Quench Hardening Research Articles

Modelling of austenitising with non-constant heating rate in hypereutectoid steels

The calculation of distortion during heating for quench hardening needs an accurate modelling of the austenitising process. In dilatometer tests with constant heating rates, the parameter of a transformation model, which is based on a Johnson-Mehl-Avrami equation, can be determined in a simple manner. Whether the model and the transformation parameters are also valid for austenitising with non-constant heating rates is tested in this work. For this purpose, dilatometer tests were conducted with a change in heating rate during the transformation process of the hypereutectoid steel AISI 52100 (EN 100Cr6). With transformation parameters, which have been determined from austenitising with constant heating rates, the experimental and the calculated strain show no sufficient correlation during continuous heating with a non-constant heating rate. Transformation parameters have to be adjusted to get a good agreement between experiment and simulation.

3D FEM simulation of steel quenching and investigation of the effect of asymmetric geometry on residual stress distribution

During quench hardening of steel components, obtaining the desired distribution of microstructure and residual stresses with minimum distortion is essential in order to achieve production goals and reliable service performance. In this study, a 3D FEM based model, which is integrated into commercial FEA software Msc.Marc ® via user subroutines, has been developed to predict temperature history, evolution of microstructure and internal stresses during quenching. For experimental verification, eccentrically drilled C60 steel cylinders were quenched from 830 °C into water at 20 °C. The results indicate that the model can effectively predict the trends in the distribution of residual stresses for 3D asymmetric components.

Properties of friction welds between 9Cr-ODS martensitic and ferritic–martensitic steels

Friction welding of oxide-dispersion-strengthened-steel (ODS) and ferritic–martensitic 11Cr–0.5Mo–2W, V, Nb steel (PNC-FMS) was examined to investigate the feasibility of the welding of this alloy combination. Forge pressure was varied in the welding test to investigate the effect on the soundness of the weld joint. Post-weld heat treatment was necessary for the weld joint because of quench hardening in the heat-affected zone in the as-welded condition. The welds were cross-sectioned and examined to determine their metallurgical structure, hardness and tensile strength. Since the heat treatment produced a softened zone near the weld interface, the furnace-cooling rate was investigated to determine the rate at which the softening did not occur. The weld joints were cold-rolled and the soundness of the weld interface was determined by tensile testing the cold-rolled weld joints.

Virtual production platform for intelligent quench hardening of large steel moulds for plastic forming

AbstractAn innovative R&D route to improve process design, recently successfully employed by Shanghai Jiao Tong University (SJTU) in cooperation with Fushun Special Steel Co. Ltd and Yanshan University, is described.

A study of particle size effect and interface fracture in aluminum alloy composite via an extended conventional theory of mechanism-based strain-gradient plasticity

Recent experiments have shown that the particle-reinforced composites display significant particle size effect. The classical plasticity theories have no intrinsic material lengths and cannot explain the observed size effects. The strain-gradient plasticity theories have been applied to study the particle size effects in composites, but they tend to predict the stress–strain curves in uniaxial tension that are lower than the experimental data at the small strain (<2%) and become higher than the experimental data at relatively large strain. The present study shows that the discrepancy at the small strain is mainly because the effect of quench hardening is not accounted for in prior strain-gradient plasticity models. The discrepancy at relatively large strain is due to the particle/matrix interfacial debonding. We have extended the conventional theory of mechanism-based strain-gradient plasticity (CMSG) established from the Taylor dislocation model to account for the effect of quench hardening. We have also used the cohesive zone model to study the particle/matrix interface decohesion. The numerical results accounting for quench hardening and interfacial decohesion agree well with Lloyd’s experimental data.

Effect of machining and heating parameters on distortion of AISI 52100 steel bearing rings

In this work, the influences of different heating parameters on distortion of bearing rings (bearing steel AISI 52100, EN 100Cr6) are examined. The rings were machined in two different ways, which led to significant differences in roundness and residual stress distribution after machining. The heating parameters (heating rate, austenitising temperature, and stacking arrangement) were combined in a 23 full factorial matrix. In addition, the influence of preheating and soaking was examined. The cooling rate was very slow in order to avoid additional distortion during the cooling process. Also, distortion after heating and slow cooling is compared to that after quench hardening. The distortion of the rings during austenitising and slow cooling, in terms of change in roundness and change in flatness, is mainly influenced by stacking arrangement. The heating rate has a significant effect on the change in flatness and also influences the change in roundness. In addition, interactions of heating rate and stacking arrangement influence the change in flatness.

