CN1293222C - Easy cut by flame abrasion-resistant steel in high rigidity, in toughness and preparation method - Google Patents

Abstract

A wear-resistant steel plate with high hardness, high toughness and easy flame cutting, characterized in that the steel plate contains iron and the following additive elements in weight percentage: 0.10%-0.17%C, 0.05%-0.55%Si, 0.80%-1.60% Mn, 0.01%～0.10%Nb, 0.005%～0.03%Ti, 0.0005%～0.003%B, 0.05%～1.0%Cr, and can also contain at least one additional element selected from the following group: 0.05%～0.8% Ni, 0.05%～0.60%Mo, 0.01%～0.06%Al, 0.05%～0.50%Cu, 0.01%～0.10%V, 0.00001%～0.006%Ca, 0.00001%～0.02%REM, 0.00001%～0.006%Mg . Adopt online direct cooling and quenching after rolling or offline quenching after rolling, and quench from a temperature not lower than the Ar3 transformation point at a cooling rate of at least 10°C/s to a quenching end temperature at least as low as the Ms transformation point. Obtained wear-resistant steel plate with hardness HB≥320, impact toughness Akv-40℃≥30J, easy flame cutting and good welding performance in winter northern regions.

Description

A wear-resistant steel plate with high hardness, high toughness and easy flame cutting and preparation method thereof

Technical field:

The invention relates to metal plates, and in particular provides a wear-resistant steel plate with hardness HB≥320, impact toughness Akv-40°C≥30J, easy flame cutting and good welding performance in winter and its preparation technology.

Background technique:

Wear-resistant steel plates are widely used in loader blades in construction machinery, buckets in excavators, arc plates in bulldozers, bottom plates in dump trucks, and scraper conveyors in coal mining machinery, etc., with huge consumption. At present, there are two ways to manufacture wear-resistant steel plates:

The first method uses low-carbon and low-alloy chemical composition combination, and is manufactured by off-line quenching and tempering after rolling.

Its chemical composition is shown in Table 1:

Table 1 C Si mn P S Cr Mo Ti B 0.16～0.21 0.20～0.50 1.0～1.5 ≤0.02 ≤0.015 0.4～0.7 0.25～0.35 0.01～0.03 0.0005～0.003

The heat treatment process is:

The steel plate is off-line after rolling, reheated at 900-930°C, water-cooled to room temperature in a roll-type quenching machine, and tempered at 400-450°C.

The mechanical properties are shown in Table 2:

Table 2 Rp0.2, MPa Rm, MPa A,% HB Akv-40,J ≥900 ≥1080 ≥10 320～400 ≤30

The analysis of flame cutting cold crack tendency is as follows:

When the high-strength thick steel plate is flame-cut in winter when the ambient temperature is low, in order to avoid delayed cracks on the flame-cut surface of the steel plate, it is necessary to preheat the steel plate before cutting. The calculation formula of the preheating temperature Tph can be expressed by formula (1).

Tph＝500〔Ceq(1+0.0002t)-0.45〕 ^1/2 --------------------------------- ---(1)

In the formula: Ceq is the cutting carbon equivalent

Ceq＝C+0.155(Cr+Mo)+0.14(Mn+V)+0.11Si+0.045(Ni+Cu)-----------(2)

t is the plate thickness.

According to the composition range in Table 1, the chemical composition takes the middle and lower limits, that is, C: 0.19 Si: 0.3 Mn: 1.2Cr: 0.5 Mo: 0.28 is substituted into the formula (2), and the Ceq value is obtained:

Ceq＝C+0.155(Cr+Mo)+0.14(Mn+V)+0.11Si+0.045(Ni+Cu)

＝0.19+0.155(0.5+0.28)+0.14(1.2+0)+0.11×0.3

＝0.51

When the plate thickness is less than or equal to 100mm, the 0.0002t item can be ignored, and the final Tph value is:

Tph＝500〔Ceq-0.45〕 ^1/2

=500 [0.51-0.45] ^1/2

＝122(℃)

It can be seen from the above that when this kind of wear-resistant steel plate is flame-cut in winter in northern China, it needs to be preheated above 120°C. Otherwise, when the ambient temperature of the steel plate is low, normal flame cutting conditions are used, that is, no preheating or post-heating measures are used. , After the steel plate is cut, severe delayed cracks are prone to occur on the flame-cut surface. However, it is very difficult and costly to preheat the steel plate above 100°C before flame cutting, and users cannot take this measure. In fact, because of this reason, when this kind of wear-resistant steel plate is used in the northern region in winter, a large number of delayed cracks will occur on the flame-cut surface of the steel plate, causing huge economic losses to users and steel mills.

