Difference between Stainless Steel AISI 420 Mod (modified) VS AISI 434

Here is the explanation of the differences between modified AISI 420 stainless steel and AISI 434 in terms of phase, chemical composition, physical properties, and mechanical properties:

  1. Phase:
    • AISI 420 Mod: AISI 420 modified is typically in the martensitic phase. It has a hardened microstructure characterized by a high density of dislocations and a fine-grained structure.
    • AISI 434: AISI 434 is predominantly in the ferritic phase. It has a body-centered cubic (BCC) crystal structure and is known for its good formability.
  2. Chemical Composition:
    • AISI 420 Modified: AISI 420 modified typically contains about 0.3% carbon (C), 16% chromium (Cr), and smaller amounts of other elements such as manganese (Mn), silicon (Si), phosphorus (P), and sulfur (S).
    • AISI 434: AISI 434 generally contains lower carbon (C) content, along with chromium (Cr), nickel (Ni), molybdenum (Mo), manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), and other trace elements.
  3. Physical Properties:
    • AISI 420 Modified: AISI 420 modified exhibits good corrosion resistance, moderate to high hardness, and moderate ductility. It has a density of around 7.8 g/cm³ and a melting point of approximately 1450-1525°C.
    • AISI 434: AISI 434 possesses relatively good corrosion resistance, lower hardness compared to AISI 420 modified, and higher ductility. It has a slightly lower density of about 7.75 g/cm³ and a similar melting point range.
  4. Mechanical Properties:
    • AISI 420 Modified: AISI 420 modified is known for its high strength, hardness, and wear resistance. It exhibits good tensile strength, typically ranging from 700 to 1200 MPa, and high Rockwell hardness (HRC) values.
    • AISI 434: AISI 434 generally has lower strength and hardness compared to AISI 420 modified. It typically has lower tensile strength, ranging from 450 to 600 MPa, and relatively lower hardness values.

Disclaimer: It is important to note that the specific properties may vary depending on the heat treatment and processing conditions applied to the materials. Therefore, conducting thorough testing and analysis specific to the actual material samples is crucial to accurately determine their properties.

AISI 420 Mod & 420 Reguler Stainless Steel

Here is a comprehensive explanation of AISI 420 modification (420 Mod) with a chromium (Cr) content of approximately 16%, compared to regular 420 with a Cr content of 12-14%. Please note that AISI 420 modification may have variations in its exact composition and properties depending on specific manufacturer specifications and processes.

Phase:

  • AISI 420 Mod: AISI 420 Mod is typically in the martensitic phase. It undergoes a transformation from austenite to a hard and brittle martensitic structure upon quenching.

Chemical Composition:

  • AISI 420 Mod: AISI 420 Mod generally consists of around 0.3% carbon (C), 16% chromium (Cr), and smaller amounts of other elements such as manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), and sometimes molybdenum (Mo). The increased Cr content enhances its corrosion resistance and other properties.

Physical Properties:

  • AISI 420 Mod: AISI 420 Mod exhibits good corrosion resistance, moderate to high hardness, and moderate ductility. It has a density of around 7.8 g/cm³ and a melting point of approximately 1450-1525°C.

Mechanical Properties:

  • AISI 420 Mod: AISI 420 Mod possesses high strength, hardness, and wear resistance. It has a good combination of toughness and edge retention. The specific mechanical properties may vary depending on the heat treatment and processing conditions applied.

Heat Treatment:

  • AISI 420 Mod: AISI 420 Mod undergoes heat treatment processes such as quenching and tempering to achieve the desired hardness, strength, and toughness. The exact heat treatment parameters may vary based on specific application requirements.

Applications:

  • AISI 420 Mod: AISI 420 Mod is commonly used in applications that require high hardness, corrosion resistance, and good mechanical properties. It finds applications in the manufacturing of cutting tools, surgical instruments, dental equipment, industrial blades, and components for the oil and gas industry.

Other Supporting Information:

  • AISI 420 Mod is known for its excellent wear resistance, which makes it suitable for applications involving abrasive environments.
  • The higher chromium content in AISI 420 Mod provides improved corrosion resistance compared to regular 420 steel.
  • The addition of other alloying elements like molybdenum (Mo) can further enhance certain properties, such as increased strength and toughness.

It is important to consult with steel manufacturers or industry specifications for the exact composition, heat treatment, and application considerations specific to AISI 420 Mod in order to ensure its suitability for a particular use case.

