1.2379 Tool Steel Forgings: Bars, Rings, Discs, Blocks and Sleeves

What 1.2379 steel is

1.2379 is a ledeburitic cold work tool steel listed in EN ISO 4957 as X153CrMoV12. Its 1.5 % carbon and 12 % chromium form a dense network of chromium carbides that stands up to abrasive wear. Molybdenum and vanadium refine those carbides and let heavier sections harden right through.

It hardens in still air. Sections therefore move very little, and a tool room can machine close to size in the annealed condition, harden, then clean up by grinding or EDM. On a 300 mm block the movement is normally a few tenths of a millimetre. Plenty of tool rooms specify the grade for that alone, even where a cheaper steel would carry the wear.

Twelve percent chromium does not make the steel stainless. Almost all of it is tied up in carbides instead of dissolved in the matrix, so 1.2379 rusts like any other tool steel. Oil it in storage. It also softens once the working face runs above about 200 °C, so it stays in cold work.

Forged bar is not the same thing as rolled bar here. Open-die forging at a controlled reduction ratio breaks up the coarse as-cast carbide network and spreads the carbides more evenly across the section. On heavy blocks and large diameters it is what keeps corners from cracking in service.

Equivalent grades and standards

Every country has its own name for this steel. The grades below are treated as equivalents in the trade, but the ranges allowed for vanadium, molybdenum and residuals are not identical, so they are not interchangeable on paper.

Where a drawing names one specific standard, confirm the required element ranges at enquiry stage so the correct melt is selected.

Chemical composition of 1.2379

Typical analysis in weight percent for forged 1.2379 supplied from Jiangyin.

Carbon and chromium do the wear work. Molybdenum adds hardening depth and the secondary hardness peak. Vanadium refines grain and forms its own hard carbides. Every heat ships with its own ladle analysis on the certificate.

Heat treatment and forging data for 1.2379

Forging 1.2379

Heat slowly and evenly to 1050 °C and soak until the section is through-heated. Forge with light, frequent blows. Stop before the piece falls below about 900 °C and return it to the furnace rather than working it cold, since the carbide network makes this grade crack easily. Cool the finished forging in the furnace or in dry ash, then anneal it without delay.

Soft annealing and stress relieving

Anneal at 820-860 °C, hold, then cool in the furnace at 10 to 20 °C per hour down to about 600 °C before letting the piece cool in air. That gives a machinable structure at 255 HB or below. Stress relieve at 600-700 °C after rough machining and cool slowly, so machining stresses do not pull the tool out of shape when it is hardened.

Hardening and quenching

Pre-heat in two steps, usually around 600-650 °C and 850 °C, then austenitise at 960-1030 °C. A lower austenitising temperature favours toughness. A higher one gives more secondary hardness after high temperature tempering. Quench in still or moving air, in a hot bath at 500-550 °C, in oil, or under gas pressure in a vacuum furnace. Start tempering as soon as the tool has cooled to 50-70 °C.

Tempering

Temper at least twice. Hold one hour per 25 mm of section as a minimum and cool to room temperature between cycles. Below 250 °C the tool keeps maximum hardness, which suits blanking work. Around 500 °C the steel passes through its secondary hardening peak, and that is the range to use when the tool will be nitrided or PVD coated afterwards.

Hardness and tempering curve

Hardness of 1.2379 after hardening and two tempering cycles. Hardness settles near 58 HRC through the middle of the range, climbs again around 500 °C at the secondary hardening peak, then falls away sharply above 550 °C. Bar colours match the oxide colours the steel shows at each tempering temperature.

Typical physical properties

Physical values are typical for the grade and are given for design guidance. Properties that must be guaranteed should be written into the purchase specification and verified on the mill certificate.

Forged 1.2379 forms and sizes

We forge every piece to the customer drawing with machining allowance and anneal it before it leaves the works. One-off tooling blocks and repeat production are both fine.

Delivery conditions: black forged, soft annealed, rough turned or milled with allowance, or finish machined. Hardening, tempering and nitriding to a stated hardness can be arranged before shipment.

Applications of 1.2379 tool steel

1.2379 turns up wherever a cold forming tool has to take abrasive wear and still hold its size through hardening.

Cutting and blanking tools

Blanking dies, trim dies, cutting dies, plate cutting dies, fine blanking tools, slitting cutters, rotary cutting dies, shear blades and knives, food processing knives, lamination dies, tire shredders and scrap chopper blades.

Forming and drawing tools

Forming dies, deep drawing tools, drawing dies, bending and flanging tools, coining dies, cold extrusion dies, cold heading tools, thread rolling dies and jaws, knurling tools, seaming rolls and tube section forming rolls.

Rolls, rollers and mill tooling

Cold and semi hot rolling rolls, rolls for screw rolling, threading rolls, straightening rolls, forming rolls and rollers, cold mill rolls, and punching knives for nail making machinery.

Wear parts and tooling components

Wear plates and wear parts, sliding guides, guide rails, jaw holders, mould plates and inserts, die chasers, burnishing tools, gauges, injection screw and tip components, dies for injection of thermosets, sandblast nozzles and grinding wheel tooling.

1.2379 against other tool steels

Choosing a cold work grade is mostly a question of how much toughness you are willing to give up for wear resistance. The table below shows where 1.2379 sits against the grades it usually competes with.

Related grades forged in the same works: AISI 4140, 42CrMo4, AISI 4340, 34CrNiMo6 and 18CrNiMo7-6.

Forging process, testing and certificates

We start from electric furnace steel and work it on open-die hydraulic presses, at a reduction ratio high enough to break the as-cast carbide network down through the full section. Pieces are annealed and inspected before they ship.

• Chemical analysis by spectrometer, ladle analysis as standard and product analysis on request.
• Hardness, Brinell in the annealed condition and Rockwell C on anything supplied heat treated.
• Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, acceptance class agreed at order.
• Dimensional inspection against the customer drawing, with allowance confirmed.
• Certification, mill test certificate to EN 10204 3.1. Third party inspection by SGS, BV or TUV can be arranged.

Marking, packing and heat number traceability follow the customer requirement. Export packing on steel pallets or in wooden cases is standard for sea freight.

Supplier and how to order

Technical data on this page is published by Jiangyin Jiangnan Metal Co., Ltd. Last reviewed 5 September 2026. Values are typical for the grade. Guaranteed properties are those stated on the mill certificate supplied with the order. A Markdown version of this page is available.