Cast iron and steel
What is the difference between steel and cast iron?
Steel contains less than 1,7% coal, while in cast iron it is 2-4% coal. The carbon content in the cast steel is 1,7-2,0%. Compressive strength and hardness increase with increasing carbon content, on the other hand, the weldability and malleability decrease. In this respect, too, steel differs from cast iron. The differences in properties also affect the use of both materials.
Why does a layer of scale form on the steel?? The scale layer is formed due to the self-binding of oxygen (oxidation) at a temperature above 843 K (570°C). This temperature is exceeded in the steel production process.
What is the difference between scale and scale??
Scale is formed during the manufacture of steel, and the scale is formed by welding it. Due to different formation conditions, the chemical structure of scale and scale is also different. However, these differences are of little practical importance.
Why both scale, as well as scale should be thoroughly removed prior to coating?
Scale and scale should be thoroughly removed from the steel surface prior to coating, Because:
1. Scale and scale are very brittle, therefore, after some time, they break and fall off.
2. scale, scale and steel expand differently when exposed to heat, consequently between the scale (or scale) and steel, differences in stress arise. This leads to the removal of scale and scale.
3. Between the scale (or scale) and steel there is a difference in electrochemical potentials, leading to the formation of rust under the layer of scale (the zendry). Therefore, scale (the zendra) comes off due to rusting on the underside.
How can scale and scale be distinguished??
Scale and scale can already be identified visually, on the gray-blue surface. Certainty can be obtained by conducting a test with copper sulphate. After coating the surface with an aqueous solution of copper sulfate, on the surface of the steel, if there is no scale or scale on it, copper precipitates.
The course of the reaction is as follows:
Fe + CuS04 → FeSO4 + Cu
iron copper sulfate iron sulfate copper
The concept of corrosion
Corrosion is understood to mean the processes taking place on the surface of the material, caused by unintended chemical or electrochemical reactions, causing changes in the surface of this material.
In common parlance, this term only means the formation of rust on steel, but other materials, including plastics, they also corrode.
How is electrochemical corrosion?
Various metals, e.g. zinc and. iron, along with the electrolyte (salt solution, acid or base) form a galvanic cell. There is a potential difference between the two materials. The material in the area of the negative pole is "eaten away"”.
Then, electrochemical corrosion occurs, when different metals in structurally defective items are in direct contact with each other or then, when the various structural components line up next to each other during the manufacturing process (intercrystalline corrosion).
What is meant by rust raid?
The term rust bloom is understood as the initial stage of corrosion formation on steel in the air environment. There is also talk of a rust bloom then, when rust particles – as foreign bodies – they settle on the surface of other bodies, e.g. on the facades of houses.
When paint coats rust? The surface spread of rust on the surface of the coating then occurs, when iron salts are formed on a rusting substrate and can move through the porous structure of the coating.