JPH0615686B2 - Manufacturing method of abrasion resistant structural steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a wear-resistant structural steel material, and more specifically, to a wear-resistant steel and a steel excellent in strength, toughness, and weldability. The present invention relates to a method for manufacturing a composite steel material for wear-resistant structures.

(Prior art and problems) In recent years, the performance and weight of civil engineering machinery such as bulldozers and power shovels have advanced, and wear-resistant steel has been used to extend the service life of parts that are subject to wear. As a wear steel, the hardness according to the conventional BHN (Brinell hardness) is 2
The ones of 70, 310, 360 were used,
Recently, BHN400 and 450 steel materials have been used in order to further extend the service life, and this tendency is gradually increasing in hardness.

In general, as such wear-resistant steel, materials having different properties corresponding to the application, that is, the mechanism causing wear are used. For example, civil engineering machines such as bulldozers are subject to impact, sliding, etc. due to soil, sand, rocks, etc., and generally increasing hardness is the main countermeasure, but in this case, SC material (JIS G4051, mechanical structure For carbon steel), SK (JIS
G4401 carbon tool steel) or SCR, SCM materials (JIS G4052) are considered to be steel materials having a C content of about 0.2 to 1.5%, and these are known to have low toughness and extremely poor weldability.
Next, the low alloy wear-resistant steel, in which the quenching hardenability is enhanced by adding alloy elements such as Mn, Ni, Cr, Mo, Nb, and V in place of the C content to 0.2% or less, has relatively high toughness. Since it has good weldability, it has recently been used for wear-resistant parts of civil engineering machines. The advantage of this steel is that it can be relatively easily welded and can be field-welded even when it is worn and repaired by overlaying. In addition, dredger pipes for seabed drilling and riverbed drilling are corroded by seawater and sewage, which promotes wear. Added steel is used.

On the other hand, steel having a certain degree of toughness is considered to be good for wear that is subjected to a large impulse load rather than sliding wear. In this example, a crusher for crushing ore or the like is often used with high carbon high Mn steel (JIS G5131 etc.). The structure of this steel is austenite at normal temperature, but when strained, it easily transforms into high-carbon martensite and increases wear resistance.

These wear resistant steels are usually used after having been given hot rolling and water toughening treatment by heating again after finishing hot rolling and once cooling.

However, since these wear resistant steels generally have high strength, they are poor in toughness and weldability, and may cause bending cracks and weld cracks during mechanical assembly, and stress corrosion cracking during use in a corrosive environment. And the like, which may cause fatal defects, and generally lack the properties as a strength member structural member that requires toughness and weldability. Therefore, there is no effective means at present for these requirements, and it is considered that the upper limit of the characteristics of the wear resistant steel is BHN of 400 to 450, and it is difficult to develop a steel material having the characteristics exceeding this.

(Means for Solving the Problem) Then, as a result of various studies by the present inventors, a wear-resistant material was formed on the surface layer requiring wear resistance, and the toughness and weldability were excellent as the lower layer. It is possible to manufacture wear-resistant steel as a strength member by manufacturing a composite steel material in which structural steels are arranged, and the wear-resistant steel material usually obtains a quenched structure by water cooling, etc. Since it increases the toughness as much as possible, by hot rolling the steel slabs with such a composite structure, it is possible to improve the hardness and toughness of the wear-resistant steel and at the same time improve the strength and toughness of structural steel. We have come to the conclusion that we can. That is, the properties that a structural material should have, that is, a certain degree of strength and toughness, are imparted to the structural steel material, while the wear resistance characteristics are imparted to the wear resistant steel. And, it has been found that it can be combined with the characteristics as a wear-resistant material, the wear-resistant steel having a chemical composition previously selected according to the purpose as its manufacturing method, and the strength and toughness of the water-cooled after rolling. Both steels, whose components are designed so that both can be improved, are laminated so as to have a predetermined thickness ratio (cladding ratio), heated and hot-rolled, and the temperature at which any steel is still in the austenite state after rolling. Based on a completely new finding that it is possible to fully impart the characteristics of each steel by water cooling from the region, and thereby to fully realize the synergistic effect as a composite steel material. Te is that none of the present invention.

