Precipitation Of Fine Carbides Research Articles

The Effect of Tempering Temperature on Microstructure and Wear Behavior of Tungsten and Boron Alloyed Ni-Hard 4 White Cast Irons

AbstractThis study investigates the effect of tempering temperature on the microstructure and wear resistance of high-alloy white cast iron (Ni-Hard 4) with 1.15% W and 0.5% B additions. Specimens were austenitized at 850 °C for 5 h, quenched in air, and tempered at temperatures between 250 and 650 °C for 4 h. Equilibrium and non-equilibrium thermodynamic calculations were performed using Thermo-Calc software. After the microstructural investigations, hardness testing was carried out. A pin-on-disk tribometer was used to conduct wear tests under dry sliding conditions. Microstructure and worn surfaces were examined using light and scanning electron microscopes. The results showed that increasing tempering temperature resulted in a higher volume fraction of carbides. It was found that tempering at 550 °C for four hours increases resistance to wear giving the lowest measured values of weight loss and wear rate. Accordingly, tempering allows the precipitation of fine carbides in the martensitic matrix which may increase wear resistance.

Effects of deep cryogenic treatment on the microstructure evolution, mechanical and thermal fatigue properties of H13 hot work die steel

The service life of hot work die steel is significantly influenced by its microstructure and thermal fatigue properties. This paper explores the impact of deep cryogenic treatment (DCT) on H13 hot work die steel's microstructural evolution and mechanical as well as thermal fatigue properties. The results demonstrate that a portion of unstable retained austenite transforms into martensite during deep cryogenic treatment and numerous finely dispersed carbides precipitate from the matrix, thereby enhancing hardness. Analysis of the average crack length and distribution of thermal fatigue test samples reveals that the average crack length and crack density of DCT-treated samples are lower than those of non-DCT-treated samples. Thermal fatigue cracks in the specimens primarily originated from trigeminal grain boundaries and the carbides are found at the crack tips. DCT facilitates the precipitation of fine and dispersed carbides, imparting a robust pinning effect on boundary migration and thereby impeding the initiation and propagation of thermal fatigue cracks. Furthermore, deep cryogenic treatment results in a reduction in the number of M23C6 type carbides with large particles and an increase in smaller M6C type carbides during the thermal fatigue test. This indicates a positive influence on the carbide distribution and further contributes to the improved thermal fatigue resistance of the hot work die steel.

Influence of solution temperature on microstructure and mechanical properties of DZ411 alloys with different Ta compositions

The influence of solution treatment temperature on microstructure and mechanical properties of DZ411 alloys with different Ta compositions (2.72, 3.10, and 4.00 wt.%) is studied in details. With the increase of Ta composition, the average values of the primary dendrite arm spacing (PDAS) in superalloys before heat treatment are found to increase from 145.9 ± 3.7 to 209.8 ± 7.6 μm, the area fractions of carbides increase from 0.59 ± 0.05% to 0.65 ± 0.05%, the area fractions of γ-γ′ eutectics increase from 4.6 ± 0.05% to 8.1 ± 0.05%, and the cubicity of the γ′ phase also increases. After heat treatment, since the γ′ phase shows more superior high temperature performance in alloys with higher Ta composition, the solution temperature of alloys with higher Ta composition should be increased to promote the dissolution of the coarse γ′ phase. The evolution of carbides is mainly divided into two types: the decomposition of MC carbides: MC + γ → M23C6 + γ′ and the precipitation of fine M23C6 carbides. The increase of cubicity of γ′ phase will increase the interfacial energy of two phases, which can lead to the pile-up of dislocation and improve the microhardness of alloys. The fine M23C6 carbides will hinder the initiation and propagation of cracks, and the interaction of fine carbide particles reduces the stress concentration and improve the fracture strength of alloys. Therefore, the addition of Ta increases the mechanical properties including both tensile properties and microhardness of alloys with higher Ta composition increases more obviously after heat treatment at higher temperature.

Variation of liquation cracking susceptibility for over–aged 247LC superalloy repair weld heat–affected zone

In this study, the liquation cracking temperature range (LCTR) of over-aged 247LC superalloy repair welds was quantitatively evaluated using spot-Varestraint testing, especially for application in the repair weld heat-affected zone (HAZ). The metallurgical mechanism of the evaluated liquation cracking susceptibility and variation of the LCTRs of the over-aged 247LC superalloys was clarified by analyzing the microstructural characteristics at the liquation cracking surface, and using thermodynamic calculations. From the spot-Varestraint tests of the over-aged materials, the LCTR was quantitatively evaluated to be 410 and 620 K for the 500 and 1000 h over-aged specimens, respectively. These results demonstrate that the over-aged 247LC superalloys face significant and serious liquation cracking susceptibility in repair weld HAZ. Based on local element distributions at the liquation cracking surface, analyzed by transmission electron microscopy and the Thermo-Calc calculations, the underlying metallurgical mechanism of high LCTRs of overaged materials could be attributed to the precipitation of fine MC and M6C carbides during the over-aging treatment. The carbides promote local liquation at the interface between the gamma phase at temperatures lower than the equilibrium solidus (1530 K) of the 247LC. The estimated liquation initiation temperatures at the MC/γ and γ/M6C interfaces were 1125 and 1420 K, respectively.

