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Home > Forming Basics

Selecting Metal Alloys for Stamped Parts

Brad F. Kuvin,

Brad F Kuvin is editor of MetalForming magazine, published by PSI Services Inc., a division of the Precision Metalforming Association, Independence, OH. www.metalformingmagazine.com.

Metal stampers work with numerous types of metal alloys—ferrous (carbon and stainless steels) and nonferrous (copper and its alloys, aluminum and titanium alloys, and others) to create parts. Here is a rundown of those materials and their typical metal stamping applications.

Metal stampers work with numerous types of metal alloys—ferrous (carbon and stainless steels) and nonferrous (copper and its alloys, aluminum and titanium alloys, and others).

The overwhelming majority of the steel consumed in the metal-stamping industry is carbon steel, also called plain-carbon steel. As the carbon content in a carbon-steel alloy rises, the material has the ability to become harder and stronger (through heat treating), albeit less ductile.

Selecting Metal Alloys for Stamped Parts

Carbon steel

Within the carbon-steel family, stampers work primarily with low-carbon (also called mild) steel. Mild steels typically contain a maximum of 0.25 percent carbon and 0.4-0.7 percent manganese, 0.1-0.5 percent silicon and traces of other elements.

These alloys are everywhere, including structural applications in buildings, bridges, etc.; automotive parts of all kinds including clutch housings, bushings and suspension components such as brackets, control arms, cross members etc.; kitchen utensils such as pots and pans; metal shelving, cabinets and other types of office furniture; bicycle frames; ships; and nuts, bolts and screws.

The main types of formable mild steel are commercial quality (CQ), draw-quality (DQ) rimmed and aluminum-killed draw quality (AKDQ).

Parts requiring severe forming or drawing operations too difficult for the drawing properties of commercial-quality cold-rolled steel sheet may be formed from aluminum-killed draw-quality (AKDQ) steel. Aluminum-killed steelsare deoxidized with aluminum and, possibly, with silicon. Exceptional resistance to thinning through the sheet thickness can be developed through the controlled processing of these steels. These alloys find use in automotive sheet applications such as inner door panels, and in challenging forming applications such as guardrails.

Also available are high-strength low-alloy (HSLA) steels, offering higher strength as compared to mild steels, combined with improved toughness and good weldability. HSLA steel typically contains 0.07-0.12 percent carbon. These alloys attain their favorable properties by their refined production process—thermo-mechanical rolling that maximizes grain refinement. They find great acceptance where light weight is a must—in automotive applications for example, where the alloys also offer optimum crash-worthiness. Applications include seating components, body-in-white and suspension assemblies and chassis components.

Higher-carbon steels

These steel alloys (in medium, high.  ultrahigh-carbon grades) contain 0.30-2.00 percent carbon by weight. Manganese may be added to improve hardenability. Alloys with 0.30-0.60 percent carbon (considered medium-carbon steels) offer a good balance of ductility and deliver good wear resistance.

Alloys with 0.6-0.99 percent carbon are higher in strength and find use in springs and high-strength wires. And when steelmakers add between 1.0 and 2.0 percent carbon to the steel recipe, the resulting alloy can be tempered to a hardness greater than Rc 60--applications include knives, axles and punches

Stainless steels

Metalformers fabricating products destined for corrosive environments most likely are stamping austenitic grades of stainless steels--iron-chromium-nickel steels in the 300-series of alloys.

The most common 300-series alloy found in metalforming shops is Type 304, containing18 percent Cr and 8 percent Ni, which finds use in chemical-processing equipment, in equipment for the food and beverage industries and in heat exchangers. 

Also common is Type 316 stainless steel, which contains 16-18 percent chromium and is higher in nickel content, 11-14 percent. It also includes molybdenum, used to control a form of corrosion called pitting. As such, it finds use in more severe chemical-processing applications, and in equipment found in the pulp and paper industry.

Shops tasked with welding stamped stainless-steel parts typically work with the "L" grades of alloys, the L indicating low carbon content. Carbon in these grades is limited to less than 0.03 percent, to improve weldability. These designations include 304L and 316L, for example.  In addition to finding use in processing environments to battle corrosion, you’ll also find these alloys stamped for decorative applications, such as for automotive wheel covers, and as fasteners—nuts, bolts, screws and washers.

