JPS58213865A - Erosion-resistant material and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a material with superior erosion resistance and superior corrosion resistance at high temp., by treating a carbon steel or a ferritic alloy steel contg. Cr with boron under specified conditions of temp. and time. CONSTITUTION:A carbon steel or a ferritic alloy steel contg. Cr is treated with boron at 700-1,000 deg.C under conditions of temp. and time represented by equation I [where T is absolute temp. ( deg.K) and t is time (hr)]in case of <=4% Cr and by equation II (where T and t are idential with said T and t) in case of >4% Cr. By the treatment a boron treated steel provided with a boride layer having >=about 30mum thickness can be obtd. This boron treated steel shows superior resistance to erosion due to fly ash during the burning of coal, and it has corrosion resistance at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a resistant material made of carbon steel or ferritic alloy steel containing Cr to prevent erosion caused by solid particles in high-temperature PC, especially ash erosion caused by coal combustion, and to prevent cast iron. Erosion property @ ladle and its manufacturing method. In recent years, due to the smarter energy situation, there has been a call for diversification of energy sources. However, new thermal power plants are now coal-fired instead of conventional oil-fired boilers, and some conventional oil-fired boilers are now being switched to coal-fired boilers. With the expansion of coal use, erosion by solid particles at high temperatures has become a problem in the materials field, but until now very little research has been done and no measures have been taken to address erosion at high temperatures. The current situation is that this is not the case. For example, in the case of coal-fired boilers, the main countermeasures are taken from a design perspective (flow velocity reduction, use of protectors, etc.), and material countermeasures such as the application of erosion-resistant materials are rarely taken. Currently, boilers are manufactured using the same material composition as oil-fired boilers.

Erosion, for example ash erosion seen in coal-fired boilers, is a phenomenon in which ash generated during coal combustion collides with the group of high-temperature boiler heat transfer tubes, causing wear and thinning of the tube surface. Similar phenomena are also observed in coal gasification and liquefaction plants.

Therefore, materials suitable for this type of environment are required to have erosion resistance and high temperature strength at high temperatures. - On the other hand, boron treatment is a surface treatment method that embeds the material to be treated in powder containing borium and performs diffusion treatment at high temperature.
This is a method traditionally used industrially to improve the wear resistance of carbon steel or low alloy steel. It has been found that it is very effective to form a dispersed precipitate layer (hereinafter referred to as a dispersed precipitate layer)12, and that such a dispersed precipitate layer needs to have a thickness of about 10 μm or more.

The present inventors further investigated high-temperature erosion based on such findings, and found that the surface boride layer is similar to that described above in carbon steel and ferritic alloy steel containing Cr, which are often used at temperatures below 60°C. If it has a surface roughness of about 30μ or more due to boron treatment, it will be confirmed that it has excellent erosion resistance. The present invention was completed by selecting conditions 1 to 1 for obtaining IN by subjecting it to boron treatment pressure.

That is, the present invention is an erosion-resistant material in which a boride layer with a thickness of 30μ or more is formed on the surface of a ferritic alloy steel containing Cr, and a ferritic alloy steel containing carbon steel or ferritic alloy steel containing Or. ~1000℃
In the temperature range of, if Cr<:4%: ``If Cr>4%: Matadashi T: Absolute temperature ('K), t: Time (hr
This is a method for producing an erosion-resistant material characterized by performing boron treatment under temperature and time conditions that satisfy the following relationship:

Carbon steel and ferritic alloy steel containing Cr to which the present invention is applied are not particularly limited, but carbon steels such as ferritic steel such as boiler steel 5TB42°5TB52, STBA 22. Cr-Mo low alloy steel such as 5TBA24.

Further, the boron treatment performed in the present invention is not limited, but a typical boron treatment operation is 75 to 97
Bun SiC, 1~1o%-B4c and 2~15% Na
A boron treatment agent consisting of BF4 is used and the material to be treated buried therein is heated to 700 to 1000°C.

