ASTM A693 Type 631 Stainless Steel Plate
What is ASTM A693 Type 631 (UNS S17700) Stainless Steel Plate?
As a stainless steel supplier and China mill-direct exporter, SHH STEEL supplies ASTM A693 Type 631 (UNS S17700) Stainless Steel Plate. Type 631 (UNS S17700) is a semi-austenitic precipitation-hardening stainless steel with 16.00 – 18.00 % chromium, 6.50 – 7.75 % nickel and 0.75 – 1.50 % aluminium. It is formable when solution treated and is hardened by a conditioning treatment followed by ageing.
Type 631 is the semi-austenitic precipitation-hardening grade of ASTM A693, and SHH STEEL supplies the standard grade. Its European counterpart is EN 10088-2 1.4568 plate, and the Chinese grade is GB/T 4237 07Cr17Ni7Al S51770 plate.
This page summarises the requirements for ASTM A693 Type 631 plate and sheet: chemical composition, mechanical properties, heat treatment and the general delivery requirements of ASTM A480/A480M. Values are taken from ASME SA-693 (2023 BPVC Section II-A), which is identical with ASTM A693-02ε1 except for changes to the XM-16 elongation, the maximum hardness of XM-12 and 630 in Table 5 and Note B of Table 1; check the ASTM edition named on your order. SHH STEEL confirms the edition named on the drawing before an order is placed.
Type 631 material specification and SHH STEEL supply scope
| Item | Requirement | SHH STEEL supply |
|---|---|---|
| Standard | ASTM A693 / ASME SA-693, precipitation-hardening stainless and heat-resisting steel plate, sheet and strip | Full compliance; edition confirmed at order |
| Grade | Type 631, UNS S17700 | Confirmed by heat analysis on the certificate |
| General requirements | ASTM A480/A480M: dimensions, tolerances, testing and marking | Tolerances checked against ASTM A480/A480M |
| Product forms | Plate, sheet and strip | Plate, sheet, strip and cut-to-size blanks |
| Delivery condition | Solution treated (Condition A) unless the purchase order states otherwise | Written into the mill order |
| Inspection document | Mill test report per ASTM A480/A480M | EN 10204 3.1 standard; 3.2 with third-party witness on request |
ASTM A693 requires the heat treatment to be stated on the purchase order. Solution-treated material must pass a 180° bend test: around 1T up to 4.76 mm and 3T from 4.76 to 6.98 mm (Table 6).
Chemical composition of Type 631 (ASTM A693, %)
| Element | Content (%) |
|---|---|
| Carbon (C) | ≤ 0.09 |
| Manganese (Mn) | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.040 |
| Sulphur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 1.00 |
| Chromium (Cr) | 16.00 – 18.00 |
| Nickel (Ni) | 6.50 – 7.75 |
| Aluminium (Al) | 0.75 – 1.50 |
Aluminium forms the hardening precipitates; the nickel range keeps the steel austenitic and formable after solution treatment.
Mechanical properties of Type 631 (SA-693 Tables 4 and 5)
| Condition / thickness | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Solution treated, over 0.25 mm | ≤ 1 035 MPa | ≤ 380 MPa | ≥ 20 % | ≤ B92 HRB |
| TH1050, 0.51 – 4.76 mm | ≥ 1 240 MPa | ≥ 1 035 MPa | ≥ 6 % | ≥ C38 |
| TH1050, 4.76 – 15.88 mm | ≥ 1 170 MPa | ≥ 965 MPa | ≥ 7 % | ≥ C38 / 352 HB |
| RH950, 0.51 – 4.76 mm | ≥ 1 450 MPa | ≥ 1 310 MPa | ≥ 4 % | ≥ C44 |
| RH950, 4.76 – 15.88 mm | ≥ 1 380 MPa | ≥ 1 240 MPa | ≥ 6 % | ≥ C43 / 401 HB |
| Cold rolled at mill (Condition C), to 1.27 mm | ≥ 1 380 MPa | ≥ 1 205 MPa | ≥ 1 % | ≥ C41 |
Thinner strip has lower elongation minimums in Table 5. Condition C can be aged at about 482 °C for still higher strength.
