JPS6383225A - Manufacture of high hardness steel sheet - Google Patents

Abstract

PURPOSE:To obtain a high hardness steel sheet having superior wear resistance and used especially for various members of civil engineering and construction machinery by heating a steel contg. prescribed amounts of C, Si, Mn, Cr Al, Ti and B, hot rolling it, finishing the hot rolling at the Ar3 transformation point or above and immediately quenching the resulting steel sheet. CONSTITUTION:A steel contg., by weight, 0.15-0.45% C, 0.20-1.50% Si, 0.50-2.50% Mn, 0.60-1.80% Cr, 0.020-0.080% Al, 0.010-0.050% Ti and 0.0010-0.0060% B is heated to 950-1,150 deg.C and hot rolled. The hot rolling is finished at the Ar3 transformation point or above and the resulting steel sheet is immediately quenched to obtain a desired high hardness steel sheet having >=2.5mm thickness and >=500 Vickers hardness. The steel sheet can be obtd. in reduced stages at a low cost.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for manufacturing high-hardness steel sheets, particularly those with excellent wear resistance used as various parts of civil engineering construction machines such as bulldozers and power shovels. The present invention relates to a method for manufacturing high-hardness steel sheets.

<Conventional technology> Various parts used in civil engineering construction machines include earth and sand, gravel,
Sufficient wear resistance against concrete and rock is required, and various heat-treated wear-resistant steels are being researched and developed depending on the purpose. However, in recent years, there have been increasing demands for larger sizes, higher hardness, and lower costs for the members used, and it has become difficult to meet these demands using only conventional technology.

Regarding this high hardness steel plate, for example, Japanese Patent Publication No. 59-2502
In Publication No. 2, C: 0.21 to 0.35%, Si
: 0.10-0.90%, Mn: 0.
50-2.00%, P: 0.015% or less, A1
: 0.005-0.07%, rare earth element or Ca
A steel component containing a total of 0.0005 to 0.050% of one or more of the following has been proposed. However, with such components, there is a concern that hardness will decrease due to insufficient quenching depth when the m-plate becomes thicker and larger, and furthermore, cost increases due to lowering the P content are unavoidable.

Similarly, in Japanese Patent Application Laid-Open No. 59-140351, C
: 0.25-0.3%, Mn: 1.35-1.
75%, Cr2: 0.2-0.35% as a basic component, Si: 0.15-0.35%, A1:
0.02-0.04%, p:o, oa% or less, N:
A wear-resistant tough mesh that contains 0.01% or less of C and is quenched and tempered has been proposed, but even in this proposal, there is a concern that the hardness will decrease as the steel material becomes larger.

Furthermore, in Japanese Patent Application Laid-Open No. 60-243250, C
: 0.3-0.5%, Si: 0.05-0.5
%, Mn: 0.5-1.5%, P: 0.010%
Below, S: 0.005% or less, Cr: 0.
1-1.0%, Mo: 0.02-0.4%, so
A wear-resistant steel has been proposed in which a steel plate containing 0.01-0.1% of AI is quenched or quenched and then tempered at a low temperature. This is difficult and also involves an increase in cost for reducing impurities.

Furthermore, in JP-A No. 60-215743, CF 0.35 to 0.050, S i : 0.6
0 to 1.50%, Mo: 1.80% or less, Cr:
2.50-4.50%, Mo: 0.20-1.00%
Although a steel composition containing Cr and MO has been proposed, it is somewhat economically unsatisfactory due to the large amounts of Cr and MO added.

Furthermore, in Japanese Patent Publication No. 61-3367, C:0
．． 21-0.35%, Si: 0.05-0.1
%, Mn: 0.30-2.0%, Cr:
0.5-2.0%, Cu < 0.10-0.50%,
B: 0.0005-0.0030%, AI:
0.0.11-0.08%, S: 0.015%
The following steel composition has been proposed, with appropriate additions of Ca, REM, and Zr depending on the C content, but the quenching depth is relatively small, and there are concerns about increasing the size and hardness. ing.

As mentioned above, it remains difficult to increase the thickness and hardness of steel sheets from the viewpoint of chemical composition with the development of conventional technology, and the manufacturing method also requires quenching, tempering, and impurity reduction treatments. Therefore, an increase in manufacturing costs cannot be avoided. In addition, as seen in Japanese Unexamined Patent Publication No. 61-96028, a manufacturing method has been proposed in which the toughness of medium carbon steel is improved by using the direct quenching method, which has become popular in recent years.
The strength level (hardness level) of the target steel is 7 in terms of tensile strength.
It is as low as 0 to 90 kgf/mm, and thickening and hardness cannot be achieved.

<Problems to be solved by the invention> As stated above, the conventional technology has advantages and disadvantages in making steel plates for civil engineering and construction machinery thicker (larger), harder, and lower in cost. . The object of the present invention is to provide a method that solves the above problems all at once by appropriately combining component compositions and manufacturing methods.