Addition of Mo element in 420 Mod stainless steel material

When manufacturers add molybdenum (Mo) to AISI 420 modified steel, it is typically done to enrich the steel with certain additional properties. Here are some advantages and disadvantages of adding Mo to AISI 420 modified material:

  1. Purpose of Adding Mo:
    • Improved Corrosion Resistance: The addition of Mo to 420 mod material aims to enhance its corrosion resistance, particularly against chloride-based corrosion, such as pitting corrosion and crevice corrosion in salt-containing environments. And, Enhanced Resistance to Pitting and Crevice Corrosion: Mo can also improve the material’s resistance to pitting corrosion and crevice corrosion. This reduces the risk of localized damage on the material’s surface.
  2. Advantages of Adding Mo to 420 mod Material:
    • Enhanced Corrosion Resistance: The addition of Mo can improve the corrosion resistance of 420 mod material, making it suitable for harsher and more corrosive environments.
    • Increased Mechanical Strength: Adding Mo can enhance the tensile strength and hardness of the material, providing advantages in applications that require higher mechanical properties.
    • Improved Toughness: Mo can improve the toughness of the material, reducing the risk of cracking and failure under dynamic loading or harsh environmental conditions.
  3. Disadvantages of Adding Mo to 420 mod Material:
    • Cost: Adding Mo can increase the production cost of 420 mod material, as Mo is considered a rare metal and has a relatively higher price.
    • Impact on Machining Processes: The presence of Mo in 420 mod material can influence machining processes, such as increasing tool hardness and wear. Therefore, adjustments in the machining process of Mo-containing materials may be required.

It is important to note that the addition of Mo to 420 mod material should be tailored to specific requirements and application environments. Consult with steel manufacturers or material experts to obtain proper recommendations regarding the use of Mo-containing materials in particular applications.

AISI 434 Steel

Phase:

  • AISI 434: AISI 434 is primarily in the ferritic phase. It possesses a body-centered cubic (BCC) crystal structure, which contributes to its unique properties.

Chemical Composition:

  • AISI 434: AISI 434 typically contains about 0.12-0.17% carbon (C), 16-18% chromium (Cr), and smaller amounts of other elements such as manganese (Mn), silicon (Si), phosphorus (P), sulfur (S), and sometimes molybdenum (Mo). The carbon content in AISI 434 is relatively low compared to other stainless steels.

Physical Properties:

  • AISI 434: AISI 434 exhibits moderate corrosion resistance and good formability. It has a density of around 7.7 g/cm³ and a melting point ranging from approximately 1400-1425°C.

Mechanical Properties:

  • AISI 434: AISI 434 possesses relatively lower strength and hardness compared to martensitic stainless steels. It has a lower tensile strength, typically ranging from 450 to 600 MPa, and exhibits moderate ductility.

Heat Treatment:

  • AISI 434: Unlike martensitic stainless steels, AISI 434 cannot be hardened through heat treatment. It is not responsive to typical hardening processes such as quenching and tempering. The ferritic structure of AISI 434 limits its ability to undergo phase transformations that result in increased hardness.

Applications:

  • AISI 434: AISI 434 is commonly used in applications that prioritize formability and corrosion resistance over high strength or hardness. It finds applications in automotive components, kitchen appliances, architectural structures, and decorative purposes.

Reason for Inability to Harden:

  • The inability of AISI 434 to be hardened through heat treatment is due to its ferritic microstructure. Ferritic stainless steels have a body-centered cubic structure, which does not undergo a martensitic transformation upon quenching. As a result, the steel does not experience a significant increase in hardness through heat treatment.

It’s important to note that the specific properties and applications of AISI 434 can vary based on specific manufacturer specifications and processing conditions. Consulting with steel manufacturers or experts is recommended to obtain detailed information regarding the use and characteristics of AISI 434 stainless steel.

Portable PMA (Portable Mass Spectrometry Analyzer) is a device used to test the chemical composition of ferrous and non-ferrous materials. It operates based on the principles of mass spectrometry, where the sample material is vaporized and ionized, and then analyzed based on their mass-to-charge ratio (m/z).

Portable PMA (Portable Mass Spectrometry Analyzer)

Portable PMA devices are typically equipped with gas-phase ionization techniques, such as electron impact (EI) or chemical ionization (CI), which enable the ionization of molecules in the gas phase for detection and analysis. Some PMA devices also allow for simultaneous elemental analysis using inductively coupled plasma (ICP), which is commonly used for non-ferrous material analysis.

The main advantage of portable PMA devices is their high portability, allowing them to be used in the field or in remote locations. These devices often come with software that can process data in real-time and provide quick analysis results of elemental compositions.

However, there are certain components that may not be included in the analysis provided by portable PMA devices. Some examples of components that may not be detectable or measurable include:

  1. Carbon (C): Portable PMA devices typically cannot directly measure the carbon content in materials. Carbon content analysis is often performed using other techniques such as combustion analysis or carbon analyzers.
  2. Hydrogen (H): Measuring hydrogen content is also challenging for portable PMA devices. Hydrogen content analysis is commonly done using other techniques such as thermal analysis or infrared analysis.
  3. Nitrogen (N): Portable PMA devices usually cannot directly measure the nitrogen content in materials. Nitrogen content analysis often requires other techniques such as combustion analysis or Kjeldahl analysis.
  4. Trace components: Portable PMA devices may not be able to detect or measure trace elements, which are elements present in very small amounts in the material.