Heat treatment and delivery condition of Type 631
| Treatment | SA-693 Table 3 |
|---|---|
| Solution treatment | 1 065 ± 15 °C, water quench |
| RH950 | 954 ± 8 °C, 10 min, cool rapidly; within 24 h cool to −73 ± 6 °C, hold ≥ 8 h; warm to room temperature; 510 ± 6 °C, 1 h, air cool |
| TH1050 (alternative) | 760 ± 15 °C, 90 min; cool to 15 ± 3 °C within 1 h, hold ≥ 30 min; 566 ± 6 °C, 90 min, air cool |
The customer usually forms the solution-treated sheet, then applies RH950 or TH1050.
Lead time from the mill is normally 30 – 40 days after order confirmation, depending on size, finish and rolling schedule. Dimensional tolerances follow ASTM A480/A480M unless the order states otherwise.
Key characteristics of Type 631 (UNS S17700)
- Semi-austenitic: formable when solution treated.
- RH950: ≥ 1 450 MPa tensile up to 4.76 mm.
- TH1050: ≥ 1 240 MPa tensile up to 4.76 mm.
- 180° bend test in the solution-treated condition.
- Ordered by standard and UNS number: ASTM A693 Type 631, UNS S17700.
Type 631 equivalent grades
| System | Grade | Comment |
|---|---|---|
| EN 10088-2 | EN 10088-2 1.4568 (X7CrNiAl17-7) | Counterpart; condition limits differ |
| JIS G4305 | SUS631 | Counterpart; RH950 and TH1050 conditions |
| China | GB/T 4237 S51770 (07Cr17Ni7Al) | Cross-referenced in GB/T 20878 |
Because the standards set different limits for the hardened conditions, a substitution must be checked condition by condition. For the martensitic Type 630 (UNS S17400), see EN 10088-2 1.4542 plate and JIS G4305 SUS630 steel plate.
Applications of ASTM A693 Type 631 (UNS S17700) Stainless Steel Plate
JSSA lists springs, aircraft structural material and jet engine parts for JIS G4305 SUS631, and Euro Inox lists for the EN equivalent 1.4568:
- Springs
- Hinges and hose clips
- Valve parts
- Pressure vessels
- Aircraft structural parts
A693 notes that some of these steels are suitable for moderate to severe drawing and forming in the solution-treated condition. SHH STEEL supplies 631 stainless steel plate for these uses as full plates or cut-to-size blanks.
Type 631 compared with other ASTM A693 grades
The table compares Type 631 with the other common precipitation-hardening grades of ASTM A693, using SA-693 Tables 1, 3 and 6.
| ASTM A693 type (UNS) | Cr % | Ni % | Hardening elements | Solution treatment (Table 3) | Bend test (Table 6) |
|---|---|---|---|---|---|
| 630 (ASTM A693 S17400) | 15.00 – 17.50 | 3.00 – 5.00 | Cu 3.00 – 5.00, Nb + Ta 0.15 – 0.45 | 1 050 ± 25 °C | None required |
| 631 (S17700) | 16.00 – 18.00 | 6.50 – 7.75 | Al 0.75 – 1.50 | 1 065 ± 15 °C, water quench | 180°, 1T to 4.76 mm, 3T to 6.98 mm |
| 632 (S15700) | 14.00 – 16.00 | 6.50 – 7.75 | Al 0.75 – 1.50, Mo 2.00 – 3.00 | 1 038 ± 15 °C, water quench | 180°, 1T to 4.76 mm, 3T to 6.98 mm |
| XM-12 (S15500) | 14.00 – 15.50 | 3.50 – 5.50 | Cu 2.50 – 4.50, Nb + Ta 0.15 – 0.45 | 1 038 ± 15 °C | None required |
| XM-13 (S13800) | 12.25 – 13.25 | 7.50 – 8.50 | Al 0.90 – 1.35, Mo 2.00 – 2.50 | 927 ± 15 °C | None required |
Type 631 and Type 632 are semi-austenitic and need a bend test in the solution-annealed condition because they are intended for forming; 632 adds 2.00 – 3.00 % molybdenum. The EN counterpart of 631 is EN 10088-2 1.4568 and the Chinese grade is GB/T 4237 S51770; for the martensitic 630 type see EN 10088-2 1.4542 and JIS G4305 SUS630. SHH STEEL can quote these grades side by side.
