JPH01225751A - Work roll for heavy-load cold rolling excellent in spalling resistance and its production - Google Patents

Abstract

PURPOSE:To manufacture a work roll for heavy-load cold rolling excellent in spalling resistance and wear resistance by subjecting a steel having a composition consisting of C, Si, Mn, Cr, Ni, Mo, V, P, S, and Fe to forging and then to specific heat treatment. CONSTITUTION:A steel having a composition consisting of, by weight, 0.80-1.00% C, 0.10-0.65% Si, 0.20-1.60% Mn, 4.0-6.5% Cr, 0.10-0.70% Ni, <=0.30% Mo, <=0.10% V, <=0.25% P, <=0.010% S, and the balance Fe with inevi table impurities is forged into the prescribed roll shape. Subsequently, the forg ing is subjected to quench-and-temper treatment, by which toughness inside the roll is secured. The roll formed part is subjected to induction heating, by which the surface layer part is subjected to temp. rise up to 930-1,000 deg.C to undergo austenitizating and hardening treatment. Then, the roll is subjected to subzero treatment at 0--50 deg.C to produce sufficient hardness. Successively, the above roll is tempered at 110-150 deg.C. By this method, the work roll in which is Vickers hardness in the surface layer part exceeds HV 800 and the amount of residual austenite is regulated to >=5vol.% can be obtained.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a work roll for cold rolling having a surface hardness with a Vickers hardness (Hv) of 800 or more and a method for manufacturing the same, and particularly relates to a work roll for cold rolling having a surface hardness of 800 or more in Vickers hardness (Hv), and a method for manufacturing the same. The aim is to increase durability against accidents.

<Prior Art> In cold rolling, there has been a strong demand in recent years for materials with high deformation resistance and for rolling thinner materials, so the load on work rolls has tended to increase more and more. As a result, the wear of the rolls has become significant, the frequency of roll replacement has increased, and rolling efficiency has been reduced.Therefore, there is no way to improve wear resistance by increasing the hardness or the amount of carbide. It's being used. On the other hand, an increase in the load applied to the work rolls tends to increase the probability of damage to the rolls, and it is also necessary to improve the accident resistance of the rolls. However, an increase in hardness and an increase in the amount of carbide tend to reduce accident resistance, and there has been a demand for further improvement in accident resistance.

Japanese Patent Publication No. 61-21300 contains 2 to 4% (same weight %) Cr, 1 to 2% C, and 1 to 1% ■.
Contains 2% and increases wear resistance by increasing the amount of carbide contained, as well as crack resistance.

A large diameter work roll with improved breakage resistance is disclosed. Furthermore, in Japanese Patent Application Laid-open No. 57-47849, 0.4~
A high Cr cold rolling work roll containing 3.0% Mo and 0.2 to 2% V has been proposed. This has a hardness of Hv80
0 or less, and the wear resistance is improved by increasing the amount of alloy carbide, but since the hardness is kept low, there is a concern about the problem of roll dents during rolling.
, Mo+V was high, so the forgeability was poor and the manufacturing cost was high.

<Problems to be Solved by the Invention> These conventional techniques have poor forgeability, contain large amounts of expensive alloying elements, and contain V.

Since the content of Mo, Cr, etc. is increased and the hardness is increased, the toughness is poor, the roll life is short, and there remains a problem particularly in spalling resistance.

The present invention provides a roll that is less likely to cause accidents such as spalling during high-load rolling, and has excellent wear resistance, and a method for manufacturing the roll.

Means for Solving the Problems> The present invention provides (11% by weight, C: 0.80-1.00%
, Si: 0.10-0.65%, Mn: 0.20
~1.60%+Cr: 4. O~6.5%, Ni
: 0.10~0.70%, Mo: 0.30%
Below, ■: O, XO% or less, P: 0.25% or less,
S: 0.010% or less, the balance consists of Fe and unavoidable impurities, and the hardness of the surface layer is 11 on Vickers hardness.
A work roll for high-load cold rolling with excellent spalling resistance characterized by having a residual austenite content of more than 800 and a volume fraction of 5% or more, and (2) a C: 0. 80-1.00%, Si: 0
．． 10~0.65%, Mn: 0.20~1.60
%, Cr: 4.0-6.5%, Ni: 0.
10-0.10%.

