JP2024049709A - Steel Plate - Google Patents

Abstract

To provide a steel plate with excellent resistance to corrosion and wear.SOLUTION: A steel plate comprises, in mass%, C: 0.24% or more and less than 0.32%, Si: 0.05% or more and 1.00% or less, Mn: 0.10% or more and 2.00% or less, P: 0.030% or less (excluding 0%), S: 0.0300% or less (excluding 0%), Al: 0.005% or more and 0.100% or less, Cr: 3.00% or more and 11.50% or less, with the balance being Fe and inevitable impurities, where its surface hardness is 460 or more and 590 or less, measured by Brinell hardness HBW10/3000.SELECTED DRAWING: None

Description

The present invention relates to steel plates used for components that require wear resistance in industrial machinery, transport equipment, etc., and in particular to steel plates that have excellent corrosion and wear resistance in acidic corrosive environments such as coal mining environments.

Components of industrial machinery and transport equipment, such as power shovels, bulldozers, hoppers, buckets, dump trucks, and conveyors, are subject to wear due to contact with soil, ores, coal, etc. For this reason, thick steel plates with excellent wear resistance are used to extend the lifespan of components. The actual use environments of industrial machinery and transport equipment vary from dry to wet, and when used in wet conditions, they often contain corrosive substances. It is known that corrosive wear in such environments is very severe. In particular, in coal mining environments, the leachate from the coal may be acidic, which causes even more severe corrosive wear. For this reason, there has been a demand for steel plates with excellent corrosion and wear resistance.

In response to such demands, for example, Patent Document 1 discloses a steel with excellent wear resistance in a corrosive environment, which has a composition containing, in mass %, C: 0.18-0.25%, Si: 0.05-1.00%, Mn: 0.10-2.00%, P: 0.020% or less, S: 0.0050% or less, Al: 0.005-0.100%, Cr: 0.05-2.00%, Nb: 0.005-0.100%, Ti: 0.005-0.100%, W: 0.05-1.00%, and as necessary, one or more of Mo, Cu, Ni, V, B, REM, Ca, and Mg, with an appropriate amount of W. Note that Patent Document 1 evaluates wear resistance using an aqueous NaCl solution as the corrosive environment.

In addition, in Patent Document 2, the alloy contains, in mass %, C: 0.20-0.35%, Si: 0.02%-1.00%, Mn: 0.1-2.0%, P: 0.020% or less, S: 0.005% or less, Al: 0.005-0.100%, Sb: 0.005-0.20%, B: 0.0003-0.0030%, and further contains one or more selected from Cr: 0.05-2.0% and Mo: 0.05-1.0%, The steel has a composition that satisfies 0.05≦(Crsol+2.5Mosol)≦0.2 (where Crsol: amount of Cr dissolved in steel (mass%), and Mosol: amount of Mo dissolved in steel (mass%)), and the amount of dissolved Cr and Mo is kept within an appropriate range to create a component system that can suppress corrosive wear to a certain extent. In addition, Sb and B are essentially contained in combination, resulting in a wear-resistant steel plate with excellent corrosive wear resistance. In Patent Document 2, wear resistance is evaluated using an aqueous NaCl solution as the corrosive environment.

Patent Document 3 discloses a corrosion-resistant steel that contains C: 0.01-0.25%, Si: 0.01-0.50%, Mn: 0.1-2.0%, P: 0.035% or less, S: 0.035% or less, Al: 0.003-0.10%, Cu: 0.05-0.35%, Ni: 0.02-0.40%, Sb: 0.01-0.2%, W: 0.005-0.5%, Nb: 0.003-0.025%, Cr: 0.1% or less, N: 0.0010-0.0080%, with the balance being Fe and unavoidable impurities, and that has a Vickers hardness of 140 or more at a position 2 mm deep from the surface, thereby exhibiting excellent corrosion resistance, wear resistance, and high toughness in a specific environment.

