Materials

When technological limits are stretched and new boundaries are formed, products and materials with special properties are often needed.

Technical information of spring materials

Lesjöfors has amassed a vast amount of experience since the first spring was made in 1852, about spring materials and the demands made on springs in the unique environments where they will be used.

Lesjöfors represents high quality. It is not enough just to create the optimum spring geometry, you also have to use the right spring materials. Spring materials properties form the basis of a functional spring.

The choice of spring materials are entirely governed by the application that the springs will be used in, and must consider important factors such as stress, temperature, risk of corrosion etc. The Lesjöfors group works with all types of metallic spring materials in all types of cross-section.

Examples of spring materials that we work with

  • Cold drawn and cold rolled low-alloy steel
  • Patent and cold drawn wire
  • Hardenable spring steel
  • Oil tempered spring wire and bainite hardened strip
  • Stainless spring steel
  • Stainless spring steel with extremely good corrosion properties
  • Stainless spring steel for higher temperatures
  • Stainless non-magnetic steel
  • Alloys for medical applications
  • Copper alloys
  • Anti-magnetic acid-resistant spring steel etc
  • Titanium alloys

Expertise in super alloy springs

Lesjöfors has long experience, technical calculation skills and production capacity in the area, and also stocks a standardized range of super alloys in sheet, strip and wire suitable for springs. Examples of product areas are disc springs, compression springs, torsion springs, tension springs and leaf springs.

The following alloys are kept in stock:

  • Inconel X-750®1
  • Inconel 718®1
  • Nimonic 90®1
  • Hastelloy C-276®2
  • MP 35N®3
  • AISI 316
  • Elgiloy®4

In addition to these, a number of other alloys are orderable.

Relaxation of springs at high temperatures

When metals are subjected to stresses and increased temperatures a permanent deformation may take place. This phenomenon is called relaxation, a load loss at a constant deformation, or creep, an increased deformation at a constant load. This is an important performance parameter for coil springs which mostly are designed to give a controlled deflection at a certain load or inversely.

At temperatures above 500°C the relaxation performance for low alloyed and stainless steels are so low that they can not be used for coil springs. Super alloys give better performance at these temperatures. In the following the relaxation performance for some super alloys at temperature 550°C and above is presented.

Super alloys tested

In this investigation three different super alloy wires and one stainless steel wire were tested. The main chemical analysis and the mechanical strengths were as presented in the following table:

Material
Ni
Cr
UTS [MPa]
Super Alloy A
58
19
1300
Super Alloy B
55
19
1050
Super Alloy C
53
17
1200
Stainless steel*
2090

Note * Grade 17/7PH

Relaxation test method

A number of coil springs from these spring materials were manufactured according to the Lesjöfors standard production methods for this type of material and springs. The springs were then compressed with a static load to a specified stress level with help of a mechanical joint.

The compressed springs with joints were exposed to specified temperatures for different times. After cooling, the load for each spring was tested again and the loss of load was noted.

The relaxation figure presented was defined as follows:

(Fb-Fa) / Fb ∙ 100 = Relaxation (%)

Fb = Load at compression before heating

Fa = Load at compression after heating

Following times and temperatures were used with different stress levels at each:

Material
Time
Temp 1
Temp 2
Temp 3
[h]
[°C]
[°C]
[°C]
Super Alloy A
50
550
600
650
Super Alloy A
110
550
600
650
Super Alloy B
50
550
600
650
Super Alloy B
110
550
650
600
Super Alloy C
50
550
600
650
Super Alloy C
110
550
600
650
Stainless steel
50
550

Results

The stainless 17/7PH steel failed as expected after 50 hours at 550°C and stress level 150 MPa. The relaxation received was close to 100 %. No more tests were made with this grade. Examples of relaxation results are presented in following diagrams.

Conclusions

The results show that stainless steel can not be used at these high temperatures. It also shows the big difference between different super alloy grades. From tested super alloy grades the C grade had the lowest relaxation and performed best at all temperatures. It can also be seen that depending on alloy, temperature and stress the relaxation has to be considered when designing coil springs to be used in applications where high temperatures can be expected.