The second method uses bainite structure and adopts low temperature tempering after rolling.

The chemical composition is shown in Table 3:

table 3 C Si mn P S Cr Mo 0.16～0.22 1.40～1.70 1.8～2.2 ≤0.02 ≤0.015 0.5～0.8 0.4～0.60

The heat treatment process is:

The steel plate is air-cooled after rolling, and then heated to 350°C for tempering.

The mechanical properties are shown in Table 4:

Table 4 Rp0.2, MPa Rm, MPa A,% HB Akv-40,J ≥900 ≥1080 ≥10 320～420 ≤30

The analysis of flame cutting cold crack tendency is as follows:

According to the composition range in Table 3, the chemical composition takes the middle and lower limits, that is, C: 0.17 Si: 1.5 Mn: 2.0Cr: 0.5 Mo: 0.5 is substituted into the formula (2), and the Ceq value is obtained:

Ceq＝C+0.155(Cr+Mo)+0.14(Mn+V)+0.11Si+0.045(Ni+Cu)

＝0.17+0.155(0.5+0.5)+0.14(2+0)+0.11×1.5

＝0.77

Tph＝500〔Ceq-0.45〕 ^1/2

=500 [0.77-0.45] ^1/2

＝282(℃)

It can be seen from the above that this kind of steel is used for flame cutting of steel plates in winter in northern China, and the steel plates need to be preheated above 280°C.

In short, although the current domestic wear-resistant steel plate has high strength, its impact toughness is low, and due to the high cutting carbon equivalent, it is easy to produce serious damage during normal flame cutting operation under low ambient temperature. The cut surface delays cracking.

Invention content:

The purpose of this invention is to produce a kind of hardness HB≥320, impact toughness Akv-40℃≥30J through reasonable chemical composition design and special control water quenching process technology, which has easy flame cutting and good welding performance in winter northern regions. wear-resistant steel plate.

Usually, the local heating and cooling during cutting affect the distribution of the hardness of the cutting end. In the case of low ambient temperature in winter, flame cutting of thicker steel plates will result in extremely high cooling speed within the range of 2-3 mm in the heat-affected zone of the flame cutting surface. Fast, if the carbon equivalent Ceq of the high-strength steel plate is high, the heat-affected zone of the flame cutting surface will be quenched into martensitic structure at this time, resulting in the hardening of the heat-affected zone of the cutting surface, and the decrease of plasticity and toughness. The surface is prone to delayed cracks. If the steel plate has low plasticity and toughness, the ability of the steel plate to prevent crack growth is low, and the delayed crack on the cut surface is very easy to propagate.

According to formula (1), in order to prevent delayed cracks from normal flame cutting of high-hardness steel plates in winter when the ambient temperature is low, the chemical composition of the steel must be controlled so that the cutting carbon equivalent Ceq≤0.46%. In order to ensure that the wear-resistant steel plate has high hardness and high plasticity and toughness at the same time, a special heat treatment process must be adopted to rapidly quench and cool the steel plate from the austenite zone to a suitable final cooling temperature, so as to obtain martensite And a small amount of bainite structure, and can realize the fully self-tempering controlled water quenching process technology.

Accordingly, the present invention specifically provides a high-hardness, high-toughness and flame-cut wear-resistant steel plate, which is characterized in that: the steel plate contains iron and the following additive elements in weight percentage, (unless otherwise specified in the present invention, all as weight percentage):

0.10%～0.17%C,

0.05%～0.55% Si,

0.80%～1.60%Mn,

0.01%～0.10%Nb,

0.005%～0.03%Ti,

0.0005%～0.003%B

0.05% to 1.0% Cr.

In addition, the wear-resistant steel plate with high hardness, high toughness and easy flame cutting of the present invention may also contain at least one additional element selected from the following group:

0.05%～0.8%Ni,

0.05%～0.60% Mo,

0.01%～0.06%Al,

0.05%～0.50%Cu,

0.01%～0.10%V,

0.00001%～0.006%Ca,

0.00001%～0.02%REM,

0.00001% to 0.006% Mg.

When used in winter, in the wear-resistant steel plate with high hardness, high toughness and easy flame cutting of the present invention, the composition should also meet the following conditions,

C+0.155(Cr+Mo)+0.14(Mn+V)+0.11Si+0.045(Ni+Cu)≤0.46%.

