JIS G4305 SUS631 Steel Plate | 631 Stainless Steel
What is JIS G4305 SUS631 Steel Plate?
As a stainless steel supplier and China mill-direct exporter, SHH STEEL supplies JIS G4305 SUS631 Steel Plate, also known as 631 stainless steel. SUS631 is a semi-austenitic precipitation-hardening grade of JIS G4305:2021, the Japanese Industrial Standard for cold-rolled stainless steel plate, sheet and strip. It contains 16.00 – 18.00 % chromium, 6.50 – 7.75 % nickel and 0.75 – 1.50 % aluminium, and is supplied solution treated, then hardened by the RH950 or TH1050 treatments.
SUS631 is the JIS counterpart of UNS S17700 (ASTM A693 S17700); SHH STEEL supplies the standard grade. GB/T 20878 cross-references it to EN 1.4568, supplied as EN 10088-2 1.4568 plate, and to the Chinese grade GB/T 4237 07Cr17Ni7Al S51770 plate. Within JIS G4305, JIS G4305 SUS630 steel plate is the other precipitation-hardening grade.
This page summarises the requirements of JIS G4305:2021 for SUS631: chemical composition, mechanical properties, surface finishes, standard sizes and the informative heat-treatment conditions of Annex JA. Hot-rolled plate of the same grade is ordered to JIS G 4304:2021, which also lists SUS631. SHH STEEL quotes either standard and confirms the edition named on the drawing before an order is placed.
SUS631 material specification and SHH STEEL supply scope
| Item | JIS G4305:2021 requirement | SHH STEEL supply |
|---|---|---|
| Standard | JIS G 4305:2021, cold-rolled stainless steel plate, sheet and strip | Full compliance; JIS G 4304:2021 for hot-rolled plate |
| Grade | SUS631 (precipitation-hardening) | Confirmed by heat analysis on the certificate |
| Standard plate sizes (Table 16) | Thickness 0.30 – 20.0 mm; 1 000 × 2 000, 1 219 × 2 438, 1 219 × 3 048 and 1 524 × 3 048 mm | Other sizes by agreement, as Table 16 allows |
| Standard strip thickness (Table 17) | 0.30 – 6.0 mm | Coil and slit strip |
| Surface finish (Table 15) | No.2D, No.2B, BA, HL; polished finishes by the manufacturer’s method | Finish written into the mill order |
| Inspection document | JIS G 0415, inspection certificate 3.1, unless otherwise specified | 3.1 standard; 3.2 with third-party witness on request |
Mechanical properties in JIS G4305 apply to thickness 0.30 mm and above, and the standard notes that properties after heat treatment carried out by the user are not specified. Properties after precipitation hardening are specified in Table 14; Annex JA gives the RH950 and TH1050 treatment examples.
Chemical composition of JIS G4305 SUS631 (heat analysis, %)
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.09 |
| Silicon (Si) | ≤ 1.00 |
| Manganese (Mn) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.040 |
| Sulphur (S) | ≤ 0.030 |
| Nickel (Ni) | 6.50 – 7.75 |
| Chromium (Cr) | 16.00 – 18.00 |
| Aluminium (Al) | 0.75 – 1.50 |
Aluminium forms the precipitates that harden the steel. The nickel range is set so that the steel is austenitic and formable after solution treatment, then transforms to martensite during the conditioning step.
Mechanical properties of SUS631 in the solution-treated and precipitation-hardened conditions (JIS G4305 Table 14)
| Condition | 0.2 % proof stress | Tensile strength | Elongation | Hardness |
|---|---|---|---|---|
| Solution treated (S) | ≤ 380 N/mm² | ≤ 1 030 N/mm² | ≥ 20 % | ≤ 192 HBW |
| RH950 | ≥ 1 030 N/mm² | ≥ 1 230 N/mm² | ≥ 4 % (over 3.0 mm) | ≥ 40 HRC |
| TH1050 | ≥ 960 N/mm² | ≥ 1 140 N/mm² | ≥ 3 % / ≥ 5 % by thickness | ≥ 35 HRC |
In the solution-treated condition the limits are maximums, because the steel must be soft enough to form; after hardening they are minimums.
