This will then be followed by cooling the reheated metal in the air until it fully cools. This will enable the metal to attain a minimum yield strength of about 900-1100Mpa which is within the range that was required.
Surface hardening is a form of corrosion that occurs on the outer surface of the metal that is caused by direct electrochemical or chemical attack on the surface of the metal. It is characterized by etching of the surface of the metal and deposition of the powdery products that result from the chemical attack on the surface of the metal
This type of corrosion is intensely localized that normally takes place within crevices and other shielded areas that are on the surface of the metal but exposed to a given corrosive. This corrosion occurs when a small volume of a stagnant solution corrodes small holes in the surface of the metal such as in gasket surfaces, bolt and rivet heads as well as in lap joints.
Pitting corrosion is also a form of localized corrosion that occurs on the surface of a metal. This kind of corrosion results in the formation of holes or pits on the surface of the metal. These pits are usually very small and they tend to be localized in a certain region of the metal. They are sometimes so very tiny and close together and might tend to look like a rough surface of the metal. This kind of corrosion is characterized by small localized holes that are usually of the same depth
Yes, iron can be corroded by de-aerated dilute hydrochloric acid. This can be proved by calculation of the Gibbs energy during the process. The reaction between hydrochloric acid and Iron is as shown below
Ratchet marks, on the other hand, are an indicator of stress concentration in one particular area leading to failure. The small but instantaneous zones may show that the stress was low during fracture. However, multiple origin ratchet marks indicate that there was sufficient of enough stress to cause cracking in that region.