In the present invention, a surface boride layer with a thickness of 30 μm or more is formed by the boron treatment as described above, but if the thickness of the boride layer is less than 30 μm, erosion occurs in carbon steel or ferritic alloy steel. It is insufficient to improve the resistance and extend the life of the component. 'ffc,,30
In order to obtain a boride layer with a thickness of more than .mu.m, the boron treatment must be carried out in the temperature range of 700 DEG to 1000 DEG C. under temperature and time conditions based on the following empirical formula. , that is, 1 in the case of Cr≦4q6; 1 in the case of 1゛Cr>4; however, 'ri absolute temperature ('K), t1 time (hr) In the boron treatment of the present invention, Cr contained in the base material combines with B. A (Fear)zB layer is formed below the FeB layer in Table 1.1-1 This prevents further penetration of B. This effect changes depending on the Or content of the 4th coefficient, so in the above experimental formula, the two equations (1)
, (2) shows that when Cr is up to 4%, it becomes difficult to form a boride layer as the amount of Cr increases, and when Or is 4% or more, Cr
The effect of is not significant (this is because the dependence on the amount of Cr decreases).

In this case, if it is less than 700 DEG C., it takes too much time to obtain a boride layer with a thickness of 30 .mu.m, and a temperature of 100 .mu.m or more is required, which is economically disadvantageous. On the other hand, 1000
If the temperature exceeds ℃, problems will occur with the durability of the processing equipment.
Otherwise, the crystal grains of the base material become coarser.

In this way, boron-treated steel with a boride layer of 30 μm or more in thickness exhibits excellent resistance to erosion by solid particles such as fly ash during coal combustion at high temperatures, and also has corrosion resistance at high temperatures. be.

Next, the present invention will be further explained by examples.

Example A high-temperature forged steel pipe having the chemical fraction shown in Table 1 below was used as the test material. 20 (W) xso(z)X
3(t) Test pieces of the shell were cut out 17, and these test pieces were mixed with boron-containing agent powder (B4C, NaBF4, SiC
) and was sealed in a steel container and heat treated at a constant temperature and for a constant time. Table 2 below shows the composition of the boron treatment agent powder. The treated specimens were subjected to a high temperature erosion test and a high temperature corrosion resistance test together with a comparative material.
The results are shown in Tables 3 and 4.

The high-temperature erosion test uses a plastic-type high-temperature erosion test device.1~ Temperatures of 300°C and 500°C, gas (Ar) flow rate of 120 W's, solid particles (artificial silica sand 7
-Odor, average particle size 150μ) 1201/-1 collision angle 20°
The test was carried out for 3 hours.

As shown in Table 3, the results show that the boron-treated specimens have overwhelmingly superior erosion resistance compared to the untreated specimens. Test order 5 to 7 exhibited the effect of boron treatment [~
However, the treatment thickness has been removed under the above test conditions, and the lifespan is short and reliability is poor in severe erosion environments. In comparison, those treated under the conditions of the present invention showed a very small amount of erosion and sufficient erosion resistance.

Further, the boron treatment was carried out using two powders, A and B, and it can be seen that both powders provided an effective boron treatment layer. Next, the high temperature corrosion resistance test was performed under the two conditions C and D shown in Table 4.
It was done by As can be seen from Table 4, those treated with boron exhibit better corrosion resistance than those not treated.

Table 1 Chemical composition of sample material (weight %) Table 2 Blend ratio of boron-treated powder (weight) Test conditions CI In air, 650'C, 100 Jar
ID: 1596001+1'lCO+1I
t02+0.2tI) 8020Nl (Ba 1.)
Medium, 500℃, soo! Patent applicant: Sumitomo Kinkaede Industries, Ltd.

Claims (2)

[Claims] (1) An erosion-resistant material characterized by forming a surface hardening layer with a thickness of 30μ or more by boron treatment on the surface of carbon steel or ferritic alloy steel containing Cr. (2) Carbon steel or ferritic alloy steel containing Cr in the temperature range of 700 to 1000°C, Cr≦4
%: ...(1) When Cr > 4%: ■ However, the boron treatment is performed under temperature and time conditions that satisfy the following relationship: T: absolute temperature (01, t; time (hr)) Manufacturing method of erosion resistant material