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Stainless Steels for Springs
SUS301, 304, 631, 632J1, 420J2

Overview

Spring Material is specified in JIS G 4313 and is used for springs because it can obtain high strength through cold working and heat treatment. SUS301, SUS304, SUS631, SUS632J1, and SUS420J2 are the five common grades of stainless steel used in TOKKIN's spring manufacturing. Depending on the application and requested specifications, TOKKIN can assist you in selecting the correct material for you. TOKKIN provides stainless steel foil and other specifications (plate thickness and temper) that are not generally distributed, in optimal conditions, because we can produce to order from small lots.

Examples of Applications

Springs, Springs for Seat Belts, Other Automotive Parts, Tactile Switches, Membrane Switches, Clocks, Stationery

Product Shapes

Product Size Range

Thickness : 0.010mm-2.5mm 
*Availability may vary by steel grade.

Width          : 3.0mm-300mm *Contact Sales if your desired values is over 300mm.

Length        : COIL or SHEET less than L2000mm

Features

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Type Grade Description
Austenitic SUS301 Most widely used stainless steels, chosen for its very good work hardening properties, corrosion resistance and workability.
  • Excellent corrosion resistance without plating or coating. Can withstand corrosion from most oxidising acids.
  • Can withstand use up to about 300°C.
  • Compared to copper alloy spring materials, the specific gravity is lighter and the modulus of elasticity is higher, enabling weight reduction.
  • Has strongre anisotropy as it is a cold-rolled product.
  • Has high electrical resistance.


*Notice :

  • Can be somewhat difficult to weld or braze.
  • Has higher tensile strength compared with other grades of the same elasticity, making it difficult to process.
SUS304
Precipitation Hardening SUS631
(17-7PH)
This is a typical precipitation hardening stainless steel grade whose hardness can be increased by heat treatment, but it is a difficult material to obtain due to its relatively small distribution volume.
Material A (solution-treated) is soft in austenite phase and can be processed more complexly than other grades, but it requires subsequent heat treatments twice, so it takes some time and effort. Material C (cold-rolled) is supplied after cold working to an appropriate hardness.
Compared to Material A, Material C cannot be processed complexly. However, by applying heat treatment under optimum conditions, Material C can achieve a strength second only to high-carbon martensitic hardened materials.
SUS632J1
(15-7PH)
SUS632J1 has high strength even in solution heat-treated condition because of its martensitic phase, and a certain degree of strength can be obtained without cold working, which deteriorates the anisotropy. You need precipitation hardening heat treatment only once, which is very easy.
Since there is little difference in strength at welded joints, it is sometimes used for steel belts and other applications that involve welding.
Martensitic SUS420J2 SUS420J2 is a material that can be hardened by quenching and tempering heat treatment due to its high carbon content.
In our annealed finish condition, the carbides are completely spheroidized, which makes machining easier and provides excellent hardenability.
  1. Suitable wear and heat resistant applications.

    This grade is ideal as a stainless steel for wear-resistant applications and can also be used for heat-resistant applications due to its high tempering resistance.

  2. Less mechanical and physical anisotropy.

    Because of hardening by microstructural transformation, mechanical and physical anisotropy is reduced compared to austenitic spring materials that are hardened by rolling.

  3. Saves thickness and width.

    Martensitic stainless steel has a higher Young's modulus than non-ferrous or austenitic spring materials, enabling reduce the thickness and width of flat springs.

Standards

Unless otherwise specified, we manufacture in accordance with JIS standards. Equivalent overseas standards are for reference only.

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Grade Japan the U.S.A Europe International
JIS G4313 UNS AISI/ASTM EN ISO
SUS301 SUS301 S30100 301 1.4319 X5CrNi17-7 
SUS304 SUS304 S30400   304  1.4301  X5CrNi18-10
SUS631
(17-7PH)
SUS631 S17700 631 1.4568 X7CrNiAl17-7
SUS632J1
(15-7PH)
SUS632J1 - - - -
SUS420J2 SUS420J2 S42000 420 1.4028
1.4034
X30Cr13
X30Cr13

Chemical Compositions

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Grade C Si Mn P S Cr Ni Mo Fe Others
SUS301 0.15 max 1.00 max 2.00 max 0.045 max 0.030 max 16.00-18.00 6.00-8.00 - Bal. -
SUS304 0.08 max 1.00 max 2.00 max 0.045 max 0.030 max 18.00-20.00 8.00-10.50 - Bal. -
SUS631
(17-7PH)
0.09 max 1.00 max 1.00 max 0.040 max 0.030 max 16.00-18.00 6.50-7.75 - Bal. Al 0.75-1.5
SUS632J1
(15-7PH)
0.09 max 1.00-2.00 1.00 max 0.040 max 0.030 max 13.50-15.50 6.50-7.75 - Bal. Cu 0.40-1.00
Ti 0.20-0.65
SUS420J2 0.26-0.40 1.00 max 1.00 max 0.040 max 0.030 max 12.00-14.00 0.60 max - Bal. -

