New Method for Evaluating Thermal Wear of Rolls in Rolling Process

A new method was developed by a thermal wear machine to evaluate the thermal wear of roils in steel rolling process. The steel strip and rolls were simulated by upper and lower heating disks. The upper heating disk could he kept at a temperature of over 900 ℃ by induction heating. The pressure between the disks as high as 323.2 MPa could be achieved and the slipping rate could be 12. 7 %. The thermal wear of high speed steel （HSS） roll material, the wear rate of the HSS roll, and the SEM morphology of a worn HSS roll surface were investigated. This method was useful and could be employed to simulate friction and wear between strip and roll during the strip rolling process.     

高碳高钼高速钢导辊的研究与应用

导辊是高速线材轧机上的主要消耗工具 ,要求高耐磨性、抗粘钢性和热疲劳抗力。普通奥氏体耐热钢 ,马氏体耐磨钢或耐磨铸铁导辊满足不了上述要求 ,使用寿命短 ,降低了轧机作业率。硬质合金导辊具有良好的耐磨性和高温稳定性 ,使用效果好 ,但生产成本高。高碳高钼高速钢具有硬度高、红硬性和耐磨性好等特点 ,但铸造高速钢脆性大 ,采用RE -Mg -Ti复合变质处理 ,可以改变共晶碳化物的形态和分布 ,使铸造高速钢冲击韧性提高 86 .2 % ,热疲劳抗力和耐磨性也明显改善。变质处理高速钢导辊使用中不粘钢、不破碎、不剥落 ,使用寿命比高Ni-Cr合金铸钢导辊提高 3倍以上 ,接近硬质合金导辊     

全机架高速钢轧辊轧制无取向硅钢的应用研究

研究分析了高速钢轧辊的特性、轧辊磨损及高速钢的热膨胀,并通过在无取向硅钢的轧制中使用全机架高速钢轧辊的上机试验,优化轧制工艺,结果表明:与普通轧辊相比,高速钢轧辊轧制无取向硅钢后,有利于延缓边降,利于无取向硅钢的断面控制,从而提升后工序的同板差精度.     

变质处理高碳高速钢导板的研究

导板是线材轧机的关键备件，要求有优良的耐磨性，抗断裂性，抗粘钢性和热冲击抗力，常用高镍镍钢导板和高铬铸铁导板满足不了上述要求，使用寿命短，更换频繁，降低了轧机作业率，增大了工人劳动强度，高速钢具有硬度高，红硬性好和耐磨性好等特点，但铸造高速钢脆性大，通过调整高速钢成分和采用RE－Mg-Ti复合变质处理，可改变共晶碳化物的形态和分布，使高速钢冲击韧性大幅度提高，变质处理高速钢导板使用中不粘钢，不断裂，耐磨性明显优于普通导板。     

Effects of heat treatment and counterface on the wear behaviour of Cr21 cast iron

The unlubricated sliding wear test of high chromium white cast irons (HCCIs) was conducted using a pin-on-disc configuration under different heat treatments and different hardnesses of the counterface. With the increase of counterface hardness (20?HRC–47?HRC–54?HRC), the mass loss of the sample first increases then decreases. When the counterface hardness is 20?HRC, adhesion wear mainly takes place between the high chromium cast iron and the surface of 1045 steel. When the hardness is 47 or 54?HRC, first HCCI’ matrix wear takes place, then carbide bump flakes under alternating stress. The mass loss of the counterface decreases with the increase of hardness for the same sample. The mass loss of quenching, once tempering and twice tempering sample decreases gradually for the same counterface hardness, but fluctuation of the samples’ surface increased. The disc material is always softer than the pin material and results in a severe wear regime operation.     

