Type of stainless Steel
1 Austenitic grade
2 Martensitic grade
3 Ferritic grade
4 Duplex Grade
5 Precipitation Hardening Grades
6 Super Alloy Grade
1. Austenitic Grades
• Austenitic grades are those alloys which are commonly in use for stainless applications.
• The austenitic grades are not magnetic.
• The most common austenitic alloys are iron-chromium-nickel steels and are widely known as the 300 series.
• The austenitic stainless steels, because of their high chromium and nickel content, are the most corrosion resistant of the stainless group providing unusually fine mechanical properties.
• They cannot be hardened by heat treatment, but can be hardened significantly by cold-working.
• Straight Grades
– The straight grades of austenitic stainless steel contain a maximum of .08% carbon.
• Low Carbon Grades
– The “L” grades are used to provide extra corrosion resistance after welding.
– The carbon is kept to .03% or under to avoid carbide precipitation
– The letter “L” after a stainless steel type indicates low carbon (as in 304L)
– "L" grades are more expensive
• High Carbon Grades
– The “H” grades contain a minimum of .04% carbon and a maximum of .10% carbon and are designated by the letter “H” after the alloy.
– People ask for “H” grades primarily when the material will be used at extreme temperatures as the higher carbon helps the material retain strength at extreme temperatures.
Austenitic
Grades and Type
• Type 304
– The most common of austenitic grades, containing approximately 18% chromium and 8% nickel. It is used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for the milder chemicals.
• Type 316
– Contains 16% to 18% chromium and 11% to 14% nickel
– Type 316 is used in chemical processing, the pulp and paper industry, for food and beverage processing and dispensing and in the more corrosive environments. The molybdenum must be a minimum of 2%
• Type 317
– Contains a higher percentage of molybdenum than 316 for highly corrosive environments. It must have a minimum of 3% “moly”
• Type 321 & Type 347
– developed for corrosive resistance for repeated intermittent exposure to temperature above 800 degrees F. Type 321 is made by the addition of titanium and Type 347 is made by the addition of tantalum/columbium. These grades are primarily used in the aircraft industry
Martensitic
Grades
• developed in order to provide a group of stainless alloys that would be corrosion resistant and hardenable by heat treating.
• The martensitic grades are straight chromium steels containing no nickel.
• They are magnetic and can be hardened by heat treating.
• The martensitic grades are mainly used where hardness, strength, and wear resistance are required
Martensitic Grades Type
• Type 410
– Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410).
– Low cost, general purpose, heat treatable stainless steel.
– Used widely where corrosion is not severe (air, water, some chemicals, and food acids.
– Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners
• Type 410S
– Contains lower carbon than Type 410, offers improved weldability but lower hardenability.
– Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting application
• Type 414
– Has nickel added (2%) for improved corrosion resistance.
– Typical applications include springs and cutlery
2. Martensitic Grades
• Type 416
– Contains added phosphorus and sulphur for improved machinability. Typical applications include screw machine parts
• Type 420
– Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments
• Type 431
– Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps
• Type 440
– Further increases chromium and carbon to improve toughness and corrosion resistance
Ferritic Grades
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