KR100386300B1 - Surface hardening method of a roll using carbide - Google Patents

Abstract

By carburizing the surface of a roll made of steel material containing chromium (Cr), molybdenum (Mo), etc., which forms carbides, and forming a carbide on the martensite matrix, it is possible to obtain a high hardness, excellent wear resistance and corrosion resistance. Surface hardening methods are disclosed. According to the present invention, 0.4-1.0 wt% carbon (C), 0.3-1.0 wt% silicon (Si), 0.5-1.5 wt% manganese (Mn), 1-6 wt% chromium (Cr), 0.3- A roll made of a steel material containing 2.0 wt% molybdenum (Mo) was carburized at a temperature of 800 to 1,050 ° C. for 2 to 100 hours to form 20 to 80% of carbide on the surface of the roll to be cold or air cooled. After the high-frequency curing or low-frequency curing to obtain a structure consisting of the carbide and martensite, and then tempering at a temperature of 150 ~ 350 ℃. Alternatively, 20 to 80% of the carbide is formed on the surface of the roll and quenched in water, oil or polymer refrigerant to obtain martensite structure reinforced with carbide and then tempered or tempered to cure low or high frequency. At this time, the carburization is performed using any one of carburizing methods of gas carburizing, vacuum carburizing, plasma carburizing and solid carburizing.

Description

Surface hardening method of a roll using carbide

The present invention is a work roll (back-up roll), leveler roll (bride roll), guide roll (guide roll) used in the rolling process of the metal material and the plating process of the rolled material It relates to the surface hardening method of various rolls such as guide rolls, and more particularly martensite matrix by carburizing the surface of the roll made of steel material containing chromium (Cr), molybdenum (Mo), etc. The present invention relates to a method for hardening the surface of a roll, by forming carbides in which high hardness, excellent wear resistance and corrosion resistance can be obtained.

In general, work rolls are used to roll metal materials or remove oxide scales, and backup rolls support work rolls to impart their required functions. The leveler roll is used in a washing process, a plating process, a pickling process, a continuous annealing process, a cold rolling process, an annealing pickling process, and the like to convey and flatten the rolled material. The braid roll serves to maintain tension in various rolling processes of the sheet material.

By the way, the surface of such a roll is badly abrasion due to the heat generation phenomenon due to the contact with the workpiece or oxide of high hardness, or the high-speed transfer of the rolled material. In addition, the corrosive medium introduced from the pickling and plating process causes corrosion with wear. Therefore, these rolls must have sufficient abrasion resistance as well as excellent strength and toughness, thermal shock and corrosion resistance, depending on the required function.

Conventionally, when abrasion resistance is required, high chromium rolls (Shore Hardness HS70-80), chilled rolls (HS75-80), and adamite roll (HS55) containing 8-25% of chromium (Cr) are required. Casting rolls such as? These casting rolls are reinforced with martensite matrix by chromium carbide formed during melt casting. Since the carbides are large in size and carbides exist both inside and outside the rolls, they cannot be used for leveler rolls because of their low strength and toughness.

In addition, when strength and toughness are conventionally required, forging materials (HS85 to 90) containing a small amount of chromium (Cr) of about 3%, bearing steel (HS85 to 90) such as SUJ2, and STD11 (HS80) Tool steels such as ˜85) were used after high frequency hardening. However, these rolls have a short lifespan, so that various composite rolls such as those made of structural forged materials and surfaces made of high speed tool steel or high carbon high speed tool steel (HS80 to 90) containing a large amount of carbon of 1.5 to 3.5% are available. Has been used. And, in a special case, a carbide using a powder metallurgy and a roll using a ferro- titanite material is used, but the material is expensive and difficult to process.

The present invention has been made to solve the conventional problems as described above, the object of the present invention is to provide sufficient wear resistance, excellent strength and toughness, excellent thermal shock and corrosion resistance to various rolling rolls used in the rolling process to greatly increase the life It is to provide a method of hardening the surface of the roll that can be extended.

1 is an optical microscope photograph of a 50 times magnification of the surface of a carbide surface-cured roll according to the present invention;

2 is an optical microscope at 400 times magnification of the surface portion of the carbide surface-cured roll in accordance with the present invention, and

3 is a photograph showing the appearance of the roll cured with carbide according to the present invention.

