Why does heat set stains

Discoloration of the stainless steel - why does the grill discolour when it is hot?

High-quality stainless steel has the property of turning brown after the first heating. Many grillers panic - I really have a high quality one Stainless steel grill acquired? We get your concerns out of the way and explain in our post why they are Discoloration of the stainless steel occur and what they mean.

The components that are most affected by the discoloration are those that are in direct contact with the embers and therefore have to bristle with the greatest heat. This applies to the following components:

  • the flame guards of a gas grill
  • Stainless steel grill grates
  • Rear burner covers
  • Chimney grills (shaft, lid)

Table of Contents

The discoloration on the stainless steel grill

However, you don't have to worry about the lid, the side panels or the control panel and the base cabinet of your gas grill. These parts are either well insulated or simply not getting enough heat to discolor.

If brownish colored areas appear, this is completely normal. The discoloration of the stainless steel does not represent a quality defect and does not affect the function of your grill.

But why is that so? We would like to give you a little material science on the subject of "discoloration of stainless steel".

Heat treatment for stainless steel

Stainless steel is a type of steel whose degree of purity is particularly high. That means that the proportion of the so-called Iron companion, such as phosphorus, is below 0.025%.
Like all other types of steel, this is strong temperature sensitive.

If steel is now exposed to a high temperature - e.g. the heat when grilling - then the steel is discolored by heat oxidation on the surface and takes a so-called "Annealing color" at.
With the help of this color you can find out afterwards by means of tables in which temperature range the steel was heated.

“Tempering” is actually an industrial heat treatment of the steel in order to adjust its properties.
Most often this method is used to reduce the internal stresses of a steel after hardening or welding. This is how he becomes more stretchy and softer. The desired properties can be set as desired, depending on the selected tempering temperature.

The temperatures of the tempering stages

In general: The higher the tempering temperature, the softer the steel becomes.
There are at least 3 generally recognized event levels.

The first stage of the event is in the temperature range from 80 ° C to 200 ° C. In this temperature range, the tetragonally distorted martensite at this point in time changes into a cubic martensite due to the precipitation of an iron carbide.

In the second stage of the event (200 ° C to 350 ° C) the cubic space lattice of the martensite relaxes further and the previously precipitated iron carbides are transformed into Fe3C.

Above 350 ° C, i.e. at the third stage of the event, the martensite separates its carbon as cementite, and the previously carbon-containing martensite is converted into cubic ferrite.
Some literatures also divide into 4 event levels.

Annealing colors and properties of steel

This method was developed because in most areas of application a more ductile - i.e., malleable and therefore not brittle - steel is desired, not only to increase possible force fractures, but also to better bring the steel into the desired shape.

This treatment is carried out with commercially available stainless steel at 100 ° C-350 ° C, depending on the content of carbon and alloying elements, with high-alloy (i.e. the mass fraction of one of its alloying elements is over 5%) temperatures of up to 600 ° C are used . Commercially available charcoal can reach an average temperature of 200 ° C to even 400 ° C, which is the tempering temperature for stainless steel.

The tempering colors range from a light white-yellow (at 200 ° C) through a purple-red (at approx. 270 ° C) to a blue-gray / pure gray at approx. 340 ° C to 360 ° C.

Conclusion

Discoloration on stainless steel parts of your grill is a sign that really pure stainless steel has been used here. The discoloration is irreversible and cannot be prevented.

Are you looking for a high quality stainless steel grill? In our shop you can choose your stainless steel charcoal grill or stainless steel gas grill from many different models.