(Structure / Operation of the Invention) The present invention has been made based on the above findings, and the gist thereof is to provide a steel having a chemical component with excellent wear resistance and a C0.02 weight% content. ~ 0.22%, Si 0.5% or less, Mn
0.3-2.0%, Total Al 0.1% or less, respectively, and (A) Nb 0.005-0.05 if necessary.
%, V 0.005-0.05%, Cr 0.6% or less, Ni
1.3% or less, Cu 0.3% or less, Mo 0.5% or less, B
0.0005-0.012%, Ti 0.005-0.03
%, And the total of Cr, Ni, Cu, Mo is 0.2 to 2.5%, or (B) Ca is 0.005% or less, either (A) or (B). One or both of them, the balance of which is steel composed of Fe and unavoidable impurities, the hot rolling is performed on a composite billet, and after rolling, all steels are water-cooled from the temperature range where the structure is in the austenite state. The method for producing a wear-resistant structural steel material is characterized in that

The present invention will be described in detail below.

First, in the present invention, steel having a chemical composition with excellent wear resistance means wear resistance according to the purpose, that is, according to the mechanism of wear such as impact wear, sliding wear, and corrosion wear as mentioned above. Steel materials having wear resistance with corresponding properties, such as the above-mentioned high carbon steel, medium carbon low alloy steel, and high carbon high
Mn steel, corrosion-resistant high-carbon steel, etc. refers to various wear-resistant steels that have been provided with wear resistance by increasing hardness and toughness by heat treatment mainly for quenching treatment. The type of steel is not particularly specified, and the chemical composition may be selected according to the purpose of the wear resistant structural steel material to be manufactured by the manufacturing method of the present invention.

Next, as a steel material having characteristics as a structural material, that is, various characteristics such as strength, toughness, and weldability, a tensile strength of 40 to 8 is used.
0 kgf / mm ² and toughness has an impact value (at Charpy test temperature) of 3.5 to 4.8 at a temperature generally used.
About kgf.m or more is used. In order to obtain a steel having such characteristics, the steel must have the following composition.

First, C is an element necessary for ensuring hardenability and strength, but if it is less than 0.02%, a transformation structure such as pearlite or bainite, which is the C diffusion-controlling rate, cannot be obtained. I can't get steel. 0.22
%, The toughness and weldability become poor and it is difficult to obtain the characteristics as a structural steel, so C is 0.02 to 0.
22%. Of these, the best range is 0.05-
It is 0.18%.

Next, Si is contained in the steel to some extent in the ordinary steelmaking method and contributes to the strength increase due to solid solution hardening, but if added in a large amount, the toughness deteriorates, and if it exceeds 0.5%, the toughness of the welded part also deteriorates significantly. Therefore, it was set to 0.5% or less.

Mn is an element effective in increasing the strength without significantly impairing the toughness, and is usually contained in steel, but if it is less than 0.3%, it is difficult to secure the strength as structural steel. ,
On the other hand, if it exceeds 2%, it causes a large decrease in weldability.

Al is usually added to the steel for deoxidization and is combined with N to help prevent coarsening of austenite grains during heating, but if the addition amount exceeds 0.1%, it warps. This may lead to grain coarsening and increase in the amount of inclusions such as Al ₂ O ₃ and impair toughness and workability. Therefore, the upper limit of the Al content is 0.1% in total.

Although the above is a basic element, as a steel other than the above in the steel targeted by the present invention (A) Nb, V, Cr, Ni, Cu, Mo, B,
Depending on the steel plate and cross-sectional thickness, one or more types of Ti may be used to secure a predetermined balance of strength, toughness and weldability as a structural material, or (B) Ca to improve the toughness of the welded part or Either or both of (A) and (B) can be added for the purpose of reducing the direction of mechanical properties of the base material.