Influence of Cryogenic Treatment on the Corrosion Properties of 42CrMo Low Alloy Steel.

In this paper, the effect of deep cryogenic treatment on the corrosion resistance of 42CrMo low alloy steel is investigated and compared with conventional heat-treated counterparts. The low-temperature treatments of the cryogenic process are -120 °C, -160 °C, and -190 °C, respectively. Electrochemical corrosion tests show that the self-corrosion current density of -120 °C, -160 °C and -190 deep-cooled specimens is reduced by 38%, 20% and 30% respectively compared to the usual heat-treated specimens. Scanning electron microscope analysis shows that the precipitation of fine carbides on the surface of the samples treated at -120 °C has improved their corrosion resistance. Electrochemical impedance spectroscopy also shows that the samples treated with -120 °C cryogenic treatment have the smallest corrosion tendency. At a -160 °C deep-cooling process, the precipitated carbide aggregation limits the corrosion resistance of the material. The corrosion resistance of the samples in the -190 °C process group is between the two. The simulation results also express a similar trend to the electrochemical corrosion results.

Study of solid state transformations and their effect on mechanical response in the stoichiometric Ni2Cr using in-situ synchrotron radiation diffraction experiments

A complete microstructural characterization of the stoichiometric Ni2Cr alloy after different ageing times in which different degrees of order are attained has been carried out. The study of order-disorder transformation has been done using synchrotron radiation diffraction monitoring eventual changes in high-energy X-ray diffraction (HEXRD) patterns every six seconds in the course of differential scanning calorimetry DSC experiments. According to acquired data, the onset of the order-disorder transformation occurs at 630 °C, temperature higher than that reported in previous works. In addition, the appearance of fine carbide precipitation has also been found inside the grains and at grain boundaries. Both ordering of the stoichiometric Ni2Cr and carbide precipitation seems to be responsible for the strengthening of the alloy.

Influence of vacuum graded austempering treatment on microstructure and mechanical properties of M50 steel

By means of microstructure observation and mechanical property tests, the effects of vacuum graded austempering treatment on carbide precipitation, bainite transformation, hardness and impact toughness of M50 steel were studied. Results show that after the steel was vacuum grading treated at 560 °C for 10 min, 20 min, 30 min and 60 min and austempered at 200 °C for 2 h, the microstructure is mainly composed of martensite, acicular lower bainite, retained austenite, and carbides (C) in different shapes. With the extension of the grading time from 10 min to 60 min, the content of precipitated carbides after austempering treatment increases from 2.38% to 3.79%, that of the lower bainite increases from 13.14% to 16.03%, and the hardness decreases from 65.06 HRC to 64.26 HRC. After tempering treatment at 550 °C × 2 h for 3 times, the content of precipitated secondary carbides increases from 3.86% to 5.37%, and the hardness of the steel decreases compared to the corresponding austempered steel. Thereinto, the hardness of the tempered steel with the grading time of 20 min is the highest to be 62.92 HRC. After vacuum grading treatment at 560 °C × 10 min, austempering and tempering treatments, the impact toughness of the M50 steel is 16.63 J/cm2, which is enhanced by 50.6% compared to the steel only with vacuum quenching and tempering. This is related to the formation of bainite after graded austempering treatment and the uniform precipitation of fine carbides after tempering.

Effects of vibration aging on residual stress and performance of instrument-grade TiC reinforced steel matrix composite

• The influence of vibration aging on residual stress relief of composite. • The residual stress, hardness and magnetic property were analyzed. • The underlying mechanisms of the composite were revealed. • An optimal improvement of the composite was achieved. To further improve the long-term service reliability of high-precision inertial instruments prepared with TiC reinforced steel matrix composite materials, vibration aging treatment was carried out to improve the comprehensive properties of the instrument-grade composite. The effects of vibration aging on microstructure, stress relief, hardness, and magnetic properties of the stabilized composite were investigated, and the underlying mechanisms were also elucidated. The results showed that the vibration aging treatment significantly released the residual stress and improved the Vickers hardness of the composite, while also promoting the precipitation of fine carbides in the matrix and the microstructure transformation of metastable retained austenite to relatively stable martensite. When the vibration aging was conducted at 80 °C for 30–60 min, the composite possessed excellent comprehensive properties. During the vibration aging process, various mechanisms, such as residual stress relief, retained austenite–martensite transformation, and carbides precipitation acted on the composite, resulting in a significant improvement in the performance of TiC reinforced steel matrix composite.

