CN1062025C - Production method for black-cored malleable cast iron - Google Patents

Abstract

The present invention discloses a producing method for malleable cast iron with a black core, which comprises a conventional producing technology for malleable cast iron with a black core. The producing method is characterized in that the limitation that the input amount of B can not exceed 0.004% is broken through, and the weight percentage of components of a used B-Bi-Al composite nucleating agent relative to molten iron is 0.004 to 0.006% of B, 0.007 to 0.01% of Bi and 0.008 to 0.012% of Al. Simultaneously, a new corresponding heat treatment technology is used for changing the original residual flaky pearlite of the inner texture of the product into granular pearlite, and the residual pearlite is smaller than 10%. Thus, the elongation rate of the malleable cast iron with a black core is greatly improved. The producing method has the characteristics of low production cost, high quality of the produced product and high elongation rate. All products produced by the producing method can reach the KTH350-10 standard.

Description

A kind of production method of black heart malleable cast iron

The present invention relates to a kind of production method of black heart malleable cast iron.

At present, use black heart malleable cast iron to step on iron plate as the builder's finish hardware standardized component, use it for climbing to a higher point of water tower, chimney and mark time or water drain, underground electricity is pulled, the marking time of the inspection chamber of underground gas pipeline, and has been a trend.Usually the standard as the black heart malleable cast iron of the usefulness of marking time is KTH350-10.But at present by this standard production black heart malleable cast iron be made as the usefulness of marking time step on iron plate the time, exist the not enough problem of unit elongation, in use often find to have the fracture microgroove.Its reason is, the product by this normal structure is produced exists unstable situation on unit elongation, and it is low that unit elongation reaches 10% yield rate, is no more than 50% usually.And the product that is lower than 10% unit elongation in use just the microgroove that ruptures may occur.This is a serious unsafe factor for as climbing to a higher point down low marking time.The input amount of boron can not surpass 0.004% of weight of molten iron in the regulation nucleating agent in the production method of existing black heart malleable cast iron, thinks to surpass the greying that 0.004% meeting hinders malleable iron, and just unit elongation not only can not get improving, and can reduce on the contrary.

The objective of the invention is to: a kind of production method of new black heart malleable cast iron is provided, and the material that it can improve black heart malleable cast iron greatly improves its unit elongation, and it is by the content that strengthens boron in the nucleating agent and adopts new thermal treatment process to realize.

Implementation of the present invention is as follows: it comprises the conventional production process of black heart malleable cast iron; Be characterized in: in the stokehold inoculated technology before cast, the nucleating agent of employing is boron-bismuth-aluminium composite inoculant; Each component of described boron-bismuth-aluminium composite inoculant with respect to the weight percent of molten iron is:

0.004%＜boron≤0.006%

0.007%≤bismuth≤0.01%

0.008%≤aluminium≤0.012%

Corresponding thermal treatment process is:

(1) green compact heating: 18～24 hours heat-up times, with blank heating to 940～980 ℃;

(2) insulation: kept 12～18 hours down at 940～980 ℃;

(3) cooling: blank temperature is reduced to 750 ℃～780 ℃, temperature fall time 2-3 hour;

(4) insulation once more: blank kept 22～26 hours down at 750 ℃～780 ℃;

(5) come out of the stove: blank temperature is reduced to 600 ℃～650 ℃, and it is empty cool to come out of the stove.

Compared with the prior art, nucleating agent used in the present invention has adopted corresponding with it new thermal treatment process simultaneously owing to broken through the qualification that former technology can not surpass weight of molten iron 0.004% on the input amount of boron.Make the product interior tissue change granular pearlite into, and residual pearlite is less than 10% by original remaining lamellar pearlite.Thereby improved the unit elongation of black heart malleable cast iron greatly.The black heart malleable cast iron that cupola furnace adopts the present invention to produce, the cupola furnace that can reach the U.S. add the highest trade mark 35018 standards in the ASTM standard that the duplex explained hereafter of main frequency furnace reached, and surpass Britain BS1247-75 standard.It is low that the present invention has a production cost, and the product material of production is good, the characteristics that unit elongation is high.Product by the present invention produces can absolutely reach the KTH350-10 standard.

Below the specific embodiment of the present invention is described in further detail.

Embodiment 1, will drop into the composite inoculant of being made up of boron, bismuth, aluminium before cast by the molten iron after KTH350-10 standard batching, the melting, each component with respect to the weight percent of weight of molten iron is:

0.004%＜boron≤0.006%

0.007%≤bismuth≤0.01%

0.008%≤aluminium≤0.012%

The input amount of boron, bismuth, aluminium if in above-mentioned scope all can, inoculation method is identical with the KTH350-10 standard.Behind the cast green compact, heat-treat by following step.

1. green compact are heated to 940 ℃～980 ℃ from normal temperature, the time is between 18～24 hours;

2. between 940 ℃～980 ℃, be incubated 12～18 hours;

3. through 2～3 hours cooling, make blank temperature reduce to 750 ℃～780 ℃;

4. between 750 ℃～780 ℃, be incubated 22～26 hours;

The air cooling of coming out of the stove when 5. making blank temperature reduce to 600～650 ℃ naturally.

The time value of heating, insulation, cooling and temperature value concrete the selecting in span with the same in the former thermal treatment process, determined according to the chemical ingredients of green compact.

The black heart malleable cast iron that adopts the present invention to produce can absolutely reach the 350-10 standard, and wherein 350-16 can reach 60%, and 350-18 can reach 20%, and 350-20 can reach 10%

Claims (1)

1, a kind of production method of black heart malleable cast iron, it comprises the conventional production process of black heart malleable cast iron; It is characterized in that: in the stokehold inoculated technology before cast, the nucleating agent of employing is boron-bismuth-aluminium composite inoculant; Each component of described boron-bismuth-aluminium composite inoculant with respect to the weight percent of molten iron is:

0.004%＜boron≤0.006%

0.007%≤bismuth≤0.01%

0.008%≤aluminium≤0.012%

Thermal treatment process is:

(1) green compact heating: 18～24 hours heat-up times, with blank heating to 940～980 ℃;

(2) insulation: kept 12～18 hours down at 940～980 ℃;

(3) cooling: blank temperature is reduced to 750 ℃～780 ℃, temperature fall time 2-3 hour;

(4) insulation once more: blank kept 22～26 hours down at 750 ℃～780 ℃;

(5) come out of the stove: blank temperature is reduced to 600 ℃～650 ℃, and it is empty cool to come out of the stove.