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: STAINLESS STEEL :

In recent times we have seen a significant increase in requests for tools to be manufactured from common 300 series stainless steel to exotic alloys such as Inconel 718 and BioDur 108. Although we believe ‘the customer is always right’, in many cases customers may require a little guidance in selecting a stainless steel alloy that better suits their specific environment and intended use.

Stainless steel is a low carbon steel which contains 10% or more chromium by weight. Chromium gives stainless steel its corrosion resistant properties. The chromium content of the steel allows the formation of an invisible chromium-oxide film on its surface. If oxygen is present, even in small quantities, this film self-repairs if damaged mechanically or chemically. Corrosion resistance of stainless steel is enhanced by increased chromium content and the addition of other elements such as molybdenum, nickel, and nitrogen.

The three main classifications of stainless steel are identified by the alloying elements which form their microstructure:

Austenitic Steelshave austenite (face centered cubic crystal) as their primary phase. These are alloys containing chromium and a major proportion of nickel. Austenitic steels are not thermally hardenable but have excellent corrosion resistance. 

Ferritic Steels: have ferrite (body centered cubic crystals) as their main phase. These steels have low carbon content and contain chromium as the main alloying element, usually between 13% ~ 17%. Ferritic steel is less ductile than austenitic steel and is not thermally hardenable. 

Martensitic Steels: are low carbon steels typically containing 12% chromium, a moderate level of carbon, and very low levels of nickel. Martensitic steels are distinguished from other stainless steels in their ability to achieve high hardness by a heat treatment that produces martensite (a supersaturated solid solution of iron characterized by a needle-like microstructure).

NON-MAGNETIC STAINLESS STEELS: Most suitable for use in magnetic environments such as maintenance of MRI machines but tend to be soft.

Type 304: An austenitic stainless steel with a minimum of 18% chromium, 8% nickel, and a maximum of .08% carbon. It is non-magnetic and cannot be hardened by heat treatment. Corrosion and oxidation resistance is provided by the chromium content. The alloy's metallurgical characteristics are established primarily by the nickel content which also extends resistance to corrosion caused by chemicals. Because of its ability to withstand the corrosive action of various acids found in fruits, meats, and vegetables, 304 is widely used for sinks, tabletops, refrigerators, cooking appliances, pots, pans, and flatware.

Typical hardness = 25 ~ 32 HRC. Good up to 4 Tesla (measure of magnetic field). This alloy is not recommended for high torque applications. Not recommended for sockets, wrenches, pry bars, hex keys, chisels, hammers, or any other tools that will be used to apply impact, leverage, or high levels of torque. Suggested use: low torque applications in a magnetic environment.

Type 316: Similar to 304, 316 is an austenitic, non-magnetic, and thermally non-hardenable steel alloy. Carbon is held at .08% maximum, while the nickel content is increased slightly. What distinguishes 316 from 304 is the addition of molybdenum up to a maximum of 3%. 

Molybdenum is one of the most useful additives in the fight against corrosion. It increases the resistance of the alloy against many industrial chemicals and inhibits pitting caused by chlorides. 316 can withstand sodium and calcium brines, hypochlorite solutions and phosphoric acid. This alloy is used for industrial equipment that handle corrosive chemicals used to produce inks, rayons, photographic chemicals, paper, textile, bleaches, and rubber.

Typical hardness = 28 HRC. Good up to 4 Tesla (measure of magnetic field). This alloy is not recommended for high torque applications. Not recommended for sockets, wrenches, pry bars, hex keys, chisels, hammers, or any other tools that will be used to apply impact, leverage, or high levels of torque. Suggested use: low torque applications in a magnetic environment or highly corrosive environment.

We typically limit the use of 316 to the production of handles and square drive collars for our line of non-magnetic tools.

BioDur 108: BioDur 108 is a nickel-free austenitic stainless steel alloy which was originally designed for medical implants and was intended to replace type 316 stainless steel. It contains a minimum of 21% chromium, 0.3% nickel, maximum of .08% carbon and 0.7% Molybdenum. BioDur has tensile and fatigue strengths that are superior to type 316 Stainless Steel.

Typical hardness = 43 ~ 50 HRC. It is a non heat-treatable alloy and availability is limited. BioDur 108 exhibits excellent non-magnetic characteristics and is good up to 10 Tesla (measure of magnetic field).

Read a Carpenter press release for Steritool products made from Custom 465 & BioDur 108.

Inconel 718: An austenitic superalloy with a minimum of 17% chromium, 50% nickel, .08% carbon, and 2.8% Molybdenum. It is non-magnetic and is hardened by heat treatment. Inconel resists pressure and high temperatures better than most alloys and is often used in jet engines, turbine blades, exhaust systems, and pressure vessels.

Typical hardness = 38 HRC. Good up to 5 Tesla (measure of magnetic field).

Do to limited availability and very high cost, it is typically used when high strength, non-magnetic tools are needed and cost is of no concern. It is a better choice for high torque applications that type 316 and is more readily available in plate form than BioDur 108.

MAGNETIC STAINLESS STEELS: Most common type of Stainless Steel alloys used by Steritool to produce corrosion resistant and durable tools for use in most critical environments that demand low particulate contamination, long cycle life, corrosion resistance and durability.

17-4PH: Is a martensitic precipitation hardening (PH) alloy which offers high strength and hardness while maintaining excellent corrosion resistant properties. It surpasses 400 series and more closely resembling the corrosion resistant properties of type 304 while offering a superior hardness.

It contains a maximum of .07% Carbon, 5% Nickel, 1% Manganese, 17.5% Chromium, 5% Copper, .03% Sulfur, 1% Silicon, 0.04% Phosphorus, and 0.15/0.45% of Columbium/Tantalum.

Typical hardness = 45 HRC after heat treatment. It is the #1 go to alloy here at Steritool for manufacturing wrenches, sockets, and many custom items where durability and corrosion resistance is demanded.

Type 420: *** The use of this alloy is being phased out due to lack luster performance in corrosion resistance and brittleness ***A martensitic alloy that is strengthened by the addition of carbon at a 0.15% minimum (0.30% nominal) compared to the 0.15% maximum for type 410. Along with carbon, chromium content is also slightly increased to offset the tendency of the higher carbon content to lower the alloy's resistance to corrosion. In the hardened and tempered condition, the alloy's yield strengths are substantially greater than type 410. Type 420 is used for such applications as surgical and dental instruments, cutlery, scissors, valves, and ball bearings.

Typical hardness = 50 HRC. Most commonly used in our pliers, early wrenches, early punches and chisels.

Type 440-C: is a thermally hardenable, martensitic stainless steel alloy combining corrosion-resistant properties with maximum hardness. Both carbon (0.95% - 1.2%) and chromium (16-18%) contents are increased substantially to impart hardness. While it is the strongest of all stainless steel alloy, its high carbon content reduces its corrosion resistance.

Typical hardness = 60 HRC. Most commonly used in our line of files, early punches and chisels. 440C is used in applications where hardness takes priority over corrosion resistance. It is a brittle alloy and its use is not recommended in applying leveraged force.

Custom 465: A proprietary Carpenter Technology alloy, is a martensitic, age-hardenable alloy capable of about 200 ksi ultimate tensile strength in the H900 condition. With corrosion resistant properties approaching that of type 304, this alloy is designed to yield an exceptional combination of strength and corrosion resistance. Read a Carpenter press release for Steritool products made from Custom 465 & BioDur 108.

Typical hardness = 54 HRC. It is the #1 go to alloy here at Steritool for manufacturing our extensive line of hex keys, power bits, hex bits, screw drivers, and various square drive bits.

 

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