STEEL MADE THEREBY

FIELD OF THE INVENTION

The present invention relates to a method of alloying cast steel with sulphur in a sand mould for making the high sulphur cast steel, and High Sulphur Cast Steel, the antifriction and wear resistance material that has high impact value and doesn't include any expensive alloying elements.

BACKGROUND OF THE INVENTION

In Chinese patent No.CNl 01643815A titled "The method of alloying sulphur in the smelting process of High Sulfur Stainless Steel" the method of alloying sulphur using the ferrous sulfide ore that is used in production after baking was introduced, but the process is complicated and the emission of sulphur from the ferrous sulfide ore in baking process was not mentioned.

In Chinese patent No.CN l 068858 A titled "High Sulfur alloy steel and its preparation" it was only mentioned that the content of sulphur is 0.5 to 1 1 % in the high sulphur alloy steel and it is a steel which is alloyed with Mo, W or Mn but no other data relating to material such as its mechanical and processing properties, chemical properties, maximum permissible pressure [p], maximum permissible linear velocity [v] or permissible [pv] except for its abrasion resistance were given.

In Chinese patent No.CNl 644748A titled "High-Sulphur abrasion-resistant casting steel and production thereof it was suggested the high sulphur cast steel that is composed of S 1 .2 to 6.3% and has self-lubricating and sliding properties by alloying it with 4-7 elements among the ones in certain content such as S 1.2 to 6.3%,C 0.25 to 2.3%, Cr 0.95 to 7.0%, Al 0.7 to 1.6%,Si 0.5 to 1.5%, Mo 0.1 to 2.6%, W 0.6 to 1.6%, Ni 0.8 to 1.8%, V 0.6 to 1.4%, Cu 0.2 to 1.0% and P 0.03 to 1.2%. But many expensive alloying elements are used in production and it is very limited of application because its impact value; 0.06 to 0.08 MJ/m ² is very low.

In the above documents the methods of alloying sulphur are just the same, in which ferrous sulfide ore is put in a furnace and melted in it.

In case of applying these methods the composition of sulphur may be adjusted, but the emission of harmful gases such as sulfurous gas, hydrogen sulfide and etc. can't be cut in the process of melting ferrous sulfide ore in furnace and the pollution of furnace by sulphur, which may affect the melting for the next charge, can't be prevented.

And it is difficult to adjust exactly the composition of sulfur because the duration of melting that depends on the shape of scrap steel charged in furnace is increased or reduced whether the shape of crap steel is shape of lumps or shape of plate.

Consequently, these methods couldn't be industrialized because of causing the pollution of furnace and environment, the difficulty to adjust exactly the composition of sulphur. So they developed the method of alloying steel with sulphur in the casting mould. As regards the methods introduced in Chinese patent No.CN 1068858A and Chinese patent No.CN1644748A, the content of sulphur inside steel is very high and it reduces the impact value inevitably.

Most of sliding bearings usually work in very heavy shocks, and the material can widely apply to it in industry as long as its impact value is as high as the one of copper alloy.

And the alloying elements; Mo and W, is transformed into MoS ₂ and WS ₂ , the excellent solid lubricants, in the process of production, but, when FeS is contained inside the steel that is made through the smelting and casting process MoS ₂ and WS ₂ inside steel become into solid-solution of FeS.

Consequently MoS ₂ and WS ₂ can't work as solid lubricants independently and the antifriction and wear resistance properties are similar to the ones when FeS works alone.

So MoS ₂ and WS ₂ don't much affect the antifriction and wear resistance properties. And thus, we developed the material that has better mechanical properties and antifriction and wear fesistance ones than the copper alloy's ones by adjusting the proper composition of other alloy elements; S, C and Mn inside steel.

The object of the present invention is to alloy cast steel with sulphur in a reaction chamber which is particularly set up in a sand mould and to produce High Sulphur Cast Steel, the antifriction and wear-resistance material which doesn't include any expensive alloy materials and has high impact value.

SUMMARY OF THE INVENTION

The present invention relates to a method of alloying cast steel with sulphur in a sand mould for making the high sulphur cast steel, and to produce High Sulphur Cast Steel, the antifriction and wear resistance material that has high impact value and doesn't include any expensive alloying elements.

The melting and boiling temperatures of sulphur are 119°C and 445°C respectively and its affinity with oxygen is very strong.

Besides, the specific gravity of sulphur is very smaller than one of iron.

Therefore, it is difficult to be absorbed in molten steel as it is changed into sulfurous gas or hydrogen sulfide in an instant on the condition that the air exists, and escapes into air.

That's why it is very difficult to make molten steel contain sulphur.

Industrial sulphur that is out of moisture is used.

The thin chips of cast iron are used. If they use thick ones, they have to crush them into the particles with grain size smaller than 3 mm.

And the moisture, oil and dirt in the chips of cast iron must be removed.

The essential point of the present invention is to set up a reaction chamber in a sand mould. (Fig. l)

The reaction chamber is set up at the bottom of spout as shown in Fig.1.

The top and bottom section of the chamber is shape of rectangle and the vertical section is shape of trapezium.

This is for making molten steel flow in it as slowly as possible so that the chips of cast iron are not dug and it is for removing the slag when molten steel flows out.

Then proper quantity of sulphur is put and equally spread in the reaction chamber and some chips of cast iron are covered over it.

The thickness of the layer of the chips of cast iron is below than 3 to 16mm.

The height of the top side of the reaction chamber from the chips surface is above 3 to 20 mm.

The reaction chamber is set up in the downward mold, and the article of the cast steel and ingate system are made in the upward mold.

A sand mould is used.

After the upward mold and the downward mold are assembled, molten steel is poured. Molten steel that has arrived at the reaction chamber does not react with sulphur due to the chips of cast iron and begins to fill in the space of the article of cast steel through the reaction chamber.

After the molten steel fill in to a certain extent the chips of cast iron are melted and sulphur reacts with molten steel without any contact with the air.

Sulpur is soon evaporated in the high temperature above the boiling point of the sulphur 445°C. The temperature of evaporated sulphur arises to the one of molten steel and the partial pressure suddenly increases.

By this high pressure sulphur is equally contained all over the molten steel.

The whole process above is done in an instant.

After all, sulphur is safely absorbed into molten steel.

The absorbing rate of sulphur is 92-98%.

The coefficient of friction of the high sulphur cast steel made in this method is 0.006 to 0.009 under the liquid lubricating condition, its abrasive quantity is 1/7 to 1/10 of copper alloy and the damage to an axis is almost equal or less in comparison with copper alloy.

The tensile strength is 340 to 470MPa, the elongation percentage is 8 to 15%, the impact value is 0.20 to 0.30 MJ/m ² and the hardness is 105 to 150HB.

As the result of the field test, the lifetimes of various sliding bearings are 3 to 7 times longer than the one of copper alloy.

Table 1.The result of the field test

Its chemical composition is C 0.14 to 0.38%, Si 0.17 to 0.37%, Mn 0.1 to 0.5%, P 0.03% or less, and S 0.5 to 3.8%.

The amount of Mn should be as little as possible. Sulphur first makes a compound with Mn if there is Mn because its affinity with sulphur is stronger than Fe.

Then, the amount of a solid lubricant is decreased as the amount of iron sulfide is relatively decreased. And Mn makes the sulfide edged.

The content of C is set little in order to strengthen the impact value.

The experiment to determine the permissible specific pressure and linear velocity performed in a wear tester of IHW-2 type.

The result of the experiment is shown below.

The result of the experiment to determine [P] and [V]

In the experiment the linear velocity was measured at the moment the coefficient of friction is increased suddenly while gradually increasing the linear velocity in the condition the specific pressure was fixed.