<Means for solving the problems> The present invention provides C: 0.15 to 0.45 wt%, Si
: 0.20-1.50wt%, Mn: 0.50
~2.50wt%, Cr20.60~1.8(ht%
, A Il: 0.020-0.080 wt%, Ti
:l[1 0.010-0.0501llt%, B: 0.
0010 to 0.0060 wt%, the balance being Fe and unavoidable impurities, is heated to 950 to 1150°C,
After finishing with Ar by hot rolling at a temperature above the transformation point,
A method for producing a high-hardness steel plate by immediately quenching, C: 0.15 to 0.45 wt%, Si:
0.20-1.50wt,%.

Mn: 0.50-2.50wt%, Cr
: 0.60-1.80wt%.

AIl: 0.020-0.080111t%, T
i: 0.010-0.050 uL%, B:
Contains 0.0010 to 0.0060 wt%3, further Mo: 0.10 to 0.60 wt%, V:
950-1 steel containing 0.015-0.05 wt% of one or two kinds, the balance being Fe and unavoidable impurities.
This is a method for producing a high-hardness steel plate by heating the steel plate to 150°C, finishing it by hot rolling at a temperature equal to or higher than the Ar+ transformation point, and then immediately quenching the steel plate.

<Function> The present inventors considered the following items and determined that C, Si, Mn
, Ti, B, and Cr, as well as the heating temperature and quenching temperature during direct quenching, the present invention was achieved as a result of various thorough examinations.

(1) In order to achieve good wear resistance and high hardness, we should create a uniform martensite structure that undergoes low-temperature transformation, and study a component system that strengthens (hardens) the martensite itself.

(2) Considering the balance of the amount of added ingredients and aiming to reduce the cost of the ingredients, at the same time, reduce the manufacturing cost by omitting manufacturing steps and not performing special steps.

In the above-mentioned study, the present invention mainly takes into account the steel plate properties of a plate thickness of 25 mm or higher and a Vickers hardness of 500 mm or higher, and to reduce costs by reducing processes as much as possible.

The reasons for limiting the ingredients will be explained below.

C is an element that increases the strength of steel sheets and has a high quench hardening ability, and is necessary in an amount of 0.15% or more to obtain a specified hardness, but if added in excess of 0.45%, welding This impairs the hardenability improvement effect of B, which is added later, as well as the hardenability and processability, and also increases the amount of retained austenite, resulting in a decrease in wear resistance.

Sr is not only indispensable as a de#ring agent, but also suppresses C diffusion and strengthens martensite, and requires a content of 0.20% or more for solid solution strengthening. 0.20 to 1.5, as the toughness decreases significantly.
The range is 0%.

M・n ensures the specified strength and toughness of the steel plate, and M
0.50% or more is necessary to lower the s-point and contribute to the strengthening of martensite, but if it is added in excess of 2.50%, weldability will be significantly reduced, and cracks in the steel plate and segregated areas will occur frequently. Therefore, the content should be in the range of 0.50 to 2.50%.

Cr is relatively inexpensive and improves the hardenability of steel, and
0.60 to increase wear resistance also by carbide precipitation.
% or more, but if it is added in excess of 1.80%, weldability and economical efficiency will deteriorate, so it should be in the range of 0.60 to 1.80%.

AI is an essential element for deoxidizing steel, and at the same time, if the effect of Ti, which will be described later, is insufficient, 0.020% or more of B is required to fully exhibit the hardenability improvement effect of B. Even if it is added in excess of 0.02%, the effect related to B will be saturated and the weldability will be impaired.
The range is 0-0.080%.

Ti fixes N in the steel and B! 7) 0.010% or more is required to improve hardenability and prevent cracking during continuous casting, but adding more than 0.050% will have little effect; Further, since it causes a decrease in toughness, it is set in the range of 0.010-0.050%. Note that the amount added is preferably about 3 to 4 times the amount of N in the steel.

B significantly improves hardenability in small amounts, and when N is fixed by adding Ti, it usually exhibits an effect at 0.0005% or more, but in medium carbon steel such as the steel of the present invention, B Since the amount of Bl that becomes ineffective as carbide also increases, the lower limit is set to 0.0010%. Also, 0.006
Even if it is added in an amount exceeding 0%, the effect will be saturated and the toughness will deteriorate, so it is set in the range of 0.0010 to 0.0060%.

Furthermore, the object of the present invention can be similarly achieved even if one or both of Mo and V are contained as necessary.

Mo is preferably added in an amount of 0.10% or more in order to improve the hardenability and toughness of the steel sheet, but 0.60% or more is desirable.
If added in excess of %, weldability and economic efficiency will be impaired.
The range is 0.610% to 0.60%.

■ has the effect of increasing the strength of the steel plate, so 0.0
It is necessary to add 1.5% or more, but if it is added in excess of 0.100%, the toughness will deteriorate significantly, so 0.015 to 0.
The range is IO'0%.

