With increasing carbon content the tensile strength shows a steady rise. Aprx, an increase of 0,01 % carbon causes a rise of the tensile strength of about 7,5 MPa. When performing a PWHT, the tensile strength drops with increasing C value. A certain minimum carbon content is necessary to obtain the required minimum tensile strength. It comes clear that a too low carbon content (for example C = 0,16 %) will lead to a significant risk to fail the minimum tensile strength when performing PWHT. A chemical composition with a carbon content > 0,20 will fulfill the tensile properties of the code.
The situation becomes more complicated when there are additional requirements on Notch toughness. To fulfill these requirements micro alloys are added like Cr, Ni, Cu, Mo, V etc, and anything excess will have detrimental effect in weld, HAZ, hence long formulae of CE is often used to restrict the equivalent effect of carbon.
you may refer previous posting titled Carbon and Carbon equivalent in this group
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of desaid@toyoindia.com
Sent: Thursday, December 24, 2009 10:52 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:3887] RE: 3884] <Security Level 2>Carbon Equivalent
Below extract i understand that can be achieved by just specifying the Max. Carbon content. i.e. limiting the % of carbon in CS material.
But specifically what is the role of limiting CE?
It is something related to role of Manganese; am not able to recollect at this moment under pressure.
Thanks & Regards,
Dhwani Desai.
TOYO - PLANNING & PIPING DEPT.
91-22-2573 7681.
| "Bathula Raghuram (Mumbai - PIPING)" <R.Bathula@ticb.com> Sent by: materials-welding@googlegroups.com 12/24/2009 10:40 AM
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lower the carbon, CE reduces hardenability and good Weldability. high CE or carbon has higher chances of HAZ cracking. see an exert from AWS handbook below
"Carbon is the most important of all alloying additions to steels because of the effects it produces on the microstructure as the welds cool from the very high temperatures associated with the deposition of weld metal. This applies as much to the heat-affected zone (HAZ) of the plate as it does to the weld metal. In addition, when carbon equivalents are of concern, they are generally related to the HAZ. Two of the most troublesome problems associated with fabricating steels are hydrogen-induced cracking and poor toughness or ductility. Both are aggravated by a microstructure called martensite. Since martensite is very hard, its presence can be inferred by measuring the hardness of the HAZ, particularly in the coarsegrained regions which are close to the weld deposit. Carbon has a profound and direct effect on hardness. Other alloying elements also affect hardness, although not to the same degree. In total, they affect the facility with which a given hardness can be obtained in an alloy steel. This is called hardenability. However, the most important use of this concept has not been in predicting hardness, but predicting the minimum preheat temperature needed to avoid the formation of the hard martensite. Since martensite is produced at higher cooling rates, anything that can be done to reduce cooling rates can be beneficial toward avoiding that microstructure or a high hardness. Preheat is important because it has a very strong effect on the rate at which welds cool. Weldability, energy input and cooling rates are important variables."
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of desaid@toyoindia.com
Sent: Thursday, December 24, 2009 10:30 AM
To: materials-welding@googlegroups.com
Subject: [MW:3884] <Security Level 2>Carbon Equivalent
Dear All,
For carbon Steel specifications, it is specified as the maximum carbon content shall be 0.25% and the maximum carbon equivalent (CE) shall be 0.43%,where CE=C%+Mn%/6+(Cr% + Mo% +V%) / 5 + (Ni% + Cu%) / 15.
Why carbon equivalent is required to specify while procurement of Carbon steel components.
Thanks & Regards,
Dhwani Desai
TOYO Engg. India Ltd.
Planning & Piping Dept.
Ext.-7681
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