High Chromium Cast Iron Alloy Research Articles

Erosion behavior of various high chromium cast iron alloys exposed to gas-blast stream of ferric oxide particles

Depositing hardfacing material onto a surface with the welding method is a common way of protecting surfaces against wear damage. In this study, five high chromium hardfacing alloys were used to prepare samples for the gas blasting erosion test. Erodent particles were ferric oxide specks with a hardness of 657 HV and an average size of 260 μm. Impinging stream eroded the surface of samples with the gas flow of 100 m/s at an angle of 30° while the particle feed was increased from 140 to 630 g. The results indicated that erosion resistance is dominated by bulk hardness of hardfaced alloys. In addition, the erosion rate for a sample containing Mo, Nb, V, and W was the lowest since it had the highest bulk hardness among all other samples.

Inoculation mechanism and strengthening effect of V-based multi-element multiphase inoculant on high chromium cast iron

High chromium cast iron (HCCI) has been widely used as an antiwear material in the industry. Adding inoculants is an effective way to improve the microstructure and mechanical properties of HCCI. In this paper, a new multi-element V-Fe-Ti-Nb-C-Zr-B ribbon inoculant was prepared by the melt-spinning method, and the effect of inoculant addition on the microstructure and mechanical properties of HCCI was studied. The results show that the inoculant consists of V(Fe, M) matrix, V0.89Ti0.11C0.50-, V2C-, VC1−x-, and V3B2-type multiphase nanocrystalline. Adding inoculant to molten HCCI alters the morphology and size of M7C3 carbide, and the possible inoculation mechanism to the as-cast alloy is: the V(Fe, M) matrix melts first, and then the exposed nanograins are dispersed in the melt; The atoms on the particle surface diffuse into the melt, reducing the nanoparticle size; During pouring, the primary M7C3 carbide, austenite, and the eutectic M7C3 carbide nucleate and grow with these nanoparticles as the cores. After inoculation, the grain size of the as-cast and heat-treated HCCI alloy decreased by 39.8 % and 69.1 %, respectively. The combined effect of solution strengthening and fine grain strengthening increased the hardness of as-cast and heat-treated HCCI alloy by 4.1 % and 6.9 %, respectively. Finally, the impact toughness of the heat-treated HCCI alloy increased by 26.8 %, the friction coefficient decreased by 13.5 %, and the wear loss decreased by 21.1 %.

Effect of Multi-Element Microalloying on the Structure and Properties of High Chromium Cast Iron.

High chromium cast iron (HCCI) has been widely used as wear-resistant material in the industry. Alloying is an effective way to improve the microstructure and mechanical properties of HCCI. This paper added multi-component V-Fe-Ti-Nb-C-Zr-B alloy (VFC) to HCCI, showing a significant synergistic solution-strengthening effect. The results show that the added V-Ti-Nb-B are dissolved in M7C3 carbide to form the (Cr, Fe, V, Ti, Nb)7(C, B)3 alloy carbide, and a small amount of V and all Zr are dissolved in austenite and martensite. Adding VFC into HCCI improved the hardenability of HCCI, decreased the residual austenite content from 6.0 wt% to 0.9 wt%, increased the martensite content from 70.7 wt% to 82.5 wt%, and changed the structure and content of M7C3 carbide. These changes increased the hardness of as-cast and heat-tread HCCI by 1.4% and 4.1%, increased the hardness of austenite and martensite by 7.9% and 7.0%, increased the impact toughness by 16.9%, and decreased the friction coefficient and wear loss by 2.3 % and 7.0 %, respectively. Thus, the hardness, toughness, wear resistance, and friction resistance of HCCI alloy are improved simultaneously.

Study on the Subcritical Quenching Process of High-Chromium Cast Iron Prepared by Squeeze Casting

In this study, the heat treatment process of a high-chromium cast iron (HCCI) alloy prepared via 128 MPa squeeze casting at different subcritical quenching temperatures was investigated. The results showed that subcritical heat treatment can change the martensite content, the carbide type and size of the squeeze casting HCCI microstructure. Furthermore, it was revealed that the subcritical quenching heat treatment can improve the hardness of the liquid-forged HCCIs. When the quenching temperature increased from 500 °C to 530 °C, the hardness of the alloy increased significantly, reaching a maximum value of 57 HRC. Thereafter, if the temperature continued to rise to 630 °C, the hardness decreased rapidly. For impact toughness, when the quenching temperature was 500 °C, the toughness of alloy increased by 0.9 J/cm2 than that of the no heat treatment group. If the quenching temperature continued to increase, the toughness was reduced. Taking hardness and toughness into account, the microstructure evolution diagram of the optimal process-500 °C subcritical quenching process was established, various characterisation techniques were used to gain insights into the optimal heat treatment process. Compared with high temperature heat treatment, subcritical heat treatment can improve the performance of the HCCI alloy and reduce costs.

