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We are a world-class supplier of engineering raw materials. Our objective is to provide all our customers, from the small machine shop to the large multi-national corporation, a supply path that continuously delivers the highest levels of service, quality and value.

4140 (AMS 6349, SAE 4140)

Chromium Molybdenum Alloy Steel

4140 Steel Alloy

AMS 6349 chromium-molybdenum alloy is a deep hardening steel used where strength and impact toughness are required.

High Fatigue Strength

It has high fatigue strength making it suitable for critical stressed applications at normal as well as elevated temperatures. For increased resistance to wear and abrasion, it may be nitrided. This grade is a quality product melted under the best of steel making practices for aircraft quality steels. It is vacuum degassed to meet the magnetic particle inspection standards of AMS 2301. The alloy is supplied in the normalised and cold finished, hot finished and normalised or normalised and cold finished condition. The density of this material is typically 7.85kg/dm³.


Intended for general use for parts with sections ½” or less in thickness at time of heat treatment which require a through-hardening steel capable of developing hardness as high as Rockwell “C” 50; also for fittings and forgings of greater hardness or variation in thickness at proportionately lower hardnesses. It is frequently used in applications in which 8640 (MIL-S-6049) is specified.

Typical Applications

Commercial applications for this engineering material include:

  • Fittings and forgings
  • Aircraft components

We stock AMS 6349 (4140) in flats, round bar, round tube, hollow bar and square bar.

Technical Assistance

Our knowledgeable staff and resident metallurgists will be pleased to assist you further on any technical topic. Smiths Metal Centres Limited also boasts an in-house UKAS Accredited Testing Laboratory which is unique within the multi-metal and plastic stockholding sector. We believe this underlines our total commitment to quality and our ethos of being the complete service provider.

Additional Info

A technical datasheet for AMS 6349 (4140) is available in PDF file format. To view and download, please click here.

We offer in-house processing options - for more information, please refer to our processing services.

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