How the steel grades actually differ

Carbon buys hardness. Chromium and nickel buy corrosion resistance.

The differences in composition come down to one trade-off, and you can check both halves of it against a published standard without asking any supplier for anything.

Carbon is what a steel can be hardened to hold. AISI 410 is 0.08 to 0.15 per cent carbon: the lowest of the three instrument grades, so the toughest and the least hard. AISI 420 is 0.15 per cent minimum, so it hardens further and holds a ground edge or a jaw through repeated use and resharpening. AISI 440C is 0.95 to 1.20 per cent, the highest of the three. If the instrument has to keep its bite through many resharpenings, carbon is the number you are actually buying.

Chromium is what the steel resists corrosion with. 410 is 11.5 to 13.5 per cent, 420 is 12.0 to 14.0 per cent, 440C is 16.0 to 18.0 per cent. There is a second-order effect the composition figures do not show: a higher chromium figure does not automatically mean better corrosion performance in a hardened instrument steel. In a hardened part, some of that chromium is locked up as carbide and is no longer free to protect the surface. So corrosion behavior in 440C depends on the heat treatment and the passivation as much as on the chromium percentage printed in the standard.

These figures are the published composition limits for the grade: ASTM A276/A276M carries the instrument rows (410, 420 and 440C, which has no row in A240) and ASTM A240/A240M the hollowware rows (202 and 304), read from the 2016a and 2020a editions and named as such on the steel tiers page. ASTM F899 is the specification written for surgical instrument steels; it covers the instrument grades, reads 410 at 0.09 to 0.15 per cent carbon and splits 420 into 420A, 420B and 420C.

Nickel: not specified is not the same as nickel-free

The nickel row for 410, 420 and 440C reads not specified, and the wording is deliberate. ASTM A276 sets no nickel requirement for these grades: it prints an ellipsis in that column rather than a figure. ASTM A240 permits up to 0.75 per cent nickel as a residual in 410 and 420.

So none would be the wrong word. None reads as a guarantee, and no mill certificate for these grades could support it. If nickel content matters for your market or your end user, that is a question to put in writing on the order and to check on the mill certificate for your batch, not something to infer from a grade name.

Why no hardness number appears anywhere on this site

Hardness is what lets a ground edge or a jaw keep its bite through repeated use and resharpening. Published HRC ranges for these grades exist and are easy to find.

No hardness figure is published here, and the absence is on purpose. A hardness figure describes a heat treatment, not a grade. The same 440C bar can leave two different factories at two different hardnesses depending on how it was treated. Publishing a general range for the grade would let a buyer hold a manufacturer to a number that manufacturer never stated. A grade number alone never answers the hardness question.

Hardness is measured by a published method, ISO 6508 for the Rockwell test that produces the HRC figure, ISO 6507 for the Vickers equivalent. If a hardness range is a requirement for you, ask any manufacturer to state the figure and to name the method it was measured by, and get both in writing. No hardness figure is published on this site, for the reason above.

440 and 420 are families of grades, not single grades

AISI 440 is not one steel. 440A is 0.60 to 0.75 per cent carbon, 440B is 0.75 to 0.95, and 440C is 0.95 to 1.20. There is no unsuffixed 440 row in ASTM A276, SAE J405 or ASTM F899. So a quotation that says only 440 has left out the letter that decides how hard the instrument can be made. On this site the grade is named as 440C, and the carbon range published is 440C's range.

AISI 420 carries a smaller version of the same ambiguity. ASTM A240 and A276 do have a plain 420 row, at 0.15 per cent carbon minimum with no ceiling stated, so a bare 420 is a real and defensible grade name. But ASTM F899, the standard written specifically for surgical instrument steels, splits it further into 420A, 420B and 420C by carbon range. If your market or your registration file needs that level of precision, ask which sub-grade the mill certificate names. If it names plain 420, that is a complete answer as well: A240 and A276 both carry that row.

The hollowware grades are not a fifth and sixth rung

Trays, bowls, kidney dishes, sterilization boxes and containers are made in two other grades: AISI 202 and AISI 304. Meeting them after 410, 420 and 440C invites a wrong reading, so it is worth stating flatly: they are different steel for a different job. The instrument grades are chosen to hold a cutting edge; 202 and 304 are chosen for form and corrosion resistance in a drawn or spun container.

The instrument grades are hardened by heat treatment, because an edge has to stay sharp. The hollowware grades are formed, not hardened: they press and draw into deep shapes without cracking and stand up to repeated washing and autoclaving. Neither 202 nor 304 is hardened by heat treatment, so neither is harder than the instrument grades. An edge is not what a tray needs.

