CN102071297A - Sub-high-temperature treatment method for gray cast iron - Google Patents

Abstract

The invention discloses a sub-high-temperature treatment method for gray cast iron. The heating temperature is between the lower limit temperature and upper limit temperature of Ac1. The method comprises the following steps: firstly, putting gray cast iron castings in a heating furnace, and heating in the heating furnace from the furnace temperature lower than 200 DEG C to 790-810 DEG C at the heating rate of 95-110 DEG C/hour; then, keeping the temperature for 2-4 hours; taking out the castings, and carrying out furnace cooling to the temperature lower than 300 DEG C at the cooling rate of lower than 50 DEG C/hour; and finally, taking out the gray cast iron castings, and cooling in the air to normal temperature. The treatment method disclosed by the invention is realized between high-temperature graphitizing annealing and low-temperature graphitizing annealing; on the premise of improving the cutting property of the castings, the invention also ensures that the properties of the gray cast iron casting structure are not influenced by massive accumulated graphite; and meanwhile, the invention is also applicable to the gray cast iron castings of which the properties can not achieve the requirements after high-temperature graphitizing annealing.

Description

A kind of grey cast iron Ya Rewen treatment process

Technical field:

The present invention relates to the thermal treatment field, relate in particular to a kind of grey cast iron Ya Rewen treatment process.

Background technology:

At present, the annealing heat treatment process about grey cast iron mainly concentrates on stress relief annealing, low-temperature graphitization annealing and high-temperature carbonization annealing.The purpose of graphitizing annealing is to make that cementite is decomposed into graphite and ferrite in the cast iron.The theoretical basis of graphitizing annealing: calculate according to mutually stable free energy, cementite is Jie's stable phase in the cast iron, and graphite is stable phase, and the stability of cementite when low temperature is lower than high temperature.Therefore see that from thermodynamic (al) angle cementite can be decomposed into graphite and iron carbon sosoloid under arbitrary temperature, and at low temperatures, ooze body decompose easier.But can graphitizing process carry out, and also depends on the forming core of graphite and the kinetic factors such as diffusibility of carbon.For solid-state phase changes, can the diffusion couple phase transformation of atom play an important role.Because when temperature was higher, the diffusion ratio of atom was easier to, so the decomposition of cementite only just might be carried out when temperature is higher.When Heating temperature was lower than 550 ℃, cementite did not decompose, and THE STRUCTURE OF CASTINGS does not change, and when Heating temperature is higher than 550 ℃, cementite begins to change, and generated graphite and ferrite.Discuss according to the front, in fact only when Heating temperature surpassed 720 ℃, cementite could effectively decompose, but because the diffusion of graphite can not effectively be carried out, had hindered the further decomposition of cementite.

Find aborning, (100 ℃/h is heated to 700 ℃ when adopting low-temperature graphitization annealing technology, come out of the stove after cooling to 300 ℃ after the insulation with the furnace) insulation 2 hours after, the white structure of foundry goods obtains a part to be improved, and after being incubated 4 hours, the white structure of foundry goods still has residual greatly, when soaking time extends to 6 hours, the white structure of foundry goods is a large amount of minimizing the because of holding time prolonging not, this just causes the difficulty of mechanical workout, the follow-up water test, 15712 pump housing qualification rates 98%; (100 ℃/h is heated to 920 ℃ when we adopt high-temperature carbonization annealing technology, come out of the stove after cooling to 300 ℃ after the insulation with the furnace) be incubated 2 hours, all white structures change the ash mouth into, 15712 pump housing qualification rates are lower than 50% during the water test, the technology soaking time changes 1 hour into, all white structures change the ash mouth into, and water test qualification rate still is lower than 50%.

Therefore, when there is a certain amount of white structure in the grey cast iron foundry goods, the Heating temperature of foundry goods should be higher than the Ac1 lower limit, and the Heating temperature of high-temperature carbonization annealing is to be higher than the Ac1 upper limit, when being higher than Ac1, Heating temperature goes up in limited time, the carbon atom rate of diffusion is too fast, can't control the accumulation of graphite by soaking time, so just cause the bulk deposition of graphite when high temperature, and then the continuity of destruction foundry goods, reducing every mechanical property of part, and the destruction of the continuity of foundry goods and tightness, is critical defect for the stopping property of pressure-bearing foundry goods.

