Metallurgy
1. Introduction to Metallurgy
The study of metallurgy includes investigation of the mechanisms of metal production and coping with properties of metal from raw material to the final product. These mechanisms enable us to better understand how different variables can affect the quality of a metal product. This corresponds to copious amounts of information compiled into computer databases and logic engines used to simulate the metallurgical production process.
Metallurgical development has led to increased performance and reliability of metal products while using an ever-decreasing amount of material and energy. This, in turn, has led to significant savings of natural resources and an increase in environmental protection. It also serves as the cornerstone for mechanical and chemical design practice. A basic understanding of the behavior of metals is essential to the application of existing metal or the development of new materials.
It began with the simple use of native metals to advanced metallic production. These technologies have had a profound impact on human history. Archaeologists know the evolution of different cultures from the study of the artifacts they left behind. These artifacts give good time resolution data of the technology used. Germany is a good example of this analysis.
Metallurgy is the art of extracting metals from ores, refining them, and preparing them for use. It has been the primary source of technology throughout many different cultures. The use of metals has built our current activity level and set a low energy consumption.
2. Types of Metallurgical Processes
An Ellingham diagram is a graph showing the temperature at which a particular compound is reduced by another. It is useful in predicting the feasibility of a reaction at a certain temperature. An example of an Ellingham diagram is shown below. An endothermic reaction is shown by a positive gradient, and vice versa.
Carbon reduction is a type of primary pyrometallurgical process of extracting metal from an ore and refining it. During this process, the metal is heated with a substance that the metal will combine with to form a non-soluble compound. The most common example of carbon reduction is the extraction of iron. This is a simple redox reaction of iron (III) oxide. High temperatures are required for this type of reaction, so it is easy to assign standard enthalpy and entropy values to the reaction and determine whether it is feasible under standard conditions.
In terms of processing of ores and minerals, the methods employed to obtain metals from their ores are usually termed primary processes. It is distinct from the pyrometallurgical and electrometallurgical techniques employed for recycling metals from consumer and industrial wastes. Pyrometallurgical processes would be those that use heat to separate and refine metals. Electrometallurgy involves metallurgical processes that take place in some form of electrolytic cell. An electrolytic cell is a cell in which thermal or electrical energy is used to drive a non-spontaneous chemical reaction. Sometimes the energy is used to produce a needed chemical reaction which is spontaneous. Electrolysis can be used to make a non-spontaneous reaction occur.
3. Properties and Testing of Metals
The most basic mechanical test is tensile testing. Tensile tests are usually conducted with a Universal Testing Machine, which measures the stress on a material in tension. This type of test is ideal because it is cheap, easy to do, and provides a lot of information on the material. It measures the stress on the material (engineering stress) as force per unit area. It also shows how much a material can deform before necking and/or fracturing, and finally, it measures the strain on the material compared to the deformation of the loading points and is a ratio of the elongation of the material to the original length (engineering strain). Engineering stress and strain can be used to find the stress and strain using true values. This method can be used at any point during the deformation and gives a more accurate value for stress and strain. The tensile test provides important information about the material and is generally used as the first test to be conducted on a new material.
Physical and mechanical properties provide information on the behavior of a metal under given loads and conditions. The information is needed in engineering and design to aid in selecting the most suitable material. In forming or casting operations, it is necessary to know the behavior of the metal when force is applied. If a metal is to be used for a spring, it must have adequate elastic properties. To be used as a shaft or connecting rod, it must be able to withstand impact and shock loading without deformation. These properties also determine the suitability and behavior of a metal when under different environmental conditions. A good example is the behavior of an automobile panel being subjected to collision forces or corrosion behavior of a metal in a marine environment.
4. Applications of Metallurgy
A growing need for the understanding of process-structure-property-performance relationship has provided a subsequent increase in the variety of methods used to manipulate the microstructure of metals to enhance properties and performance. This has ushered in a new era of opportunity in the development of advanced materials for use in many different engineering and scientific applications. Support of theoretical predictions with practical experiments is also a burgeoning area of interest, with many experimental methods aimed at a better understanding of the fundamentals that dictate alloy and microstructure behavior. These methods are often defined by sophisticated characterization techniques specific to a particular alloy system, and an example is the use of atom probe field ion microscopy in studying grain boundary segregation of sulfur in nickel-based superalloys.
Alloying of base metals to produce better materials is an application which is moving back to front in the technology (from the cutting edge to the old). An example is about combining the process of FCAW (flux cored arc welding) of new filler metals with the high heat input characteristics of old welding process. Another example is combining the process of hot rolling and cold rolling, replacing the single rolling process for reducing the number of passes and increasing the properties of the materials. These days, many state and industrial demands require specific and complex products. This condition is creating a new challenge for the metallurgical sector, which must be able to help in producing these products and in the effective cost.
5. Future Trends in Metallurgical Technology
Current research in process metallurgy is driven by a number of factors. As summarized by the participants in the Shaping Conference, this work is both ‘push’ and ‘pull’. The ‘push’ comes from the need to improve energy efficiency, to develop processes using non-reactive or non-contaminating processes, and to produce at lower cost for high volume products. The ‘pull’ comes from the demand of the special metals industry for greater purity and control, from the steel industry for processes which can directly produce high quality steels or strip products, and from all sectors for processes which are more flexible. At the same time, society is demanding processes which are environmentally more benign. This encompasses issues of resource usage or depletion, waste treatment, emission control, and component recycling. These considerations are leading process metallurgy toward a phase of increased science input and modeling, and to the development of innovative high technological solutions to metallurgical processing problems. There is a growing realization that to achieve the level of process intensification required and to innovate successfully, new process technology will need to be developed as a package involving all engineering and scientific disciplines from basic science to final engineering design. This will necessitate collaboration within the process industries and between the universities, national laboratories, and industry in a manner not seen since the development of the basic oxygen steelmaking process. In summary, future metallurgical technology will be driven by the need to economically provide better materials using more precise process control with less harmful environmental impact, and it is likely that these key features will generate a pattern of research focusing on the development of new processes and process concepts, often with a high level of innovation. An interactive R&D marketplace between the special metals, ferrous metals, and aluminum industries will stimulate a competitive environment aiding the development and cross-fertilization of new process technologies.
