KR20130045900A - Abrasion-resistant steel plate or sheet with excellent weld toughness and delayed fracture resistance - Google Patents

Abstract

Provided is a wear-resistant steel sheet having excellent toughness and delayed fracture resistance for welded parts suitable for construction machinery and industrial machinery. Specifically, in mass%, C: 0.20 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.40 to 1.2%, P: 0.010% or less, S: 0.005% or less, Cr: 0.40 to 1.5%, Nb: 0.005 to 0.025%, Ti: 0.005 to 0.03%, Al: 0.1% or less, N: 0.01% or less, if necessary, one of Mo, W, B, Cu, Ni, V, REM, Ca, and Mg Or 2 or more types, and DI * is DI * (= 33.85 × (0.1 × C) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.75 × V + 1) × (1.5 × W + 1)): 45 to 180, C + Mn / 4-Cr / 3 + 10P ≦ 0.47 and the microstructure causes martensite to be known phase Steel plate.

Description

ABRAION-RESISTANT STEEL PLATE OR SHEET WITH EXCELLENT WELD TOUGHNESS AND DELAYED FRACTURE RESISTANCE}

The present invention is a wear-resistant steel sheet having a plate thickness of 4 mm or more suitable for providing construction machines, industrial machines, shipbuilding, steel pipes, civil engineering, construction, etc. It relates to abrasion resistant steel plate or steel sheet, and in particular, to excellent weld toughness and delayed fracture resistance.

When hot rolled steel sheets are used in steel structures such as construction machinery, industrial machinery, shipbuilding, steel pipe, civil engineering, construction, and the like, abrasion resistant properties of the steel sheets may be required. Conventionally, in order to retain the excellent wear resistance as a steel material, it is common to raise the hardness, and it is possible to remarkably increase the martensite single phase microstructure. It is also effective to increase the amount of solid solution carbon in order to increase the hardness of the martensite structure itself.

Therefore, wear-resistant steel sheets generally have high cold cracking susceptibility and are inferior in toughness of welds, and thus are used in rock or earth and sand when used in welded steel structures. It was common to bond and use as a liner on the surface of the steel member which contacts back. For example, in a vessel of a dumped motor lorry, after assembling by welding using mild steel, the wear-resistant steel sheet may be bonded to only the surface of the vessel in contact with the soil. .

However, in the manufacturing method which can join a wear resistant steel plate after assembling a weld structure, since the manufacturing labor and manufacturing cost increase, the wear resistant steel plate which can be applied as a strength member of a weld structure is desired. It was.

Patent document 1 relates to a wear-resistant steel sheet excellent in delayed fracture resistance and a method for manufacturing the same, and in order to improve the delayed fracture characteristics, Cu, V in a low Si-low P-low S-Cr, Mo, Nb-based composition It is described to directly quench (quenching, also referred to as DQ) steels containing one or two or more of, Ti, B and Ca, and tempering as necessary.

Patent document 2 relates to a high wear-resistant steel and a method for producing a steel product, the composition satisfying a parameter formula consisting of the content of these elements in 0.24-0.3 C-Ni, Cr, Mo, B system The steel which has martensite or martensitic baintic structure containing 5-15 volume% of austenite, and improved abrasion resistance is described, and the steel of the said component is austenite It is described to cool between austenitizing temperature and 450 deg. C at a cooling rate of 1 deg. C / sec or more.

Patent document 3 relates to a wear resistant steel having excellent toughness and delayed fracture resistance, and a method for manufacturing the same, wherein the composition and the surface layer of Cr, Ti, and B are required are tempered martensite. Steel material whose internal part is tempered martensite and tempered lower bainitic structure and defines the aspect ratio of prior austenite grain diameter in the thickness direction and in the rolling direction And quenching and tempering the steel of the said component composition directly after hot-rolling at a cumulative reduction ratio of 50% or more at 900 degrees C or less.

Patent document 4 relates to a wear resistant steel having excellent toughness and delayed fracture resistance and a method for producing the same, wherein the composition and surface layer of Cr, Ti, and B are essential and martensite, and the inner part has martensite and lower bainite structure. And a steel structure in which the elomgation rate of the old austenite grains, which is a mixed structure of or a lower bainite single phase structure and is expressed as a ratio of the old austenite grain size in the rolling direction to the old austenite grain diameter in the plate thickness center portion; It is described that the steel of the said component composition is directly quenched after hot rolling at 900 degreeC or less by 50% or more of a cumulative reduction ratio.

Patent document 5 relates to a wear resistant steel excellent in weldability, wear resistance and corrosion resistance of a welded part, and a method for producing the same, wherein 4 to 9 mass% of Cr is used as an essential element, and one or more of Cu, Ni, or It contains two kinds and hot-rolls the steel which satisfy | fills the parametric formula which consists of content of a specific component, and the steel of the said component composition at cumulative reduction ratio 30% or more at 950 degreeC or less, and then reheats at Ac3 or more, and performs a quenching process. Is described.