The influence of grain size and dispersoids on the quench hardening of a mechanically alloyed Fe-40Al intermetallic

The room temperature strength of FeAl alloys can be increased significantly by freezing in the high thermal vacancy concentrations present at elevated temperatures. In contrast, because of their lower thermal vacancy concentrations, vacancy strengthening in quenched Fe3Al alloys is believed to be much smaller and has not received much attention to date. In the present work, the influence of annealing time and quench temperature on the room temperature strength of extruded and recrystallized Fe3Al alloys is evaluated. For aluminum concentrations between 28 and 32 at% and quench temperatures between 400 and 900 °C both the magnitude and the kinetics of strengthening are found to be consistent with reported values for the thermal vacancy concentrations and vacancy migration rates. To assess the potential contributions of other strengthening mechanisms, appropriate heat treatments will need to be designed in follow-on studies that alter microstructural features relevant to those mechanisms while maintaining a constant vacancy concentration.

The role of carbon and vacancies in the quench hardening and age softening of a Fe-40Al-C alloy

Rapid sintering of FeAl based ultrafine composites by a mechanically activated field-assisted process was evaluated. The influence of applied load and isothermal holding time on the as-sintered microstructure and mechanical properties was investigated. Hardness of the nanocomposite was determined by micro- and nano-indentation techniques, while the grain size was ascertained from electron backscatter diffraction and image analysis of scanning electron micrographs. A higher applied load as well as the isothermal holding time led to better dispersion of the in situ grown Fe3AlCx carbide particles in FeAl matrix. Significant improvement in the hardness and marginal rise in elastic constant were also observed in the fast sintered ultrafine composites when compared to previous reports. The increase in hardness was attributed to the presence of a carbide phase and fine-grained microstructure.

The Role of Carbon and Vacancies in Determining the Hardness of FeAl Intermetallic in the Quenched and the Aged States

ABSTRACTThe role of quenched-in vacancies in FeAl intermetallics on producing considerable hardening is well known, as is the softening on annealing as vacancies are annihilated. The present study examines quench hardening and anneal softening by quenched-in vacancies and interstitial carbon solute in Fe-40Al-C. Interstitial carbon is seen to be a more potent hardening agent than the vacancy, while the co-annihilation of vacancies and carbon atoms from solution during annealing leads to dislocation loop debris, and equiaxed or plate-like carbide precipitation, according to the annealing conditions. The processes occurring have been followed by detailed TEM studies, and are discussed in terms of the relative solubilities and diffusion rates of vacancies and carbon. The relevance of such interstitial solute hardening to the behaviour of other FeAl intermetallics is also briefly considered.

Effect of Microalloying and Thermomechanical Processing on the Structure and Mechanical Properties of Constructional Steel

The effect of microalloying with carbide-forming (V,Ti,Nb) and rare-earth elements and of high-temperature thermomechanical processing (HTMP) on the structure, mechanical properties and low temperature behaviour of 38CrSi steel has been investigated. It has been shown that in the case of dissolution of carbides during heating for quench hardening, the tempering resistance of the steel increases. It has also been found that - as a result of HTMP - the susceptibility of the steel irreversible temper brittleness decreases, irrespective of the steel having been microalloyed or not. The data, originating from tensile testing and impact testing (with the help of laser interferometry) in the temperature range from +20 to -196 degC, has been explained in terms of fractographic analysis. It has been shown that microalloying and HTMP favour the occurrence of ductile microvoids in the fracture. On the other hand, HTMP and rare-earth elements chanches the nature of the fracture at low temperatures, this being in accordance with the data relating to specific energy consumption during fracture.

Mechanical properties and structure of CVD-coated and post heat-treated steels

Post heat treatment of high temperature (HT)-CVD TiN-coated steel substrates 42CrMo4 (4140) and X155CrVMo12-1 (D2) was investigated. The desired substrate structures and hardness could be achieved by post quench hardening and tempering. The coating structure seemed unchanged under light microscopy. The support of the coating by higher substrate hardness was confirmed by higher critical loads in scratch tests. Technological experiments, such as bending tests, alternating bending tests and notched-bar tests, were performed. CVD TiN-coated/post hardened and tempered, and uncoated hardened and tempered steel 4140, reached the same bending 0.2%-yield strength, lifetime at alternating bending, and notch toughness. Bending strength and lifetime at alternating bending of CVD TiN-coated D2 were low compared to the uncoated quench-hardened state because of decarburisation during deposition. These differences disappeared after post quench hardening and tempering. TEM-investigations of the coating/substrate interface were done to explain the structure and mechanical properties of CVD-coated and post heat-treated steels.

