AISI 4145 is a chromium molybdenum alloy steel grade widely used in the oil and gas sectors.Similar to AISI 4140 but with a higher carbon content. 4145 is more popular in larger diameters due to its increased strength and hardenability. AISI 4145 is commonly supplied quenched and tempered with a hardness of between 30 to 36HRc.AISI 4145H is a chromium – molybdenum low alloy tempered steel.AISI 4145H has improved hardenability and is more is commonly used in the high strength condition with min.110 KSI yield. Similar to AISI 4140 but with a higher carbon content. 4145 is more popular in larger diameters due to its increased strength and hardenability.