Effect of Deep Cryogenic Time on Martensite Multi-Level Microstructures and Mechanical Properties in AISI M35 High-Speed Steel.

High-speed steel is widely used for cutting tools due to its convenience of preparation and cost-effectiveness. Previous research has shown that deep cryogenic treatments improve the mechanical properties of high-speed steel, due to the transformation of the residual austenite and the precipitation of carbide, while few studies have researched martensitic changes. The variations in martensite multi-level microstructures in AISI M35 high-speed steel, treated over different deep cryogenic time periods, were investigated in this study. Meanwhile, the effect of these variations on the mechanical properties of the selected steel was discussed. It was found that prolonging deep cryogenic time facilitated an increase in dislocation, low-angle grain boundary, and the coincident-site lattice boundary (especially the twin boundary) of martensite. The size of the martensite block (db) and lath (dl) decreased with deep cryogenic time. However, the effect on the microstructure was limited when the cryogenic treatment time exceeded 5 h. The increase in dislocation decreased the temperature for carbide precipitation and promoted fine carbide precipitation during tempering. The refinement of martensite multi-level microstructures and the greater precipitation of fine carbides gave the tempered specimens excellent impact toughness. The impact toughness of the tempered samples undergoing deep cryogenic treatment for more than 5 h was about 32% higher than the sample without deep cryogenic treatment.

Microstructure, Mechanical and Wear Behaviour of Deep Cryogenically Treated EN 52 Silchrome Valve Steel.

This study has compared the performance of cryogenically processed EN 52 Silchrome valve steel with untreated material. After completing the standard heat treatment process, EN 52 steel material specimens are subjected to a deep cryogenic process with varying soaking temperatures. The parameters of the deep cryogenic procedure were changed to find the best wear qualities. The key features of valve steel, such as microstructure, mechanical, and wear behaviour are evaluated by conducting a test study. The evolution of wear mechanisms after enhancing qualities of EN 52 steel is studied using scanning electron microscopy. The mechanical and wear behaviour improved due to factors such as fine carbide precipitation, conversion of residual austenite, and carbide refining formed after cryogenic treatment. With a maximum reduction in wear rate of up to 45%, the deep cryogenic treatment of EN 52 steel with a soaking temperature of −140 °C was the ideal parameter. All three cryo-treated samples had better properties than the untreated EN 52 valve steel.

Characterisation of heat-treated cobalt–chromium alloy fabricated by selective laser melting

The present work focuses on the stress-relief annealing (SRA) modification and porcelain firing (PF) treatment effect in biomedical Cobalt–Chromium (Co–Cr) components for dental applications components produced by the SLM process. The specimens’ phase transformation was examined by X-ray diffraction, optical microscopy, scanning and transmission electron microscopy, combined with energy dispersive X-ray spectroscopy. The corresponding mechanical properties were assessed by compression tests and Vickers hardness measurements. The matrix microstructure consisted mainly of the FCC γ phase with a small amount of the HCP-structured ϵ phase. SRA at 750°C and 950°C, followed by PF at the 930°C treatment, increased the percentage of the ϵ phase and caused the precipitation of fine carbides and intermetallic precipitates, thus improving the final mechanical properties.

Precipitation of Fine Carbides, Transformation of the Retained Austenite and Corrosion Properties on EN-31 Steel by Cryogenic Treatment Process

Investigate of precipitation carbides transformation of the retained austenite and corrosion properties on EN-31 steel by cryogenic treatment method. In this work to identify the percentage of retained austenite and corrosion rate, was presented on EN 31 bearing steel by which cryogenic treatment process. Further, the hardness values of CHT and DCT were compared by using the microstructure view of the CHT and DCT samples. The optimized cryotreated samples were prepared for metallographic examination as per ASTM E3-01. Then the specimen was subjected to factor level setting like cooling rate, soaking period, soaking temperature and tempering temperature at various conditions. Moreover, the precipitation of fine carbides and the transformation of retained austenite to martensite showed considerable variations in the hardness of the optimized DCT samples compared to the CHT samples. The mean hardness value of this sample is 861HV and 19.20%, 847HV and 17.25%, 838HV and 17.10%, 857HV and 18.40%, 790HV and 13.45% improvement in the hardness compared to CHT.

