Hardness of Untempered Martensite

[Kathalingam Babu]

Hi

 

Any body have the idea on hardness for the untempered Martensite ?

 

What will be the morphology of micro?

 

Thanks & Regards,

 

K.Babu
Singapore

 

[Chandra, Vasanthan (Lagos)]

Micro: Needle Like structure

Hardness: 300 to 350 VHN

 

Regards,

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[John Du Plessis]

 

 

Untempered martensite harness is approximately 60 – 65 HRc and not as soft as 300 to 350 Vickers as has been suggested

John du Plessis

Technology Manager

 

Tel: +27 (11) 298 2100

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[Prabhu Kumar L]

Dear Babu,

 

Untempered Martensite is brittle in nature, which will have high hardness level. Martensite will be formed in carbon and low alloy steel, when the cooling rate is higher than the critical cooling rate. For example, quenching the steel into water/oil from austenitizing temperature range will produce martensite (brittle) structure at room temperature. In order to convert brittle martensite to less brittle and also to retain toughness, tempering process shall follow after quenching

 

During quenching, some % of austenite may retain to room temperature due to some of the alloying elements (austenitic stabilizing elements such as Mn, Ni, C) and cooling rate. This austenite may try to convert as secondary martensite when tempering treatment is carried out. Hence this martensite is called “untempered martensite” which is brittle in nature. This may contribute to the overall brittleness to the material/ structure.

 

Microstrural analysis can reveal the untempered martensite in the steel micro-structure.

 

Regards,

 

L. Prabhu kumar,

Sr. Principal Engineer,

 

Equipments & Materials Dept.,

Saipem India Projects Limited,

Nungambakkam High Road, Chennai - 600 034, India.

Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,

Mobile Ph. No.: +91 9003010978.

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From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Kathalingam Babu

Sent: Tuesday, June 08, 2010 6:21 AM
To: material...@googlegroups.com

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[Warke, Robert]

Mr. Babu,

 

The hardness of untempered martensite is determined almost entirely by its carbon content, as shown in the attached diagram.

 

Regards,

R. W. Warke

 

Robert W. Warke, P.E.
Associate Professor of
Welding & Materials Joining
School of Engineering & Engineering Technology

LeTourneau University

 

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From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Kathalingam Babu
Sent: Tuesday, June 08, 2010 6:21 AM
To: material...@googlegroups.com
Subject: [MW:5437] Hardness of Untempered Martensite

 

Hi

[Kathalingam Babu]

Hi Prabhu,

 

Thanks for the response.

 

I would like to know that, what will be the hardness value , which is the indication of, presence of the untempered Martensite in Q& T Steel

 

And

 

What will be the morphology of the Microstructure.

 

Is there any specs. or stds ?

 

Regards,

 

K.Babu

Singapore

[Kathalingam Babu]

Mr.Robert,

 

Thanks,

 

Will this figure applicable to alloy steels ?

 

I assume that, it will applicable to plain carbon steels only.

 

 

Regards,

 

K.Babu

Singapore

 

----- Original Message -----

From: Warke, Robert

To: material...@googlegroups.com

--

[Warke, Robert]

You’re welcome, Mr. Babu.  The previous figure does apply to alloy steels as well as to plain-carbon. 

 

Alloy content in a ferritic steel strongly influences its hardenability, which is how easily martensite can be produced by quenching its austenite.  Carbon content, on the other hand, determines the hardness of any martensite that is produced, and thus determines the maximum attainable hardness of a steel.  The attached figure demonstrates both of these principles.

 

~RWW

[limesh M]

Dear all,

 

What is meant for 4340,4140,8640,5140 and 1040 on the graph.It will be highly helpful if any one explain the graph in detail.Hope someone will take initiative.

 

Thanks and Regards

[John Henning]

These are AISI designations and the chemistry requirements are quite commonly published.  Briefly the first two numbers indicate the alloy type and the last two numbers indicate the nominal carbon content.  Thus for the figure shown you have carbon steel (1040) hardness vs. various alloy steels hardness all with the same nominal carbon content (~0.40%).  The figure also shows that alloying content will affect the depth of hardening as demonstrated in the Jominy test.  At the maximum cooling rate, at the quenched end of the Jominy specimen, the hardnesses are nearly the same for all the steels because martensite is formed almost exclusively.  This is as expected, since the hardness of martensite is solely dependent on carbon content and all the steels have the same carbon content.  As the cooling rate decreases (increasing distance from the quenched end of the specimen, i.e. DQE) the formation of martensite is dependent on the alloy content, thus you see a rapid fall off in the carbon steel hardness (1040) (no deliberate alloying elements) as opposed to alloy steels.  The figure shows that various alloying schemes increase hardenablility more than others and is shown in the figure as higher hardness with distance from the quenched end. 

 

You may find additional and more complete discussion of hardenability and the Jominy test in any basic metallurgy/materials textbook or a beginning book on heat treatment of steels.

 

John