JP2005240135A - Method for manufacturing wear-resistant steel having excellent bendability, and wear-resistant steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing wear-resistant steel having excellent bendability, and wear-resistant steel. <P>SOLUTION: In the manufacturing method, steel having a composition consisting of, by mass, 0.13-0.20% C, 0.05-1.0% Si, 0.1-2.0% Mn, ≤ 0.020% P, ≤ 0.005% S, 0.005-0.03% Nb, 0.005-0.05% Ti, 0.0003-0.002% B, further as necessary, one or two or more of 0.03-2.0% Cu, 0.03-2.0% Ni, 0.03-2.0% Cr, 0.03-1.0% Mo, and 0.005-0.1% V, and the balance Fe with inevitable impurities is heated at 1,100-1,200°C, subjected to hot rolling with the cross ratio of ≤ 15 and at the draft of ≥ 15% at the temperature of ≤ 950°C, cooled, and re-heated at 850-950°C, and quenched. In the manufacturing method, the microstructure of the steel of the above-described composition is the martensitic structure of the average grain size of ≤ 30μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing wear-resistant steel and wear-resistant steel used in industrial machinery, transportation equipment, and the like, and particularly relates to a material having a surface hardness of HB361 or higher and excellent bending workability.

  In order to ensure the service life of industrial machines, structural parts, transport equipment, etc. (power shovels, bulldozers, hoppers, buckets, etc.) used in the fields of construction, civil engineering, mining, etc., the steel surface is a hardened structure, A steel plate having a high surface hardness and excellent wear resistance is used.

  Wear-resistant steel sheets have high hardness and therefore have low ductility, and often cause cracks starting from A-based inclusions in the bending process when forming the final product shape. Moreover, since the ductile rolling anisotropy is large, the chamfering of parts from the steel plate and the bending direction are restricted.

  In order to improve the ductility of the wear-resistant steel plate, various proposals have been made for the steelmaking process, rolling process and heat treatment process.

  Regarding the steelmaking process 1 Method to reduce S that causes the formation of inclusions 2 Method to add Ca, Ce, Zr, etc. to control sulfide morphology 3 Add a small amount of V to obtain V carbonitride There has been proposed a method (Patent Document 1) in which ductility, particularly uniform elongation, is improved by finely dispersing, refining crystal grains, and reducing solid solution N.

  Regarding the rolling process, a method of cross rolling has been proposed in order to prevent the A-based intervention from extending in only one direction.

Regarding the heat treatment step, 1 proposes a method of spheroidizing A inclusions by solution treatment, then aging treatment, dispersing and precipitating carbides, and then refining by conventional quenching and tempering treatment (Patent Document 2) Has been.
Japanese Patent Laid-Open No. 1-142023 JP 51-52316 A

    In the method of reducing S in steel in the steel making process, the effect cannot be obtained unless the S content in steel is reduced to 0.003% or less, and the production cost is increased. In the method of controlling the form of sulfide by adding Ca, Ce, Zr, etc., the production cost is increased, and the addition amount is difficult to control, resulting in an excessive addition amount and a decrease in cleanliness.

  In the method of adding a small amount of V, the reduction of solid solution N and the refinement of crystal grains are not sufficiently achieved, and the ductility improvement in the direction perpendicular to the rolling is not sufficient. In the method of cross rolling in the rolling process, the upper limit of the cross ratio is restricted due to the restriction of the rolling dimension of the steel sheet, and the bending workability in the direction perpendicular to the rolling is not sufficiently improved. In the case of a method of performing an aging treatment after the solution treatment, the production cost is increased by a plurality of heat treatments, and the production process becomes long.

  Therefore, the present invention aims to solve the above-mentioned problems and to provide a method for producing wear-resistant steel excellent in bending workability having hardness of HB361 or higher and excellent wear resistance and wear-resistant steel. .

  When the present inventors have rolled a steel having a component composition to which a small amount of Nb and Ti have been added, the cross ratio and the rolling reduction in a specific temperature range are specified, and then reheated and quenched, the average particle size is 30 μm or less It has been found that by having a martensite structure, excellent wear resistance and elongation characteristics in the direction perpendicular to the rolling can be obtained.

The present invention has been made by further studying the obtained knowledge. That is, the present invention is 1% by mass, C: 0.13 to 0.20%, Si: 0.05 to 1.0%, Mn : 0.1 to 2.0%, P: 0.020% or less, S: 0.005% or less, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.05%, B: 0.0003-0.002%, the balance Fe and steel consisting of inevitable impurities are heated to 1100-1200 ° C., and hot rolling is performed at a reduction ratio of 15% or more at a cross ratio of 15 or less and 950 ° C. or less. A method for producing a wear-resistant steel excellent in bending workability, characterized by reheating to 850 to 950 ° C. and quenching after cooling.

