Heavy Forgings Research Articles

Experimental verification of preform design for axisymmetric heavy forging on a model hammer

A new technique for designing preforms within the capacity limit of forging equipment has been developed for axisymmetric heavy forgings. In order to prove this technique, model experiments were carried out. Plasticine was used as a model material to simulate AISI4130 steel at elevated temperature and a model gravity drop hammer was constructed by the conversion of 35 tonne · m counter-blow hammer. From these experiments, it has been verified that a dome-shaped heavy product can be forged successfully from the systematically designed preforms resulting from the present work.

Examples of the evolution of materials for nuclear applications: metallurgical improvement of 16MND5 steel and new technologies for manufacturing heavy components

Creusot-Loire Industrie has been constantly improving and adjusting the quality of its products (heavy forgings, castings or plates) based on knowledge of their in-service behaviour. The development of steel manufacturing techniques has been oriented to increasing the quality of steel, in particular by reducing drastically the impurity content (S, P), by better control of the basic range of chemical composition, and by decreasing the gas content (N, H, O). Changes in ingot shapes have been made to optimize the quality of the steel with respect to segregation (development of hollow and LSD ingots to reduce the effect of irradiation embrittlement at the inner surface and sub-surface area). The effects of these developments on the toughness of nuclear materials are illustrated by two examples: 16MND5 steel used for pressurized water reactors; ASTM A350LF5 steel used for cask bodies for the transport of irradiated fuel elements. Modifications in hot working (mainly forging) procedures have enabled the development of products with shape adapted to easier construction and/or best quality and/or reduction in the number of welds, thus decreasing the construction and in-service inspection costs. New forging products to be used in nuclear pressurized water reactor power plants are presented.

The investigation of the FM heavy forging process by the Moiré method part I: Single-reduction results

There exist some metallurgical defects, such as voids, microcracks, loose structure, etc., in the core of the heavy forging ingots. To insure a good quality of the finished product, these defects must be eliminated during the forging processes. In this paper, using the Moiré method, a newly developed 1200 °C high-temperature Moiré modelling technique and apparatus for measuring the critical closing reduction of artificial cavities, the single reduction of the FM heavy free-forging process has been investigated systematically, the critical closing reduction rate curve of artificial cavities and the internal strain/stress distribution having been obtained. The Moiré analysis shows that when the anvil width ratio (AWR) W/ H 0 = 0.6, the maximum deformation penetrates into the core of the specimen and, a nearly symmetrical deformation distribution is obtained in the use of an unsymmetric anvil arrangement, where W/ H 0 = 0.5 is the transition anvil width ratio of the central axial stress (from tension to compression). Experiments on porous material also show that W/ H 0 = 0.6 has the strongest forging effect. The author thus conclude that W/ H 0 = 0.6 is the optimum anvil width ratio for the FM forging process. The Moiré patterns obtained after the 1200 °C forgings process are very successful. The development of this technique affords a powerful tool in research into hot-forming processes, especially useful in the integration of plasticity theory with materials science. Finally, some suggestions are made for the improvement of the FM process.

The investigation of the FM heavy forging process by the Moiré method Part II: Consecutive reduction results

In part I of this work (preceding paper), single-reduction results on the FM forging process were reported. In the work reported in this paper, the cavity closing laws of the consecutive reduction process were investigated, the appropriate turn-over and feed procedure being obtained, along with the strain distribution of the consecutive reduction process, with and without anvil staggering, and the maximum relative deflection of the centre line after the carrying out of the forging process. The minimum forging ratio for the direct reduction process is discussed, which ratio is very helpful for the design of production processes.

Effect of post-forging heat treatment on the microstructure and room temperature tensile properties in Ti-25 Al-10Nb-3V-1Mo (super α2)

The room temperature tensile and fracture behaviour of super α2 have been assessed as a function of a range of thermomechanical treatments. It has been shown that the best properties are obtained in samples which have been forged in the β phase field using cool dies, followed by aging at 800 °C for 2 h. These property measurements have been correlated with the microstructural changes caused by the various heat treatments. It has been found that the highest strength is associated with a two-phase structure of transformed β phase containing about 17% primary α2 and that improved fracture behaviour is associated with a transformed fine Windmanstätten structure. It is concluded that the room temperature tensile ductility improved by aging at 800 °C for 2 h, which reduces the dislocation density and the stress concentration caused by the heavy forging deformation within the α2 and B2 grains. Grain boundary α2 films and the high Nb interface α2 phases at primary α2 and B2 matrix interfaces form after high temperature solution treatments. Also, these two kinds of α2 phase result in low room temperature tensile ductility. Grain boundary strengthening plays a dominant role in super α2, and transgranular fracture is the main failure feature of this alloy.

