BG420CL钢在冲压成型过程中出现的开裂进行了研究，通过低倍检验、金相检验及扫描电子显微镜断口观察发现钢板冲压开裂是连铸坯表面的裂纹缺陷残存在成品表面形成裂纹源而引起的。     

风电用行星轮轮齿开裂原因分析

某风电齿轮箱在运行3年6个月后监测到运行异常,拆解后发现其中一个行星轮发生断齿失效。实验通过对行星轮断口宏微观形貌分析、化学成分分析、力学性能分析、金相组织分析、残余应力分析和晶粒分布分析等,确定了行星轮轮齿的断裂原因。分析结果表明,行星轮材料母材各化学元素含量及轮齿表面碳元素含量均满足标准规范要求。行星轮轮齿力学性能满足标准规范要求,轮齿渗碳层金相组织和行星轮母材金相组织均未见异常,表明行星轮渗碳工艺和热处理工艺均满足材料使用要求。轮齿断口起裂源区存在大尺寸非金属夹杂物的聚集是运行过程中在该处萌生裂纹并扩展的主要原因。     

中厚钢板探伤不合格的原因及预防

针对邯钢Q345RT中厚板生产中出现的钢板探伤不合格缺陷,并且在钢板缺陷处取样,断口有时存在层状现象.采用化学分析、气体含量检验、铸坯低倍检验、金相组织分析和扫描电镜、断口形貌分析等方法,分析钢板探伤不合格的原因.结果表明：铸坯中心偏析严重,因偏析产生的少量马氏体、贝氏体组织导致轧后应力集中,在冷却速度较快的条件下钢板产生微裂纹,以条状MnS和CaO-A12O3为基体的硫化物夹杂和硅酸盐类夹杂物较高,铸坯中氢含量偏高引起氢致裂纹,均可导致钢板探伤不合格.通过控制炼钢工艺过程,减少了铸坯中的夹杂物和氢含量,该中厚板探伤合格率由92％提高到98.2％.     

Q460C中厚钢板伸长率不合格的原因分析

针对热轧Q460C中厚钢板在拉伸试验中出现伸长率不合格的问题,通过对拉伸试样断口形貌、断口区域的金相组织以及低倍硫印检验分析,认为钢板中夹杂物含量较高、中心偏析、中间裂纹和板材带状组织是导致伸长率不合格的主要原因,并提出相应解决措施。     

Stress corrosion cracking of alpha brass in a tarnishing ammoniacal environment: Fractography and chemical analysis

Alloy 260 brass specimens under stress were exposed at room temperature to 15 N aqueous ammonia solution with 8 g/1 of cupric copper predissolved. This environment causes tarnishing of the brass surface and intergranular stress corrosion cracking. Scanning electron microscopy, energy dispersive X-ray analysis, and Auger electron spectroscopy were employed to study fractography, corrosion product composition and distribution within the stress corrosion crack, and fracture surface chemistry characteristic of stress corrosion cracking in this system. A thin oxidized film was detected by Auger spectroscopy at the leading edge of the propagating crack. With continued exposure to the corrosive environment, deposits form on the fracture surface, then coalesce to form a continuous tarnish film that is depleted of zinc. No bulk depletion of zinc was detected in the alloy at the stress corrosion crack leading edge. No evidence of noncrystallographic crack arrest marks was found on the intergranular fracture surface.     

40Cr汽车钢板U型螺栓调质开裂原因分析

在汽车钢板u型螺栓生产过程中,调质后发现工件都有纵向开裂现象,造成产品报废。本文对报废产品取样进行了化学成份、金相高、低倍、硬度等项目的检测分析。分析发现螺栓用原材料工件为∮28mm正是处于最危险淬裂尺寸范围,其化学成份碳、锰、铬等元素均处于标准要求的上限,从而提高了其淬透性,在淬火冷却时,表面拉应力超过材料的断裂强度造成开裂。     

