Heat Treatment Of Large Forgings Research Articles

Influence of Spacers and Skid Sizes on Heat Treatment of Large Forgings within an Industrial Electric Furnace

The influence of stacking patterns, through the different spacer and skid sizes, on the transient temperature distribution uniformity of large-size forgings in a 112-m3 electrical heat treatment furnace was investigated by conducting CFD simulations and real-scale experimental validation. A 3D CFD model of the electrical furnace was generated, including a heat-treating chamber, axial flow fans, large size blocks, skids, and spacers. Real-scale temperature measurements on instrumented test blocks during the heat treatment process were carried out to validate the CFD simulations. Results indicated that the CFD model was capable enough to determine the transient temperature evolution of the blocks with a maximum average deviation of about 6.62% compared to the experimental measurements. It was found that significant temperature non-uniformities of up to 379 K on the surfaces of the blocks due to the non-optimum stacking pattern were experienced by the blocks. Such non-uniformities could be reduced between 24% to 32% if well-adapted spacer and skid sizes were used in the stacking configurations. Based on simulation results and experimental validation work, optimum spacer and skid sizes for uniform temperature distribution were proposed for different stacking patterns.

The Application and Research on Manufacturing Technology of the Heavy Forging

For large forging is high-tech product of material, smelting, forging, heat treatment and it is the bottleneck which restricts the development of the modern heavy equipment manufacturing industry. The key technology such as forging and heat treatment of large forgings is researched. Finally, with the ultra supercritical power generation units of low-pressure rotor, the production process control technology such as smelting, forging and heat treatment is introduced. The method provides a reliable basis for the localization of production of ultra supercritical steam turbine rotor and has the important practical application value.

Discussion on Metal Heat Treatment in Nuclear Power Plant

To improve mechanical properties and corrosion resistance, heat treatment is applied to the mechanical equipment (equipment and piping, etc.) during manufacture or installation. The nuclear class mechanical equipment with high reliability is required in nuclear power plant, but heat treatment is an important factor which affects reliability of mechanical equipment. To have a better view on issues of metal heat treatment, this paper will provide reference for subsequent heat treatment of mechanical equipment in nuclear power plant by analyzing and summarizing existing problems in heat treatment, especially during the reactor pressure vessel such heat treatment of large forgings, so as to avoid same problems.

Effect of Duration of High-Temperature Tempering on the Texture and Grains of Superheated Rotor Steel

The influence of the duration of high-temperature tempering after air hardening from 900 and 1250°C on the properties, texture, and brittle point of steel 25KhN3MFA is studied. It is shown that the negative effect of superheating of the steel is weakened after high-temperature tempering. Recommendations are developed for optimization of heat treatment of large forgings.

On the problem of hydrogen removal during heat treatment of large forgings

The solutions to a differential equation for the problem of heating of a cylinder in a medium with a fixed temperature are used to obtain equations for estimating the change in the hydrogen concentration in forgings from data on the hydrogen concentration at the cylinder axis or on the average bulk hydrogen concentration. Similar equations are also obtained for forgings having square cross sections. The calculation demonstrates that, for the case of a twofold decrease in the hydrogen concentration in a forging, the calculated times of annealing of a cylindrical forging differ by three times.

Charakterisierung des Werkstoffzustandes durch Verknüpfung präparativer Vorortmetallographie und zerstörungsfreier Abschätzung der Ultraschallschwächung an normalgeglühten Schmiedestücken und Stahlgussteilen/ Characterising the Condition of Normalised Forged and Cast Steels by Combined Non-Destructive Metallography and Ultrasonic Attenuation Measurements

Because of the general price situation, considerable variation in the quality of large forgings and steel castings is currently being experienced throughout the sector, most especially in in the quality of the heat treatment. Test certificates to EN 10 204 sent with the deliveries are also proving to be an unreliable guarantee of the quality of the product. The logical consequence of this is the need for quick, cheap and effective methods of goods inwards inspection for such articles. This article describes a simple and effective method of testing the quality of the heat treatment of large forgings and steel castings. Using this method, at least in particular areas, deficiencies in the heat treatment of actual components, such as coarse grain size, Widmannstatten microstructure and secondary banding, have repeatedly been identified.

Modeling the basic parameters of heat treatment of large forgings

In the search for new materials and the development of technologies of heat treatment of critical parts the processes are modeled under laboratory conditions. In addition, in order to evaluate the quality of the metal over the cross section of large forgings, such as rotors of turbines and generators, is necessary to cut either a prepared rotor or its model, which is an expensive operation. In order to solve these problems a special modeling installation has been designed and produced.

