Equipment required:

Gas & Oxygen cylinder + pressure regulators; Oxygen 4 bars & Acetylene 0.8 bars

• Nozzle Number 3 : Acetylene/ Oxygen : 600 liters / hour - d 1,75 mm
• Nozzle Number 4 : Acetylene/ Oxygen : 1000 liters / hour - d 2,20 mm
• Nozzle Number 5 : Acetylene/ Oxygen : 2000 liters / hour - d 3,00 mm

Remove rust, dirt, grease, oil, heat scale and other contaminants from the surfaces to be welded.

Previous hardfacing deposits should be removed if:

They are unknown, they are incompatible with the new deposit, they are porous, they are badly cracked and deformed and work-hardened surfaces should be removed by grinding and repaired

A sound base is required and this may necessitate removing fatigued or rolled-over metal, high ridges or other major surface irregularities. This may be done by gouging, grinding or machining. Cracks in the base metal should be arc gouged or ground out and repaired using compatible electrodes. If cracks are through the base metal, make sure the end of the crack is removed by drilling or cutting at the end before gouging out the crack.

If the surface is severely work-hardened, about 1/8" (3 mm) of work hardened surface should be removed before hardfacing or build-up of a worn area. Failure to do so might result in weld bead spalling. Arc gouging removes surface irregularities, work-hardened surfaces and/or cracks.

Base metals may sometimes contain an unknown element (such as sulfur in steel) that affects the overlaying alloy. This condition can be overcome by undercutting the area and then applying a buffering layer with austenitic manganese or low alloy build-up before welding with the hardfacing alloy.

The degree of cleanliness required is greater when gas hardfacing is to be used, and for this process, the job should always be dressed back to clean, shiny base metal

Before starting any hardfacing operation, the welder must consider the thermal mass of the work piece to be hardfaced, its shape, nature and intend use of the tool.

Manganese Steel: Manganese should be preheated to about 200 ºF, but should NEVER exceed 500 ºF. Temperatures above 500 ºF (preheat or interpass) cause manganese carbides to form on austenite grain boundaries, reducing deposit toughness.

Cast Iron: Cast iron requires high preheat temperatures for hardfacing applications. A good rule of thumb is a dull red.

Carbon and Low Alloy Steels: Preheating of some carbon and low alloy steels may be necessary to prevent spalling, underbead cracking and cracking in the base metal.

In oxyacetylene hardfacing, it is recommended to use an excess of acetylene. The outer envelope should be three times the size of the inner cone. A carburizing flame lowers the surface melting temperature and protects the base metal surface from excess oxidation during hardfacing.

This is called a 3X flame, because the feather is three times the inner cone. See photo.

Torch tip sizes from #3 to #6 are used depending on the size of the rod and size of the parts.

Nickel base alloys require a neutral flame.

Produce "sweating surface" (just melting surface) by excess acetylene feather before starting hardfacing.

The torch flame must form an angle of about 45° with the work piece surface, and AgroCrom at a 45° angle to the same surface. The flame must swing from side to side of the coating. The tip of the tube should not be lowered or lifted during the fusion process. The procedure should take into account the required thickness of coating to provide a maximum wear resistance.

Welding position: Horizontal position.

Low hill, 15º, decrease the thickness.

Up hill, 15º, increase the thickness.

Avoid excessive build-up of hardfacing materials, since they may crack or break off rapidly in service. If excessive thickness is required, use the appropriate build-up material first.

Redry the tubular rod at 200ºF (100 ºC) for one hour.

Distortion

Heat from the welding process may cause parts to distort, rendering them ineffective after treatment. Use appropriate clamping and welding methods.

Use skip welding to avoid localized over heating of particular area.

This is the best process to control dilution by the base metal because the Oxy-Acetylene flame is much lower than that of an arc, so melting of the rod and preheating of the base metal is easily controlled.

Austenitic steels should be welded with minimum interpass temperatures and cooling rates are not a factor.

Martensitic steels, the objective is to complete the formation of martensite or some other metallurgical phase. Typically a component should be air cooled to 250ºF from the interpass temperature. This ensures that the desired structure is achieved and avoids any cracking. Because hydrogen is always a potential threat, it is advisable to soak the component at 250ºF for approximately 2 to 3 hours. This allows hydrogen to escape and avoids hydrogen embrittlement.

This term usually encompasses stress relieving and tempering. It is done below the critical temperatures of the overlay and is quite dependent upon the chemistry.

Typically postheating is done anywhere from 900ºF to 1200ºF. Time at temperature varies according to the desired result and is typically carried out at (1 hr/inch of thickness). While a drop in hardness can be expected (only a few points HRc), there are occasions where an actual rise in hardness is noted. This is called secondary hardening and usually takes place at low tempering temperatures. 

Fumes from the normal use of these products contain significant quantities or Chromium, Manganese and Tungsten Carbide compounds which my be harmful.

FLAME SETTINGS:

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