2 Further, Cu: 0.03-2.0%, Ni: 0.03-2.0%, Cr: 0.03-2.0%, Mo: 0.03-1.0%, V: One method of adding 0.005 to 0.1%, or 2 or more types, The manufacturing method of the wear-resistant steel excellent in bending workability of 1 characterized by the above-mentioned.
3% by mass, C: 0.13 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.0. 005% or less, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.05%, B: 0.0003 to 0.002%, balance Fe and inevitable impurities and steel composition and average crystal A wear-resistant steel excellent in bending workability, characterized by having a martensite structure with a particle size of 30 μm or less.
4 Furthermore, Cu: 0.03-2.0%, Ni: 0.03-2.0%, Cr: 0.03-2.0%, Mo: 0.03-1.0% in steel composition V: Wear resistant steel excellent in bending workability according to 3, characterized by adding one or more of 0.005 to 0.1%.

  According to the present invention, it is possible to produce a wear-resistant steel of HB361 or higher, which has high strength and excellent bending workability, which is extremely useful industrially.

In the present invention, the composition of steel components and production conditions are defined.
[Ingredient composition]
C
C is an important element for increasing the hardness of the steel. In order to obtain such an effect, the content is made 0.13% or more. On the other hand, if added in a large amount exceeding 0.20%, bending workability is deteriorated, so 0.13 to 0.20% (0.13% or more and 0.20% or less) is contained.

Si
Si is effective as a deoxidizing element and for strengthening solid solution, and in order to obtain such an effect, it is made 0.05% or more. On the other hand, if it exceeds 1.0%, ductility is deteriorated or the amount of inclusions is increased, so 0.05 to 1.0% is contained.

Mn
Since Mn improves the hardenability, in order to obtain such an effect, the content is made 0.1% or more. On the other hand, if over 2.0%, weldability deteriorates, so 0.1 to 2.0% is contained.

P
P is an inevitable impurity in the present invention, and if it exceeds 0.020%, the toughness deteriorates, so it is made 0.020% or less.

S
In the present invention, S is an unavoidable impurity, and precipitates as an A-based inclusion made of MnS in the steel, becomes a starting point of fracture occurrence during bending, and degrades bending workability, so is 0.005% or less. .

Nb
Nb exists as a composite precipitate with Ti nitride at the time of reheating, and in order to refine the crystal grains, in order to obtain such an effect, the content is made 0.005% or more. On the other hand, if it exceeds 0.03%, the welded product deteriorates, so 0.005 to 0.03% is contained.

Ti
Ti fixes N, which is harmful to toughness, as TiN, and also exists as a starting point for composite precipitation with Nb during reheating, and refines the crystal grains after reheating and quenching. Moreover, in order to ensure the solid solution B which improves hardenability, in order to acquire such an effect, it shall be 0.005% or more. On the other hand, if it exceeds 0.05%, the toughness deteriorates, so 0.005 to 0.05% is contained.

B
B has an effect of improving hardenability by adding a small amount, and in order to obtain such an effect, the content is made 0.0003% or more. On the other hand, if it exceeds 0.002%, the toughness decreases, so the content is made 0.0003 to 0.002%.

  The basic components of the present invention are as described above, and excellent effects can be obtained. However, when further improving the characteristics, one or more of Cu, Ni, Cr, Mo, and V can be added.

Cu
Cu raises hardenability and makes it 0.03% or more when improving strength. On the other hand, if over 2.0% is added, the hot workability decreases, so 0.03% to 2.0%.

Ni
Ni increases the hardenability, improves the strength, and improves the low temperature toughness, it is 0.03% or more. On the other hand, if it exceeds 2.0%, the product cost rises, so 0.03 to 2.0%.

Cr
When Cr improves the hardenability and improves the strength, the Cr content is 0.03% or more. On the other hand, if it exceeds 2.0%, the weldability deteriorates and the product cost increases, so the content is made 0.03% to 2.0%.

Mo
Mo increases to 0.03% or more when improving hardenability. On the other hand, if it exceeds 1.0%, the welded product will deteriorate and the product cost will rise, so 0.03 to 1.0%.

V
V increases to 0.005% or more when improving hardenability. On the other hand, if it exceeds 0.1%, weldability deteriorates, so the content is made 0.005% to 0.1%.

