Materials with alloy content exceeding 5%
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GB50236 stipulates that when materials with an alloy content of more than 5% are welded by argon arc welding, the root backside must be protected to prevent the oxidation of the alloy components. How do you understand that the alloy content exceeds 5%? For example, 15CRMO argon arc welding does not require root protection, but similarly low chromium molybdenum steel 1CR5MO requires root protection?
Just take a look at the specific chemical composition. C in 15CrMo: 0.16%, Si: 0.27%,Mn: 0.55%,Cr: 0.95%,Mo: 0.50%, S≤0.40%, P≤0.035%. The Cr content in 1Cr5Mo is 5.3%. Of course, root protection is required.