A study on heat conduction with variable phase transformation composition during quench hardening

Based on the practices employed with a metal workpiece during quenching, a heat-conduction governing equation set, including variable physical properties, the shape effect, a subcooling boiling boundary and variable phase transformation composition, is put forward and is solved by means of the Finite Element Method. The distributions of the transient temperature and various phase transformation compositions for all elements at different time are obtained, the calculated results being satisfying. A way of optimizing and simulating the technology of the heat treatment by computer is explored.

Stone-working axe heads fabricated by convicts at an early Australian colony

The axe heads are thought to have been manufactured before 1857 by transported convicts in a jail at Fremantle, Western Australia, which was then a remote and isolated British colony. They were of a type used to quarry and dress building blocks from a soft, local limestone and had been fabricated by joining on a central plane by forge welding two plates of puddled wrought iron, a central region being left unwelded to form a shaft hole. A section of crucible steel was then inset into the bit edge, also by forge welding (a process known as “steeling”). This procedure obviously required a high level of blacksmithing skill, and at least a reasonable level of skill had been achieved at the Fremantle jail. However, a number of fabrication abnormalities were present in the axe heads, drawing attention to some intrinsic deficiencies in the fabrication procedure. Examples are the difficulties of achieving weld bonding in regions adjacent to the shaft hole and that of avoiding “burning” in both wrought iron and steel during the steeling operation. High-carbon hypereutectoid steels had been used in the inserts, but they were in a normalized condition; that is, they had not been quench hardened as might have been expected if full advantage were to be taken of steeling. This may have been due to ignorance of quench-hardening heat treatment or to a lack of skill in its application, but it may have been by choice. It may have been realized that the properties of the normalized steel were adequate for the intended use, to which fact one of the axes examined bears witness, thus avoiding the hazards of quench hardening. Even in this event, it would be unnecessary and even undesirable to use insert steels with carbon contents as high as those actually used. Their use may have been due to ignorance in steel selection or it may simply indicate that smiths in such isolated communities had to use whatever materials happened to be at hand.

Finite element simulation of quench hardening

In this study, an efficient finite element model for predicting the temperature field, volume fraction of phases and the evolution of internal stresses up to the residual stress states during quenching of axisymmetrical steel components is developed and implemented. The temperature distribution is determined by considering heat losses to the quenching medium as well as latent heat due to phase transformations. Phase transformations are modelled by discretizing the cooling cuves in a succession of isothermal steps and using the ITdiagrams. For diffusional transformations both Scheil's additivity method and Johnson-Mehl-Avrami equation are used, while KoistinenMarburger equation is employed for martensitic transformation. Internal stresses are determined by a small strain elasto-plastic analysis using Prandtl-Reuss constitutive equations. Considering long cylinders, a generalized plane strain condition is assumed. The computational model is verified by several experimental measurements and by comparison with other known numerical results. Case studies are performed with St50, Ck45 and C60 type of solid and hollow steel components. The complete data and result sets provided for the verification examples establish a basis for benchmark problems in this field.

Comparative study of cooling curves with JIS silver specimens and alloy 600 specimens in relation to additive effectiveness

Quenching- oil cooling curves obtained using a silver specimen (Japanese Industrial Standard K 2242) in-dicate three stages of cooling: vapor blanket, boiling, and convection. The temperatures at which the va-por blanket stage transfers to the boiling stage and the boiling stage transfers to the convection stage are referred to as the characteristic temperature (CT) and the convection- stage starting temperature (CSST), respectively. As the amounts of CT- improving additives are increased in increments of 1,2,3,6, 8, 10, and 12%, the CTs become higher, as clearly shown in the cooling curves obtained using a silver specimen. Likewise, as the amounts of CSST- improving additives are increased from 1 to 2 to 3%, the CSSTs become lower. These tendencies are similarly observed when using an Alloy 600 specimen, and both additives effectively improve cooling performance. However, in the case of 6,8,10, and 12% CT- im-proving additions, the differences among the additive concentrations are more pronounced in cooling curves obtained using the silver specimen than in those obtained using the Alloy 600 specimen. This can be attributed to the greater temperature sensitivity of the silver specimen thermocouple. In field quench-ing operations, such phenomena as insufficient hardness, inverse quench hardening, and unstable distor-tion can be remedied by additive treating. However, one must know what type of additive and how much to use. To this end, cooling curve measurement using silver specimens is useful.