The present invention also provides a method for preparing the above-mentioned high-hardness, high-toughness and flame-cut wear-resistant steel plate, which is characterized in that the final rolling temperature of the steel plate after rolling is greater than Ar3; It is quenched at a temperature not lower than the Ar3 transformation point, and the quenching end temperature is from the Ms transformation point to room temperature.

The present invention provides another method for preparing the above-mentioned high-hardness, high-toughness, easy-to-flame-cut wear-resistant steel plate, which is characterized in that after the steel plate is rolled and cooled, it is reheated to above Ac3, and the cooling rate is never lower than Quenching at the temperature of the Ar3 transformation point, and the quenching end temperature is from the Ms transformation point to room temperature.

In the preparation method of the high-hardness, high-toughness and flame-cut wear-resistant steel plate of the present invention, the quenching end temperature can be between Ms and 150° C., the quenching is stopped, and the quenched steel plate is air-cooled to room temperature.

In the high-hardness, high-toughness and easy-to-flame-cut wear-resistant steel plate of the present invention, the effects of various alloy elements in the steel and their preferred concentration ranges are as follows:

Carbon plays a key role in the hardenability of steel in quenched steel. When its content is less than 0.10%, the hardness of steel after quenching will not reach HB320, and when its content is greater than 0.17%, it will affect the flame cutting performance of wear-resistant steel plate. And welding performance will have adverse effects, and reduce the low temperature impact toughness of the steel, so the carbon content of the steel is controlled within the range of 0.10% to 0.17%.

The addition of silicon is to deoxidize and improve the strength of the steel, and the upper limit of the addition is 0.55%, because excessive silicon content will reduce the impact toughness of the steel and deteriorate the weldability of the steel.

Manganese plays a role in improving hardenability and strength in this steel. When its content is less than 0.80%, the strength of steel is low, but when its content exceeds 1.60%, the hardenability of steel is too strong, which is harmful to wear resistance. The flame cutting performance and welding performance of the steel plate will be adversely affected.

The addition of niobium is to refine the grains of the microstructure after steel rolling, so that the strength and toughness of the steel are improved, because during the steel plate rolling process, the precipitation of niobium carbonitrides hinders recrystallization and inhibits The role of grain growth; the second is to improve the hardenability of steel. In order to obtain these effects, the minimum content of niobium in steel should not be lower than 0.01%, and its content exceeding 0.1% will have a harmful effect on welding performance. The preferred content of niobium is controlled at 0.03% to 0.06%.

Titanium forms fine-grained titanium nitride particles and promotes microstructural refinement by inhibiting austenite grain coarsening during slab reheating. In addition, the presence of titanium nitride particles suppresses grain coarsening in the heat-affected zone at the weld. Therefore, titanium has the effect of improving the low-temperature toughness of the base metal and the heat-affected zone of the weld. Since titanium fixes free nitrogen in the form of titanium nitride, titanium prevents nitrogen from adversely affecting hardenability due to the formation of boron nitride. To achieve these goals, the amount of titanium is at least about 0.005%, and the upper limit is set at about 0.03%, because excess titanium will cause coarsening of titanium nitride and will produce carbide-induced precipitation strengthening of titanium, both of which will Damage to low temperature toughness. The preferred content of titanium is controlled at 0.01%-0.03%.

Adding boron in a small amount, about 0.0005% to 0.003%, in low carbon steel (the carbon content is less than about 0.3%) will significantly improve the hardenability of the steel. A boron amount exceeding 0.003% promotes the formation of brittle particles Fe ₂₃ (C,B) ₆ . The preferred content of boron is controlled at 0.0008%-0.002%.

Chromium generally improves the hardenability of steel and also improves corrosion resistance. When its content exceeds about 1.0%, it will have an adverse effect on the flame cutting performance and welding performance of the wear-resistant steel plate. The preferred content is controlled at 0.15% to 0.7%.

The addition of nickel can not only improve the hardenability of the steel, but also improve the low-temperature impact toughness, but the addition of nickel will greatly increase the manufacturing cost of the steel.

Molybdenum increases the hardenability of steel. When its content exceeds about 0.6%, it will have an adverse effect on the flame cutting performance and welding performance of the wear-resistant steel plate.

The addition of copper can increase the strength of steel and also improve corrosion resistance. When its content exceeds about 0.5%, it adversely affects the surface quality of the steel sheet.

Vanadium has a similar effect to niobium, but not as pronounced as Nb. Its preferred content is controlled at 0.03% to 0.08%.

Aluminum is added to the steel for deoxidation, and it is also effective for the refinement of the steel microstructure. If the amount of aluminum added is too high, that is, more than 0.06%, there will be a tendency to form Al ₂ O ₃ inclusions, which is not good for the toughness of the steel.

