1.3965 Non-Magnetizable Steel Forgings (X8CrMnNi18-8)

What is 1.3965?

1.3965 is listed in SEW 390, the German material sheet covering non-magnetizable steels. The sheet sets a numerical acceptance limit: relative magnetic permeability must not exceed 1.01, normally verified at a field strength of 8000 A/m. Material above that figure is off specification even where chemistry and mechanical properties are within limits.

The limit is met by composition as well as by heat treatment. Manganese at 7.50 to 9.50% and nitrogen at 0.10 to 0.20% are strong austenite formers, so the face-centred cubic austenite structure stays stable at room temperature with only 4.50 to 6.50% nickel. Austenite is paramagnetic, while ferrite and martensite are ferromagnetic. Permeability stays close to unity only while the structure remains fully austenitic and free of delta ferrite and deformation martensite.

Nitrogen also acts as an interstitial solid solution strengthener. Minimum yield strength is therefore 295 MPa, against roughly 190 to 210 MPa for a standard 18/8 austenitic steel such as 1.4301, with elongation still above 50%.

Position within the SEW 390 range

SEW 390 covers grades from lean manganese types through to heavily alloyed seawater-resistant austenites. 1.3965 is among the more economical of them and is normally specified where the requirement is magnetic neutrality together with general corrosion resistance comparable to a standard austenitic stainless steel. It contains no molybdenum, so its pitting resistance equivalent number is only about 19 to 22 and it is not used for seawater or chloride pitting duty. For those conditions the grade from the same sheet is 1.3964.

1.3965 chemical composition

Composition limits below are the requirements of SEW 390 for X8CrMnNi18-8, in percent by mass. Jiangyin Jiangnan Metal Co., Ltd. melts to these limits and reports the actual heat analysis on every certificate.

Optional restrictions

SEW 390 does not limit the items below, but generator, instrument and drilling specifications often add them. They are held when stated at enquiry stage, since they govern which heat the forging is drawn from.

Mechanical and physical properties

The values below apply to the solution annealed condition, which is the normal delivery condition for forgings. Cold worked bar reaches higher strength at lower elongation, and its permeability requires separate verification for the reason given in the section on austenite stability.

Physical values for austenitic Cr-Mn-Ni-N steels vary between sources by a few percent. They are given here for screening, not for design calculation.

Low temperature service

Austenitic steels show no ductile to brittle transition. In European practice 1.3965 in the strain hardened condition is applied to pressure-retaining components down to minus 180 °C. Where a specific impact test temperature is required, state it at enquiry stage. Charpy testing is carried out in house down to minus 60 °C and placed with an accredited laboratory below that.

Magnetic permeability requirement

Relative permeability is the controlling property for this grade. The following sets out what the limit covers and which conditions raise it.

A paramagnetic material has a relative permeability just above 1. The SEW 390 figure of 1.01 is an acceptance limit applied to the delivered part rather than a fixed property of the alloy. Three conditions raise the permeability of a nominally austenitic steel above it:

• Delta ferrite retained from solidification. Ferrite is ferromagnetic. A chemistry balanced towards the ferrite formers, or a slow cooled heavy section, leaves ferrite dispersed in the austenite, and permeability rises with the ferrite content.
• Deformation martensite from cold work. Cold forming, straightening, hard turning, grinding and heavy machining can transform surface austenite into martensite, which is also ferromagnetic. Chemistry and heat treatment records stay within limits in this case, so the cause is often identified late.
• Carbide precipitation after slow cooling. Chromium carbides formed between roughly 500 and 800 °C deplete the surrounding austenite of chromium, destabilise it locally and allow ferrite to form.

Control measures are a solution anneal at 1000 to 1050 °C followed by rapid cooling, an aim analysis in the upper half of the nickel and nitrogen ranges, and measurement of permeability on the finished part rather than on the billet. For critical components the permeability check is repeated after final machining, since machining is the operation most likely to introduce martensite.