Influence of Niobium Addition on Microstructure and Machinability of High Chromium Cast Iron

High Chromium Cast Iron (HCCI) is mostly utilised in environments under severe abrasion and corrosion wear conditions, and research on this material with added niobium obtained positive results regarding wear resistance. The casting process has surface finish and dimensional accuracy limitations compared to machining processes. There are too few studies about HCCI machinability and no one about HCCI with niobium additions. HCCI machinability studies may allow new applications for this material when excellent surface finish and high dimensional accuracy are required. This study analyses the influence of 0.5% Nb addition on the microstructure and machinability of a HCCI alloy with 25.6% Cr and 3.2% C. The samples were heat treated and subsequently machined in dry cutting conditions. Annealing was used to facilitate the pre-machining of the samples, which were later quenched and tempered. Microstructure and hardness were analysed at each stage of the heat treatment. The material was machined after tempered using polycrystalline cubic boron nitride (pcBN) tools. The alloys solidified in the hypereutectic condition. The addition of niobium reduced the hardness and carbide volumetric fraction, increased the service life of the cutting tools in all tests, provided better surface finishing and modified the wear mechanisms.

Effect of niobium addition on the properties and microstructure of a high chromium cast iron alloy

High chromium cast iron (HCCI) is usually employed in equipment that experience high abrasive wear and therefore requires high resistance. Niobium could be added to these alloys to improve their resistance to wear. This study consisted in addressing the influence of 0.5% and 1.0% of niobium on the microstructure of a 26% Cr and 2.8% C HCCI alloy. Standard samples – without niobium – and samples with 0.5% and 1.0% Nb were melted, cut and then machined into adequate dimensions for tests. Two groups of samples – with and without heat treatment – were analyzed through X-ray Diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), Vickers and Rockwell-C hardness. Carbides Volume Fraction (CVF) was quantified in the heat-treated samples. The majority of NbC carbides were observed to be thin and presented a hook shaped morphology. In addition, it was noted a precipitation of Nb-rich layers around the M7C3 carbides, which could act as a higher hardness coating. There was significant reduction in carbide volume fraction, from an initial 33.3% to 28.1% for the 0.5 % Nb alloy, and further reduction to 24.9% for the 1.0% Nb alloy, it was also noted an alteration on the quasi-eutectic microstructure to a hypoeutectic microstructure. The NbC carbides prevented hardness reduction as a result of lowering the CVF in heat-treated alloys; however, the alloys without heat treatment experienced reductions in hardness. Keywords: Heat treatment, niobium, high chromium cast iron, microstructure. 1

Green Preparation and Dry Sliding Wear Properties of a Macro-ZTA/Fe Composite Produced by a Two-Step Method

In this paper, a two-step method, rapid-flow mixing followed by high-pressure compositing was used to prepare a macro-ZTA (ZrO2-toughened Al2O3) particles reinforced high chromium cast iron (HCCI) matrix composite. The method is based on the squeeze casting process without general casting pollution problems. The microstructure, mechanical properties and dry sliding wear performance of the fabricated composite were investigated. The results showed that the particles were distributed uniformly throughout the iron matrix and a tightly bonded interface was obtained. Under dry sliding wear conditions, the wear resistance of the composite was significantly improved in comparison with the HCCI alloy, and the relative wear resistance was 1.8 and 2.9 times at the applied load of 300 and 900 N, respectively. When the load increased from 300 N to 900 N, the wear characteristics of the composite changed from shallow and narrow grooves and scratches to damages in the form of fragmentation of particles, transfer layer and interface cracking.