Heat treatment of large forgings with heating in the intercritical temperature range

1. In large forgings the investigated Mn-Ni-Mo-steels provide with slow cooling rates of 30–50°C/h a mixed ferritic-pearlitic-bainitic structure with a bainite content of not less than 30%. Such steels must have a low carbon content (about 0.1%) to increase the quantity of ferrite in the ferritic-pearlitic mixture and the necessary quantity of alloy elements to obtain the required stability of the supercooled austenite. 2. Heating to intercritical range temperatures and slow cooling leads to a reduction in the temperature of the bainitic transformation and the formation of a significant quantity of lower bainite causing phase strain hardening of the ferritic matrix. Obtaining of a structure of lower bainite in combination with the strain hardened ferritic matrix and also the presence of a fine grain, provide quite high mechanical properties. 3. After heat treatment from the intercritical temperature range with slow cooling it is necessary to temper at 400–450°C. This provides the greatest stability of the structure, preservation of phase strain hardening, and the maximum strength, plasticity, impact strength, and fracture toughness. 4. To obtain guaranteed mechanical properties of large forgings produced from the heterophase steels (σt ≥ 600 N/mm2, σ0.2 ≥ 350 N/mm2, σ5 ≥ 20%, ψ ≥ 60%,a0.25+20 ≥ 150 J/cm2,a0.2550 ≥ 100 J/cm2) the following heat treatment is recommended: anneal or normalize with heating to 920°C; final heat treatment by heating to 750°C, cooling at a rate of 30–50°C/h, and tempering at 400–500°C.

Investigation of the quality of metal in large forgings formed from steel 25Kh2NMFA in the annealed state

1. The quality of the metal in axial trepans, which was sampled from two large forgings, is satisfactory along the entire length: no cracks, flakes, or other defects that disturb the metal's continuity are detected. 2. Nonmetallic inclusions are observed in the metal of the trepan: sulfides, oxides, and oxysulfides, arranged in the form of chains along the grain boundaries, and small lines in the direction of deformation; this exerts an unfavorable influence on the plastic and ductile properties of the forgings. 3. The presence of a dendritic and banded macrostructure suggests inadequacies in plastic-deformation technology. 4. The level of strength, plastic, and ductile characteristics of the metal after treatment in accordance with the new regime is lower, and the critical brittleness temperature higher by 30° C than after treatment in accordance with the regime previously adopted. 5. The new regime for the preliminary heat treatment of large forgings ensures decomposition of the austenite in accordance with a diffusion mechanism and the production of a grain corresponding to Nos. 5–7 in the central zones; this is positively manifested in the properties of the metal after final heat treatment.

Reversible temper brittleness in heat treatment of large forgings

The results of the investigation of the kinetics of temper brittleness of steels with a view to the structural state and the theoretical data on the real distribution of characteristics of resistance to brittle and ductile failure over the cross section of parts make it possible to devise rationally alloyed steels and regimes of high tempering ensuring the required complex of properties and improved operational reliability.

Energy-saving technology for the preliminary heat treatment of large forgings

Energy-saving technology for the preliminary heat treatment of large forgings

Heat treatment of large forgings of titanium alloy VT3-1

The optimal heat treatment for large forgings of alloy VT3-1 consists of heating at 870° for 2 h, air cooling, heating at 650° for 2 h, and air cooling.

Heat treatment of large forgings

1. The use of the similarity theory to analyze the quenching process makes it possible to obtain a generalized quenching graph for oil and water that characterizes the temperature field during cooling of forgings (machine parts) of different diameters. 2. A method was developed for determining the hardenability by means of superposing the quenching graph on the thermokinetic diagram of the steel. This method makes it possible to determine the hardened zone in forgings of different diameters with given requirements (absence of pearlitic transformation, absence of transformation in the upper bainite range, etc.). 3. To obtain high mechanical properties (high strength and low ductile-brittle transition temperature) it is necessary that the cooling time during quenching of large forgings be sufficient to lower the temperature in the center of the forging to 200–300°C. 4. To obtain high mechanical properties due to decomposition of austenite in the martensite transformation range and in the lower bainite range it is expedient to quench large forgings with unvarying section in water or through water in oil. 5. For parts varying in section (barrels and necks) the best method is water-air or sprayer cooling, permitting separate cooling of the barrel and the neck and thus permitting prolonged cooling of the barrel to the required temperature.

The primary heat treatment of large forgings

The primary heat treatment of large forgings

The heat treatment of large forgings of N18K9M5T maraging steel

The heat treatment of large forgings of N18K9M5T maraging steel

Effect of microheterogeneity on the kinetics of phase transformations in large forgings of steel 34KhN3M

1. The microheterogeneity of the structure is clearly evident in the central areas of forgings of steel 34KhN3M. 2. The phase transformations during heat treatment of large forgings do not conform with the C-shaped curves that are characteristic for the average composition of the steel. Due to the microheterogeneity, the transformation of austenite in the central area of large forgings begins earlier and ends much later than in sections of the steel of average composition. This must be taken into account in heat treatment, particularly annealing after forging, when the absence of segregation ensures the maximum decomposition of austenite. 3. The microheterogeneity is retained and may increase during heating for quenching or normalization—the difference in the grain size increases as the result of preferential growth of large grains, and individual microsections are enriched because of the migration of carbon.

The Heat Treatment of Large Forgings

The Heat Treatment of Large Forgings