Mo: 0.30% or less, V: o, to% or less, Pl
, 25% or less, s: o, oto% or less, the remainder being Fe and unavoidable impurities. After forging the steel into a predetermined shape, it is quenched and tempered, and then the surface layer is heated to 930 to 1000°C by induction heating. It has excellent spalling resistance, characterized by being heated to a temperature range to austenitize, then quenched, then subjected to sub-zero treatment in a temperature range of 0 to -50 degrees Celsius, and then tempered in a temperature range of 110 to 150 degrees Celsius. This is a method for manufacturing work rolls for high-load cold rolling.

Effects〉 As an indicator of the accident resistance of work rolls for cold rolling, transfer fatigue life is cited because large spalling occurs with cracks introduced due to transfer fatigue as a starting point. A long transfer fatigue life increases the accident resistance of the roll. Therefore, as a result of examining various factors to determine the transfer fatigue life, especially at high surface roughness, it was discovered that the transfer fatigue life greatly changes depending on the appropriate combination of retained austenite amount and chemical components.

Figure 1 shows the relationship between the transfer fatigue test results and the amount of retained austenite for steels in the composition range of the present invention and steels with low Cr content. It can be seen that the transfer fatigue life is significantly longer at (volume ratio), and that it can withstand long-term loads until spalling occurs. As described above, retained austenite is an important factor in the accident resistance of rolls, but the effect of retained austenite on rolling fatigue life in particular varies greatly depending on the chemical composition.
When rfi is low, the effect of retained austenite is not significant.

If a roll with high hardness is cranked, it will immediately be severely damaged and lead to an accident, so it is important to increase the rolling fatigue life. To achieve this, it is necessary to secure a stable amount of retained austenite, and conventionally the idea was to reduce the amount of retained austenite to ensure hardness, but the present invention adopts a different idea as described above. It is based on

The roll of the present invention has a surface hardness of Hv' in terms of Vickers hardness.
The hardness is limited to 800 or more, which is necessary from the viewpoint of wear resistance as a work roll for high-load cold rolling and prevention of occurrence of dents.

Next, the reason for limiting the ingredients of the present invention will be described.

c: o, so~1.00% In this component system, C is an element that partially dissolves in the matrix and improves hardenability, and forms carbides with Cr and Mo+v, improving wear resistance. Improve. However, if it is less than 0.80%, it has little effect on hardenability, and if it exceeds 1.00%, huge eutectic carbides will crystallize, impairing workability. % range.

Si: 0.10-0.65% Si has the effect of increasing hardenability and temper softening resistance, and the effect of retarding the decomposition of martensite, but if it is less than 0.1%, the effect is small and 0. If it exceeds .65%, it promotes embrittlement, so it is limited to a range of 0.10 to 0.65%.

Mn: 0.20-1.60% Mn is an element that increases hardenability and stabilizes austenite, but if it is less than 0.2%, the effect is small, and if it exceeds 1', 60%, it becomes brittle. 0.2
The range was 0 to 1.60%.

(:r: 4.0-6.5% Cr is a carbide-forming element. Carbide is dispersed in the matrix and improves wear resistance, and some of it is dissolved in solid solution to stabilize austenite and improve hardenability. Increase C.
It has been conventionally known that an increase in the amount of r brings about an increase in the amount of Cr carbide and improves wear resistance. In the present invention, we have further discovered that by adding 4.0% or more and optimizing the heat treatment in combination with the amount of Ni added, the amount of stable retained austenite increases and the transfer fatigue properties are improved. However, when Cr1l exceeds 6.5%, the amount of C dissolved in the matrix decreases due to the increase in the amount of carbides, which impairs hardenability. Therefore, the amount of Cr is 4.
The range was 0 to 6.5%.

Old 1.10 to 0.70% Ni is an element that increases hardenability and stably increases retained austenite, and is an element necessary for high-load rolling rolls. If it is less than 0.1%, the effect is small and 0.
．． If it exceeds 7%, the effect of ensuring hardness is saturated and is not economical, so it is set in the range of 0.10 to 0.70%.

Mo: 0.30% or less Mo is an element that increases hardenability 1 wear resistance, but addition of a large amount is limited to 0.30% or less because it impairs hot workability and from the economic point of view. Ru.

V: 0.10% or less ■ is a carbide-forming element, and like Cr, it is dispersed in the matrix and improves wear resistance, but if it exceeds 0.10%, grindability deteriorates, so 0. It was set to 10% or less.

S: 0.010% or less S increases the amount of inclusions and reduces fatigue life, so o, o
io% or less.

P: 0.025% or less Like S, P is a harmful element and promotes embrittlement, so its amount must be reduced and is limited to 0.025% or less.