Bake hardening of 7Mn–3Al-0.2C steel: Influence of intercritical annealing temperature

Bake-hardening behavior in a medium Mn steel was investigated after intercritical annealing at either 680 °C or 760 °C. After 2% prestraining and baking at 180 °C for 20 min, the 760 °C -annealed steel exhibited bake hardening response (BHR) equal to 156 ± 3 MPa, while the BHR of 680°C-annealed counterpart was 60 ± 1 MPa. The BHR difference was attributed to martensite in the 760°C-annealed steel, which generated dislocations near adjacent austenite and ferrite on martensite transformation during quenching and prestraining. Baking enabled pinning of more dislocations by carbon and precipitation of fine carbides by martensite tempering, which could effectively increase the strength. Moreover, baking changed the state of strain incompatibility between the phases and stabilized austenite in the 760°C-annealed steel. As a result, strain hardening rate stayed at a high level, which enhanced ductility.

Cryogenic treatment of tool steels: A brief review and a case report

Tool steels used in marine industries demand for the effective approach to enhance their properties. Normally, conventional heat treatment is widely used to increase the performance of tool steels. However, this method cannot fully enhance the tool steel performance. On the other hand, cryogenic treatment is a supplementary process to the conventional heat treatment, which can promote the conversion of retained austenite to martensite and accelerate the precipitation of fine carbides. In this paper, a systematic review of cryogenic treatment of tool steels was presented. A wide range of useful investigations was reviewed, particularly in the details of the transformation of retained austenite to martensite and the precipitation of the fine carbides. A case study on a tool steel subjected to conventional heat treatment, conventional cold treatment, and deep cryogenic treatment was also given and discussed to give an insight in the cryogenic treatment of tool steels.

The development of a588 modified laterite steel using thermomechanical and low-temperature tempering process for weather resistant steel

Laterite Steel A-588 has the potential to be a high strength low alloy for Corten steel application. Laterite steel A-588 is developed through a thermomechanical process followed by a tempering process to obtain high strength and corrosion resistance. This study aims to determine the correlation between the addition of nickel content, the variation of the cooling rate during heat treatment to the mechanical properties, and the corrosion resistance of A-588 laterite steel. The Cu, Cr, Ni, P, and Si elements significantly impact microstructure transformation. Laterite Steel A-588 with nickel and thermo-mechanical process variation has been focused on in this research. Laterite steel with 0,42%, 1%, 2%, and 3% nickel varied was homogenized, hot rolled, and heat treated with three cooling variations by water, oil, and air. They are processed with 150 C tempering. Low tempering temperature caused fine carbide precipitation and phase transition of martensite to bainite. This resulted in bainite as the final microstructure, lath tempered martensite, carbide, and ferrite. 3% Ni with a fast cooling rate increased the tempered martensite and bainite phase formation. It allowed the strength and hardness to increase relatively, followed by decreased elongation and corrosion resistance caused by the galvanic reaction. Most optimal of mechanical properties determined at a sample with 2% nickel in a water medium (strength 1203 MPa, elongation 10%, hardness 404 BHN, corrosion rate 1,306 mpy).

Quantifying deep cryogenic treatment extent and its effect on steel properties

Deep cryogenic treatment (DCT) has been known since the 1930s to improve hardness, fatigue resistance, and wear resistance of steel. While the effect of DCT on wear properties has been well documented, there is no consensus regarding the causal mechanisms, nor a widely accepted quantitative description of them. DCT transforms retained austenite into martensite and triggers the precipitation of fine carbides, among other things. We observed that DCT had a negligible effect on Young's modulus and the yield limit of high carbon spring steel. The observed microstructural changes (presence of specific dendritic inhomogeneities typical for inclusions of austenitic phase in non-treated specimens and homogeneous microstructure of treated ones) can serve for qualitative purposes only. However, we found that DCT led to a decrease in steel electrical resistivity which can be explained by noticeable differences between the resistivities of the martensitic and austenitic phases. We propose a micromechanical model for electrical resistivity which allows monitoring of the content of retained austenite and postulate that it can be used for other materials as well. We also observed increased resistivity after mechanical loading of the specimens, correlating with increased dislocation density caused by loading. This quantity can be used to assess the average dislocation density.