[Production conditions]
Steel plate heating temperature The steel piece heating temperature is set to 1100 ° C. or higher so that Nb is completely dissolved in order to make the austenite grain size at the time of reheating fine and improve the bending property in the direction perpendicular to the rolling. On the other hand, if heating is performed at a temperature exceeding 1250 ° C., surface flaws are generated on the surface of the steel sheet.

Rolling conditions In order to improve bending workability, the cross ratio (ratio stretched in the rolling direction before and after rolling / stretched in the direction perpendicular to the rolling before and after rolling) so as not to extend the A-based inclusions in a specific direction. Ratio) is 15 or less.

  In order to refine the austenite grain size after completion of rolling and obtain a fine structure after quenching, the rolling reduction (rolling amount / rolling start thickness) at 950 ° C. or lower is set to 15% or more. When the rolling temperature exceeds 950 ° C. or the reduction ratio is 15% or less, the structure after quenching is not sufficiently refined and bending workability is not improved. In the present invention, cooling after hot rolling is allowed to cool to room temperature.

Heat treatment conditions The reheating temperature for quenching is 850 ° C. or higher for austenitization. On the other hand, if it exceeds 950 ° C., the austenite grain size at the time of reheating becomes coarse, and a martensite structure having an average grain size of 30 μm or less cannot be obtained after quenching, so that the bending characteristics in the direction perpendicular to the rolling are not improved. .

  The wear-resistant steel according to the present invention can be formed into a shape such as a steel plate, a steel bar, or a steel pipe.

  The effects of the present invention will be described using examples. No. of component composition shown in Table 1. Steels 1 to 13 were hot-rolled, allowed to cool to room temperature, and then re-heated and hardened to obtain steel plates having a thickness of 6 to 40 mm. The obtained steel sheet was tested for surface hardness and bending characteristics in the direction perpendicular to the rolling. In Table 1, a blank indicates that the element is not added.

The test method of surface hardness was based on JISZ2243, measured about arbitrary 5 points | pieces on the steel plate surface, and calculated | required the average value. The method for measuring the average particle size of the martensite structure is based on JISG0551, and is a micrograph of a 200-fold magnification of a test piece obtained by corroding a cross section parallel to the rolling direction with a nitrate alcohol solution. The diameter was determined. The bending characteristics were evaluated in accordance with JISZ2248, and the push bending method was performed at a test piece width of 150 mm and a bending angle of 180 °. 1 and 2 are explanatory diagrams of the press bending method, where 1 is a test piece, 2 is a punch, and 3 is a test piece support roller. Table 2 shows manufacturing conditions, surface hardness test results, and press bending test results. The wear-resistant steel sheets according to the present invention (examples of the present invention: steel sheets Nos. 1 to 10 in Table 1 manufactured under the manufacturing conditions within the scope of the present invention) are all HB ≧ 361 and have a high surface hardness and a small limit bending radius ( R ≦ 3.0 t).

    On the other hand, steel 11 has a low C content and a low surface hardness. Steel 12 has a coarse grain structure because Nb is not substantially added, and has poor bending properties. Steel 13 has a high S content and poor bending properties. Steel 1-2, Steel 7-2 and Steel 9-2 are within the scope of the present invention, but the production conditions are outside the scope of the present invention, resulting in a coarse grain structure and poor bending properties.

Explanatory drawing of a push bending test method. Explanatory drawing of a push bending test method.

Explanation of symbols

1 Test piece 2 Punch 3 Test piece support roller

Claims (4)

In mass%, C: 0.13 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.005 %, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.05%, B: 0.0003 to 0.002%, balance Fe and steel consisting of unavoidable impurities, 1100 to 1200 Excellent bending workability, characterized by heating to ℃, performing hot rolling at a reduction ratio of 15% or more at a cross ratio of 15 or less and 950 ° C or less, and after cooling, reheating to 850 to 950 ° C and quenching A method for producing wear-resistant steel. Further, Cu: 0.03-2.0%, Ni: 0.03-2.0%, Cr: 0.03-2.0%, Mo: 0.03-1.0%, V The method for producing wear-resistant steel excellent in bending workability according to claim 1, wherein one or more of 0.005 to 0.1% is added. In mass%, C: 0.13 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.005 % Or less, Nb: 0.005 to 0.03%, Ti: 0.005 to 0.05%, B: 0.0003 to 0.002%, the steel composition and the average crystal grains comprising the balance Fe and inevitable impurities A wear-resistant steel excellent in bending workability, characterized by having a martensite structure with a diameter of 30 μm or less. Further, Cu: 0.03-2.0%, Ni: 0.03-2.0%, Cr: 0.03-2.0%, Mo: 0.03-1.0%, V The wear-resistant steel with excellent bending workability according to claim 3, wherein 0.005 to 0.1% of one or more are added.

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