How Plasma Cutting Affects HAZ and Other Metallurgical Properties on Stainless Steel

Plasma cutting stainless steel has evolved rapidly over the past few decades. In fact, it’s evolved so drastically that underwater cutting is almost obsolete. Now, many manufacturers are looking to dry plasma cutting, as it offers a range of benefits. However, others are concerned about the potential issues associated with the heat-affected zone (HAZ) created by the plasma process.

Some manufacturers posit that the slower cooling rate may result in an expanded HAZ and a cut edge with inferior metallurgical properties. So, what is the answer? In short, dry plasma cutting stainless steel doesn’t affect the hardness of the edge within the HAZ, but there are some considerations you should keep in mind. Let’s dive in.

What is the Heat-Affected Zone?

When a part undergoes a plasma cutting operation, the area between the melted part and unaffected base metal sees chemical and structural modifications. This is what is referred to as the heat-affected zone (HAZ). This section will be larger or smaller depending on a few variables.

Part Thickness

With thicker parts, the torch must travel slower, meaning the HAZ will be larger as more heat is transferred to the part. Thinner parts have a shorter cutting time, resulting in a smaller HAZ.

Part Geometry

In straight-line cutting, the torch goes at its maximum speed, which will minimize the HAZ. But on geometrically sophisticated parts with many corners, segments, holes, or slots, the torch will cut slower as it decelerates and accelerates into each segment. The longer it takes, the larger the HAZ will be.

Consumable Setup

Consumable setup also plays a role in HAZ creation. For example, a piece that is ¾-inch thick would require either a 170-amp or 300-amp setup. The 300-amp consumable cuts much faster, which results in a smaller HAZ. The 170amp setup would go slower, resulting in a larger HAZ and more dross.

Benefits of Dry Cutting vs. Underwater Cutting

As mentioned above, dry cutting offers a range of benefits over underwater cutting. These include:

  • Better cut quality: dry plasma cutting will generally produce smoother edges. It also has less chance of dross formation compared to underwater cutting.
  • Faster cutting speeds: dry cutting will usually allow for faster cutting speeds, as there is no water resistance to slow down the process.
  • Lower equipment costs: underwater systems will generally be more expensive than dry cutting systems. Underwater equipment often requires complex water tables with removable slat assemblies and pneumatically controlled raise/lower mechanisms.

It’s no surprise that many manufacturers are looking to move to dry cutting systems for their non-ferrous cutting needs. But the question remains, how does dry cutting affect stainless steel?

Water Injection vs. Dry Cutting Impact on Stainless Steel HAZ

When we look at 304 and 316 stainless steels, dry cutting has a minimal impact on the HAZ. These steels are single-phase materials, meaning they can’t be hardened by thermal treatment like plasma cutting.

At AKS Cutting Systems, we’ve had customers perform their own independent analysis of the total HAZ area of stainless steel after the VWI plasma process. They have found it to be less than 0.020-inch at any thickness. One customer tested ¾-inch stainless steel and found the total depth of the HAZ to be within 0.006-0.010-inch for the perimeter of the part.

Overall, the HAZ was minimized around only 0.006-0.008-inch. But, in tight geometry areas like inside corners and holes, the HAZ grew as large as 0.020-inch. To fix this issue, the customer learned to change the part drawing and just “round off” the tight geometry and cut a round line. With either cut path, the customer would have had to mill the part in a secondary process. Relying on just dry cutting overall made the process faster and more efficient.

Other Dry Cutting Considerations for Stainless Steel

While dry plasma cutting stainless steel doesn’t have a large impact on the HAZ, there are other considerations to keep in mind. Possible metallurgical reactions that can occur in 304 and 316 stainless steel at the HAZ include:

Grain Growth

In annealed or hot rolled conditions, grain growth will not occur. However, in a cold-worked state, grain growth will cause some softening of the HAZ. Since the HAZ is only a few millimeters thick, grain growth is not expected to have any adverse effect on edge quality.

Ferrite Formation

Depending on the composition of the steel, some ferrite may form at the grain boundaries. This reaction can be beneficial because ferrite slows grain growth, preventing grain boundary liquation. The rate at which ferrite forms is slow and likely unchanged by underwater or above-water cutting.


During plasma cutting, the area adjacent to the cut experiences temperatures high enough to dissolve precipitates in the base metal. As this region cools, these dissolved elements can reform as carbides and nitrides. While the formation of these compounds is often associated with a reduction in corrosion resistance, this effect is not immediate or guaranteed.

For corrosion resistance to be significantly impacted, the metal must remain within a specific temperature range of 600-850°C for at least 30 seconds. This temperature window is critical for the precipitation process to occur to a degree that would compromise the material’s corrosion-resistant properties.

Interestingly, rapid cooling can mitigate potential losses in corrosion resistance. In the context of typical plasma cutting speeds, even when performed in dry conditions, it’s improbable that the metal would remain within the critical temperature range long enough to cause substantial adverse effects on its corrosion resistance. The swift nature of the cutting process often allows the material to cool before significant precipitation can occur, thus preserving its corrosion-resistant qualities.

Have Questions About How Plasma Cutting Affects HAZ? Connect with the Experts

If you have questions about the HAZ in plasma cutting, contact AKS Cutting Systems. With over 100 years of experience in the cutting industry, AKS has developed extensive expertise in plasma cutting technology and its effects on materials. Our team of experienced professionals can provide valuable insights into how the HAZ impacts your specific cutting applications and offer guidance on minimizing its impact.

We offer a wide range of plasma cutting machines, from entry-level models like the PLASMATIC and PLASMATIC PRO to advanced industrial systems like the dura-kut. We also partner with Hypertherm to deliver the best consumables to our customers. Our expertise and made-in-America machinery can help you improve cut quality, reduce the extent of the HAZ, and ultimately enhance the performance of your cutting operations.

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Want to hear more about what we can do for you? Reach out to our team for an initial consultation.