Selecting a shielding gas for carbon steel MIG welding is one of the fastest ways to influence arc stability, spatter levels, bead profile, and how forgiving the process is to real-world conditions such as mill scale, oily plate, variable fit-up, and positional welding.
Coregas offers multiple carbon steel MIG shielding gases with different compositions and intended use cases. This article is a practical guide to selecting among the most commonly compared options in the Coregas welding gases range:
If you want a broader overview of welding gas selection principles and how Coregas positions its portfolio, start here: Welding and metal fabrication and then browse the full list here: Welding gases.
What changes when the mix changes (simple, workshop-relevant)
Carbon steel MIG shielding gases in the Coregas range are generally argon-based mixtures with CO₂ and or O₂. Each component is there for a reason.
Argon (Ar)
Argon provides a stable base for the arc and is the primary component in these mixes.
Carbon dioxide (CO₂)
CO₂ is an “active” component in MIG welding on steel. In argon blends, increasing CO₂ generally shifts arc behaviour and can change how tolerant the weld is to surface condition and how the weld bead forms. Coregas positions different CO₂ levels for different steel thicknesses and applications.
Oxygen (O₂)
O₂ is used in small percentages in some mixes and is positioned by Coregas to influence bead profile, wetting, and arc characteristics. Oxygen is present in Coregas 07 and Coregas 5/2.
The correct choice depends on the type of work you actually do, not only what is “generally recommended” online. That is why this guide is structured around thickness, typical jobs, and practical constraints.
The Coregas carbon steel MIG options (what each is, in plain terms)
Below is a fact-based snapshot of each gas as Coregas describes it on the product pages.
1) Coregas 07
Composition: Argon (balance) with oxygen 5–9%
Positioned for: MIG welding steel up to 6 mm, minimal spatter, good profile, and noted as good for galvanised steel
Product page: Coregas 07
How workshops typically use this positioning
Coregas 07 is often shortlisted when appearance and clean running matter, and where thin to moderate thickness work is common.
2) Coregas 09
Composition: Argon 91% + CO₂ 9%
Positioned for: MIG welding steel of all thicknesses, smooth weld appearance, little spatter, and noted as good for robotic welding
Product page: Coregas 09
How workshops typically use this positioning
Coregas 09 is often considered as a “general purpose” argon-CO₂ blend option where consistent appearance and stable running are priorities, including production settings.
3) Coregas 18
Composition: Argon (balance) with CO₂ 16–20%
Positioned for: MIG welding heavy section material and spray transfer, and referenced for FCAW applications (carbon and stainless)
Product page: Coregas 18
How workshops typically use this positioning
Coregas 18 is typically shortlisted when heavier section work is frequent and productivity goals are tied to transfer mode and deposition.
4) Coregas 25
Composition: Argon 75% + CO₂ 25%
Positioned for: MIG welding heavy section material, short arc, and reduced porosity risk where plates are dirty, oily, or have mill scale
Product page: Coregas 25
How workshops typically use this positioning
Coregas 25 is often considered in fabrication and repair environments where surface condition is not always perfect and the workflow needs a gas that is positioned to be more forgiving.
5) Coregas 5/2
Composition: Argon 93% + CO₂ 5% + O₂ 2%
Positioned for: MIG welding steel up to 8 mm, good positional control, and a wider bead profile
Product page: Coregas 5/2
How workshops typically use this positioning
Coregas 5/2 is often shortlisted when positional control and bead profile are key, while staying in a range Coregas positions for up to 8 mm work.
A decision tree you can use in under 2 minutes
Use the questions below in order. Most workshops can narrow their choice to one or two gases quickly.
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Question 1: What thickness do you weld most often?
Mostly up to 6 mm: Start by reviewing Coregas 07, Coregas 09, and Coregas 5/2
Mostly up to 8 mm with positional needs: Shortlist Coregas 5/2
Heavy section is common: Shortlist Coregas 18 and Coregas 25
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Question 2: How clean is the steel in your normal workflow?
Clean, controlled production: Coregas 09 is positioned for smooth appearance, little spatter, and suitability for robotic welding
Variable cleanliness, mill scale, oily plate happens: Coregas 25 is positioned to reduce porosity risk under those conditions
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Question 3: Is galvanised steel a routine part of your work?
If yes, Coregas highlights suitability of Coregas 07 for galvanised steel
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Question 4: Is positional control and bead profile a priority?
