AKA the “18-8” grades of stainless. 18-8 stands for the chromium and nickel contents which provide the steel with excellent corrosion resistant properties
Considered Austenitic stainless grades: typically cannot be hardened by heat treatment. Instead, they are hardened by cold working or drawing
PH stands for precipitation-hardening. Parts gain strength after being heat treated at 900 degrees for I hour. This allows the spring maker to coil the spring in a softer state (Condition C) and then heat treat the springs to gain strength (Condition CH 900)
Not considered to be 18-8 stainless due to the lower chrome and nickel, HOWEVER…
17-7PH has the addition of aluminum which precipitates out of the steel during the heat treat process, giving the steel: o additional strength o potential gain in tensile strength of 30,000+ PSI
Grades 304, 321, 347
Austenitic (Cr-Ni) grades of stainless: Cannot be hardened by heat treat. Instead, they are hardened by cold working or drawing
Uses: Pool cover springs, non-invasive surgical devices, clips, springs, fasteners
400 Series Stainless Spring Wire
Grades 410, 420, 430
Martensitic (Cr) grades of stainless: can be hardened by heat treatment
Normally used in the annealed condition due to being easily formed
Compared to the 300 Series: cheapest grades of stainless with less strength and inferior corrosion properties
Uses: applications such as fasteners, lock wire, springs, clamps, clips, wire-form
Type
%Cr
%Ni
Other
Max Strength KSI
Comments
302
17-19
8-10
350 KSI
Widely used, high strength, and good corrosion properties. Used for springs & wire forms.
304
18-20
8-12
320 KSI
Typically softer than T-302. Easier to form. Used in annealed condition for fasteners & cold heading applications. Some 302 may meet chemistry of 304 but not vice versa. Tempered, 304 is used for springs & wire forms.
316
16-18
10-14
Mo
240 KSI
Superior corrosion properties when compared to 302 & 304 due to addition of Mo, however, lesser strength. Used in spring form for medical devices.
17-7PH
16-18
6-8
Al
380 KSI
17-7 PH Cond C gains strength after heat treat 1 hr at 900 degrees. Same corrosion properties as 302.
Coatings Available for Stainless Wire
Coatings are put on wire for ease of drawing the wire but also to provide lubricant for the spring coilers.
Soap Coated
Gibbscote™: Gibbs trade name for soap drawn stainless
Non-metallic coating
Most common and least expensive coating available
How it is applied – Soap coating is a two-step process:
First, a precoat is put on the wire in the annealed condition. Drawing soaps then adhere to the precoat during the drawing stage. Thus, the coating is composed of pre-coat and drawing soaps.
Note: Each mill uses different pre-coats and drawing soaps
Nickel Coating
Metallic premium coating
Higher cost than soap coated
Provides excellent lubricant for the spring coiler. A very consistent coating.
Can be drawn in soaps or oil
Soap-Drawn Nickel: provides more lubrication as soap will adhere to the nickel during the drawing process
Oil-Drawn Nickel: provides less lubricant but cleaner material (no soap residue)
How it works –
Nickel is put on the process wire (annealed condition) electrolytically and then drawn providing excellent adherence to the surface of the wire
Note: not all wire mills have the capability to provide this type of coating
Bright Finish
Very little lubricant
Not typically recommended for spring coiling
Used mainly where a bright wire is needed for aesthetics (luster) and/or a functional bright finish (when surface finish, Ra, RMS, roughness can affect the performance of the end product)
Example Application: Bright Finish is standard in medical wire
How it works –
Wire is drawn in diamond dies and oil to provide the bright, lustrous finish
Note: Generally finer diameters (.030 & below) are requested in this finish in the spring temper condition
Other Stainless Wire Info:
Operating Temperatures
Operating temperatures for the 300 series are typically 400-450 degrees. If higher operating temperatures are required, we suggest 17-7PH (550- 600 degrees)
Have even higher temperature requirements? Go with superalloys such as Inconel X750 or Inconel 600.
