JPS6099408A - Rolling roll made of high chrome cast iron - Google Patents

Abstract

PURPOSE:To obtain a rolling roll made of high chrome cast iron excellent in wear resisting properties, toughness, and heat cracking characteristics by forming the roll consisting of an outer layer having prescribed hardness and containing the prescribed percentages of C, Si, Mn, Cr, Ni, and Mo and an inner layer having high toughness. CONSTITUTION:A rolling roll made of high chrome cast iron is formed by an outer layer of high chrome cast iron having <=5% (vol%) residual austenite and >=70HS hardness and an inner layer having high toughness. The outer layer contains, by wt%, 3-3.5% C, 0.3-1.2% Si, 0.5-1.5% Mn, 15-27% Cr, 0.5-2% Ni, 0.5-3.5% Mo, and the balance Fe. Further, the inner layer contains, 3-3.6% C, 0.3-1.2% Si, <=0.5% Cr, 0.02-0.1% Mg, one or more kinds of Mn, Ni, and Mo, and the balance Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a high chromium cast iron roll having abrasion resistance, toughness and roughness resistance that can withstand high load rolling conditions. The roll according to the present invention is applied to a work roll for a second rolling mill in a hollow I/strip mill, a work roll for a cold strip mill, and the like.

(Conventional technology) Recently newly installed strip mills are designed to dramatically improve the quality of the two-dimensional precision of the finished plate.
New techniques such as Hi milling and 4Hi milling cross J!
j is being adopted. In these mills, the surface pressure between the rolls increases significantly, and locally it is more than 1.5 times that of conventional mills1]
As a result of contact stress, the surface of the work roll becomes rough1.
It becomes easier.

In other words, with the Adamite roll that has been used conventionally, there are concerns about roughness due to plastic flow under high contact stress, spalling due to transfer fatigue, and punting due to peeling of free eutectic carbide FeC. Graphite chips often cause damage such as falling off, which seriously hinders work, and a solution to this problem has been desired.

On the other hand, high chromium casting mouth 20-l is made of adamite roll or Ni.
It has superior wear resistance compared to grain rolls and is used in work rolls for hot strip mills and work rolls for cold strip mills, and the performance of the outer layer is highly evaluated. However, depending on the rolling usage conditions, heat #i attack,
Deterioration of the roll surface due to thermal fatigue was observed, and the roughness resistance was not necessarily sufficient.

(Object of the Invention) An object of the present invention is to provide a high chromium cast iron coal that maintains 11III abrasion resistance and toughness, has excellent heat crack properties, and has good Mf and roughness resistance.

For the above purpose, we investigated and analyzed the roughness of high chromium cast iron rolls, and found that roughness begins with vertical cracking (cracking in the direction perpendicular to the roll surface) at the interface between carbide and matrix structure due to thermal fatigue. Next, transverse cracking (cracking parallel to the roll surface) occurs due to transfer fatigue and thermal stress.

It has become clear that the disease progresses by propagation. For this reason, it has been found that suppressing the coarsening of the IM cell size of the high chromium cast iron roll material and refining the irregularly precipitated carbides is effective in preventing roughening of the surface. It has also been found that when a large amount of retained austenite is present, it undergoes transformation due to thermal load and generates microscopic stress, which promotes rough skin.

(Structure and operation of the invention) The characteristics of the present invention are that in order to solve the problems mentioned above, the amount of retained austenite is regulated to 5% or less to ensure Hs and hardness of 70 or more, and if necessary, High chromium H'#Nr with a fine solidified structure with a crystal cell size of 50 lm or less:
The purpose is to obtain an I-le. Here, the primary cell size is the size of the primary dendrite a or the secondary dendrite b, as shown in FIG.

In order to satisfy this characteristic, the outer layer component is C:3. Q~3.
5OA, Si: 0.3-1.2%, Mn: 0.
5-1.5g, N1: 0.5-2.0x, Cr: 15
~27'X, Mo: 0.5-3.5X.

