Critical Cooling Rate Research Articles

Construction and Application of Quenching Critical Cooling Rate Model

Based on exploring quenching mechanism, three types of quenching critical cooling rate models of medium-carbon steel and low-carbon steel and low-alloy construction steel were established, as modified Maynier model, El-dis model and isothermal curve model, respectively. During construction process, regression analysis and Newton interpolation method were used for higher calculated precision. Through comparing and analyzing, the superior one was selected to evaluate the full hardening thickness after quenching. According to hardness analyzing, the deviation between predicted hardness distribution and the experimental value is within 6%.

Stabilizing Glass Bonded Waste Forms Containing Fission Products Separated from Spent Nuclear Fuel

A model has been developed to represent the stresses developed when a molten, glass-bonded brittle cylinder (used to store nuclear material) is cooled from high temperature to working temperature. Large diameter solid cylinders are formed by heating glass or glass-bonded mixtures (mixed with nuclear waste) to high temperature (915°C). These cylinders must be cooled as the final step in preparing them for storage. Fast cooling time is desirable for production; however, if cooling is too fast, the cylinder can crack into many pieces. To demonstrate the capability of the model, cooling rate cracking data were obtained on small diameter (7.8 cm diameter) glass-only cylinders. The model and experimental data were combined to determine the critical cooling rate which separates the non-cracking stable glass region from the cracked, non-stable glass regime. Although the data have been obtained so far only on small glass-only cylinders, the data and model were used to extrapolate the critical-cooling rates for large diameter ceramic waste form (CWF) cylinders. The extrapolation estimates long term cooling requirements. While a 52-cm diameter cylinder (EBR-II-waste size) can be cooled to 100°C in 70 hours without cracking, a 181.5-cm diameter cylinder (LWR waste size) requires 35 days to cool to 100°C. These cooling times are long enough that verification of these estimates are required so additional experiments are planned on both glass only and CWF material.

Corrosion Resistances of Iron-Based Amorphous Metals with Yttrium and Tungsten Additions in Hot Calcium Chloride Brine & Natural Seawater: Fe48Mo14Cr15Y2C15B6 and W-Containing Variants

Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) of approximately 80 Kelvin per second, while SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) with no yttrium has a higher critical cooling rate of approximately 600 Kelvin per second. SAM1651's low CCR enables it to be rendered as a completely amorphous material in practical materials processes. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The passive film stability of these Fe- based amorphous metal formulations have been found to be superior to that of conventional stainless steels, and comparable to that of Ni-based alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates.

Method for Estimating the Critical Cooling Rate for Glass Formation from Isothermal TTT Data

A method is proposed for estimating the critical cooling rate for glass formation and continuous cooling transformation curve (CCT) from isothermal TTT data. The critical cooling rates and CCT curves for a group of lithium disilicate glasses containing different amount of Pt as nucleating agent estimated through this method are compared with the experimentally measured values and it shows this method can give a reasonable estimation.

Sensitization behaviour of modified 316N and 316L stainless steel weld metals after complex annealing and stress relieving cycles

Sensitization behaviour of austenitic stainless steel weld metals prepared using indigenously developed modified 316N (C=0.05%; N=0.12%) and 316L (C=0.02%; N=0.07%) electrodes was studied. Detailed optical and scanning electron microscopic examination was carried out to understand the microstructural changes occurring in the weld metal during isothermal exposure at various temperatures ranging from 500°C to 850°C (773–1123K). Based on these studies the mechanism of sensitization in the austenite–ferrite weld metal has been explained. Time–temperature–sensitization (TTS) diagrams were established using ASTM A262 Practice E test. From the TTS diagrams, critical cooling rate (CCR) above which there is no risk of sensitization was calculated for both materials. The heating/cooling rates to be followed for avoiding sensitization during heat treatment cycles consisting of solution-annealing and stress-relieving in fabrication of welded components of AISI 316LN stainless steel (SS) were estimated taking into account the soaking time and the number of times the component undergoes thermal excursions in the sensitization regime. The results were validated by performing controlled heating and cooling heat treatment trials on welded specimens.