无莱氏体超硬高韧高速钢M2Si

与Ｍ２钢对比，新型高速钢Ｍ２Ｓｉ的硅含量提高到１．０％，碳含量降至０．５５％。该钢渗碳、淬、回火后的表面硬度高于６７￣６８ＨＲＣ，心部硬度为５５ＨＲＣ，无碳化物偏析及粗大碳化物，是一种价廉的超硬高韧高速钢。     

高速钢复合辊环离心铸造技术研究

高速钢具有硬度高和红硬性好等特点，适合于制造轧钢机辊环，普通离心铸造高速钢辊环工艺简单，操作方便，但辊环内孔硬度高，加工困难，而且合金用量大，成本高，研究了高速钢／球墨铸铁离心复合铸造辊环工艺，对影响复合层质量的因素进行了分析，金属浇注温度和浇注间隔时间是影响复合层质量的关键因素，严格控制离心铸造工艺参数和注注中加入助溶剂，得到了复合层结合良好的辊环，高速钢淬火温度高，降低内层力学性质，通过改进成分，获得的高速钢辊环铸态直接回火后，硬度达HRC64。     

Surface Wave Based Ultrasonic Technique for Finding the Optimal Grinding Condition of High Speed Steel (HSS) Work Rolls

Over the last few years, the use of work rolls for hot rolling of flat steel has been changed from clear chill rolls to indefinite chill, then high chrome steel and now high speed tool steel (HSS). HSS rolls are highly crack‐sensitive because of its high surface hardness. The crack propagation develops within the working surface of the roll, gradually increases in depth and width followed by a large “cats‐tongue” band type spalls of the overlying barrel surface and that leads to abnormal roll failure. This paper presents the development of surface wave based ultrasonic technique to optimize the grinding procedure for having crack free roll surface.     

Effect of composition and milling time on mechanical and wear performance of copper–graphite composites processed by powder metallurgy route

Abstract

Copper–graphite (Cu–Gr) composites with 0, 5, 10 and 15 vol.-% graphite were processed via powder metallurgy route. The effect of composition and milling time on mechanical properties and wear resistance were studied. With increase in vol.-% of graphite, there was decrease in hardness of the composites. However, increasing milling time showed significant increase in hardness of the composites. Compressive strength of the composites containing 5 and 10 vol.-% of graphite was found to be 515 and 393 MPa respectively. The wear tests were carried out using a block-on-ring tribometer at a load of 30 N with varying sliding speed. The wear performance of the composites was found to be better with increase in milling time. The worn surfaces were analysed using FESEM. With increase in graphite content from 5 to 15 vol.-%, the coefficient of thermal expansion of the Cu–Gr composites decreased from 14·1 to 12·2×10^?6/°C.     

淬火温度对M4粉末高速钢组织和性能的影响

为了研究淬火温度对M4粉末高速钢组织和性能的影响, 利用光学显微镜观察高速钢试样的金相组织, 对淬火组织的晶粒度进行评级, 并对回火组织中碳化物的组成和分布进行统计; 采用洛氏硬度计和材料万能试验机测试试样的硬度和抗弯强度。结果表明: 随淬火温度的升高, M4粉末高速钢淬火后硬度先上升后下降, 在1200 ℃时出现最大值HRC62.9;淬火态试样的晶粒度随淬火温度的升高而降低。经三次回火后M4粉末高速钢硬度值较淬火态均有提高, 且随淬火温度的升高, 先增高后下降, 在淬火温度为1190 ℃时达到最大值HRC66.4。随淬火温度的升高, 回火态试样的抗弯强度逐渐下降, 碳化物聚集长大倾向明显, 尺寸均匀性下降。M4粉末高速钢的最优淬火温度区间为1180~1190 ℃。     

Effects of carbon and chromium additions on the wear resistance and surface roughness of cast high-speed steel rolls

The effects of carbon and chromium additions on the wear resistance and surface roughness of five high-speed steel (HSS) rolls manufactured by a centrifugal casting method were investigated in this study. High-temperature wear tests were conducted on these rolls to experimentally simulate the wear process during hot rolling. The wear-test results revealed that the wear resistance increased with increasing carbon content because of the increased total carbide fraction. In the HSS roll containing a smaller amount of chromium, the wear resistance was improved because it contained a number of very hard MC carbides. However, it showed a very rough roll surface because of the preferential removal of the matrix and the sticking of the rolled material to the roll surface during the wear process. Rolls containing a higher chromium content had very low surface roughness, because of the formation of a larger amount of M₇C₃ carbides of slightly lower hardness and homogeneous wear of the matrix and carbides. In order to improve wear resistance with consideration of surface roughness, the increase in the chromium content, i.e., the increase in the amount of M₇C₃ carbides, which can result in a low surface roughness, was suggested.     

