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对含Nb、Ti船板钢的中板表面微裂纹进行了试验研究,结果表明:中板表面微裂纹不是轧制时新产生的裂纹,而是由坯料裂纹扩展形成的,轧制过程中对裂纹有延伸作用,影响裂纹形核的主要因素有钢中C、P、S、Nb、Al含量和各种应力。 相似文献
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降低含铌低合金钢铸坯的裂纹敏感性,是实现热装热送工艺的必要条件,采用超高温激光共聚焦显微镜(HT-CLSM)、透射电镜(TEM)等手段研究了钛含量不同的含铌低合金钢(Q390、Q390GJD)高温铸坯的晶粒度及析出物特征,旨在揭示微钛固氮降低含铌钢皮下裂纹敏感性的机理。热力学计算与TEM检测结果表明,增加钢中钛质量分数(由0.010%上升到0.023%)提高了氮化钛粒子的析出温度(大于1 400 ℃),高温析出细小弥散的氮化钛粒子可钉扎奥氏体晶界,细化高温铸坯的晶粒度(由4级变成6.5级),晶粒尺寸降低了约44%,使高温铸坯的裂纹敏感性明显降低;氮化钛粒子优先析出固氮降低了铌碳氮化物、氮化铝的开始析出温度,并作为异质形核核心,抑制了铌、铝析出物在晶界析出概率,降低了析出物脆化晶界的危害。通过微钛固氮调控氮化物的析出温度、析出位置及细化晶粒的作用,有效降低了含铌钢第三脆性温度槽的宽度和深度,同时,高温抗拉强度提高了21.3%~27.5%,铸坯皮下裂纹发生率降低了80%以上。为了避免析出物的晶界链状析出导致含铌钢铸坯热装轧制裂纹,应将其钛质量分数控制在0.015%~0.020%的合理范围。 相似文献
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本文以新型的含铌高强细晶IF钢为研究对象,在实验室进行了热轧、冷轧以及轧后模拟连续退火实验。通过微观组织观察可以发现化学成分的改善、轧制及退火工艺的控制不仅可以使这种钢具有细小的晶粒,而且存在大量细小的析出物Nb(C、N);同时晶界附近析出物非常稀少,称之为PFZ带(晶界无析出物区),且仅存在于晶界的一侧。实验结果表明由于Nb系析出物非常细小以及晶粒细化作用使实验钢具有较高强度和良好的延伸率;而PFZ带的存在,这种钢具有较低的屈服强度。与传统的IF 钢相比,实验钢具有晶粒细小、屈强比低、延伸率良好且塑性应变比r值较高的特点。 相似文献
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为了研究Ti-Zr微合金钢轧制变形过程中变形温度和Zr含量对内部应力应变的分布及奥氏体组织演变的影响,通过热模拟实验和金相分析获得3种不同Zr含量的Ti微合金钢应力应变曲线及奥氏体的晶粒尺寸及分布情况。研究结果表明:变形温度的升高会降低3种实验钢的内部应力,促进应力均匀分布,其中0.12Ti-0.02Zr钢应力下降的最明显,Zr的加入会促进Ti微合金钢再结晶奥氏体的形核和形变诱导析出相的析出,形变储能消耗量增大,不容易在变形过程中积累应力和应变;但过多的Zr会因为大量析出相而使实验钢的变形抗力增大,导致应力和应变累积。综合考虑,使用Ti-Zr复合微合金化技术实现奥氏体组织的超细化均匀时,Zr元素的添加量应控制在0.02%左右。 相似文献
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为实现低合金钢宽厚铸坯的直装轧制,结合生产实际,选取Q345B钢为代表钢种,以入炉前铸坯表面温度为参数,分3个温度区域进行直装工艺研究,结果发现低温区和高温区直装轧制钢板裂纹较少,中温区直装轧板裂纹的较多,这是由于γ晶界析出的先共析铁素体(α相)网膜造成;对低温区直装轧制钢板冷弯裂纹进行了检验分析,发现钢板内带状组织、MnS夹杂是产生裂纹的重要原因;分析铸坯金相组织控制、夹杂物控制、析出物控制对直装轧制钢板质量的影响,直装工艺要避免铸坯的金相组织进入两相区,避免γ晶界析出先共析铁素体(α相)网膜,生产中应尽可能降低硫含量或添加一定量的稀土元素以改变MnS夹杂的存在状态,调整微合金元素含量,以保证充分发挥微合金元素的强化作用。 相似文献
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连铸坯裂纹成因及预防 总被引:2,自引:0,他引:2
梁伟红 《金属材料与冶金工程》2002,(1):28-31,42
分析了钢的高温力学性能和作用在连铸坯上的各种应力以及化学成分对铸坯产生裂纹的影响,指出裂纹产生的外因是钢水的静压力,热应力,组织收缩应力和其它外力的作用,当这些应力之和超过了钢的高温临界强度和变形量时,就在凝固前沿或凝固壳中产生裂纹,在二冷区凡是增加共内应力,降低强度和塑性的因素将促进裂纹的发生和扩展,裂纹产生的因是钢的高温力学性能和化学成分,提出了防止连铸坯产生裂纹应从两方面考虑,一是工艺参数和设备运转状态,设法降低连铸坯承受的应变和应变速率,二是钢的化学成分,提高钢水纯净度。 相似文献
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Microstructure and Cyclic Deformation Behavior of a Friction-Stir-Welded 7075 Al Alloy 总被引:1,自引:0,他引:1
Microstructural changes and cyclic deformation characteristics of friction-stir-welded 7075 Al alloy were evaluated. Friction
stir welding (FSW) resulted in significant grain refinement and dissolution of η′ (Mg(Zn,Al,Cu)2) precipitates in the nugget zone (NZ), but Mg3Cr2Al18 dispersoids remained nearly unchanged. In the thermomechanically affected zone (TMAZ), a high density of dislocations was
observed and some dislocations were pinned, exhibiting a characteristic Orowan mechanism of dislocation bowing. Two low-hardness
zones (LHZs) between the TMAZ and the heat-affected zone (HAZ) were observed, with the width decreasing with increasing welding