Lowering critical cooling rate for forming bulk metallic glass

Small volumes of Pd44Ni10Cu26P20 and Pd43.2Ni8.8Cu28P20 were encapsulated in B2O3 and thermally cycled between Tg−60°C and Tl+60°C, where Tg and Tl denote the alloys’ glass transition and liquidus temperatures. After this thermal treatment, the critical cooling rates (CCRs) for glass formation can be lowered by an order of magnitude, resulting in a critical cooling rate significantly lower than that reported for any other glass forming alloy melt. These experiments demonstrate that the CCR is not constant but strongly dependent on the degree of heterogeneous nucleation.

A High-Performance Corrosion-Resistant Iron-Based Amorphous Metal - The Effects of Composition, Structure and Environment on Corrosion Resistance

ABSTRACTThe passive film stability of several Fe-based amorphous metal formulations have been found to be comparable to that of high-performance Ni-based alloys, and superior to that of stainless steels, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The high boron content of this particular amorphous metal also makes it an effective neutron absorber, and suitable for criticality control applications, as discussed in companion publications. Corrosion data for SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) is discussed here.

Direct Comparison between Critical Cooling Rate and Some Quantitative Parameters for Evaluation of Glass-Forming Ability in Pd-Cu-Ni-P Alloys

The quantitative parameters such as supercooled liquid region or several reduced glass transition temperatures were applied for evaluating the glass-forming ability of Pd-based metallic glasses. A distinct proportional tendency was recognized between measured critical cooling rates and reduced glass transition temperature by liquidus temperature rather than eutectic temperature. Significance and physical meanings of the quantitative parameters for evaluating of glass-forming ability were also discussed. Furthermore, a new concept of a modified reduced glass transition temperature was proposed to evaluate the glass-forming ability. The modified reduced glass transition temperature as a function of critical cooling rate was found to exhibit a much clear linearity.

Critical Cooling Rate and Thermal Stability in Zr-Ti-Cu-Ni-Be Bulk Metallic Glasses

AbstractThe crystallization behavior of a series of alloys in the Zr-Ti-Cu-Ni-Be system is studied. Upon cooling from the molten state with different rates, alloys with compositions ranging along a tie line from (Zr75Ti25)55(Ni45Cu55)22.5Be22.5 (Vit1) to (Zr85Ti15)55(Ni57Cu43)17.5Be27.5 (Vit4) show a continuous increase in the critical cooling rate to suppress crystallization. In contrast, thermal analysis of the same alloys shows that the undercooled liquid region, the temperature difference between the glass transition temperature and the crystallization temperature, is largest for compositions midway between the two endpoints, revealing that glass forming ability does not correlate with thermal stability. The relationship between the change in glass forming ability and thermal stability is discussed with reference to a chemical decomposition process.

Critical Cooling Rate Vs. Reduced Glass Transition: Scaling Factors and Master Curves

AbstractThe aim of the present paper is to analyse the glass formation and stability of bulk metallic glasses. Attention is focused to metallic alloys as systems which may develop a large glassforming ability. Glass formation when quenching from the liquid state is discussed in terms of the thermodynamics and kinetics of the stable/metastable competing phases. Thermodynamics is required to relate glass transition temperature, Tg, to the energetics of the supercooled liquid. Kinetic destabilisation of equilibrium solidification and, consequently, glass forming ability are favoured by the high viscosity values achieved under continuous cooling. The relative thermal stability of the supercooled liquid depends on the thermodynamic driving force and interfacial energy between each competing nucleating phase and the molten alloy. It is shown that the quantities representative of the process, once scaled, have a temperature dependence that is mostly fixed by the reduced glass transition temperature, Tgr= Tg/Tm, Tm being the melting temperature. Based on the classical models of nucleation and crystal growth, the reduced critical cooling rate is shown to follow master curves when plotted against Tgr. Experimental trends for specific systems are compared to predicted values from these master curves.