Surface finishes for SUS631 sheet and plate
| Finish (Table 15) | Description |
|---|---|
| No.2D | Cold rolled, heat treated and pickled (or equivalent); may include a final light pass on dull rolls |
| No.2B | Cold rolled, heat treated, pickled, then lightly cold rolled for a suitable lustre |
| BA | Bright annealed after cold rolling |
| HL | Polished with abrasive of suitable grit to give continuous polishing lines |
JIS G4305 leaves polished finishes such as No.3, No.4, #240, #320 and #400 to the manufacturer’s method, so SHH STEEL writes the finish, the grit and any protective film into the purchase order. For precipitation-hardening sheet, No.2D and No.2B are the usual finishes.
Heat treatment and delivery condition of SUS631
| Treatment | Condition (Annex JA, Table JA.5) |
|---|---|
| Solution treatment | 1 000 – 1 100 °C, rapid cooling |
| RH950 | 955 ± 10 °C for 10 min, air cool to room temperature; within 24 h cool to −73 ± 6 °C and hold 8 h; 510 ± 10 °C for 60 min, air cool |
| TH1050 | 760 ± 15 °C for 90 min; within 1 h cool to 15 °C or below and hold 30 min; 565 ± 10 °C for 90 min, air cool |
Annex JA is informative and gives the detailed temperatures and times for each treatment. The customer usually forms the solution-treated sheet and then applies RH950 or TH1050.
Table 19 of JIS G4305 gives a basic mass of 7.93 kg/(mm·m²) for SUS631, which is used to calculate plate weight (equivalent to a density of 7.93 g/cm³). Lead time from the mill is normally 30 – 40 days after order confirmation, depending on size, finish and rolling schedule.
Key characteristics of 631 stainless steel
- Semi-austenitic: formable when solution treated, high strength after hardening.
- RH950: ≥ 1 230 N/mm² tensile strength and ≥ 40 HRC.
- TH1050: ≥ 1 140 N/mm² tensile strength and ≥ 35 HRC.
- Aluminium 0.75 – 1.50 % provides precipitation hardening.
- Density 7.93 g/cm³ (JIS G4305 Table 19).
SUS631 equivalent grades
| System | Grade | Comment |
|---|---|---|
| UNS / ASTM | S17700 (Type 631 in ASTM A693) | Same composition type |
| EN 10088-2 | EN 10088-2 1.4568 (X7CrNiAl17-7) | Cross-referenced in GB/T 20878 Table C.1 |
| China | GB/T 4237 S51770 (07Cr17Ni7Al) | Cross-referenced in GB/T 20878 Table C.1 |
ASTM A693 Type 631 uses different condition names and limits (for example TH1050 at 1 240 MPa tensile strength for thickness up to 4.76 mm), so the JIS and ASTM tables should be compared before substituting.
Applications of JIS G4305 SUS631 Steel Plate
The Japan Stainless Steel Association lists the main uses of SUS631 as:
- Springs of various types
- Aircraft structural material
- Jet engine parts
Euro Inox lists hinges, hose clips, springs, valve parts and pressure vessels for the EN equivalent 1.4568.
SUS631 compared with related JIS G4305 grades
The table compares SUS631 with the JIS G4305:2021 grades that buyers most often consider alongside it. Chemistry is taken from Tables 3 – 7 and the minimum mechanical properties from Tables 8 – 14 of the standard, all in the condition in which the grade is normally supplied.
| JIS G4305 grade | Cr % | Ni % | Hardening element | Condition | 0.2 % proof stress, N/mm² | Tensile, N/mm² |
|---|---|---|---|---|---|---|
| JIS G4305 SUS630 | 15.00 – 17.50 | 3.00 – 5.00 | Cu 3.00 – 5.00, Nb 0.15 – 0.45 | H900 | ≥ 1 175 | ≥ 1 310 |
| H1150 | ≥ 725 | ≥ 930 | ||||
| SUS631 | 16.00 – 18.00 | 6.50 – 7.75 | Al 0.75 – 1.50 | RH950 | ≥ 1 030 | ≥ 1 230 |
| TH1050 | ≥ 960 | ≥ 1 140 |
SUS630 is martensitic after solution treatment and is hardened by ageing alone; SUS631 is austenitic after solution treatment and needs a conditioning step before ageing, which makes it the formable choice. The EN counterparts are EN 10088-2 1.4542 for SUS630 and EN 10088-2 1.4568 for SUS631. SHH STEEL can quote the grades in this table side by side when a buyer is still choosing between them.
