Cov khoom tseem ceeb ntawm cov hlau phaj yog hlau (Fe) thiab carbon (C). Hlau, raws li cov hlau tseem ceeb, tsim cov qauv ntawm cov khoom siv, thaum carbon yog qhov tseem ceeb ntawm kev txiav txim siab nws qhov kev ua tau zoo. Cov ntsiab lus carbon feem ntau yog li ntawm 0.02% mus rau 2.1%. Kev hloov pauv hauv cov ntsiab lus carbon hloov lub zog, hardness, thiab toughness ntawm cov hlau, ua rau nws yog qhov tseem ceeb ntawm kev ua tau zoo sib txawv ntawm cov pa roj carbon steel.
Dhau li ntawm hlau thiab carbon, carbon steel daim hlau kuj tseem muaj me me ntawm manganese (Mn) thiab silicon (Si). Manganese feem ntau txhim kho lub zog thiab kub ua haujlwm, thaum silicon pab txhim kho cov hlau elasticity thiab oxidation tsis kam. Cov ntsiab lus no feem ntau muaj nyob rau hauv cov nqi qis tab sis ua lub luag haujlwm tseem ceeb hauv kev tswj hwm qhov kev ua tau zoo ntawm cov khoom siv.
Cov pa roj carbon steel kuj tseem muaj cov kab tsis huv xws li phosphorus (P) thiab sulfur (S), uas feem ntau yuav tsum tau tswj nruj. Cov ntsiab lus phosphorus ntau dhau txo cov tawv nqaij, thaum leej faj tuaj yeem cuam tshuam cov khoom siv thiab vuam cov khoom. Yog li ntawd, impurities feem ntau yog tswj thaum lub sij hawm smelting txheej txheem los xyuas kom meej ruaj khov zoo thiab txhim khu kev qha siv carbon steel daim hlau.