冷轧工作辊裂纹及剥落原因及预防

该文要针对冷轧机工作辊的裂纹和剥落产生的原因进行了分析,同时制定了避免其可能出现裂纹和剥落情况的预防对策,以便在后期的冷轧辊使用维护中加以修整,保证了冷轧机工作辊的良好性能,延长了轧辊的使用寿命,提高了产品质量及产量,降低了生产成本。     

不锈钢热连轧机粗轧支持辊剥落影响因素的有限元分析

该文分析某2250不锈钢热连轧粗轧机频繁发生支持辊严重边部剥落难题的影响因素。通过理论及实际剥落断口形貌分析,指出世界上不锈钢产量最大的该生产线复杂轧制工艺条件和服役期内辊系力学行为引起的不均匀辊间接触压应力分布是该轧机轧制过程中轧辊剥落的主要原因。根据现场跟踪实测数据,采用大型通用有限元软件建立了四辊轧机辊系三维有限元模型,仿真分析了带钢宽度、轧制力、轧辊磨损对辊间接触压应力峰值和位置的影响。结果表明:随着带钢宽度和轧制力的增大,辊间接触压力峰值增幅明显,辊间接触压力分布不均匀度系数基本不变;在不同磨损阶段,当工作辊和支持辊都处于服役后期时,压力峰值、不均匀度系数显著增大,均在距轧辊辊身边部附近存在接触压应力尖峰,且此位置与实际剥落位置一致。研究结果为成功研制的新支持辊形技术投入长期稳定工业应用累计轧制600万t以上未再发生剥落提供了理论依据。     

高铬离心复合铸铁轧辊辊身工作层剥落分析

高铬离心复合铸铁轧辊辊身工作层在热处理后发生大面积剥落,采用金相检验和化学分析等测试手段对 辊剥落进行了分析,结果表明,化学成分的不均匀分布,造成轧辊辊身工作层组织不连续、碳化物形态各异使螺身工作层硬度不均匀,产生大面积剥落,最终导致轧辊报废。     

轧辊再制造及其表面强化技术的研究进展

轧辊失效形式主要有辊身剥落掉块、大面裂纹、辊身和辊颈断裂等,通过对轧辊的修复和表面强化可以延长轧辊的使用寿命,减少轧辊的消耗并降低轧钢成本。综述了辊身修复和表面强化的几种表面处理技术的工艺、特点与用途;分析了堆焊层的作用机理和气泡产生的原因,指出了使用氮元素在堆焊中的作用;阐述了轧辊表面感应淬火获得较深的硬化层的限制性因素,指出残余应力的产生和分布还需要进一步研究;介绍了热喷涂技术裂纹产生的原因和机理,并讨论了激光重熔对减少热喷涂层裂纹和内应力的影响;总结了轧辊激光表面改性的近期研究进展,讨论了熔池流动性对熔凝层和熔覆层组织性能的影响;最后展望了现有技术的重点研究方向及3D打印技术在轧辊再制造和表面强化中的应用前景。     

轧辊断裂原因分析

某轧辊直径由840mm减少到780mm时发生断裂,未达到其正常使用寿命,采用化学成分分析、断口分析、金相检验以及硬度检测等方法对轧辊断裂原因进行了分析。结果表明：轧辊辊颈与辊身交界处的表面存在微裂纹是导致其发生断裂的根本原因;由于套密封环时操件不当使得该处的表层显微组织发生淬火,形成薄且脆的淬火组织,加之该处为应力集中处,从而导致该处产生微裂纹;已经形成的微裂纹在轧辊工作时所承受压力和扭转力的作用下,由于应力集中裂纹尖端不断向轧辊中心扩展,当裂纹达到一定深度后,辊颈处无法承受外力的作用时便会发生瞬间失稳扩展,导致轧辊断裂。     

关于轧辊肖氏硬度试验方法的研究

关于轧辊肖氏硬度试验方法的研究林巨才（中国测试技术研究院，成都６１００６１）１概述轧辊的硬度是评价轧辊质量的一项十分重要的指标。在轧辊的制造过程中，生产厂家要检查轧辊硬度的高低和辊面硬度的均匀性。即使是轧辊使用厂家，在轧辊的使用过程中，也要经常检查辊...     

