Enhanced machinability as standard

Sanmac^® is a family of stainless steels produced by Alleima with improved machinability, available as both bar and hollow bar. As Alleima's preferred distribution partner for duplex and super duplex stainless steels, we stock Sanmac grades because they make our customers' machining more predictable.

What makes Sanmac different

UNS and EN standards for chemical composition allow a wide tolerance, but Alleima does not target the lower end of these tolerances. Instead, compositions are optimised for machinability, corrosion resistance and weldability. Once that target composition is achieved, products are manufactured to very tight tolerances, so machining settings (speeds and feeds) can be repeated from job to job with a high degree of consistency.

The quality Sanmac grades excel at is chip breaking. Chip formation is one of the most crucial aspects of any machining activity: poorly managed chip breaking can harm the workpiece, the cutting tool and even the operator. Chip breaking is difficult when machining austenitic and duplex stainless steels for three main reasons.

Toughness and ductility

Both austenitic and duplex stainless steels have high toughness and ductility, mainly due to the high elasticity of the austenitic (FCC) phase. High ductility often leads to poor chip breaking, with long, continuous chips that can wrap around the workpiece or tool.

Low thermal conductivity

Stainless steels have approximately a third of the thermal conductivity of carbon steels. Less heat leaves the cutting process with the chip and more is transferred into the insert, which requires a lower cutting speed. Low thermal conductivity also leads to built-up edges, where material smears onto the insert, ripping away the coating and deteriorating the edge.

High proof strength

Austenitic stainless steels and normal carbon steels are comparable in strength, but duplex stainless steels are about twice as strong as regular austenitic or ferritic grades. Machining duplex produces strong, hard chips, which can cause chip-hammering at the insert and create high cutting forces. The high proof strength also limits both the feed rate and the cutting speed.

Microstructure and chip breaking

Chip breaking, and energy consumption, are closely related to microstructure. During hot working (forging and rolling), the steel develops an even, optimised microstructure along the full length of the bar. Non-metallic inclusions manipulate that microstructure so that when the material is heated in the cutting zone it yields at a lower mechanical load, allowing the chip to break off easily. This gives very predictable machining with the lowest possible energy consumption. An uneven microstructure would directly affect chip breaking, tool life and component quality. Sanmac materials are designed to give better chip breaking than similar products on the market.

The Sanmac grades we stock

Sanmac 316L (UNS S31603 / DIN 1.4404 / ASTM A276 / ASTM A479)

Hollow bar, from 32mm to 250mm OD

Sanmac 2205 duplex stainless steel (UNS S31803 / UNS S32205 / F51 / F60 / DIN 1.4462)

Hollow bar, from 32mm to 250mm OD
Solid bar, from 5/8" to 16"

Frequently asked questions

What makes Sanmac stainless steel different from standard grades?

Alleima optimises Sanmac compositions for machinability, corrosion resistance and weldability rather than targeting the lower end of standard tolerances, then manufactures to very tight tolerances so machining settings can be repeated from job to job with high consistency.

Why is chip breaking so difficult with standard duplex and austenitic grades?

Three factors combine against good chip breaking: high toughness and ductility from the austenitic phase produce long, continuous chips; low thermal conductivity causes built-up edges on the tool; and duplex's high proof strength creates strong, hard chips that hammer the insert.

How does Sanmac improve chip breaking specifically?

Non-metallic inclusions manipulate the microstructure during hot working so that, when heated in the cutting zone, the material yields at a lower mechanical load, letting the chip break off easily. This gives predictable machining with the lowest possible energy consumption.

Which Sanmac grades are stocked, and in what sizes?

Sanmac 316L hollow bar is stocked from 32mm to 250mm outside diameter. Sanmac 2205 duplex is stocked as hollow bar in the same size range, plus solid bar from 5/8" to 16" diameter.

Request a quote

Tell us the grade, form and sizes.

Fast quotes from UK and US stock - bar, plate and pipe, cut and certified to spec.