If yes, Coregas positions Coregas 5/2 for good positional control and a wider bead profile
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Question 5: Are you optimising for heavy section and transfer mode?
If yes, Coregas positions Coregas 18 for heavy section and spray transfer, and positions Coregas 25 for heavy section and short arc
Comparison table
Scroll
| Gas | Composition (as listed by Coregas) | Positioned for | Quick fit |
|---|---|---|---|
| Coregas 07 | Ar (balance) + O₂ 5–9% | Steel up to 6 mm, minimal spatter, good profile, good for galvanised | Thin panel and sheet, appearance-first jobs |
| Coregas 09 | Ar 91% + CO₂ 9% | Steel all thicknesses, smooth appearance, little spatter, good for robotic | General purpose production, consistent results |
| Coregas 18 | Ar (balance) + CO₂ 16–20% | Heavy section, spray transfer, also FCAW references | Thick steel where productivity and transfer mode matter |
| Coregas 25 | Ar 75% + CO₂ 25% | Heavy section, short arc, reduced porosity risk on dirty plate | Repair and fab where surface condition varies |
| Coregas 5/2 | Ar 93% + CO₂ 5% + O₂ 2% | Steel up to 8 mm, positional control, wider bead profile | Positional welds and profile control in the stated thickness range |
Product links for reference:
Selection guidance by common workshop scenarios
This section is written to match how people actually search and how supervisors actually decide.
Scenario A: Thin sheet, light fabrication, visible welds
Typical priorities: stable arc, minimal spatter, good bead profile, less clean-up.
Where to start (Coregas positioning):
Coregas 07 is positioned for steel up to 6 mm and minimal spatter with good profile
Coregas 09 is positioned for steel of all thicknesses with smooth appearance and little spatter
Practical note: If your thickness range is mostly below 6 mm and you are appearance-driven, shortlist 07 and 09 first. If you also need positional control and regularly approach higher thickness within the stated range, add Coregas 5/2 to the shortlist.
Scenario B: General purpose fabrication across varied thickness
Typical priorities: one gas that covers most jobs, predictable results, fewer gas changes.
Where to start (Coregas positioning):
Coregas 09 is explicitly positioned for steel of all thicknesses and is noted as good for robotic welding, which implies stable and repeatable behaviour in production settings
Practical note: “All thicknesses” does not remove the need for correct parameters, consumable selection, and joint prep. It does, however, make 09 a logical baseline candidate when standardisation matters.
Scenario C: Heavier section work, including higher deposition approaches
Typical priorities: productivity, penetration, transfer mode compatibility, repeatability.
Where to start (Coregas positioning):
Coregas 18 is positioned for heavy section and spray transfer
Coregas 25 is positioned for heavy section and short arc
Practical note: If you are actively optimising around spray transfer procedures, 18 belongs in the shortlist. If your work often sits in short arc procedures and you want a gas positioned to handle less-than-ideal plate condition, 25 belongs in the shortlist.
Scenario D: Plate is not always clean, porosity risk is a recurring issue
Typical priorities: more forgiveness to surface condition, fewer rejects, less rework.
Where to start (Coregas positioning):
Coregas 25 is explicitly positioned to reduce porosity risk where plates are dirty, oily, or have mill scale
Practical note: Gas choice is only one variable in porosity. Leaks, drafts, flow rate, nozzle condition, and contamination can still dominate. Use the troubleshooting section later in this blog to eliminate those common causes.
Scenario E: Galvanised steel is part of your routine
Typical priorities: stable welding approach for galvanised work, practical suitability.
Where to start (Coregas positioning):
Coregas 07 is noted by Coregas as good for galvanised steel
Practical note: Galvanised steel welding also requires appropriate safety controls and fume management. If you need safety resources, start here: Safety and SDS.
Scenario F: Positional welding and bead profile control is a priority
Typical priorities: bead control and positional handling, consistent profile.
Where to start (Coregas positioning):
Coregas 5/2 is positioned for good positional control and a wider bead profile, up to 8 mm steel
Practical note: If you are choosing between 5/2 and another option, test on your most common positional joint and assess bead wetting and tie-in using the same consumables, parameters, and operator.
