残余奥氏体对贝氏体钢轨性能的影响

 无碳化物贝氏体组织中的残余奥氏体对提高贝氏体钢轨的韧塑性作出了突出贡献,为了在铁路运营时使钢轨仍保持较高的韧塑性,需要控制好贝氏体钢轨残余奥氏体的稳定性。通过对热轧空冷、热轧空冷+低温回火贝氏体钢轨在不同环境温度下残余奥氏体稳定性的分析,回火贝氏体钢轨在不同试验温度（包括低温）条件下拉伸性能的分析,在模拟钢轨运营的试验条件下疲劳性能的分析及相应条件下残余奥氏体含量的测定,说明低温回火处理提高了贝氏体钢轨中残余奥氏体的稳定性,模拟钢轨运营的试验条件下,贝氏体钢轨中的残余奥氏体基本是稳定的。     

贝氏体钢轨矫直前后回火的组织性能分析

利用TEM、磁性分析法和拉伸试验对矫直前后回火贝氏体钢轨显微组织、残余奥氏体含量、稳定性以及拉伸性能进行分析。结果表明:与矫直前回火相比,矫直后回火获得贝氏体钢轨的显微组织为无碳化物贝氏体+少量残余奥氏体和M/A+微量回火马氏体;抗拉强度平均提高139 MPa;屈服强度平均提高138 MPa;残余奥氏体机械稳定性明显提高;贝氏体钢轨强韧性优良。     

热处理钢轨残余应力对疲劳裂纹扩展速率的影响

钢轨残余应力对其疲劳性能影响较大,文章采用回火试验和金相分析方法,研究了不同残余应力值对U75V热处理钢轨疲劳裂纹扩展速率的影响。通过回火试验,分析不同回火时长对钢轨残余应力的影响,得出随着回火时间的增加残余应力逐渐减小;通过对回火工艺处理后的钢轨进行金相组织检测,观察不同回火时长的钢轨金相组织,分析疲劳裂纹尖端处裂纹扩展路径,根据裂纹扩展的方式与长度来分析不同回火时长对疲劳裂纹扩展速率的影响;通过回火工艺控制,可有效降低钢轨残余应力,进而有效地降低钢轨裂纹扩展速率,提高钢轨抗疲劳性能。     

回火工艺对贝氏体钢轨组织性能影响研究

利用TEM、磁性分析法、液压伺服万能材料试验机对不同回火温度和二次回火的贝氏体钢轨组织性能进行分析.结果表明,350℃回火时,贝氏体钢轨残余奥氏体稳定,冲击韧性和-20℃断裂韧性较好;325℃保温10 h二次回火比325℃保温4 h二次回火得到的伸长率及断面收缩率更好,适用于实际生产工艺.     

在线热处理钢轨残余应力的测试与分析

文章介绍了包钢热处理钢轨标准残余应力的研究情况,通过贴片法、切口法、X衍射等方法对包钢热处理钢轨进行实验分析,与热轧钢轨进行对比分析了包钢在线热处理钢轨的残余应力状态。贴片法检验结果表明包钢生产的热处理钢轨轨头残余应力大于热轧钢轨,切口法检验表明钢轨整体残余拉应力大于热轧钢轨,X衍射法表明钢轨表面残余应力分布不平均。     

钢轨的矫直及其对性能的影响

通过钢轨静态棍矫模拟试验及一, 二次矫直钢轨的性能对比试验、残余应力等研究、探讨矫直对钢轨性能的影响。结果表明,钢轨在矫直过程中发生大面积屈服、立矫与卧矫有不同的应力状态:二次矫直降低了钢轨的抗疲劳能力,从微观机制上探讨了二次矫直对钢轨性能的影响。     

矫直工艺对热处理钢轨残余应力的影响

为了研究钢轨矫直工艺与残余应力的关系,结合ABAQUS有限元分析软件,模拟钢轨矫直过程中钢轨应力应变情况。对多种钢轨矫直工艺方案进行模拟分析,确定最优矫直工艺方案,并结合现场工艺调试的结果进行研究。结果表明：各矫直方案的最小弹性芯均处于第Ⅱ变形区内,所以降低2^#、4^#矫直辊压下量能有效降低钢轨残余应力,并且降低钢轨矫直速度也能有效降低钢轨残余应力。     