SUS631 to JIS G4305 (cold rolled) or JIS G4304 (hot rolled)?
SUS631 is listed in both JIS G4305:2021 (cold-rolled plate, sheet and strip) and JIS G4304:2021 (hot-rolled plate, sheet and strip). The chemistry and the mechanical property tables are the same in both standards, but the product range, finish and tolerances differ:
| Item | JIS G4305 (cold rolled) | JIS G4304 (hot rolled) |
|---|---|---|
| Standard plate thicknesses (Table 16) | 0.30 – 20.0 mm | 2.0 – 35.0 mm |
| Standard plate sizes | 1 000 × 2 000, 1 219 × 2 438, 1 219 × 3 048, 1 524 × 3 048 mm | Same four sizes |
| Standard strip thicknesses (Table 17) | 0.30 – 6.0 mm | 2.0 – 9.0 mm |
| Surface finish (Table 15) | No.2D, No.2B, BA, HL | No.1 (hot rolled, heat treated and pickled) |
| Plate thickness tolerance | Table 20, or ET / ST on request | Classes A, B or C (Tables 20 – 22); B and C use an addition to thickness for calculated mass |
As a rule, thin sheet and anything that needs a bright or brushed surface is ordered to JIS G4305, while heavier plate for fabrication is ordered to JIS G4304. Sizes outside the tables are possible by agreement in both standards. SHH STEEL confirms which standard and finish suit the part before quoting.
Corrosion resistance of SUS631
A common way to rank resistance to pitting is the pitting resistance equivalent number, PREN = %Cr + 3.3 × %Mo + 16 × %N. Calculated from the JIS G4305 limits, SUS631 has a PREN of about 16.0 at the minimum of every range and about 18.0 at the maximum. PREN is a ranking tool, not a guarantee of performance in a given environment, and actual heats normally sit between these values; the certificate analysis gives the real figure for each heat. SHH STEEL can calculate the PREN of the heat offered from its certificate before the order is confirmed.
SUS631 is chosen mainly for strength. JSSA gives it a pitting index (Cr + 3.3 Mo) of about 17.0, the level of a 17 % chromium steel without molybdenum, so it is not intended for aggressive chloride service. Corrosion resistance should be judged in the hardened condition in which the part will be used.
Where resistance to intergranular corrosion must be demonstrated, clause 7 of JIS G4305 lets the purchaser specify one of four test methods: JIS G 0571 (oxalic acid etch test), JIS G 0572 (ferric sulphate – sulphuric acid test), JIS G 0573 (65 % nitric acid test) or JIS G 0575 (copper sulphate – sulphuric acid test). One test piece is taken per heat and heat-treatment lot. SHH STEEL writes the chosen method and acceptance criterion into the mill order when a project requires it.
Physical properties of SUS631
| Property | Typical value (Euro Inox, Tables of Technical Properties, EN 1.4568) |
|---|---|
| Density | 7.8 g/cm³ |
| Modulus of elasticity at 20 °C | 200 GPa |
| Thermal conductivity at 20 °C | 16 W/(m·K) |
| Specific heat at 20 °C | 500 J/(kg·K) |
| Electrical resistivity at 20 °C | 0.80 Ω·mm²/m |
JIS G4305 gives physical data only as the basic mass of 7.93 kg/(mm·m²) in Table 19. The other values are typical figures published for EN 1.4568 (Euro Inox) and are given for design guidance only; they are not acceptance requirements for SUS631. On request, SHH STEEL can pass on the producing mill’s own data sheet for the heat supplied.
Welding, forming and machining SUS631
The usual sequence is to form SUS631 in the solution-treated condition, when it is austenitic and ductile (proof stress ≤ 380 N/mm², elongation ≥ 20 %), and then harden it by the RH950 or TH1050 treatment of Annex JA Table JA.5. Dimensional change during hardening should be allowed for in the design of precision parts.