speed. Cyclic hardening and fatigue life increased with increasing welding speed from 100 to 400 mm/min, but were only weakly
dependent on the rotational rate between 800 and 1200 rpm. The cyclic hardening of the friction-stir-welded joints exhibiting
a two-stage character was significantly stronger than that of the base metal (BM) and the energy dissipated per cycle decreased
with decreasing strain amplitude and increasing number of cycles. Fatigue failure occurred in the LHZs at a lower welding
speed and in the NZ at a higher welding speed. Fatigue cracks initiated from the specimen surface or near-surface defects
in the friction-stir-welded joints, and the initiation site exhibited characteristic intergranular cracking. Crack propagation
was characterized by typical fatigue striations along with secondary cracks. 相似文献
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Wei-di Cao R. L. Kennedy A. Choudhury 《Metallurgical and Materials Transactions A》1993,24(9):1909-1917
An auger electron spectroscopy (AES) study was performed to characterize grain boundary segregation behavior and grain boundary
precipitation occurring during slow strain rate tensile tests (SSRTTs) of alloy K-500. It was discovered that flake-like precipitates
formed on grain boundaries of some test alloys which had a high bulk Cu level. Auger electron (AE) spectra taken from precipitates
and AE mapping of grain boundary facets containing precipitates indicated that these precipitates were most likely titanium
carbides. The grain boundary segregation that existed in as-processed alloys was also changed in the course of SSRTTs. A significant
reduction in C segregation and a noticeable increase in Cu segregation were observed in test alloys after SSRTTs. Graphite
precipitation was not detected in any of the test alloys before or after SSRTTs. The carbide precipitation and change in segregation
pattern are qualitatively understandable on the basis of available thermodynamic data, but further study is necessary to fully
explain the observed phenomena. 相似文献
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应用配有能谱仪的场发射扫描电镜分析了A105钢中裂纹处及基体内残余元素Cu、As和Sn以及P含量.应用Thermo-Calc热力学计算软件计算了A105钢的主要析出相以及钢液中P含量随固相质量分数变化关系.应用Gleeble 1500热模拟试验机对A105钢的高温热塑性进行了研究.发现P偏析是该钢产生横裂的主要原因,残余元素Cu、As和Sn在晶界的偏聚加剧了裂纹的形成,矫直温度偏低加速了裂纹的扩展,而裂纹的形成可能与AlN的析出无关,因为析出的AlN很少. 相似文献
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T23钢较高的再热裂纹敏感性严重危害了超超临界火电厂的安全运行。为了改进T23钢再热裂纹敏感性,主要通过改变其碳、钨等元素的质量分数,并且采用Gleeble热模拟及等温缓慢拉伸方法评判T23钢和改进型T23钢焊接热影响区粗晶区(CGHAZ)的再热裂纹敏感性。利用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)研究两者CGHAZ的微观组织,探讨了微观组织对改进型T23钢再热裂纹敏感性的影响。结果表明,改进型T23钢的再热裂纹敏感性得到极大的改善,且其常规力学性能均达到ASME规范要求。与T23钢相比,改进型T23钢CGHAZ晶界M23C6相和晶内MX相数量均较少,同时,其固溶强化元素碳、钨质量分数较低。因此,改进型T23钢CGHAZ晶内晶界的强度差降低,再热裂纹敏感性改善。另外,较小的CGHAZ晶粒尺寸及较少的M-A组元也有助于降低改进型T23钢的再热裂纹敏感性。改进型T23钢晶界较少的M23C6相还使得晶界上孔洞连接和裂纹扩展的速率降低。设计的改进型T23钢成分可以为以后进一步改善T23钢再热裂纹敏感性提供参考。 相似文献
