高速钢复合轧辊表面大面积剥落的原因

通过化学成分分析、力学性能检测、显微组织和断口形貌观察等方法,对高速钢复合轧辊表面大面积剥落的原因进行了分析。结果表明：三次浇注工艺控制不当及心部球墨铸铁液纯净度不够导致复合轧辊中间层与高速钢表层及心部铸铁层的界面处存在大量粗大碳化物、片状分布的疏松孔洞以及聚集分布的夹杂物带等严重缺陷,使得界面处的结合不良;在轧制力的作用下,裂纹在上述缺陷处萌生,并沿缺陷处快速扩展,最后导致轧辊表面发生大面积剥落失效。     

球墨铸铁疲劳裂纹扩展的微观机制

研究了在恒幅拉伸循环载荷作用下球铁的疲劳裂纹扩展的微观机制，分析了石墨形态对铸铁疲劳裂纹萌生及扩展行为的影响。结果表明：铸铁的石墨形态对疲劳裂纹的萌生及扩展有很大影响。灰铁由于在共晶团内石墨片相互连接，疲劳裂纹总是沿着与外应力相垂直的石墨片／基体边界扩展。球铁的疲劳裂纹扩展受基体组织及石墨形态所左右，但在石墨球／基体界面产生的滑移带、塑性区及裂纹尖端钝化区决定着疲劳裂纹萌生及扩展的整个过程。球铁的疲劳裂纹扩展规律是：裂纹连续扩展—急速扩展—裂纹尖端钝化—重新诱发裂纹—连续扩展。     

变质处理铸造高速钢研究的进展

高速钢作为一种重要的高速切削用刀具材料,自从20世纪初问世以来,一直得到广泛的应用。近年来高速钢轧辊应用于轧钢生产中也获得了较好的效果。在高速钢凝固过程中,由于C及碳化物形成元素W、Mo、Cr、V等的偏析,在高速钢晶界上形成大量粗大的连续网状共晶碳化物。网状共晶碳化物既严重割裂基体,又可作为高速钢断裂时的裂纹源和裂纹扩展的途径,使得高速钢晶界脆化     

轧辊用高速钢铸态组织分析

利用XRD、SEM和EDS等方法对几种轧辊高速钢铸态组织中碳化物的类型、形态和分布等进行了研究,并对碳化物的体积分数进行了测定。分析了碳化物对铸态组织的影响以及合金成分与碳化物类型、体积分数之间的关系。结果表明：轧辊高速钢铸态组织主要由马氏体基体和少量的残余奥氏体以及MC型、M6C型和M2C型碳化物组成,其中MC型碳化物是影响轧辊高速钢铸态组织的重要因素。碳化物的体积分数随合金碳含量的增加而增加,并在一定程度上受到钨当量的影响。     

高钒高速钢、高铬铸铁复合轧辊界面对比

采用电磁半连续复合铸造法制成芯轴为45钢的高钒高速钢和高铬铸铁两种复合轧辊,对复合界面的组织和性能进行了研究。结果表明:电磁复合铸造高钒高速钢和高铬铸铁复合轧辊界面两侧都发生了明显的成分扩散,界面(扩散层)显微组织处于过渡状态,宽度基本相同,约为50μm;界面显微硬度均介于耐磨层和芯轴之间,过渡平缓;与高铬铸铁相比,高钒高速钢复合轧辊界面硬度略低,抗剪强度和冲击韧度略高,但两者差别不大,均能满足使用要求。     

高钒高速钢的耐磨性研究

作者通过改变高速钢中含钒量和含碳量,得到不同微观组织和机械性能的磨料基体,并对其磨损性展开研究.结果表明:高速钢的耐磨性通常取决于其硬度和微观结构.硬度低于58HRC时,高速钢耐磨性主要受硬度影响;硬度高于58HRC时,其耐磨性主要取决于基体中VC的含量、形态及分布.当钒和碳含量分别在8.15％～10.20％和2.70％～3.15％之间时,可以得到大量的均匀分布球形组织或块状VC化合物,这种基体组织可以有效抵抗三氧化铝磨料的微切割,并且削弱裂纹的扩展和加深.正因为如此,高钒碳含量的高速钢表现出优良的耐磨性.     