For the EN equivalent 1.4568, Euro Inox lists 1.4316 filler material. Welding is normally done before hardening, and the welded part is then hardened as a whole. Machining is easiest in the solution-treated condition.
SHH STEEL can deliver SUS631 cut to size, bevelled or pre-formed through its processing partners, so that the fabricator receives parts ready for welding.
Dimensional tolerances for SUS631 plate and sheet (JIS G4305)
JIS G4305:2021 clause 9 sets the tolerances for cold-rolled plate, sheet and strip, and SHH STEEL checks thickness at the positions the standard defines before shipment. Thickness tolerances for plate are given in Table 20 and depend on thickness and width:
| Thickness (mm) | Width < 1 250 mm | Width 1 250 – 1 600 mm |
|---|---|---|
| 0.30 – < 0.60 | ± 0.05 | ± 0.08 |
| 0.60 – < 0.80 | ± 0.07 | ± 0.09 |
| 0.80 – < 1.00 | ± 0.09 | ± 0.10 |
| 1.00 – < 1.25 | ± 0.10 | ± 0.12 |
| 1.25 – < 1.60 | ± 0.12 | ± 0.15 |
| 1.60 – < 2.00 | ± 0.15 | ± 0.17 |
| 2.00 – < 2.50 | ± 0.17 | ± 0.20 |
| 2.50 – < 3.15 | ± 0.22 | ± 0.25 |
| 3.15 – < 4.00 | ± 0.25 | ± 0.30 |
| 4.00 – < 5.00 | ± 0.35 | ± 0.40 |
| 5.00 – < 6.00 | ± 0.40 | ± 0.45 |
| 6.00 – < 8.00 | ± 0.50 | ± 0.50 |
| 8.00 – < 10.0 | ± 0.60 | ± 0.60 |
| 10.0 – < 16.0 | ± 0.70 | ± 0.70 |
| 16.0 – 25.0 | ± 0.80 | ± 0.80 |
Tighter thickness tolerances can be ordered with the symbols ET (Table 22) or ST (Table 23), and narrower width tolerances with EW (Table 26). Plate width tolerance (Table 24) is +10 / 0 mm for lengths up to 3 500 mm, and plate length tolerance (Table 27) is +10 / 0 mm for thickness under 10 mm and lengths up to 3 500 mm. Flatness is measured on request: Table 28 allows 15 – 20 mm per 3 500 mm length, or 3 – 6 mm when the special flatness symbol EF is ordered.
For hot-rolled SUS631 plate ordered to JIS G 4304, the tolerances of that standard apply. SHH STEEL states the tolerance symbols on the quotation so that the buyer knows exactly which table the plate will be measured against.
Testing, inspection and marking of SUS631
Clause 11 of JIS G4305 sets the test rules. Chemical analysis follows JIS G 0404 and JIS G 0320, and a product (check) analysis to JIS G 0321 can be requested by the purchaser. For mechanical tests, one sample is taken from plate or strip of the same heat and the same heat-treatment condition, and one test piece is used for each test.
- Tensile test to JIS Z 2241 at 23 ± 5 °C, using test piece No. 4, No. 10 or No. 13B (No. 14A, 14B or 5 also allowed).
- Hardness test to JIS Z 2243-1 (Brinell), JIS Z 2244-1 (Vickers) or JIS Z 2245 (Rockwell), at 23 ± 5 °C.
- Bend test to JIS Z 2248 where the grade has a bend requirement; the manufacturer may omit it, but the material must still meet it, and it must be done if the purchaser asks.
- Inspection of chemistry, mechanical properties, surface finish, dimensions and appearance under clause 12; corrosion resistance only when specified.
Under clause 13 each plate or bundle is marked with the grade symbol, dimensions, any special tolerance or flatness symbols (ET, ST, EW, EF), the surface finish, the heat-treatment symbol where applicable, the manufacturer’s name or mark, and the heat or inspection number. Clause 14 makes the inspection document JIS G 0415 type 3.1 unless another type is ordered; SHH STEEL checks the marking against the certificate before shipment, and a third-party inspector arranged by SHH STEEL can witness the tests when a 3.2 document is required.