Japanese Patent Laid-Open No. 5-51691 Japanese Patent Laid-Open No. 8-295990 Japanese Laid-Open Patent Publication No. 2002-115024 Japanese Laid-Open Patent Publication No. 2002-80930 Japanese Laid-Open Patent Publication No. 2004-162120

By the way, when the steel is welded and joined, the most deterioration in toughness is a problem of toughness in the bond area of the fusion line, but the martensite structure remains quenched. In wear resistant steels, toughness degradation, called low temperature tempering embrittlement, is also a problem even in welded heat affected zones (hereinafter referred to as HAZ) which are reheated to around 300 ° C away from the melting boundary. Becomes Low temperature tempering embrittlement is considered to be due to the effect of the morphology change of carbide in martensite and the intergranular segregation of impurity elements.

In the region reheated at a low temperature tempering embrittlement temperature, hydrogen penetrating into the welding portion from a shielding gas or the like during welding, and residual stress generated by the heat of welding are superimposed, resulting in delayed fracture (generated at the welding portion). Such cracking is generally caused by low temperature cracking), and particularly, delayed fracture is likely to occur in high strength wear-resistant steel.

Therefore, when the wear resistant steel sheet is applied to the strength member of the welded structure, it is necessary to improve the toughness of the weld heat-affected portion that is reheated around 300 ° C away from the bond portion and the melt boundary line, but the conventional wear resistant steel sheet is a welded portion. In order to prevent cold cracking and to prevent cold cracking, it is necessary to perform a process such as preheating or postheating before and after welding to reduce the release of hydrogen in the steel sheet and the residual stress. there was.

It is not described in patent documents 1 and 2 to improve the toughness of a weld part in abrasion resistant steel, and patent documents 3 and 4 also define a micro structure for the purpose of improving the toughness of a base material. Although patent document 5 has examined the weldability and the wear resistance of a weld part, it does not aim at the improvement of weld part toughness, but in wear-resistant steel proposed by patent documents 1-5 etc., both the toughness and delayed fracture characteristic of a weld part are proposed. It was not early to improve.

Therefore, an object of the present invention is to provide a wear resistant steel sheet excellent in toughness and delayed fracture resistance of a welded portion without causing a decrease in productivity and an increase in manufacturing cost. In the present invention, the welded part toughness means the toughness of the weld heat affected zone, and the excellent welded part toughness means particularly excellent toughness in the bond part and the low temperature temper embrittlement temperature range.

MEANS TO SOLVE THE PROBLEM In order to achieve the said subject, the present inventors earnestly research about the various factors which determine the chemical composition of a steel plate, a manufacturing method, and a microstructure, in order to ensure the toughness and delayed fracture characteristic of a weld part with respect to a wear resistant steel plate. Was carried out to obtain the following recognition.

1. In order to secure excellent wear resistance, it is essential to use martensite as the base or main structure of the steel sheet. For this purpose, it is important to strictly manage the chemical composition of the steel sheet to secure hardenability.

2. In order to achieve excellent weld toughness, it is necessary to suppress coarsening of crystal grains in the bond portion. To this end, it is effective to disperse fine precipitates in the steel sheet and utilize the pinning effect. Do.

3. It is important to properly manage the amount of alloying elements such as C, Mn, Cr, P, etc. in order to secure excellent toughness in the low temperature temper embrittlement temperature range of the weld heat affected zone and suppress delayed fracture.

The present invention has been made by further examining the obtained recognition, that is, the present invention,

1.% by mass, C: 0.20 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.40 to 1.2%, P: 0.010% or less, S: 0.005% or less, Cr: 0.40 to 1.5%, Nb: 0.005 to 0.025%, Ti: 0.005 to 0.03%, Al: 0.1% or less, N: 0.01% or less, the hardenability index DI * represented by the formula (1) is 45 or more, and the balance Fe and inevitable. A wear-resistant steel sheet having a composition made of impurities and excellent in welded toughness and delayed fracture resistance, in which a microstructure has martensite as a base phase.

DI * = 33.85 × (0.1 × C) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.75 X V + 1) x (1.5 x W + 1)... ... (One)

In the formula (1), each element symbol is content (mass%).

2. The steel composition further comprises one or two or more of Mo: 0.05 to 1.0%, W: 0.05 to 1.0% and B: 0.0003 to 0.0030% in mass%. Abrasion resistant steel plate with excellent weld toughness and delayed fracture resistance.

3. Weld part of 1 or 2 base material characterized by containing 1 type (s) or 2 or more types of Cu: 1.5% or less, Ni: 2.0% or less, V: 0.1% or less in the said steel composition further. Abrasion resistant steel sheet with excellent toughness and delayed fracture resistance.