The investigation of the JTS forging process ∗ by a high-temperature Moiré modelling technique

In order to make heavy rotor and roll forgings that are of the required standard, shrinkage porosity and cavities within the ingot cores have to be eliminated by direct forging alone. The precooling ingot (JTS) forging process is one of the most important free-forging processes for producing heavy forgings. In this work, the JTS process was investigated systematically using a newly developed Moiré high temperature (1200 °C) modelling technique. The internal stress and strain distributions and the rational selection of technological parameters such as the temperature gradient, the anvil width ratio, the reduction rate etc., in the JTS process were explored. The distribution and nature of the internal temperature gradient of heavy forgings subjected to water-spray cooling and air-cooling in the JTS forging process were examined by the numerical calculation method. Some suggestions for improving the forging technology are advanced and discussed.

A study of hole closure in hot rolling as influenced by forced cooling

The centres of ingots often contain voids or even a central longitudinal hole. If the ingots are hot-rolled to semi-manufactured artickes such as blooms or billets intended for the closed-die forging of components for the automobile industry, it is of utmost importance that these kinds of defect are eliminated during hot rolling. If they are not, pores might be found in the material after finishing forging, which is not acceptable considering that many components constitute so-called “safety-details” such as crankshafts, steering spindles and connecting rods. Under some circumstances the problem of pore closure is especially pronounced. If, for example, the production in a workshop is to be changed from light forgings to heavy forgings, it might be necessary to close the holes during only a small reduction in rolling. If a heavy rolling mill with large rolls is not available and sub-contract rolling is not possible from the economical point of view, it is then necessary to search for other solutions to the problem. In the present work the influence of cooling of the hot workpiece surface is studied. For this purpose full-scale hot-rolling experiments in steel were carried out. The results indicate that a temperature gradient in the stock, obtained by water cooling and especially by means of interrupted water cooling, improves the possibility of eliminating a central longitudinal hole.

State of the art in the manufacture of heavy forgings for reactor components in the Federal Republic of Germany

The aim of system manufacturers and operators, to reduce the number of welds in components and piping to a minimum for technical and economic reasons, has led to an optimised design for the entire reactor coolant system of LWRs as regards forging technology. It is shown, by way of examples, that the technological limits (concerning ingot weights and forging methods) have been continually extended through intensive research and development, as well as through the best use of available manufacturing capacity and equipment. Results from destructive testing and non-destructive examination of component parts are illustrated and evaluated. It is shown how these results and the experience from material qualification have been taken into account in the KTA nuclear safety standards.

Analysis of special forging processes for heavy ingots by finite element method

For the application of numerical simulation to forming processes, one outstanding problem area is the analysis of three-dimensional deformation problems and the evaluation on the effect of closing and consolidation of internal cavities at the cores of large forgings. Considering the balance of solution accuracy and computational efficiency, a simplified 8-node element was employed. A new way to explore the effect on elimination of internal defects by means of shrinkage rate and shrinkage energy which are computed by finite element method is introduced. Analyses for WHF process which can improve the soundness of heavy forgings have been performed. The optimum geometrical parameters for the process are proposed. The results show an excellent agreement between theory and experiments.

FINITE ELEMENT SIMULATION OP INTERNAL VOID CLOSURE IN OPEN-DIE PRESS FORGING

Abstract In the manufacturing of heavy forgings, one of the most important aspects of the process is the consolidation of internal voids which result from the ingotmaking process. To insure a good quality finished product, these voids must be closed by proper choice of forging practices - including such factors as die geometry* amount of reduction, reduction speed, and workpiece temperature. This paper focuses on the first two of these factors and reports the results of a study on the effects of die width and reduction on the closing of a void. The deformation state in the cross-section of an ingot is predicted using a two-dimensional elastic-plastic finite element code for large strain, large deformation analysis. Simulations of forging with no void present are reported and compared with results from plasticine experiments. The effects of die width and amount of reduction on the internal deformation state are examined. A single internal void is then modeled in the same geometry ingot as a smooth cavity a...

Effect of heat treatment and precipitation state on toughness of heavy section Mn-Mo-Ni-steel for nuclear power plants components

With regard to the mechanical properties of heavy forgings, made from steel grade 508 ASTM Class 3 (20 MnMoNi 5 5) the influence of the cooling intensity during hardening was investigated and the possibilities and limits of accelerating the cooling rate were studied. The importance of the transformation heat is discussed. It can be concluded from this, that it is impossible to avoid the formation of upper bainite as a typical microstructure of heavy forgings from this steel type. To obtain high impact energy the annealing condition must be conform with this type of microstructure. The reason for impact decrease by over-annealing is related to Mo 2C precipitation in the bainitic ferrite. Finally, experiences with intercritical heat treatment of this steel type are described and the special behaviour of the microstructure obtained is demonstrated.

