Showing papers on "Quenching published in 1985"

Turbulent flame propagation in obstacle-filled tubes

Abstract: Turbulent flame acceleration experiments have been carried out in steel tubes of 5 cm, 15 cm and 30 cm diameter and ranging from 11 m to 17 m in length. Circular orifice plates spaced on diameter apart were used as flow obstructions. The blockage ratios BR=1−(d/D)2 are 0.44, 0.39 and 0.28 corresponding to orifice diameters of 3.74 cm, 11.7 cm and 25.8 cm for the 5 cm, 15 cm and 30 cm diameter tubes, respectively. Mixtures of hydrogen, acetylene, ethylene, propane and methane with air were used over a range of fuel compositions. The results indicate the existence of four propagation regimes: the quenching, the choking, the quasi-detonation and the C-J detonation regimes. In the quenching regime, the flame is first found to accelerate and then extinguish itself after propagating past a certain number of orifice plates. The flame propagation process in the quenching regime can be considered as the successive ignition of a sequence of chamber separated by the orifice plates. Ignition in one chamber is due to the venting of the hot combustion products from the upstream chamber through the orifice. Quenching occurs when the jet fails to ignite the mixture due to too short a mixing time when compared to the chemical reaction time. For mixtures very near the limits, an alternative quenching mechanism due to flame stretching is proposed. When the flame is not quenched, it eventually reaches a steady state. It is found that gasdynamic choking (sonic conditions) due to friction and heat release provide the controlling mechanism for the steady state flame speed. Again, for near limit mixtures, the steady state condition may be brought about by the positive and negative effects of flame stretching in the augmentation of the burning rate. For most of the cases of interest, the choking mechanism prevails. For the more sensitive mixtures, transition to detonation is observed. The transition criterion requires that the ratio of the orifice diameter d to detonation cell size λ be in the range 1d/λ≤13. In the present study where the blockage ratios are of the order of BR≈0.4, the critical value is d/λ≈3. The detonation under these conditions is observed to travel in the obstacle-filled tube at velocities significantly below the normal C-J value in accord with the previous observations of detonation propagation in very rough tubes. Such detonations are referred to as quasi-detonations. When the mixture is sufficiently sensitive such that d/λ13, then the detonation propagation becomes insensitive to the blockage effects of the obstacles and the combustion front is observed to propagate as a normal C-J detonation wave.

Mathematical model coupling phase transformation and temperature evolution during quenching of steels

Abstract: To calculate the internal stresses in steels during quenching it is necessary to be able to predict accurately the evolution of phase transformations during the cooling process. After a review of published papers, a mathematical model coupling phase transformations with temperature field predictions at each instant during the cooling process is proposed. Incubation and growth periods are treated separately, using Scheil's method and the Johnson–Mehl–Avrami formulation, respectively. Martensitic growth is considered separately using the Koistinen and Marburger law. The temperature field calculation is carried out by the resolution of the heat equation using an implicit finite–difference method. An internal heat source term has been included in the heat equation to take into account the heat generated by the phase transformation. The results of the theoretical calculations are compared with those obtained by experiment, and the validity of the model and the effect of internal stresses on the theoret...

Some heat treatment experiments for Nd-Fe-B alloys

Abstract: Since the Curie temperature (Tc) of R-Fe-B permanent magnets is lower than conventional 1/5 and 2/17 magnets, the irreversible loss due to the change of coercivity is critical when considering their application. The simple way to guarantee the thermal properties is to raise the coercivity at room temperature. The effect of heat treatment on coercivity was studied. The typical heat treatment is as follows: (1) The first heating at T 1 , 900°C × 2 hrs is followed by the continuous cooling at the rate of 1.3°C/min to room temperature. (2) The second heating at T 2 , near the eutectic temperature for 1 hr is followed by quenching. When employing this heat treatment, the following magnetic properties were obtained for Nd(Fe 0.92 B 0.08 )6. Br=13800 G, bH c =9150 Oe, iHc=9200 Oe and (BH)max=44.0 MGOe.

