The first sequence, in which the austenitizing
temperature was 850[degrees]C, the soaking time was 100 s and cooling took place at 16[degrees]C/s, ending at the quenching temperature of 150[degrees]C, produced a martensitic-bainitic microstructure with a hardness of 716 HV10 (Fig.
It is hardening, the combination of austenitizing
above the upper critical (austenitic transition) temperature and rapid cooling, that forms martensite.
To accomplish these structural changes in tool steels, four primary heat treating steps are used: preheating, austenitizing
, quenching, and tempering.
Vacuum heat treatment, followed by gas quenching, has been found to be the optimum austenitizing
presence of lower carbon content in austenite from base metal compare to weld metal is considered to be responsible for lesser amount of retained austenite in base metal after austempering.
and tempering times are 30 minutes and 120 minutes, respectively.
The proposed heat treatment for grade AISI 422 is: a) austenitizing
to temperature 1000-1050[degrees]C for 60 min and quenching in oil; b) tempering in the temperature range of 200-300[degrees]C for 60 min for achieving high tensile strength and fair toughness and second tempering in the range of 600-700[degrees]C for 60 min is preferred for getting fair strength with high toughness which should be carried out carefully .
After analysing the results, a schedule with reduced austenitizing
time of 15 seconds was designed (H15-1).
The castings are heat treated per the ASTM A958 specification (1,700F austenitizing
, water quench and 1,150F temper cycle).
, care must be taken to avoid carburization or decarburization by carefully monitoring the heat-treating atmosphere.
% after room temperature quenching from the austenitizing
temperature of 1050[degrees]C.
During hardening the steel is heated up to austenitizing
structure then is cooled in oil.
Variable parameters include austenitizing
temperature, grain size and lowest volume fraction percentage of the phase detected.
The section size and chemical composition of the casting will determine the time and temperature for austenitizing
. The goal is to achieve an austenitic matrix with a uniform carbide content.