Critical Cooling Rates for the Formation of Glass for Silicate Melts.

The critical cooling rate required for the formation of glass is one of the important characteristics for silicate slag. The critical cooling rates have been measured for R2O (R=Li, Na and K)-SiO2 and R'O (R'=Ca, Sr and Ba)-SiO2 systems by the combined use of the hot-thermocouple method and an ordinary melt-quenching method. In all systems, the minima in critical cooling rate corresponded with the composition range of low liquidus temperatures near the eutectics; the critical cooling rates decreased with increasing viscosities at the liquidus temperatures. The measured critical cooling rates were similar to those predicted by the Uhlmann equation and Ota equation. Some factors affecting the critical cooling rate were discussed.

Nonisothermal crystallization of glass-forming melts of the SeTe system

The crystallization kinetics of Se 100−yTe y (O⩽y⩽25%) melts has been studied under the conditions of cooling the melt at a constant rate Q which influences the total value of a crystallinity degree x in a solidified substance. The x value has been determined quantitatively by DTA upon cooling vitro-crystalline samples. Experimental data x = f(y, Q) have been analyzed on the basis of the classical theory of crystallization and the concept of critical cooling rate (CCR). It has been shown that: 1) in the region of low y (< 5%) tellerium exerts a strong and complex effect on selenium crystallization; 2) the problem of a comparative crystallization ability in the series of substances-can be posed only when crystallization conditions are strictly determined (e.g., the x value, if crystallization ability is expressed as Q = f(y) for x = const); and, hence, 3) the CCR value is not a simple characteristic of the glass-forming ability of a substance.

Critical Cooling Rate of 18Cr-8Ni Stainless Steel for Sensitization and Subsequent Intergranular Stress Corrosion Cracking in High Temperature Water

Abstract Calculation of critical cooling rates for sensitization occurring in transient metal forming processes of austenitic stainless steel were carried out using isothermal time-temperature-sensitization curves. A series of 18Cr-8Ni stainless steels each containing a different level of carbon were melted and cooled at various rates from a solution annealing temperature. Two types of tests were run on these alloys to evaluate the degree of sensitization. One test was the 10% oxalic acid electrolytic etch test. The other technique was constant strain rate tests which were conducted at a strain rate of 5 x 10−4 minute−1 in aerated high temperature water containing 10 ppm chloride ions. A good correlation was found between both sets of tests results. Dual structures exhibited intergranular cracking. An actual critical cooling rate for sensitization and subsequent intergranular stress corrosion cracking (SCC) was located in the range between two calculated critical cooling rates.

Repeatability number, Deborah number and critical Cooling Rates as characteristic parameters of the vitreous state

Glasses may be defined as solid systems characterized by the absence of short time fluidity and having structures characterized by the absence of long range order. This definition is rather vague; nevertheless it expresses that the glasses do show some fluidity (certainly at longer observation times) and that their structures are definitely not completely random. In attempts to describe these features in a more quantitative way, it is useful to define two parameters, the Repeatibility Number and the Deborah Number. The former is a parameter giving the degree of order of a given structure in space. The latter is the ratio of the relaxation time of the adaption of the structure to equilibrium and the time of the measuring experiment (time of observation). By introducing these parameters a better and more clear-cut definition can be given of amorphous solids, glassy or vitreous solids, real, “nearly” perfect and perfect crystals. A diagram can be drawn showing the relations between the various states of matter (including amorphous and vitreous states) as a function of the Repeatability Number and the Deborah Number. The relation between the Deborah Number and the Critical Cooling Rate is also discussed.

Cu-Co&lt;SUB&gt;2&lt;/SUB&gt;Si合金の高温電気抵抗，高温硬さおよび溶体化処理における臨界冷却速度

Cu-Co&lt;SUB&gt;2&lt;/SUB&gt;Si合金の高温電気抵抗，高温硬さおよび溶体化処理における臨界冷却速度