All steel works like this the first two numbers are the , and the second is the carbon content percentage . You ' re using the exact same steel , 41 xx , with . 4 % carbon instead of . 3 %. Carbon content in steel can go up to 2 %, anything greater than this is cast iron . The grain structure will still be largely pearlitephasediagramespv 2 biw 1920 bih 950 tbmischimgil 1 LKJh 1 ljdH 7 IM % 253 A % 253 BuoMZsGOgJ 9 PmQM % 253 Bsourceiupfmfir 1 LKJh 1 ljdH 7 IM % 253 A % 252 CuoMZsGOgJ 9 PmQM % 252 CusgG 6 KFJuRBZrG 7 i 2 OORFRDOkY % 3 Dved 0 ahUKEwi 7 tc 39 nsPQAhWCKyYKHRLZA 2 EQyjcIMweiHtU 3 WLuuKYLXmAGSsoIBg # t b m i s c h q s t e elcarbonphasediagramimgrc 7 XqykQpWn 3 jLxM % 3 A . You shouldn ' t see any welding problems . The 4140 can become slightly harder , because that is what carbon does in steel , but ultimately you should have no problem welding what is , in essence , exactly the same thing together .