近疲劳强度载荷下WC/Co涂层对300M钢疲劳性能的影响

研究了在近疲劳强度载荷下超音速火焰喷涂WC/Co涂层和电镀铬层对300 M低合金钢疲劳性能的影响.结果表明：WC/Co涂层、电镀铬层试样和300 M钢基体的疲劳强度分别为753,600和720 MPa.在近疲劳强度载荷下,WC/Co涂层试样的疲劳寿命分别为基体和电镀铬层试样的1.5～2和5～10倍.三者的主裂纹源均为基体内部的Al2O3和SiO2夹杂物.电镀铬层中的次裂纹穿过界面并向基体中扩展,在基体表面形成新的次裂纹源,加快了基体中主裂纹源的形成和主裂纹的扩展;而WC/Co涂层中的次裂纹经过界面时向界面方向偏转,形成无支撑涂层,并最终使涂层剥落.     

表面强化300M低合金钢疲劳性能评价及断裂分析

评价了对300M合佥钢2种表面强化技术的疲劳性能。结果表明，HVOF WC／Co，电镀铬涂层和300M基体的疲劳极限强度分别为753．3MPa，600．0MPa和726．7MPa。HVOF WC／Co使基体疲劳寿命提高25％～150％；电镀铬大幅度降低基体的疲劳性能，疲劳寿命降低幅度达70％～95％。疲劳断裂分析表明，三者的主裂纹源均是基体内夹杂物质。电镀铬中的裂纹穿过界面并向基体中扩展，加快了裂纹源的形成和裂纹的扩展，而HVOF WC／Co涂层中的裂纹在经过界面时偏转向沿界面方向，这对裂纹源的形成和主裂纹的扩展没有影响。     

高速钢热轧辊表面温度场的测定与应用

根据热轧生产过程中轧辊的实际边界条件,借助于有限元软件ANSYS建立了高速钢和高铬铸铁热轧辊温度场的数值计算模型,对其工作时的温度场进行了对比分析。结果表明:模型的计算结果与现场下机后辊面温度的实测数据比较吻合;在相同的轧制参数和冷却参数条件下,下机后高速钢轧辊表面温度高于高铬铸铁轧辊的;由于高速钢轧辊的导热率及摩擦因数较高铬铸铁的大,使其旋转一周后达到的最高温度较高铬铸铁轧辊的高65℃左右,达到582.5℃;结合现场的情况,优化了高速钢轧辊的冷却参数,可使其下机后的温度保持在65℃以下。     

高速钢碳化物形貌对热加工及工具寿命的影响

高速钢属莱氏体钢 ,含有大量的合金元素 ,形成了大量的一次碳化物和二次碳化物。一次共晶碳化物呈粗大骨骼状或树枝状分布于钢基体。钢锭虽经轧制或压延 ,但碳化物偏析依然严重 ,沿轧制方向呈带状、全网状、半网状或堆集状分布。碳化物的不均匀度随原材料的直径和厚度的增加而增加。共晶碳化物相当稳定 ,不能用正常的热处理方法消除 ,只有通过改锻击碎共晶碳化物和相应的热处理配合 ,才能使碳化物呈细、小、匀、圆形态分布于钢基体。新技术新工艺的发展 ,使高速钢得以在工具上广泛应用。但往往因原材料碳化物未能得到改善 ,影响产品在国内市…     

Effect of Carbides on Wear Characterization of High-Alloy Steels under High-Stress Rolling–Sliding Condition