In addition, the impurity elements P, S, and N deteriorate the toughness of steel sheets, the toughness during welding, and various workability, so it is desirable to keep them as low as possible. There is no need to make full use of special reduction techniques that may cause problems.

In addition, the current content level that does not cause a cost increase is P: 0.010-0.015%, S:
0.001=0.003%, N: 0.0030-0
．． 0.0050%, and within this range, the usefulness of the present invention can be fully demonstrated.

These component steels are heated to 950°C to 1150'c, and A
High hardness can be achieved by finishing hot rolling at a temperature equal to or higher than the rz transformation point and immediately quenching.

Here, if the heating temperature is lower than 950°C, the solid solution of the added alloying elements will not be sufficient, the austenite grained single phase structure will not be formed, and it will be difficult to secure a high quenching temperature after rolling. , the lower limit was 950°C. Also, 11
If the heating temperature exceeds 50°C, the austenite grains will become coarser too much, and the improvement in hardenability due to B will be reduced.Also, retained austenite will tend to remain, which may cause a decrease in strength. Set the upper limit of temperature to 1
The temperature was 150°C.

Furthermore, when the quenching temperature is lower than the Ar3 transformation point temperature, ferrite precipitates and it becomes impossible to maintain a predetermined strength, so quenching at a temperature higher than the Ar transformation point temperature is essential.

In this way, the combination of the component composition of the present invention and the direct quenching process allows for
It is possible to reduce the steel components and the heating unit consumption, making it possible to manufacture high-hardness, thick-walled steel plates at low cost, which has great benefits. In addition, tempering treatment may be performed to improve toughness, but since the advantages of the present invention do not change, this is not particularly limited.

<Example> The present invention will be explained in detail below.

Each component steel ingot shown in Tables 1 and 2 was melted using a vacuum melting method, and a 30mm thick steel plate was produced under predetermined rolling conditions, and the Vickers hardness of the central part of the copper plate was measured. The results are shown in Tables 1 and 2. Here, in the terms between the categories in the table, "the present invention" means that the ingredients and rolling conditions are both within the scope of the present invention, and "Comparative Example A" means that the components are outside the scope of the present invention, and "↓ In "Comparative Example B", the rolling conditions were outside the scope of the present invention, and in "Comparative Example C", the steel ingot was heated to 1200°C.
This indicates that the steel plate was heated, rolled at 900°C into a 3° thick steel plate, air cooled to room temperature, heated again to 900°C, and quenched.

As can be seen from Steel Sheet Nos. 1 and 2, applying the present invention can ensure a Vickers hardness of 500 or more, but inappropriate rolling conditions or reheating quenching may reduce the effect or cause Vickers hardness of 500 or more.
Unable to satisfy 0 or more.

Although the steel plates 11h3 to 11h8 have a reduced amount of each alloying element, it is difficult to ensure a Pinkers hardness of 500 or more in all of them.

Although the hardness cannot be ensured, it can be seen that the application of the rolling conditions within the range of the present invention results in the highest Vickers hardness.

Steel plates 1'h9 to 12 in Table 2 have the same basic composition as steel plate 1 and have added Mo and V.
It can be seen that the hardness increases with addition.

However, as can be seen in the steel sheet magnet 12, no increase in hardness is observed when adding a small amount outside the scope of the present invention.

As described above, according to this embodiment, the "present invention" product is "
It is clear that the products of Comparative Examples are superior in hardness.

<Effects of the Invention> As explained above, according to the present invention, by appropriately combining the component composition with sufficient hardening depth and manufacturing conditions, high hardness and thickness required for wear-resistant steel can be achieved. The effect is remarkable because it has made it possible to realize meat production and lower costs.

Claims (2)

[Claims] (1) C: 0.15-0.45wt%, Si: 0.20
~1.50wt%, Mn:0.50~2.50wt%,
Cr: 0.60~1.80wt%, Al: 0.020~
0.080wt%, Ti: 0.010-0.050wt
%, B: 0.0010 to 0.0060 wt%, and the balance is Fe and unavoidable impurities.
A method for producing a high-hardness steel sheet, the method comprising heating the steel sheet to a temperature of 0.degree. (2) C: 0.15-0.45wt%, Si: 0.20
~1.50wt%, Mn:0.50~2.50wt%,
Cr: 0.60~1.80wt%, Al: 0.020~
0.080wt%, Ti: 0.010-0.050wt
%, B: 0.0010 to 0.0060 wt%, further Mo: 0.10 to 0.60 wt%, V: 0.015
Contains ~0.100wt% of one or both of them, with the balance being Fe
and unavoidable impurities at 950-1150°C.
A method for producing a high-hardness steel sheet, the method comprising: heating the steel sheet to a temperature of Ar_3 transformation point or higher by hot rolling, and immediately quenching the steel sheet.