Magnetic properties of high-concentration Fe-Ag alloys produced by vapour quenching

Abstract: Alloys of Fe1-xAgx obtained by vapour quenching have been investigated by X-ray diffraction and magnetisation measurements. The single BCC phase extends up to about x=0.14, while the single FCC phase exists above x=0.6. For x=0.14-0.6, there is a mixed BCC and FCC phase. The average magnetic moment decreases with increasing x. It deviates upwards from the simple dilution law in the BCC and FCC alloys with x=0.6-0.7. The Curie temperature, TC, is about 900K for the BCC alloy with x=0.1, while TC is about 550K for the FCC alloy with x=0.6 and decreases with increasing x to zero at about x=0.95.

Formation, structure, and crystallization of metastable quasi-crystalline Al-transition metal alloys prepared by rapid solidification

Abstract: Metastable Al86Cr14, Al86Mn14, and Al86Fe14 were prepared by rapid quenching from the melt at a rate of approximately 2 × 106 K/s. The X-ray measurements of all three alloys show similar non-Bravais structures. Broadened diffraction peaks for the Al–Fe alloy suggest a crystallite size of about 60 A. Thermal-analysis measurements show that all of the alloys transform into conventional crystal structures at approximately 670. The crystalline phases for the three alloys are Al11Cr2 + Al, Al6Mn + Al, and Al6Fe + Al. At approximately 800 K, Al–Fe undergoes the further transition Al6Fe → Al3Fe + Al.

Analysis of residual stress and distortion resulting from quenching in large low-alloy steel shafts

Abstract: In order to predict residual stresses and distortion caused by quenching in a large low-alloy steel shaft, a computer program based on the finite element method was developed, and uniaxial restraint testing of the transient strain during cooling was carried out. Using the program, the transient stresses occurring during quenching are calculated by a step-by-step procedure, and the effects of transformational behaviour on residual stresses and distortion discussed. The results show that the transient stresses and the transformation affect each other, and that residual stresses and distortion are strongly related to the transformational behaviour.MST/8

Modified heat treatment for lower temperature improvement of the mechanical properties of two ultrahigh strength low alloy steels

Abstract: In the previous papers, a new heat treatment for improving the lower temperature mechanical propertise of the ultrahigh strength low alloy steels was suggested by the authors which produces a mixed structure of 25 vol pct lower bainite and 75 vol pct martensite through isothermal transformation at 593 K for a short time followed by water quenching (after austenitization at 1133 K). In this paper, two commercial Japanese ultrahigh strength steels, 0.40 pct C-Ni-Cr-Mo (AISI 4340 type) and 0.40 pct C-Cr-Mo (AISI 4140 type), have been studied to determine the effect of the modified heat treatment, coupled above new heat treatment withγ ⇆ α′ repctitive heat treatment, on the mechanical properties from ambient temperature (287 K) to 123 K. The results obtained for various test temperatures have been compared with those for the new heat treatment reported previously and the conventional 1133 K direct water quenching treatment. The incorporation of intermediate four cyclicγ ⇆ α′ repctitive heat treatment steps (after the initial austenitization at 1133 K and oil quenching) into the new heat treatment reported previously, as compared with the conventional 1133 K direct water quenching treatment, significantly improved 0.2 pct proof stress as well as notch toughness of the 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel at similar fracture ductility levels from 287 to 123 K. Also, this heat treatment, as compared with the conventional 1133 K direct water quenching treatment, significantly improved both 0.2 pct proof stress and notch toughness of the 0.40 pct C-Cr-Mo ultrahigh strength steel with increased fracture ductility at 203 K and above. The microstructure consists of mixed areas of ultrafine grained martensite, within which is the refined blocky, highly dislocated structure, and the second phase lower bainite (about 15 vol pct), which appears in acicular form and partitions prior austenite grains. This newly developed heat treatment makes it possible to modify the new heat treatment reported previously so as to raise 0.2 pct proof stress to a higher level and keep notch toughness at the same level. The improvement in the mechanical properties is discussed in terms of metallographic observations and the modified law of mixtures and so forth.

Crystallography and tempering behavior of iron-nitrogen martensite

Abstract: Iron-nitrogen martensite was prepared by the gaseous nitrogenization of iron in the austenite-phase field, followed by quenching. Low- and high-nitrogen contents (lathvs plate morphology) were investigated. Optical microscopy, transmission electron microscopy and diffraction, and differential thermal analysis were employed to study the crystallography and the tempering behavior of the martensites. The orientation relation between austenite and martensite, the habit plane and types of (post-) transformation twins were determined. Tempering-induced changes in hardness and release of heat were related to structural changes as revealed by electron diffraction. Differences with analogous iron-carbon martensites were discussed. Aging at room temperature leads to nitrogen diffusion-controlled precipitation of coherentα″-Fe16N2 platelets, which process is completed after about one day. Aging at higher temperatures (up to about 475 K) results in incoherentα″particles, which, at temperatures above 460 K, exhibit small deviations (≃18 deg) from the usual {001}α′/α habit plane.

