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SUS Stainless Grades for Machined Parts, with Their Equivalents

The JIS stainless grades the network machines, what each one costs you on the machine and what it gives back in service. We are a trading company: we buy the bar and the machining, the engineer on your order checks the grade against your drawing, and the grade on the quote is the grade on the parts.

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JIS, AISI, EN and UNS equivalents

The eleven grades that carry most machined stainless work. Equivalents are close matches, not identical chemistry, so the standard written on the drawing decides what we buy.

SUS stainless grades with AISI, EN and UNS equivalents, family, machinability index and PREN
JISAISI / ASTMENUNSFamilyMachinabilityPREN
SUS3033031.4305X8CrNiS18-9S30300Austenitic7817Sulphide inclusions are pitting initiation sites, so real corrosion performance sits below what PREN suggests.
SUS3043041.4301X5CrNi18-10S30400Austenitic4519
SUS304L304L1.4307X2CrNi18-9S30403Austenitic4519
SUS3163161.4401X5CrNiMo17-12-2S31600Austenitic3625
SUS316L316L1.4404X2CrNiMo17-12-2S31603Austenitic3625
SUS3213211.4541X6CrNiTi18-10S32100Austenitic3619
SUS4104101.4006X12Cr13S41000Martensitic5412
SUS420J24201.4028X30Cr13-Martensitic4513
SUS4304301.4016X6Cr17S43000Ferritic5417
SUS440C440C1.4125X105CrMo17S44004Martensitic4017Much of the chromium is tied up in carbides, so usable corrosion resistance is well below the PREN figure.
SUS630630 / 17-4 PH1.4542X5CrNiCuNb16-4S17400Precipitation hardening4817

Machinability is a typical handbook index for annealed bar, 100 being AISI B1112 free machining steel. PREN is Cr + 3.3Mo + 16N from typical mid-range chemistry (pitting resistance equivalent number). Twenty grades, searchable both ways: JIS stainless grade converter.

What each family does on the machine

The family decides more about cost and sequence than the grade number does. These are the four that appear on JIS drawings for machined parts, as described in thestainless steel classification.

FamilyGradesMagneticHardeningOn the machine
AusteniticSUS303, SUS304, SUS304L, SUS316, SUS316L, SUS321No when annealed. Cold worked areas can turn slightly magnetic.Not by heat treatment. Annealed bar up to about 187 HBW.Work hardens under a dull or dwelling tool, long stringy chips, poor heat conduction. Sharp edges and a feed that never rubs.
FerriticSUS430YesNot by heat treatment. Annealed bar up to about 183 HBW.Closer to carbon steel than to SUS304. Shorter chips, less work hardening, lower corrosion resistance.
MartensiticSUS410, SUS420J2, SUS440CYesBy quench and temper. Typically 40 to 45 HRC for SUS410, around 50 HRC for SUS420J2, around 58 HRC for SUS440C.Machined annealed, then hardened, then the critical features are ground or hard turned. Allow for distortion.
Precipitation hardeningSUS630 (17-4 PH)YesBy ageing at low temperature. JIS G 4303 minimums: 40 HRC in H900, 28 HRC in H1150.Roughed in condition A, aged to the H condition on the drawing, then the tight features finished. Little distortion on ageing.

Hardness values are typical, from JIS G 4303 and handbook data. The hardness your part reaches is stated on the quote and measured on the inspection report.

Choosing a SUS grade from the requirement

Start from what the part has to survive and move up only when the cheaper grade fails it. A grade change on the drawing is a cost change in the quote.

  • General machined parts, indoorsSUS304. The default on most JIS drawings, stocked in every bar size and the cheapest austenitic grade to buy.
  • Turned parts in volume, no weldingSUS303. Roughly twice the cutting speed of SUS304. Not for welded parts, and it pits sooner in chlorides.
  • Chlorides, food, pharma, wet dutySUS316 or SUS316L, passivated. The molybdenum lifts PREN from about 19 to about 25.
  • Welded and not annealed afterwardsSUS304L or SUS316L. The low carbon keeps chromium carbides out of the heat affected zone.
  • Service between 400 and 800 °CSUS321. Titanium stabilised for exhaust, heat exchanger and hot gas parts.
  • Hardness, edges and wearSUS420J2 for blades and mould inserts, SUS440C when the part has to reach around 58 HRC.
  • Strength with corrosion resistanceSUS630 in the H condition the load needs. H1150 is tougher, H900 is harder.
  • Magnetic, lower cost, dry indoor useSUS430 for trim, panels and hardware that never sees chlorides.
  • Hardenable shafts and fastenersSUS410 when SUS304 is too soft and SUS440C is more than the job needs.

Cost side by side: SUS303 vs SUS304 vs SUS316. Hardened grades: SUS440C and SUS420J2.

How the grade is bought on your order

We sell you the finished part, so the material is ours to answer for. An engineer follows every order from the drawing review to the shipment, the weekly progress update says when material is what the date is waiting for, and every order is inspected before packing.

The full sequence: how it works. What ships with the parts:quality. Certificate types:EN 10204 vs JIS mill sheet.

  • The standard behind the gradeBar is bought to JIS G 4303, plate and sheet to JIS G 4304 or G 4305. A drawing that names an AISI or EN grade is quoted against the close JIS equivalent, and the quote says so before you order.
  • The certificate lineWe state the standard the certificate has to name, the shop buys bar to it, and the engineer on your order checks the material before the run. A JIS mill sheet or an EN 10204 3.1 certificate ships with the parts when the drawing asks for one.
  • Condition, not only gradeSUS630 means little without H900, H1025 or H1150. Martensitic grades need a hardness range and a note on which surfaces are finished after heat treatment.
  • No silent substitutionA free cutting grade in place of SUS304, or SUS304 in place of SUS316, is a change to your drawing. It goes back to you in writing before anyone cuts metal.

Material notes that take cost out of a SUS part

  • Pick the grade for the duty, not by habitSUS316L where SUS304 would do adds cycle time and insert wear to every part in the order.
  • Design to standard barA diameter that matches a stocked JIS G 4303 size avoids turning down the next size up and buying the difference.
  • Leave grind stock on hardened featuresOn SUS420J2, SUS440C and SUS410, mark the surfaces finished after hardening and allow stock for them.
  • Call out passivation by nameMachining leaves free iron on the surface. Name the treatment and the standard, for example ASTM A967, so it is quoted as its own line.
  • Respect deep small holesDrilling and tapping deep holes in austenitic grades is where tools break. A shorter thread engagement or a through hole costs less.

Processes, typical tolerances and finishing for each grade: capabilities.

Grade guides

Questions about SUS grades

Is SUS304 the same as AISI 304 and EN 1.4301?

Close, not identical. The three standards overlap on chemistry and properties and the grades are used interchangeably on commercial parts. Where the certificate has to name one standard, write it on the drawing and we buy bar certified to that standard.

Which SUS grade is cheapest to machine?

SUS303, by a wide margin. Its sulphur additions break the chip, so it cuts at roughly twice the speed of SUS304. It is the wrong grade for welded parts and for chloride service, which is why it should be chosen on purpose rather than as a quiet substitute.

Can you supply SUS630 already aged to H900 or H1150?

Yes. The part is roughed in condition A, aged to the condition on your drawing, then finished on the tight features. The H condition and the hardness check are stated on the quote and on the inspection report.

Do you machine stainless grades outside this list?

We take the JIS stainless range on this page. Another SUS grade on your drawing is checked on the quote before we commit to it. Titanium, nickel alloys, aluminium and carbon steel are outside what we take, and we say so rather than quote a material we do not manage well.

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