The Transformation of Carbides during Austenization and Its Effect on the Wear Resistance of High Speed Steel Rolls

The transformation of carbides with austenization time of a high speed steel (HSS) roll material, manufactured by a centrifugal casting method, has been studied. The correlation between wear resistance and the type, morphology, volume fraction, and distribution of the carbides has also been investigated. Microstructural observations, X-ray diffraction (XRD) analysis, hardness measurements, and energy dispersive spectroscopy (EDS) have been used to characterize the carbides. The type and volume fraction of carbides were found to change with austenizing time. During austenization, the transformation of the M₃C carbides can be postulated as M₃C + γ-Fe → M₂C, with much finer nodular and rodlike MC carbides also forming through a solid-state transformation. The M₂C carbide decomposes as M₂C + γ-Fe → MC + M₇C₃ + M₆C. The decomposed carbide substantially maintains a platelike shape until the end of decomposition. The most important finding of this study is that austenization results in changes in the type, morphology, volume fraction, and distribution of carbides and that it can be controlled to produced a homogeneous distribution of hard carbides, resulting in an improvement in the wear resistance of HSS rolls. This finding may be of great use for the industrial production of HSS rolls.     

Roll performance – technical overview and future outlook

Abstract

An overview is given of roll developments and experience in the context of hot mills and flat rolled products. After 30 years of slow change, there are now strong productivity and quality incentives driving developments in roll technology. International developments are noted, in particular the acceptance that high speed steel (HSS) rolls must be used to meet current surface finish requirements. The most significant need at present is for an improvement of late stand work rolls.     

Development and Application of Die-Casting High Speed Steel Rolls

Therollslikenickelchromiuminfinitechilledcastiron ,bainiticductileiron ,highchromiumcastironandhardalloyrollhavebeeninvestigated[1- 4] .Theformerthreerollsarecost effectiveandhaveashorterservicelife .Forthelatterone ,ithasexcellentwearresistancebutmuchhig…     

Effect of compacting pressure on microstructure and mechanical properties of carbide cutting tools

Abstract

The effects of compaction pressure on properties of carbide cutting tools containing 80·5 wt-%WC, 5 wt-%TiC, 5 wt-%TaC–NbC and 9·5 wt-%Co were studied. These tools were formed by powder metallurgy with different compacting pressures ranging from 77 to 231 MPa (5–15 tons in^?2) and sintered in a vacuum furnace at a constant sintering temperature (1450°C) and at a constant heating and cooling rate of 5°C min^?1. Green and bulk densities, shrinkage and hardness of the produced compacts were measured. Tool cutting performance has been assessed based on machining a medium alloyed steel workpiece under different cutting conditions and measuring the tool flank wear and the workpiece surface roughness. The microstructure of the compacts was metallographically examined using scanning electron microscopy. The results have revealed that both densities and hardness figures increase with increasing compaction pressures, while shrinkage decreases. Cutting performance has not demonstrated a substantial improvement of the tool's performance and life due to the increasing compacting pressure of these tools.     

高速钢复合轧辊辊套热处理新工艺研究

高碳高速钢是取代普通耐磨合金制造轧辊的新材质,淬火高速钢辊套硬度高,内孔加工性能差.采用控制辊套内层冷却技术,在热处理条件下,获得了内外层组织和性能呈梯度分布的高速钢复合辊套.利用神经网络对保温板的厚度和导热系数、保温涂料的厚度和导热系数与辊套内层硬度样本集的学习,采用改进的BP网络算法,建立了复合辊套热处理保护工艺人工神经网络模型,具有较高的精度和很好的泛化能力,且运算速度快,可方便用于指导实际生产.     