In addition, in Patent Document 4, the steel contains, by mass%, C: 0.10 to 0.35%, Si: more than 1.00% and 2.00% or less, Mn: 0.10 to 2.00%, P: 0.0200% or less, S: 0.0100% or less, Cr: more than 0.05% and 2.00% or less, Al: 0.010 to 0.100%, N: 0.0020 to 0.0100%, B: 0.0003 to 0.0030%, and the balance is composed of Fe and impurities. In particular, the steel contains more than 1.00% Si, which is presumed to promote the formation of an oxide film and thereby improve corrosion resistance in a wet environment, and H≧235+706[C](1−0.3[C] ² ) (wherein H represents the surface layer hardness (HV) of the corrosion-resistant and wear-resistant steel plate, and [C] represents the C content (mass%)) is satisfied, thereby providing a corrosion-resistant and wear-resistant steel plate that is excellent in toughness and also has both corrosion resistance and wear resistance. In addition, in Patent Document 4, the wear resistance is evaluated using artificial seawater as the corrosive environment.

In addition, Patent Document 5 describes a steel containing, by mass%, C: 0.01-0.15%, Si: 0.05-1.00%, Mn: 0.10-2.00%, Cr: over 0.05% and 3.00% or less, Al: 0.01-0.10%, and B: 0.0003-0.0020%, and in particular Cr, an alloy element that improves the hardenability of the steel and contributes to improving hardness, and the Ceq (%) is expressed by the following formula (Ceq (%) = [C] + [Mn]/6 + [Si]/24 + [Ni]/40 + [Cr]/5 + [Mo]/4 + [V]/4) (where [X] represents the content of element X in mass%) of 0.20% or more, the surface layer has a lath structure area ratio of 90% or more, the lath structure has a major axis/minor axis ratio of 2.00 or more for the cementite in the lath structure, and the surface layer has a hardness of 200 or more at HV5, making the steel plate suitable for the holds of coal carriers or coal-mine carriers. This steel plate has excellent corrosion resistance and wear resistance.

JP 2015-193873 A JP 2016-222969 A JP 2017-128762 A JP 2020-007589 A JP 2020-132994 A

However, in Patent Documents 1, 2, and 4, the corrosive environments targeted for improving corrosion resistance are NaCl aqueous solutions and artificial seawater, so there is a problem in that corrosion and wear resistance in acidic environments such as coal mining environments cannot be improved. In addition, Patent Documents 3 and 5 have a problem in that the hardness of the steel material is low, at 365 or less in Vickers hardness, making it unsuitable for industrial machinery, transport equipment, etc. Also, industrial machinery, transport equipment, etc. need to have appropriate toughness due to the harsh environments in which they are used.

In view of these circumstances, the present invention aims to provide a steel plate with excellent corrosion wear resistance and toughness.

In order to solve the above problems, the influence of various factors from the viewpoint of corrosion wear resistance was thoroughly studied, and as a result, it was found that the corrosion wear resistance in an acidic environment such as a coal mining environment can be improved by simultaneously satisfying the following (1) and (2) in order to simultaneously improve the wear resistance and corrosion resistance of a steel material.
To improve wear resistance,
(1) Increases hardness.
To improve corrosion resistance in acidic environments,
(2) In an acidic corrosive environment, Cr is added, which is effective in improving corrosion and wear resistance by being eluted as an ion through an anodic reaction and suppressing corrosion through an inhibitor effect.
That is, it was found that in order to solve the above problems, it is necessary to add Cr while increasing the hardness so as to simultaneously improve the wear resistance and corrosion resistance.
[1] In mass%,
C: 0.24% or more and less than 0.32%;
Si: 0.05% or more and 1.00% or less,
Mn: 0.10% or more and 2.00% or less,
P: 0.030% or less (excluding 0%)
S: 0.0100% or less (excluding 0%)
Al: 0.005% or more and 0.100% or less,
Cr: 3.00% or more and 11.50% or less;
The balance is Fe and unavoidable impurities,
Surface hardness is 460 to 590 on the Brinell hardness scale HBW10/3000.
A steel plate characterized by:
[2] Further, in mass%,
Mo: 1.000% or less,
Nb: 0.100% or less,
Ti: 0.100% or less,
V: 0.200% or less,
Zr: 0.100% or less,
Sn: 0.200% or less,
Sb: 0.200% or less,
Cu: 2.00% or less,
Ni: 2.00% or less,
Co: 2.00% or less,
W: 1.000% or less,
B: 0.0030% or less,
REM: 0.0100% or less,
Ca: 0.0100% or less,
Mg: 0.0100% or less,
The steel sheet according to [1], characterized in that it contains one or more selected from the following:

According to the present invention, it is possible to obtain steel plates with excellent corrosion and wear resistance.