4. In any one of 1 to 3, characterized in that the steel composition further contains, in mass%, one or two or more of REM: 0.008% or less, Ca: 0.005% or less, Mg: 0.005% or less. Abrasion resistant steel sheet having excellent welded toughness and delayed fracture resistance.

5. The wear resistant steel sheet excellent in the weld part toughness and delayed fracture-breaking characteristic in any one of 1-4 whose surface hardness of the said steel plate is 400HBW10 / 3000 or more as Brinell hardness.

6. The steel sheet according to any one of 1 to 5, wherein the steel sheet has excellent weld zone toughness and delayed fracture resistance with a hardenability index DI * of 180 or less.

7. The steel sheet according to any one of 1 to 6, wherein the steel sheet according to formula (2) is excellent in weld toughness and delayed fracture resistance.

C + Mn / 4—Cr / 3 + 10P ≦ 0.47... ... (2)

In the formula (2), each elemental symbol is content (mass%).

According to the present invention, a wear resistant steel sheet having excellent toughness and delayed fracture resistance of a welded portion can be obtained, which greatly contributes to the improvement of manufacturing efficiency and safety at the time of steel structure fabrication, and has an industrially significant effect.

1 is a diagram illustrating a T-type fillet weld crack test.
It is a figure which shows the sampling position of the Charpy impact test piece of a welding part.

(Mode for carrying out the invention)

In the present invention, the ingredient composition and the microstructure are defined.

[Component Composition] In the following description,% is mass%.

C: 0.20 to 0.30%

C needs to contain 0.20% or more in order to raise the hardness of martensite and to acquire the effect as an important element in order to ensure the outstanding wear resistance. On the other hand, when it contains exceeding 0.30%, not only weldability will deteriorate but toughness in a bond part and a low temperature tempering area | region will also deteriorate. For this reason, it limits to 0.20 to 0.30% of range. Preferably, it is 0.20 to 0.28%.

Si: 0.05 to 1.0%

Si acts as a deoxidizing agent and has the effect of hardening the steel sheet by solid solution strengthening in addition to steelmaking and need. Moreover, it has an effect which suppresses toughness deterioration in the temper embrittlement area | region of a welding heat affected zone. In order to acquire such an effect, 0.05% or more of containing is required. On the other hand, when it contains exceeding 1.0%, since the toughness of a weld heat affected zone deteriorates remarkably, it limits to 0.05 to 1.0% of range. Preferably, it is 0.07 to 0.5%.

Mn: 0.40 to 1.2%

Mn has the effect of increasing hardenability of the steel, and 0.40% or more is necessary to secure the hardness of the base material. On the other hand, when it contains more than 1.2%, not only the toughness, ductility, and weldability of a base material deteriorate, but it promotes grain boundary segregation of P, and encourages generation of delayed fracture. For this reason, it limits to 0.40 to 1.2% of range. Preferably, it is 0.40 to 1.1%.

P: 0.010% or less

When P contains more than 0.010%, it will segregate in a grain boundary, become a starting point of delayed fracture, and deteriorate the toughness of a weld heat affected zone. For this reason, it is preferable to make 0.010% an upper limit and to reduce as much as possible. In addition, since excess P reduction leads to an increase in refining cost, which is economically disadvantageous, it is preferable to be 0.002% or more.

S: not more than 0.005%

Since S deteriorates low-temperature toughness and ductility of the base material, it is preferable to reduce S to an upper limit of 0.005%.

Cr: 0.40 to 1.5%

Cr is an important alloy element in the present invention, has an effect of increasing the hardenability of steel, and has an effect of suppressing the deterioration of toughness in the temper embrittlement region of the weld heat affected zone. This is because, when Cr is contained, the diffusion of C in the steel sheet is delayed and the form change of carbide in martensite is suppressed when reheated to a temperature range where low temperature temper embrittlement occurs. In order to have such an effect, 0.40% or more of containing is required. On the other hand, when it contains exceeding 1.5%, an effect will be saturated, it will become economically disadvantageous, and weldability will fall. For this reason, it limits to 0.40 to 1.5% of range. Preferably, it is 0.40 to 1.2%.

Nb: 0.005% to 0.025%

Nb is precipitated as carbonitride to refine the base metal and the microstructure of the weld heat-affected zone, and the solid solution N is fixed to improve the toughness of the welded heat-affected zone and suppress the occurrence of delayed fracture. It is an important element that combines effects. In order to acquire such an effect, 0.005% or more of containing is required. On the other hand, when it contains exceeding 0.025%, coarse carbonitride may precipitate and it may become a starting point of destruction. For this reason, it limits to 0.005 to 0.025% of range. Preferably, it is 0.007 to 0.023%.

Ti: 0.005% to 0.03%

Ti has the effect of suppressing the coarsening of crystal grains in the bond portion by fixing the solid solution N to form TiN, and at the low temperature tempering temperature range due to the reduction of the solid solution N, It has the effect of suppressing occurrence. In order to acquire such an effect, 0.005% or more of containing is required. On the other hand, when it contains exceeding 0.03%, TiC will precipitate and a base material toughness will deteriorate. For this reason, it limits to 0.005 to 0.03% of range. Preferably, it is 0.007 to 0.025%.

