What H12 Tool Steel Is
H12 is a chromium-molybdenum-tungsten hot-work tool steel, designated 1.2606 in the European numerical system and X35CrWMoV5 in EN ISO 4957. It is designed for tools that operate at high surface temperatures, such as extrusion dies, forging dies and hot-forming tooling, where resistance to softening, thermal fatigue and wear is essential.
Chemical Composition
The composition balances hardenability, toughness and hot hardness:
Carbon: 0.32-0.40 percent
Chromium: about 4.5-5.5 percent, providing hardenability and oxidation resistance
Molybdenum: about 1.2-1.6 percent, adding hot hardness and tempering resistance
Tungsten: about 1.0-1.6 percent, improving hot strength
Vanadium: about 0.25-0.50 percent, refining grain size and adding wear resistance
Properties After Heat Treatment
In the annealed condition, H12 round bars are supplied at a hardness of about 229 HB maximum for machining. After hardening and double or triple tempering, working hardness is typically 44-52 HRC depending on the application, with the exact tempering temperature chosen to achieve the required strength-toughness balance for the die.
Forging and Machining Practice
H12 forges well in the range of 1050-1150 degrees C and should be cooled slowly after forging to avoid cracking, then annealed before machining. The steel machines reasonably in the annealed state and is usually finish-ground or EDM-cut after hardening, since the high hardness after heat treatment makes conventional machining difficult.
Comparison with Other Tool Steels
H13 (1.2344): similar hot-work family with vanadium but no tungsten; the most common general-purpose hot-work grade
D2 (1.2379): a high-carbon, high-chromium cold-work grade for cutting and blanking tools
P20 (1.2311): a plastic mould steel with lower hardness for injection moulds
S7 (1.2355): a shock-resistant grade for chisels and impact tools
Applications
Hot extrusion dies for aluminium and copper
Hot forging dies and inserts
Die casting dies for aluminium and magnesium alloys
Hot shears, punches and hot-forming tooling
Frequently Asked Questions
Q: What does X35CrWMoV5 mean?
It is the EN designation of H12: X for alloy tool steel, 35 for the carbon content in hundredths of a percent, and Cr, W, Mo, V for the main alloying elements.
Q: What hardness can H12 achieve?
After hardening and tempering, H12 is typically used at 44-52 HRC, with the tempering temperature selected for the specific tool application.
Q: How does H12 differ from H13?
H12 contains tungsten in addition to chromium and molybdenum, which improves hot hardness slightly, while H13 relies on vanadium and is more common in general hot-work use.
Q: What sizes are available as forged round bars?
Forged H12 round bars are commonly supplied from 20 mm to 500 mm diameter, with larger sizes available by arrangement.
Q: What certificates are supplied?
Bars are delivered with mill certificates stating heat number, chemical composition and hardness in the delivery condition.