carbon equivalent

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I first came across the term \"carbon equivalent\" during a professional exam; I was completely confused at that time – what exactly is carbon equivalent? What is it for? After that, special attention was paid to this parameter. I encountered this again today, so I’ve organized the relevant information to share it with everyone. What is carbon equivalent? Carbon equivalent refers to the conversion of various alloying elements in steel into an equivalent carbon content. The main factor determining the strength and weldability of carbon steel is its carbon content. What is the carbon equivalent used for? Most steels used in pressure vessels need to be welded. Therefore, the welding properties of its steel directly affect the welding process and welding quality. Experimental studies have shown that there is a definite relationship between the carbon equivalent (Ceg) and the highest hardness in the welded heat-affected zone. Generally, the higher the strength, the higher the hardness in the heat-affected zone, and the greater the likelihood of welding cracks occurring. If HVmax≤350, the tendency for cracking is low, and the steel has good weldability. The causes of welding cracks are often the combined effect of factors such as the microstructure of the heat-affected zone, the hydrogen content in the welded area, and external constraints. To improve the weldability of steel, some have proposed requirements to control the carbon equivalent of the steel. For example, the standards established by the Japanese Welding Society specify different carbon equivalent requirements based on the steel plate’s strength grade and various heat treatment conditions.