The wear resistance and worn metallography of pearlite,bainite and tempered martensite rail steel microstructures of high hardness

In order to find out whether it is worthwhile to produce premium rail steels harder than 36–39 HRC and to discover the best microstructure for wear-resistant rail an experimental Cr-Mo alloy rail steel was heat treated to pearlite, bainite and tempered martensite. Each microstructure was prepared at hardness levels of 38, 42 and 45 HRC. These were tested in a dual disk-on-disk machine that closely simulates wheel-rail contact in curves at 1/10 scale. Wear rates were established for dry, grease-sand and pure grease environments. Dry wear rates decreased significantly with increasing hardness in high rails with tempered martensite or bainite microstructures but were almost independent of hardness for pearlite in the range tested. Lubrication reduced the wear rates by up to two orders of magnitude for all microstructures. It is concluded that pearlite gives the best dry wear performance, and there is no advantage in increasing the hardness beyond 38–40 HRC. The superior performance of pearlite in dry wear appears to be due to a very pronounced work hardening near the wearing surface. Electron microscopy reveals a marked refinement in the pearlite microstructure near the wearing surface, and this may explain the high work hardening observed.     

钢轨接口的焊接

唐钢冷轧薄板厂的桥式起重机钢轨以前采用预留间隙的夹板连接方法,此连接方法将钢轨直接固定在梁上,当受到振动、热胀冷缩等因素的影响易发生夹板松动使接口处错位,造成行走轮磨损或毁坏,严重威胁安全生产。现采用在梁与钢轨间铺胶垫板,钢轨接口焊接的无间隙柔性处理后,经一段时间运行,收到良好的效果。为安全生产和经济效益提供了保障。     

Rolling contact fatigue of a rail steel

A laboratory test program to determine the rolling contact fatigue behavior of a 0.5 wt.% C steel under water-lubricated conditions is described. It is shown that the relation between fatigue life and contact pressure is a function of creepage.     

Decarburisation and rolling contact fatigue of a rail steel

Decarburisation is present on all new rails and unless ground off, will be on the running surface once installed. This paper presents a detailed investigation into the effect of decarburisation of rolling contact fatigue and wear. Twin disc testing has been used to study the phenomenon under water-lubricated rolling/sliding contact. Rail discs have been cut from grade 220 rail and heat-treated to give samples with varying depths of decarburisation. It was found that as the depth of decarburisation increased the wear rate of the rail disc increased while that of the wheel disc decreased. The effect of decarburisation on rolling contact fatigue was to increase the crack growth rate of samples with increasing depth. Cracks under rolling contact fatigue were propagated by contact stresses via the fluid pressure mechanism and influenced by microstructure. The effect of decarburisation was predicted to have little effect on rail/wheel contact when scaled from the laboratory tests using the depth of maximum shear stress.     

Magnetic inspection of the hardness of cast-iron milling rolls

The effects of the chemical composition and parameters of the cast-iron smelting and teeming process on the coercive force have been studied. It is shown that only chromium and carbon appreciably affect the coercive force. For rolls with cylindrical surfaces cast from ТПХН-60 iron, a reliable correlation has been established between the hardness and readings of a coercimeter with an attachable electromagnet. For flanges and blooming passes of sizing rolls made from ТШХН-50 cast iron, equations for the relation between the hardness and readings of a coercimeter have been obtained and analyzed. These equations can be used in nondestructive testing of hardness.     

