3 Key Points to Know: Is the Corrosion Resistance of 304 Stainless Steel Sheet Affected After Stamping?

about 900 words · 4 min read
Selina Su · Oct. 11, 2025

For many hardware accessory brand owners, a critical question is: after our widely used 304 stainless steel sheet is stamped into the precision components we need, will its acclaimed corrosion resistance be compromised? The answer is yes; the stamping process generally weakens the corrosion resistance of 304 stainless steel to some extent. However, this is not an unsolvable problem.

This article will delve into the reasons behind this phenomenon and provide brand owners with practical remedies and application advice to ensure your products maintain exceptional quality in any environment.

Table of Contents

1. Causal Analysis of Stamping: Why Does Corrosion Resistance Decrease?

2. Key Remedial Measures: How to Restore and Enhance Anti-Corrosion Performance?

3. Practical Application Advice for Brand Owners: How to Ensure Long-Term Product Stability?

1. Causal Analysis of Stamping: Why Does Corrosion Resistance Decrease?

The "stainless" property of 304 stainless steel comes from a dense, stable, chromium-rich oxide layer on its surface, known as the "passive film." This invisible protective film isolates the steel from external corrosive media. However, the aggressive plastic deformation process of stamping damages this protection in two main ways.

• Microstructural Changes: The significant stress during stamping can cause the austenitic structure of the stainless steel to transform into strain-induced martensite. This phase transformation, along with accompanying micro-stresses, can lead to the formation of "Chromium-depleted Zones" at the grain boundaries. As chromium is the key element for forming the passive film, the corrosion resistance of these areas is significantly reduced, making them particularly susceptible to intergranular corrosion.

• Physical Damage to the Passive Film: The shearing, stretching, and bending actions of stamping can directly scratch, damage, or make the original passive film incomplete and discontinuous. This is equivalent to tearing holes in a sturdy suit of armor, allowing corrosive media (like moisture and salt) to penetrate and accelerate the corrosion of the base material.

2. Key Remedial Measures: How to Restore and Enhance Anti-Corrosion Performance?

Fortunately, through scientific post-treatment processes, we can repair this damaged "armor" and even make it stronger than before. The main methods include polishing and pickling & passivation.

• Polishing: This involves mechanically or electrochemically smoothing the surface of the stamped part to remove scratches, burrs, and stressed layers from processing. A smooth surface is less likely to retain corrosive substances and provides an excellent foundation for the formation of a uniform passive film.

• Pickling and Passivation: This is the most crucial and effective restoration method.

  • Pickling: An acid solution is used to remove surface scale, weld discoloration, and other contaminants.

  • Passivation: The cleaned part is immersed in an oxidizing medium (typically nitric acid) to artificially and controllably promote the re-formation of a new passive film that is thicker, denser, and more uniform than the one formed naturally.

The table below summarizes the problems caused by stamping and their corresponding solutions:

3. Practical Application Advice for Brand Owners: How to Ensure Long-Term Product Stability?

As a brand owner, when sourcing and producing hardware accessories, you can take the following steps to ensure the final corrosion resistance of your products meets standards:

• Evaluate the Application Environment: If your products (e.g., bathroom hardware, outdoor door locks, marine fittings) will be used in humid, coastal, or chemically corrosive environments, post-stamping surface treatments like passivation are essential and should not be omitted.

• Specify Process Requirements: When placing orders with suppliers, clearly specify post-treatment processes such as "pickling and passivation" or "electropolishing" in the technical specifications, along with corresponding inspection standards.

• Optimize the Stamping Process: Collaborate with experienced suppliers who can minimize excessive material deformation and stress concentration by optimizing die design, selecting appropriate lubricants, and controlling stamping speed. This helps preserve the original corrosion resistance of the stainless steel from the outset.

In conclusion, the corrosion resistance of 304 stainless steel sheet does indeed decrease after stamping due to physical damage and microstructural changes. However, this is a manageable issue. Through systematic post-treatment, especially pickling and passivation, its protective properties can be fully restored or even enhanced, ensuring your branded products remain durable and pristine for years to come.

Frequently Asked Questions (Q&A)

Q1: Do all stamped 304 stainless steel parts require passivation?

A1: Not necessarily. If the product is used exclusively in a dry, indoor environment with very low corrosion risk, the naturally formed oxide layer after stamping might be sufficient. However, for any application with potential corrosion risk, passivation is highly recommended to ensure long-term reliability.

Q2: Which is better, polishing or pickling & passivation?

A2: They serve different purposes. Polishing primarily improves the physical surface, making it smooth and aesthetically pleasing. Pickling and passivation, on the other hand, is a chemical restoration aimed at rebuilding a powerful anti-corrosion layer. For applications requiring the best possible corrosion resistance, the ideal process is often to polish first, followed by pickling and passivation, to achieve a "1+1>2" effect.

Q3: Will adding these post-treatment processes significantly increase costs?

A3: It will add to the cost, but this investment is usually worthwhile. Compared to the costs associated with customer complaints, brand reputation damage, and replacements due to rusting, the return on investment for proactive surface treatment is very high.

Q4: How can we test if the corrosion resistance of a stamped part is adequate?

A4: The standard method is the Salt Spray Test. By simulating an accelerated corrosive environment, this test can evaluate in a short period whether a sample's corrosion resistance meets design or industry standards.

Q5: Besides 304, are other stainless steel grades (like 316, 201) similarly affected by stamping?

A5: Yes, this principle applies to all austenitic stainless steels that rely on a passive film for corrosion protection. 316 stainless steel, which contains molybdenum, has superior inherent corrosion resistance, but it is still affected by stamping and benefits from passivation to maximize its performance. 201 stainless steel has weaker corrosion resistance to begin with, so the performance degradation after stamping is more pronounced, making surface treatment even more critical.