Objectives:
- Heating steel to appropriate temperature, and then quenching it using different quenching media.
- Measuring the hardness after quenching by different media.
- Study the changes in hardness of steel due to the changes of the quenching media.
Introduction:
Plain carbon steels and alloy steels are among relatively few engineering materials, which can be usefully heat-treated in order to vary their mechanical properties. Steels are heat treated, because of the structural changes that can take place within solid iron carbon alloys. The various heat-treatment process appropriate to plain carbon steels are:
- Full annealing.
- Normalizing.
- Process annealing.
- Hardening.
- Tempering.
In all above process the steel is heated slowly to the appropriate temperature according to its carbon content and then cooled.
It is the rate of cooling which determines the ultimate structure and properties that the steel will have at the end of each of the pre-mentioned heat treatment process.
The process of hardening involves rapidly quenching the steel from appropriate temperature into quenching media. Hypereutectoid steels are heated up to 30-50˚ C above their upper critical temperature prior to quenching. There is no particular advantage in heating hyper-eutectoid steels above their Acm when hardening them, and in practice; the hardening temperature normally used is just 30-50˚ C above their lower critical temperature. Quenching hypereutectoid steels from this lower temperature helps to prevent cracking and distortion.
If the steel is cooled quickly, there will be no transformation into Pearlite and ferrite or Pearlite and Cementite, but into a new harder, but less ductile structure called Martensite. This is due to the allotropic transformation of the face-centered Austenite.
The most commonly used quenching media are:
- Compressed air blast.
- Oil.
- Water.
- 10% Brine (water + 10% salt).
In this Experiment we studied the effect of heat treatment on the properties of carbon steel especially its hardness. We used three quenching media which are air, water and inside the furnace.
* Continue reading the full report from the attached PDF below, pages 34-38
Hardening Steel Using Different Quenching Media.pdf