Temper
Stainless wire is drawn from the annealed state. Annealing is a process where the wire is transformed during heat treat. • After annealing, wire is considered soft in the tensile range of 80-120,000 PSI. The wire is then drawn to a particular size • During the drawing process, the wire hardens due to cold work and gains strength How it works – Example: A mill would like to result in wire .040” diameter in the spring temper condition. In order to achieve the diameter and desired temper, each finish size of material has a specific drawing process. This process may have to be adjusted slightly depending on the exact chemistry of the material involved. The goal is to meet the diameter tolerance per the ASTM A313
Typical Process for Tempering:
The manufacturing mill would start with a larger diameter wire than desired in the soft or annealed condition
It would then be drawn through a series of dies to reduce the diameter but will gain strength during the reduction process. However, it can only be drawn so far before becoming too hard or brittle
In this example let’s say we draw the .250” to .100”. The material is now cold worked (drawing process) and at .100” becomes very hard, too hard to draw any further or it will become brittle. But we still need to get it down to .040”
At .100” in the hard state we must again anneal to soften. During the annealing process the wire will be cleaned before annealing. Pre-coating will be put on after annealing
After the annealing process is completed the material is again soft at .100”, pre-coated, and now ready to draw down to .040. Now the wire is drawn again through a series of dies, reducing it a little through each die (reduction in area) until it gets to its finished size of .040”. At that point, it will be within its tensile strength requirement and be ready to sell to spring customers
Passivating Treatment
Corrosion properties of stainless steel are attributable to a very thin, invisible oxide film that completely covers the surfaces of the parts and prevents corrosion from taking place. Passivation removes any surface contamination, usually iron so that this film layer is not interrupted. • Passivation enhances the formation of the oxide film for maximum corrosion resistance • Passivation removes metallic and non-metallic coatings • How it works – done by immersing the parts in a nitric acid solution, normally for 30 minutes
Stress Relief
The process of heating material to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly enough to minimize the development of new residual stresses.
Often suggested for stainless finished parts such as springs after the coiling process
How it works – During the spring coiling process, additional stresses are introduced into the wire. Heat treatment post coiling relieves the stress
Suggested Stress Relief: o 300 Series = 700 degrees for one hour
17- 7PH = 900 degrees for one hour
Common Specifications for Stainless
ASTM A 313
Most common specification Gibbs orders to
Covers all grades that we order, T-302/304 and T-316
AMS-5688
Grade T302/304
ASTM A313 Type 631
Type 631 covers 17-7 PH
AMS-5678
Also covers 17-7 PH
Contact Us For More Information or To Submit A Request for Quote
The current market conditions for carbon steel wire products are very fluid. We have received several price increases from our wire suppliers in the past few months and expect there could be more going forward.
The wire price changes are primarily influenced by rapid increases in carbon scrap used to make wire rod. In addition to scrap price increases, the freight and logistics cost of moving materials locally and globally have been increasing.
Due to the above, Gibbs is increasing our prices for carbon wire products as follows:
$3.00/CWT effective October 26, 2020
$3.00 – $4.00/CWT effective December 21, 2020
Min of $6.00/CWT effective January 11, 2021
Certain carbon wire products may differ slightly from the increases mentioned above. Please contact your Gibbs salesperson for specifics related to these increases. We appreciate your business and will continue to do our best to manage this unprecedented situation.
Spring makers, fastener manufacturers, and wire formers use 300 series stainless steel wire when corrosion resistance and strength are important product features. Gibbs provides many stainless wire alloys including the most commonly used grades:
302
304
316
300 series stainless steel is also sometimes referred to as 18-8 grades. All 300 grades are austenitic. Austenitic grades will not gain strength after heat treatment. They gain their tensile and yield strength by cold working or drawing. If hardening by heat treatment is required 400 series stainless wire should be considered.
302, 304, and 316 stainless steel wire is used for countless applications where high strength and corrosion resistance are required. For added corrosion resistance 316 may be selected. It is lesser in strength than 302 but it offers improved corrosion characteristics due to the added Molybdenum.
Common industries relying on 300 series stainless wire:
Automotive
Aerospace
Chemical Processing
Commercial Products
Electronics
Machinery
Medical
Oil & Gas
Recreational Vehicles
Many coatings and finishes are available including Bright, Soap, and Nickel. Coatings are added for drawing purposes and lubricity for many processes including spring coilers. Bright wire or “diamond drawn” is typically supplied under 0.025” diameter and often used for medical applications
Common specifications for 300 series wire:
ASTM A 313
SAE J230
AMS 5688
SUS304 WPB
All 300 grades can be supplied as Spring Temper, ¼ hard, ½ hard, ¾ hard and fully annealed. Gibbs can provide custom-drawn wire to your specific tensile range.
Most 300 series wire is rated for maximum operating temperatures of 400 to 450 degrees (check specifications by alloy).
Much of the wire Gibbs provides to the industries noted above is used to manufacture springs. When springs are made they go through a spring coiling process. That process adds stress to the formed spring. Most manufacturers stress-relieve their springs after forming. Stress-relieving reduces the work-hardened stresses making the spring stronger. Many spring makers include this operation in-line with their coiling operation.
After coiling and stress relieving, the springs may also be passivated. The purpose of passivating is to protect the invisible oxide film that completely covers the surface of the parts by removing surface contamination so that the protective film layer is not interrupted. Passivating is done by immersing the parts in a nitric acid solution.
Gibbs is a premier supplier of tempered stainless steel wire in the US, Canada, and Mexico. In addition to 300 series, we offer PH grades, 400 series, carbon steel, nickel alloys, specialty metals,cobalt alloys, and more. For more information or to request a quote: CONTACT US
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