SAE 4140 steel introduction

What is 4140 steel?
4140 steel is a Chromium-Molybdenum through-hardening steel of medium hardenability. It is a general purpose high-tensile steel with medium strength level and good impact properties. Similar to sae 1045 steel grade and sae 5140 steel grade, the y are all medium carbon steel.
The difference between sae 1045 steel material and sae 4140 steel material:
SAE 4140 steel has alloy element, it is kind of alloy steel bar. After heat treatment, sae 4140 steel material can get between mechanical properties.
SAE 5140 vs SAE 4140:

SAE4140 steel grade has better hardenability than sae 5140 steel material. After quenching and tempering, sae 4140 can be whole pre hardened from core to side.