大型支承辊置裂原因分析

通过对置裂的大型支承辊进行套料分析得知 ,大型支承辊的置裂与钢中氢含量较高、热应力大以及预备热处理工艺不当等因素有关。为提高大型支承辊的质量提出了相应的对策     

1780mm轧机支承辊置裂原因分析

一支1 780 mm轧机支承辊在使用现场放置时自然开裂。利用金相分析、扫描电镜分析等方法对断口取样进行研究,结果表明冶金缺陷和辊身较大的内应力是造成该支承辊置裂的主要原因。     

70Cr3Mo钢支承辊热处理断裂的原因分析

对于尺寸较大的高碳合金钢轴(辊)类件而言,外圆表层在快速加热喷冷淬火时,一定深度的表层部分会因为相变而产生体积膨胀,从而使心部承受拉应力。加热温度越高、冷却越激烈,则淬硬层越深,心部拉应力就越大。但喷淬过程中心部温度尚处于较高状态,可以通过应变使这种应力得到协调或松弛,因而一般不会造成开裂。心部的这种开裂常常发生在热处理后的放置过程中,即所谓"置裂"。本文运用常规金相分析的方法,确定70Cr3Mo钢支承辊的断裂属于置裂并具体指出该支承辊发生置裂的主要原因是:最后热处理加热温度偏高,导致淬层马氏体粗大、残余奥氏体增多。     

大型锻钢支承辊生产状况及最终热处理工艺

概述了支承辊的工作条件及性能要求,国内大型锻钢支承辊的生产状况、工艺及设备;重点介绍了大型锻钢支承辊的最终热处理工艺,包括差温淬火、感应淬火。     

碳偏析和氢脆共同作用产生的置裂

在支承辊的断裂源部位取样,运用失效分析手段,结合化学成分数据、物理性能指标、金相高低倍观察和扫描电镜等分析手段,分析了其断裂的过程以及原因。从中发现造成零件置裂的原因很多,但主要是零件心部所受轴向残余拉应力最大的区域内存在着严重碳偏析和氢脆导致其断裂。严重的碳偏析破坏了基体的连续性,形成薄弱环节。此外相关化学成分超标、晶粒粗大也对支承辊的断裂起到了促进作用。     

支承辊镶套修复

针对大型支承辊采用堆焊修复而使辊面组织不均匀的问题,采用了支承辊镶套修复技术,根据支承辊的使用情况设计镶套轧辊的配合直径及联接过盈量,根据配合直径及过盈量确定热装温度,保证安装顺利进行.支承辊镶套修复后,镶套轧辊联接紧固,可以满足支承辊使用性能.实际使用中效果良好.     

二重成功签订国内最大支承辊制造合同

近日，二重与五矿营口中板有限公司签订5m宽厚板轧机6件支承辊制造合同。该合同的成功签订，为全面提升集团公司大型辊类锻件，尤其是大型支承辊的制造技术创造了有利条件。     

大型铸钢支承辊电加热冒口工艺的计算机模拟

以大型铸钢支承辊为例,利用数值模拟方法对电渣热冒口工艺参数进行了全面研究,建立了凝固热传导、相变以及移动热源的数学模型,利用商品化软件包ProCAST求解,确定了电渣热冒口工艺参数对支承辊缩孔、疏松的影响,并制定了最佳工艺参数.模拟结果与大型铸钢支承辊的实际解剖结果相吻合.利用电渣热冒口模拟结果指导大型铸钢支承辊生产获得成功.结果表明,建立的数学模型可以用来指导大型铸件电渣热冒口的实际生产.     

基于田口方法的大型Cr5钢支承辊喷雾淬火工艺优化

为了提高大型Cr5锻钢支承辊的综合力学性能,论文基于数值模拟技术,并采用田口方法,以某大型Cr5锻钢支承辊喷雾淬火后辊身表面与中心温差、淬硬层深度以及轴向残余拉应力为性能指标,以淬火温度、淬火方式、冷却时间和介质温度为控制因子,以工件的转移时间、环境温度和淬火温度测量误差为噪声因子,对该大型Cr5锻钢支承辊的喷雾淬火工艺进行了优化。通过方差分析得到了影响各性能指标的显著因素,并经综合分析给出了其最佳喷雾淬火工艺。结果表明,优化后的喷雾淬火工艺能有效降低支承辊辊身中截面的温度梯度,提高支承辊的淬硬层深度,并显著降低支承辊的淬火残余拉应力。     

3500mm宽厚板轧机支承辊锻造工艺研究

详细介绍了3 500 mm轧机支承辊的锻造工艺。阐述了工艺难点和工艺要点。采用一次镦粗加KD法拔长的工艺方法,保证了支承辊的技术和质量要求,并为生产更大型支承辊积累了经验。     

应力促进PZT铁电陶瓷的电致滞后断裂

用单边缺口拉伸试样研究了外加应力强度因子对PZT-5铁电陶瓷电致瞬时断裂以及在硅油中电致滞后断裂的影响。结果表明，在硅油中发生瞬时断裂的临界电场强度EF随外加应力强度因子KI的升高而线性下降，外加正、负恒电场在硅油中能发生滞后断裂，外加KI则促进电致滞后断裂，电致滞后断裂的门槛电场EDF随KI升高而线性下降，且和电场符号无关，外加应力促进恒电场下的滞后断裂表明，应力、电场和环境对铁电陶瓷的断裂存在耦合作用。     

TiNi形状记忆合金的氢致滞后断裂

用单边缺口拉伸试样研究了TiNi形状记忆合金在恒载荷下动态充氢时的滞后断裂过程，以及原子氢、氢致马氏体和氢化物在氢致滞后断裂中所起的作用，结果表明，TiNi合金能发生氢致滞后断裂，归一化门槛应力强度因子随总氢浓度对数的增加而线性下降，即KIH/KIC=2.01-0.25lnCT。在恒载荷动态充氢时氢化物含量不断升高，材料的断裂韧性不断下降，这是氢致滞后断裂的主要原因；而原子氢和氢致马氏体在氢致滞后断裂中所起的作用则极小。     

