Overview

Precipitation hardening stainless steels are materials that maintain corrosion resistance*¹ as stainless steel while its strength can be increased by precipitation hardening (age hardening)*² .
In particular, SUS631 is a soft metastable austenite phase in the annealed (solution heat-treated) state. As a result, it can withstand complex machining as well as austenitic stainless steel, and its strength can be increased by precipitation hardening (heat treatment) after machining.
TOKKIN supplies three types of steel: SUS631 (17-7PH), SUS632J1 (15-7PH), and TOKKIN™ 350, and can propose steel grades according to customer applications and processing methods.

*1  The general order of corrosion resistance for each type is as follows: austenitic > precipitation hardening > ferritic.
*2  Precipitation hardening refers to the process of artificially performing aging treatment (precipitation hardening) after solution heat treatment. Typical examples of precipitation hardening are stainless steels in the 600 series and maraging steels introduced on this page.

• Applications /
  Shapes / Size Range
• Features
• Standards
• Chemical Compositions
• Physical Properties
• Mechanical Properties
• Precipitation Hardening Treatment
• Difference between SUS631 and SUS632J1
• Advantages of TOKKIN

Examples of Applications

Diaphragms, Bellows, Reed Valves, Band Saws, Mask Frame Springs, Various Springs, Bellows, etc.

Manufacturable Shapes

Manufacturable Range

Thickness : 0.030mm-3.0mm　*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

Standards

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

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Chemical Compositions

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Physical Properties

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Mechanical Properties

SUS631（17-7PH）

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SUS632J1（15-7PH）

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TOKKIN™ 350

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* Hardness is provided for reference only. Please contact us for more information.

Precipitation Hardening Treatment

What is precipitation hardening treatment?

Solution treatment (solution treatment) is followed by artificial age hardening (precipitation hardening). Typical examples are the precipitation hardening stainless steels (No. 600 series) and maraging steels shown on this page.

Click here for a list of precipitation hardenable materials we supply.

The precipitation hardening heat treatment methods for each steel grade are as follows.

SUS631（17-7PH）

SUS631 is hardened from the solution treatment (annealed) condition (material A) by one of the following three methods.

The upper and middle TH1050 and RH950 treatments are hardened by a two-step heat treatment process. The first T and R treatments are primary hardening heat treatments to martensitize the metastable austenite phase A material as in quenching, while the second H treatment completely hardens the material by precipitation hardening, which is the main feature of this steel grade.
*Precipitation hardening is not possible even if only H treatment is performed in the solid solution state (Condition A material).
*TOKKIN does not have the equipment to perform TH and RH hardening treatment, so these heat treatments are performed by the customer.

The CH(900) treatment in the lower row is cold-work hardening instead of martensitizing by heat treatment, and we provide it after cold rolling to an appropriate hardness(Condition C material) .
Therefore, for customer use, only one more precipitation hardening heat treatment (H treatment) is required.

Remarks

• The numbers at the end of TH, RH, and CH indicate the precipitation hardening treatment temperature in degrees Fahrenheit and classify the treatment.

SUS632J1（15-7PH）

Precipitation hardening heat treatment conditions for SUS632J1 are as follows：
　　480°C x 1 hour holding
While SUS631 requires intermediate hardening treatment (martensification treatment), SUS632J1 can be hardened by only one heat treatment in any condition.

TOKKIN™ 350

TOKKIN™ 350 is precipitation hardened from the annealed state to obtain high strength through two treatments: primary hardening, which transforms the metastable austenite structure in the annealed state into martensite, and precipitation hardening, which completely hardens the structure.
The temperature conditions are as shown in the SCT850 heat treatment conditions below.

Precautions for Heat Treatment

• Low temperature scale such as H treatment：　① 10% hydrochloric acid → 30% nitric acid, or ② 15% nitric acid + 2% hydrofluoric acid (nitro fluoric acid)
• High temperature scale such as T and R treatments：　①Caustic soda + 30% sodium nitrate molten salt → nitro fluoric acid, or ②10% caustic soda + 3% potassium permanganate boiling solution → nitro fluoric acid
• In addition to the above, mechanical polishing, blasting, and peening are also used to remove oxide scale.

• Putting a mixture of alcohol or acetone and dry ice in a heat-resistant container will produce an appropriate temperature in the vicinity of -73°C.
• If large quantities are processed continuously, a refrigerator is used.

Comparison of Grades

Difference between SUS631 and SUS632J1

（1）Hardness increase depends on the cold rolling rate.

The following figure (left), "Cold Rolling and Mechanical Properties," shows reduction ratio-hardness and hardness after precipitation hardening.
SUS631 C (dashed line) has a large increase in hardness as the rolling ratio increases, on the opposite, SUS632J1 C (solid line), even if the rolling ratio is increased, the hardness does not increase as much as SUS631 C.
SUS632J1 has a certain degree of strength without strong cold working, and its hardness increase due to cold working is smaller, it is recommended for those who are concerned about directional properties or who require formability and punching workability.

（2）The amount of hardness increase due to precipitation hardening heat treatment (H treatment) differs.

When H treatment (precipitation hardening heat treatment) is applied to C material (cold-rolled material) of SUS631, the maximum increase in hardness (the higher the rolling ratio, the greater the increase in hardness after H treatment) is about HV80-90, but with SUS632J1, the increase is over HV150 regardless of rolling ratio.

Thus, for SUS631, it is possible to greatly increase the hardness by applying TH1050 or RH950 treatment to A material (soft material of HV200 or less), so we recommend A material of SUS631 if complex shapes are required.

However, for A material, martensitization treatment (T treatment, R treatment) must be performed prior to H treatment, so please pay attention to the heat treatment conditions.

Advantages of TOKKIN

Although precipitation hardening stainless steels are generally scarce in circulation, we can provide the following services;

• Ultra-thin foil
  We can also manufacture ultra-thin foil down to 0.010 mm to 0.099 mm in thickness.
• Small Lot
  We accept orders for minimum lot size of 100 kg or more. (Smaller lot is also available upon request.)
• Hardness Adjustment
  Since it is made-to-order, it can be adjusted to your desired hardness. We can flexibly adjust to general 3/4H material as well as other       hardness.
• Surface Finish
  Smooth finish or Matt Finish is available.