First, Nb and V, which are the components of the (A) group, both increase the upper limit temperature of the unrecrystallized region during controlled rolling to expand the grain refining effect region of rolling and to some extent quenching. Property is an important element for maintaining the austenite grain growth during heating of steel slab, but if the amount is less than 0.005% each, the desired effect cannot be obtained, while 0.05% is required. If it exceeds the above range, the above effect is not only saturated, but also becomes a factor of lowering the toughness of the welded portion. Therefore, the content range of both Nb and V is 0.0
It was set to 05 to 0.05%.

Cr, Ni, Cu, and Mo have the same effects as Mn, and all of them are effective elements for delaying the transformation of steel and lowering the transformation temperature, so part of Mn is replaced with one or more of these elements. The effect can be further promoted by coexisting with Mn. At that time, in order to obtain the target strength by the cooling rate of the central portion of the thickness of thick steel, Cr 0.6% or less, Ni 1.3%
Below, Cu 0.3% or less, Mo 0.5% or less, and Cr, Ni, C
The total of u and Mo must be at least 0.2%. Among these elements, Ni and Cu are 1.3% or less and 0.3%, respectively.
By including the following is particularly effective in improving toughness, Cr, Mo is an effect of improving the hardenability when water cooling after rolling and the effect of improving the composition and morphology of carbides, Mo is further Strength of 60 kg when tempering after water cooling
Since there are many effects such as the effect of preventing embrittlement due to stress relief annealing of the welded part of high-strength steel of f / mm ² or more, it is effective to contain Cr 0.6% or less and Mo 0.5% or less.
However, adding too much of these elements impairs weldability and the like, so the total of these four components was limited to 2.5% or less.

B has an effect of improving hardenability, but if it is less than 0.0005%, its effect is small, and if it exceeds 0.0012%, a compound of B is produced in the weld heat affected zone and the like and deteriorates toughness.

Since Ti has the property of fixing N and enabling B, Ti.
It is effective to add 005% or more. However
If Ti exceeds 0.03%, it may form a solid solution in the base metal, resulting in marked deterioration of toughness.

Further, Ca, which is a component of (B), controls the morphology of sulfides,
It is effective if added to improve the notch toughness in the direction perpendicular to the rolling direction and the notch toughness of the weld heat affected zone, but if Ca exceeds 0.005%, many surface and internal defects occur.

Thus, the chemical composition of the structural steel is specified in the present invention in order to obtain the above-mentioned various properties by performing hot rolling after lamination and then water cooling in the following steps. That is, prior to rolling, the wear-resistant steel and the structural steel are laminated to form a composite steel slab, but as a means of lamination, for example, casting is used, in a CC slab or in a steel ingot mold. With the method of injecting molten steel into the cast iron, the method of welding the surroundings after stacking at the stage of steel slab, the explosive welding method, or the welding method such as submerged arc welding, electrogas, and electroslag welding. There are many means such as the overlaying method using the strip electrode used.

All of them sufficiently satisfy the object of the present invention, and may be selected in consideration of the chemical composition of the steel to be selected and the dimensions, thickness, thickness ratio, etc. of the composite steel slab. The thickness ratio between the wear-resistant steel and the structural steel that compose the billet is maintained after rolling, so the thickness ratio that takes into consideration the thickness of the final product is adopted in advance according to the intended use and purpose. Will be needed. In this case, as the composite billet, even if wear-resistant steel and structural steel are arranged on the front and back to form two layers, the structural steel is formed on the central layer.
It may be a three-layer structure in which wear-resistant steel is arranged on the front and back layers.

Although the conditions for heating and hot rolling of such composite steel slabs are not specified, in order to correct the strength difference in the plate thickness direction due to the difference in cooling rate in the plate thickness direction during water cooling, it is necessary to perform water cooling after rolling. For the purpose of refining the microstructure for improving the toughness of steel and structural steel, it is also preferable to perform controlled rolling such as heating at a temperature of 950 to 1150 ° C. and rolling conditions to a certain degree at 950 ° C. or less. .

