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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