The Effect of Type of Welding Sequence During Hardfacing Chromium Cast Iron for Erosion Resistance

Abstract The paper presents the capabilities of welding techniques to creating properties of wear resistant high chromium cast iron alloy. The use of the right kind of welding sequence allows you to change the structure and properties of the obtained welds. Tests were conducted for one type of additive material in the form of self shielded core wire. In order to determine the effect of the type of welding sequence on the properties of welds performed welding using string bead and weave bead. The resulting weld was tested on hardness and research structure in an optical microscope. In the following studies have been made erosive tests wear of made hardfacing. String beads gave structure rich in carbides and harder about 270 HV of the weld with weave bead. Also, wear resistance was nearly twice as better for welds made with string beads. In the experiment a decisive role in the resistance to wear plays a high hardness of the deposit and the presence of carbides in its structure. Changes in the basic parameters of the deposition process allows for the formation of structure and properties of hardfacing welds in a wide range.

Powder Semi‐Solid Casting Technology for Preparation of High Chromium Cast Iron Alloy

AbstractA new preparation technology, termed powder semi‐solid (PSS) casting, has been developed for the preparation of fine‐grained alloys. In this process, certain amount of alloy powder, which has the same composition as the melt, is added into the melt and then immediately stirred until the powder is uniformly distributed. The M7C3 carbide phases in the as‐cast alloy are fine batten‐like or in equiaxed shape and their ratio of length to radial reduces. The eutectic colonies are refined greatly comparing with that of the conventionally cast alloys, and their size are between 20 and 50 μm. The α‐Fe transferred from primarily precipitated austenite is refined too. Furthermore, the PSS casting technology can also modify the morphology of austenite grains and refine them effectively.

Structure Evolution of the Atomized Powders of Fe-25Cr-3.9C Alloy with Addition of Ni and B Elements

High chromium cast iron alloys are widely used to produce wear resistant components. However, formation of the large carbides restricts their applied range for the components by traditional solidification techniques. The gas atomization is an effective approach to refine their structures, improve their properties and extend their application field. Based on the study of structure evolution of atomized powders of Fe-25Cr-3.9C alloy, this paper investigated the structure evolution of the atomized powders of Fe-25Cr-3.9C alloy with addition of Ni and B elements. It is found that addition of Ni and B elements make more primary lath-shaped phase be formed. As particle size decrease, width of the primary lath-shaped phase gradually decreases, and the structures are all composed of lath-shaped phase in the small powders with diameter less than 38mm. At last, a relative study between two alloys was made, and the structure formation of atomized powders was discussed.

Erosive wear behaviour of weld hardfacing high chromium cast irons: effect of erodent particles

Five commercial hardfacing high chromium cast iron alloys were deposited by flux cored arc-welding method. The solid particle erosion studies were carried out using air blast type erosion test rig with 125–150 μm cement clinker, 125–150 μm blast furnace sinter, 100–150 μm silica sand and 125–150 μm alumina particles at a velocity of 50 m s −1 and at impingement angles of 15–90°. The observed erosion rates were rationalised in terms of relative hardness of erodent particles and ability of erodent particle to cause gross fracture of the carbides. The dependence of erosion rate on impingement angle was found to be quite weak for hardfacing high chromium cast iron alloys. However, significant differences were observed in the ranking of the alloys when eroded with different erodent particles. The presence of large volume fraction of carbides proved to be beneficial to the erosion resistance when the erodent particle were softer than the carbides. With silica sand particles at normal impact and with alumina particles large volume fraction of carbides proved detrimental to the erosion resistance. The operating erosion mechanisms involved small-scale chipping, edge effect, indentation and fracture and fatigue.

Modification of high-chromium cast iron alloy by N and Ti ion implantation

The effects of single- and dual-element (N and Ti) ion implantation on the properties of high-chromium cast iron alloys are investigated. Crystal defects, secondary hardening phase of CrN, and various crystal and amorphous forms are produced by ion implantation, and as a result, the microhardness, wear fatigue resistance, wear abrasion resistance, erosion resistance, and friction coefficient are improved. The developed technology has been successfully applied by the oil industry to prolong the lifetime of cylinder liners by three to four times and that of the rubber pistons in mud pumps by a factor of 2.

Microstructural characteristics and corrosion behaviour of high-chromium cast iron alloys in sugar media

The work is aimed at using high-Cr White Irons in manufacturing equipment for sugar cane industry.