Tool steel is expensive, hard to weld, and highly sensitive to cracking. When a punch, die, or forming tool cracks, throwing it away is often not an option - the lead time for a replacement can cost more than the machine downtime. This is where ER312 welding wire proves its value.
Why Tool Steel Is Hard to Weld
- High carbon and alloy content (C often > 0.5 %)
- Hardenable martensitic microstructure
- Very sensitive to hydrogen and thermal shock
- High residual stress, high restraint
How ER312 Solves the Problem
The 29/9 high-ferrite deposit buffers the tool steel from cracking in three ways:
- Absorbs carbon dilution without embrittling
- Ferrite matrix relieves thermal stress during cooling
- Ductile deposit accommodates residual stress in the HAZ
Typical Tool Steel Repair Procedure
- Grind out the crack to sound metal, U-groove preferred
- Preheat 200–350 °C depending on tool steel grade
- Butter 2–3 layers of ER312 with short stringer beads, peening each bead
- Cap the joint with either more ER312 or, for critical wear surfaces, a matching hardfacing wire
- Slow cool under insulation to room temperature
- Post-weld temper at the tool steel's tempering temperature to restore hardness in the HAZ
Applications
- Cracked forging dies
- Broken punch and die inserts
- Damaged plastic injection molds (in tool steel construction)
- Worn stamping dies (buildup + hardfacing)
- Cracked shear blades and cutting tools
Cost Justification
A typical tool steel repair with ER312 costs a fraction of a new die, and a properly executed repair often runs 60–80 % of original service life. For high-value tooling, this economics is decisive.
Dayang Welding supplies AWS A5.9 ER312 in TIG cut lengths and MIG spools to tool rooms, die shops, and mold repair specialists worldwide.