This article describes the wear characterizations of high-speed steel composed of vanadium carbide and high-chromium cast iron composed of chromium carbide. These metals were studied under rolling–sliding conditions with a sliding ratio of 10% using a self-made ring–ring wear testing machine. The fine microstructure of carbides and failure behaviors were analyzed by scanning electron microscopy and high-resolution electron microscopy. The results showed that carbide significantly affected the wear properties and failure behaviors of metals. The relative wear resistance of high-speed steel reinforced by vanadium carbides was twice that of high chromium cast iron composed of chromium carbides. Chromium carbide was characterized by a stacking fault substructure, and slips occurred in chromium carbide under high-stress contact, resulting in crack formation. Vanadium carbide was reinforced and pinned by large amounts of nanoparticles, which prevented its dislocation under high-stress rolling–sliding conditions, thereby effectively resisting crack initiation. Furthermore, the (200) lattice plane of vanadium carbide is coherent with the (111) lattice plane of austenite, preventing cracks from forming at the interface of the vanadium–carbide matrix. The morphology and hardness of vanadium carbide also contributed to the excellent wear property of high-speed steel.     

基于GTN模型的冷轧硅钢边部裂纹扩展研究

针对硅钢板容易在冷轧过程中形成边部裂纹,使用Gurson-Tvergaard-Needleman(GTN)微观损伤模型对带有边部微小缺口的硅钢板在冷轧过程中损伤分布以及裂纹的萌生和扩展进行研究。通过拉伸试验和扫描电镜观察分析得到材料的损伤参数f0、fc和fF,进而通过有限元软件ABAQUS模拟得到各轧制工艺参数对缺口尖端区域损伤分布及微裂纹萌生与扩展的影响,仿真与试验结果表明,在缺口尖端形成两条损伤带,最大损伤值随着压下率的增大而增大,同时裂纹长度随着压下率的增大而迅速增加;当工作辊半径较小时更加容易出现裂纹;沿着轧制方向缺口前侧的比后侧更容易产生裂纹,两侧的裂纹长度都随着摩擦因数的增大而增大;裂纹长度会随着张力的增大而明显增大。研究结果为轧制工艺参数的选择提供理论依据和参考。     

X80管线钢焊接接头TEM观察下的断裂行为对比

对X80管线钢焊接接头3个区域的试样在透射电子显微镜（TEM）下进行原位拉伸试验,通过观察各个区域裂纹的萌生与扩展过程,对其微观断裂行为进行了研究和分析。结果表明：母材区中,裂纹萌生扩展主要以多裂纹起裂为主,表现为沿晶扩展的断裂形式,最后造成在切应力作用下的剪切脆性断裂;热影响区内,主裂纹首先在切应力作用下以45°方向起裂,整个扩展过程是主裂纹钝化、位错发射、主裂纹前方无位错区形成、微裂纹形核、主裂纹与微裂纹连接扩展这一多尺度过程不断重复的过程,最后导致准解理穿晶断裂;焊缝区中,从主裂纹分支出多条裂纹,裂纹均以与拉伸轴成45°的方向起裂,表现为沿晶与穿晶混合的断裂模式,最后造成穿晶脆性解理断裂。     

高碳贝氏体轴承钢滚动接触疲劳性能的研究

以GCr15Si1Mo贝氏体轴承钢为研究对象,在油润滑条件和无润滑条件下,对不同初始碳化物体积分数的试样进行滚动接触疲劳试验,采用扫描电镜观察试验前后试样的表面形貌和碳化物分布,并通过Weibull曲线确定试样滚动接触疲劳性能的优劣性。结果表明,在无润滑条件下,碳化物体积分数为1.9%的试样滚动接触疲劳性能优于碳化物体积分数为5.1%的试样。在油润滑条件下,贝氏体轴承钢的滚动接触疲劳性能的优劣性依次为：无初始碳化物试样、碳化物体积分数为5.1%试样、碳化物体积分数为1.9%试样。碳化物作为基体的硬质相,很容易成为疲劳源,无初始碳化物的贝氏体轴承钢的滚动接触疲劳性能优于有碳化物的贝氏体轴承钢;碳化物脱落后的凹坑增大了润滑油和试样表面的粘着力,有利于增加油膜厚度,从而提高滚动接触疲劳寿命。     