DQ50钢的显微组织对硬度的影响

试验研究了DQ50钢显微组织对硬度的影响,以及该钢在不同冷速下得到的显微组织。研究得出该钢适宜的冷速应选为10－60℃／min。     

Research on overlaying welding rod of high hardness maraging steel

The development of new maraging steel overlaying welding rod, which contains Co, Mo, W and V alloy, solved the problems of poor homogeneity of hardness and mechanical process, prolonged the service life of wear-resistant components and increased the productive efficiency of repairing, greatly benefiting the national economy. __________ Translated from China Surface Engineering, 2006, 19 (3) (in Chinese)     

Analysis and tests of boned insulted rail joints subjected to vertical wheel loads

In traditional railroad tracks, joint bars are being used to connect the ends of adjoining rails. Because the vertical bending stiffness of two bars is generally much lower than of the rails, the passing wheels generate larger deflections in the joint region. This in turn leads to larger wheel forces caused by the dynamics of the passing vehicles and to accelerated track deterioration. In recent decades these expansion joints are being eliminated by the introduction of the continuously welded rails (CWRs). However, the retention of the automatic block signaling system created the need for electrically insulated joints is that the bending stiffness of the insulated joints bars is even smaller than of the non-insulated bars that are being eliminated. There are very few published analyses of joints in track; especilly of insulated joints. The purpose of this paper is to contribute to a better understanding of the mechanics of rail joints. At first an analysis is presented for the joint tests to be conducted. Then a test program is described that utilizes actual bonded joints. The obtained test results are then compared with the corresponding analytical results. The agreement is good. This confirms the validity of the assumed joint model and of the presented analysis. The paper concludes by analyzing the effect of a rail joints in a CWR track caused by a vertical wheel load.     

高铁与城铁混合底架结构的制造新工艺与工装设计研究

研究了由高铁底架结构与城铁底架结构混合而成的轨道车辆车体底架的制造新工艺,该工艺方法有别于以往车辆在底架组成之前将牵引梁与枕梁进行预先合成的组焊方法,而是采用将枕梁单件、牵引梁单件和边梁拼焊成一个底架框架的方法进行组焊。经试验确定,当工艺流程为分别预先组焊地板单件、牵引梁单件和枕梁单件,然后将边梁、牵引梁单件和枕梁单件拼焊成底架框架,最后将预先组焊的地板单件落入底架框架内,最终完成焊接时,得到的焊后变形量最小。变形趋势为宽度方向上两边梁向反面弯曲,长度方向上两端部向正面弯曲。通过设计专用的工装夹具,可使焊后变形量减小;通过焊前预制反变形,可使焊后变形量进一步减小。当焊前预制反变形量达到10 mm时,最大焊后变形量为3 mm。     

Initiation and propagation of surface cracks in rolling fatigue of high hardness steel

Surface cracks initiating flaking failure observed by Sugino in rolling fatigue were further studied.Surface crack initiation was influenced by either running or material conditions, affecting the residual tensile stress just below the rolling contact surface. The fatigue crack is thought to initiate very near the surface by the stress cycle of small tensile residual stress and large compressive contact stress. The amount and direction of the tensile residual stress due to rolling contact varies with the contact geometry, which probably determines the direction of the surface crack and the appearance of flaking. The transition from the surface crack to flaking failure or complete section fracture is material and running condition dependent and is explained by a fracture mechanics concept.     

Improving surface hardness of austenitic stainless steel using waterjet peening process

The present study addresses the effect of multiple jet passes and other parameters namely feedrate and pressure in waterjet peening (WJP) of austenitic stainless steel 304. An analysis of surface integrity was used to evaluate the performance of different parameters in the WJP process. An increase in the number of jet passes as well as pressure leads to a higher roughness and more erosion of the surface. However, the feedrate shows a reverse effect on the surface roughness and erosion. The surface microstructures also show the mechanism of material removal process involving initial and evolved damages. The subsurface hardness shows that treating the surface with a higher number of passes and pressure produces a higher increase of hardness and also a deeper hardening layer. But, a reverse effect on the subsurface hardness was found for the feedrate. Furthermore, cross-sectional microstructures show a higher density of slip bands in the deformed grains of the specimen treated with a higher number of jet passes and pressure. However, the amount of slip bands in the deformed grains is lower with increasing feedrate.     