On low-temperature ion-beam mixing of thin markers in nickel

Abstract: Thin gold and platinum markers in nickel have been mixed in the temperature range 20–300 K with incident ions ranging from N + to Xe + , including Sb + and Sb + 2 . In this way, the energy density and quenching time of the cascade and the chemical properties of the mixed species are varied. After mixing, the composition is measured as a function of depth by in situ Rutherford backscattering. In addition to ballistic mixing, the data indicate that interstitial diffusion, or some other low-temperature diffusion mechanism, may play an important role. Also, spike effects are indicated.

Influences on development of thermal and residual stresses in quenched steel cylinders of different dimensions

Abstract: In the numerical treatment of thermal and transformation stresses produced during quenching, and of the resulting residual stresses, calculations carried out using computer programs are for economi...

Structure and hardness of laser-processed Fe-0.2%C-5%Cr and Fe-0.2%C-10%Cr alloys

Abstract: The effects of high quench rates achieved through a laser surface-alloying process on the martensitic transformations of Fe-0.2%C-Cr steels (up to 10wt% chromium) were investigated. The microstructural variables: martensitic morphology and its substructure; amount of retained austenite; and carbide precipitation were characterized by optical metallography and thin foil transmission electron microscopy (TEM). The microstructures exhibited were fully lath martensitic type, the substructure of which consisted of dislocations. The morphology and substructure of martensite were influenced neither by the chromium content of the alloy nor by the laser parameters (or melt depth) employed. Thin films of retained austenite were observed at packet and lath boundaries of martensite and at prior austenite grain boundaries. The amount of retained austenite was found to decrease with decrease in melt depth. TEM studies also revealed the presence of more or less continuous cementite films both at the lath boundaries and within the laths. Microhardness measurements had shown that the hardness increased with increase in chromium content of the alloy but appeared to be independent of melt depth.

Process for forming seamless tubing of zirconium or titanium alloys from welded precursors

Abstract: Seamless tubing is formed from welded precursors of zirconium or titanium material by heating successive axial segments of welded tubing completely through the wall of the tubing to convert the material to the beta phase and then rapidly quenching the segments, with the heating and quenching effected so as to prevent the growth of beta grains within the material.

Amorphous superconducting Nb3Ge and Nb3Ge1−xAlx powders prepared by mechanical alloying

Abstract: Amorphous superconducting Nb 3 Ge and Nb 3 Ge 1− x Al x powders were prepared by mechanical alloying in a high-energy ball mill in a purified argon atmosphere. For the characterization of the fine powders and microcompacts and the relationship between the effective particle size and the milling time, X-rays, scanning transmission electron microscopy (STEM), differential scanning calorimetry (DSC), and chemical analysis were used. The medium effective particle size of the amorphous alloys carried out by STEM and X-rays was between 1.3 and 3.0 nm. The exothermic peaks of the crystallization of the amorphous NbGeAl prepared by mechanical alloying are very similar to those of the liquid quenching splats. The transition temperature (90% of T c onset) of the amorphous powders was between 3.44 K ( ΔT c =1.32 K ) for Nb 75 Ge 25 and 1.95 K ( ΔT c =0.42 K ) for the Nb 75 Ge 13 Al 12 .

Lithium quench‐condensed microstructures and the Aharonov–Bohm effect

Abstract: We describe an apparatus and our method for fabricating and measuring in situ lithium quench condensed microstructures at dilution refrigerator temperatures. We then discuss our observation of normal‐metal flux quantization in these structures.

A comparison of glass forming ability in Ag-Si and Au-Si alloys

Abstract: Ag-Si alloys of various compositions were produced by laser-induced melting and quenching of vapour-deposited thin films. Despite cooling rates approaching 1010K/s the procedure fails to yield glassy phases for all compositions except those around 80 at.-% Si. This behaviour contrasts with that of the Au-Si system which under similar experimental conditions yields glasses at almost arbitrary concentrations. The difference in glass forming ability of these two systems, which have similar phase diagrams, is explained in terms of the difference in the heat of mixing of the liquid, and its consequent effect on both the thermodynamics and kinetics of these alloys.