Calcium and rare earth metals (REMs) are generally used to control the morphology of manganese sulfide (MnS) inclusions and improve low temperature toughness. The addition of at least about 0.001% calcium or about 0.001% REM is required to control the sulfide morphology. However, if the calcium content exceeds about 0.006% or the REM content exceeds about 0.02%, large amounts of CaO-CaS (a calcium oxide-calcium sulfide) or REM-CAS (a rare earth metal-calcium sulfide) are formed, And it turns into large aggregates and large inclusions, which will not only damage the purity of the steel, but also affect the welding performance of the steel.

Magnesium can generally form fine and dispersed oxide particles, which can inhibit grain growth and/or promote the formation of intragranular ferrite in the HAZ, thereby improving the toughness of the heat-affected zone. For the addition of magnesium to be effective, at least about 0.0001% magnesium needs to be added, however, if the magnesium content exceeds about 0.006%, coarse oxides will form, impairing the toughness of the HAZ region.

According to the composition design and special preparation method of the high-hardness and high-toughness easy-to-flame-cut wear-resistant steel plate of the present invention, the mechanical properties of the obtained wear-resistant steel plate are shown in Table 5:

table 5 Rp0.2, MPa Rm, MPa A,% HB Akv-40°C, J Cold bending at 180°C, d=3a ≥900 ≥1080 ≥10 ≥320 ≥30 qualified

In a word, the advantages of the present invention are:

1. The design of the actual chemical composition of the present invention is simple, the alloy elements are few, and the content is low.

2. The invention does not need tempering after controlling water quenching.

3. The present invention has relatively ideal comprehensive mechanical properties, not only has high hardness, but also has relatively high low-temperature impact toughness.

4. The cutting carbon equivalent Ceq of the present invention is less than or equal to 0.46%. In the case of low ambient temperature in winter, normal flame cutting conditions are adopted, that is, no preheating or postheating measures are adopted, and delayed cracks on the cutting surface will not occur, so it has better Oxygen cutting performance.

Detailed ways:

The embodiment of the present invention can be realized by using any of the following process methods:

1. On-line direct cooling (quenching) process after rolling

According to the thickness of the steel plate, if the cooling capacity of the on-line cooling equipment at the rear of the rolling mill is strong, and the on-line high cooling speed control cooling after rolling can be realized, or even quenching cooling, then this process is adopted. The specific process requirements are that the final rolling temperature of the steel plate is greater than Ar3 after rolling; the hot-rolled steel plate is quenched from a temperature not lower than the Ar3 transformation point at a cooling rate of at least about 10°C/s to at least as low as the quenching end of the Ms transformation point The temperature is based on the hardened steel plate, the preferred cooling rate is at least about 20°C/second, the more preferred cooling rate is at least about 30°C/second, and the even more preferred cooling rate is at least about 40°C/second, and the quenching end temperature is preferably between about Ms～ Between room temperature, more preferably between about Ms ~ 150 ° C; stop quenching, and air-cool the quenched steel plate to room temperature, so as to promote the completion of the transformation of the quenched structure of the steel.

2. Off-line quenching process after rolling

For thicker steel plates, or the cooling capacity of the on-line cooling equipment at the back of the steel rolling is weak, the water quenching process can be controlled after the steel plate is rolled and cooled, reheated and austenitized. The specific process requirements are that after the steel plate is rolled and cooled, it is sent to the heating furnace, and reheated to a suitable temperature above Ac3 to make it completely austenitized; after the steel plate is released from the furnace, it is quenched and cooled on a special quenching machine. The cooling rate of ℃/second is quenched from a temperature not lower than the Ar3 transformation point to a quenching finish temperature at least as low as the Ms transformation point to harden the steel plate, the preferred cooling rate is at least about 20 ℃/second, and the more preferred cooling rate is at least about 30 °C/sec, even more preferably the cooling rate is at least about 40°C/sec, the quenching end temperature is preferably between about Ms～room temperature, more preferably between about Ms～150°C; stop quenching, and air cool the quenched steel plate to room temperature to promote the completion of quenching structural transformation of the steel, and to achieve sufficient self-tempering and reduce the structural phase transformation stress.

