Stainless steel is an alloy of Iron that contains at least 11% chromium. It also can contain nickel, molybdenum and other elements.
Stainless steel is broken down into three major groups:
1.) Austenitic Grades
Suncor uses mostly type 304 and 316 stainless steel of the 300 series, which are the most important members of the Austenitic family and arethe most widely used of stainless steels. The Austenitic grades are generally nonmagnetic andhardenable only by cold working.However they can be magnetic to a small degree especially formed parts. They can be softened by “annealing” heat treating.
2.) Ferritic Grades
Generally Suncor does not usetheferritic grades, which aremagnetic and nonhardenable.
3.) Martensitic Grades
The Martensitic Group are hardenable byheat treatment and are magnetic. Varieties such as Type 440 find major applications as products that must resist atmospheric oxidation, mildly corrosive chemicals and wet or dry corrosion. This type contains up to 1% carbon. Suncor uses this type in some products such as Quick Attach Wedges. However these parts have a plating to protect against further corrosion.
Typical Contents of Stainless Steel:
- Nickel— to stabilize the austenitic structure, improve forming properties, increaseductility, high temperature strength and corrosion resistance (particularly in industrialand marine atmospheres, chemical, food and textile processing industries).
- Silicon— to increase scaling resistance and resist carburizing at high temperatures.
- Manganese— to improve hotworkingproperties, increase yield and tensile strengths (above 2%), partially replace nickel and stabilize the austenitic structure.
- Molybdenum— to increase corrosion resistance (particularly in sulfite, sulfate, aceticacid and acetate solutions and salt water atmosphere), increase creep resistance, increase strength at elevated temperatures, expand range of passivity andcounteract tendency to pit.
- Titanium, ColumbiumTantalum—to prevent intergranular corrosion by stabilizingthe carbon as titanium or columbium carbides instead of chromium carbides, producefiner grain size, reduce stretcher strains from drawing and forming in Type 430.
- Sulfur, Phosphorus and Selenium— to improve machinability.
- Additional Chromium— to increase scaling, wear and corrosion resistance and increase tensile strength.
Types of Stainless and Grades:
Austenitic:
Type 301 contains less chromium and nickel than 302 for more work hardening.
Type 302 is the basic type of the 300 series, 18% chromium— 8% nickel group. It is therenowned 188
Stainless and is the most widely used of the chromiumnickelstainless and heatresisting steels.
Type 303 contains added phosphorus and sulphur for better machining characteristics.Corrosion resistance is slightly less than 302/304.
Type 303Se contains Se and P added to improve machinability.
Type 304304Lchromium and nickel increased and carbon lowered to reduce carbideprecipitation and increase corrosion resistance. Carbon is lowest in 304L for weldingapplications.
Type 305 has increased nickel to lower work hardening properties.
Type 309309Shave added chromium and nickel for more corrosion resistance and hightemperature scaling resistance. 309S contains less carbon to minimize carbide precipitation.
Type 310310Shave higher nickel content than 309309Sto further increase scaling resistance.310S contains less carbon than 310 to minimize carbide precipitation.
Type 316 (Cast 316 is called CF8M) and316L(Cast 316L is called CF3M) contain substantial molybdenum additions for improved corrosion resistance(particularly pit typecorrosion), creep resistance and high temperature strength. Carbon content316L is low for welding purposes, and also reduced corrosion.
Type 321 contains titanium to tie up the carbon and avoid chromium carbide precipitation inwelding.
Type 330 ultra high nickel content provides best corrosion resistance to most furnaceatmospheres. This grade has low coefficient of expansion, excellent ductility and high strength.
Type 347 – 348 have columbiumtantalumadded to tie up the carbon and avoid chromiumcarbide precipitation in welding. Use for temperatures from 800to 1650 degrees F.
Ferritic:
Type 405 contains 12% chromium with aluminum added to prevent hardening.
Type 430 is the basic type in the ferritic group, possessing good ductility and excellent resistance to atmospheric corrosion. Its scaling resistance is higher than 302 in intermittentservice, somewhat lower in continuous use.
Type 430F430Sehave sulfur and selenium (respectively) added for increased machinability.
Type 442 has added chromium for improved resistance to scaling.
Type 446 has still higher chromium content (27%) for added scaling resistance and is highest of the standard straight chromium types. Alloys with over 30% chromium become too brittle toprocess.
Martensitic:
Type 410 is the basic Martensitic type. It is the general purpose corrosion and heat resisting chromium stainless steel. It can be hardened by thermal treatment to a wide range of mechanicalproperties. It can be annealed soft for cold drawing and forming. This grade is always magnetic.
Type 403 is a special high quality steel made for blades and buckets for steam turbine and jetengine compressors. This grade is eminently suited for very highly stressed parts. This material is magnetic in all conditions.
Type 416416Se
are modifications of Type 410, being the freemachining,nonseizing,nongallingalloys. These properties are obtained by the addition of sulphur or selenium to Type 410.This is a heat treatablegrade with corrosion resistance and other characteristics closelyapproaching those of Type 410.
Type 420 is a chromium stainless steel capable of heat treatment to a maximum hardness ofapproximately 500 Brinell. It has a maximum corrosion resistance only in the fully hardenedcondition. Type 420 is magnetic in all conditions.
Type 431 is a nickel bearing (1.252.00%)chromium stainless steel which may be heat treatedto high mechanical properties. It is magnetic in all conditions of use. It has superior corrosionresistance to Types 410, 416, 420, 430 and 440 stainless steels.
Type 440C is the stainless steel that can be heat treated to the highest hardness of any of the
corrosion resistant steels. Its best corrosion resisting properties are obtained when it is in the fully hardened condition. It is recommended where high hardness,wear and corrosion resistance are paramount. This type is magnetic in all conditions.