Views: 0 Author: Site Editor Publish Time: 2025-04-12 Origin: Site
In the field of stainless steel processing, "heat treatment" is a very critical process, which directly determines the hardness, strength, toughness and even corrosion resistance of the material. For industries such as cutting tools, medical equipment, and mechanical parts, stainless steel heat treatment is a "training of internal strength".
This article will give you an in-depth understanding of the principles, classifications, process flows and treatment priorities of stainless steel heat treatment, allowing you to truly understand the materials science behind stainless steel.
1 What is heat treatment?
Heat treatment refers to a process that changes the internal structure and performance of a part by heating, heat preservation, cooling, etc. without changing the overall shape of the part.
For stainless steel, the purpose of heat treatment is usually:
Improve hardness and strength
Eliminate residual stress
Improve corrosion resistance
Improve processing performance (such as softening, stabilizing size, etc.)
2 Classification of common heat treatment processes for stainless steel
Different types of stainless steel (austenite, martensite, ferrite, duplex) have different heat treatment methods.
1) Annealing
Purpose: softening materials, eliminating stress, refining grains, improving machinability
Process parameters:
Temperature: 800~950℃
Cooling method: slow cooling or furnace cooling
Applicable steel types: austenite, ferrite, and some martensite
2) Solution Annealing
Purpose: fully dissolve alloy elements into austenite to restore the plasticity and corrosion resistance of the material
Process parameters:
Temperature: 1000~1150℃
Cooling method: rapid water cooling (to prevent carbide precipitation)
Applicable steel types: austenitic stainless steel (such as 304, 316)
3) Quenching
Purpose: To obtain martensitic structure, improve hardness and strength
Process parameters:
Heating temperature: 950~1100℃
Cooling method: Oil cooling, water cooling or air cooling
Applicable steel type: Martensitic stainless steel (such as420, 440C)
4) Tempering
Purpose: To eliminate brittleness after quenching and adjust the balance between hardness and toughness
Process parameters:
Temperature: 150~600℃
Cooling method: Air cooling
Applicable steel type: Martensitic stainless steel (generally used in conjunction with quenching)
5) Aging
Purpose: To improve the strength and hardness of the material by precipitating strengthening phases
Applicable steel type: Precipitation hardening stainless steel (such as 17-4PH)
3. Effect of heat treatment on organization and performance
Heat treatment is essentially a redesign of the organizational structure, which has a huge impact on the performance of stainless steel:
| Process | Organization change | Performance impact |
Solution treatment | Carbides dissolve into austenite | Improve corrosion resistance |
| Quenching | Austenite → martensite transformation | Improve hardness and strength |
| Tempering | Martensite tempering decomposition | Enhance toughness and reduce brittleness |
| Aging | Precipitation strengthening phase precipitation | Strengthen the material and improve fatigue performance |
Note: Improper heat treatment may lead to quality problems such as intergranular corrosion, insufficient hardness, and cracks.
4. Heat treatment characteristics of different types of stainless steel
Austenitic stainless steel (such as 304, 316)
Cannot be hardened by quenching
The key heat treatment is solution treatment
The key to preventing intergranular corrosion is rapid cooling and low-carbon design (such as 304L)
Martensitic stainless steel (such as 420, 440C)
High hardness can be obtained by quenching + tempering
Hardness can reach HRC 50~60 after heat treatment
Commonly used in knives, scissors, bearings and other parts
Ferritic stainless steel (such as 430)
Not suitable for quenching and strengthening
Annealing treatment can be performed to improve plasticity
Relatively brittle, not suitable for high-load occasions
Duplex stainless steel (such as 2205)
The heating temperature and cooling rate need to be controlled to maintain the balance of austenite + ferrite
Prevent σ phase precipitation (high temperature embrittlement phase)
The key lies in the accuracy of heat treatment temperature control
5.Vacuum heat treatment vs. conventional heat treatment
| Project | Conventional heat treatment | Vacuum heat treatment |
| Atmosphere | Air or protective gas | Oxygen-free/low-oxygen vacuum environment |
| Surface | Easy to oxidize and discolor | Bright and non-oxidized |
| Precision | Medium | High dimensional accuracy |
| Application | Ordinary components | High-end precision tools, medical equipment, etc. |
6.Key points of heat treatment quality control
Temperature control: error control within ±5℃
Heating/cooling speed: prevent thermal stress cracking
Insulation time: set according to thickness and equipment
Atmosphere control: prevent decarburization and oxidation
Surface protection: use protective film, packaging, vacuum or nitrogen environment
7. Summary
Heat treatment is one of the core processes that determine the performance of stainless steel.
Different steel grades require different heat treatment methods and cannot be generalized.
Accurate heat treatment not only improves product quality, but also significantly extends service life.
Enterprises should pay attention to the improvement of heat treatment capabilities and quality control, especially for high-end knives, medical, aviation and other fields.