Effect of hardness difference on the surface durability and surface failure of steel rollers

Experiments with pairs of rollers of different hardnesses designed to assess the effect of hardness difference on surface durability and surface failure are described. Sliding-rolling contact fatigue tests were performed with combinations of thermally refined, through-hardened and induction-hardened 0.45% C steel rollers. The mode of failure is discussed in relation to the hardness difference between the rollers and the presence of residual stresses. The effect of hardness on the modulus of elasticity was also examined. An empirical equation was devised to describe the relationship between the rolling contact fatigue limit under hertzian stress and the surface hardness.     

钢结构框架的施工组织管理

介绍在电除尘工程中钢结构制作、安装的施工组织管理的有效性和经济性。     

基于Online LS-SVM的钢铁件淬硬层深度在线检测

为了实现钢铁件淬硬层深度的在线电磁无损检测,提出了在线最小二乘支持向量机（Online Least Square Support Vector Machine）的建模方法。OnlineLS-SVM是以增量学习训练SVM,以减量学习减少样本数,实现小样本估计的训练方法。实验结果表明,Online LS-SVM不仅能实现钢铁件淬硬层深度的在线电磁无损检测,而且具有学习速度快,泛化性能好,对样本依赖程度低的优点。     

Magnetic method for testing steel ropes

The dependence between the coercive force, the temperature of thermal influence, and the strength of steel ropes has been obtained on the basis of experimental data. A technique for nondestructive testing of the strength of steel ropes operating under conditions of elevated temperatures is proposed.     

磁场作用下轮轨黏着特性研究

利用JD-1轮轨模拟试验机研究水和油介质工况下磁场对轮轨黏着特性的影响。结果表明:在水和油介质工况下,磁场作用下的轮轨黏着力大于无磁场作用的黏着力,其中加磁水介质黏着力相对增幅达20%,加磁油介质黏着力相对增幅达50%;水和油介质工况下,施加磁场时速度对轮轨黏着力影响不大。     

Magnetic and electromagnetic inspection of mechanical properties of high-carbon steel with an initial fine-pearlite structure subjected to high-temperature annealing

We study the possibilities of applying the measurements of major and minor magnetic hysteresis loops and electrical and eddy-current parameters for estimating changes in the strength and plastic characteristics of the high-carbon steel У 10 (with 1.03 wt % C) with a fine-pearlite structure during annealing at 650°C for 10–300 min. We analyze the correlations between the mechanical and physical properties of this steel with pearlite structures differing in morphology and imperfection of cementite, as well as the levels of solid-solution hardening and microdistortions of the ferrite-component lattice.     

Magnetic inspection of the depth and hardness of surface-hardened layers on articles (review)

Examples of nondestructive testing of the quality of surface-hardened layers produced via carburizing, hardening after induction heating, and surface rolling are considered and generalized.     

电磁挂梁起重机吊运钢轨的电气控制系统

随着我国铁路运输列车速度的连续提高,铺设用的钢轨大都采用了型号为60kg／m的钢轨,每根长度达到100m。要吊运这样长度的钢轨,必须对原有吊运设备进行改造。下面介绍为鞍钢大型厂吊运设备改造所设计的电气控制系统。     

Effects of hardness on the solid particle erosion mechanisms in AISI 1060 steel

The mechanisms of mass loss were studied using impacts of single particles (WC spheres $\text{3}\text{16}$ in in diameter) for a 0.6% C steel (AISI 1060 steel) heat treated to give hardnesses of 12, 45 or 60 HRC. Both oblique and near-normal angles of impact were used. A new foil laminate was developed to measure rebound velocity and angle. Velocities of 100–200 m s^?1 were studied. A measurable mass loss was found only at 200 m s^?1. At a hardness of 12 HRC the mode of metal loss involved the loss of shear lips. At 60 HRC the dominant loss mode involves the intersection of adiabatic shear bands (ASBs) and shows a maximum mass loss at near-normal impact. The material with a hardness of 45 HRC shows both modes of mass loss and a maximum mass loss rate at oblique (30°) impact. ASBs on the surface and welding of target material to the impacting ball indicate a high temperature at the surface. However, the material welded to the particle is not a significant fraction of the material lost.