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为研究微合金钢第Ⅲ脆性区形成机理及其影响因素,控制连铸坯的表面裂纹,采用Gleeble热力模拟机测定了S355微合金钢在不同温度下的抗拉强度及断面收缩率。使用扫描电镜对拉伸断口进行观察分析,同时采用透射电镜对析出物进行观察分析。在此基础上对拉伸试样进行金相实验,对第二相析出进行热力学计算,分析了组织状态及第二相析出规律对脆性区的影响。结果表明,在第Ⅲ脆性区(660~850℃)内,拉伸断口呈冰糖状,韧窝较浅,形貌表现为沿晶脆性断裂。铁素体网膜沿奥氏体晶界优先析出、第二相沿晶界析出是第Ⅲ脆性区形成的主要原因。 相似文献
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《Acta Metallurgica Materialia》1991,39(12):3111-3118
This work is a contribution to understand the hot ductility drop mechanism of the Fe36Ni alloys (Invar). In contrast to the literature data, the present results show that sulfur alone causes a hot ductility loss. The precipitates, especially BN, only increase the damage of the material by multiplying the cavity nucleation sites. The nucleation of intergranular microcracks results from the decrease of the grain boundary cohesion associated with both the interfacial sulfur segregation and the contribution of grain boundary sliding to plastic deformation. Sulfur strongly segregates on the tip sof these internal cracks and decreases the propagation energy of cracks, thus leading to the material damage. The ductility recovery at high temperatures results from grain boundary migration and only dynamic recrystallization permits such a motion. 相似文献
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M. A. Daeubler A. W. Thompson I. M. Bernstein 《Metallurgical and Materials Transactions A》1990,21(3):925-933
This work examined the influence of microstructure on the surface fatigue crack propagation behavior of pearlitic steels.
In addition to endurance limit or S(stress amplitude)-N(life) tests, measurements of crack initiation and growth rates of
surface cracks were conducted on hourglass specimens at 10 Hz and with aR ratio of 0.1. The microstructures of the two steels used in this work were characterized as to prior austenite grain size
and pearlite spacing. The endurance tests showed that the fatigue strength was inversely proportional to yield strength. In
crack growth, cracks favorably oriented to the load axis were nucleated (stage I) with a crack length of about one grain diameter.
Those cracks grew at low ΔK values, with a relatively high propagation rate which decreased as the crack became longer. After
passing a minimum, the crack growth rate increased again as cracks entered stage II. Many of the cracks stopped growing in
the transition stage between stages I and II. Microstructure influenced crack propagation rate; the rate was faster for microstructures
with coarse lamellar spacing than for microstructures with fine lamellar spacing, although changing the prior austenite grain
size from 30 to 130 jμm had no significant influence on crack growth rate. The best combination of resistance to crack initiation
and growth of short cracks was exhibited by microstructures with both a fine prior austenite grain size and a fine lamellar
spacing.
Formerly with Carnegie Mellon University 相似文献