大型非均质轧辊辊间接触应力分布规律的研究

针对轧辊表面剥落失效现象,采用非线性有限元方法,考虑轧辊表面淬硬层与其心部金属材料组织性能差别,对四辊轧机工作辊与支撑辊间接触应力问题进行模拟。并将模拟结果与传统强度校核方法进行了对比分析,结果表明非均质条件下的辊间接触应力和支撑辊辊内剪应力峰值及其作用深度均大于传统Hertz公式的计算结果,对于深入分析轧辊的失效行为具有重要意义。     

降低宽厚板轧辊消耗的方法与措施

本文结合莱钢4300mm宽厚板现场轧辊使用情况,分析了影响轧辊消耗的各种因素,找出TSL辊消耗偏高的主要原因,并通过采用各种技术手段,优化了裂纹辊磨削方案以及换辊周期,同时针对影响辊耗的其他因素逐一研究,制定了相应措施,大大降低了轧辊消耗。     

降低中型型钢轧辊辊耗的措施探讨

中型型钢轧辊是工业生产的重要机械设备,对于提高轧件质量和生产效率有着不可替代的重要作用,特别是还可以有效减少轧辊辊耗。在中型型钢轧辊生产过程中,由于轧辊和钢坯直接相接触,因此轧辊的消耗非常大,因此针对中型型轧辊辊耗的原因,积极采取有效措施,最大程度地降低中型型钢轧辊辊耗,延长轧辊的使用寿命。本文分析了中型型钢轧辊辊耗的主要原因,阐述了降低中型型钢轧辊辊耗的有效措施。     

R2粗轧工作辊扁头断裂失效分析

采用宏观断口分析及金相检验，对R2粗轧辊辊颈断裂进行失效原因分析。此辊外层为高铬铸铁，芯部为球墨铸铁，采用离心复合铸造。结果表明，此轧辊在制造过程中出现石墨球化和孕育不良及中心部分缩松等铸造缺陷，组织中出现枝晶点状和厚片状石墨，导致轧辊辊颈强度明显下降，一上机使用即发生断裂。为预防事故的发生，同时提出了一些改进措施。     

冷连轧机工作辊剥落失效分析及改进措施

采用化学成分分析、宏微观检验等方法对1700mm冷连轧机工作辊剥落失效进行了分析,结果表明,工作辊辊身表层基体组织不符合技术要求、显微硬度和残余奥氏体含量过高是导致工作辊内裂剥落的主要原因。提出了改进措施。     

A NEW METHOD FOR THE MEASUREMENT OF MODE II FATIGUE THRESHOLD STRESS INTENSITY FACTOR RANGE ΔKτth

Abstract— In order to evaluate the threshold value Δ K _τth for mode II fatigue crack growth, a new measurement method of mode II fatigue crack growth has been developed. This method uses a conventional closed-loop tension—compression fatigue testing machine without additional loading attachments. Mode II fatigue tests for structural steel and rail steel have been carried out. This method has proved successful and has reproduced mode II fatigue fracture surfaces similar to those found in the spalling of industrial steel-making rolls. The crack length during testing was measured by an AC potential method. The relationships between d a /d N and Δ K _τ and AK _τth for several materials have been obtained.     

Fractographic and Metallographic Study of Spalling Failure of Steel Straightener Rolls

Spalled fragments from work rolls of a steel bar straightening machine were received for failure analysis. Visual inspection coupled with optical and scanning electron microscopy (SEM) were used as the principal analytical techniques for the investigation. Fractographic observations clearly revealed the presence of a characteristic fatigue crack propagation pattern (beach marks) and radial chevron marks indicating the occurrence of final overload through a brittle intergranular fracture mode. The collected evidence suggests strongly that surface-initiated cracks propagated by fatigue mechanism led to spalling, resulting therefore in severe work roll damage and subsequently high machine downtime and maintenance costs.     

