Stainless Steel

What Is Stainless Steel and Why Is it Stainless?

In 1913, English metallurgist Harry Brearly, working on a project to improve rifle barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance. In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel. It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or stain ‘less’ than other types of steel. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the passive film. The sizes of chromium atoms and their oxides are similar, so they pack neatly together on the surface of the metal, forming a stable layer only a few atoms thick.

If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from oxidative corrosion. (Iron, on the other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide forms a loose rather than tightly-packed layer and flakes away.) The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and poor circulation environments. In seawater, chlorides from the salt will attack and destroy the passive film more quickly than it can be repaired in a low oxygen environment.

Types of Stainless Steel

The three main types of stainless steels are austenitic, ferritic, and martensitic. These three types of steels are identified by their microstructure or predominant crystal phase.

Austenitic:
Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not hardenable by heat treatment. The most familiar stainless steel is probably Type 304, sometimes called T304 or simply 304. Type 304 surgical stainless steel is an austenitic steel containing 18-20% chromium and 8-10% nickel.

Ferritic:
Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium, based on the Type 430 composition of 17% chromium. Ferritic steel is less ductile than austenitic steel and is not hardenable by heat treatment.

Martensitic:
The characteristic orthorhombic martensite microstructure was first observed by German microscopist Adolf Martens around 1890. Martensitic steels are low carbon steels built around the Type 410 composition of iron, 12% chromium, and 0.12% carbon. They may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle, so few steels are fully hardened.

There are also other grades of stainless steels, such as precipitation-hardened, duplex, and cast stainless steels. Stainless steel can be produced in a variety of finishes and textures and can be tinted over a broad spectrum of colors.

Stainless Steel – Summary

Type 301 – 1/4 Hard – AMS 5517

QUARTER HARD COLD ROLLED TYPE 301 – (chrome-nickel) Stainless Steel Strip. This is one of the group of five different tempers stocked by us in this alloy. This quarter hard temper is used in many ways for light drawing, stretching and forming operations where heat and corrosion resistant properties are required. It possesses greater ductility and elongation than its counterparts Types 302 and 304 but work hardens much more rapidly. At 1/4 Hard, Type 301 develops a tensile strength of 125,000 PSI minimum, minimum yield strength of 75,000 PSI and elongation in 2 inches of 25% minimum.

TYPE 301 CHARACTERISTICS
TYPE 301 – (chrome-nickel) Austenitic. The chemistry of this alloy permits cold working to the ideal combination of mechanical properties desired for springs. To illustrate; in the Full Hard condition, it will maintain a minimum of 9% elongation in 2” as compared with Type 302 Full Hard at 2% approximately. This retained elongation on the part of 301 accounts for its great hardness, toughness and superior fatigue life in the finished part. In addition, it possesses a high strength-to-weight ratio. Type 301 work hardens excessively – For this reason its general demand is in the harder tempers. It is not heat-treatable for hardening purposes, is non-magnetic as annealed but slightly magnetic following cold working. Type 301 possesses good heat and corrosion resistance and welds easily. To solution anneal, cool rapidly in air or water from about 2000° F.

Type 301 – 1/2 Hard – AMS 5518

HALF HARD COLD ROLLED – This Type 301 – (chrome-nickel) Stainless Strip has been produced to meet a need for an in-between forming Quality Strip within a hardness range calling for minimum tensile and yield strengths at 150,000 PSI and 110,000 PSI respectively with elongation in 2 inches at 15-18%. Its ductility and elongation are superior to Types 302 and 304, but it work hardens much more rapidly.

Type 301 – 3/4 Hard

THREE QUARTER HARD COLD ROLLED – This temper in Type 301 (chrome-nickel) Stainless Strip differs from our other Type 301 stainless strip steels only to the degree to which it has been hard cold rolled to its 3/4 hard condition. Its minimum tensile and minimum yield strengths are cataloged at 175,000 PSI and 135,000 PSI respectively with elongation in 2 inches at 10 – 12%. Like all Type 301 Stainless Steels it possesses great hardness and toughness. Although it work hardens much more rapidly than the other Austenitic Stainless Steels, this very property makes it altogether suitable for many applications.

TYPE 301 – FULL HARD

FULL HARD COLD ROLLED – Type 301 – (chrome-nickel) Stainless Steel permits cold working to the ideal combination of mechanical properties desired for springs. Its unique combination of hardness and toughness makes for better forming quality in this Full Hard Temper plus increased fatigue life in the finished spring. In this temper, it develops an approximate minimum tensile strength of 185,000 PSI and 140,000 PSI yield strength with elongation in 2 inches at 8% to 9% minimum.