贝氏体和珠光体钢轨的断裂及疲劳损坏

1引言 联邦铁路管理局发起研究贝氏体钢断裂和疲劳损坏的科研项目。低碳贝氏体钢具有潜在的优势,特别在一些关键部位,例如,弯轨和道岔。本研究检查了贝氏体钢轨断裂和疲劳损坏的显微组织,并将其与珠光体钢轨进行了比较。结果发现：贝氏体钢轨的显微组织由回火马氏体和铁素体的混合物组成,并且伴随着条内碳化物。珠光体钢轨的显微组织由非常柔软和延性的铁素体以及非常坚硬的碳化物共同组成的细小片状聚合体。本文研究的J6贝氏体钢强度极限、屈服强度和延伸率极限大约分别为1500MPa、1100MPa和13％,这些值均高于珠光体钢的性能,具体如图1所示。从图中可以看到：与珠光体钢相比较,贝氏体钢在第二阶段的裂纹速率明显减缓,疲劳裂纹延伸动力学曲线具有较低的斜率。这证明贝氏体钢轨具有较高的抗疲劳破坏性能,文献报道也为贝氏体钢轨具有较高的轧制抗疲劳性能提供了依据。     

UIC60钢轨试制

对UIC60钢轨的生产进行了总结,并对钢轨性能进行了研究及评价.通过在台湾北部地区试铺,性能稳定,易于焊接,使用效果较好.     

回火工艺对热轧U20Mn2SiCrNiMo贝氏体钢轨组织性能的影响

U20Mn2SiCrNiMo贝氏体钢轨的生产流程为150 t 转炉-LF-VD-280 mm×380 mm铸坯 轧制,终轧930~980 ℃,空冷-340 ℃ 4 h两次回火,空冷。U20Mn2SiCrNiMo钢热轧态(终轧930~980 ℃空冷）和(320 ℃一、二次回火)组织均由贝氏体、马氏体和残余奥氏体组成。力学性能试验结果表明：U20Mn2SiCrNiMo钢轨最佳回火工艺为320 ℃ 4 h空冷+320 ℃ 4 h空冷二次回火,其性能为：屈服强度1242 MPa,抗拉强度1393 MPa,HBW硬度值417,伸长率15.0%,断面收缩率60%,冲击吸收功K_U2 98 J,轨底纵向残余应力+180 MPa。     

国内外贝氏体钢轨综述

主要介绍了贝氏体钢轨的合金设计原理和各元素的作用,分析了国内外贝氏体钢轨的成分设计、力学性能和回火工艺,并展望了抗拉强度为1 400 MPa的贝氏体钢轨生产.     

硅对贝氏体铸钢高应力冲击磨损性能的影响

研究了不同硅含量（0．7％－2．4％,质量分数,下同）贝氏体铸钢的抗高应力磨损性能和失效机制。结果表明：高效硅贝氏体铸钢的耐磨性能较低硅钢显提高,其磨损失重约是低硅贝氏体铸钢的1．2,这是因为硅使氏体铸钢在高应力冲击磨损下表现出不同的失效机制。低硅（0．7％）贝氏体铸钢由于韧性低、组织结构粗大及树枝晶的微区成分偏析,故材料抵抗冲击的能力很低,常在表面还未形成强烈变形层（白层）甚至变形层时,就在变形层和材料基体内产生裂纹并扩展,故低硅贝氏体铸钢的失铲方式为变形层和基体剥落机制。而硅含量为1．65－2．4％的高硅贝氏体铸钢,因脆性的渗碳体被韧性的残余奥氏体所代替,钢的韧性显提高,失效方式表现为白层的剥落机制。     

Effects of B and Cu Addition and Cooling Rate on Microstructure and Mechanical Properties in Low-Carbon, High-Strength Bainitic Steels

The effects of B and Cu addition and cooling rate on microstructure and mechanical properties of low-carbon, high-strength bainitic steels were investigated in this study. The steel specimens were composed mostly of bainitic ferrite, together with small amounts of acicular ferrite, granular bainite, and martensite. The yield and tensile strengths of all the specimens were higher than 1000?MPa and 1150?MPa, respectively, whereas the upper shelf energy was higher than 160?J and energy transition temperature was lower than 208?K (?C65?°C) in most specimens. The slow-cooled specimens tended to have the lower strengths, higher elongation, and lower energy transition temperature than the fast-cooled specimens. The Charpy notch toughness was improved with increasing volume fraction of acicular ferrite because acicular ferrites favorably worked for Charpy notch toughness even when other low-toughness microstructures such as bainitic ferrite and martensite were mixed together. To develop high-strength bainitic steels with an excellent combination of strength and toughness, the formation of bainitic microstructures mixed with acicular ferrite was needed, and the formation of granular bainite was prevented.     

准贝氏体高强耐磨钢的开发和工艺研究

研究在典型贝氏体钢的成分基础上加入阻止碳化物析出的元素S i,开发出以贝氏体铁素体(BF)和残余奥氏体(AR)组成的准贝氏体组织的高强耐磨钢,在适当的工艺下钢板可获得最佳的综合性能,具有良好的强韧性、耐磨性和焊接性。     

残留奥氏体对微纳贝氏体钢塑韧性的影响

采用高碳和中碳低温贝氏体转变工艺（095C钢为200℃等温10d,030C钢为320℃等温1d）研究了残留奥氏体对微纳结构钢塑韧性的影响,对不同试样的显微组织、各相体积分数、伸长率和冲击韧性进行观察、检测和分析。试验结果表明,中碳钢贝氏体转变的塑韧性明显高于高碳钢贝氏体转变,主要原因是中碳钢贝氏体转变中存在一定的亚微米级薄膜状残留奥氏体,在拉伸或冲击过程中引起的残留奥氏体的塑性变形,使断裂的能量增加,可以显著提高样品的塑韧性。     

Influence of microstructure on fracture toughness of austempered ductile iron

An investigation was carried out to examine the influence of microstructure on the plane strain fracture toughness of austempered ductile iron. Austempered ductile iron (ADI) alloyed with nickel, copper, and molybdenum was austenitized and subsequently austempered over a range of temperatures to produce different microstructures. The microstructures were characterized through optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and was correlated with the microstructure. The results of the present investigation indicate that the lower bainitic microstructure results in higher fracture toughness than upper bainitic microstructure. Both volume fraction of retained austenite and its carbon content influence the fracture toughness. The retained austenite content of 25 vol pct was found to provide the optimum fracture toughness. It was further concluded that the carbon content of the retained austenite should be as high as possible to improve fracture toughness.     

终轧温度对低碳Mn系贝氏体钢性能的影响

 Gleeble热模拟试验表明,低碳Mn系贝氏体钢随着变形温度降低,仿晶界铁素体和粒状贝氏体都发生了细化,冲击韧性显著提高。加Nb后的Mn系贝氏体钢在相同工艺下组织得到了进一步细化。实验室试轧数据表明,含Nb的Mn系贝氏体钢降低终轧温度后,韧性提高的幅度比不含Nb钢更大,工业化前景广阔。     

Railroad rails made of bainitic steel

Results are presented from a study of the mechanical characteristics and microstructure of rails made at the Novokuznetsk Metallurgical Combine from steel alloyed with manganese, silicon, chromium, molybdenum, and vanadium. It was established that obtaining high strength and hardness in the steel by increasing its contents of carbon and alloying elements has an adverse effect on the service properties of rails made of steels with a bainitic structure. Normalizing is the most effective means of increasing strength and improving microstructure. The required level of mechanical characteristics can be obtained by tempering the steel at 350–370°C. The adverse effect of cold straightening-which is manifest in a reduction in the rails’s impact toughness-can be offset by subjecting the steel to preliminary tempering or normalizing and tempering. Rather than further increasing the strength of rail steel to improve its overall quality, this objective is better served by making sure that the steel is cleanly made, that the rails have little or no curvature, and that the residual stresses in the steel are favorably distributed. __________ Translated from Metallurg, No. 4, pp. 51–53, April, 2007.     

残留奥氏体对中碳双相钢冲击性能的影响

采用不同的热处理工艺研究了残留奥氏体对中碳双相钢冲击韧性的影响。利用金相显微镜、扫描电镜、透射电镜和摆锤式冲击试验机,对不同试样的显微组织与冲击韧性进行观察、检测和分析。试验结果表明：中碳贝氏体钢的冲击性能显著高于Q/P马氏体钢（室温冲击功是57J对应15J,-40℃冲击功是33J对应9J）,可能的原因是贝氏体钢中薄膜状残留奥氏体,对裂纹扩展的阻止效应更显著。