How to order SUS631 plate and sheet
A complete enquiry avoids delays and wrong deliveries. For SUS631 we recommend stating:
- Standard and edition: JIS G 4305:2021 (cold rolled) or JIS G 4304:2021 (hot rolled), grade SUS631.
- Product form: plate, sheet, coil or strip; thickness, width and length, or coil inner diameter and weight.
- Tolerance and flatness symbols if tighter than standard (ET, ST, EW, EF).
- Surface finish from Table 15 (No.2D, No.2B, BA, HL) or a polished finish with grit and protective film.
- Heat-treatment condition, and any intergranular corrosion test method (JIS G 0571 – 0575).
- Inspection document type (JIS G 0415 3.1 by default, 3.2 if third-party witness is needed).
- Any dual certification required, for example to ASTM A240 or EN 10088-2, and any product analysis or PMI.
- Packing, marking and destination port; SHH STEEL can add customer marking or bar codes on request.
SHH STEEL reviews every enquiry against these points and confirms in writing anything that the mill cannot meet before the order is placed.
How to calculate the weight of SUS631 plate
Table 18 of JIS G4305 calculates plate mass from the basic mass in Table 19, which for SUS631 is 7.93 kg per mm of thickness per m² of area. The basic mass is multiplied by the thickness in millimetres to give the unit mass in kg/m², then by the plate area in m², and the result is rounded as the table specifies.
| Example | Calculation | Mass |
|---|---|---|
| SUS631, 3.0 × 1 219 × 2 438 mm | 7.93 × 3.0 × (1.219 × 2.438) | about 70.7 kg per sheet |
Invoiced weight may be calculated (theoretical) or actual (weighed), and this should be agreed at the order. SHH STEEL states which method is used on the quotation, and the SHH STEEL packing list shows both the calculated and the actual weight of each bundle.
Why choose SHH STEEL for SUS631
As a SUS631 supplier, we find that buyers usually worry less about price than about getting the right material on time. The table below lists the concerns we hear most often and how SHH STEEL deals with each one.
| Buyer concern | Risk | How SHH STEEL handles it |
|---|---|---|
| Wrong condition | Hardened sheet delivered when forming is needed. | Delivery condition (normally solution treated) is written into the order. |
| Hardening response | Aluminium or nickel off target changes the response. | Chemistry is checked on the certificate. |
| Thin-gauge elongation | Elongation tested against the wrong thickness band. | Table 14 thickness bands are checked on the certificate. |
| Minimum order | Mills set high minimums for less common grades. | Orders are consolidated so smaller lots can join a mill rolling where the mill makes the grade. |
| Delivery tracking | Delays at rolling, annealing or testing are found too late. | A dedicated person follows the schedule and reports progress at each stage. |
SHH STEEL also offers steel cutting services, bending and forming services, a third-party testing service with partner laboratories, and a worldwide shipping service. See our full range of stainless steel sheets and plates.
FAQ
- What is SUS631 equivalent to?
- SUS631 is the JIS counterpart of UNS S17700, which appears as Type 631 in ASTM A693. GB/T 20878 Table C.1 cross-references it to EN 1.4568 (X7CrNiAl17-7) and to the Chinese grade 07Cr17Ni7Al, ISC S51770. Purchase orders should name the standard, the grade and the delivery condition. ASTM A693 sets higher minimum strengths than JIS G4305 after RH950 and TH1050, so a heat certified to JIS does not automatically meet A693. The chemistry is close across these standards, but the hardened-condition limits differ. SHH STEEL compares the tables for each order. Every SUS631 plate shipped by SHH STEEL carries an inspection document to JIS G 0415, type 3.1 by default. Purchase orders should name JIS G4305, its edition, the grade, the thickness and the inspection document required, so the certificate can be checked against the same tables.
- What is the chemical composition of JIS G4305 SUS631?