Austenite stability and cold work

The SEW 390 analysis band for 1.3965 is wide, and material at opposite ends of it responds differently to cold work. Austenite stability is normally indexed by the Md30 temperature, at which 30% deformation transforms half the volume to martensite; a lower Md30 indicates more stable austenite. Applying the Nohara relationship to the SEW 390 limits gives the following values.

Ordering to the grade name alone therefore does not fix magnetic performance after fabrication, since two heats can both satisfy SEW 390 and still behave differently in production. Where the part is to be cold formed, heavily machined, straightened or thread rolled after delivery, specify an aim analysis in the upper half of the nickel and nitrogen ranges and require permeability to be verified after those operations.

Jiangyin Jiangnan Metal Co., Ltd. melts its own steel rather than buying billet, so the aim analysis is set at the furnace. Where service conditions exceed what the grade can carry, an alternative grade applies; the comparison table below lists the alternatives held in production.

Forging and heat treatment

Three temperature ranges govern the condition of a 1.3965 forging at delivery. All three are instrumented, and furnace charts are issued with the order on request.

1.3965 cannot be hardened by heat treatment. Strength is raised only by cold work, which also raises permeability, so forgings are supplied solution annealed as standard. The cold worked condition is used for bar and fasteners where permeability has been verified in that state.

1.3965 equivalents and cross-reference

1.3965 is a German works sheet designation, so exact equivalents in other systems are rare. The pairings below are the ones used in practice for enquiry purposes. They are close, not identical, and any substitution needs the purchaser's written approval.

1.3965 compared with the other SEW 390 grades

Grade selection within SEW 390 follows alloy content. Higher nickel, nitrogen and molybdenum give greater austenite stability, higher strength and better corrosion resistance, at higher cost.

Select against the service conditions. For parts that must not perturb a magnetic field and operate indoors or in a mild atmosphere, 1.3965 is adequate and the higher alloyed grades add cost without benefit. For seawater, chloride or sour service, 1.3964 or 1.3974 applies. Where high strength is required without corrosion duty, the manganese grades 1.3817 and 1.3813 are lower in cost. Jiangyin Jiangnan Metal Co., Ltd. forges every grade in this table.

What 1.3965 forgings does Jiangyin Jiangnan Metal produce?

Jiangyin Jiangnan Metal Co., Ltd. is an integrated melting works and open-die forge at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 1997. Steel is melted on site, so the 1.3965 aim analysis is set for the forging it will become, and the certificate traces to the melt number rather than to a purchased billet.

This has more effect on 1.3965 than on most grades. As the austenite stability table above shows, the position of the heat within the SEW 390 band governs magnetic behaviour after machining, and that position is fixed at the furnace rather than at the forge.

Product forms produced in 1.3965 are seamless rolled rings, forged rings, shafts and spindles, round bars, flat bars and blocks, discs and tube sheets, sleeves, bushings and hollow cylinders, flanges and valve bodies, bonnets, stems and seat rings.

Delivery condition is solution annealed as standard, supplied as forged with an agreed machining allowance, rough machined, or finish machined to drawing. Anti-rust treatment and seaworthy packing are included for export.

How a 1.3965 forging is produced

The sequence below is the standard production route used by Jiangyin Jiangnan Metal Co., Ltd. for this grade.

