CN88101145A

CN88101145A - Improved method of heat treating ferrous alloys

Info

Publication number: CN88101145A
Application number: CN198888101145A
Authority: CN
Inventors: 威廉姆·H·莫里; 阿里·莱托南
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-03-06
Filing date: 1988-03-05
Publication date: 1988-09-14
Also published as: FI880858A0; JPS63317620A; DK68788D0; FI880858A; DK68788A; EP0281249A1

Abstract

A kind of improvement of Ovshinsky drawing process, former way comprise to be transferred to foundry goods the groove of receiving liquid medium in the Ovshinsky stove.In the process of having improved, replace foundry goods and adopt jet to cool off on the spot, promptly finish Ovshinskyization and Ovshinsky drawing process with same stove such as empty G﹠W.

Description

The present invention relates to cast iron or steel heat-treating methods, more particularly, it relate to a kind of produce bainite structure and improve machinery and physical property improvement treatment process.

As everyone knows, cast iron or steel can be from condition of high temperature austenitic structure, replace austenite to suppress normal pearlitic formation and the martensite rate of cooling cools down.Austenite and martensite under room temperature, are stable when low temperature.We also know, selected keep for some time as cast iron or steel under higher Ovshinsky temperature and the temperature between the room temperature one, if perlite light is suppressed, then replace the formation bainite structure again.This bainite can hold the perlite of inequality, austenite or martensite, and this depends on the definite recurrent cooling conditions and the definite composition of cast iron or steel.

The process of this bainite that is produced by thermal treatment is called austempering.Conventional operation comprises cast iron or steel be heated to and surpasses 1300 °F and make it become austenitic structure.This temperature is called the Ovshinsky temperature.For practical purpose, this Ovshinsky temperature remains on 1900 maximum fully, each inch foundry goods time is generally 1 hour adds 30 minutes, and this time is also depended on the total mass of cast iron under the stove load to a certain degree and adds the interior heat of stove.Cast iron or steel are quickly cooled to changeless temperature then, promptly are called the Ovshinsky temperature, usually between 400 °F to 800 °F.Kept under this temperature 1 to 4 hour, it depends on the quality and the composition of foundry goods.Cast iron or steel cool to room temperature more then.

Austempering makes it can maintain the austempering temperature in hot salt or deep fat or liquid medium groove usually.Cast iron or cast steel section bar take out in the stove under austenitizing temperature to be put into the austempering groove and quenches.This class is handled and is related to two furnace systems and cast iron and steel hot profiles, such as forging or foundry goods, transfer.In addition, behind cool to room temperature, foundry goods or forging must clean to remove the vestige of remaining salt or used quenchant.Because salt bath is very expensive, usually the foundry goods of doing austempering under the conventional state or the size of section bar are limited to some extent.

We have found a kind of method, and the thermal treatment that can make requirement produce martensitic structure in cast iron or steel with it is carried out in a stove and need not be immersed fluidized bed patenting medium or salt bath.

Our Fang Ming is based on this invention, be that the available trickle water or the jet of gaseous media such as liquid nitrogen or carbonic acid gas directly are incident upon foundry goods or the forging that is in the stove, these foundry goods or forging are cooled down, and stove self also can be cooled to the austempering temperature.This has just been avoided foundry goods or forging are transferred to the necessity of carrying out austempering in second stove.

So one of purpose of the present invention is to reduce the cost of austempering process.

Another purpose provides the device of only finishing the austempering process with a stove.

Also having a purpose is to make large-scale foundry goods or forging can carry out austempering economically.

The patent right of other purpose file proposition from then on requires and understands from the description of a preferential embodiment of the present invention and with accompanying drawing with will be apparent from, and these accompanying drawings are:

Fig. 1 is the synoptic diagram of the preferential process that adopts of the present invention.

Fig. 2 is the cooling curve of typical time and temperature in the process after the process describing to use in the past and the present invention improve.With

Fig. 3 is that the spheroidal graphite cast iron piece adopts the cooled photomicrography of process of the present invention.

Circulate and cool off stove and foundry goods load and arranged by the HEAT TRANSFER LAW of complexity with containing saturated steam or cold air in the air, it relates to specific heat of water, vaporization heat and be used for the specific heat of round-robin air or gas.Our be willing to water and steam requires to suppress to form pearlitic quick and cheap cooling because of it can provide in process of cooling.

Know the people of this respect technology for those, can understand at once, it is a very big problem that stove itself is cooled to the austempering temperature from the Ovshinsky temperature, and it relates to the heat that is comprised by the stove refractory materials.The conventional refractory materials that is used for the inner lining of furnace pad is owing to have huge thermal capacity and owing to require quick cooling to cause cracked and can go wrong.

For this reason, we more prefer to use the stove of making liner with refractory fibre, and this material weight is light, and having Jue Re And can unlikely damage under temperature changes fast.

In the preferential embodiment of process of the present invention, stove rises to and places on the foundry goods or recede so that foundry goods is come out.Can more easily cool off stove and cooling foundry goods like this.In case stove and foundry goods have reached desired austempering temperature, stove just descends or tumbles and return to cover on above the foundry goods, and the temperature of stove maintains the austempering temperature levels in the desirable timed interval then.

Whole by this way austempering process can mobile foundry goods or second stove of needs.

Fig. 1 is the synoptic diagram that the present invention preferentially adopts method.Position (A) expression stove has comprised the Zhu spare And and the stove that are placed on the stove base plate and has been in the Ovshinsky state in the lump.Position (B) has represented that stove is in as-quenched condition towards hypsokinesis to realize cold but And.Position (c) expression stove is got back to original position on foundry goods, and foundry goods is in the austempering state.

Fig. 2 shows the temperature-time cooling curve of a typical given foundry goods, is that a diameter is 3 inches a iron block in this example, immerses a salt and bathes And and then be placed in one to produce bainite.Also showing a curve shows and ought handle the rate of cooling the when air cycle of foundry goods and stove is cooled to the austempering temperature to foundry goods for water in stove.We find, for the control of water consumption and return air quantity the rate of cooling in the foundry goods are changed in relative wide cooling range.

In Fig. 2, the rate of cooling that the curve A representative obtains in salt bath, the CC line is the Ovshinsky temperature line, the DD line is the austempering temperature line that reached in 10 minutes.The curve B representative is worked as air at the stove internal recycle and to the rate of cooling under the situation of foundry goods water.In this case, in 12 minutes, just can reach the austempering temperature.

Fig. 3 illustrates a spheroidal graphite cast iron piece and handles resulting bainite structure with speed water-cooled shown in Figure 2.

By 12 diameters 2 " to 4 " length is 24 " load of differing in size places 3 ' * 4 ', height is 4 ' stove in.This stove lining is supported in dorsal part with the anti-fiery material material And of fibering with the hinge form, so it can place the foundry goods on the fixed floor to topple over backward certainly.Stove has a series of propane-air burner as thermal source.

Stove load is broken to be heated to 1650 ° of F And and to close propane flammable gas kept 2 hours under this temperature, and the stove hypsokinesis is to expose the foundry goods load then.When the stove hypsokinesis, air blows air so that it be cooled to 620 °F with an additional fan to stove from burner circulation ， And.

Directly blow air with fan to foundry goods, and with high-pressure spray inject water with direct impact in the foundry goods load, a thermopair crucially places in the foundry goods load, be used to refer to the moment that this load reaches the temperature that roughly is 600, stove after cutting off air and water cycle inclined back and covered foundry goods this moment.

Stove is kept 620 temperature 2 hours, and the foundry goods load is shifted out in stove then.

Afterwards, several iron block Bei Qie Cheng Pian And place microscopically.Find that these iron blocks have the structure based on the Bei Shi structure, in heavier iron block, keep austenite 15-20% and in lighter iron block, keep austenite 20-35%.

The fluidic temperature that is used for foundry goods colony, speed and quantity will determine rate of cooling, this for those technical familiar people clearly or be easy to determine, this speed must satisfy at 10 to 12 minutes internal cooling foundry goods to avoid pearlitic formation, therefore can obtain desired bainite.Determine definitely for special metal usable time-temperature transition figure although the desired rate of cooling of inhibition perlite changes ， And according to the composition that participates in ferrous metal, yet be generally less than 20 minutes desired cooling time.

We have done similar test, promptly blow to the air on the foundry goods with cooled with liquid nitrogen and place in the foundry goods load with carbonic acid gas dry ice, yet in general, we find that water and air is easy to use and control.Rate of cooling is quickened with discharge in this case.

We also find the particulate of cold metallic steel fines or steel is added in the foundry goods load that is cooled, and will quicken the cooling of foundry goods load, yet in general, we would rather use freezing air and water as heat-eliminating medium.

We have described the present invention with a special example, yet will recognize that some corrections and change all can adopt not departing under spirit of the present invention and the category.This class is that conspicuous change and revise is all thought at authority of the present invention and category so that within the scope that appended patent right requires to those technical familiar people.

Claims

1, a kind of method of ferrous castings austempering, it is characterized in that placing in this method the foundry goods in the stove under the Ovshinsky temperature, to be cooled with above-mentioned stove, be cooled to the austempering temperature, foundry goods keeps the austempering temperature in this same stove then always.

2, in the process of austempering black casting, it is characterized in that utilizing a kind of material or several material in above-mentioned foundry goods and not with above-mentioned foundry goods from the Ovshinsky temperature action is cooled to austempering temperature with above-mentioned foundry goods from the Ovshinsky temperature in the method that the stove transfer of above-mentioned foundry goods is shifted out.Above-mentioned used material or several material under such temperature and the quantity with above-mentioned foundry goods under enough short time internal cooling in above-mentioned foundry goods, to produce the Bei Shi structure.

3, the desired process of claim 2 is characterized in that above-mentioned material or multiple material are a kind of fluid or multiple fluid.

4, the desired process of claim 3 is characterized in that the above-mentioned fluid of indication or multiple fluid are to elect from the combination of being made of empty G﹠W.

5, the desired process of claim 3 is characterized in that at least one class in above-mentioned fluid and the multiple fluid acts on above-mentioned foundry goods by a pressure jet.

6, a kind of method of austempering ferrous castings may further comprise the steps:

(a) above-mentioned foundry goods is placed in the stove.

(b) above-mentioned foundry goods is heated to the Ovshinsky temperature,, is lower than 1900 °F promptly greater than 1300 °F.

(c) above-mentioned foundry goods was remained on above-mentioned Ovshinsky temperature 1-8 hour, it depends on the section of foundry goods.

(d) use the heat-eliminating medium water and air, so above-mentioned foundry goods and above-mentioned stove all are cooled to 300 to 800 austempering temperature being less than in 20 minutes.

(e) above-mentioned foundry goods is retained in the above-mentioned stove 1-5 hour under above-mentioned austempering temperature, then

(f) above-mentioned foundry goods is taken out from above-mentioned stove.