TYPE 301 – EXTRA HARD – AlSl 301 Chemistry Only

EXTRA HARD COLD ROLLED – Type 301 – (chrome-nickel) Stainless Steel Strip has been stocked to meet the demand for exceptionally high strength and where a high strength-to-weight ratio is desired and good corrosion and heat resistance are necessary. Type 301 excels Type 302 in its high strength due to its lower nickel content causing it to work harden more rapidly. Its principal use is for mechanical springs and parts where exceptional hardness and toughness are required.

TYPE 302 – Soft Annealed and Skin Passed

SOFT and DUCTILE – Type 302 (18/8 chrome-nickel) Stainless Steel Strip. This is the BASIC and most widely used of all the Chrome-Nickel steels. It is recognized as the best all purpose drawing and forming quality type in this stainless group with mechanical and forming qualities intermediate to Types 301 and 304. Type 302 offers the benefits and avoids the shortcomings of both of these types. Note – Deep Drawing and Extra Deep Drawing qualities are available but only as negotiated to meet special requirements. Type 302 applications are wide and various including formed products, drawn parts, flexible metal hose, household appliances, certain spinning operations, tubing and countless other stainless fabricated parts.

TYPE 302 CHARACTERISTICS
TYPE 302 (18/8 chrome-nickel) Austenitic. This type differs but little from its companion Alloy Type 301. However, the slight increase in Chromium and Nickel contents in Type 302 over 301 develops marked changes in its mechanical properties and in its forming behavior. Type 302 work hardens much less rapidly than does Type 301 but with strength and toughness second only to 301. It possesses excellent heat and corrosion resistance and welds easily. To solution anneal, cool rapidly in air or water from about 2000° F. It is not heat treatable for hardening purposes and is slightly magnetic following cold working. We stock Type 302 in five different tempers – Soft to Full Hard inclusive. Note – We do not guarantee mechanical properties on Type 302 tempers. We do for Type 301.

TYPE 302 – 1/4 HARD –

QUARTER HARD COLD ROLLED TYPE 302 (18/8 chrome-nickel) Stainless Steel Strip. At C25 – 30 this quarter hard temper differs from Soft Temper Type 302 Stainless Strip Steel ONLY in its hardness. This added hardness or stiffness makes it possible to use in place of somewhat thicker material in numerous applications. It can be stamped, blanked, formed and lightly drawn. It does not work harden as quickly as Type 301. Note – We do not guarantee mechanical properties for Type 302 in Tempers. We do for Type 301.

TYPE 302 – 1/2 HARD –

HALF HARD Cold Rolled Type 302 (18/8 chrome-nickel) Stainless Steel Strip. This temper has been accurately cold rolled to its half hard condition (Rockwell – approx. C30-35) ready for stamping, blanking or forming. Its higher nickel content causes it to work harden less rapidly than Type 301 and its higher percentage of chromium makes for greater corrosion and heat resistance.
(Note – The AISI Stainless Manual does not show tensile, yield or elongation for this temper.) We stock the Half Hard temper in both Type 302 and Type 301. Your choice will depend on the nature of the job at hand and its specifications.

TYPE 302 – 3/4 HARD –

THREE QUARTER HARD Cold Rolled Type 302 (18/8 chrome-nickel) Stainless Steel Strip at C-35/40. Due to demand this temper is stocked alongside of its 3/4 Hard counterpart in Type 301. Both have their place in the Austenitic family of hard rolled tempers. The 302 is characterized as possessing somewhat less hardness, toughness, elongation and spring back but easier to form. Also Type 302 possesses greater heat and corrosion resistance. Your choice will depend on the degree of forming required to do the job at hand or to the specifications. If you have temper problems, we invite your inquiries. We will be happy to help you select the proper material for your needs. Note – The AISI Stainless Manual does not show tensile, yield or elongation for Type 302.

TYPE 302 – FULL HARD –

FULL HARD COLD ROLLED – Type 302 (18/8 chrome-nickel) Stainless Steel Strip at C-40/45. Note – The AISI Stainless Manual does not show tensile, yield or elongation for Type 302. This is the most often used temper in the Type 302 grade. Wide application for spring clips, washers, retainers, etc. We stock a full range of sizes in this temper.

