Microstructure and wear resistance of highchromium cast iron containing niobium

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content.     

Microstructure and wear mechanism change by Nb added in slag free self-shielded flux cored wire

Abstract

The iron based hardfacing alloys were produced using slag free self-shielded flux cored wires with varying niobium contents. The results show that NbC acted as the nucleus of primary M₇(C, B)₃ (M?=?Cr, Fe mainly) carbides and decreased the amount of M₇(C,B)₃ carbides when niobium was added into the alloys. When 18?wt-%Fe–Nb (60?wt-%Nb) was added, the microstructure of hardfacing alloy transformed from hypereutectic structure to a eutectic one due to the formation of NbC, which consumed a mass of carbon. The microstructure changed into a hypoeutectic structure when the Fe–Nb content was up to 24?wt-%. With the increase in Fe–Nb content, the main abrasive wear mechanism changed from microcracking to microcutting and microploughing due to the formation of NbC and the reduction of primary M₇(C, B)₃ carbides. The wear loss of the alloy with 18?wt-%Fe–Nb addition was the smallest among all the alloys.     

Effect of Ti-V-Nb-Mo addition on microstructure of high chromium cast iron

The effects of trace additions of multi-alloying elements (Ti,Nb,V,Mo) on carbides precipitation and ascast microstructure of eutectic high chromium cast iron containing 2.85wt.％C and 31.0wt.％Cr were i...     

Correlation of microstructure with the wear resistance and fracture toughness of white cast iron alloys

The objective of this investigation was to set down (on the basis of the results obtained by the examination of white cast iron alloys with different contents of alloying elements) a correlation between chemical composition and microstructure, on one hand, and the properties relevant for this group of materials, i.e., wear resistance and fracture toughness, on the other. Experimental results indicate that the volume fraction of the eutectic carbide phase (M₃C or M₇C₃) have an important influence on the wear resistance of white iron alloys under low-stress abrasion conditions. Besides, the martensitic or martensite-austenitic matrix microstructure more adequately reinforced the eutectic carbides, minimizing cracking and removal during wear, than did the austenitic matrix. The secondary carbides which precipitate in the matrix regions of high chromium iron also influence the abrasion behaviour. The results of fracture toughness tests show that the dynamic fracture toughness in white irons is determined mainly by the properties of the matrix. The high chromium iron containing 1.19 wt% V in the as-cast condition, showed the greater fracture toughness when compared to other experimental alloys. The higher toughness was attributed to strengthening during fracture, since very fine secondary carbide particles were present mainly in an austenitic matrix.     

Effect of Nb addition on microstructure and properties of laser cladding NiCrBSi coatings

NiCrBSi coatings with different Nb additions have been prepared by laser cladding. The microstructure, phase composition, hardness, and wear resistance of the coatings were studied by scanning electron microscopy (SEM), electron probe microanalyser (EPMA), X-ray diffraction (XRD), microhardness tester and M-200 wear tester. The results show that the phases in the NiCrBSi coating without Nb addition include γ-Ni, Cr₂₃C₆, Cr₇C₃, Ni₃B, Ni₃Si₂ and CrB. The NbC phase appears in coatings after the addition of Nb element. When the addition of Nb is 2?wt-%, the NbC particles with a size of about 1.2?μm were found in the coating, and the amount of NbC is about 1.8?vol.-%. With the increase of Nb addition, the size and amount of NbC in the coatings also increased. When the addition of Nb is 6?wt-%, the size of NbC is about 2.3–6.1?μm and the morphology of NbC changed from particle to quadrangular and petaloid shaped. In addition, when the addition of Nb is 2?wt-%, the hardness and wear resistance of the coating are the best, and the wear resistance of the coating is 104% higher than that without Nb addition.     

Optimal heat treatment conditions and properties of bimetal (high Cr cast iron/alloyed steel) hammers

Abstract

This study intended to establish the optimal heat treatment conditions for the desired hardness and wear resistance property for the bimetal hammers developed by the authors. The objective of this study is to attain bimetal hammers that have a tough Cr–Ni alloyed steel shank and a high wear resistant high Cr cast iron head to replace conventional single alloy (high Mn steel) hammers. The results show that the optimal heat treatment condition obtained for the bimetal hammers is: destabilisation: 1000–1050°C for 2 h, quench: FAC and tempering: 480–500°C for 6 h. By employing this optimal heat treatment condition, the highest hardness value can be attained along with the best wear resistance property for the head portion and acceptable toughness for the shank portion. The microstructure of the head portion that corresponds to the optimal properties consists of eutectic M₇C₃ carbides, secondary M₇C₃ carbides, tempered martensite and almost nil retained austenite.     

