What can DEW this kind of damage? Normal, open-air fire does not melt steel, that takes a blast furnace – Why farming equipment, (1200+) food production sites spontaneously combusting?

The effects of open-air fire on steel can vary depending on several factors, including the temperature of the fire, the duration of exposure, and the specific composition of the steel. Here are some potential effects:

1. Softening and Weakening: Prolonged exposure to high temperatures can cause steel to soften and weaken. This is due to the fact that elevated temperatures can cause changes in the microstructure of the steel, such as grain growth and recrystallization, which can reduce its mechanical properties.
2. Oxidation: Steel is susceptible to oxidation (rusting) when exposed to air and moisture, and this process can be accelerated at high temperatures. In an open-air fire, the oxygen content is increased, which can lead to rapid oxidation of the steel, forming iron oxide (rust) on its surface. This can weaken the steel and compromise its structural integrity.
3. Distortion and Warping: Uneven heating during exposure to fire can cause distortion and warping of steel components. Temperature gradients within the steel can result in differential expansion and contraction, leading to bending, twisting, or buckling of the material.
4. Loss of Dimensional Stability: High temperatures can cause steel to undergo thermal expansion, which may result in dimensional changes. This can be particularly problematic for steel structures where precise dimensions are critical, as excessive expansion or contraction can lead to misalignment or failure of connections.
5. Potential for Brittle Fracture: In some cases, exposure to high temperatures followed by rapid cooling (such as during firefighting operations) can induce thermal stresses in the steel, increasing the risk of brittle fracture. This is especially true for certain types of steel with high carbon content, which are more susceptible to embrittlement at elevated temperatures.

Overall, the effects of open-air fire on steel can range from surface oxidation and softening to more severe damage such as distortion, warping, and loss of mechanical properties. Proper design considerations and fire protection measures are essential to mitigate the potential risks associated with exposure of steel structures to fire.

Eddy currents can indeed be induced in steel by microwaves, just as they can be induced by electromagnetic fields of various frequencies. This phenomenon occurs due to electromagnetic induction, where a changing magnetic field (in this case, oscillating microwaves) induces electric currents in a conductor (such as steel).

When microwaves interact with steel, they generate rapidly changing magnetic fields. According to Faraday’s law of electromagnetic induction, this changing magnetic field induces electric currents in the steel. These electric currents, known as eddy currents, circulate within the steel material.

The presence of eddy currents in steel can have several effects, depending on the specific application:

1. Heating: Eddy currents dissipate energy as they flow through the steel material, leading to localized heating. In the context of microwave ovens, this heating effect is utilized to cook food. The eddy currents generated in the steel casing or other metallic components of the oven may contribute to heating, although the primary heating mechanism in a microwave oven is the absorption of microwaves by water molecules in the food.
2. Energy Losses: Eddy currents in steel can result in energy losses, particularly in magnetic materials such as ferromagnetic steel. These losses, known as magnetic hysteresis losses, can reduce the efficiency of electromagnetic devices and systems.
3. Electromagnetic Shielding: In some cases, the presence of eddy currents in steel can be undesirable, such as in electronic devices where electromagnetic interference (EMI) needs to be minimized. However, steel’s ability to conduct eddy currents can also be harnessed for electromagnetic shielding purposes by providing a path for the dissipation of electromagnetic energy away from sensitive components.

Overall, the induction of eddy currents in steel by microwaves is a well-understood phenomenon with various practical implications in engineering, materials science, and electromagnetic applications.