Types of steel – Classification of steel

 

Based on the chemical compositions, Steel can be categorized into four basic groups:

  • Carbon Steel
  • Alloy Steel
  • Stainless Steel
  • Tool Steel
  1. CARBON STEEL: Carbon steel is the most utilized steel in the industries and accounts for more than 90% of the total steel production. Based on the carbon content, Carbon steels are further classified into three groups.
  • Low Carbon Steel/Mild Steel
  • Medium Carbon Steel
  • High Carbon steel

Carbon content is given in the table below:

S.No. Type of carbon steel Percentage of Carbon
1 Low Carbon Steel/Mild steel Upto 0.25%
2 Medium Carbon Steel 0.25% to 0.60%
3 High Carbon steel 0.60% to 1.5%

 

  1. ALLOY STEEL: In alloy steel, varying proportions of alloying elements are used, in order to achieve desired (improved) properties such as weldability, ductility, machinability, strength, hardenability and corrosion resistance etc. Some of the most used alloying elements and their effects are as follows;

Manganese – Increases strength and hardness, decreases ductility and weldability;

Silicon – Used as deoxidizers used in steel making process

Phosphorus – Increases strength and hardness and decreases ductility and notch impact toughness of steel.

Sulfur Decreases ductility, notch impact toughness and weldability. Found in the form of sulfide inclusions.

Copper –improved corrosion resistance

Nickel – Increases hardenability and Impact strength of steels.

Molybdenum – Increases hardenability and enhances the creep resistance of low-alloy steels

  1. STAINLESS STEEL: Stainless steels – Stainless steel is an alloy steel with 10.5% Chromium (Minimum). Stainless steel exhibits extraordinary corrosion resistance due to formation of a very thin layer of Cr2O3 on the surface. This layer is also known as passive layer. Increasing the amount of Chromium will further increase the corrosion resistance of the material. In addition to Chromium Nickel and Molybdenum are also added to impart desired (or improved) properties. Stainless steel also contains varying amounts of Carbon, Silicon and Manganese.

Stainless steels are further classified as

  1. Ferritic Stainless Steels
  2. Martensitic Stainless Steels
  3. Austenitic Stainless Steels
  4. Duplex Stainless Steels
  5. Precipitation-Hardening (PH) Stainless Steels
  • Ferritic: Ferritic steels consists of Iron-Chromium alloys with body-centered cubic crystal structures (BCC). These are generally magnetic and cannot be hardened by heat treatment but can be strengthened by cold working.
  • Austenitic: Austenitic steels are most corrosion resistant. It is non-magnetic and non heat-treatable. Generally austenitic steels are highly weldable.
  • Martensitic: Martensitic stainless steels are extremely strong and tough but not as corrosion-resistant as the other two classes. These steels are highly machinable, magnetic and heat-treatable.
  • Duplex Stainless Steels: Duplex stainless steel consists of a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel ( i.e Ferrite + Austenite). Duplex steels are about twice as strong as austenitic or ferritic stainless steels.
  • Precipitation-Hardening (PH) Stainless Steels: Precipitation-Hardening (PH) Stainless Steels possess Ultra high strength due to precipitation hardening.
  1. TOOL STEEL: Tool steels have high carbon content (0.5% to 1.5%). Higher carbon content provides higher hardness and strength. These steels are mostly used to make tools and dies. Tool steel contains various amounts of tungsten, cobalt, molybdenum, and vanadium to increase the heat and wear resistance and durability of the metal. This makes tool steels very ideal for using as cutting and drilling tools.

 

12 comments

    1. Dear Mr. Praphulla biswal
      Thank you for visiting my website. I am planning to upload both study materials and preparatory questions for NDT level II and III exams. It will take around 2 to 3 months, please be in touch for the updates. You can also watch my welding and NDT tutorial videos on http://www.youtube.com/weldingandndt
      Regards
      sandeep Anand

  1. Can you organize study materials and classes for NDT personnel qualifications under 9712.
    Regards
    SRINIVASAN
    9892258785
    President IIW INDIA

    1. Dear Sir,
      Thank you for visiting my website. Yes I can organize study materials and classes for NDT personnel qualifications under 9712, even I will upload many relevant topics on my website and my YouTube channel also.
      Regards
      Sandeep Anand

  2. I found this listing very interesting and useful. One suggestion would be to list the stainless steels in the order:

    Martensitic
    Ferritic
    Austenitic
    No suggestions after this.

    The reason for my suggestion is that martensitic and ferritic stainless steels are essentially iron-chromium alloys and should be grouped together. The martensitic stainless steels have the lower chromium contents and thus lower corrosion resistance. Listing these three in the order I have suggested gives the approximate order of corrosion resistance and is a common way of listing them in many other documents.

    1. Dear Mr. Bob Heidersbach
      Thank you for visiting my website, your suggestions are valuable for me. Yes you have suggested the most appropriate method of grouping of stainless steel, Certainly i will do the changes. I request you to kindly give your valuable feedback on my other articles too.
      Regards
      Sandeep Anand

  3. Nice articles sir, sir i have need to ASNT level 3 study material on topics on NDT basics &RT level 3.I am very happy , when you can post this types of articles.Finally you can do great job.

  4. Sir,I request you to make an article names title as
    “ how the steels varey with respect to chemical composition”

    Expectation
    This article would may clearly say about :
    with a some permanent elements what elements to be added in what ratio to convert as different types of steels.
    In a simple form of understanding

  5. Sir please explain how select filler wire through section.i have seen your video on the same topic.please explain with section wise it will better for more understanding.
    Thank you.

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