Most steel forgings are normalised, annealed, or hardened and tempered after forging. Some are also case hardened, induction hardened or stress relieved, and stainless forgings are usually solution annealed.
Heat treatment decides the final strength, hardness, toughness and machinability. A forging in the right grade but with the wrong heat treatment is the wrong part.
Why forgings need it
Forging leaves a coarse and uneven grain structure, especially where the part cooled at different rates. It also leaves internal stresses. Heat treatment refines the grain, evens out properties through the part and brings hardness to the level the drawing asks for.
The main treatments
- Normalising heats the steel above its transformation range and cools it in still air, refining the grain and giving uniform, moderate strength.
- Annealing heats and cools the steel slowly in the furnace, making it softer and easier to machine.
- Hardening and tempering, also called quenching and tempering, heats the steel, quenches it in water, oil or polymer, then reheats it to a lower temperature to reach the target strength and toughness.
- Case carburising adds carbon to the surface of low-carbon steel before hardening, giving a hard case over a tough core.
- Induction hardening heats only a surface zone, such as a bearing journal or gear tooth, and quenches it.
- Stress relieving heats the part to a moderate temperature to reduce residual stress, often after rough machining or welding.
- Solution annealing heats austenitic stainless steel and quenches it to restore corrosion resistance.
What to put on the drawing
Name the heat treatment condition and the result you need, not just the process. For example, a hardened and tempered 42CrMo4 shaft should carry a hardness range, and if needed a tensile and impact requirement. For case-hardened parts, give surface hardness, effective case depth and core hardness.
Say where the test is taken. Properties at the surface of a thick forging can differ from the centre, so heavy parts may need test locations agreed in advance, or a test piece cut from an extension of the forging.
Checking the heat treatment
Ask whether heat treatment is done in-house or at an outside heat treatment shop. Both are common in Gujarat. Either way, you want to see furnace temperature records for your batch, the quench medium, and hardness results.
Furnace control matters. Ask how temperature uniformity is checked across the furnace and how often thermocouples are calibrated. Large batches in a poorly controlled furnace give scattered hardness. Hardness testing is covered in how hardness is tested on castings and forgings.
Ask for heat treatment details on the material test certificate, linked to the batch number. That record lets you trace a problem if a part fails later.
Next step
Grade choice is covered in steel grades for forgings. We check heat treatment records and have hardness and mechanical tests done on your lots before shipment. To plan this for your parts, book a free sourcing review.