Type 631 properties by thickness (SA-693 Table 5)
| Condition | Thickness | Tensile min, MPa | Yield min, MPa | Elongation min, % | Hardness min |
|---|---|---|---|---|---|
| TH1050 | 0.038 – 0.124 mm | 1 240 | 1 035 | 3 | C38 |
| TH1050 | 0.25 – 0.505 mm | 1 240 | 1 035 | 5 | C38 |
| TH1050 | 0.51 – 4.760 mm | 1 240 | 1 035 | 6 | C38 |
| TH1050 | 4.762 – 15.88 mm | 1 170 | 965 | 7 (RA 20) | C38 / 352 HB |
| RH950 | 0.038 – 0.124 mm | 1 450 | 1 310 | 1 | C44 |
| RH950 | 0.51 – 4.760 mm | 1 450 | 1 310 | 4 | C44 |
| RH950 | 4.762 – 15.88 mm | 1 380 | 1 240 | 6 (RA 20) | C43 / 401 HB |
| Cold rolled at mill (C) | 0.038 – 1.27 mm | 1 380 | 1 205 | 1 | C41 |
| C + 482 °C | 0.038 – 1.27 mm | 1 655 | 1 580 | 1 | C46 |
Thin strip has lower elongation minimums, and Condition C (cold rolled at the mill) is limited to thin gauges. SHH STEEL confirms that the certificate reports the tests for the condition and thickness band ordered.
Corrosion resistance of Type 631
JSSA gives SUS631, the JIS counterpart, a pitting index (Cr + 3.3 Mo) of about 17.0, so Type 631 is chosen for strength and springiness with moderate corrosion resistance rather than for aggressive chloride service. A693 states that these steels are used for parts requiring corrosion resistance and high strength at room temperature or up to 315 °C.
Corrosion resistance should be judged in the hardened condition in which the part will be used, and surfaces should be cleaned after heat treatment to remove scale or discoloration. SHH STEEL can supply the material in the condition and finish that best suits the final treatment.
Physical properties of Type 631
| Property | Typical value (Euro Inox, 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 |
These are typical values published for the EN equivalent and are not requirements of ASTM A693. The solution-treated material is largely austenitic and becomes magnetic after the transformation steps of RH950 or TH1050. On request, SHH STEEL can pass on the producing mill’s data sheet.
Forming, welding and machining Type 631
A693 notes that some of its steels are particularly suitable for moderate to severe drawing and forming in the solution-treated condition; Type 631 is one of them, as shown by its 180° bend requirement around 1T up to 4.76 mm. Parts are formed soft and then hardened by RH950 or TH1050. Dimensional change during the transformation and ageing steps should be allowed for in precision parts.
For the EN equivalent 1.4568, Euro Inox lists 1.4316 filler material. Welding is normally done before hardening, and the welded assembly is then hardened as a whole. SHH STEEL can supply Type 631 sheet slit or cut to blank sizes for forming.
Manufacture, testing and inspection of Type 631
ASTM A693 clause 4 allows the steel to be melted in an electric furnace (with optional separate degassing and refining) or a vacuum furnace, optionally followed by consumable remelting in vacuum, inert gas or electroslag, or by electron beam refining; other commercial methods may be agreed. General requirements for sampling, testing, retests and certification follow ASTM A480/A480M.
- Clause 6: material is furnished solution annealed unless the purchase order specifies another condition.
- Clause 7: test specimens must meet Table 4 in the delivered condition and be capable of meeting Table 5 after hardening.
- Clause 8: solution-annealed samples must pass the cold bend of Table 6 without cracking on the outside of the bend.
- Clause 9: samples are hardened as specified in Tables 2 and 3 to verify the Table 5 properties.
SHH STEEL checks that the certificate reports both the delivered-condition results and the results on hardened samples for the condition ordered, and can arrange third-party witness testing for Type 631.
How to order Type 631 plate
- Specification: ASTM A693 or ASME SA-693, with edition.
- Grade: Type 631, UNS number.
- Product form and dimensions: plate, sheet or strip; thickness, width, length, quantity.
- Heat treatment: A693 clause 3.1.3.1 requires it to be stated on the purchase order (delivery condition and, where relevant, the hardened condition to be verified).
- Hardened condition to be verified on test samples (TH1050 or RH950), or Condition C
- Inspection document (3.1 or 3.2) and any third-party inspection.
- Marking, packing and destination.
SHH STEEL reviews the order against A693 before it is placed and confirms in writing any requirement the mill cannot meet.