AISI 304 is the 18/8 grade: 18.0 to 20.0 per cent chromium, 8.0 to 11.0 per cent nickel, 0.08 per cent carbon maximum. AISI 202 is 17.0 to 19.0 per cent chromium with 4.0 to 6.0 per cent nickel and 7.5 to 10.0 per cent manganese: it replaces about half of 304's nickel with manganese. 202 draws and presses well and has a higher yield strength than 304, but it resists corrosion less well: in damp, salty or chemical conditions it can stain or pit sooner. Which of the two an article ships in follows the line you order, and it is confirmed on the order. Hollowware starts at Clinical; there is no Economy line in these two grades.

What each check proves, and what it does not

A grade claim is one of the few things a buyer can check against a published document rather than against a supplier's word, because composition limits are fixed by the standard and not by any manufacturer. The relevant published specifications are ASTM F899 for wrought stainless steels for surgical instruments and ASTM A240 for the sheet and plate grades used in hollowware and sterilization containers.

A mill certificate is the steel mill's own document. It identifies the mill and states the grade of that batch. That is real evidence, and it is also a limit worth naming: it is a document about raw material, not an independent laboratory test of the finished instrument in your parcel. If you need the certificate for your batch, ask for it on the order, and ask whether the batch can be traced to what ships to you. What this manufacturer states about its own incoming steel check is published on the steel page, in its own words, including the sentence that says what that check is not.

The other checks each answer a narrow question. The boil test (instruments held in boiling water, then examined for rust, staining or pitting) shows whether the protective surface layer holds, and it is where a fault in the steel, the grinding or the passivation shows up first; the published methods are ASTM F1089 and ISO 13402. Passivation matters because grinding exposes fresh iron at the surface; an acid bath takes that iron off so the chromium oxide film can re-form, and the check is an immersion in copper sulphate or boiling water that makes any free iron visible. ASTM A967 covers that. Dimensional and visual inspection has no single international method, because the reference is the drawing for that article and the agreed specification for the order, not a general standard.

One boundary is important enough to state on its own. Naming a published method is not the same as being certified to it, for any manufacturer. Tahir Group of Industries does not claim certification, accreditation or third-party testing to any standard named in this article: the ISO and ASTM numbers here are listed so each test can be looked up and understood, and they are references rather than certifications. Certificates are worth more when the number, the issuer and the dates are published as text, with a link to the issuer's own registry wherever the issuer runs one, and a plain statement where none exists. That is how they are set out on the certification page.

What this page does not settle

Three things here are left as questions on purpose, and each is answered by a document rather than by a web page.

No hardness figure appears for any grade or any line, because a published HRC range describes a heat treatment and not a grade. Which ASTM F899 sub-grade of 420 a mill certificate names is not answered here either: ask for the certificate and read it. And not specified in the nickel column is not the same as none: if a nickel limit matters in your market, it goes in writing on the order and is checked against the mill certificate for the batch.

None of the three closes by reading harder. Each closes on the paperwork for a specific order.

Which line suits which buyer?

TGI makes every instrument pattern on four locked lines, and the buyer chooses the line:

Line: Economy; Steel: AISI 410; Finish: satin, passivated; Inspection: sample: visual + dimensional; Typical buyer: training institutes, veterinary, volume / UN-NGO tenders.

Line: Clinical; Steel: AISI 420; Finish: satin, passivated; Inspection: sample + boil test; Typical buyer: hospitals, distributors.

Line: Premium; Steel: AISI 420-440C; Finish: fine polish, passivated; Inspection: tighter sample + hardness test; Typical buyer: quality-focused distributors, private label.

Line: Executive; Steel: AISI 440C; Finish: mirror polish, passivated; Inspection: 100% inspection + laser mark; Typical buyer: OEM flagship / top private label.

The tier is not a grade of care: every instrument is made on the same line, by the same people. What changes is the steel, the finish, and how much of the batch is inspected.

How do I check a supplier's grade claim?

Ask for the grade by AISI number, not "surgical steel" or "German steel".

Ask for the mill certificate: every batch of steel TGI buys arrives with the mill's own certificate, which identifies the mill and states the grade.

Ask where the steel comes from. TGI publishes it per line: Pakistani or Taiwanese for Economy, Pakistani or German for Clinical, German or Japanese for Premium and Executive.

Ask for samples in the grade you will order, and test them yourself.

No hardness figure is published on TGI's site, deliberately: a published HRC range describes a heat treatment, and TGI states no figure for its own.