Steel Tempering: Section 8 Increase

Steel Tempering: Section 8

Increase Hardness

Strength will decrease slightly at temperatures below 400, then increase. Hardness and ductility are largely unaffected by heating at temperatures below 400, but also increase after this temperature is reached. Toughness is imparted at lower levels of heating, and can be diminished by higher heating.

The actual effects of hardening followed by quenching on steel microstructures can vary greatly depending on the specific alloy of steel being tempered, but essentially the heating allows crystalline structures to form in the steel which greatly increase the hardness of the steel, while the tempering and quenching act on these crystals to reduce fracture points and thus decrease brittleness and cracking.

Low tempering temperatures are used to increase toughness, while higher tempering is needed to increase the strength and hardness of steel. Ductility is also affected by higher heats, though to a lesser degree.

Yes

Tempering time can greatly affect the strength and toughness of the steel, with faster times (especially faster quenching) creating much more brittle steels in many instances (though this s actually reversed in certain steels). Overall, however, the temperature of the tempering process appears to have a greater effect on the mechanical properties of the steel produced.

7) There appeared to be greater change in mechanical properties at some times than would be expected based on the published literature. This variance is probably the result of a lack of true precision (and accuracy, possibly) in many measurements as well as the lack of conditions actually controlled to a point that the results of this research would be empirically valid.

8) Impact testing.

9) i. Less than 400/toughness is more important than hardness; high temperatures would cause greater brittleness, and the direction of force applied to the tool during its use could cause it to snap

ii. Temperatures of 400 and greater/the force experienced by the die is compression, and the hardness of the crystal structures formed at these temperatures is required for prolonged use

10) a. Applications: structural elements, making of intricate shapes (cutting dies) Mechanical property: ductility

b. Applications: deep-draw dies, jack-hammers

Mechanical property: hardness

11) Needle-like grains can form at higher tempering and quenching temperatures, creating a steel with different mechanical properties than those that retain the regular crystal structures created by heating alone. Lower quenching temperatures create microstructures that demonstrate a greater elasticity, with smaller and less brittle connections forming between microstructures.

12) Martensite is a high-carbon steel formed from the rapid cooling of austenite in a process that does not allow carbon to diffuse out of the heated metal. Tempered Martensite has reduced hardness but increased toughness, and the metal is partially decomposed into ferrite and cementite by the tempering process.

13) Yes; there are some limited applications where the brittleness of quench-hardened steel will not pose a significant barrier to use. In most applications, however, tempering is required after quench hardening in order to reduce brittleness and increase the toughness of the steel.

14) Furnace: All heat shields must be in place, and the area in and around the furnace must be kept clear of all dust, debris, and other equipment. Ventilation paths must be substantial and remain free from blockages, and indicators in the area should clearly show when the furnace is on. Izod Impact Testing Machine: Ensure safety is on the pendulum arm whenever first approaching the machine and upon completing any test. Ensure safety is on before proceeding with any other work (until experimentation). Wear safety glasses and avoid placing any clothing or body parts in the potential pinch area at all times. All participants/observers must remain at a safe distance from the machine until the pendulum has been brought to a full stop by application of the break.