For more comprehensive analysis or to measure the content of elements not included in portable PMA devices, specialized and comprehensive laboratory analysis methods such as inductively coupled plasma mass spectrometry (ICP-MS) or other techniques may be required.

Misidentification of AISI 420 Mod and AISI 434

The Intriguing Case: Unveiling the Misidentification of AISI 420 Mod Steel as AISI 434 Material in PMA Test Results

aisi 420
Take a look at the picture above, from left to right: PMA test results of AISI 420 Mod steel – 431 and 420

There is an interesting thing, why aisi 420 mod steel (far left) based on PMA test results, is actually detected as AISI 434 material?

The detection of AISI 420 modified material as AISI 434 in a portable PMA spectrometer, despite the technical difference in carbon (C) content between the two materials, can be explained by several factors.

Sensitivity and Resolution of the Spectrometer:
Portable PMA spectrometers have certain limitations in terms of sensitivity and resolution compared to larger, laboratory-grade spectrometers. These limitations can result in less accurate identification and differentiation of materials, especially when the differences are subtle, such as variations in carbon content.

Calibration Inaccuracies: PMA devices require accurate calibration to identify the correct material. If the calibration is not done properly or if the tool is not updated with the latest data, then detection errors may occur. In this case, it is possible that the PMA tool calibration does not recognize the difference between AISI 420 and AISI 434 effectively.

Reference Data Error: The PMA tool uses a reference database to compare the spectrum of the material under test with known materials. If the reference database does not provide enough or inaccurate information about AISI 420 and AISI 434, then the PMA tool may not be able to distinguish between them correctly. For example, if the reference data does not record the difference in carbon (C) content between the two materials, then the PMA tool may identify them as AISI 434.

Spectrum Similarity: Although carbon (C) content technically distinguishes AISI 420 stainless steel and AISI 434, the spectra of other elements detected by the PMA tool in these materials may be similar enough that it is difficult to accurately distinguish between them. In this case, the PMA tool may rely on other elements in the spectrum to identify the material, and this may lead to errors in detection.

It is important to note that this kind of detection error can be resolved or reduced by updating the calibration of the PMA tool, obtaining an accurate reference database, and ensuring that the tool is used according to the usage guide provided by the manufacturer. If you are facing the issue of improper detection, it is advisable to consult a specialist or the PMA tool manufacturer for further assistance.

To explain comprehensively, AISI 420 is a modified stainless steel material that contains higher carbon content compared to AISI 434 stainless steel. The detection of AISI 420 modification as AISI 434 in a portable PMA (Positive Material Identification) device or spectrometer could occur due to several reasons.

  1. Similar Elemental Composition: Both AISI 420 and AISI 434 stainless steels have similar elemental compositions, primarily consisting of iron, carbon, chromium, and other alloying elements. The portable PMA or spectrometer analyzes the composition of the material based on the characteristic elemental signatures.
  2. Analytical Limitations: Portable PMA devices or spectrometers have certain limitations in accurately identifying materials, especially when they possess similar elemental compositions. The device may use a library or database of known materials to match the analyzed composition, and if the library does not include AISI 420, it may identify it as the closest match, which in this case is AISI 434.

To prove that the detected material is indeed AISI 420 and not AISI 434, you can consider the following steps:

  1. Chemical Analysis: Perform a chemical analysis of the material using a more precise and comprehensive laboratory technique, such as X-ray fluorescence (XRF) or inductively coupled plasma (ICP) analysis. These techniques can provide a detailed elemental composition of the material, allowing for accurate identification.
  2. Microstructural Examination: Conduct a microstructural examination of the material using techniques like optical microscopy or scanning electron microscopy (SEM). AISI 420 and AISI 434 may have different microstructural features due to variations in their chemical compositions. By examining the microstructure, you can differentiate between the two materials.
  3. Mechanical Testing: Perform mechanical tests on the material, such as hardness testing or tensile testing. AISI 420 and AISI 434 have different mechanical properties due to their varying carbon content. By comparing the mechanical properties of the detected material with known values for AISI 420 and AISI 434, you can confirm its actual composition.

By combining chemical analysis, microstructural examination, and mechanical testing, you can provide conclusive evidence to prove whether the detected material is AISI 420 or AISI 434, thereby verifying the identification made by the portable PMA device or spectrometer.

Actually, by testing the hardness of the material, it can be proven that there is an error reading the material. For example, the 420 mod material is in a preharden condition with a hardness of around 30 HRC, while the 434 material, due to its ferritic phase, cannot be heat treated, meaning its hardness is far below that of modified AISI 420 stainless steel material.

The second is by testing the microstructure which can show the content of element C. Material 420 Mod contains element C around 0.3% while material 434 is below 0.2%

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