JPS61174318A - Roll for heat treating furnace - Google Patents

Abstract

PURPOSE:To improve the wear resistance and to prevent build-up by forming a cermet layer contg. prescribed percentages of silicon carbide or silicon nitride having <=1% Si content and Mo on the base of a hearth roll. CONSTITUTION:A roll for a heat treating furnace is obtd. by forming a thermal sprayed cermet layer on the base of a hearth roll. The cermet is composed of 15-58vol% silicon carbide and/or silicon nitride having <=1wt% Si content and the balance Mo.

Description

Detailed Description of the Invention (Field of Application of the Invention) The present invention relates to a roll disposed in a heat treatment furnace for conveying materials to be heat treated, which has excellent wear resistance and prevents build-up. This relates to a roll for use in the hearth (hereinafter referred to as a hearth roll).

(Prior art) For example, when continuously annealing a steel plate, 600 to 1000
The steel sheet is passed through an oxidizing or reducing atmosphere, but since the hearth rolls used to convey the entire steel sheet are used continuously for long periods of time, the surface of the hearth rolls is worn out, and the steel sheet may become completely boned. The attached oxides or iron powder are deposited on the surface of the hearth roll, forming so-called build-up.

When such wear f build-up occurs, the surface of the steel plate is damaged while it is being conveyed on the hearth rolls, causing deterioration of the quality of the steel plate, and sometimes immediately interrupting production operations. Therefore, the surface of the hearth roll is forced to be ground and maintained.

For this reason, we have changed the material of hearth rolls,
Alternatively, as described in Japanese Patent Publication No. 57-29549, attempts have been made to coat the roll surface with a thermal spray coating of zirconia or alumina.

However, none of these known attempts has been fully satisfactory in terms of hot wear resistance or prevention of build-up.

Therefore, one of the applicants had previously filed Japanese Patent Application No. 58-24541.
No. 0 (hereinafter referred to as the prior invention), containing 30 to 70% by weight of silicon carbide, silicon nitride, or a mixture thereof with a metal silicon content of 1% by weight or less, and the balance being Co, Cr, Mo,
Provided is a roll for a heat treatment furnace, characterized in that it has a thermally sprayed coating of a cermet layer made of Ni, AI, W, Y1m or two or more kinds of heat-resistant metals on the base of the hearth roll.

In the prior invention, by suppressing the amount of metallic silicon contained in silicon carbide and silicon nitride to an extremely small amount (1 wt To or less), the condensation of oxides, iron powder, etc. adhering to the surface of the steel sheet to the hearth roll is prevented. It can effectively prevent buildup and deposition, and the build-up resistance is significantly improved.On the other hand, when silicon carbide and silicon nitride are used as a cermet in a specified amount (70 to 30 wt fb)
By containing all of the heat-resistant metals, a thermally sprayed coating with high strength and good adhesion can be obtained, and a cermet layer with excellent integration properties can be obtained by hearth rolling.

(Problems to be Solved by the Invention) The present invention focuses on Mo among the heat-resistant metals included in the prior invention, and as a result of a detailed study of the amount of Mo.
olt- A roll for a heat treatment furnace is provided which contains a predetermined amount exceeding the range of the prior invention and has an effect equal to or greater than that of the prior invention.

(Means for Solving the Problems) The present invention provides 15 to 58 vol of silicon carbide, silicon nitride, or a mixture thereof containing 11% by weight or less of metallic silicon.
This roll for a heat treatment furnace is characterized in that it has a thermally sprayed coating of a cermet layer containing less than To and the remainder being Mo on the base of the hearth roll.

In the above prior invention, Mof is used as the heat-resistant metal.

If selected, the silicon carbide and silicon nitride content is 30 to 70 wt% when converted to heavy J1%tvoJ%, and 58 to 88 wt%.
The remaining amount is MO. In the present invention,
The content of silicon carbide and silicon nitride is expressed as f, vol % because the specific gravity of silicon carbide and silicon nitride is approximately 3.25'/c.
m”, while the specific gravity of MO is approximately 10.25’/
cm' is larger than that of ceramics, and it was determined that vol% expression was appropriate for explaining the invention in detail.

The present invention will be explained in detail below.

The base of the hearth roll is made of heat-resistant steel, for example.

A cermet layer containing less than 15 to 58 vol 4 of silicon carbide, silicon nitride, or a mixture thereof with an extremely small amount of metallic silicon, the remainder being MO, is formed on the surface of these substrates by thermal spraying. be done.

The metallic silicon content in silicon carbide, silicon nitride, or mixtures thereof must be 1 wt % or less.

If metallic silicon is present in silicon carbide, silicon nitride, or a mixture thereof in the cermet layer of the hearth roll, iron powder adhering to the steel plate will adhere and accumulate at high temperatures, making it easy to cause build-up.

Iron powder was placed on the fired bodies of silicon carbide and silicon nitride containing different amounts of metallic silicon, and in a non-oxidizing atmosphere at 900C,
By pressing with a half-moon roll and rubbing for 4 hours,
The adhesion and deposition properties of iron powder were investigated.