Method for monitoring the mechanical state of a material

A simple but precise method is described for simultaneously measuring the flight times for shear and longitudinal ultrasonic pulses. This measurement can be used to calculate the average tensile or compressive stress component along the propagation path because the two sound speeds depend differently on stress. It can also be used to monitor the ductilities of structural components because the modulus ration G/B which can readily be derived from the two flight times is a measure of the ease of plastic flow relative to the ease of brittle fracture. As an example, it is shown that as a tool steel becomes more ductile during tempering after quench hardening, its G/B ratio decreases. Also, it is shown that G/B varies systematically with atomic number, and that f.c.c. metals with small G/B are ductile but those with high G/B are intrinsically brittle.

Development of Sintered Low Alloy Steels

Abstract Three routes for increasing the strengths of sintered steels are identified. First, strength can be increased by increasing the density of the material, either during the compaction process or during sintering: several possible approaches are suggested. Second, strength can be increased through alloying the metallic matrix: the reasons for the selection of alloying elements, and the methods of alloying are considered. Third, the alloyed metallic matrix can be strengthened either by quench hardening and tempering, or by precipitation hardening heat treatments, but the response to heat treatment depends on the homogeneity of the matrix. The extremely heterogeneous compositions and structures of steels made from elemental or master alloy mixes, partially prealloyed powders, or coated powders present a unique opportunity to engineer structures that have desired combinations of properties. PM/0492

TITANIUM-NICKEL SHAPE MEMORY ALLOY PROCESSED BY RAPID SOLIDIFICATION

ABSTRACT A rapidly solidified equiatomic titanium-nickel alloy for shape memory applications has been produced by melt spinning under an argon atmosphere. The effect of rapid solidification processing and subsequent annealing treatment on the structure and transformation characteristics of the melt spun ribbons have been investigated. Most of the fine grained ribbons have been ground to powder in a vibratory mill and consolidated by a powder metallurgy method to produce bulk shape specimens. In addition, titanium-nickel powder compacts containing varying amount of nickel from 49 to 55 atomic per cent have been examined. The thermoelastic martensitic reaction characteristics are discussed in relation to the refined grain structure and the state of order of the spun products. The quench hardening capability of nickel-rich alloys (≥ 51 at %Ni) is described and related to the supersaturated structure produced by quenching.

A method to judge the quench-hardening of steel from cooling curves of quenching oils

The features of cooling curves for oils using a silver specimen (JIS K-2242) were shown. The cooling curves of steel specimens for the same oils were also measured and compared with those of silver specimen. The CCT diagrams of steels were classified into four types and the temperature range in which rapid cooling is required for quench-hardening for each type of steel was determined and compared with the temperature range for the boiling stage in the quenching of steel, converted from the results obtained from a silver specimen. The V-value is defined as the ratio of the temperature range of the boiling stage to the temperature range which requires rapid cooling. The V-value is a better criterion for quench hardening in oil quenching for given steel than the H-value as a measure of quench severity.

Effect of composition and thermal treatment on the yield stress and resistivity of Pb(Au) alloys

Resistivity measurements show that the earlier reported clustering of Au. presumably to Au 4, in Pb can be largely suppressed by quenching from the homogenization temperature, T h , into cold acetone at 178 K. The extent of suppression is greater the lower is T h . Apparently the clustering goes to completion when the specimens, containing 200 at. ppm Au. are reheated in the temperature range 300–330 K. We also report measurements of the dependence of the critical resolved yield stress. τ cr of singly oriented Pb(Au) crystals stretched at 77 K. on Au concentration. C Au , (0–500 at. ppm) and thermal treatment. τ cr of pure Pb crystals varied by a factor of 5 with the degree of quench hardening, attributed to dislocation loops formed by vacancy condensation. The amount of such hardening was markedly reduced by the presence of Au in solution at T h : the reduction increased with T h . At higher C Au τ cr of specimens, as-quenched or reheated in the range 213–293 K. increases markedly with C Au . This hardening is attributed to the presence of intermediate clusters, presumed to be doublets. Au 2. formed during quenching and upon reheating to 210–215 K. τ cr decreases substantially in the transition, at 300–330 K., of the Au from its state of intermediate to full association. However, when quench hardening is minimal and Au is in its fully associated state. τ cr increases as ( C Au ) 1.2. The results support models in which some vacancies are annihilated in the transitions of dissolved Au from its high temperature to its low temperature, unprecipitated. states.