The present invention will be described in detail below. Note that "%" in the component composition means "% by mass" unless otherwise specified.

C: 0.24% or more but less than 0.32% C is an element that increases the hardness of steel. It is necessary to include 0.24% or more in order to ensure the desired hardness. On the other hand, if it is 0.32% or more, the hardness becomes too high and the target hardness cannot be ensured. Therefore, the C content is set to 0.24% or more but less than 0.32%. It is preferably 0.25% or more but 0.30% or less. It is more preferably 0.26% or more but 0.29% or less.

Si: 0.05% to 1.00% Si is an effective element that acts as a deoxidizer for molten steel. To ensure this effect, a content of 0.05% or more is required. On the other hand, if the content is more than 1.00%, the ductility decreases and the number of inclusions increases, which causes the inclusions to become the starting point for the decrease in toughness. Therefore, the Si content is set to 0.05% to 1.00%, and preferably 0.10% to 0.40%.

Mn: 0.10% to 2.00% Mn is an element that improves hardenability, and must be contained at 0.10% or more to ensure a certain level of hardenability. On the other hand, excessive Mn content exceeding 2.00% deteriorates weldability. Therefore, the Mn content is set to 0.10% to 2.00%. It is preferably set to 0.15% to 1.80%. It is more preferably set to 0.20% to 1.80%.

P: 0.030% or less (excluding 0%)
If a large amount of P is contained in steel, it deteriorates weldability. Therefore, the upper limit is set at 0.030%. It is desirable to reduce it as much as possible, preferably to 0.015% or less. In order to ensure the properties, it is desirable to reduce it as much as possible, but excessive reduction leads to high refining costs, so 0.001% or more is preferable.

S: 0.0300% or less (excluding 0%)
If a large amount of S is contained in the steel, it precipitates as MnS, which deteriorates the gas cutting properties, so it is desirable to reduce the S content as much as possible, and it is necessary to keep it at 0.0300% or less. However, since an excessive reduction leads to an increase in refining costs, it is preferable to keep the S content at 0.0001% or more.

Al: 0.005% to 0.100% Al is an element necessary for deoxidation during steelmaking, and has the effect of forming nitrides to reduce the austenite grain size and improve toughness. In order to obtain these effects, the Al content must be 0.005% or more. On the other hand, if it exceeds 0.100%, the cleanliness of the steel material or steel plate decreases, resulting in a decrease in toughness. Therefore, the Al content is set to 0.005% to 0.100%. It is preferably 0.070% or less, and more preferably 0.050% or less. It is preferably 0.010% or more.

Cr: 3.00% or more and 11.50% or less Cr is an important requirement in the present invention, and has the effect of significantly improving corrosion wear resistance, especially in an acidic corrosive environment such as a coal mining environment. Cr is an element that improves hardenability and has the effect of increasing hardness. In addition, in an acidic corrosive environment such as a coal mining environment, Cr is dissolved as a Cr acid ion by an anodic reaction, and has the effect of suppressing corrosion by an inhibitor effect, thereby improving corrosion wear resistance. In order to obtain such an effect, it is necessary to contain 3.00% or more. On the other hand, if it is contained in excess of 11.50%, the weldability decreases and the manufacturing cost rises, so it is limited to the range of 3.00% or more and 11.50% or less. The upper limit of the Cr content is preferably 11.00% or less, more preferably 10.00% or less.

The steel of the present invention can obtain the desired properties with the above essential elements, but in addition to the above essential elements, one or more elements selected from the following elements can be added as necessary.

Mo: 1.000% or less Mo is an effective element for improving hardenability and has the effect of increasing hardness. In order to obtain such an effect, it is necessary to contain 0.001% or more. On the other hand, if it exceeds 1.000%, it will lead to an increase in cost due to the increase in Mo consumption. Therefore, if it is contained, the upper limit of the Mo content is 1.000% or less, preferably 0.800% or less. Furthermore, if it is contained, the lower limit of the Mo content is preferably 0.100% or more.