Sub-surface damage investigation by high frequency ultrasonic echography on 100Cr6 bearing steel

This paper presents an original ultrasonic technique devoted to the early detection of sub-surface fatigue cracks in 100Cr6 bearing steels. Echographic experiments were carried out during interrupted rolling contact fatigue tests. Crack initiation and crack propagation stages were both investigated. Quantitative measurements of sub-surface crack position, depth and angle with respect to the bearing surface are presented. Experimental results are analysed and discussed in relation to rolling contact fatigue theories. Contrary to what is generally accepted the presented results show that the crack propagation stage could represent an important part of bearing life.     

A study of the structure of forged pieces of 75X3MΦ steel using the ultrasonic method for quality control

The microstructures of 75X3M?? steel specimens that were sampled from forged pieces of support shafts of rolling mills was investigated. A correlation between the presence of a carbide network and increased attenuation of ultrasonic waves was established. Ultrasonic testing was performed using a Krautkremer ultrasonic flaw detector. The microstructure was studied using conventional metallographic-analysis methods. The nanoindentation method was used to measure the Young modulus of the phase components of 75X3M?? steel specimens, carbides, and the matrix. A comparative evaluation of their acoustic characteristics was performed.     

25-12型奥氏体耐热铸钢时效后的组织与性能

研究了经N，Nb和Re微合金化的25－12型奥氏体耐热铸钢的显微组织。该钢淬火时效后的组织由树枝状初晶奥氏体及分布于枝晶间的M23C6共晶碳化物组成，奥氏体中析出了二次M23C6，共晶碳化物附近存在无析出区现象；测试分析了材料的常温力学性能。     

钢轧辊局部冷焊焊缝显微组织控制

在钢轧辊局部缺陷冷焊焊缝中,研究了多元强碳化物元素和RE元素对碳化物数量、形态和基体组织的影响。结果表明,经Nb、Ti、V、Zr、RE的综合作用,促进了碳化物早期、大量弥散析出,抑制了导致脆化的沿柱状晶界的网状析出;由于C主要补固定在第二相,使其固溶态份额降低而导致奥氏体“贫C”,从而形成低碳板条马氏体而避免了韧性较差的高碳马氏体基体产生,显著提高了焊态韧性的冷焊抗裂性。     

稀土及热处理对半钢力学性能的影响

研究了稀土及热处理对半钢组织中碳化物的形貌与力学性能的影响。结果表明：稀土变质后再经热处理能显著加速半钢共晶碳化物的溶解、断网及团聚化,促进颗粒状碳化物的析出,提高其综合力学性能。     

Abrasive wear resistance of spheroidal vanadium carbide cast irons

The effect of the chemical composition and heat treatment on the microstructure and abrasive wear resistance of V-Mn, V-Ni-Cr, and V-Mo spheroidal vanadium carbide cast irons (18–23 vol %) has been studied. The wear resistance has been determined under conditions of wear by abrasives with various hardnesses, i.e., corundum and quartz and compared to that of high-chromium cast iron with 13% Cr. It has been found that the advisability of using high-vanadium cast irons is governed by the hardness of the abrasive. When a hard abrasive, i.e., corundum was used, V-Mo cast iron with the maximum concentration of spheroidal VC carbides, which were uniformly distributed in the martensitic matrix, had the highest wear resistance. When a soft abrasive, i.e., quartz, was applied, high-chromium cast iron with a hardness of 68 HRC, which contained the largest amount of M₇C₃ carbides, was more wear-resistant. In the course of isothermal exposure at 300–1000°C, V-Ni-Cr and V-Mo cast irons with an austenitic structure had high resistance to phase and structural transformations. However, the properties and microstructure of V-Mo cast irons with a martensitic matrix depended strongly on the temperature of exposure during heat treatment.