Match the following.

Heat treatment		Effect
P:	Tempering	1.	Strengthening
Q:	Quenching	2.	Toughening
R:	Annealing	3.	Hardening
S:	Normalizing	4.	Softening

The correct option is P-2, Q-3, R-4, S-1.

As illustrated in the provided diagram, the general heat treatment process involves a sequence of Heating a Material and then subjecting it to controlled Cooling. This sequence alters the microstructure of the substance to yield a "Stress-free and refined material with better properties." Depending on the heating temperature, soaking time, and the rate of cooling, different heat treatment techniques are utilized to achieve specific material effects. Let's break down each heat treatment method and its primary effect:

1. Tempering (P → 2: Toughening):
Tempering is performed on metals (typically steel) that have already been hardened by quenching. Quenched steel is extremely hard but also highly brittle and prone to cracking under stress. By heating the hardened steel to a temperature below its critical point and cooling it, tempering reduces brittleness and internal stresses while increasing ductility and toughness. Therefore, the primary effect of tempering is toughening.

2. Quenching (Q → 3: Hardening):
Quenching is the process of heating a metal to an elevated temperature (above its critical temperature range) and then cooling it very rapidly, usually by immersing it in a medium such as water, oil, or brine. This rapid cooling prevents the formation of softer microstructures and promotes the formation of a very hard, needle-like phase called martensite. Consequently, the primary effect of quenching is hardening.

3. Annealing (R → 4: Softening):
Annealing involves heating the material to a high temperature, holding it at that temperature to allow recrystallization, and then cooling it very slowly (typically inside the furnace itself). This slow cooling rate allows the material to reach a stable, stress-free crystalline structure. Annealing relieves internal residual stresses, increases ductility, refines grain structures, and makes the metal much easier to machine or cold-work. Thus, the primary effect of annealing is softening.

4. Normalizing (S → 1: Strengthening):
Normalizing is similar to annealing, but the heated metal is cooled in still air at room temperature rather than slowly inside a furnace. Because the cooling rate in air is faster than furnace cooling, it produces a finer, more uniform grain structure with higher tensile strength and yield strength compared to annealed steel. This results in the strengthening of the material.

By matching each heat treatment to its corresponding effect, we get:
• P (Tempering) → 2 (Toughening)
• Q (Quenching) → 3 (Hardening)
• R (Annealing) → 4 (Softening)
• S (Normalizing) → 1 (Strengthening)