The results are shown in Figure 1. When the metallic silicon content is 1 wt% or more, the adhesion area of iron powder increases rapidly, making it unsuitable. However, when the metallic silicon content is below 1 wt%, extremely excellent build-up resistance is achieved. shows. High purity silicon carbide and silicon nitride are 1o
oot: 'less than',;r Fe,' It has excellent build-up resistance and is hard due to the fact that it is difficult to form a reaction product with Fe oxide, and because it is a covalent bond and stable, it has poor reactivity at high temperatures. Because it is a material, it also has excellent wear resistance.

Regarding wear resistance and build-up resistance, the higher the content of silicon carbide and silicon nitride, the better the properties generally are. However, when MoF is used as a binder, silicon carbide etc. is 15 vol%. If the above conditions are met, sufficient wear resistance and build-up resistance can be obtained. - In particular, as a measure of wear resistance, cold microhardness measurements were performed on Mo silicon carbide sprayed samples. The results are shown in Figure 2. When silicon carbide is contained in t-15voJ11 or more, the microhardness increases by more than twice as much as in the case where the content is lower than that, and sufficient wear resistance is obtained, making it suitable for industrial use. It can be used in many ways.

On the other hand, the upper limit of the content of ceramics such as silicon carbide is effective up to 8 8 voJ, which is the upper limit of the earlier invention, but in order to avoid duplication with the earlier invention, It is set to be less than 58 vol%, which is the lower limit of .

As is clear from the above, according to the present invention, in terms of build-up resistance and abrasion resistance, it is possible to obtain characteristics that are comparable to the prior invention and can be used industrially.
On the other hand, regarding needle releasability, according to the present invention, M, which acts as a binder, is better than the prior invention.

Since the amount of .

Although the present invention shows the case where MO is added alone as a binder, the same effect can be obtained by adding Mo and W in combination.

Further, the roll of the present invention can be suitably used in a non-oxidizing atmosphere.

(Example) ■ Metallic silicon 0.7 wt To or less silicon carbide 10
Wagchi, Mo 90 vol%f Hearth roll coated by thermal spray coating with a thickness of 400 pm ■ Silicon carbide with metal silicon 0.7 wt% or less 15 voJ
H, Mo 85 vol%'it hearth roll coated by thermal spray coating with a thickness of 400 pm ■ Silicon carbide with metal silicon 0.7 wt% or less 40 voJ
H, hearth roll coated with Mo 60 vol% by thermal spraying to a thickness of 400 μm ■ Silicon nitride 40 voJ with metal silicon 0.8 wt% or less
H, Mo 60 vol% Total 1% Hearth roll coated by thermal spray coating with a thickness of 0 μm ■ Silicon carbide 40 vol% with metal silicon 1.6 wt%,
Mo 60 voJ To t-Hearth roll coated by thermal spray coating with a thickness of 400 μm ■ Mixture of silicon carbide and silicon nitride of metallic silicon O, S* (
Mixing ratio SiC: 5isN4=17:83)
40vol%, Mo 60vol%? 400μm
Heat spray coated hearth roll with a thickness of 0.7mm silicon carbide 65 vol%, Mo
A hearth roll (35volTo') coated by thermal spray coating with a thickness of 400 μm. Hearth rolls using SCH22 and higher were subjected to a long-term actual machine test at a reducing atmosphere temperature of 750C. The results are shown in Table 1.

As can be seen from Table 1, the rolls of the present invention ■ and ■.

Items ① and ② exhibited very excellent build-up resistance and wear resistance, and there was no peeling phenomenon that is generally a problem during cermet thermal spraying.

Comparative example (■) contained 10 vol % of SiC, and was worn by approximately 300 μm after 500 hours, and the present invention examples (■) and (■) could not withstand long-term use in terms of roll life. In ,
/ hr) is hotter than comparative example ■. If the content is 15 vol 1 or more, the wear resistance can be dramatically improved.

In Comparative Example (2), build-up occurred in 1000 hours due to the metal silicon 'ii being contained in an amount of 1.6 wt% or more. Moreover, according to the example of the present invention, effects comparable to those of the example (2) of the prior invention can be obtained.

(Effects of the Invention) As detailed above, according to the present invention, a no-throttle roll with excellent build-up resistance, wear resistance, and peeling resistance can be obtained, which greatly contributes to heat treatment of steel plates, etc. It is something.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the adhesion of various samples to iron powder and the amount of metallic silicon contained in the sample, and Figure 2 is a graph of the amount of silicon carbide (v
ol'lx) and the microhardness of a thermal sprayed body. 4 cheap C; droplet soup bowl

Claims (1)

[Claims] The base of the hearth roll is coated with a thermally sprayed cermet layer containing 15 vol% or more and less than 58 vol% of silicon carbide, silicon nitride, or a mixture thereof with a metallic silicon content of 1% by weight or less, the balance being Mo. Roll for heat treatment.