In order to achieve the above object, the present invention,

0.4-1.0 wt% carbon (C), 0.3-1.0 wt% silicon (Si), 0.5-1.5 wt% manganese (Mn), 1-6 wt% chromium (Cr), 0.3-2.0 wt% molybdenum A roll made of a steel material containing (Mo) was carburized at a temperature of 800 to 1,050 ° C. for 2 to 100 hours to form 20 to 80% of carbide on the surface of the roll, followed by furnace cooling or air cooling, followed by high frequency curing. Or low-frequency hardening to obtain martensite structure reinforced with carbide, and then tempering at a temperature of 150 to 350 ° C. to provide a surface hardening method for the roll.

In contrast, the present invention,

0.4-1.0 wt% carbon (C), 0.3-1.0 wt% silicon (Si), 0.5-1.5 wt% manganese (Mn), 1-6 wt% chromium (Cr), 0.3-2.0 wt% molybdenum A roll made of (Mo) -containing steel material was carburized at a temperature of 800 to 1,050 ° C for 2 to 100 hours to form 20 to 80% of carbide on the surface of the roll, and then in water, oil or polymer refrigerant. It is quenched to obtain martensite structure reinforced with carbide and then tempered to provide a method for hardening the surface of a roll.

The carburization is performed using any one of carburizing methods of gas carburizing, vacuum carburizing, plasma carburizing and solid carburizing.

As mentioned above, in the surface hardening method of the roll according to the present invention, very high hardness, excellent wear resistance and corrosion resistance can be obtained through the martensite structure reinforced with carbide.

Hereinafter, the surface hardening method of the roll which concerns on this invention is demonstrated in detail.

In the present invention, the surface of a roll made of a steel material of the components shown in Table 1 containing chromium (Cr), molybdenum (Mo), etc., carbide forming element is carburized at a carbon concentration of 1 to 4%, Carbide of -80% is formed to give a high hardness of HS80 to 100 to obtain excellent wear resistance and corrosion resistance.

Table 1

Alloy elements C Si Mn Cr Mo content(%) 0.40 to 1.0 0.30 to 1.0 0.50 to 1.5 1 to 6 0.3 to 2.0

The roll having such an alloying element composition is composed of carbide and martensite structure from about 1 to 5 mm from the surface, and martensite structure of 5 mm or more. Carbide and martensite mixed structure is to give the wear resistance, fatigue strength and corrosion resistance of the roll, a large amount of carbide should be finely formed into a spherical (sphere).

In order to form a large amount of carbide, chromium (Cr) and molybdenum (Mo) were added, and in the case of out of the range of addition, the amount of carbide formation was reduced. In addition, silicon (Si) prevents carbides from depositing at the grain boundaries, and serves to deposit carbides in the crystal grains. At this time, when the content of silicon (Si) is 0.3% or less, the effect is not great, and when it exceeds 1.0%, since carbides are suppressed from forming, it is not preferable.

The internal martensitic structure is intended to impart the strength of the roll, in which carbon (C) and manganese (Mn) are added to obtain a hardened layer suitable for it, that is, to obtain sufficient hardness and depth of cure. Ni) is added. Within the range of the addition of the alloying element, carbon (C) increases the hardness, and manganese (Mn) and nickel (Ni) increase the hardenability to easily obtain a deep hardening depth during high frequency hardening.

The gas carburizing process is carried out for a time to obtain the required hardening depth at a carbon concentration of 1 to 4% by heating a roll made of a steel material having a desirable component to a temperature range of 800 to 1,050 ° C, which is not less than A _c3 or A _cm temperature. Carburization is carried out by a method such as vacuum carburization, solid carburization, or plasma carburization.

After the carburizing process is completed, the mixture is cooled to a temperature range of 820 to 950 ° C., held for a predetermined time, quenched in water, oil or polymer refrigerant, tempered or tempered, and then subjected to high frequency curing. In addition, when carburizing is completed, the furnace is cooled by cold or air, then hardened or tempered by low frequency or high frequency.

