Chemical Analysis
C% Carbon
0.35 – 0.40
Mn% Manganese
0.70 – 0.90 max
Si% Silicon
0.20 – 0.35
P% Phosphorus
0.035 max
S% Sulfur
0.040 max
Mo% Molybdenum
0.20 – 0.30

General characteristics of Alloy Steel 4037

Alloy steel 4037 is a direct hardening, molybdenum-bearing engineering steel that may be readily forged, machined and welded.


This grade may be forged into parts for the aerospace industry, for example landing gear parts, and for shafts and collets for the oil and gas industry.


The alloy should be forged at 2250ºF (1230ºC) and forging should preferably be finished at a temperature above 1700ºF (925ºC).

Heat treatment


For optimum machinability, this alloy should have a microstructure that is primarily coarse pearlite, with a minimum of ferrite. This would involve annealing at 1525ºF (830ºC) and slow furnace cooling.


A typical normalizing temperature for 4037 forgings is 1600ºF (870ºC), but based on production experience this temperature may vary from 100ºF (38ºC) above to 50ºF (10 ºC) below this figure. If normalizing is carried out before a hardening and tempering treatment, then the upper temperature range is used; if normalizing is the final treatment then the lower range is used.


The austenitizing temperature used for this grade is in the range 1525- 1575ºF (830-860ºC). Quenching will be in oil or water, depending upon the section size and the complexity of the part being treated. A qualified heat treat operation should be consulted to obtain a detailed heating, soaking and quenching procedure.


The tempering temperature – and time – will of course determine final hardness figures, but a typical 4037 alloy will give a hardness of Rc52 after 1 hour at 400ºF (205ºC) and a hardness of Rc25 after 1 hour at 1200ºF (650ºC).


Machining of this alloy is best done with a microstructure of coarse pearlite, which will be obtained by following the annealing procedures described above. Any finish machining to be done on say a hardened and tempered part should be undertaken following professional advice or according to experience.


This grade may be welded by fusion or resistance methods. Preheating and post-weld stress relief are advised. Welding in the hardened and tempered condition may result in loss of required mechanical properties in the weld and heat-affected zones.

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