Water cooling after rolling is performed from a state where both steels are both austenite, but the purpose is different for both steels. That is, by water cooling in the case of wear-resistant steel hardened tissue or such as a high carbon martensite, in order that of improving the wear resistance by obtaining the granulated austenite structure for high Mn steel, in this case Ar ₃ When the points are cut to form ferrite, the quenched structure becomes incomplete and the hardness is extremely reduced. In high Mn steel, the Ar ₃ point is below room temperature, but if the water-cooling start temperature after rolling is low, precipitates will form at grain boundaries and reduce toughness.

On the other hand, in the case of structural steel, if the temperature is lowered to the Ar ₃ point or lower, the effect of grain refinement of the structure during transformation is not sufficient and the prescribed strength and toughness cannot be obtained.

Therefore, it is necessary to perform water cooling from a temperature above both Ar ₃ points of both steels, but which common temperature above ₃ Ar points depends on the thickness of the steel during water cooling and the length of the water cooling device. It is determined in consideration of water density, length of rolled material, and the like.

Water cooling is performed until the steel reaches a temperature near room temperature, and 3
It may be stopped at a temperature of 00 to 400 ° C and then air cooled,
The selection depends on the characteristics of the target steel, but in order to sufficiently quench the wear-resistant steel, it is usually desirable to continuously carry out the quenching. Further, in water cooling, water is cooled from above and below the rolled material, but if the thermal expansion coefficients of both steels are different, it is effective to intentionally change the water density above and below in order to prevent bending.

Next, the effects of the present invention will be described more specifically with reference to examples.

(Example) Steel having the chemical composition shown in Table 1 and Table 2 was melted, and a composite billet and a steel plate were manufactured under the casting and rolling conditions shown outside the table. Then, the composite steel pieces shown in Table 3 were laminated according to the thickness ratio and subjected to rolling.

As the laminating means, the so-called vacuum drawing method of degassing the air in the gap between both steels with a vacuum pump after welding the four circumferences with covered metal arc welding, and the electron beam welding method of performing the four circumference welding by electron beam welding in the casting of the vacuum chamber 2 types were used. After rolling, all were water-cooled, but part of them was tempered at 500 ° C. A steel material produced by the method of the present invention and, on the other hand, for comparison, a laminated steel piece of a steel having a chemical composition specified by the present invention and an abrasion resistant steel was rolled and cooled under a condition deviating from the condition specified by the present invention. 21 to 27 and several examples of wear resistant steels, steel pieces from the same molten steel were selected, rolled, and reheat-quenched by the same method as the conventional steel types 28 to 34, and the books shown in Table 4. Steel pieces having a chemical composition deviating from the chemical composition specified by the invention are laminated as structural steel, and a steel slab is rolled and cooled under the conditions specified by the present invention to produce steel types 35 to 40, respectively. Hardness, tensile test, and impact test at 0 ° C. were performed.

The results are shown in Tables 3 and 5.

All steel types Continuous casting method Steel types A1-9 Slab thickness 200 mm, width 1550 mm, drawing speed 0.55 m
/ Min A10-17 Slab thickness 200 mm, width 1550 mm, drawing speed 0.4 m / min, respectively, after casting, cooling once, then reduction rolling is required for the purpose of the present invention depending on the thickness and thickness ratio of the composite steel slab. Carried out accordingly.

Ar ₃ points were calculated using the following formula.

Ar ₃ (℃) = 868-396C + 24.6Si-68.1Mn-24.8Cr-36.1Ni-20.7Cu + 29.6Mo Steel type B-5 is manufactured by the steel ingot method. A wide 32 ton steel ingot (steel ingot size average thickness 875 mm, average width 2317 mm, height 2500 mm, riser ratio 20%) is cast, and immediately put into a soaking furnace after die cutting. After soaking in 1300 ℃ 25
Slab rolling on 0x2300x2600 billets.

