Alloy steels such as 01, 4140, 4340 and 8620 are typically heat treated overnight if Atlantic Heat Treating gets a pick-up call before 10AM depending on size of components. This process can done in open air or vacuum furnaces according to Customer requirements. Note that an even greater surface hardness may be obtained by combining a standard heat treating process with a nitriding process which can be done with 4140 and H13 alloys. This category of steels also includes 1045 medium carbon steel and 1080 steels that may be used for springs.