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Description

A martensitic machining bar with machinability enhanced through the addition of Sulphur. As for most other free-machining stainless steels the improvement in machinability is achieved by addition of sulphur which forms manganese sulphide inclusions; this sulphur addition also lowers the corrosion resistance, weldability and formability to below that of its non-free machining equivalent Grade 410. Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.

Related Standards

Equivalent Materials

Properties

Electrical

Electrical resistivity ρel

5.5E-8 Ω·m at 20 °C

General

Density ρ

7.75 g/cm³ at 20 °C

Mechanical

Elastic modulus E

200 GPa at 20 °C

Tensile strength Rm

700 - 950 MPa at 20 °C

Yield strength YS

500 - 600 MPa at 20 °C

Thermal

Coefficient of thermal expansion α

1.03E-5 1/K at 20 °C

Thermal conductivity λ

24.9 W/(m·K) at 20 °C

Chemical properties

Element

Weight %

Comment

Fe

-

Balance

Cr

12 - 14 %

Mn

1.5 %

Si

1 %

C

0.16 - 0.25 %

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Technological properties

Corrosion properties

Corrosion resistance is lower than the common austenitic grades. Useful resistance to dry atmospheres, fresh water and mild alkalies and acids, but less resistant than the equivalent non-free-machining grades. Less corrosion resistant than the austenitic grades and also less than 17% chromium ferritic alloys such as Grade 430. High sulphur content free machining grades such as 416 are totally unsuitable for marine or other chloride exposure. Maximum corrosion resistance is achieved in the hardened condition, with a smooth surface finish.

General machinability

Grade 420 offers exceptionally good machinability, the highest of any of the commonly available stainless steels. Best machinability is in the sub-critical annealed condition.

Welding

Grade 420 has poor weldability. Pre-heat to 150-320°C and post-heat at 610-760°C. Grade 420 coated welding rods are recommended for high strength joints, where a post-weld hardening and tempering heat treatment is to be carried out. If parts are to be used in the "as welded" condition, a ductile joint can be achieved by using Grade 309 filler rod. AS 1554.6 pre-qualifies welding of 420 with Grade 309 rods or electrodes.

This material data has been provided by Righton Blackburns.

All metrics apply to room temperature unless otherwise stated. SI units used unless otherwise stated.
Equivalent standards are similar to one or more standards provided by the supplier. Some equivalent standards may be stricter whereas others may be outside the bounds of the original standard.