Al: 0.1% or less

Al acts as a deoxidizer and is most widely used in the molten steel deoxidation process of steel sheets. In addition, by fixing the solid solution N in the steel to form AlN, it has the effect of suppressing coarsening of the crystal grains in the bond portion, and deterioration of toughness and delayed fracture in the low temperature tempering temperature range due to the reduction of the solid solution N. It has the effect of suppressing occurrence. On the other hand, when it contains exceeding 0.1%, since it mixes with a weld metal at the time of welding, and degrades the toughness of a weld metal, it is limited to 0.1% or less. Preferably, it is 0.01 to 0.07%.

N: 0.01% or less

N forms nitride with Nb and Ti, and has the effect of suppressing grain coarsening of the weld heat affected zone. However, when it contains exceeding 0.01%, since a base material and weld part toughness will fall remarkably, it will limit to 0.01% or less. Preferably, it is 0.0010 to 0.0070%. The remainder is Fe and inevitable impurities.

In the present invention, in order to further improve the characteristics, one or two or more of Mo, W, B, Cu, Ni, V, REM, Ca, and Mg may be contained in addition to the basic component system.

Mo: 0.05% to 1.0%

Mo significantly increases the hardenability and is an element effective for high hardness of the base metal. In order to acquire such an effect, it is preferable to set it as 0.05% or more, but when it exceeds 1.0%, since it adversely affects base material toughness, ductility, and weld crack resistance, it is made into 1.0% or less.

W: 0.05 to 1.0%

W is an element which is remarkably increased hardenability and is effective for high hardness of a base material. In order to acquire such an effect, it is preferable to set it as 0.05% or more, but when it exceeds 1.0%, since it adversely affects base material toughness, ductility, and weld cracking property, it sets it as 1.0% or less.

B: 0.0003 to 0.0030%

B is an element which is remarkably increased hardenability by addition of a trace amount, and is effective for high hardness of a base material. In order to acquire such an effect, it is preferable to set it as 0.0003% or more, but when it exceeds 0.0030%, since it will adversely affect base material toughness, ductility, and weld cracking property, it shall be 0.0030% or less.

Cu, Ni, and V are all elements which contribute to the strength improvement of steel, and can be appropriately contained according to the desired strength.

Cu: 1.5% or less

Cu is an element which increases hardenability and is effective for high hardness of a base material. In order to acquire such an effect, it is preferable to set it as 0.1% or more, but when it exceeds 1.5%, it will be saturated and hot brittleness will generate | occur | produce, and it will be 1.5% or less because it degrades the surface property of a steel plate.

Ni: 2.0% or less

Ni is an element which increases hardenability and is effective for high hardness of a base material. In order to acquire such an effect, it is preferable to set it as 0.1% or more, but when it exceeds 2.0%, since an effect becomes saturated and it becomes economically disadvantageous, it is referred to as 2.0% or less.

V: 0.1% or less

V is an element which increases hardenability and is effective for high hardness of a base material. In order to acquire such an effect, it is preferable to set it as 0.01% or more, but when it exceeds 0.1%, since it will degrade base material toughness and ductility, it shall be 0.1% or less.

REM, Ca, and Mg all contribute to toughness improvement and are selected and added according to desired characteristics. When adding REM, it is preferable to set it as 0.002% or more, but since an effect is saturated even if it exceeds 0.008%, let 0.008% be an upper limit.

When adding Ca, it is preferable to set it as 0.0005% or more, but since effect is saturated even if it exceeds 0.005%, let 0.005% be an upper limit.

 When adding Mg, it is preferable to set it as 0.001% or more, but since an effect is saturated even if it exceeds 0.005%, let 0.005% be an upper limit.

DI * = 33.85 × (0.1 × C) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.75 X V + 1) x (1.5 x W + 1)... (One)

Each element symbol is taken as content (mass%).

This parameter: DI * (quenchability index) is prescribed | regulated in order to have excellent abrasion resistance by making martensite the base structure of a base material within the range of the above-mentioned component composition, and makes the value of this parameter 45 or more. When it is less than 45, the quenching depth from a plate | board thickness surface layer is less than 10 mm, and the lifetime as an abrasion resistant steel becomes short.

When the value DI * of this parameter exceeds 180, the matrix structure of the base material is martensite, and the wear resistance is good, but the low temperature cracking property at the time of welding and the low temperature toughness of the welding part are deteriorated. More preferably, it shall be 50-160.

C + Mn / 4—Cr / 3 + 10P ≦ 0.47... (2)

Each element symbol is taken as content (mass%).