In high-temperature carbonization annealing and low-temperature graphitization annealing, be named as Ya Wen (Ya Rewen) annealing between the present invention, when improving foundry goods smear metal performance, having guaranteed also that foundry goods is not organized is influenced its performance by a large amount of accumulative graphite.

Summary of the invention:

The purpose of this invention is to provide a kind of grey cast iron Ya Rewen treatment process, be applicable to the grey cast iron foundry goods that produces certain white structure, what be specially adapted to be similar to the non-assembly pump housings such as 15712 models bears the hydraulic pressure foundry goods, be applicable to high-temperature carbonization annealing in addition after performance can not meet the requirements of castings of gray cast iron.

Technical scheme of the present invention is as follows:

A kind of grey cast iron Ya Rewen treatment process, it is characterized in that: Heating temperature specifically may further comprise the steps between Ac1 lower limit temperature and ceiling temperature:

(1) the grey cast iron foundry goods is put into process furnace, and process furnace is lower than 200 ℃ from furnace temperature and begins heating, makes furnace temperature be heated to 790 ℃-810 ℃ with the rate of heating of 95 ℃/h-110 ℃/h;

(2) grey cast iron is incubated 2-4h for 770 ℃-820 ℃ in envrionment temperature in process furnace;

(3) after the grey cast iron foundry goods was incubated 2-4h in process furnace, it is cold that stove is carried out in taking-up, is cooled to below 300 ℃ with the speed of cooling that is lower than 50 ℃/h.

(4) stove cold after, the grey cast iron foundry goods that is cooled to below 300 ℃ is taken out, air cooling is to normal temperature.

Advantage of the present invention is:

Heating temperature of the present invention is between Ac1 lower limit temperature and ceiling temperature, promptly in high-temperature carbonization annealing and low-temperature graphitization annealing, when improving foundry goods smear metal performance, having guaranteed also that the grey cast iron foundry goods is not organized by a large amount of accumulative graphite influences its performance, also be applicable to high-temperature carbonization annealing simultaneously after performance can not meet the requirements of castings of gray cast iron.

Description of drawings:

Fig. 1 is process curve figure of the present invention.

Embodiment:

A kind of grey cast iron Ya Rewen treatment process, it is characterized in that: Heating temperature specifically may further comprise the steps between Ac1 lower limit temperature and ceiling temperature:

(1) the grey cast iron foundry goods is put into process furnace, and process furnace is lower than 200 ℃ from furnace temperature and begins heating, makes furnace temperature be heated to 790 ℃-810 ℃ with the rate of heating of 95 ℃/h-110 ℃/h;

(2) grey cast iron is incubated 2-4h for 770 ℃-820 ℃ in envrionment temperature in process furnace;

(3) after the grey cast iron foundry goods was incubated 2-4h in process furnace, it is cold that stove is carried out in taking-up, is cooled to below 300 ℃ with the speed of cooling that is lower than 50 ℃/h;

(4) stove cold after, the grey cast iron foundry goods that is cooled to below 300 ℃ is taken out, air cooling is to normal temperature.

Additional instruction: soaking time can be determined according to casting section thickness, spoken parts in traditional operas degree and batch, the experimental formula t(min that obtains by the several testing data according to the experimenter)=60min+2.5H calculates soaking time, in the formula: H is the wall thickness of part (grey cast iron), unit: mm; 2.5 experience factor, unit: min/mm.H in the formula is generally 24-96mm, and the wall thickness of part is mostly in this scope.

Claims (1)

1. grey cast iron Ya Rewen treatment process, it is characterized in that: Heating temperature specifically may further comprise the steps between Ac1 lower limit temperature and ceiling temperature:

(1) the grey cast iron foundry goods is put into process furnace, and process furnace is lower than 200 ℃ from furnace temperature and begins heating, makes furnace temperature be heated to 790 ℃-810 ℃ with the rate of heating of 95 ℃/h-110 ℃/h;

(2) grey cast iron is incubated 2-4h for 770 ℃-820 ℃ in envrionment temperature in process furnace;

(3) after the grey cast iron foundry goods was incubated 2-4h in process furnace, it is cold that stove is carried out in taking-up, is cooled to below 300 ℃ with the speed of cooling that is lower than 50 ℃/h;

(4) stove cold after, the grey cast iron foundry goods that is cooled to below 300 ℃ is taken out, air cooling is to normal temperature.

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