1. Melting and nitrogen control The heat is melted in the electric arc furnace, refined in the ladle furnace and decarburised under vacuum. Nitrogen is trimmed at this stage, since it must be held in solution, and the aim analysis is placed in the upper half of the nickel and nitrogen ranges unless the order states otherwise.
2. Analysis before teeming Heat chemistry is taken and confirmed by optical emission spectrometry before the ingot is cast. Incoming stock is verified by positive material identification, since 1.3965, 1.3964 and the standard austenitic grades cannot be distinguished visually.
3. Preheat and soak The billet is through heated to 1150 to 1180 °C and held until core and surface temperatures equalise. High manganese and nitrogen contents raise the flow stress, so the soak is held for the full time.
4. Upsetting and drawing The billet is upset to break down the cast structure, then drawn to a shaft, or punched and expanded over a saddle mandrel for rings and sleeves. Ring blanks go to the 6 m, 3 m or 1 m radial-axial ring mill.
5. Controlled reheats The forging is reheated as often as required so that deformation always finishes above 750 °C. Working below that temperature produces cracking that is detected later at ultrasonic inspection.
6. Solution annealing The forging is soaked at 1000 to 1050 °C and cooled rapidly through the 800 to 500 °C range, in water or forced air according to section thickness and distortion risk. Long shafts are treated vertically in the 15 m well furnace.
7. Rough machining and volumetric inspection The forging is rough machined to a testable surface, then examined ultrasonically to ASTM A745 or EN 10228-4, the austenitic procedures, against the acceptance class stated on the order.
8. Permeability check Relative magnetic permeability is measured and recorded, on the finished surface where the order requires it. A reading above the limit is corrected by a repeat solution anneal rather than by grinding.
9. Testing and certification Heat chemistry, tensile and yield strength, elongation, impact energy and surface examination are documented on an EN 10204 3.1 inspection certificate, with third-party witness added when ordered.

Testing, inspection and certification

The works holds CCS, BV, DNV, LR and NK classification society approvals and operates its own laboratory. Steel is melted on site, so chemistry is verified at the furnace rather than taken from a supplier certificate.

EN 10204 3.1 inspection certificates are supplied as standard, reporting heat analysis, mechanical results, heat treatment records, permeability and non-destructive examination. EN 10204 3.2 certificates witnessed by a classification society or a third-party body such as SGS or TUV are available on request, together with dimensional reports.

Where 1.3965 forgings are used

What to include in a 1.3965 enquiry

Jiangyin Jiangnan Metal Co., Ltd. can quote from a sketch, but a complete enquiry is quoted faster and more accurately. For this grade, two of the items below affect the melt rather than the price.

Frequently asked questions about 1.3965

Glossary

Non-magnetizable steel

A steel held to a relative magnetic permeability of 1.01 maximum under SEW 390, normally verified at a field strength of 8000 A/m. Achieved by a stable, fully austenitic structure free of ferrite and martensite.

Relative magnetic permeability

The ratio of magnetic flux density in the material to that in free space under the same field. A value of 1 is a vacuum; a paramagnetic austenitic steel sits just above it; ferromagnetic steels are far higher.

Austenite

The face-centred cubic phase of iron, paramagnetic in this alloy system. Held stable at room temperature by nickel, manganese, carbon and nitrogen.

Deformation martensite

Martensite formed by cold work rather than by cooling. Ferromagnetic, so its appearance raises the permeability of a nominally non-magnetic steel.

Md30

The temperature at which 30% deformation transforms half the volume to martensite. A calculated indicator of austenite stability. A lower value corresponds to greater tolerance of cold work before permeability rises.

Solution annealing

Heating to put carbides and alloying elements back into solid solution, then cooling fast enough that they stay there. For 1.3965, 1000 to 1050 °C followed by rapid cooling.

PREN

Pitting resistance equivalent number, Cr + 3.3Mo + 16N. A screening index for resistance to chloride pitting. For 1.3965 it is about 19 to 22.

Open-die forging

Hot forging between flat or simply shaped dies that do not enclose the workpiece. Used for one-offs, small batches and parts too large for a die press.

EN 10204 3.1

An inspection certificate issued by the manufacturer's own independent inspection department, reporting actual test results for the material delivered.

Data source and reuse

This page is published by Jiangyin Jiangnan Metal Co., Ltd. and reviewed by its metallurgy department. Composition and property limits are compiled from SEW 390 and from published material data for X8CrMnNi18-8. Reuse of the technical data is permitted under CC BY 4.0 with attribution.