Defects and their inspectability by UT in current heavy section steels for nuclear power plants

A proven UT technique gives us three major categories of information, i.e., 1. (1) detection and location of defects, 2. (2) sizing of defects, 3. (3) characterization of defects. However, the findings by UT should always be linked with the destructive examinations of the indication spots. Finally, with the support of statistical data, an experienced NDE engineer could make the “final diagnosis of defects”. The present paper reviews the reliability of current UT procedures in the following manner. 1. (1) Cutting examination of UT indications found in heavy forgings for Nuclear Steam Supply Systems (NSSS) and for extra large turbine generators. 2. (2) Comparison of UT findings with the results of cutting examination, showing a reasonably good coincidence between both results. 3. (3) With the fact in (2), reliability of UT with the currently common procedures is discussed referring to PISC-1 Report, and fracture mechanics evaluation of defects is also tried. 4. (4) Progress in steel making during the past two decades is briefly reviewed, which convinces us that only a few types, separately located defects might be existing in the present day quality steels and that they are adequately inspectable with current UT procedures. 5. (5) Acceptance criteria of UT indications in several Codes are also compared.

Influence of Mould Design on the Solidification and Soundness of Heavy Forging Ingots

Influence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot was analysed by using finite element method. The results of the analysis were compared with those of sectioning investigation of 100 and 135t ingots and the influence of mould and hot top design on the internal defects has been made clear quantitatively.The result shows that the geometry of hot top and mould design plays most important role in the manufacture of sound heavy ingots. The central porosities and loose structure are liable to increase when the rate of vertical solidification at the centerline of ingot exceeds the value of about 10mm/min, and the defects are strengthened at the area where the rate of solidification is accelerated.For 0.25%C-3.5%Ni-Cr-Mo-V steel ingot, “A” segregation begins to form when the rate of transverse (horizontal) solidification decreases to the value of about 0.8mm/min.

Industrial energy use—VI: Energy use in a forging plant

The paper describes energy use in a particular heavy forge; it investigates the consequences of waste heat recovery and of possible improvements to lighting, to the thermal performance of the building and to the means of distribution of power. In each case the internal rate of return on the capital investment required to produce a marginal saving of energy is calculated.

Study on Hydrogen-Induced Cracking in the Heat-Affected Zone of Heavy Forgings Overlaid by Stainless Steel

Contrary to general knowledge, it was found that cold cracks in the heat-affected zone (HAZ) under stainless steel weld overlay on the tubesheet forging of a steam generator were generated during f...

Electroslag welding in manufacture of heavy forgings

This work presents the results of a study on the application of electroslag welding (ESW) to the assembly of heavy preforms for forgings. The technique uses ESW to join two or more blocks or ingots to form a large piece for open-die forging. Results are presented describing a development programme to manufacture and test such forgings in SAE 1045 steel in relation to commercial qualification specifications for machinery shaft application. The finished forgings are found to pass all such quality standards by a good margin. The general applicability of the technique in the field of open-die forgings is also discussed.

鍛造用大型鋼塊の凝固と健全性に及ぼす鋳型設計の影響

Influence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot was analysed by using finite element method. The results of the analysis were compared with those of sectioning investigation of 100 and 135t ingots and the influence of mould and hot top design on the internal defects has been made clear quantitatively.The result shows that the geometry of hot top and mould design plays most important role in the manufacture of sound heavy ingots. The central porosities and loose structure are liable to increase when the rate of vertical solidification at the centerline of ingot exceeds the value of about 10mm/min, and the defects are strengthened at the area where the rate of solidification is accelerated.For 0.25%C-3.5%Ni-Cr-Mo-V steel ingot, “A” segregation begins to form when the rate of transverse (horizontal) solidification decreases to the value of about 0.8mm/min.

Brittle-fracture susceptibility of heavy forgings of electroslag-remelted and siemens-martin (open hearth) steels

Brittle-fracture susceptibility of heavy forgings of electroslag-remelted and siemens-martin (open hearth) steels

Some Problems of Automatization of Heavy Forgings' Production

Some Problems of Automatization of Heavy Forgings' Production

The effect of process treatment upon the fatigue strength of heavy carbon steel shafts

1. The fatigue strength of type St 35 acid steel varies very little over the cross section of large shafts. 2. Virtually identical fatigue strengths were obtained on large St 35 shafts. surrounded by sleeves, after normalizing and annealing or after quench-hardening and annealing. 3. Increase in the diameter of the specimens from 12 to 160 mm reduced the endurance limit by 11% (from 12.9 to 11.5 kgf/mm2), regardless of the form of heat treatment of the St 35 steel. 4. Normalizing heavy forgings from St. 35, instead of thermal refining, is an effective process technique: the heat treatment cycle is shortened and there is no need for normally non-available, vertical, quench-hardening, ovens. 5. Surface work-hardening by cold plastic deformation is an effective method of increasing the fatigue strength of carbon steel shafts subjected to a press-fit, and is equally effective after normalizing or after thermal refining.