While 300-series alloys comprise three-quarters of the stainless-steel applications, a great deal of 400-series alloys (dubbed ferritic stainless steels) also find use throughout manufacturing. These alloys (typical grades are Type 409, 439 and 430) contain little to no nickel, are magnetic (austenitic steels are non-magnetic); provide better resistance to stress-corrosion cracking than their 300-series brethren (although they are generally less corrosion resistant than 300-series alloys); and typically are less expensive, since their pricing is independent of the going rate for nickel.

Ferritic grades are commonly found in automotive exhaust systems, where resistance to both corrosion and heat are required. Applications also can be found in the appliance industry—in ovens, dishwashers and dryers.

Aluminum and aluminum alloys

When light weight and/or corrosion resistance are key requirements, along with strength, typically it’s time to look at aluminum alloys. Metalformers work with sheet from wrought aluminum alloys. Applications most familiar to metalformers are in packaging products—drink cans, bottle caps, trays and utensil lids. Other applications around the house include window frames, railings, grills and toasters.

Cookware manufacturers favor aluminum due to its high thermal conductivity—it quickly spreads heat evenly. High reflectivity also makes aluminum a material of choice the solar-power industry, and high ductility allows aluminum alloys to be drawn into wires.

The transportation industry also favors aluminum alloys. Stamped aluminum parts are found in boats and railway carriages. For automobile manufacturers, metalformers process aluminum wheels, suspension components, closures (hoods and deck lids), transmission housings, impellers and fan clutch parts.

Copper and its alloys

The marine industry, chemical and processing facilities and electrical-distribution industry use stamped and fabricated copper-alloy sheet and plate. Copper is alloyed with nickel for non-electrical applications such as architectural products—curtain walls, skylights and awnings. You’ll also find copper-alloy sheet in solar collector panels, pressure vessels, condensers and heat exchangers.

These are soft, malleable alloys that cut, draw, stamp, bend and form easily, so designers have a field day developing artistic applications for furniture, lighting and décor companies.

Silver is the primary alloying element (albeit only 8 to 25 oz./ton minimum) for electrical applications—conductors, rotors, contacts, etc.  More than half of the applications for copper are in power-generation and electrical-transmission products—transformers, generators and motors, and wiring and contacts.

Add zinc (25-50 percent) to copper (and a few other elements) and you get brass--offering strength and corrosion resistance ideal for naval and marine applications like offshore oil rigs the ship-building industry. Metal stamping companies also work with brass alloys in low-friction applications such as locks, gears, bearings, doorknobs, ammunition and valves, and (due to its attractive color) in musical instruments.

Add tin (5-20 percent) to copper and you get bronze, harder and more brittle than brass. Stampers fabricate bronze sheet, plate and wire to manufacture bearings, clips, electrical connectors and springs.

Discussion Question:

  • What steps does your company take to make sure that delivered materials meet your specifications?
Typical Stampings Produced from Metal Alloys
Low-Carbon (mild) steel
  • Structural applications in buildings, bridges, etc.; automotive parts--clutch housings, bushings and suspension components;
  • Kitchen utensils such as pots and pans;
  • Metal shelving, cabinets and other office furniture;
  • Bicycle frames; Ships; Nuts, bolts and screws
AKDQ
  • Automotive applications such as inner door panels; guardrails
HSLA
  • Applications requiring light weight, such as automotive for seating components, body-in-white and suspension assemblies, and chassis components
Higher-Carbon steels
  • Springs; high-strength wires; Knives; Axles; Punches
Type 304 stainless steel
  • Chemical-processing equipment; equipment for the food and beverage industries; Heat exchangers
Type 316 stainless steel
  • More severe chemical-processing applications; Equipment for the pulp and paper industry
Type 300-series stainless steel with “L” low carbon content designation
  • Processing environments to battle corrosion;
  • Decorative applications--automotive wheel covers; fasteners
Type 400-series stainless steel
  • Automotive exhaust systems;
  • Large household appliances--ovens, dishwashers, dryers
Aluminum
  • Packaging products—drink cans, bottle caps, trays and utensil lids;
  • Window frames, railings, grills and toasters;
  • Cookware; Solar-power applications;
  • Transportation applications--boats and railway carriages;
  • Automobile wheels, suspension components, closures (hoods and deck lids), transmission housings, impellers, fan clutch parts
Copper
  • Marine industry, chemical and processing facilities and electrical-distribution industry;
  • Architectural products; solar collector panels, pressure vessels, condensers and heat exchangers;
  • Artistic applications for furniture, lighting and décor;
  • Locks, gears, bearings, doorknobs, ammunition and valves, musical instruments, clips, springs

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