As shown in table, the maximum permissible specific pressure [P] is 8.5MPa, the maximum permissible linear velocity [V] is 18.23m/s, and [PV] is 1 8MPa-m/s.

This material can be applied instead of copper alloy to sliding bearing, angle screw, worm gear, slider, etc. working in oil lubrication on the condition with the maximum permissible pressure [P], 8.5MPa, the maximum permissible linear velocity [V], 1 8.23m/s, and the permissible [PV], 1 8MPa-m/s.

The advantages of the present invention are as follows:

First, no harmful gas is emitted when sulpur is alloyed.

Thus the environment pollution is prevented and the working conditions of the workers are improved.

Second, sulphur can be absorbed up to 98% and there is no loss of sulphur.

Third, it can be applied widely to industrial fields as the pollution of furnace is prevented.

Fourth, it is easy to adjust exactly the content of sulphur inside steel.

Fifth, the economic effect is very high, because many alloy elements including nonferrous metal elements are not used for production and the lifetime of the material is increased as three to seven times longer as the one of copper alloy.

Sixth, the manufacturing process is simple and stable, the abundant and cheap raw materials are used, and the production is possible without any initial investment wherever is furnaces able to melt the steel including induction furnaces.

Seventh, it can be widely applied to industry as the maximum permissible pressure [P], the maximum permissible linear velocity and the permissible [PV] of it have been determined.

BRIEF DESCRIPTION OF DRAWINGS

Fig. l shows the structure of a mould in which a reaction chamber is set up.

Fig.2 shows the way of putting sulphur into the reaction chamber and the method of alloying sulphur in a mold.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMMENTS

The induction furnace, electric furnace or arc furnace can be used as a smelting furnace. At first the steel is melted in a furnace.

The composition of molten steel is adjusted.

Some amount of sulphur is prepared.

Moisture of sulphur should be removed and its amount is weighed as considering the sum of the weights of article of cast steel, ingate system and reaction chamber and the absorption ratio of sulphur.

The thin chips of cast iron are used preferably. If the thick chips are used, they must be crushed.

Sulphur must be dried at temperature below 100°C as its melting point is 119°C.

Once moisture of sulphur is removed, it must be kept in a dry place; it doesn't have to be packed as it is insoluble in water.

The smelting temperature of the molten steel must be above 1550 to 1600°C.

A sand mold is used.

The reaction chamber is set up in the sand mold as shown in Fig. l .

The reaction chamber should be firmed well and there should not be any keen edges in it.

The chips of cast iron are used as covering material.

Their particle size should be smaller than 3mm and they should not contain moisture, oil and dirt.

The process of the method of alloying sulphur in a sand mold is as below:

First, the part of the article of cast steel is molded in upward mould and the part of the reaction chamber is molded in downward mould.

Second, sulphur is put in the reaction chamber and the chips of cast iron are covered on it.

The covering material, the chips of cast steel, should be equally covered on the sulphur and the thickness of the layer should be less than 3 to 16mm.

And the height of the top side of the chamber from the surface of the covering material should be above than 3 to 20mm.

The dimension of the reaction chamber is adjusted according to the amount of the sulphur.

Third, the upward mould is assembled on the downward mould. (Fig.2)

Fourth, molten steel is poured in through the ingate.

Fifth, molten steel flows in the space of the article of cast steel through the reaction chamber.

At first, molten steel flows into the space without reacting with the sulphur as there are the chips of cast iron covering the sulphur.

After the molten steel fill in to a certain extent the chips of cast steel is completely melted and the sulphur begins to react with the molten steel surrounding itself.

Sulfur is equally contained all over the cast product as it is soon evaporated at the high temperature of the molten steel much higher than the boiling point of the sulphur, 445°C.

Sixth,the pouring of molten steel should not be interrupted to the last once it is started.

Seventh, the shake-out process is similar to the ordinary steel's one.

The machinability of the high sulphur cast steel are very good.

Before machining, it can be annealed.

The oiling is done in the same way as in copper alloy sliding bearing.