Nb: 0.100% or less Nb is an effective element for increasing strength. In order to fully obtain this effect, it is necessary to contain 0.001% or more. On the other hand, if it exceeds 0.100%, the effect is saturated. Therefore, if Nb is contained, the upper limit of the Nb content is 0.100% or less. Furthermore, if Nb is contained, the lower limit of the Nb content is preferably 0.001%.

Ti: 0.100% or less Ti is an element necessary for increasing strength. In order to fully obtain this effect, it is necessary to contain 0.001% or more. On the other hand, if it exceeds 0.100%, the effect is saturated. Therefore, if Ti is contained, the upper limit of the Ti content is 0.100% or less. Furthermore, if Ti is contained, the lower limit of the Ti content is preferably 0.001%.

V: 0.200% or less V is an effective element for increasing strength. In order to fully obtain this effect, it is necessary to include 0.001% or more. On the other hand, if it exceeds 0.200%, the effect is saturated. Therefore, if V is included, the upper limit of the V content is set to 0.200% or less. Furthermore, if V is included, the lower limit of the V content is preferably set to 0.001%.

Zr: 0.100% or less Zr is an effective element for increasing strength. In order to fully obtain this effect, it is necessary to include 0.001% or more. On the other hand, if it exceeds 0.100%, the effect is saturated. Therefore, if Zr is included, the upper limit of the Zr content is set to 0.100% or less. Furthermore, if Zr is included, the lower limit of the Zr content is preferably set to 0.001%.

Sn: 0.200% or less Sn is an effective element for suppressing the anodic reaction of steel materials in acidic corrosive environments such as coal mining environments, and suppressing the hydrogen generation reaction, which is a cathodic reaction, thereby improving the weather resistance of steel materials. In order to fully obtain such effects, it is necessary to contain 0.001% or more. On the other hand, if Sn is contained in excess, the effect is saturated. Therefore, when Sn is contained, the upper limit of the content is set to 0.200% or less. Furthermore, when Sn is contained, the lower limit of the Sn content is preferably set to 0.001%.

Sb: 0.200% or less Sb is an effective element for suppressing the anodic reaction of steel materials in an acidic corrosive environment such as a coal mining environment, and for suppressing the hydrogen generation reaction, which is a cathodic reaction, thereby improving the weather resistance of steel materials. In order to fully obtain such effects, it is necessary to contain 0.001% or more. On the other hand, even if Sb is contained in excess, the effect is saturated. Therefore, when Sb is contained, the upper limit of the Sb content is set to 0.200% or less. Furthermore, when Sb is contained, the lower limit of the Sb content is preferably set to 0.001%.

Cu: 2.00% or less Cu densifies the corrosion product and inhibits the penetration of corrosion-promoting factors such as water, oxygen, sulfate ions, and chloride ions into the base steel, thereby inhibiting the corrosion reaction. This effect improves corrosion wear resistance. To obtain such an effect, it is preferable to contain 0.01% or more. On the other hand, if it exceeds 2.00%, hot workability decreases and manufacturing costs increase. Therefore, if it is contained, the upper limit of the Cu content is 2.00% or less, preferably 1.50% or less, and even more preferably 1.20% or less. If it is contained, the lower limit of the Cu content is preferably 0.01% or more, more preferably 0.10% or more, and even more preferably 0.60% or more.

Ni: 2.00% or less Ni is an effective element for improving hardenability. In order to obtain such an effect, it is necessary to include 0.01% or more. On the other hand, since the content exceeding 2.00% increases the manufacturing cost, when Ni is included, the upper limit of the Ni content is limited to 2.00% or less, preferably 1.50% or less, and more preferably 0.60% or less. When Ni is included, the lower limit of the Ni content is preferably 0.01% or more, more preferably 0.10% or more, and even more preferably 0.30% or more.

Co: 2.00% or less Co is an effective element for improving hardenability. To obtain this effect, a content of 0.01% or more is required. On the other hand, a content exceeding 2.00% increases the manufacturing cost, so if Co is contained, the upper limit of the Co content is limited to 2.00% or less. If Co is contained, the lower limit of the Co content is preferably 0.01% or more.

W: 1.000% or less W is an effective element for improving hardenability and has the effect of increasing hardness. In order to obtain such an effect, it is necessary to include 0.001% or more. On the other hand, if it exceeds 1.00%, it will lead to an increase in cost due to an increase in W consumption. Therefore, if W is included, the upper limit of the W content is 1.000% or less, preferably 0.800% or less. Furthermore, if W is included, the lower limit of the W content is preferably 0.050% or more, more preferably 0.100% or more.