Effect of TiC Particle Additions on Structure and Properties of Hypereutectic High Chromium Cast Iron

The present work studies the effects of titanium carbide (TiC) particle additions on the microstructure and mechanical properties of hypereutectic high chromium cast iron containing about 20%Cr and 4.0%C by the optical microscopy (OM), the transmission electron microscopy (TEM), the X-ray diffraction (XRD) analysis, the digital image analysis system, impact tester, and hardness tester. The carbides of high chromium cast iron are refined gradually and the shape of the primary M₇C₃-type carbides became more isotropic with the increase of TiC particles. When the addition of TiC particles exceeds 1.0 wt.%, the change of microstructure is not obvious. The hardness of high chromium cast iron has a slight increase and impact toughness has a obvious increase with the increase of TiC additions. However, when the addition of TiC particles exceeds 1.0 wt.%, the impact toughness has no obvious change.     

Nb在铸铁中的物理冶金学作用原理

介绍了Nb在铁基合金中的存在形式,根据NbC和NbN在不同铁基合金中的溶度积公式,分析了Nb在铸铁中的存在形式。在此基础上,分析了Nb在铸铁中的作用机理。固溶Nb具有非常重要的调节共析相变及强化铁素体基体的作用,凝固过程析出的Nb（C,N）可显著提高耐磨性,在奥氏体温度区间晶界析出的Nb（C,N）能有效阻止晶粒长大,合适的成分设计和工艺措施可充分发挥Nb的作用效果。     

Development of boron white cast iron

Abstract

With boron substituting for carbon in cast iron composition and eutectic borides substituting for eutectic carbides in microstructure as the hard wear resistant phase, a new kind of wear resistant white cast iron has been developed. The microstructure and mechanical properties of this new white cast iron both in the as cast state and after appropriate heat treatments were studied. The results show that the as cast microstructure of the boron white cast iron comprises a dendritic matrix and interdendritic eutectics, and the eutectic compound is that of M₂B or M′_0˙9Cr_1˙1B_0˙9 type, where M represents Fe, Cr or Mn and M′ represents Fe or Mn. The morphology of the eutectic borides is much like that of carbide in high chromium white cast iron, but the hardness of boride is higher than that of carbide. The matrix in as cast microstructure comprises martensite and pearlite. After austenitising and quenching, the matrix mostly changes to lath type martensite and the eutectic borides remain unchanged. In addition, two different sizes of particles, with different forming processes during heat treatment, appear in the matrix. The boron white cast iron possesses higher hardness and toughness than conventional white cast iron and nickel hard white cast iron, and has a better balance between hardness and toughness than high chromium white cast iron.     

Effect of niobium in medium alloyed ductile cast irons

The present work studies the effect of niobium addition on the mechanical properties and microstructure of an as-cast 4·3%Ni alloyed ductile iron. The experimental iron was made from high purity raw materials in a laboratory induction furnace. Eight castings were produced with niobium content in the range 0–0·8%. Silicon and carbon content were fixed at 2·4 and 3·1% respectively for all the castings. A complete micro-structural characterisation was undertaken for all the as-cast alloys. Niobium was observed to be directly related to the formation of polygonal niobium carbides of the type NbC. Such carbides increased in size and amount as niobium content increased in the alloys. The amounts of pearlite and ferrite phases were not affected by the niobium content added in the present study. Neither nodule count nor nodularity was affected by such niobium addition. Mechanical properties such as hardness, tensile strength, yield strength and ductility were measured for the alloy; a small strengthening of the alloys was observed as the niobium amount increased. Such strengthening is explained in terms of NbC formation during solidification. IJCMR/372     

Effect of structure on the properties of white chromium cast irons

White chromium cast irons are used as wear-resistant materials operating under conditions of intense abrasive and impact-abrasive wear. The high wear resistance of white chromium cast irons is determined primarily by the presence of a large amount (30% or more) of solid chromium carbides of the M₇C₃ type. At the same time, an important effect on their operating characteristics is exerted by the state of the metallic base, which can have various structures depending on the alloying conditions and the heat treatment.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 7 – 10, April, 1996.     