Transfer mode and procedure notes (keep it aligned to your WPS)
Coregas references transfer mode explicitly on some product pages. For example:
Coregas 18 is positioned for spray transfer
Coregas 25 is positioned for short arc
In practical terms, gas selection should be consistent with:
your WPS requirements
the wire classification and diameter
the joint design and fit-up
the welding position
your accepted heat input and distortion constraints
If your workshop is formalising procedures or needs help aligning gas choice with production outcomes, the best starting point is to speak with Coregas:
Troubleshooting guide: before you blame the gas
Many gas-related issues are actually equipment and setup issues. Use this checklist to rule out common faults.
1) Porosity
Check these first:
Leaks at connections, damaged hoses, loose clamps
Drafts and airflow (fans, open roller doors, extraction pulling shielding away)
Flow rate set too low or too high (excessive flow can create turbulence)
Nozzle spatter build-up and poor gas coverage
Contaminated wire and base material
Gas selection note (Coregas positioning):
If surface condition cannot be controlled and you want a gas positioned to reduce porosity risk on dirty or oily plate, review Coregas 25
2) Excess spatter
Check these first:
Voltage and wire feed speed balance
Stick-out, torch angle, travel speed consistency
Contact tip condition and correct size
Ground clamp connection and electrical path
Gas selection note (Coregas positioning):
For steel up to 6 mm and minimal spatter positioning, review Coregas 07
For smooth appearance and little spatter positioning across thicknesses, review Coregas 09
3) Lack of fusion and inconsistent tie-in
Check these first:
Joint prep and fit-up
Heat input adequacy for thickness
Travel speed
Technique consistency, especially in positional work
Matching procedure to intended transfer mode (short arc vs spray)
Gas selection note (Coregas positioning):
If your procedure is intended for short arc and surface condition is variable, review Coregas 25
If heavy section and spray transfer is relevant to your WPS, review Coregas 18
Standardising gas across a workshop (how to choose one primary and one secondary)
Many workshops aim to minimise gas changes. A practical approach is:
Step 1: Pick one “primary” gas for 70 to 90% of carbon steel MIG work
For many environments, Coregas 09 is the simplest starting point because it is positioned for steel of all thicknesses, smooth appearance, little spatter, and production suitability.
Step 2: Pick one “secondary” gas for your most common constraint
Choose the constraint that causes the most downtime or rejects:
Dirty plate and porosity risk: Coregas 25
Thin sheet and appearance-first welding: Coregas 07
Positional control and bead profile: Coregas 5/2
Heavy section with spray transfer focus: Coregas 18
Step 3: Validate the selection with a short in-house trial
Run a controlled test on:
your top 3 joint types
your typical thickness range
your most common weld position
your normal operators
Track outcomes that matter to you:
rework count
cleaning time
reject rate
consistency across shifts
If you want help setting up a practical trial plan, contact Coregas:
Need a fast recommendation based on your actual jobs?
If you share four details, you can usually shortlist the right gas quickly:
your material (carbon steel)
your typical thickness range
your welding position and transfer mode requirements
your main constraint (appearance, speed, dirty plate, porosity, positional)
Get support and supply options here:
FAQ
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1) What is the main difference between Coregas 07 and Coregas 09 for carbon steel MIG?
Coregas 07 is an argon and oxygen blend (oxygen 5–9%) positioned for MIG welding steel up to 6 mm with minimal spatter and good profile, including galvanised steel. Coregas 09 is an argon and CO₂ blend (argon 91%, CO₂ 9%) positioned for steel of all thicknesses with smooth appearance and little spatter, and is noted as good for robotic welding.
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2) Which gas is positioned for heavy section steel MIG welding?
Coregas positions Coregas 18 for MIG welding heavy section material and spray transfer, and positions Coregas 25 for MIG welding heavy section material with short arc procedures.
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3) Which gas is positioned to reduce porosity risk on dirty or oily plate?
Coregas positions Coregas 25 to provide less risk of porosity where plates are dirty, oily, or have mill scale.
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4) What is Coregas 5/2 used for in carbon steel MIG welding?
Coregas 5/2 is an argon, CO₂ and oxygen blend (argon 93%, CO₂ 5%, oxygen 2%) positioned for MIG welding steel up to 8 mm, with good positional control and a wider bead profile.
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5) Which gas is positioned as good for galvanised steel MIG welding?
Coregas notes Coregas 07 as good for galvanised steel, and positions it for MIG welding steel up to 6 mm with minimal spatter and good profile.
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6) Where can I browse all Coregas welding gases and get supply support in NZ?
Start at the welding gases range page, then use the Store Finder or Contact page for local availability and technical support.