热拔工艺对高氮无镍奥氏体不锈钢线材开裂的影响

在开发一种高氮无镍奥氏体不锈钢线材时,热拔线材表面出现了大量的裂纹。通过金相、扫描电子显微分析和能谱检测,对其开裂原因进行研究。发现线材的表面裂纹基本垂直于拉拔方向,裂纹在表面产生,之后向线材内部发展。线材表层存在着大量的富Cr和N的氮化物析出,沿晶析出的析出相,会导致孔洞形成,这些孔洞相连,形成微裂纹,最终导致沿晶开裂。通过加长加热区、提高拉拔速率保证了线材表面温度,避免了表面裂纹的产生,获得了质量满足要求的高氮无镍奥氏体不锈钢线材,并最终给出了建议的热拔工艺。     

Equilibrium and growth characteristics of hydrogen-induced intergranular cracking in phosphorus-doped and high purity steels

By means of fracture mechanics analyses, acoustic emission techniques, and fracture surface analyses by scanning Auger microscopy and X-rays, it was determined how segregated phosphorus, yield strength and grain size affect the equilibrium and growth characteristics of hydrogen-induced intergranular cracking in high strength steels. The effect of yield strength on the threshold stress intensity was found to be greater than those of phosphorus segregation and grain size. The intergranular phosphorus segregation greatly accelerated the growth rate of hydrogen-induced intergranular cracking and caused a large number of acoustic signals to be emitted during the crack growth. The crack growth rate increased in a steel with segregated phosphorus and slightly decreased in high purity steels, where only occasional acoustic emissions were measured during the cracking process, by increasing grain size. Fracture surface analyses indicated more featureless intergranular fracture facets and higher levels of residual strain in the lattice adjacent to the fracture surface in the phosphorus-doped steel than in the high purity steels. These results suggest that while in steels with segregated impurities the macrocrack tends to grow by discretely rapid formation of intergranular microcracking which gives rise to dislocation emissions at the growing crack tip, in high purity steels slow growth of intergranular microcracking proceeds which is accompanied by either the absence or substantial mitigation of dislocation generation at the crack tip.     

480QZ汽车传动轴钢管开裂原因分析

采用化学成分分析、力学检测、宏观和微观断口分析、金相检测分析了480QZ汽车传动轴管开裂原因。结果表明。轴管上的平衡块贴片焊接区存在的马氏体组织和明显的焊趾表面应力集中是导致传动轴管开裂的主要原因。     

Crystallographic study of fatigue cracking in Ni3Al(CrB) single crystal

The effect of crystallographic orientation on the fatigue-crack initiation and propagation in Ni₃Al(CrB) single crystal was studied using a compact-tension specimen. Stage I crystallographic cracking and cleavage fracture were observed. Crystallographic cracking can occur on two or more {111} slip planes simultaneously. It was shown that the threshold stress intensity for crack initiation from the notch root exhibits a dependence on crystallographic orientation. In addition, an effect of orientation on microcracking behavior was also shown. The number of {111} planes intersecting with each other determines the different microscopic features on the cleavage fracture surface.     

The effects of environment on the elevated temperature fatigue behavior of nickel-base superalloy single crystals

The effects of air and vacuum on the fatigue behavior of a nickel-base superalloy, Mar-M200, in single crystal form were investigated. Between 800° and 1400°F fracture is entirely in the Stage I mode in air and vacuum, and fatigue life is unaffected by environment. At 1700° F in both environments, fracture is predominantly in the Stage II mode and fatigue life in air is greater than that in vacuum. At both temperatures, fatigue cracking in air is internally initiated, whereas in vacuum cracking is generally initiated at the specimen surface. Identical fatigue lives in air and in vacuum between 800° and 1400° F are attributed to the fact that internally initiated cracks in air are actually propagating in a high vacuum, surface cracking being inhibited by dynamic oxidation of emerging surface slip offsets. The subsurface portion of the Stage I fracture surface produced in air tests and all of the Stage I fracture produced in vacuum tests shows a dimpled structure, whereas the Stage I fracture surface produced while the crack propagation is in air shows a cleavage appearance. At 1700° F, bulk oxidation of surface initiated cracks interferes with the plastic blunting mechanism of Stage II crack growth normally observed at this temperature, internally initiated cracks causing ultimate failure. Shorter lives in vacuum are thought to result from enhanced Stage II surface crack propagation. Formerly with Materials Engineering and Research Laboratory, Pratt and Whitney Aircraft, Middletown, Conn.