- JIS G4305:2021 sets the following heat-analysis limits for SUS631: Carbon (C) ≤ 0.09; Silicon (Si) ≤ 1.00; Manganese (Mn) ≤ 1.00; Phosphorus (P) ≤ 0.040; Sulphur (S) ≤ 0.030; Nickel (Ni) 6.50 – 7.75; Chromium (Cr) 16.00 – 18.00; Aluminium (Al) 0.75 – 1.50. Aluminium is the hardening element in SUS631. Elements not listed are not added intentionally; where the standard asks for the content of optional elements to be reported, it appears on the inspection certificate. SHH STEEL checks every certificate against these limits before shipment and can arrange an independent check analysis by a partner laboratory. Where a project specification adds requirements beyond JIS G4305, they should be written into the enquiry so the mill can confirm them before rolling.
- What are the mechanical properties of SUS631 plate?
- JIS G4305 Table 14 sets maximum values for solution-treated SUS631: proof stress up to 380 N/mm², tensile strength up to 1 030 N/mm², elongation at least 20 % and hardness up to 192 HBW, so the sheet can be formed. After RH950 treatment the minimums are 1 030 N/mm² proof stress, 1 230 N/mm² tensile strength and 40 HRC; after TH1050 they are 960 N/mm², 1 140 N/mm² and 35 HRC, with elongation depending on thickness. SHH STEEL checks the condition and results on the 3.1 certificate for every heat. Any supplementary test, such as a product analysis or a corrosion test, has to be agreed at the enquiry stage because it cannot be added after delivery. The figures quoted are the limits of JIS G4305; the actual values for a given heat are those reported on the mill test certificate.
- How is SUS631 heat treated?
- Annex JA of JIS G4305 gives solution treatment at 1 000 – 1 100 °C with rapid cooling, followed by the RH950 or TH1050 hardening sequences as the example heat treatment for SUS631. The annex is informative, so it shows typical conditions rather than mandatory limits, and the mill applies its own qualified practice within the requirements of the standard. The customer usually forms the soft sheet and then hardens it. SHH STEEL supplies SUS631 in the heat-treated condition stated on the order and asks the mill to record the treatment on the inspection certificate, so the fabricator knows the starting condition of the material. If a drawing names more than one standard, the material must meet each of them, and the certificate should state every standard it claims.
- What sizes and finishes of SUS631 can SHH STEEL supply?
- JIS G4305 lists standard plate thicknesses from 0.30 mm to 20.0 mm and sheet sizes from 1 000 × 2 000 mm to 1 524 × 3 048 mm; strip is listed from 0.30 mm to 6.0 mm. The standard finishes are No.2D, No.2B, BA and HL, with polished finishes made by the manufacturer's method. Other sizes are possible by agreement, and hot-rolled plate is ordered to JIS G 4304. SHH STEEL confirms with the mill which sizes it can roll in SUS631, then offers cut-to-size blanks, slit coil or full plates. Lead time is normally 30 – 40 days. Any supplementary test, such as a product analysis or a corrosion test, has to be agreed at the enquiry stage because it cannot be added after delivery.
- What is the difference between SUS631 and SUS630?
- Both are precipitation-hardening grades in JIS G4305, but they work differently. SUS630 (UNS S17400 type) is martensitic after solution treatment and is hardened by a single ageing treatment; copper and niobium provide the hardening. SUS631 (UNS S17700 type) is austenitic after solution treatment, so it can be formed, and it is hardened by a conditioning step followed by ageing; aluminium provides the hardening. JSSA lists high-strength bolts, valves, aircraft parts and shafts for SUS630, and springs, aircraft structures and jet engine parts for SUS631. SHH STEEL supplies both grades and can help a buyer decide which one suits a formed or machined part. The figures quoted are the limits of JIS G4305; the actual values for a given heat are those reported on the mill test certificate.
Conclusion
JIS G4305 SUS631 Steel Plate (631 stainless steel) is the semi-austenitic precipitation-hardening grade of JIS G4305 (UNS S17700 type), formable when solution treated and hardened by RH950 or TH1050 for springs and aircraft parts. SHH STEEL supplies it with full JIS G4305 compliance, 3.1 inspection certificates and optional third-party testing, with a normal lead time of 30 – 40 days. Contact SHH STEEL for availability, sizes and a quotation for your SUS631 requirement.
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