Informative Speech - Metals
Purpose: My purpose is to inform the audience of how different types of steel are formed by
explaining the different mechanical properties of Iron and Carbon compositions.
A. Have you ever noticed that some steel, such as a long bridge is able to bend and have slack, whereas other types of steel are more brittle yet much harder, such as a propeller. If a bridge were more brittle, a strong perpendicular wind could easily break it in half, and a soft propeller would not give you the torque to accelerate to high velocities because the water would have more effect on it's definition.
B. These properties have real life relevance, when steel was discovered in the middle ages it quickly became much more popular than bronze, because of its strength. (Kramer, E. 1992) Steel was a revolution that would affect the world from then on.
II. Statement of Central Idea
A. The change of iron and carbon to steel has had a profound affect on the world, it has revolutionized science and technology that we understand in the 20th century.
B. Different ratios of carbon to iron and different hardening and cooling techniques have furthered our advancements in reaching a utopian compound that has equally elastic and plastic deformation properties.
C. Separate processes have been distinguished between the carbon-iron ratio, which allow us to make steel either brittle or elastic.
A. First issue- Dislocations are the strength of all forms of steel. Each individual dislocation forms with another to create a "knot" that holds the matrices of atoms together. The more "knots" there are the stronger the material. The more carbon, up to 6.67%, that is added will create large obstacles that form tangles of dislocations, increasing the strength of the solid.
B. Second issue- If we examine the decomposition of Austenite, steel, we see that different levels of % of carbon and temperature can create new variations to a not so simple compound. If we combine .025% or more Carbon to iron and keep the temperature below 750 degrees Celsius we can make a very plastic material, ferrite, that is soft and has little brittility. However, if the compound is heated up and there is less than 2% carbon added we come up with Martensite, which is very brittle but extremely strong to uniaxial force.
C. Third issue- When we examine the cooling rates of carbon and iron to the amount of time it takes for them to reach a certain temperature, we can see different characteristics of each solid formed. For example, letter A is Martensite, it is cooled very rapidly and has a very isothermal transformation. If we examine letter B or C we see that they both pass through the Ferrite stages denoted by the hyperbolas bound to the regions Ae1 and Ms. These have a less isothermal transformation and become more elastic.
A. Each time I have discussed iron to steel to temperature we have been able to understand how different variables have explained the properties of different forms of steel. Each form has had some sort of impact on the world and even today more steel compounds are being formed that are lighter, stronger and more flexible
B. Steel can be viewed from two stand points, the "I'll just sit back and enjoy the rewards of other people work" stand point, or the "That's pretty interesting, I think I can help engineers in their research and add to the work" stand point. If research isn't for you, then your options are pretty narrow, but if there's any interest then get up and invent some new compounds!