November, 1999 - An upgrade of the 15Cr-5Ni stainless steel that has been used widely by the aerospace industry offers improved machinability and with it, the opportunity to reduce part costs, cut cycle time and increase productivity.

Carpenter Project 7000 15Cr-5Ni stainless (UNS S15500) has been developed by Carpenter Technology Corp., Reading, PA, to provide superior machinability while meeting all requirements of Aerospace Material Specification AMS 5659 covering bars, wire, forgings, rings and extrusions.

The new alloy, offering potential also for increased capacity and longer tool life, is available as a "drop-in" replacement for conventional 15Cr-5Ni stainless in applications where improved machining productivity is desired.

Possessing high strength and hardness, along with excellent corrosion resistance, the new precipitation hardening stainless alloy is a candidate material for rod-end bearings, a variety of aircraft structural components, and some engine parts.

It may be considered also as a more machinable version of the standard 15Cr-5Ni stainless, which has been used for industrial applications such as gun barrels, valve parts, fittings and fasteners, shafts, gears and process equipment.

The new Project 7000 alloy is vacuum melted, chemically balanced and processed to optimize machinability in the solution-annealed as well as age-hardened conditions. The machinability of this and other age-hardened materials improves as the aging temperature increases.

Carpenter reports that metalworking plants participating in beta site production machining trials increased their parts productivity by up to 145% using Project 7000 15Cr-5Ni stainless alloy. Increases were of such magnitude that some plants gained enough capacity to accept new business, without having to purchase expensive new equipment. A few experienced two-to-three times longer tool life.

Depending on the heat treated condition of the material, Carpenter obtained machinability improvements of 32 to 10 times when it machined the new Project 7000 stainless in its own research and development screw machine facility.

This martensitic stainless steel will allow shops to push their machining speeds and feeds to higher levels, challenging the material for best results. Carpenter has offered to work with users to maximize machinability since results ultimately depend, the producer says, on the application, equipment and operator skills.

In addition to its improved machinability, the new alloy can be headed, rolled and otherwise formed by cold working. It can be forged by heating the work piece uniformly to 1950/2050°F (1066/1121°C) and held one hour at temperature before forging in accordance with a recommended schedule. The material can be welded by the shielded fusion and resistance welding processes.

Corrosion resistance of the Project 7000 15Cr-5Ni stainless grade approaches that of Type 304 stainless, and is similar to that of Carpenter 15Cr-5Ni and Custom 630 (17Cr-4Ni) stainless steels in most media. It offers good resistance to stress corrosion cracking by age hardening at temperatures of 1025°F (552°C) and higher.

The new alloy displays excellent resistance to oxidation up to approximately 1100°F (593°C). Although toughness may decline (typical of PH stainless steels) after long term exposure to temperatures between about 600-900°F (316-482°C), that reduction may be minimized by using higher aging temperatures.

Typical analysis of Project 7000 15Cr-5Ni stainless is: carbon 0.07% max., manganese 1.00% max., silicon 1.00% max., phosphorus 0.030% max., sulfur 0.015% max., chromium 14.00/15.50%, nickel 3.50/5.50%, copper 2.50/4.50%, molybdenum 0.50% max., columbium 5XC/0.45, tantalum 0.05% max., iron balance.

Project 7000 15Cr-5Ni stainless steel is available from Carpenter in billets, wire, bars and wire rods.

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