When the base structure of the base material is martensite, and a welding composition is used to form a component composition having excellent toughness in any of the bond portion and the low temperature temper embrittlement region, within the range of the above-described component composition, this parameter: C + Mn The value of / 4-Cr / 3 + 10P is made 0.47 or less. Even if it exceeds 0.47, although the matrix structure of a base material is martensite and abrasion resistance is favorable, the toughness of a weld part will remarkably deteriorate. Preferably, it is 0.45 or less.

[Micro organization]

In the present invention, in order to improve wear resistance, the base phase or main phase of the microstructure of the steel sheet is defined as martensite. Structures such as bainite and ferrite other than martensite are preferably not mixed as much as possible because they reduce wear resistance, but if the area ratio of the sum of these structures is less than 10%, The effect can be ignored. In addition, when the surface hardness of the steel sheet is less than 400HBW10 / 3000 in Brinell hardness, the life as wear-resistant steel is shortened. Therefore, it is preferable to make surface hardness 400HBW10 / 3000 or more by Brinell hardness.

The microstructure of the bond portion is a mixed structure of martensite and bainite. Structures such as ferrite other than martensite and bainite are preferably not mixed as much as possible because the wear resistance is lowered. However, if the area fraction of the total of these structures is less than 20%, the effect can be ignored.

In addition, in order to secure the toughness of the bond portion, the carbonitrides of Nb and Ti have an average particle diameter of 1 µm or less and 1000 or more mm 2, an average grain size of the old austenite is less than 200 µm, and a radial hook The average grain size of the lower microstructure surrounded by a large tilt grain boundary of 15 ° or more is preferably less than 70 μm.

The wear-resistant steel according to the present invention can be produced under the following manufacturing conditions. In description, the "degreeC" display regarding temperature shall mean the temperature in 1/2 position of plate | board thickness. It is preferable to melt | dissolve the molten steel of the said composition by a well-known solvent method, and to make it steel materials, such as slab of a predetermined dimension, by the continuous casting process or the lump-fragment rolling method.

Subsequently, after heating the obtained steel raw material immediately after cooling, or after cooling, it is hot-rolled and it is set as the steel plate of a desired plate thickness. It is quenched by water cooling immediately after hot rolling, or reheating. Then, tempering at 300 degrees C or less is performed as needed.

Example 1

In the steel converter-ladle refining-continuous casting method, the steel slab prepared by the various component compositions shown in Table 1 is heated to 1000-1250 degreeC, and is shown in Table 2, Under manufacturing conditions, hot rolling is performed, and some steel sheets are water cooled immediately after rolling (quenching (DQ)), and for other steel sheets, air cooling after rolling is carried out, and after cooling, water cooling (quenching (RQ)) is performed. Done.

The obtained steel sheet was subjected to surface hardness measurement, abrasion resistance evaluation, base material toughness measurement, T-type fillet weld crack test (evaluation of anti-destructive fracture characteristics), weld regeneration heat cycle test and toughness test of welded joints. Was carried out as a tip. The obtained results are shown in Table 3.

[Surface hardness 1]

Surface hardness measurement was based on JIS Z2243 (1998), and measured the surface hardness under the surface layer (hardness of the surface measured after removing the scale of the surface layer). The measurement used the tungsten hard ball of diameter 10mm, and the load was 3000 kgf.

[Material toughness 1]

From the direction perpendicular to the rolling direction of the sheet thickness 1/4 position of each steel plate, a V notch test specimen was taken in accordance with the provisions of JIS Z 2202 (1998), and JIS Z 2242 (1998). Charpy impact tests of three temperatures at each temperature were carried out in accordance with the provisions of the above, and the absorbed energy at the test temperature of 0 ° C was obtained to evaluate the base metal toughness. The test temperature of 0 ° C. was selected in consideration of use in a warm zone.

It is excellent in the three mean values is the base material toughness of 30J or more (that is sometimes referred to as vE ₀₎ absorbed energy at a test temperature of 0 ℃ was (within the scope of the present invention).

[Wear resistance 1]

Abrasion resistance was subjected to the rubber wheel abrasion test in accordance with the provisions of ASTM G65. Test piece is 10 mmt (t: plate thickness) x 75 mmw (w: width) x 20 mmL (L: length) (when the plate thickness is less than 10 mmt, t (plate thickness) x 75 mmw x 20 mmL) and 100% SiO ₂ abrasive sand was used as the wear material.

The weight of the test piece before and after the test was measured and the amount of abrasion was measured. The test result was evaluated based on abrasion resistance: (abrasion amount of mild steel sheet) / (abrasion amount of each steel sheet) on the basis of the wear amount of the mild steel plate (SS400) as a reference (1.0). The larger the wear resistance, the better the wear resistance. In the scope of the present invention, the wear resistance was 4.0 or more.

[Delayed Destruction 1]

In the T shape fillet weld cracking test, after performing a restrictive welding of shielded metal arc welding on a test body assembled with a T-shape as shown in FIG. V) After preheating to 25 ° C x 60% humidity or 100 ° C, test welding was performed.

