Steel, like all materials, reacts to changing temperatures in both useful and damaging ways. Here we discuss how steel reacts to low and high temperatures, so you can be prepared for all seasons.
Cold air affects steel in a range of ways, and thermal cracking is one of them. It’s important to understand what it is and how you prevent it, to ensure that your steel properties don’t crack in the brisk weather.
Most of the metals that are flexible at room temperature tend to become much stiffer in the cooler air, causing fractures in steel to change from ductile to brittle. Put simply, instead of bending, the steel will break.
To ensure that your steel properties survive the colder temperatures, you need to properly preheat them before using. If it’s a thin sheet of steel, it could come to room temperature on its own within hours or days. The thicker the steel, the longer it takes to come to room temperature. Keep this in mind when planning your usage of the steel.
Steels at low temperatures
As mentioned, steel properties are heavily impacted in cold temperatures and are susceptible to breakage. Here, we offer some more information about the transition from ductile to brittle.
The transition temperature at which brittle fracture occurs is reduced by:
- a decrease in carbon content, less than 0.15% is desirable
- a decrease in velocity of deformation
- a decrease in depth of ‘notch’
- an increase in radius of ‘notch’
- an increase in nickel content
- a decrease in grain size
- an increase in manganese content; Mn/C ratio should be greater than 21, preferably 8
Steels at high temperatures
Steel properties under a constant stress result in a slow plastic deformation known as creep. This is relevant in:
- The soft metals used at about room temperature, such as lead pipes and white metal bearings.
- Steam and chemical plant operating at 450-550°C.
- Gas turbines working at high temperatures
It’s crucial to know that creep can take place and lead to fracture at static stresses – much smaller than those which will break the specimen – when loaded quickly in the temperature range 0.5-0.7 of the melting point. Keep this in mind when working with steel properties at high temperatures.
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