含硼高速钢轧辊的组织和性能

 设计了5种高速钢轧辊材料,利用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射(XRD)等分析手段,并通过硬度测试、冲击韧性试验和磨损试验,对含硼低合金高速钢轧辊材料在铸态、回火后的组织与性能及其耐磨性进行了系统研究。结果表明,含硼低合金高速钢轧辊材料铸态组织包括马氏体基体、残余奥氏体和不同种类的碳硼化合物,其铸态硬度大于HRC 64,碳硼化合物沿晶界呈网状分布。经RE-Mg-Ti复合变质处理后,晶界出现明显的颈缩和断网。对轧辊材料进行回火发现,随着回火温度的升高,轧辊硬度逐渐降低。相同条件下,未变质轧辊材料的韧性较变质轧辊材料韧性略低,加入过量的变质剂反而降低轧辊材料的韧性。磨损试验发现,经RE-Mg-Ti复合变质的含硼高速钢的耐磨性大于对比试样高碳高钒高速钢的耐磨性。     

Effect of Cu3P addition on sintering behaviour of elemental powders in the composition of 465 stainless steel

Abstract

The addition of Cu₃P for developing the high strength 465 maraging stainless steel from elemental powders was studied. The sintering parameters investigated were sintering temperature, sintering time and wt-%Cu₃P. In vacuum sintering, effective sintering took place between 1300 and 1350°C. The maximum sintered density of 7·44 g cm^?3 was achieved at 1350°C for 60 min with 4–6 wt-%Cu₃P. More than 6 wt-%Cu₃P content and temperature >1350°C caused slumping of the specimens. The sintered specimens were heat treated and a maximum ultimate tensile strength (UTS) of 767 MPa was achieved with 4 wt-%Cu₃P content. The maximum hardness of 45·5 HRC was achieved in heat treated condition with 4 wt-%Cu₃P content. Above 4 wt-%Cu₃P content increase in density was observed whereas the response to heat treatment decreased. Fracture morphologies of the sintered specimens were also reported. A comparison of sintering behaviour and mechanical properties of elemental powders with prealloyed powders was also given in the present study.     

轧钢助卷辊和深弯辊堆焊技术研究

采用YJ356-S和YJ358-S焊丝分别堆焊修复轧钢助卷辊和深弯辊,并详细研究了堆焊工艺.助卷辊堆焊层组织为回火马氏体 少量的贝氏体和索氏体,并在马氏体基体上含有高硬度碳化物;深弯辊堆焊层组织为回火马氏体 弥散分布碳化物.回火处理后,助卷辊工作层硬度(HRC)达到59.9,深弯辊工作层硬度达到63.1.磨损试验结果显示,YJ356-S堆焊金属的相对耐磨系数为0.105,YJ358-S堆焊金属的相对耐磨系数为0.121,都具有良好的耐磨性.另外,堆焊时加入电磁搅拌,有利于提高硬度并降低堆焊层的硬度落差,改善堆焊材料的耐磨性.     

High-speed steel rolls used for cold rolling

During cold rolled production of steel,each change of rolls causes a halt in production and affects the roll’s grinding maintenance and consumption.Consequently,rolls are very critical to the costs of steel production. Besides the rolling accidents,surface quality problems,including inhomogeneous wear and a decrease of the surface roughness of the rolls are other main reasons for outage and a change of the rolls.Therefore,safe rolls,with superior wear resistance and roughness retentivity will be a future trend in the cold rolling steel industry.In this study,the property characteristics and in-service performance of high-speed steel(HSS)cold rolling work rolls at Baosteel are discussed.The results of this study indicate that in-service performance of HSS cold work rolls has an improvement over conventional rolls.Implementation of HSS work rolls will prolong the rolling campaign and improve the rolling stability,thus,the cost of cold rolling production can be better controlled.