In the welding method, three-layer six-pass welding was performed by covering arc welding (welding material: LB52UL (4.0 mm Φ)) with a heat input of 17 kJ / cm. After welding, the sample was left at room temperature for 48 hours, and then five samples of welded section observations (bead length 200 mm were divided into five equal parts) of the test plate were collected, and the presence or absence of the occurrence of cracks in the heat affected zone of the welder was measured by the projector and the optical. It investigated by the microscope. In each of the five cross-sectional samples collected at no preheating and preheating of 100 ° C., no cracks were generated at the weld heat affected zones, which were evaluated as having excellent delayed fracture characteristics.

[Toughness of Welding Part 1-1]

The weld heat reproduction thermal cycle test (simthetic heat-affected zone test) simulated each of the bond part and the low temperature temper embrittlement area | region when the 1-layer carbon dioxide gas arc welding of 17 kJ / cm of welding heat inputs were performed. The simulation of the bond part was hold | maintained for 1 second at 1400 degreeC, and the cooling rate of 800-200 degreeC was 30 degreeC / s. In addition, the simulation of the low temperature temper embrittlement area | region was hold | maintained at 300 degreeC for 1 second, and 300-100 degreeC was cooled at 5 degree-C / s.

After applying the aforementioned heat cycle to a square bar test specimen taken from the rolling direction with a high-frequency induction heating device, the V-notch Charpy impact in accordance with JISZ2242 (1998). I did a test. The V notch Charpy impact test was performed with three test pieces about each steel plate, making test temperature 0 degreeC.

Three average values of the absorption energy (vE ₀ ) of the bonded portion and the low temperature temper embrittlement region were each 30J or more (within the scope of the present invention) having excellent weld toughness.

[Toughness of Welding Part 1-2]

In addition, in order to confirm the toughness of the seal joint, the steel sheet by shielded metal arc welding (heat input 17kJ / cm, preheating 150 ° C, welding material: LB52UL (4.0mmΦ)) Bead on plate welding was performed. The Charpy impact test piece was extract | collected at the position of 1 mm under the surface, the notch position was made into the bond part, and the V notch Charpy impact test was done according to JISZ2242 (1998). 2 shows a sampling position and a notch location of the Charpy impact piece.

The V-notch Charpy impact test of an actual weld joint was performed with three test pieces for each test temperature, making a test temperature of 0 degreeC. Three average values of absorbed energy (vE ₀ ) were 30J or more (within the scope of the present invention) having excellent bond part toughness.

Table 2 shows the production conditions of the disclosed steel sheet, and Table 3 shows the results of the above tests. Examples of the present invention (steel Nos. 1 to 5) have a surface hardness of 400HBW10 / 3000 or more, excellent wear resistance, a base material toughness of 0 ° C and 30J or more, and cracks in a T-type fillet weld cracking test. It did not generate | occur | produce, and also had the outstanding toughness also in the weld part reproduction heat cycle test and the utility welding part, and it was confirmed that it was excellent in the weld part toughness.

On the other hand, Comparative Examples (steel Nos. 6 to 14) whose component composition is outside the scope of the present invention include surface hardness, abrasion resistance, T-type fillet weld crack test, base material toughness, reproduction thermal cycle Charpy impact test, and thread joint Charpy impact test (Charpy It was confirmed that none or multiple of the impact test of actual weld joints could meet the target performance.

Example 2

After the steel slab prepared by various component compositions shown in Table 4 by the converter-ladle refinement-continuous casting method was heated at 1000-1250 degreeC, it hot-rolled on the manufacturing conditions shown in Table 5, and some steel plates After the rolling, water cooling (quenching (DQ)) was performed immediately, and for other steel sheets, air cooling was performed after rolling, and water cooling (quenching (RQ)) was performed after reheating.

About the obtained steel plate, surface hardness measurement, abrasion resistance evaluation, base material toughness measurement, T-type fillet weld cracking test (evaluation of anti-destructive fracture characteristics), weld part regeneration heat cycle test, and toughness test of the welded part of the seam were carried out as follows. . The obtained results are shown in Table 6.

[Surface hardness 2]

Surface hardness measurement measured the surface hardness (surface hardness measured after removing the scale of a surface layer) under surface layer based on JISZ2243 (1998). The measurement used the tungsten oral of diameter 10mm, and made the load into 3000 kgf.

[Material toughness 2]

From the direction perpendicular to the rolling direction of the sheet thickness quarter position of each steel plate, a V-notch test piece is extract | collected in accordance with JIS Z 2202 (1998), and according to JIS Z 2242 (1998), The Charpy impact test of each temperature of three steel plates was performed, absorption energy in test temperature of 0 degreeC and -40 degreeC was calculated | required, and base metal toughness was evaluated. The test temperature of 0 ° C. was selected taking into account the use in a warm zone and the test temperature of −40 ° C. considering the use in a cold region.