What TH1050 and RH950 mean
The condition names describe the heat treatment in SA-693 Table 3. TH1050 starts with a transformation treatment at 1 400 °F (760 °C) for 90 minutes, cooling to about 15 °C within 1 hour and holding at least 30 minutes, then ageing at 1 050 °F (566 °C) for 90 minutes. RH950 starts with conditioning at 1 750 °F (954 °C) for 10 minutes, rapid cooling, refrigeration at −73 °C for at least 8 hours within 24 hours, then ageing at 950 °F (510 °C) for 1 hour. Condition C is cold rolled at the mill and is listed in Table 5 only up to 1.27 mm.
RH950 gives the highest strength of the two heat-treated conditions, and TH1050 slightly lower strength with more elongation. For springs that do not need precipitation hardening, temper-rolled JIS G4305 SUS301 is a lower-cost alternative. SHH STEEL can help the buyer match the condition to the part.
Type 631 compared with JIS G4305 SUS631
| Condition | ASTM A693 Type 631, tensile / yield min, MPa (0.51 – 4.76 mm) | JIS G4305 SUS631, tensile / proof min, N/mm² |
|---|---|---|
| Solution treated | ≤ 1 035 / ≤ 380, El ≥ 20 %, ≤ B92 HRB | ≤ 1 030 / ≤ 380, El ≥ 20 %, ≤ 192 HBW |
| TH1050 | 1 240 / 1 035, El ≥ 6 % | 1 140 / 960 |
| RH950 | 1 450 / 1 310, El ≥ 4 % | 1 230 / 1 030 |
The solution-treated limits are almost the same, but A693 sets clearly higher minimums after hardening than JIS G4305, so a heat certified to JIS does not automatically meet A693. JIS G4305 Table 14 also uses a 3.0 mm thickness break for elongation (RH950: at least 4 % over 3.0 mm; TH1050: at least 3 % up to 3.0 mm and 5 % over), and sets hardness minimums of 40 HRC or 392 HV for RH950 and 35 HRC or 345 HV for TH1050, against A693 minimums of C44 and C38 for material under 4.76 mm. The heat-treatment temperatures in the two standards are also very close (JIS RH950 ageing at 510 ± 10 °C, A693 at 510 ± 6 °C). SHH STEEL checks the certificate against the standard named on the drawing.
Practical notes for ordering Type 631
Because Type 631 is normally formed by the customer and hardened afterwards, the order should state that material is to be supplied in the solution-treated condition and name the final condition (RH950 or TH1050) that the part will be given, so that the mill can confirm the heat will respond. The bend test of SA-693 Table 6 applies in the solution-treated condition, and the thickness band for the Table 5 properties should match the finished gauge. Where the customer cannot perform refrigeration at −73 °C, TH1050 is the condition to plan for. SHH STEEL can confirm with the mill which conditions it certifies.
How to calculate the weight of Type 631 plate
Plate weight is calculated from the dimensions and the density. Using 7.8 g/cm³ (Euro Inox, EN 1.4568), one square metre of Type 631 plate 1 mm thick weighs 7.8 kg, so the mass of a plate is density × thickness (mm) × width (m) × length (m).
| Example | Calculation | Theoretical mass |
|---|---|---|
| Type 631 plate 10 × 2 000 × 6 000 mm | 7.8 × 10 × 2.0 × 6.0 | about 936 kg |
| Type 631 sheet 3 × 1 219 × 2 438 mm | 7.8 × 3 × 1.219 × 2.438 | about 69.5 kg |
Actual weight differs from theoretical weight because of thickness tolerance; whether the invoice uses theoretical or actual weight should be agreed at the order. SHH STEEL shows both on the packing list.
Why choose SHH STEEL for Type 631
As an experienced Type 631 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 material supplied when forming is needed. | The delivery condition and heat treatment are written on the purchase order. |
| Bend failure | Solution-treated sheet cracks in forming. | Table 6 bend results are checked on the certificate. |
| Thickness bands | Elongation checked against the wrong band. | Table 5 thickness bands are checked for each order. |
| 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, heat treatment 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 Type 631 equivalent to?