Microstructure and wear characteristics of hypereutectic Fe-Cr-C cladding with various carbon contents

The current study used flux core arc welding to produce a series of hypereutectic Fe-Cr-C claddings with various carbon content. Depending on the carbon content, this research produced hypereutectic microstructures of γ-Fe + (Cr,Fe)₇C₃ carbides. As the carbon content of a cladding increased from 3.73 to 4.85 wt.%, the surface fractions of carbides increased from 33.8% to 86.1%. The morphology of primary (Cr,Fe)₇C₃ carbides also transited from a blade-like to a rod-like shape. With regard to wear performance, the relationship between wear resistance and hardness (H) is non-linear. However, the mean free path (λ) of primary (Cr,Fe)₇C₃ carbides must be considered. Wear resistance is proportional to H/λ. The primary carbides can prevent the eutectic colonies from selective abrasion. The rod-like (Cr,Fe)₇C₃ carbides also provide much better wear resistance because rod-like carbides have a greater hardness. After an abrasive wear process, abrasive particles cause plastic plows when the cladding has lower surface fractions of carbides. The fracture of primary carbides leads into the craters where it occurs in the worn cladding surface with higher surface fractions of carbides.     

Structural features and properties of deformed white cast iron alloyed with vanadium,niobium, and titanium

Conclusions Introduction of more than 0.02% titanium into white cast iron alloyed with vanadium or niobium leads to formation of complex carbides (V, Ti)C or (Nb, Ti)C of compact shape, and this provides a 15% increase in hot plasticity and 15–20% greater wear resistance.Central Scientific-Research Institute of Heavy Engineering. Ural Scientific-Research Institute of Ferrous Metallurgy. ZIL Plant Higher Education Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 55–58, May, 1982.     

含Nb元素堆焊层金属中碳化物的析出行为

以堆焊连铸辊为研究对象,研制三种不同合金元素Nb加入量的药芯焊丝,采用金相显微镜和扫描电镜对其显微组织、碳化物形貌进行了观察. 采用X射线衍射仪对其相结构进行了测定. 采用Thermo-Calc软件对含铌堆焊层金属中碳化物的析出行为进行分析. 结果表明,堆焊层金属显微组织为铁素体、M₂₃C₆和MC. 随着Nb元素含量增加,其显微组织得到细化,NbC沿晶界析出. 热力学计算结果表明,析出碳化物主要为MC,M₂₃C₆. 随着Nb元素含量的增加,MC析出量增多,M₂₃C₆析出量减小. MC中主要是Nb元素,并溶解了一定量的Mo,V,Cr和Fe元素;M₂₃C₆中主要是Fe,Cr元素,即Nb元素含量变化主要影响MC型碳化物.     

Comparative Analysis of the Microstructural Features of 28 wt.% Cr Cast Iron Fabricated by Pulsed Plasma Deposition and Conventional Casting

The effect of pulsed plasma deposition (by an electrothermal axial plasma accelerator) followed by post-heat treatment on the structure and microhardness of a 28 wt.% Cr white cast iron is analyzed and discussed with respect to the microstructure of the conventionally cast monolithic counterpart. The cast iron (as deposited on a 14 wt.% Cr cast iron substrate) had a microhardness of 630-750 HV_0.05; it had layered light contrast/dark contrast structure where dark contrast layers contain fine carbide network. Pulsed plasma deposition followed by heat treatment resulted in a substantial refinement of the microstructure: eutectic M₇C₃ coarse acicular plates in the conventional cast iron were replaced by fine M₇C₃, M₃C₂, M₃C particles (Cr depleted in favor of Fe), while the initial carbide particle of 2-3 μm was reduced to 0.6 μm. Secondary dendrite arm spacing decreased from 15 to 1.3 μm, accordingly. The carbide volume fraction in the post-heat-treated coating remarkably increased with respect to the conventional counterpart resulting in a substantial increase in the coating hardness (1300-1750 HV_0.05). The heat-treated coating displayed higher resistance to three-body abrasion than the as-deposited coating and similar resistance with that of the conventionally cast iron.     

