冷轧工作辊工频淬火开裂原因分析

利用ZEISS-AXIO金相显微镜、ZEISS-MA10扫描电子显微镜对9Cr2Mo钢冷轧工作辊工频淬火开裂后的断口进行观察,分析了工作辊淬火开裂的原因。结果表明,9Cr2Mo冷轧工作辊淬火开裂断口形貌分别由剪切唇区、放射区以及纤维区3部分组成。断口裂纹源处有明显的白点,其产生原因主要是氢和内应力的共同作用所致。改善方法首先应提高辊坯的冶金质量,降低辊坯中的氢含量;其次应改进锻后热处理工艺,例如采取降低白点敏感性的锻压方法,并对锻后辊坯进行充分的扩氢退火,降低辊坯氢含量和内应力。     

原子氢和白点对车轮钢力学性能的影响

车轮钢中白点形成的临界可扩散氢浓度为(C_0~*=1．3×10~(-6)(总氢浓度C_T~*=3．7×10~(-6)),当白点数量超过临界值(对应的可扩散氢浓度C_0＞5．6×10~(-6)),则使强度和塑性急剧下降,但实际车轮中白点含量少(Co＜3．9×10~(-6)),对材料的拉伸性能和断裂韧性没有影响,原子氢对断裂韧性K_(IC)没有影响;但如慢拉伸,则使塑性下降,如恒位移加载,则原子氢能引起氢致滞后开裂,其门槛应力强度因子K_(IH)随C_0升高而线性下降,即K_(IH)=57．8—3．9C_0,但白点对氢致滞后开裂没有影响。     

MC5轧辊辊颈表淬开裂原因分析

分析了MC5轧辊辊颈表淬裂纹形成的原因.通过减少锻造火次,合理控制锤击力和锻比,适当降低辊颈表面淬火温度,防止轧辊辊颈出现表淬开裂.     

140CrNiMo锻造半钢轧辊的试制

介绍了140CrNiMo锻造半钢轧辊的生产试制情况.采用浇铸轧辊工装铸造半钢毛坯,铸坯为轴类形状,提高了铸坯利用率.锻前采用低温长时间加热扩散;锻造时使用上平、下V型砧(型砧越旧越好)直接拔长轧辊铸坯,严格控制压下量,有效减少了拉应力而增加压应力,较好地解决了锻造半钢轧辊锻造时的裂纹问题.锻造比不小于2,较好地改变了碳化物的分布状态,大幅度提高了材料的综合力学性能.终锻温度为900℃,锻后空冷到450～500℃进炉热处理.锻后进行正火 球化 扩氢退火热处理,最终热处理后,辊身组织为细珠光体 二次碳化物,制造出合格的锻造半钢轧辊.     

热渗氢后309L和347L钢堆焊层的低频疲劳特性

研究了经高温高压渗氢后 ,30 9L 和 347L 不锈钢堆焊层短裂纹的低频疲劳特性。并用 da/d N=C(ΔJ) n 计算了裂纹扩展速度和门槛值。结果表明 ,经热渗氢后 ,30 9L和 347L堆焊层裂纹扩展的门槛值 (ΔJth)分别从空气中的 196× 10 - 6 MN/m和 35 5× 10 - 6 MN/m,下降为 144× 10 - 6 MN/m和 2 5 2× 10 - 6 MN/m;da/d N～ ΔJ曲线也比空气中的向左移 ,提高了裂纹扩展速度。说明热渗氢显著增加了不锈钢堆焊层低频破坏的敏感性     

AISI8630钢泥浆泵排出缸失效分析及工艺改进

针对AISI8630钢锻件在实际生产中出现的锻造失效问题进行了研究。采用"EAF→LF→VD→铸锭"工艺冶炼AISI8630钢锭,钢锭锻造成泥浆泵锻件,经热处理加工后探伤发现密集性缺陷。通过化学成分、低倍分析和金相显微分析,对产生的缺陷进行分析研究。结果表明:宏观检测受检面有许多裂纹,将裂纹打开,发现断口存在明显的白点缺陷;近裂纹附近有灰色硫化物夹杂,存在明显的组织偏析现象,远离裂纹处的金相组织无明显差异。通过加强冶炼过程控制,对钢锭进行锻前消氢、消应力退火及锻后250℃以下缓冷处理等工艺优化,避免了白点缺陷的形成,并经现场验证得到合格产品。     