Stresses and phase transformations occurring in quenching of carburized steel gear wheel

Abstract: A method for analysing temperature, metallic structures, stress and strain, and carbon content during the carburized quenching of a steel gear is presented, and the results of calculations using the finite element method are compared with experimentally measured data. Since carburization precedes quenching, a diffusion equation is solved in order to determine the carbon content. Calculated profiles of temperature, stresses, and martensite and pearlite volume fractions during quenching are presented, and the effects of coupling between them are also considered.MST/19

Numerical calculations of residual–stress relaxation in quenched plates

Abstract: Methods of thermal stress relief such as stretching and compression are compared for different thermal and mechanical properties during quenching. The heat equation for a simple geometric model, such as an infinite plate, is solved with an experimental surface conductance and a step–by–step method of determining the temperature field in the thickness of the plate. This field is introduced as data for the uncoupled thermal elastic–plastic model for quenching. In the calculation of the plastic–strain path, the thermal and mechanical properties are considered as temperature dependent for a homogeneous and isotropic material. Good agreement is found between the calculated residual stresses and experimental values for an aluminium alloy and a stainless steel. The predicted residual–stress distributions and strain history are then used as data for the numerical simulation of stress–relief methods with an incremental integration of the Prandtl–Reuss equation. This analysis allows the observation of the e...

Method for heat treating ferrous parts

Abstract: Ferrous parts are heat treated by preheating the part to an elevated temperature, inductively heating the preheated part to an austenitizing temperature followed by quenching and isothermal transformation in a media maintained at a predetermined isothermal transformation temperature.

Amorphization of AlAu by low temperature ion irradiation

Abstract: Crystalline Al0.67Au0.33-(Al2Au)-films were irradiated at low temperatures (T<10 K) with Ar- and He-ions, respectively. The resulting structure was analyzed by in situ electron diffraction and resistivity measurements. Both types of projectiles lead to an amorphous (a-) phase, which is identical to the one found after vapour quenching at temperatures below 80 K. Irradiation at 80 K resulted in the amorphous phase only for Ar-ions, not for He. The results will be discussed within the picture of spikes.

High strength, highly conductive heat resisting copper alloy

Abstract: PURPOSE: To obtain the titled alloy superior in strength, conductivity, heat resistance, workability and plating adhesive property, by adding specified quantities of Ti and the third element to Cu. CONSTITUTION: As for material for lead frame or connector in semiconductor integrated circuit, copper alloy in which 0.05W2.0wt% Ti and ≤5.0wt% total quantity of one or ≥2 kinds selected from Sb, Ag, Te, Si, Cr, Co, Fe, P, Sn, Mg, Al, Mn, La, Ce, Y, Be, Ni as the third element X are added to Cu, is used. The alloy is hot and cold worked and annealed at 500W650°C without soln. treatment at high temp. water quenching and aging treatment. Thereby, Ti in Cu is pptd. as Cu-Ti, Cu-Ti-X, Ti-X compd. Copper alloy having superior strength, conductivity, heat resistance, workability and plating property (solder ing property) is obtd. COPYRIGHT: (C)1986,JPO&Japio

Potential of shock-wave methods for preparing and compacting rapidly quenched materials

Abstract: Interest in rapidly quenched metal alloys (amorphous, fine- and microcrystalline) is connected with a number of their unique properties: low magentic losses; high-strength characteristics; corrosion and radiation resistance, etc. Shock-wave loading methods make it possible not only to compact amorphous materials but, according to the authors, may possibly be used for the rapid quenching process itself. These types of application for shock-wave deformation are due to several features discussed in this paper: high heating rate; nonuniform warm-up of porous materials; high cooling rate of compacts; breakdown of oxide films at particle surface, and dependence of component temperature in porous mixtures in material size fraction and properties. Criteria for obtaining strong compacts and the basic properties of materials obtained by dynamic compaction are also discussed. The features of dynamic loading for porous materials make shock-wave methods promising, both from the point of view of compacting rapidly quenched alloys, and from the point of view of carrying out the quenching process itself.