Heat treatment process of several common stainless steel forgings

(1) Austenitic stainless steel

① Solid fusion treatment: heat to the solid fusion temperature (1050-1100 ℃), make all carbides and martensite formed by cold working melt and transform into austenite, and then rapidly cool. This heat treatment can obtain the softest and highest plasticity effect.

② Stress relaxation treatment: the mechanical properties can be improved by eliminating the internal stress (275-450 ℃, 0.5-2h).

③ Stabilization treatment: heating to 900 ℃, melting most of chromium carbide, so that chromium carbide no longer precipitates in the intergranular.

④ Treatment of eliminating σ - phase: in the case of high chromium austenitic stainless steel with insufficient nickel, σ - phase may be produced during heat treatment of stainless steel forgings, which will reduce the impact toughness of the steel. Therefore, the formation temperature of σ - phase (500-970 ℃) should be avoided during heat treatment.

Heat treatment process of several common stainless steel forgings

(2) Martensitic stainless steel

The commonly used heat treatment of martensitic stainless steel includes annealing, quenching and tempering.

After annealing, the structure is chromium rich ferrite with low mechanical properties and poor corrosion. Therefore, this kind of steel is used after quenching and tempering in most cases.

Due to the different requirements of various forgings for performance, the tempering heating temperature is not the same.

Forgings that need to bear impact load shall not be tempered within 370-600 ℃.

(3) Ferritic stainless steel

The structure of the annealed ferritic stainless steel is basically ferritic with a little carbide. It has good plasticity and corrosion resistance, but its strength is not high, and its welding and forming properties are good.

There is no phase transformation in the ferrite stainless steel. Therefore, the only heat treatment is recrystallization annealing.

The purpose of recrystallization annealing is to remove the stress and to stabilize the structure. The recrystallization annealing temperature is usually in the range of 700-800 ℃, and then cooled in air.

(4) Precipitation hardening stainless steel

The heat treatment of precipitation hardening stainless steel forgings includes three processes: solidification treatment, adjustment treatment and aging treatment.

Solid fusion treatment: the treatment process is 1000-1030 ℃, LH, air cooling. The obtained structure is austenite with a small amount of ferrite.

Adjustment treatment: the purpose of adjustment treatment is to obtain a certain amount of martensite, so that the steel can be strengthened.

Aging treatment: it is another way to strengthen precipitation hardening stainless steel. When the aging temperature is higher than 400 ℃, the intermetallic compounds will be precipitated from the martensite, which will be highly dispersed and play the role of precipitation hardening. Generally, high hardness and strength can be obtained by aging at 500 ℃.

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