A quantitative model for predicting the morphology of surface initiated rolling contact fatigue cracks in back-up roll steels

ABSTRACT A previously presented qualitative model for the rolling contact fatigue and spalling failure of back‐up rolls has been quantified in terms of crack lengths and growth directions. The morphologies of surface initiated fatigue cracks have been predicted using published data on the mode I and mode II thresholds in low carbon and roll steels, respectively, and the theoretical determination of the mode I and mode II stress intensity factors at the tips of the inclined surface cracks. The predictions have been validated by using the results of the metallographic examination of rolling contact fatigue cracks produced in test discs used in experimental simulations and the examination of spalled material from a back‐up roll.     

Subsurface Rolling Contact Fatigue Damage Distribution of Backup Roll After Periodic Dressing

In this paper, subsurface rolling contact fatigue damage distribution of backup rolls after used one time and periodic dressing are theoretically analyzed. The theoretical model established is verified by experiments test on ring samples and dissection part cut from backup rolls used in production. The results reveal that the subsurface damage of ring samples and dissection parts characterized by hardness test is consistence well with the distribution predicted by theoretical model. The maximum subsurface damage of backup rolls gradually moves toward the surface and the spalling of backup rolls can be prevented if suitable dressing amount be selected.     

Silicon nitride materials for hot working of high strength metal wires

For hot rolling, tools are nowadays made of cemented carbides. In service, these rolls suffer from wear and thermal fatigue. Due to the properties of ceramics, their use could cause improvements in tool behaviour. In field tests – when rolling materials with high deformation resistance – cracks developed in the silicon nitride rolls, which grew for a long time period before large parts of the rolls broke apart. In more moderate rolling conditions the rolls operated safely.A FE model is used to analyse the in-service behaviour of cracks in the silicon nitride rolls. For the observed crack path the stress intensity factor of the cracks is determined using the weight function method. It increases up to a crack depth of around 0.35 mm and then decreases again with increasing crack depth. This explains the observed pop-in-type growth of cracks after an overload. Depending on the rolled materials, the popped in cracks have a length of up to 1.2 mm. The further growth of the cracks to a length of several millimetres, which is caused by a fatigue growth mechanism, needs several thousand additional revolutions.     

Modeling fatigue crack and spalling for rolling die under hot milling

In hot milling process, rolling die is subjected to nonsteady conditions which can rise the combinations of fatigue and spalling damage mechanism. An understanding about the failure mechanism of the rolling die is essential under hot rolling process. Fatigue crack growth and spalling process are governed by highly concentrated strain and stress in the crack tip region. Based on the theory of elastic‐plastic fracture mechanics, an analytical model are presented in this paper to determine the elliptical crack growth rate and spalling damage mechanism. The model includes new proposed constitutive equations for fatigue and spalling crack growth. To verify the models, finite element simulation and experimental data are considered. The results show good agreement with finite element simulation and experimental data.     

Life of rolls in a cold rolling mill in a steel plant-operation versus manufacture

Failures of rolls occur due to improper manufacturing and operational parameters. Prematurely failed (spalled) roll samples collected from a reputed steel plant were examined for their chemistry, inclusion content, microstructures, carbide characteristics, hardness and retained austenite content. The residual stresses were also measured on the inner and outer surfaces of the spalled roll pieces. The higher content of retained austenite was primarily responsible for the spalling of indigenous rolls for which subzero treatment has been recommended. Several suggestions have also been made for smooth operation of the mill and consequently for the life extension of work rolls.     

Failure analysis of forged and induction hardened steel cold work rolls

The premature failure of two forged and induction hardened low alloy steel work rolls used for cold rolling of high and medium carbon steel was investigated. Microhardness profiles indicated that the values of the effective induction hardening depth for both rolls are below the user's requirement. Tensile testing results of the core of the rolls indicated that the tensile and yield strengths are also below the manufacturer's requirements, the latter being 50% below the minimum requirements. The microstructure of the spalling surface presented tempered martensite, dispersed chromium carbides and spheroidised pearlite. The presence of spheroidised pearlite may have promoted the sub-superficial nucleation of rolling contact fatigue cracks. The heat-treatment schedule should be optimised in order to increase the depth of the hardening layer and the mechanical properties of the core, so that the contact fatigue life of the rolls can be improved.