Physical Properties

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Grade Density
[g/cm3
Specific Heat
[J/(kg・K)]
Electrical Resistance
[μΩ・cm]
Young's modulus
[GPa]
Coefficient of Thermal Expansion
[×10-6/K]
Thermal Conductivity
[W/(m・K)]
Melting Point
[℃]
Magnetism
SUS301 7.93 502 72 193 16.9
(0-100℃)
16.3 1380-1420 Nonmagnetic in the solution heat-treated condition, but becomes weakly magnetic when processed.
SUS304 7.90 502 72 193 17.3
(0-100℃)
16.3 1380-1420 Nonmagnetic in the solution heat-treated condition, but becomes weakly magnetic when processed.
SUS631
(17-7PH)
7.81 420 79 200 15.3
(25-100℃)
16.3
(100℃)
1414-1447 Nonmagnetic in the solution heat-treated condition, but becomes weakly magnetic when processed.
SUS632J1
(15-7PH)
7.74 502 100 196 10.9
(0-100℃)
15.9
(100℃)
-
SUS420J2 7.75 460 55 200 10.3
(0-100℃)
24.7 1454-1510
(always)

Mechanical Properties

SUS301、SUS304

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  As Rolled After Low-temperature Annealing Bending Test
Grade Temper
/Finish
Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
Spring Deflection Limit
[MPa]
Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
Spring Deflection Limit
[MPa]
SUS301 1/4H 250 min 860 min 25 min - 253 min 880 min 20 min - 1tR90°Bending Available
1/2H 310 min 930 min 10 min (315 min) 315 min 960 min 8 min (390 min) 2tR90°Bending Available
3/4H 370 min 1130 min 5 min (390 min) 380 min 1175 min 4 min (540 min) 2.5tR90°Bending Available
H 430 min 1320 min - (490 min) 440 min 1400 min - (655 min) [Note]4tR90°Bending Available
EH 490 min 1570 min - (590 min) 505 min 1665 min - (785 min) -
SEH 530 min 1740 min (650 min) 550 min 1840 min - (590 min) [Note]2tR90°Bending Available
SUS304 1/2H 250 min 780 min 6 min (275 min) 255 min 805 min 4 min (315 min) 2tR90°Bending Available
3/4H 310 min 930 min 3 min (335 min) 320 min 970 min 2 min (430 min) 2.5tR90°Bending Available
H 370 min 1130 min - (390 min) 385 min 1195 min - (590 min) [Note]2tR90°Bending Available

[Note] Rolled right angle direction`s bending can be performed well.

Fig. Correlations between rolling process and mechanical properties - SUS304 vs. SUS301

Fig. Correlations between rolling process and mechanical properties - SUS304 vs. SUS301

SUS631(17-7PH)

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  As Annealed / As Rolled As Precipitation Hardened
Grade Condition Temper/Finish Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
V bend
0.5t
W bend
1.0t
Heat Treatment Hardness
[HV]
Tensile Strength
[MPa]
Yield Strength
[MPa]
Spring Deflection Limit
[MPa]
SUS631 Condition A BA, 2B 200
max
1030
max
20
min
R90° R90° TH1050 345
min
1140
min
960
min
-
RH950 392
min
1230
min
1030
min
-
Condition C 1/2H 350
min
1080
min
5
min
1.5t R90° 2.0t R90° CH 380
min
1230
min
880
min
635
min
3/4H 400
min
1180
min
- - - 450
min
1420
min
1080
min
835
min
H 450
min
1420
min
- - - 530
min
1720
min
1320
min
980
min
EH 480
min
1620
min
- - - 560
min
1900
min
1570
min
-

SUS632J1(15-7PH)

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  As Rolled As Precipitation Hardened
Grade Temper
/Finish
Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
SUS632J1 1/2H 350 max 1200 max 1250 min 400 min 1300 min 1200 min
3/4H 420 max 1450 max 1500 min 480 min 1550 min 1400 min

SUS420J2

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  As Annealed / As Rolled After Quenching and Tempering
(Reference Values)
Grade Temper
/Finish
Hardness
[HV]
Tensile Strength
[MPa]
Elongation
[%]
Hardness
[HV]
SUS420J2 Annealed 150-200 540-655 1250 min 450-550
Full Hard 280-320 880-1030 1-3

Anisotropy

Stainless steels for springs is manufactured by cold rolling and has necessarily anisotropy.  

Therefore, it is necessary to take anisotropy into consideration when using the material. In general, strength (tensile strength, spring limit, yield point, elastic modulus, etc.) is stronger in the direction perpendicular to the rolling direction and weakest in the direction parallel to it. Elongation shows the opposite trend. Therefore,when selecting a material that will be bent, please make sure that the bending axis is perpendicular to the rolling direction, or at most 45°.

Also, the higher the strength of the material, the less toughness it has and the greater the springback will be ,therefore, please consider the processing conditions carefully before use.

Heat Treatment

Low-Temperature Annealing

SUS301 and SUS304 can be used as rolled, but if strong springiness is desired, we recommend low-temperature annealing at about 400°C after part processing. This low-temperature annealing must be performed after processing. If processing is performed on a product that has already been low-temperature annealed, the effect of low-temperature annealing will be lost. Please refer to each steel grade page for heat treatment conditions.


Fig. Work Hardening Curves - Low-Temperature Annealing

Precipitation Hardening Heat Treatment

Please refer to each steel grade page for heat treatment conditions.

Quenching and Tempering

SUS420J2 can be hardened by quenching and tempering.
Please refer to the SUS420J2 page for heat treatment conditions.



We can also provide quenched and tempered materials.

Related Pages

Stainless Steels Foils

We can make it to foils (less than 0.10 mm thick) in all the stainless steels we manufacture

Non-Magnetic Stainless Steels

This grade is based on SUS304 (18Cr-8Ni), a typical austenitic stainless steel, and has stabilized austenite phase by increasing chemical composition such as nickel, manganese and chromium, making it less susceptible to magnetization even after cold rolling.

We welcome your questions and inquiries regarding materials.