Example

See Tables 6 and 7 for specific ingredients, processes, and performance:

Table 6 steel chemical composition(%) C Si mn P S Nb Ti B Cr Ni Mo Cu al V A 0.11 0.20 1.10 0.010 0.008 0.04 0.015 0.0012 0.55 - 0.35 - 0.02 - B 0.12 0.18 1.12 0.011 0.007 0.035 0.017 0.0010 0.50 0.35 0.33 - - - C 0.10 0.19 1.21 0.009 0.005 0.04 0.02 0.0015 0.57 - 0.36 0.25 - - D. 0.12 0.20 1.25 0.009 0.006 0.04 0.015 0.001 0.25 - - - - 0.03 E. 0.13 0.20 1.24 0.008 0.006 0.035 0.02 0.001 0.3 - 0.25 - 0.015 -

Table 7 steel craft Rp0.2Mpa Mpa A% HB Akv-40°C J Cold bending 180°d=3a Cutting test -10℃ A A 230mm steel billet was heated at 1150°C, rolled into a 30mm steel plate, and air cooled to room temperature. Reheat to 920°C, heat for 75 minutes, take out the furnace, quench and cool to room temperature. 1000 1100 12 350 50 qualified qualified B A 230mm steel billet was heated at 1150°C, rolled into a 40mm steel plate, and air cooled to room temperature. Reheat to 920°C, heat for 100 minutes, take out the furnace, quench and cool to 150°C, and air cool to room temperature. 950 1150 13 360 45 qualified qualified C A 230mm steel billet was heated at 1150°C, rolled into a 30mm steel plate, and air cooled to room temperature. Then heat to 920°C, heat for 70 minutes, take out the furnace, quench and cool to 200°C, and air cool to room temperature. 930 1140 12 340 60 qualified qualified D. 230mm steel billet, heated at 1150°C, rolled into 18mm steel plate, final rolling temperature 880°C, quenched directly after rolling, starting cooling temperature 840°C, cooling rate 25°C/S, final cooling temperature 300°C, air cooling to room temperature. 950 1100 15 350 55 qualified qualified E. 230mm steel billet, heated at 1150°C, rolled into 16mm steel plate, final rolling temperature 890°C, quenched directly after rolling, starting cooling temperature 850°C, cooling rate 30°C/S, final cooling temperature 280°C, air cooling to room temperature. 940 1110 14 360 65 qualified qualified

Claims (7)

1, the wear-resisting steel plate of the easy flame cutting of a kind of high hardness high toughness is characterized in that: this steel plate contains the interpolation element of iron and following weight per-cent:

0.10％～0.17％C，

0.05％～0.55％Si，

0.80％～1.60％Mn，

0.03％～0.06％Nb，

0.01％～0.03％Ti，

0.0008％～0.002％B，

0.15％～0.7％Cr；

And described composition satisfies:

C+0.155(Cr+Mo)+0.14(Mn+V)+0.11Si+0.045(Ni+Cu)≤0.46％。

2, according to the wear-resisting steel plate of the easy flame cutting of the described high hardness high toughness of claim 1, it is characterized in that: contain at least a interpolation element that is selected from down group in addition:

0.05％～0.8％Ni，

0.05％～0.60％Mo，

0.01％～0.06％Al，

0.05％～0.50％Cu，

0.01％～0.10％V，

0.00001％～0.006％Ca，

0.00001％～0.02％REM，

0.00001％～0.006％Mg。

3, the preparation method of a kind of claim 1 or the easy flame cutting wear-resisting steel plate of 2 described high hardness high toughness, it is characterized in that steel plate rolling after finishing temperature greater than Ar3; Steel plate after the hot rolling is quenched from the temperature that is not less than the Ar3 transition point with at least 10 ℃/seconds cooling rate, and the quenching finishing temperature is that the Ms transition point is to room temperature.

4, the preparation method of a kind of claim 1 or the easy flame cutting wear-resisting steel plate of 2 described high hardness high toughness, after it is characterized in that the steel plate rolling cooling, reheat more than the Ac3, quench from the temperature that is not less than the Ar3 transition point with at least 10 ℃/seconds cooling rates, the quenching finishing temperature is that the Ms transition point is to room temperature.

5, according to the preparation method of claim 3 or the easy flame cutting wear-resisting steel plate of 4 described high hardness high toughness, the finishing temperature that it is characterized in that quenching stops to quench between between Ms～150 ℃, with the steel plate air cooling after quenching to room temperature.

6, according to the preparation method of claim 3 or the easy flame cutting wear-resisting steel plate of 4 described high hardness high toughness, it is characterized in that at least 20 ℃/seconds of cooling rates.

7, according to the preparation method of claim 3 or the easy flame cutting wear-resisting steel plate of 4 described high hardness high toughness, it is characterized in that at least 30 ℃/seconds of cooling rates.