Different Response of Cast and 3D-Printed Co-Cr-Mo Alloy to Heat Treatment: A Thorough Microstructure Characterization

The Co-Cr-Mo alloy is a biomaterial with very good corrosion resistance and wear resistance; thus, it is widely applied for knee replacements. The wear resistance is influenced by the amount of hcp phase and morphology of carbidic precipitates, which can both be altered by heat treatment. This study compares a conventional knee replacement manufactured by investment casting with a material prepared by the progressive technology of 3D printing. The first set of results shows a different response of both materials in increasing hardness with annealing at increasing temperatures up to the transformation temperature. Based on these results, solution treatment and subsequent aging at conditions to reach the maximum hardness was applied. Microstructural changes were studied thoroughly by means of optical, scanning electron and transmission electron microscopy. While increased hardness in the conventional material is caused by the precipitation of fine hard carbides combined with an increase in the hcp phase by isothermal transformation, a massive fcc → hcp transformation is the main cause for the hardness increase in the 3D-printed material.

Deep cryogenic treatment of En 31 and En 8 steel for the development of wear resistance

ABSTRACT The deep cryogenic treatment process was used to develop the wear resistance of commercially available general purpose En 31 and En 8 steel. It was carried out at −196°C for 24 h. The dry sliding pin on disc wear tester was used to find the wear loss. Deep cryogenic treatment enhances the wear resistance of En31 steel by 60% when compared with conventionally heat-treated En31 steel samples. For En8 steel, the wear resistance improvement is 32% when compared with conventionally induction hardened En8 steel samples. Scanning Electron Microscopic analysis was done on worn surface of En31 steel samples. The fine carbide precipitation is responsible for the wear resistance improvement.

Effect of Cyclic Cryogenic Treatment on Wear Resistance, Impact Toughness, and Microstructure of 42CrMo Steel and Its Optimization

Cyclic cryogenic treatment, a major cycle accompanied by zero or more subsidiary cycles, was conducted on the hardened 42CrMo steel using orthogonal design method to investigate the effect of different parameters (cryogenic temperature, holding time, and cycles number) of cryogenic treatment on wear resistance and impact toughness of the steel. Range analysis was performed to obtain the influencing order of the three parameters and their optimum values. The results show that after cryogenic treatment, the steel exhibits higher wear resistance and impact toughness, whereas no significant change in hardness. For wear resistance, the influencing order of parameters is cryogenic temperature, holding time, and cycles number, and the optimum values of the parameters are −160°C, 24 h and two cycles, respectively. For impact toughness, the influencing order of parameters is cryogenic temperature, cycles number, and holding time, and the optimum values are −120°C, 24 h and three cycles, respectively. The wear topography and fracture topography were examined using scanning electronic microscopy (SEM) to investigate the wear mechanism and fracture mechanism of the steel after cryogenic treatment, respectively. The results show that after cryogenic treatment, the wear mechanism is the combination of abrasive wear and adhesive wear with oxidative wear, and the fracture mechanism is a quasicleavage fracture. The microstructure was also examined by SEM to investigate the influencing mechanism of cryogenic treatment for improving wear resistance and impact toughness of the steel. It suggests that more precipitation of fine carbides dispersively distributed in the matrix is responsible for the beneficial effect of cryogenic treatment on wear resistance and impact toughness of the steel.

Effect of tempering and cryogenic treatment on wear and mechanical properties of hot work tool steel (H13)

The AISI H13 is a chromium based, medium carbon content hot work tool steel which is widely used in hot working as well as cold working applications. These steels are very popular because of their key characteristics such as high hardness, high strength, high fracture toughness and high wear resistance. These steels are continuously subjected to high mechanical stresses and temperature fluctuations, fatigue and wear loss which results in limited die life. It is therefore necessary to improve the properties of these tool steels. One of the methods to improve the properties of these tool steels is with the help of conventional heat treatment. But no significant improvements in the properties were observed. From the literature survey, it is realized that implementation of cryogenic treatment can improve the properties of tool steel. In the present paper, cryogenic treatment on AISI H13 hot work tool steel is studied with the help of characterization techniques such as hardness, wear and microstructure study. One set of specimens were subjected to conventional heat treatment (HTT) viz. hardening at 1020 °C followed by double tempering at 500 °C. Another set of specimens were subjected to conventional heat treatment followed by deep cryogenic treatment at −196 °C and soft tempering at three different temperatures viz. 200 °C, 300 °C and 400 °C (HTTCT). A modified heat treatment cycle (HTCT) is also proposed with varying soft tempering temperatures viz. 200 °C, 300 °C and 400 °C and comparison is made with HTT and HTTCT. The specimens were tested for hardness, wear and microstructure study. The experimental investigation shows that cryogenically treated specimens shows significant improvement in the hardness and carbide density as compared to conventionally treated specimens. It is thus concluded that HTTCT cycle gives two times higher wear resistance than conventional heat treatment cycle (HTT) because of precipitation of fine tertiary carbides.