Hardness plays a significant role in the performance of stainless-steel strips. In industries, it is important to choose the right hardness to ensure the extended service life of the material because stainless steel strips are often subjected to repeated contact, load, and friction.
Generally, the hardness helps the material to resist plastic deformation, wear, and surface damage under the applied stress. Stainless strips with the right hardness maintain their dimensional stability and surface finish even after prolonged usage.
Define hardness and its importance in determining mechanical performance
Hardness is simply the measure of resistance to indentation. In stainless steel strips, hardness directly influences the mechanical properties of the material under applied stress and environments.
If a material’s hardness is low, this means it has low strength, is more ductile, and low service life against extreme environments. On the other hand, if material hardness is high, then the material can provide high strength, be less ductile, and have a longer life cycle of the material.
How different hardness levels affect forming, welding, and durability
Different levels of hardness influence various operations, such as forming, and welding in different ways. The following section, along with Table 1, provides a detailed explanation of these effects:
- Forming: Stainless steel strips with less hardness are easy to bend, shape without losing their structural integrity. Strips having high hardness cannot be bent easily due to their greater rigidity.
- Welding: Softer stainless-steel strips can easily be welded. On the other hand, strips with high hardness are difficult to weld because there is are high chances of cracking in the heat-affected zone.
- Durability: Harder materials have high rigidity and thus provide excellent resistance against high stress, wear and dimensional instability.
Table 01: Different hardness levels’ effect on forming, welding, and durability
Hardness Level | Effect on Forming | Effect on Welding | Effect on Durability |
Low Hardness | High ductility, easy to bend, shape, and roll | Easier to weld and lower risk of cracking | Less wear-resistant and may deform under high stress |
Medium Hardness | Moderate forming ability and some resistance to deformation | Welding is feasible with moderate precautions | Balanced wear resistance and flexibility |
High Hardness | Difficult to form and may require special equipment | More challenging to weld, and there is a higher risk of cracks in the heat-affected zone | Excellent wear and abrasion resistance |
Common Hardness Grades and Testing Methods
It is not possible to use the same hardness grade for all applications. Therefore, different hardness grades are used to meet the requirements of different applications. These different types of hard grades directly influence durability, operation likes formability, and welding.
Different testing methods are used to ensure that the material achieves the required specifications for a specific application. The following section discusses different hardness grades and testing methods for different applications:
Hardness grades:
The different types of hardness grades are sorted out based on the level of work hardening done on the stainless-steel strips. These grades are discussed below:
- 1/4 Hard (1/4H): It represents the light, cold working done on the material. Due to this, it can be shaped easily, but its strength and durability are moderate.
- 1/2 Hard (1/2H): It indicates the balance between the cold working and ductility. This is best for applications where both bending and durability are required.
- 3/4 Hard (3/4H): It represents a higher level of cold working done on the material as compared to 1/2 Hard. Due to this, the material has more durability, strength, and resistance to deformation.
- Full Hard (FH): It represents the maximum cold working that can be achieved by the manufacturer. Full hard strips have higher wear resistance and durability, but their ability to bend is limited.
- Extra Hard (EH): It indicates more cold working than full hard material. These types of grades have excellent wear resistance and durability, but formability is very low.
Hardness test:
The following two hardness tests are used to ensure the required specifications are met or not:
- Vickers hardness test: It has a diamond pyramid-shaped indenter to measure the resistance to indentation. It is used for thin strips due to its smaller size of indentation.
- Rockwell hardness test: It has a conical-shaped indenter and it is commonly used for stainless steel strips due to its large size of indentation, reliability for thicker material, and speed.
Applications that Depend on Hardness
The following are some applications that depend on the hardness:
- Springs: The high-hardness grade material should be used to maintain its shape after the elastic deformation and resist cyclic loading on the material.
- Clamps and clips: For this, the material should withstand constant stress without plastic deformation.
- Blades/Cutting tools: They rely on high hardness to resist the sharp edges and maintain their wear resistance.
- Shrapnel: For this, materials should maintain their dimensional stability and toughness under stress.
- Flexible hoses: They rely on the resistance against wear and cyclic loading.
- Automotive gasket: For this, the material should balance flexibility and strength for vibration resistance.
- Heat exchanger plates: The material should resist plastic deformation and erosion under the applied pressure and temperature.
How to Choose the Right Hardness for Your Product
Selecting the appropriate hardness grade is essential to ensure optimal performance and excellent service life according to the application. For components like springs, blades, and clips, a higher hardness is preferred to ensure long-term performance.
On the other hand, applications involving the gaskets and flexible connectors require a softer grade to avoid cracking. Table 02 shows the hardness range of common stainless steel strips with their condition and application to give you an idea of your product.
Table 02: Typical hardness ranges, condition, and applications of common stainless-steel grades
|
Grade |
Typical Hardness Range (HV) |
Condition |
Applications |
|
150–250 HV |
Annealed to ½ Hard |
Kitchen sinks, exhaust systems, food processing equipment, storage tanks |
|
|
316L |
140–220 HV |
Annealed to ½ Hard |
Marine fittings, surgical instruments, and heat exchangers |
|
200–500 HV |
¼ Hard to Full Hard |
Springs, clips, shrapnel |
|
|
420 |
450–550 HV |
Hardened and Tempered |
Cutting tools such as blades and gears |
Conclusion
The hardness of stainless-steel strips is a key parameter that influences the wear resistance, appearance, and service life of the material. To ensure the better performance of stainless-steel strips, it is important to choose the right hardness strips by understanding the right hardness range, testing methods, and applications.
To select the suitable stainless-steel grade, it is important to carefully assess your application and consult your specification. Proper selection not only enhances manufacturing efficiency but also ensures reliable, long-lasting performance in your applications. Contact Jianglin to consult our experts on the right hardness selection.