TYPE 304 CHARACTERISTICS
TYPE 304 (18/8 chrome-nickel) Austenitic Stainless Steel Strip. This is a companion grade to Types 301 and 302 and characterized by an especially low carbon content while its chromium and nickel are somewhat higher.

Because of its lower carbon content Type 304 is not so prone to give trouble after welding, due to carbide precipitation and resultant corrosion. Type 304 possesses heat and corrosion resistant properties superior to Types 301 and 302. Its strength, work hardening and drawing qualities are slightly less than Type 302. Type 304 is not heat-treatable for hardening purposes. It is non-magnetic as annealed but slightly magnetic following cold working. To solution anneal, cool rapidly in air or water from about 1850° to 2050° F.

TYPE 304 – Soft Annealed and Skin Passed –

SOFT and DUCTILE – This type 304 (18/8 chrome-nickel) Stainless Steel Strip differs from Type 302 only in its low carbon content and in its slight increase in the chrome and nickel percentages. It has a high degree of ductility, excellent drawing, forming and spinning properties. Type 304 is used extensively in the chemical, refrigeration, paper and food processing industries. Also for bellows, flexible metal hose, spinning, tubing and numerous other stainless applications. Like Type 302, Type 304 finds its larger demand in the soft tempers. In its annealed condition the tensile strength is listed at approximately 75,000 PSI minimum and its yield strength at approximately 30,000 PSI minimum with approximate elongation in 2 inches at 40%.

TYPE 305 – Soft Annealed and Skin Passed

ROLLED TO RESTRICTED THICKNESS TOLERANCES

BRIGHT ANNEALED – The bright cold rolled finish is retained by final annealing in a controlled atmosphere furnace.

FOR DEEP DRAWING – Type 305 Stainless Strip Steel possesses the same excellent corrosion resistance as Type 302, but has a much lower rate of work hardening. It is well suited for cold forming operations in which this low rate of work hardening is desirable. Its yield, tensile strength, and hardness increase at rates which are exceptionally low. However, its initially good elongation falls off rapidly.

Type 305 is widely used for the production of parts by free spinning and cold heading operations, and it is particularly suitable for severe cold drawing, especially where the part can be completely formed in two draws. In many instances, the intermediate anneal can be eliminated when Type 305 is used. In drawing, the metal should be allowed to slip freely through the hold-down pads, thus holding stretching to a minimum. Used widely for electronic parts and other drawn applications.

TYPE 316 – Soft Annealed and Skin Passed –

Type 316 has better corrosion resistance to most chemicals, salts and acids and is more resistant to marine atmosphere because of an addition of 2.0 to 3.0% molybdenum. This addition improves the corrosion resistance of austenitic steels and imparts hot strength characteristics. Another valuable property of Type 316 is high creep strength at elevated temperatures. Fabrication characteristics of Type 316 are similar to Type 302 or 304.

Type 316 has extensive use in chemical processing equipment when better corrosion resistance is required than is afforded by chromium-nickel steels. Also 316 is specified for use with high purity products where product contamination must be held to a minimum. Typical applications are Food Processing, Chemical Processing, Photographic, Pharmaceutical and Textile Finishing Equipment and Marine Exterior Trim.

TYPE 321 – Soft Annealed and Skin Passed –

Type 321 is similar to Type 304, however, it contains a Titanium addition of at least five times the carbon content. This addition is made to reduce or eliminate chromium carbide precipitation – resulting from welding or exposure to high temperatures. Maximum stabilization is accomplished by annealing between 1750° and 1850° F. Type 321 has extensive use in aircraft parts, such as exhaust systems where operating temperatures are higher than 800° F. and where corrosive conditions are not too severe; also because of its resistance to scaling and vibration fatigue.

Typical applications: Aircraft Exhaust Stacks and Manifolds, Chemical Processing Equipment, Welded Equipment, Jet Engine Parts, etc.

17/7-PH CONDITION A

17/7-PH Condition A (Annealed 17/7 Cr-Ni 1 % AL) Precipitation Hardenable Stainless Steel Strip. This alloy provides design and production advantages possessed by none of the standard stainless grades. Easily formed in its Condition A, it can be hardened to high strength levels by subsequent heat treatment. It work hardens rapidly and with forming behavior similar to Type 301. Type 17/7-PH was designed primarily for manufacture into parts requiring corrosion resistance and high strength up to 600° F and where such parts may require welding during fabrication. Condition A has a tensile strength of 150,000 PSI maximum, a yield strength of 55,000 PSI maximum and elongation in 2 inches at 20% minimum. This Condition A conforms to SAE aeronautical material specification AMS 5528.