B: 0.0030% or less B is an effective element for improving hardenability. To obtain this effect, it is necessary to include 0.0001% or more. On the other hand, if it exceeds 0.0030%, the effect is saturated. Therefore, if B is included, the upper limit of the B content is set to 0.0030% or less. Furthermore, if B is included, the lower limit of the B content is preferably set to 0.0001% or more.

REM: 0.0100% or less REM is effective in fixing S and suppressing the generation of MnS, which causes cracking. In order to obtain such an effect, it is necessary to contain 0.0005% or more. On the other hand, if it is contained in an amount exceeding 0.0100%, the amount of inclusions in the steel increases, which leads to cracking, so if it is contained, the upper limit of the REM content is limited to 0.0100% or less, and preferably 0.0020% or less. If it is contained, the lower limit of the REM content is preferably 0.0005% or more.

Ca: 0.0100% or less Ca is an element that fixes S in steel and is effective in improving the toughness of the welded heat affected zone. To fully obtain this effect, it is necessary to contain 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, which can cause cracks. Therefore, if Ca is contained, the upper limit of the Ca content is 0.0100% or less. Furthermore, if Ca is contained, the lower limit of the Ca content is preferably 0.0001% or more.

Mg: 0.0100% or less Mg is an element that is effective in fixing S in steel and improving the toughness of the welded heat affected zone. In order to fully obtain this effect, it is necessary to contain 0.0001% or more. On the other hand, if it exceeds 0.0100%, the amount of inclusions in the steel increases, which may cause cracking. Therefore, if Mg is contained, the upper limit of the Mg content is 0.0100% or less. Furthermore, if Mg is contained, the lower limit of the Mg content is preferably 0.0001% or more.

The balance is Fe and unavoidable impurities. As unavoidable impurities, N and O are permissible up to 0.0100% and 0.0100%.

The steel plate of the present invention has a surface hardness of 460 to 590 in terms of Brinell hardness HBW10/3000. The term "surface hardness" as used herein refers to the value (Brinell hardness) measured in accordance with the provisions of JIS Z 2243 (2008) at a position 0.5 mm from the surface in the plate thickness direction.

Surface hardness: Brinell hardness HBW10/3000 of 460 or more and 590 or less If the surface hardness is less than 460 at HBW10/3000, the surface hardness is low, and therefore the desired wear life cannot be ensured when a severe wear environment requires higher corrosion wear resistance. For this reason, the surface hardness of the steel plate of the present invention is limited to 460 or more at Brinell hardness HBW10/3000. On the other hand, if the surface hardness exceeds 590 at HBW10/3000, bending workability deteriorates. For this reason, the surface hardness is limited to 590 or less at Brinell hardness HBW10/3000.

[Method of manufacturing steel sheet]
The molten steel having the above-mentioned composition is melted by a known method such as a converter or an electric furnace, and is made into a steel material such as a slab or a billet by a known method such as a continuous casting method or an ingot casting method. It goes without saying that the molten steel may be subjected to additional treatments such as ladle refining or vacuum degassing. In hot rolling, in order to ensure strength, it is preferable to optimize the heating temperature of the steel material and the finishing end temperature and cooling rate during hot rolling. That is, from the viewpoint of ensuring the hot finishing rolling end temperature, the steel material is preferably heated to a temperature of 1000 to 1250°C, and then hot rolled into a steel material of the desired size and shape, or, if the temperature of the steel material is high enough to be hot rolled, it is preferable to hot roll it into a steel material of the desired size and shape without heating or by soaking it.

In hot rolling, in order to ensure strength, it is preferable to optimize the hot finish rolling end temperature and the cooling rate after hot rolling. Hot rolling is completed at a temperature of 770°C or higher, air-cooled, and then reheated to 850°C to 1000°C. It is preferable to then immediately or after a short period of time cool from a cooling start temperature of 750°C or higher at a cooling rate of 0.5°C/s to 100°C/s (for example, water cooling) and end the cooling at a cooling stop temperature of 200°C or lower. Also, immediately or after a short period of time after hot rolling, accelerated cooling (for example, water cooling) may be performed from a cooling start temperature of 750°C or higher (in the case of water cooling, the water cooling start temperature) at a cooling rate of 0.5°C/s to 100°C/s and end the accelerated cooling at a cooling stop temperature of 200°C or lower.