锻钢件中白点缺陷的超声波检测

白点常以微小裂纹群的形式出现,因其低倍断口呈银白色圆形或椭圆形斑点而得名。白点可能导致制件在后续热处理或使用过程中突然断裂,酿成安全事故。因此,锻钢件不允许有白点缺陷存在,不考虑其当量值的大小。现有的超声波检测方法不能直接给出表征缺陷性质的判定信息,可能导致白点缺陷的漏检。笔者在工作中总结出白点判定的几点经验,取得较好的实际应用效果。1白点的形成机理钢在冶炼过程中富含氢气的铸坯在锻压、轧制加工过程中,如果后续热处理工艺(扩氢退火)不当,或常规工艺不能将钢中的氢气扩散含量减少到临界值(2×10-6/m3)以下,则过量的氢气与热压力加工时产生的热应力和组织应力共同作用可能导致白点产生[1]。由此得出白点表现形式上的“群集性”与“批次性”特征,即往往以密集缺陷的形式存在,同炉次浇注或相同锻后热处理工艺、截面尺寸相近的制件,白点出现几率相当。这一推断成为我们判定白点的基本理论依据。常见资料都认为合金元素铬、锰、钼、镍、钨含量较高的钢种易产生白点[2],但笔者以为检测者更应关注的是某些锻造厂家因为废钢供应、冶炼锻造工艺等因素而易在某些钢种中出现白点的偏向性。2白点的声学特征2.1密集性缺陷回波单个白点在锻件中出现的几率...     

攀钢重轨钢初轧坯堆冷的除氢效果

用石腊油法测定了U71Mn重轨钢初轧坯中的可扩散氢和氢在钢中的扩散系数,并通过解剖经过堆垛缓冷的初轧坯,测定氢在断面上的分布结果表明,重轨钢坯中的氢绝大部分均为可扩散氢,室温下氢在U71Mn钢坯中扩散系数为(0.85—1.02)×10~(-6)cm~2/s初轧坯经堆冷后,含氢量大幅度下降,它有助于形成攀钢重轨无白点现象.     

锻钢冷轧辊辊坯制造技术

阐述了锻钢冷轧辊的发展历程、锻钢冷轧辊对辊坯的技术要求和辊坯的制造技术及发展方向。通常,辊坯制造采用电渣重熔、高温扩散、锻造和锻后正火及球化退火和扩氢处理等。指出,采用微合金化技术提高使用寿命是冷轧辊的发展方向,开发电炉精炼钢冷轧辊是提高锻钢冷轧辊市场竞争力的有效途径。     

辊锻技术在我国的应用和发展

辊锻是一种新的锻造工艺。十几年来,在我国的锻造生产中得到了广泛的应用。在辊锻方面并有了新发展,辊锻设备的制造也得到了相应的发展。所谓辊锻是使坯料在一对旋转着的辊锻模中通过,借助模槽对金属的压力,使其产生塑性变形,从而获得所需要的锻件或锻坯,如图1所示。     

HYDROGEN INDUCED EMBRITTLEMENT OF ROTOR STEEL 34CrNi3Mo

本文通过系列氢含量试样的慢拉伸试验研究了34 CrNi3 Mo转子钢的氢致脆化.得到了如下结果:(1)随钢中氢含量的增加与应变速率的减慢,钢的塑性急剧下降。当钢中氢含量达到5mL/100g、拉伸应变速率为3×10~(-5)s~(-1)时,34CrNi3Mo转子钢的塑性几乎完全丧失.此转子钢的无白点极限含氢量力2mL/100g;无氢脆极限含氢量为1.48mL/100g. 扫描电镜观察表明,在慢拉伸试样中白点呈边界清晰的近于椭圆形的斑点,其微观形貌为走向比较清楚的撕裂岭与准解理小平面构成的穿晶准解理。     

冷高压分离器16MnR(HIC)抗氢钢超大型筒体研制

1 2 0× 1 0 4 吨 /年加氢裂化装置冷高压分离器和循环氢分液罐筒体锻件超长、超大 ,采用抗氢钢1 6MnR(HIC)制造 ,技术要求非常高 ,达到了二重现有设备的制造极限。我们在工艺上采用纯净钢冶炼 ;上下球面镦粗 ,预扩孔—最终扩孔、拔长—扩孔砧扩孔等超大型薄壁筒体的锻造 ;卧装、卧淬的热处理等制造技术 ,以及合理的热处理工艺参数 ,成功制造了三件筒体锻件。     

V85Ti10Y5和V85Ti10Cu5氢分离合金组织与性能研究

利用高真空非自耗电弧熔炼炉制备了V85Ti10Y5和V85Ti10Cu5氢分离合金。通过SEM、TEM、XRD、氢渗透实验、PCT吸氢实验、恒压缓冷实验,研究了Y、Cu元素的加入对合金氢渗透性能、氢溶解性能及抗氢脆性能的影响。结果表明:铸态V85Ti10Y5和V85Ti10Cu5合金组织均由V-基体和第二相组成,但前者第二相是弥散分布的富Y颗粒,而后者为既在晶内析出又沿晶界连续分布的铜钛金属间化合物。V85Ti10Y5合金中Y2O3的生成及V85Ti10Cu5合金中部分固溶Cu的斥氢作用和Cu2Ti形成使V中Ti的固溶量减少,进而降低合金中的氢浓度,减小氢固溶产生的内应力,提高抗氢脆性能。V85Ti10Y5和V85Ti10Cu5合金在缓冷过程中均未发生氢脆现象,表现出优异的抗氢脆性能,而且在673 K时的氢渗透率分别为0.139×10-6 mol H2 m-1 s-1 Pa0.5和0.174×10-6 mol H2 m-1 s-1 Pa0.5,是Pd77Ag23氢渗透率的5.5和6.9倍,与商用钯合金相比均展现出较高的渗透率。     

Optimum conditions in the thermal passivation of aisi 430 and 304 stainless steel in controlled oxygen atmosphere

The oxidation of stainless steels AISI 304 and 430 was undertaken in the temperature range 450–600°C and oxygen partial pressure range 6.7 × 10⁷ to 1.33 × 10^?5 Pa. The composition of the oxide layer formed has been analysed by AES and ESCA. Optimum conditions were determined for the formation of a ～40 nm thick oxide layer with a high chromium content. Attention is drawn to the role of the chromium content of the bulk in the passivation process.     

固溶处理对Mg-3Gd-1Zn合金在模拟体液中腐蚀性能的影响

目的探究固溶处理对Mg-3Gd-1Zn生物镁合金腐蚀性能的影响规律。方法对Mg-3Gd-1Zn镁合金进行不同温度的固溶处理,随后进行时效处理。采用扫描电镜(SEM)对合金的显微组织进行观察,利用失重法和析氢法测试合金在模拟体液(SBF)中的腐蚀性能,利用极化曲线和交流阻抗谱对合金的电化学行为进行评估。结果由失重法计算结果可知,T6-460、T6-510、T6-520和T6-530合金在SBF中浸泡120h后的腐蚀速率分别为2.48、1.19、0.86、1.17 mm/a,即随着固溶温度的增加,合金的腐蚀速率顺序为:T6-460T6-510T6-530T6-520。析氢测试结果表明,随着浸泡时间的增加,T6-460与T6-510合金的腐蚀速率升高,而T6-520与T6-530合金的腐蚀速率变化较小,浸泡120 h后的析氢分析结果与失重法计算结果趋势一致。电化学测试表明,T6-460、T6-510、T6-520和T6-530合金的电流密度分别为8.01×10~(-5)、3.85×10~(-5)、3.30×10~(-5)、3.90×10~(-5)A/cm~2。随着固溶温度的增加,合金的容抗弧半径先增加后减小。合金在腐蚀过程中发生了点蚀。结论四种测试方法均表明T6-520镁合金表现出最佳的耐蚀性。     

Surface decarburization behavior and its adverse effects of air-cooled forging steel C70S6 for fracture splitting connecting rod

Surface decarburization behavior and its adverse effects of air-cooled forging steel C70S6 for automobile engine fracture splitting connecting rod were investigated comprehensively by mechanical properties, microstructure and fracture morphology analysis. The results show that the surface decarburization in the outer surface of the fracture splitting at the big end bore and the micro-cracks in the decarburized layer are result in the uneven and spalling fracture surfaces of the waster connecting rod product. Besides, partial decarburization is produced between 900 °C and 1250 °C for heating 2 h, and decarburization sensitivity reach maximum at 1150 °C, but no complete decarburization forms for heating 2 h at 650-1250 °C. The decarburized depth follows a parabolic law with the increase of the heating time from 0.5 h to 12 h, and the decarburization sensitivity coefficient is 2.05×10^-5 m·s^-1/2 at 1200 °C. For the connecting rod manufacturing, surface decarburization must be under effective control during the hot forging process but not the control cooling process.     

低压导叶锻造及热处理工艺探讨

对某汽轮机组低压隔板导叶片X5CrMoAl12材料的锻造及热处理工艺进行了研究,提出该叶片的始锻温度为1 000℃,终锻温度为850℃。热处理工艺参数为960～990℃淬火,670℃×6 h回火。为指导低压导叶片毛坯生产提供了技术支持。     

Industry Learns From a Turbine Spindle Failure

The chemical analysis of the material used for this forging met all requirements of the specification. Mechanical tests of the specimens taken from the outside and at mid-radius of the forging also met the specification requirements. Test specimens taken near the bore tended to have lower yield and tensile strengths and frequently had very low ductility. Some reduction of ductility is to be expected at the center of a heavy mass, but in this case the reduction was considered to be excessive. The fractures of some of the deep-seated specimens contained fisheyes. Tests of duplicate specimens that had been heated to a low temperature, 400°F, resulted in normal ductility. Fisheyes and low ductility, which may be considerably improved by a low temperature heat-treatment, are typical effects of large amounts of hydrogen in steel. Macroex-amination of the forging indicated that the main body contained approximately 5000 cracks. These cracks were generally oriented in radial planes with their maximum dimensions in the longitudinal direction. They occurred most frequently in zones of sulfur segregation in the main body of the forging. These cracks are believed to be flakes produced while the forging was cooling from a high temperature or while it was standing at room temperature after such cooling and prior to a tempering or stress-relieving heat treatment. Flakes are generally considered to be caused by thermal transformation stresses combined with severe reduction in ductility caused by the collection of gaseous hydrogen under high pressure within imperfections in the steel. No cracks were observed in the portions of the shaft extensions which were forged to relatively small diameters. Apparently cracks did not occur in these smaller sections because the transformation stresses were lower and possibly because more of the hydrogen could diffuse from these smaller sections than from the main body.Ultrasonic reflectoscope indications observed in examination of the failed spindle were very similar to those observed at the time the forging was made. It must be concluded, therefore, that the thermal cracks or flakes were present at the time the forging was first inspected and that the ultrasonic indications were from flakes rather than from inclusions.It is believed that the fatigue crack that developed at the fillet between the generator end shaft extension and the main body was not a factor in this failure. Assumption of the fatigue crack as the origin of failure would not lead to the symmetrical pattern of failure which was observed. Origin of the fatigue crack was identified as a thermal crack or flake that happened to occur in the fillet between the shaft extension and the main body. This fillet was the location of moderate. stress concentration, and the additional stress concentration owing to the flake resulted in development of the fatigue crack.Detailed examination of the fractured pieces indicated that failure began in the plane shown in Fig. 5 at or near the bore toward the turbine end of the main body. The assumption of this origin of failure leads to a consistent sequence of failure and explains the high degree of symmetry of the broken parts. It is believed that the large number of thermal cracks or flakes within the spindle was the primary cause of failure.Although this was a serious failure, much has been learned from it. It is now possible to interpret tests much more accurately, and it should be possible to avoid such accidents in the future. Changes in practice in the manufacture of such forgings should also avoid hydrogen solution and subsequent cracking.     

Texture and magnetostriction in rolled Fe-Ga based alloy

添加Nb改善了Fe81Ga19合金的塑性, 采用热轧和冷轧相结合的轧制工艺制备出厚度 为0.6 mm的(Fe81Ga19)+ 1%Nb(原子分数)合金薄板. 研究了(Fe81Ga19)+1%Nb合金轧态和退 火态薄板的织构及磁致伸缩效应. 结果表明: 合金的磁致伸缩与样品的织构密切相关, 再结 晶织构取决于热处理工艺. 轧态织构以{111}面织构和近似的{001}<110>旋转立方织构为主, 样品轧向的磁致伸缩系数λ∥=26×10-6. 在1250和1300 ℃保温2 h后水淬样品的织构分别呈现为近似的{011}<100>Gauss织构和单一{001}<100>立方织构, 其磁致伸缩 (3/2)λRD分别达到106×106和134×10-6     

铁路货车钩尾框精密辊锻过程数值模拟

铁路货车钩尾框锻件为异形长轴类锻件,目前采用自由锻工艺制坯,效率低,质量差,大型自动辊锻机精密辊锻是一种优质高效的先进制坯工艺,用于钩尾框制坯有望取得良好的技术经济效益.以刚塑性有限元法为基础,利用Deform-3D软件对铁路货车钩尾框精密辊锻过程进行三维有限元模拟,揭示了钩尾框辊锻变形过程中金属的流动规律,分析了辊锻成形过程中各道次辊锻过程中模具受载荷情况,以及各道次辊锻过程中的辊锻力矩,为钩尾框精密辊锻工艺及模具设计提供了有效的参考依据.