AgroCrom / AgroTung
OXI-ACETYLENE APPLICATION GUIDE

The self-shielded alloy has a melting point of approximately 1050 °C, making it suitable for application with an oxy-acetylene torch.

Required Equipment

• Acetylene and Oxygen cylinders with pressure regulators
  • Oxygen: 4 bar
  • Acetylene: 0.8 bar
• Torch tips (approximate consumption / diameter):
  • Tip No. 3: 600 L/h – Ø 1.75 mm
  • Tip No. 4: 1000 L/h – Ø 2.20 mm
  • Tip No. 5: 2000 L/h – Ø 3.00 mm

1. Surface Preparation

• Remove rust, dirt, grease, oil, and other contaminants from the surface to be welded.
• Remove any previous hardfacing if:
  • The materials are unknown or incompatible
  • There is porosity, cracking, deformation, or work hardening due to impact
• Removal should be done by grinding. Repair the part if necessary.
• A good base is essential—remove fatigued material, protrusions, or surface irregularities.
• Cracks in the base metal must be ground out to reach solid material; drill the ends of the crack and fill with a compatible electrode.
• If the surface has been subjected to impact, remove ~3 mm before rebuilding and hardfacing.
• Poor base metal preparation can lead to weld detachment.

If the base metal is unknown or contains harmful elements (e.g., high sulfur):
Clean the surface and apply a buttering/intermediate layer using a basic low-alloy electrode (e.g., AWS E-7018) before hardfacing.
Preparation is even more critical when using a torch.

2. Preheating the Surface

Before hardfacing, the welder should assess the part’s size, shape, properties, and usage.

Recommendations:

• Manganese steels: Preheat to 100 °C but never exceed 260 °C.
  Higher temperatures (preheat or interpass) may cause manganese carbides to form along austenitic grain boundaries, reducing hardness.
• Cast iron: Requires high preheat temperatures.
  A practical method is heating the part until it reaches a dull red glow.
• Carbon and low-alloy steels:
  Preheating may be necessary to prevent cracking in the base metal or under the bead.

3. Hardfacing Procedure

• Use excess acetylene for torch hardfacing. The outer flame should be three times the length of the inner cone.
• A carburizing flame reduces surface melting temperature and protects the base metal from oxidation.
  This is known as the “3X flame” (outer feather = 3× cone size).
• Use torch tips from No. 3 to No. 6 depending on rod diameter and part size.
  Nickel-based alloys require a neutral flame.
• Heat the surface until it “sweats” (intense red glow), indicating fusion is starting.
  The flame should strike the part at a 45° angle, and the rod should approach from the opposite side, also at 45°.
• Keep the flame oscillating side to side.
  Do not remove the rod tip during fusion.
  Adjust according to desired coating thickness for maximum wear resistance.

Welding Position & Bead Direction:

• Horizontal position
• Downward direction at 15° = thinner deposit
• Upward direction at 15° = thicker deposit

Deposit Thickness:

Avoid excessive deposit thickness—it may crack or detach in service.
If high thickness is required, use proper rebuilding material first to reach the needed dimensions.

Rod preheating:
Preheat rods for at least one hour at 100 °C to eliminate moisture and avoid porosity.

Deformation:
Heat may deform parts.
Use proper clamping and alternate bead placement to avoid overheating specific areas.

4. Cooling / Postheating

This method offers excellent dilution control due to the lower flame temperature compared to arc welding, allowing precise fusion and base metal preheat.

Cooling Procedures:

• Austenitic steels: Minimal interpass temperature needed; cooling is not critical.
• Martensitic steels: The goal is full martensite formation.
  • Cool the part in air to ~120 °C from welding temperature.
  • Maintain the part at 120 °C for 2–3 hours to allow hydrogen to escape and avoid embrittlement.

Postheating

Postheating generally refers to stress relief and tempering.
Performed below critical temperature of the filler material.

• Typical postheat: 450–650 °C
• Time: Approx. 1 hour per 2 cm of part thickness
• May cause slight hardness drop (1–3 HRC), or in some cases increase it due to secondary hardening, often seen during low-temperature tempering.

IMPORTANT SAFETY NOTICE

Fumes from normal use of these products may contain chromium, manganese, and tungsten carbides, which can be hazardous.

FLAME SETTINGS

• Short flame, oxygen excess → ❌ Not recommended
• Very long flame, oxygen deficiency → ❌ Not recommended
• Short flame, acetylene excess → ✅ Recommended, prevents oxidation