Introduction

Stainless steel alloys usually have a chromium content of a least 10%. Stainless steel base metals are grouped primarily into three classes depending on their crystal structure; austenitic (such as 302, 304, 308, 316, etc.), martensitic (such as 410, and 416), and ferritic (such as 409, and 430). Austenitic grades are also available with a lowered carbon content (designated with an "L", such as 304L or 316L.)

Below is a basic step by step guide to follow when welding stainless steel.

Safety First

Select Joint Design and Fit Up

Start by determining the best manner in which to join your base metals. Correct joint design and fit up are critical steps to insuring a strong bond upon weld completion. Be sure to consider strength required, welding position, metal thickness and joint accessibility.

The five basic types of joints are butt, corner, edge, lap and tee. These five joints can be arranged in many combinations to create a large variety of welds. Fixtures and jigs are helpful in securing the work pieces in place during the joining procedure. Sheet metal and most fillet and lap joints should be clamped tightly over the entire length of the work.

Choose the Welding Process

The three most common stainless welding processes are:

• SMAW - Shielded Metal Arc Welding or Stick Electrode
  

  SMAW is an electric arc welding process in which heat for welding is generated by an electric arc between a covered metal electrode and the base metal. The electrode coating provides shielding. The welding equipment for this process is currently the most inexpensive of the methods described here. However, electrodes do create some inefficiency, such as stub loss and a slag coating, which must be removed.

• GTAW - Gas Tungsten Arc Welding or Tig Welding
  

  Tig Welding is easily performed on a variety of metals. It generally requires little or no post weld finishing. It is an electric welding process in which heat for welding is generated by an electric arc between the end of a non-consumable tungsten electrode and the base metal. Filler metal may be added, if necessary. An inert shielding gas supplies shielding for the arc. (Inert gas creates a protective atmosphere around the welding in process.)

• FCAW - Flux Cored Arc Welding
  

  Flux is contained within the electrode. It provides shielding, deoxidization and arc stabilization. Additional shielding may be added. A smoke suction nozzle around the gun or fume hood aids in reduction of smoke and fumes. Aufhauser flux cored stainless steel wire is formulated to provide all position welding and smooth, stable arc action.

• GMAW - Gas Metal Arc Welding or Mig Welding
  

  Gas metal arc welding is quick and easy on thin-gauge metal as well as heavy plate. It generally calls for little post weld cleanup. GMAW is an electric arc welding process where heat is produced by an arc between a continuously fed filler metal electrode and the base metal. Shielding is obtained from an externally supplied gas or gas mixture. The two most common types of GMAW are:

• Short Circuit Transfer - The arc is broken or short-circuited with each drop of metal and restarted. It is used on smaller, thinner gauges and produces a shallow weld.
• Spray Transfer - Metal is transferred across the arc creating a continuous spray of fine droplets of metal. These droplets are projected down to the base metal.

Determine Appropriate Inert Shielding Gas

SMAW - none required

GTAW - Argon is suggested for thicknesses up to approximately 1/2". For thicker sections, argon-helium mixtures or pure helium may be used. Pure helium may also be employed for deeper penetration. The most common tungsten utilized is 2% thoriated.

FCAW - 100% CO₂ or Argon/CO₂. The voltage may be somewhat lower if argon with 20 to 25 percent CO₂ mixtures is selected. Generally, a gas flow rate of 40 cfh is suggested. Adjustments can be made, depending upon the specifics of the application.

GMAW - For spray transfer use argon and 1% to 2% oxygen. 99% Argon/1% oxygen is predominantly used. 98% Argon/2% oxygen when welding thinner material. For short circuiting transfer use 90% helium/7.5% argon/2.5% CO₂.

See Shielding Gas Guide for further details

Select the Applicable Filler Metal

Set the Parameters

SMAW - uses a direct current (DC) or an alternating current (AC).

DC uses either straight polarity, which is electrode negative or reverse polarity, which is electrode positive. Direct current flows in one direction continuously through the welding circuit. There are several advantages of DC. It works well at low current settings and with small diameters. In addition, igniting the arc and maintaining a short arc is easier.

Stainless electrodes designated D15, (ex: 308-15) use direct current, reverse polarity. Their key characteristic is fast freezing slag, which make them suitable for out of position welding. Bead appearance is convex.

AC uses a combination of both straight and reverse polarities, which alternate in regular cycles.

The advantages of this current include: less chance of arc blow, which is an unbalance of the magnetic field around the arc causing a bend in the arc. It also works well on thick metal with a large diameter electrode.

Stainless electrodes designated D16 (ex. 308-16) use AC or DC. They produce a smooth weld bead, with a flat to slightly convex bead appearance.

Current Amperage most common settings are:

GTAW - For Gas Tungsten Arc Welding use DC current with straight polarity (electrode negative). The parameters for Tig welding are dependent upon plate thickness and welding position.

FCAW - Flux cored stainless steel welding wire generally uses direct current, reverse polarity (electrode positive). This current type provides better base metal penetration. Flux cored welding requires a longer wire extension or "stick out." Stick out is the distance between the end of the wire and the end of the contact tip. Stick out for stainless steel flux cored wire is typically 5/8" to 3/4".

GMAW - Below are suggested settings for GMAW welding:

Clean the Base Metal

Cleaning should be done just prior to welding to prevent the formation of oxides. The base metal surface must be free of grease, oil, paint, dirt, etc. A clean surface will provide a smoother, stronger joint. Brush the plate surface and edges with a stainless steel wire brush to remove burrs and oxides. Gloves should be worn to prevent hand oil or dirt from getting on the joining surface.

Preheat if Applicable

Preheat is not required for most 300 austenitic grade stainless steels. The base metal should be brought to room temperature, 60 to 75°F. Preheat is necessary when welding ferritic or martensitic grades. It is also needed when joining metals that are thick or contain a high percentage of carbon.

Welding Technique

A good welding technique is developed as a welder gains experience. The following are basic welding tips:

• Use fixtures and/or jigs to help keep work in place.
• Butting edges should be squared. A square butt joint is prevalently used for stainless sheets 18 gauge or thinner. Heavier gauge sheets and plates may require an edge bevel to assure full penetration.
• Insure adequate shielding by centering the filler metal in the gas and weld puddle area.
• Filler metal should be dipped into the weld puddle, but should not drip into it.
• Move the torch/gun along the joint at a steady, constant speed to maintain uniformity.
• Hold the torch/gun over the weld until gas stops, to keep work protected.

Cooling / Post Weld Cleaning

Postheat may be required to relieve internal stresses caused by the concentration of heat in the weld area. Postheating aids in slow down of the cooling process to minimize cracking. This is a good procedure to use when joining thick metals. SMAW and FCAW leaves a slag residue on the weld. Remove slag with a chipping hammer or by grinding.

Troubleshooting

Please consult our Frequently Asked Questions.

Aufhauser Filler Metals

Aufhauser manufactures a complete line of filler metals for stainless steel welding.