After forging, the steel ingot having the above chemical composition is subjected to the following usual heat treatment.

First, normalization and spheroidization are performed to obtain uniformity of internal quality. Furthermore, the toughness inside the roll is ensured by quenching and tempering.

After that, only the surface layer area necessary for curing is heated to 930-1000℃.
Surface hardening is performed by raising the temperature to a temperature range of .

Induction heating is used for this surface hardening. The hardened area, ie, the area where rolls are used, must be hard and have good accident resistance. If the heating temperature is less than 930°C, the hardness will be low (and if the heating temperature exceeds 1000°C, a large amount of retained austenite will remain, and the hardness will be low even if sub-zero treatment is performed.

The next sub-zero treatment transforms the unstable austenite and establishes the upper limit of hardness. On the other hand, it is necessary to obtain a stable amount of retained austenite of 5% or more in order to improve accident resistance.

C: 0.95%, Si: 0.60%, Mn
: 0.40%+Ni: 0.15%, Cr: 5.
0%, Mo: 0.30%, V: 0.07%.

P: 0.012%, S: 0.003%
Figure 2 shows the relationship between the heating temperature and the surface hardness of the roll obtained by -30''C sub-zero treatment and 120''C tempering for the steel.

If the quenching temperature is less than 930°C, the necessary and sufficient hardness cannot be obtained. On the other hand, if the quenching temperature exceeds 1000°C, the amount of retained austenite will increase, resulting in a significant decrease in hardness, and the austenite grain size will become coarse. , and the toughness decreases, which has the opposite effect. Therefore, the quenching temperature is 925-1000℃.
limited to the range of In addition, the upper limit of the sub-zero treatment temperature is 0°C to ensure hardness exceeding Hv 800.
As shown in FIG. 3, in order to obtain 5% or more retained austenite, the lower limit was set at -50°C.

<Example> Steel having the composition shown in Table 1 was melted and made into ingots in an electric furnace and then in a ladle refining furnace. These steel ingots are forged to a diameter of 600 r.
It was formed into a ta roll shape. Next, a second
The heat treatments shown in the table were performed, and the retained austenite, hardness, and transfer life ratio of the heat-treated products were examined. The results are also shown in Table 2.The heat treatment was carried out by induction heating to the quenching temperature up to about 25 mm below the surface layer, and the quenching was performed by quenching in water.

<Effects of the Invention> According to the present invention, by adding a relatively small amount of alloy, the life of the roll can be expected to be significantly extended during high-load cold rolling, and the roll unit consumption can be improved.

[Brief explanation of the drawing]

Figure 1 is a measurement diagram showing the influence of retained austenite 13 on transfer fatigue life, Figure 2 is a measurement diagram showing the relationship between quenching temperature and hardness, and Figure 3 is a measurement diagram showing the relationship between sub-zero treatment temperature and retained austenite l-ff1. It is a graph showing the relationship between. Patent Applicant: Kawasaki Steel Co., Ltd. 1st chart (R (%)) Figure 2 Kushinwa (℃) Figure 3 Sub-zero treatment temperature (℃)

Claims (2)

[Claims] (1) In weight%, C: 0.80-1.00%, Si: 0
．． 10-0.65%, Mn: 0.20-1.60%, C
r: 4.0-6.5%, Ni: 0.10-0.70%,
Mo: 0.30% or less, V: 0.10% or less, P: 0.
25% or less, S: 0.010% or less, the balance is Fe and unavoidable impurities, the hardness of the surface layer exceeds Hv800 in Vickers hardness, and the amount of retained austenite is 5% or more in volume percentage. A work roll for high-load cold rolling with excellent spalling resistance. (2) In weight%, C: 0.80-1.00%, Si: 0
．． 10-0.65%, Mn: 0.20-1.60%, C
r: 4.0-6.5%, Ni: 0.10-0.70%,
Mo: 0.30% or less, V: 0.10% or less, P: 0.
25% or less, S: 0.010% or less, the balance being Fe and unavoidable impurities. After forging the steel into a predetermined shape, it is quenched and tempered, and then the surface layer is heated to 930~1 by induction heating.
Spalling resistance characterized by raising the temperature to a temperature range of 000℃ to austenite, performing sub-zero treatment in a temperature range of 0 to -50℃ after quenching, and subsequently tempering in a temperature range of 110 to 150℃. A method for manufacturing excellent work rolls for high-load cold rolling.