The average value of at least three (that is sometimes referred to as vE ₀₎ absorbed energy at a test temperature 0 ℃ 30J, and then the average value of three (that is sometimes referred to as vE _-40) absorbed energy at a test temperature -40 ℃ This 27J or more was made into the excellent base material toughness (within this invention scope). In addition, as the thickness of the steel sheet is less than 10㎜, sub-size (5㎜ × 10㎜) V notch Charpy test specimens sampled and subjected to the Charpy impact test, the three mean values of the absorption energy (vE ₀₎ 15J of As mentioned above, the average value of three absorption energy (vE- ₄₀ ) made 13J or more the thing excellent in base material toughness (within this invention scope).

[Wear resistance 2]

Abrasion resistance was subjected to the rubber wheel test in accordance with the provisions of ASTM G65. Test piece is 10 mmt (t: plate thickness) x 75 mmw (w: width) x 20 mmL (L: length) (when the plate thickness is less than 10 mmt, t (plate thickness) x 75 mmw x 20 mmL) and 100% SiO ₂ wear sand was used for the wear material.

The weight of the test piece before and after the test was measured and the amount of abrasion was measured. The test result was evaluated based on abrasion resistance: (abrasion amount of mild steel sheet) / (abrasion amount of each steel sheet) on the basis of the wear amount of the mild steel plate (SS400) as a reference (1.0). The larger the wear resistance, the better the wear resistance. In the scope of the present invention, the wear resistance was 4.0 or more.

[Delayed Destruction 2]

In the T-type fillet weld crack test, after performing a restraint welding on the test body assembled in the T-shape by coating arc welding as shown in FIG. 1, the test welding is performed after preheating to room temperature (25 ° C x 60% humidity) or 100 ° C. Carried out.

In the welding method, three-layer six-pass welding was performed by covering arc welding (welding material: LB52UL (4.0 mm Φ)) with a heat input of 17 kJ / cm. After the test, after standing at room temperature for 48 hours, five welded cross-section observation samples (bead length 200 mm are divided into five equal parts) of the test plate were taken, and the presence or absence of the occurrence of cracks in the weld heat affected zone was determined by a projector and an optical microscope. Investigated. In each of the five cross-sectional samples collected at no preheating and preheating of 100 ° C., no cracks were generated at the weld heat affected zones, which were evaluated as having excellent delayed fracture characteristics.

[Welding Toughness 2-1]

Weld reproduction heat cycle test, the weld heat input was simulated for each of the bonded portion and the low temperature tempering embrittlement area when the first floor of 17kJ / ㎝ subjected to carbon dioxide gas arc welding _{(one pass CO 2 gas shielded arc} welding). The simulation of the bond part was hold | maintained for 1 second at 1400 degreeC, and the cooling rate of 800-200 degreeC was 30 degreeC / s. In addition, the simulation of the low temperature temper embrittlement area | region was hold | maintained at 300 degreeC for 1 second, and 300-100 degreeC was cooled at 5 degree-C / s.

After giving the above-mentioned heat cycle to the square bar test piece taken from the rolling direction with the high frequency induction heating apparatus, the V-notch Charpy impact test was performed according to JISZ2242 (1998). The V-notch Charpy impact test was performed with three test pieces of each temperature with respect to each steel plate, making test temperature 0 degreeC and -40 degreeC.

The three average values of the absorption energy (vE ₀ ) of the bonded portion and the low temperature temper embrittlement region are 30J or more, and each of the three average values of the absorption energy (vE _-40 ) is 27J or more. My).

In addition, about the steel plate whose plate | board thickness is less than 10 mm, the V-notch Charpy test piece of a subsize (5 mm x 10 mm) is extract | collected, the Charpy impact test is performed, and the absorption energy (vE) of a bond part and a low temperature tempering embrittlement area | region is carried out. Each of the three average values of ₀ ) was 15 J or more, and each of the three average values of the absorbed energy (vE- ₄₀ ) was 13 J or more (within the scope of the present invention).

[Welding Toughness 2-2]

In addition, in order to confirm the toughness of a real joint, bead-on-plate welding was performed to the steel plate by covering arc welding (heat input 17kJ / cm, preheating 150 degreeC, welding material: LB52UL (4.0mmΦ)). The Charpy impact piece was taken out from the position of 1 mm below the surface, and the V notch Charpy impact test was conducted in accordance with JISZ2242 (1998), with the position of the electrode as a bond part. 2 shows a sampling position and a notch position of the Charpy impact piece.

The V-notch Charpy impact test of a real joint was made with three test pieces about each test temperature, making test temperature 0 degreeC and -40 degreeC. Three average values of absorption energy (vE ₀ ) were 30J or more, and three average values of absorption energy (vE- ₄₀ ) were 27J or more (within the scope of the present invention) having excellent bond toughness.