Then, it was further rolled into a steel plate for composite billet by plate rolling.

Continuous casting method except for steel type B-5. Steel piece thickness 200 mm, width 1800 mm, drawing speed 0.4 m /
Min cast and then rolled to a steel plate with thickness for composite billets.

Steel types Nos. 9, 10, and 11 were water-cooled and then tempered at 500 ° C. ^{* Use of} 5 mm subsize Charpy test pieces For steel grades 1 to 8 and 12, 13 stacking is performed by vacuum drawing method Steel strip size Width 1500 mm, length 2000 mm Electron beam for steel grades 9 to 11 and 14 to 20 Small steel piece by welding (width 400-600mm, length 1000m
m) was laminated.

^{* Use of} 5 mm subsize Charpy test pieces All steel types 28 to 34 are rolled to a predetermined thickness, then once cooled, then reheated and water-cooled from 800 ° C. Steel types 21 to 27 and 35 to 40 are small by electron beam welding. Steel slab (width 400-600mm, length 1000
mm) was laminated.

According to these, all of the steel types 1 to 20 according to the method of the present invention have the desired properties as structural steel and wear resistant steel, and the effect of the present invention has been proved.

On the other hand, each of the steels 21 to 40 lacks the properties as structural steel, does not have a predetermined hardness as wear resistant steel, or lacks both of them.
It can be seen that the steel material targeted by the present invention could not be manufactured.

(Effects of the Invention) As is clear from the above examples, according to the present invention, the steel also has a function as a structural steel having good toughness and excellent strength as compared with the steel obtained by the conventional method. This makes it possible to manufacture wear-resistant steel materials and has a remarkable industrial effect.

Claims (13)