17/7-PH CONDITION C

Hard Rolled No. 2 as Rolled Finish

17/7-PH Condition C (Hard Rolled Temper 17/7 Cr – Ni 1 % AL) Precipitation Hardenable Stainless Steel Strip. This alloy provides design and production advantages possessed by none of the standard stainless steels. It can be formed in about the same way as hard rolled Type 301 with the added advantage of subsequent heat treatment for further hardening purposes and has minimum distortion on heat treatment. Its corrosion resistance is superior to that of the straight chromium grades. This temper conforms to the SAE Aeronautical Material specification AMS 5529. Condition C has a tensile strength of 200,000 PSI minimum, a yield strength of 175,000 PSI minimum and elongation in 2 inches of 1% minimum.

TYPE 410 – Cold Rolled and Annealed

Hardened by Thermal Treatment

SOFT and DUCTILE – This type 410 (Martensitic) Stainless Steel Strip is the general purpose and most widely used of all the Martensitic grades of stainless steels. In its annealed condition it may be drawn, formed or shaped and because it is an air or oil quench hardening grade it can be hardened to high strength levels by subsequent heat treatments. While Type 410 offers very good resistance to scaling up to 1200° F., and its mechanical properties are excellent, it is NOT recommended for applications in which severe corrosion is encountered. Type 410 is used for springs, scrapers, fasteners, hardware brackets, furnace parts and burners. It is magnetic in all conditions. Tensile strength (as annealed) min. 65,000 PSI, yield strength minimum 30,000 PSI, and elongation in 2 inches at 20%. For solution annealing, slow controlled cooling from 1500/1600° F. For hardening, heat to 1700/1850°F. Quench in air or oil.

TYPE 410 -Pre Hardened and Tempered

Type 410 Stainless in its cold rolled, hardened and tempered condition is used in countless applications similar to Cold Rolled High Carbon Spring Steel Strip but with the advantages inherent in being stainless and at moderate cost. Its formability is good for its yield strength and hardness range. Type 410 in its pre-hardened condition is stocked by us in coils ready for slitting to exact widths for press feed operations or to exact size blanks. At C45 Type 410 develops a tensile strength of 200,000 PSI with yield at 180,000 PSI and elongation in 2 inches of 2%.

Complete Facilities for Slitting – Shearing – Leveling and Blanking

TYPE 420 – Soft Annealed

Type 420, a modification of 410, has a higher carbon content to increase hardness, improve strength and give better wear resistance. This type maintains its best corrosion resistance in the heat treated condition. Tempering temperatures above 700° F. are not normally recommended and Type 420 must be preheated before and annealed after welding.

Principal applications: Bushings, Dental and Surgical Instruments, Pump Parts, Valve Parts, and Shafts. Our 420 is not bought or recommended to a cutlery grade.

TYPE 430 – Soft Annealed and Skin Passed

EXTRA BRIGHT ANNEALED SOFT TEMPER TYPE 430 – Stainless Strip Steel is the most popular of all the straight chrome stainless steels. Its principal use is for decorative purposes. Because of its excellent heat and corrosion resistant properties, its ductility and because it costs less than the chrome-nickel grades, this Type 430 Stainless Steel Strip is used in countless applications. These uses are primarily for stainless and decorative purposes including household appliances, metal molding, metal trim, cabinet hardware, hinges, drawn and formed parts and stampings.

TYPE 430 CHARACTERISTICS
TYPE 430 (17% straight chrome) Ferritic Stainless Steel Strip. This is the basic and most generally used straight chromium (Ferritic) Stainless Strip Steel. Because of its high chromium content, it is highly corrosion and heat resistant but somewhat less than Types 301, 302 and 304. It possesses good physical and mechanical characteristics but with ductility at about 75% of low carbon strip and inferior to that of the chrome-nickel grades. Like other straight chromium grades, Type 430 Annealed is subject to stretcher strains. Skin passing following annealing greatly reduces this possibility although this reduces ductility somewhat. Likewise a condition akin to stretcher strains may sometimes develop during deep drawing known as roping. Roping is characterized by the appearance of shallow ridges and valleys in the side walls and caused by excessive stretching. Type 430 is magnetic in all conditions, is not heat-treatable for hardening purposes and is weldable but its welds are not suitable in rigorous service. The tensile strength for Type 430 in the annealed condition is cataloged at 65,000 PSI minimum, its yield at 30,000 PSI minimum and elongation at 22%.