Microstructure of vanadium-, niobium- and titanium-alloyed high-chromium white cast irons

In the present work, additions of 2% vanadium, 2% niobium and 2% titanium were respectively made to a high-chromium white iron (17% Cr) to analyse the effect of these elements on the as-cast structure of the alloy, and their influence on the material's hardness. This study was carried out for different solidification rates, so the alloys were cast into wedge-shaped copper moulds. The recorded solidification rates for the ingots ranged from 1.5 K sec^?1 for a 2 mm thickness section, to 35 K sec^?1 for a 40 mm section. It was found that the addition of these carbide forming elements considerably increased the alloy's hardness by different mechanisms. Vanadium was shown to partition completely to the eutectic carbide phase which increased hardness and the volume fraction of this phase. Niobium and titanium formed extremely hard NbC and TiC respectively, which in turn produced a refinement in the structure and contributed to the increase in hardness of the iron. There was no evidence that these elements influenced the size and morphology of the eutectic carbide M₇C₃ for the experienced solidification rates.     

铌铬白口铸铁中碳化物的形态及其对性能的影响

介绍了铌铬白口铸铁中的碳化物形态及分布规律。认为铌在白口铸铁中以NbC形式与奥氏体形成共晶体,在共晶体内,NbC呈条形放射状;在铌铸铁中加入钛,TiC先于NbC析出,随后NbC围绕TiC结晶,最终形成团块状,使这种白口铸铁具有更高的抗磨性能和更高的韧性。     

Corrosion behavior of Ni-Cr weld overlay alloys with dispersed carbide particles in sodium chloride solution

Ni-Cr weld overlay alloys with dispersed carbide particles were prepared by a plasma transferred arc welding process. The corrosion behavior of the 40 vol% carbide/Ni-Cr materials was studied in sodium chloride solution by electrochemical techniques, scanning electron microscopy, x-ray diffraction, and electron dispersive spectroscopy. The materials under investigation were powder blends of Ni-50 mass % Cr powder mixed with NbC, TaC, TiC, WC, O₃C₂, or VC. The NbC, TaC, TiC, and WC particles partially dissolved in the molten alloy, causing the crystallization of M₂₃C₆. Blends with Cr₃C₂ and VC particles produced the crystallization of M₇C₃, V_xCr_yC_z and M₂₃C₆. The VC/Ni-Cr alloy combination caused preferential localized corrosion and the carbide remained as V_xCr_yC_z. The Cr₃C₂/Ni-Cr alloy combination became studded with the Cr-Cl corrosion product compound. With the WC/Ni-Cr alloy combination, the WC particles became oxidized and corrosion product spread over the matrix. Other carbides were not oxidized, but the matrix of the alloys with these dispersed particles did become covered with Cr-rich corrosion products. The NbC/Ni-Cr material exhibited the best corrosion resistance.     

Microstructure and properties of Cr3C2-modified nickel-based alloy coating deposited by plasma transferred arc process

The nickel-based alloy with 30 wt.% chromic carbide (Cr₃C₂) particles has been deposited on Q235-carbon steel (including 0.12 wt.% C) using plasma transferred arc (PTA) welding machine. The microstructure and properties of the deposited coatings were investigated using optical microscope, scanning electron microscope (SEM) equiped with X-ray energy spectrometer (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), microhardness testes, and sliding wear test. It was found that the γ(Ni, Fe), M₇(C,B)₃, Ni₄B₃, and (Cr,Fe)₂B phases existed in the Cr₃C₂-free nickel-based alloy coating obtained by PTA process. The typical hypoeutectic structure and composition segregation in the solid solution could be found clearly. The addition of 30 wt.% Cr₃C₂ particles led to the existing of Cr₃C₂ phase and the microstructure changing from hypoeutectic structure into hypereutectic structure. The composition segregation in the solid solution could not be found clearly. The average microhardness of the Cr₃C₂-free nickel-based alloy coating increased by 450-500 HV after the addition of 30 wt.% Cr₃C₂ particles. The partial dissolution of Cr₃C₂ particles led to the enrichment of carbon and chromium in the melten pool, and hence caused the formation of more chromium-rich carbides after the solidification process. The undissolved Cr₃C₂ particles and the increasing of chromium-rich carbides was beneficial to enhance the hardness and wear resistance of the Cr₃C₂-modified nickel-based alloy coating deposited by PTA process.     

钨对淬火回火高铬铸铁冲击性能和耐磨性的影响

通过冲击试验和磨损试验,研究了钨含量对淬火回火高铬铸铁性能的影响。结果表明,热处理对钨元素的分布影响不大,钨在基体和碳化物中均匀分布。随钨含量增加,淬火回火高铬铸铁硬度增加,冲击韧度和耐磨性先升高后降低。高铬钨铸铁硬度为62～65 HRC,冲击韧度为6～8 J/cm2,一定量钨的加入能显著提高高铬铸铁的耐磨性。