[Claims] 1. A steel having a chemical composition with excellent wear resistance and a weight percentage of C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, and Total Al: 0.1% or less, respectively. A method for producing a wear-resistant structural steel material, which comprises hot rolling a composite steel slab composed of a laminated steel sheet, and performing water cooling from a temperature range where the structure of each steel is in an austenite state after rolling. 2. A steel having a chemical composition with excellent wear resistance, and C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less and Nb: Hot rolling of composite steel slabs made by laminating with steel containing one or two of 0.005 to 0.05% and V: 0.005 to 0.05%, and the temperature at which any steel has an austenitic structure after rolling. A method for manufacturing a wear-resistant structural steel material, which is characterized by performing water cooling from a region. 3. A steel having a chemical composition with excellent wear resistance and, in weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, and Total Al: 0.1% or less. , 1% or more of Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3% or less, Mo: 0.5% or less, and the total of Cr, Ni, Cu, Mo is 0.2 to 2.5%. A method for producing a wear-resistant structural steel material, which comprises hot rolling a composite steel slab composed of a laminated steel, and performing water cooling from a temperature range where the structure of each steel is in an austenite state after rolling. 4. A steel having a chemical composition with excellent wear resistance, and C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, and B: A wear-resistant structure characterized by hot rolling a composite steel slab composed of a stack of steel containing 0.0005 to 0.012% and performing water cooling from the temperature range where the structure of each steel is austenite after rolling. Steel material manufacturing method. 5. A steel having a chemical composition with excellent wear resistance and, in weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, B: Hot rolling a composite billet composed of a stack of steel containing 0.0005 to 0.012% and Ti: 0.005 to 0.03%, and water cooling from the temperature range where the structure of each steel is austenite after rolling. A method for producing a wear-resistant structural steel material characterized by: 6. A steel having a chemical composition with excellent wear resistance and, in weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, Ca: For wear-resistant structures characterized by hot rolling a composite billet composed of a stack of steel containing 0.005% or less, and performing water cooling from the temperature range where the structure of each steel is austenite after rolling. Steel manufacturing method. 7. A steel having a chemical composition with excellent wear resistance and, by weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less and Nb: One or two containing 0.005 to 0.05%, V: 0.005 to 0.05%, one or more, and Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3% or less, Mo: 0.5% or less. Hot rolling a composite billet composed of a stack of steels containing more than one kind and having a total of Cr, Ni, Cu, Mo of 0.2 to 2.5%, and after rolling, the structure of each steel is in the austenitic state A method for producing a wear-resistant structural steel material, which comprises performing water cooling from a temperature range. 8. A steel having a chemical composition with excellent wear resistance and C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, and B: 0.0005 to 0.012% Nb: 0.005 to 0.05%, V: 0.005 to 0.05% V: 0.005 to 0.05% Composite steel slabs made by laminating with steel containing one or two kinds are hot-rolled. A method for producing a wear-resistant structural steel material, which comprises performing water cooling from a temperature range in which a structure is in an austenite state. 9. A steel having a chemical composition with excellent wear resistance, and C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, and B: Contains one or two of 0.0005 to 0.012%, Nb: 0.005 to 0.05%, V: 0.005 to 0.05%, Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3% or less, Mo: 0.5% Hot rolling a composite steel slab containing one or more of the following and laminating with a steel in which the total of Cr, Ni, Cu, Mo is 0.2 to 2.5%, and after rolling any steel A method for producing a wear-resistant structural steel material, which comprises performing water cooling from a temperature range in which a structure is in an austenite state. 10. A steel having a chemical composition with excellent wear resistance, and C: 0.02-0.22%, Si: 0.5% or less, Mn: 0.3% -2.0%, Total Al: 0.1% or less, and B: 0.0005 to 0.012%, Ti: 0.0005 to 0.03%, Nb: 0.005 to 0.05%, V: 0.005 to 0.05%, containing 1 or 2 kinds, and Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3 %, Mo: 0.5% or less, and hot rolled a composite billet composed of a stack of steels containing one or two or more and having a total of Cr, Ni, Cu, Mo of 0.2 to 2.5%. A method for producing a wear-resistant structural steel material, characterized in that, after rolling, all steels are water-cooled from a temperature range where the structure is in an austenite state. 11. A steel having a chemical composition with excellent wear resistance and, in weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, B: 0.0005 to 0.012%, Ca: 0.005% or less, Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3% or less, Mo: 0.5% or less, and contains one or more of Cr, Ni, Cu, and It is characterized in that a composite billet constituted by stacking with a steel having a total of Mo of 0.2 to 2.5% is hot-rolled, and after rolling, all steels are water-cooled from a temperature range where the structure is in an austenite state. Manufacturing method of wear-resistant structural steel. 12. A steel having a chemical composition with excellent wear resistance and, in weight%, C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, B: Contains one or two of 0.0005 to 0.012%, Ca: 0.005% or less and Nb: 0.005 to 0.05%, V: 0.005 to 0.05%, and Cr: 0.6% or less, Ni: 1.3% or less, Cu: 0.3% Hereinafter, hot rolling is performed on a composite steel slab that is formed by laminating a steel containing Mo: 0.5% or less and one or two or more, and the total content of Cr, Ni, Cu, and Mo is 0.2 to 2.5%, A method for producing a wear-resistant structural steel material, characterized in that, after rolling, all steels are water-cooled from a temperature range where the structure is in an austenite state. 13. A steel having a chemical composition excellent in wear resistance, and C: 0.02 to 0.22%, Si: 0.5% or less, Mn: 0.3% to 2.0%, Total Al: 0.1% or less, and B: 0.0005 to 0.012%, Ti: 0.005 to 0.03%, Ca: 0.005% or less and Nb: 0.005 to 0.05%, V: 0.005 to 0.05%, containing 1 or 2 kinds, and Cr: 0.6% or less, Ni: 1.3% or less. % Or less, Cu: 0.3% or less, Mo: 0.5% or less, one or two or more, and a composite steel formed by laminating with a steel in which the total of Cr, Ni, Cu, Mo is 0.2 to 2.5%. A method for producing a wear-resistant structural steel material, characterized in that hot rolling is performed on a piece, and after rolling, water cooling is performed from a temperature range in which the structure of each steel is in an austenite state.