- Type 631 (UNS S17700) is the semi-austenitic precipitation-hardening grade of ASTM A693. Its European counterpart is EN 1.4568 (X7CrNiAl17-7), its Japanese counterpart is JIS G4305 SUS631 and the Chinese grade is 07Cr17Ni7Al (ISC S51770). The chemistry is close, but the hardened conditions are tested to different limits, so substitution must be checked condition by condition. SHH STEEL compares the tables and can supply Type 631, 1.4568 or 07Cr17Ni7Al with the matching certificate. Where a project names more than one standard, SHH STEEL lists every applicable limit on the quotation so that the buyer can approve the material before production starts. Purchase orders should name ASTM A693, 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 Type 631?
- ASTM A693 sets the following limits for Type 631, in percent: Carbon (C) ≤ 0.09; Manganese (Mn) ≤ 1.00; Phosphorus (P) ≤ 0.040; Sulphur (S) ≤ 0.030; Silicon (Si) ≤ 1.00; Chromium (Cr) 16.00 – 18.00; Nickel (Ni) 6.50 – 7.75; Aluminium (Al) 0.75 – 1.50. Aluminium of 0.75 – 1.50 % is the hardening element. SHH STEEL checks every certificate against these limits before shipment and can arrange an independent check analysis by a partner laboratory. Product (check) analysis tolerances follow ASTM A480/A480M when a check analysis is ordered. Where a project specification adds requirements beyond ASTM A693, they should be written into the enquiry so the mill can confirm them before rolling. 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 are the mechanical properties of Type 631 plate?
- Solution-treated Type 631 over 0.25 mm is limited by SA-693 Table 4 to 1 035 MPa tensile and 380 MPa yield strength maximum, with at least 20 % elongation and B92 HRB maximum, so it can be formed. After TH1050, Table 5 requires at least 1 240 MPa tensile and 1 035 MPa yield up to 4.76 mm; after RH950, 1 450 and 1 310 MPa. Elongation minimums depend on thickness. SHH STEEL checks the certificate against the condition ordered. Test frequency and specimen location follow ASTM A480/A480M, and results are reported for each heat and heat-treatment lot. The figures quoted are the limits of ASTM A693; the actual values for a given heat are those reported on the mill test certificate.
- How is Type 631 heat treated?
- SA-693 Table 3 gives solution treatment at 1 065 ± 15 °C with water quench. RH950 uses 954 °C for 10 minutes, rapid cooling, sub-zero cooling to −73 °C for at least 8 hours, then 510 °C for 1 hour. The alternative TH1050 uses 760 °C for 90 minutes, cooling to 15 °C within 1 hour, then 566 °C for 90 minutes. A693 requires the heat treatment to be named on the purchase order. SHH STEEL supplies solution-treated material unless another condition is ordered. Any post-fabrication heat treatment should be agreed between the purchaser and the fabricator before work starts. 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 sizes of Type 631 can SHH STEEL supply?
- ASTM A693 covers plate, sheet and strip; its mechanical tables run from thin strip up to 102 mm (4.0 in.) for the 630 and 631 solution-treated limits. Dimensional and flatness tolerances follow ASTM A480/A480M unless the order specifies tighter values. SHH STEEL confirms with the mill which thicknesses and widths it can roll in Type 631, then offers full plates, cut-to-size blanks or slit strip, with cutting and testing services available. Typical Type 631 orders range from single cut pieces to full mill lots. Lead time is normally 30 – 40 days after order confirmation, depending on size and the mill rolling schedule. 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.
- Can Type 631 be formed?
- Yes, in the solution-treated condition. Type 631 is semi-austenitic, so after solution treatment it is austenitic and soft enough to form: SA-693 Table 4 limits the tensile strength to 1 035 MPa and the yield strength to 380 MPa, and Table 6 requires a 180° bend around 1T up to 4.76 mm and 3T up to 6.98 mm. The part is then hardened by RH950 or TH1050, which transform the structure and age it. Severe forming should be agreed with the mill. SHH STEEL supplies solution-treated sheet and plate for forming. SHH STEEL can also supply technical data from the producing mill on request. The figures quoted are the limits of ASTM A693; the actual values for a given heat are those reported on the mill test certificate.
Conclusion
ASTM A693 Type 631 (UNS S17700) Stainless Steel Plate is the semi-austenitic precipitation-hardening grade, formed in the solution-treated condition and hardened by RH950 or TH1050. SHH STEEL supplies it with full ASTM A693 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 Type 631 requirement.
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