Steels having the composition shown in Table 1 (the balance being Fe and unavoidable impurities) were melted in a vacuum melting furnace and cast into a mold to obtain steel materials. These steel materials were then hot-rolled and immediately air-cooled after the hot rolling. After air-cooling, the steels were further reheated and then water-cooled.
Test pieces were taken from the obtained steel plates and subjected to a surface hardness test and a corrosion wear test.

(1) Surface Hardness Test A test piece for surface hardness measurement was taken so that the measurement surface was 0.5 mm from the surface of the obtained steel plate, and the surface hardness HBW10/3000 was measured in accordance with the provisions of JIS Z 2243 (2008). The hardness measurement was performed using a 10 mm tungsten hard ball and a load of 3000 kgf. The measurements were performed at three points 0.5 mm from the surface, and the arithmetic average of the obtained measured values was calculated, and the average value was determined as the surface hardness of the steel plate.

(2) Corrosion wear test A wear test piece (size: 10 mmφ×75 mm length) was taken from the ¼t portion (t indicates the plate thickness) in the plate thickness direction of the obtained steel plate. The test piece was attached to an abrasion tester and a wear test was performed.
Three abrasion test pieces were attached at an angle of 120 degrees to the rotor of the test machine, 150 mm from the axis of rotation, parallel to the axis of rotation, and then the test pieces were placed in the test tank and an abrasive material was introduced inside. The abrasive material was a mixture of silica sand with an average particle size of 0.7 mm and dilute sulfuric acid with a pH of 2, with a weight ratio of silica sand to dilute sulfuric acid of 5:3.
The test conditions were a rotation speed of 500 rpm and a number of revolutions of 60,000. After the test, the weight of each test piece was measured. Then, the difference between the weight after the test and the initial weight (= weight loss) was calculated. In addition, a test piece taken from a general structural rolled steel material SS400 (JIS G3101) as a conventional example was subjected to the abrasion test in the same manner, and the weight loss of the test piece was calculated.
The corrosion wear resistance was evaluated based on the ratio of the weight loss of each test piece to the weight loss of SS400, and if this ratio was 0.70 or less, it was evaluated as good.

(3) Charpy test The toughness by the Charpy test (JIS Z 2242 (2018)) was evaluated as good if the absorbed energy was 21.0 J or more on average in one set (n = 3) at -40 ° C.

The evaluation results (1) and (2) and (3) the toughness values measured by Charpy tests are shown in Table 2.

As shown in Table 2, all of the inventive examples have both surface hardness and corrosive wear resistance.
In contrast, in the comparative steels 18 to 22, at least one of the surface hardness and the corrosion wear resistance is not sufficient, and in the comparative steels 23 and 24, the toughness is not sufficient.

As described above, the present invention provides thick steel plates for use in components that require wear resistance in industrial machinery, transport equipment, etc., and has excellent corrosion and wear resistance, particularly in acidic corrosive environments such as coal mining environments.

Claims (2)

In mass percent,
C: 0.24% or more and less than 0.32%;
Si: 0.05% or more and 1.00% or less,
Mn: 0.10% or more and 2.00% or less,
P: 0.030% or less (excluding 0%)
S: 0.0300% or less (excluding 0%),
Al: 0.005% or more and 0.100% or less,
Cr: 3.00% or more and 11.50% or less;
The balance is Fe and unavoidable impurities,
Surface hardness is 460 to 590 on the Brinell hardness scale HBW10/3000.
A steel plate characterized by: Further, in mass%,
Mo: 1.000% or less,
Nb: 0.100% or less,
Ti: 0.100% or less,
V: 0.200% or less,
Zr: 0.100% or less,
Sn: 0.200% or less,
Sb: 0.200% or less,
Cu: 2.00% or less,
Ni: 2.00% or less,
Co: 2.00% or less,
W: 1.000% or less,
B: 0.0030% or less,
REM: 0.0100% or less,
Ca: 0.0100% or less,
Mg: 0.0100% or less,
The steel sheet according to claim 1, further comprising at least one selected from the following: