AISI / Alloy Steel 4135

Chemical Analysis
C% Carbon
0.33 – 0.38
Mn% Manganese
0.70 – 0.90
P% Phosphorus
0.040 max
S% Sulfur
0.040 max
Si% Silicon
0.20 – 0.35
Cr% Chromium
0.80 – 1.10
Mo% Molybdenum
0.15 – 0.25

General characteristics of Alloy Steel 4135

Alloy steel 4135 is a low-alloy steel containing chromium and molybdenum as strengtheners. The alloy is capable of being heat treated to good strength levels while maintaining reasonable toughness.


This alloy finds applications in the aerospace, oil and gas, auto and defense industries. It is used in the production of forged shafts, spindles, fixtures, jigs and collars.


AISI 4135 grade alloy steel is forged at a temperature of around 2200ºF (1205ºC) and could be forged down to a temperature of approximately 1700ºF (925ºC). The alloy may be slow cooled after forging or transferred to a furnace held at what may be the finish forging temperature. Such a treatment would in fact amount to a type of annealing treatment.

Heat treatment

Annealing:For optimum machinability, this grade of steel should be annealed to give a microstructure of coarse pearlite with a minimum of ferrite. From an austenitizing temperature of 1575ºF (855ºC) the steel is cooled to 1400ºF (760ºC) then to 1230ºF (665ºC) at 35ºF (19ºC) per hour, or to 1250ºF (675ºC) and holding for 4 hours, for an iso-anneal. In both cases the final step is an air cool.


This steel is normalized at 1600ºF (870ºC) followed by air cooling.


The steel will be austenitized at 1550 – 1600ºF (845 – 870ºC) followed by water or oil quenching, depending upon size and intricacy of section.


The steel will be tempered at temperatures to meet required mechanical properties, based on past experience.


This grade is readily machinable following correct and appropriate heat treatment.


The steel may be welded by normal fusion methods, but only in the annealed or normalized conditions. The steel should not be welded following harden and temper operations. Pre-heat and post-heat may be required, as per past experience.

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