<Example 1>

A roll made of steel of 0.45 wt% carbon (C), 0.4 wt% of silicon (Si), 0.7 wt% of manganese (Mn), 2.35 wt% of chromium (Cr), and 0.4 wt% of molybdenum (Mo) was subjected to a temperature of 950 ° C. The solid was carburized by solid carburizing at 48 hours, and then hardened at high frequency for 1 hour at 180 ° C. As a result, a surface hardening layer exhibiting a very high surface hardness of HS95 to 98 composed of about 60% carbide and martensite structure and a curing depth of about 5 mm based on HS80 was shown.

<Example 2>

Rolls made of steel (C) 0.95 wt%, silicon (Si) 0.35 wt%, manganese (Mn) 0.5 wt%, chromium (Cr) 1.5 wt%, molybdenum (Mo) 0.45 wt% were heated at a temperature of 950 ° C. The solid was carburized by solid carburizing at 48 hours, and then hardened at high frequency for 1 hour at 180 ° C. As a result, the surface hardening layer which showed the surface hardness of HS88-92 which consists of about 45% of granular carbide and martensite structure, and the hardening depth of about 5 mm based on HS80 was shown.

<Example 3>

Rolls made of steel of 0.45 wt% carbon (C), 0.8 wt% silicon (Si), 0.7 wt% manganese (Mn), 5.5 wt% chromium (Cr), and 1.4 wt% molybdenum (Cr) were heated at 950 ° C. The gas was carburized at 24 hours, cooled to 900 ° C. for 20 minutes, and then quenched with oil and tempered at 180 ° C. for 1 hour. As a result, the surface hardening layer which showed the surface hardness of HS88-92 which consists of about 45% of granular carbide and martensite structure, and the hardening depth of about 5 mm based on HS80 was shown.

Results and Discussion

1 is an optical micrograph of a 50 times magnification of the surface portion of a carbide surface cured roll according to the present invention. In FIG. 1, the white portion is carbide, and the dark gray portion is martensite tissue.

FIG. 2 is an optical microscope in which the surface area of the roll cured with carbide is enlarged 400 times. 2, it can be seen that it is composed of about 60% of carbide and martensite. Based on the surface hardness of HS98 and HS80, the curing depth was about 3 mm.

3 is a photograph showing the appearance of the roll cured with carbide according to the present invention.

As described above, in the surface hardening method of the roll according to the present invention, very high hardness and excellent wear resistance and corrosion resistance can be obtained through the martensitic structure reinforced with carbide, so that the life of the roll when applied to various rolling rolls In addition to greatly extending the manufacturing cost of the roll can be reduced. In addition, since the life of the roll is extended, the number of roll replacement and the consumption of the roll can be reduced to increase productivity, and the cost of the steel can be reduced by reducing the cost of the roll.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below. I can understand that you can.

Claims (6)

Steel material containing 0.4 to 1.0 wt% carbon (C), 0.3 to 1.0 wt% silicon (Si), 0.5 to 1.5 wt% manganese (Mn), and 1 to 6 wt% chromium (Cr) The rolls were carburized at a temperature of 850-1,050 ° C. for 2-100 hours to form 20-80% of carbide to the depth of 5 mm from the surface of the rolls by blast-cooling or air-cooling, followed by high-frequency curing or low-frequency curing. The surface hardening method of the roll characterized by tempering in the temperature range of 150-350 degreeC after obtaining the structure which consists of these. The method of claim 1, wherein molybdenum (Mo) of 0.3 to 2.0wt% is added to the steel material. The method of claim 1, wherein 0.3 to 2.0 wt% molybdenum (Mo) and 0.5 to 3 wt% nickel (Ni) are added to the steel material. The method of claim 1, wherein the carburization is performed by using any one of a carburizing method of gas carburizing, vacuum carburizing, plasma carburizing, and solid carburizing. The method of claim 1, wherein the carbide is formed and then maintained at a temperature of 800 to 1,050 ° C for a predetermined time and quenched to obtain a structure consisting of the carbide and the martensite, and then tempering at a temperature range of 150 to 350 ° C. Surface hardening method of the roll made into. The method of claim 1, wherein after forming the carbide and then maintained at a temperature of 800 ~ 1,050 ℃ for a certain time and quenched to obtain a structure consisting of the carbide and the martensite, and first tempering in the temperature range of 450 ~ 750 ℃ Then, the surface hardening method of the roll, characterized in that the high-frequency curing or low-frequency curing to secondary tempering in the temperature range of 150 ~ 350 ℃.