Vacuum heat treatment offers an alternative method to traditional salt-bath and controlledatmosphere furnace hardening techniques for high strength steels, such as AISI 4340M and 300M. However, heat treaters must be prudent when choosing between oil and gas quenching for vacuum hardening of high strength steels, because each process has its advantages and disadvantages. High strength steel alloys, such as 4340M, 300M, and others, are most commonly used in the manufacture of landing gear components. These alloys are hardened and tempered to produce ultimate tensile strengths exceeding 280 ksi (1,930 MPa). By Jeff Pritchard and Scott Rush – VAC AERO International Inc., Oakville, Ontario, Canada
High strength steels based on the 43XX series are commonly used for aircraft landing gear components because of their desirable mechanical properties; these alloys are usually heat treated by quenching in oil from the hardening temperature, then tempered. During hardening, internal stresses created from the thermal shock of direct oil quenching almost always cause some degree of distortion in the heat treated component. Interrupted quenching techniques – such as ausbay quenching offer good potential for reducing quench distortion. However, due to the difficulty of machining these alloys in the hardened condition, machining allowances must be minimized. By Jeff Pritchard of VAC AERO International Inc., Oakville, Ontario, Canada.