In addition, as the thickness of the steel sheet is less than 10㎜, taken V notch Charpy test pieces of sub-size (5㎜ × 10㎜), and subjected to the Charpy impact test, the three mean values of the absorption energy (vE ₀₎ 15J As mentioned above, three average values of absorption energy (vE- ₄₀ ) made 13J or more the thing excellent in bond part toughness (within this invention scope).

Table 6 shows the production conditions of the disclosed steel sheet and Table 6 shows the results of the above tests. The present invention example (steel Nos. 15 to 17 (where No. 17 has a plate thickness of 8 mm)) has a surface hardness of 400 HBW10 / 3000 or more, is excellent in wear resistance, and has a base material toughness of 0 ° C. of 30 J or more, And the base material toughness of -40 degreeC has 27J or more, and it does not generate | occur | produce by a T-type fillet welding crack test, and also has the outstanding toughness also in a weld part regeneration heat cycle test and a utility weld, and it is excellent in weld part toughness. Confirmed.

On the other hand, although the component composition is within the scope of the present invention, in the case of steel No. 18 having a DI * of more than 180, the surface hardness, wear resistance, base material toughness, and T-type fillet weld cracking tests are good, but the reproducibility of the low temperature temper embrittlement zone is equivalent. It was confirmed that the heat cycle Charpy impact test and the seam Charpy impact test were close to the lower limit of the target performance, and the low-temperature toughness of the weld portion was inferior to that of other invention examples.

Steel No. 19 has good surface hardness, abrasion resistance, and base metal toughness because Si is outside the scope of the present invention in the component composition, but the toughness in the temper embrittlement region of the weld heat affected zone deteriorates, causing T-type fillet weld cracking. The test, the reproduced thermal cycle Charpy impact test and the seam Charpy impact test corresponding to the low temperature tempering embrittlement area could not meet the target performance.

Steel No. 20 has a component composition within the scope of the present invention, but since the formula (2) exceeds 0.47, vE- ₄₀ is close to the lower limit of the performance of the present invention, even in the reproduction thermal cycle Charpy impact test and the real joint Charpy impact test. It was confirmed that it was inferior compared with the other invention example. In addition, in description of Table 4, 5, 6, although steel No. 18, 20 has a component composition in the scope of this invention of Claim 3, the value of DI *, (2) Formula is outside the scope of this invention of Claims 6 and 7. Therefore, we made into a comparative example.

Claims (7)

In mass%, C: 0.20 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.40 to 1.2%, P: 0.010% or less, S: 0.005% or less, Cr: 0.40 to 1.5%, Nb: 0.005 to 0.025% , Ti: 0.005 to 0.03%, Al: 0.1% or less, N: 0.01% or less, the hardenability index DI * represented by the formula (1) is 45 or more, and has a composition consisting of residual Fe and unavoidable impurities, A wear resistant steel sheet having excellent microstructure toughness and delayed fracture resistance of a welded portion having martensite as a matrix.
DI * = 33.85 × (0.1 × C) ^0.5 × (0.7 × Si + 1) × (3.33 × Mn + 1) × (0.35 × Cu + 1) × (0.36 × Ni + 1) × (2.16 × Cr + 1) × (3 × Mo + 1) × (1.75 X V + 1) x (1.5 x W + 1)... ... (One)
In the formula (1), each element symbol is content (mass%). The method of claim 1,
The steel composition further includes, in mass%, one or two or more of Mo: 0.05 to 1.0%, W: 0.05 to 1.0%, and B: 0.0003 to 0.0030%. Abrasion resistant steel plate with excellent fracture characteristics. The method according to claim 1 or 2,
The toughness and delayed fracture resistance of the weld portion, characterized in that the steel composition contains, in mass%, one or two or more of Cu: 1.5% or less, Ni: 2.0% or less, and V: 0.1% or less. Excellent wear resistant steel plate. 4. The method according to any one of claims 1 to 3,
In addition to the steel composition, the toughness and delayed fracture resistance of the weld portion, characterized in that it contains at least one of REM: 0.008% or less, Ca: 0.005% or less, and Mg: 0.005% or less. Excellent wear resistant steel plate. 5. The method according to any one of claims 1 to 4,
Abrasion resistant steel sheet having excellent weld toughness and delayed fracture resistance in which the surface hardness of the steel sheet is 400HBW10 / 3000 or more as Brinell hardness. The steel sheet according to any one of claims 1 to 5, wherein the steel sheet according to any one of claims 1 to 5 has excellent weld toughness and delayed fracture resistance with a hardenability index DI * of 180 or less. The steel sheet according to any one of claims 1 to 6, wherein the steel sheet according to (2) formula is excellent in weld toughness and delayed fracture resistance.
C + Mn / 4—Cr / 3 + 10P ≦ 0.47... ... (2)
In the formula (2), each elemental symbol is content (mass%).

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