卡夹螺旋弹簧断裂分析

对７０钢卡夹螺旋弹簧的化学成分、金相组织及断口分析表明，其断裂的主要原因是氢脆。其断裂机制属氢致延迟破坏，系弹簧电镀工艺不当所致，并提出了改进措施。     

Determination of the critical hydrogen concentration for delayed fracture of high strength steel by constant load test and numerical calculation

The critical hydrogen concentration for hydrogen induced delayed fracture of the AISI 4135 steel at 1320 and 1450 MPa has been determined by constant load tests in combination with numerical calculations, and thus the concept of a critical hydrogen concentration has been verified. The time to fracture was obtained for circumferentially notched round bar specimens under a constant load after electrochemically pre-charged with various hydrogen contents. A numerical model was then developed for calculating the accumulated hydrogen concentration in the vicinity of the notch root, taking into account the driving effect of the hydrostatic stress on hydrogen transport. The results showed that the delayed fracture of the steel occurred when a critical hydrogen concentration at the location of the stress peak was reached by accumulation, and that the time to fracture was related to the stress-driven hydrogen accumulation process. The critical hydrogen concentration was dependent not only on the strength level, but also on the stress concentration factor of the specimens.     

梯形波周期加载下超高强度钢的氢致断裂

钢的氢脆研究,目前大部分都采用拉伸、持久和断裂韧性测试等方法。这些方法,对于促进氢脆机理的研究和工程应用都起了重要的作用。但在工程上,大部分动部件所受载荷都是交变的,而不是受静载拉伸。所以,也有人认为用低周疲劳来评价氢脆敏感性要比慢拉伸和静持久更为切合实际。我们选择了最简单的交变方式,即梯形波加载代替纯持久加载,以探讨疲劳因子对氢致滞后破坏的影响。     

Susceptibility to delayed fracture of alpha-beta titanium alloy in fluoride solutions

The susceptibility to delayed fracture of the alpha-beta titanium alloy Ti-6Al-4V has been investigated in acidic and neutral fluoride solutions at room temperature. The time to fracture decreased with increasing applied stress in 2.0% and 0.2% acidulated phosphate fluoride (APF) solutions at pH 5.0. The time to fracture in the 2.0% APF solution was shorter than that in the 0.2% APF solution, although at an applied stress higher than 1000 MPa, the times to fracture were almost the same in both the solutions. For immersion in the 0.2% APF solution, when the applied stress was lower than 700 MPa, delayed fracture did not occur within 1000 h. The fracture surface of specimens immersed in the 2.0% APF solution exhibited brittleness associated with hydrogen absorption, while that in the 0.2% APF solution was ductile and characterized macroscopically as having a cup-cone morphology. The amounts of hydrogen absorbed in 2.0% and 0.2% APF solutions for 24 h were approximately 200 and 30 mass ppm, respectively. As the immersion time increased, the amount of hydrogen absorbed in the 2.0% APF solution increased, whereas that in the 0.2% APF solution hardly increased. In neutral 2.0% and 0.2% NaF solutions, the delayed fracture did not occur within 1000 h, although general corrosion was observed. These results indicate that the susceptibility to delayed fracture of alpha-beta titanium alloy, compared with those of the alpha titanium and beta titanium alloy reported previously, is low in acidic and neutral fluoride solutions.     

30MnSi�ֽ���ѷ���

 对发生滞后断裂的30MnSi钢筋进行了检测分析，经检验其断裂的原因为钢筋在热处理加热时钢筋与加热线圈接触打火表面产生了异常的马氏体组织，由于该组织的内应力较大导致钢筋滞后断裂。     

65Mn弹簧钢簧片断裂分析

以断裂的65Mn弹簧钢簧片作为研究对象,对簧片断口的宏观形貌、微观组织、化学成分及显微硬度等进行分析,对簧片加工工艺和操作进行检查分析并试验.结果表明:由于折弯工序未采取防护措施,簧片折弯处造成损伤,且大量H原子向折弯处聚集,最终导致簧片氢致延迟脆性断裂.完善簧片的折弯工艺,减少应力集中,在技术要求范围内适当降低硬度,...     

车轮钢中的白点及其断口形貌研究

研究了车轮钢中白点的形成过程,制备了白点（氢压裂纹）的真实断口,并与含白点试样的各种断口进行了对比．结果表明,先形成氢鼓泡,然后从鼓泡壁产生微裂纹,它们互相连接形成白点．白点断口和含白点试样的断口概念不同,前者为准解理,与氢致滞后开裂断口相同;后者则依赖断裂方式和试样厚度．钢中白点除了产生二次裂纹外,对各种断口形貌均无影响．车轮钢的滞后断裂由原子氢引起,与白点无关．     

Evaluation of susceptibility of high strength steels to delayed fracture by using cyclic corrosion test and slow strain rate test

To evaluate susceptibilities of high strength steels to delayed fracture, slow strain rate tests (SSRT) of notched bar specimens of AISI 4135 with tensile strengths of 1300 and 1500 MPa and boron-bearing steel with 1300 MPa have been performed after cyclic corrosion test (CCT). During SSRT the humidity around the specimen was kept high to keep absorbed diffusible hydrogen. The fracture stresses of AISI 4135 steels decreased with increment of diffusible hydrogen content which increased with CCT cycles. Their delayed fracture susceptibilities could be successfully evaluated in consideration of both influence of hydrogen content on mechanical property and hydrogen entry.