1.2083 X40Cr14 420 SUS420J2 Stainless Mold Steel

Product Overview

1.2083 steel is a 13 percent chromium martensitic stainless steel for molds that run corrosive resin or need a cavity that will not stain between shifts. EN ISO 4957 writes it X40Cr14 with Werkstoff number 1.2083. The mould trade calls it S136 or Stavax, American mills 420 modified, Japan SUS420J2, China 4Cr13. Qilu Steel supplies forged bar and block Φ100-Φ1200 mm, hot rolled bar Φ16-Φ310 mm and cold drawn bar Φ3-Φ80 mm, annealed at 229 HB max or pre-hardened at 28-34 HRC.

This steel delivers consistent mirror polishing capability after proper heat treatment, making it popular for optical and cosmetic mould surfaces. Its chromium-rich microstructure provides resistance against acidic decomposition products released from PVC, acetate and recycled plastics, which prevents mould rust and extends service cycles compared to conventional non-stainless mould steel grades.

Steel Equivalents Standard

Product Features

Chemical Composition

Mechanical Properties

Annealed Condition (Room Temperature)

Mechanical properties for SUS420J2 from JIS G4303.

Quenched and Tempered

Read 12.5 mm below the surface. L is longitudinal, Tr transverse, both from forged bar.

Chromium carbides string out along the forging direction, so a transverse test on a 400 mm block runs 8-10 percent under the longitudinal value. Impact energy stays low above 45 HRC. The grade is notch sensitive and will not absorb overload through elongation.

Surface Hardness & Hardenability

Air hardening covers sections below about 80 mm. Above 150 mm the block needs oil or polymer with agitation, and above 400 mm even a fast quench leaves the core 3-5 HRC under the surface reading. Thirteen percent chromium slows transformation, so a large block quenched hard is halfway to a crack.

Forging Process

Heat to 1,120-1,150 °C, soak until the section is through, finish above 900 °C. Below 900 °C the steel is hot short and surface tearing opens along the bar. Above 1,180 °C delta ferrite forms and no later heat treatment removes it. Ferrite shows up months later as banding on a polished cavity.

Blocks for mirror polishing are upset and drawn at 4:1 or better, with the ingot axis parallel to the polishing direction. The block goes from the press into a furnace at 600 °C. Air cooling a 300 mm section produces martensite before the anneal and cracks the corners. UT follows EN 10228-3, class 3 for general molds, class 4 for optical work.

Heat Treatment

Avoid tempering between 400 and 500 °C. Chromium carbide precipitates at grain boundaries there, toughness and corrosion resistance fall together, and the hardness gained over a 550 °C temper is two or three points.

Supply Size & Tolerance & Stock Availability

Product Sizes

Surface Finish & Tolerance

Stock sits mainly in annealed forged bar Φ100-Φ600 mm and pre-hardened block 60-300 mm. Diameters move week to week, so confirm size, condition and hardness on the order date.

Applications

PVC, CPVC and flame-retardant tooling

Pipe fittings, drainage sockets, window profile dies, valve bodies, switch housings, connector bodies. Hydrogen chloride and halogenated additives attack unalloyed mold steel at melt temperature, and a 13 percent chromium cavity resists them at 48-50 HRC.

Optical and light guide molds

Lens elements, LED light guides, diffuser plates. These need the ESR route and a polish to Ra 0.02-0.05 μm with no inclusion pulled from the surface.

Medical and pharmaceutical tooling

Syringe barrels, IV connectors, inhaler bodies, blister tools. Cavity cleanliness matters as much as corrosion resistance.

Food contact packaging

PET preform molds, closures, thin wall containers, dairy caps. The cavity runs cool and wet, where a low-carbon 420 heat starts to spot.

Wear parts outside molding

Valve trim, pump shafts, gauge blocks, surgical scissor blanks, knife blades. Here the grade replaces 410 where 45 HRC was not enough.

Remark: The common misuse is buying 420 stock at 0.30 percent carbon for a cavity designed around 52 HRC, then finding the tool stops at 47 HRC. The second is running rigid PVC at 210 °C in 1.2083 when 1.2316 was the right call.

FAQ

Q1: Is 1.2083 the same as AISI 420?

A1: Only at the top of the 420 carbon range. AISI 420 covers roughly 0.20 to 0.40 percent carbon and most stock sits near 0.30. 1.2083 needs 0.36-0.42, which is what makes 52 HRC reachable.

Q2: Can 1.2083 be hardened to 58 HRC?

A2: No. At 0.40 percent carbon the as-quenched ceiling is 54-56 HRC on a 25 mm section. For 58 HRC with corrosion resistance the grade is 1.4125 (440C), and the price is polishability and toughness.

Q3: Why did my 1.2083 block crack during hardening?

A3: Three causes: no 500 °C and 800 °C preheat on a thick block, sharp internal corners, a single temper. Martensite forms at low temperature here and the volume change is large. Preheat in two steps, round corners to 3 mm, temper twice at 180-200 °C.

Q4: 1.2083 or 1.2316 for a PVC mold?

A4: 1.2316 carries about 16 percent chromium and 1 percent molybdenum, the safer choice for rigid PVC at high melt temperature. 1.2083 wins when the cavity needs 50 HRC or better with a mirror polish. For medical PVC with aggressive stabilisers, take 1.2316.

Q5: Does 1.2083 rust, and when do I need ESR?

A5: It resists staining, it is not a seawater stainless. At 50 HRC the matrix holds roughly 7 percent chromium once carbide formation is counted, so tap water left on a polished cavity overnight can mark it. Sulfide inclusions are pitting sites, which is the argument for ESR on food, medical and optical work. For a large non-cosmetic block the EAF plus VD route is adequate and cheaper.

Contact us for a quotation, the current stock list, a sample cut or a custom block size. Send the drawing with hardness range, UT class and certificate type, and we will confirm the forging route before quoting.