The remainder consists of cast iron substantially consisting of Fe, or cast iron further preferably containing 0.1 to 1.0% of V in the above components, and the inner layer component is C: 3. (1-3.fi%, Si:
3.0-3.5x, Cr: 0.5% or less, Mn, Ni
, Mo's type or Hani la more than 1 (7) Total power 2, 5
%” or less, Mg: 0.02 to 0.1%, remainder substantially F
It is composed of two layers of cast iron consisting of e.

In addition, as a means to reduce the primary cell size of the outer layer to 50 lm or less, in addition to using the outer layer components as described above, (υ A 0.01 to 0.1% addition as an outer layer component, 1.2j after injection of the outer layer) In order to solidify the molten metal quickly, a mold with a refractory coating on the inner surface of the mold having a thickness of 1.5 mm or less is used.

Due to these structural characteristics, high chromium cast iron roll material has excellent toughness and excellent transfer fatigue resistance and heat crank resistance, and has dramatically improved wear resistance and surface roughness. By applying the roll of the present invention to a work roll for hot stripping, it is possible to improve the rolling performance.

Furthermore, this high chromium J+ SS roll has l
If applied to work rolls for cold strip mills that require heat crack resistance, abrasion resistance, and burrability, the roll life can be expected to be significantly extended compared to conventional rolls.

In addition, when manufacturing rolls using high chromium cast iron alone, there is a risk that the residual stress in 6B inside the roll will be excessive and it will break during manufacturing or use.In order to compensate for the lack of toughness, the inner layer is made of strong cast iron. It is necessary to make it into a composite material.

The reasons for the limitations on the chemical composition of the outer layer material of the high chromium cast iron roll of the present invention will be described below.

C: 3.0-3. ! J, Cr:I5~27%C is C
It is determined based on the balance with r, but if it is less than 3.0%, austenite will remain in the matrix and I-weave, and furthermore, the primary cell size generated in the solidification process will exceed 50 gm, which is unsuitable. At 3.0% or more, the structure becomes close to a eutectic structure, and a fine solidified structure with a primary cell size of 50 gm is obtained, improving skin roughness resistance, and increasing the amount of carbides.
It is easy to ensure a hardness of s70 or higher. 3.5'/a
If it exceeds this, the amount of carbides increases, the toughness deteriorates, and the amount of austenite remaining around the carbides increases rapidly. Furthermore, the risk of roll breakage during the manufacturing process increases.

Therefore, the C-containing liquid should be 3.0 to 3.5%.

If Cr is less than 1.5%, eutectic carbide (
It is not preferable because F e -Cr )a'C is mixed therein, and if it is added in an amount exceeding 27%, it becomes coarse and precipitates romium carbide, and the carbide content 4j becomes non-uniform, which is not preferable. Therefore, the Cr content is determined by hard chromium carbide (Fe −
Cr)? C3 is uniformly precipitated in a proportion of 15 to 27%, and has the best properties in terms of resistance to cracking and toughness.

Mo20, 5-3.5LV: 0.1-], 0% When the amount of CQ and Cr increases, hard chromium carbide (Fe-Cr
) The amount of 7C3 precipitated increases, which is advantageous in reducing the amount of wear, but on the other hand, retained austenite in the matrix structure increases. Therefore, these retained austenite tl! Mo or Mo and V are added to reduce the chromium carbide and precipitate a carbide that is harder than the chromium carbide. Mo
In addition to promoting precipitation hardening due to the formation of hard carbide Mo2C, increasing base hardness and improving wear resistance, quenching.

Greatly improves tempering properties. Hs? In order to obtain a roll hardness of 0 or more, Mo needs to be 0.5% or more, and H
In the case of cold millwork rolls that require a hardness of s hardness of 90 or more, an MO content of 3.5% is sufficient.

Further, V added as necessary is 0. V at 1- from I'X
1 to precipitate C carbides and reduce austenite.
Il14 wear resistance is improved. Even if it is added in an amount of 1% or more, the effect of reducing the amount of retained austenite is small. Therefore, considering economic efficiency, the northern limit of ■ is set at 1%.

Ni: 0.5-2.0% N1 strengthens the base structure, and in order to obtain the required hardness of Hs hardness 70 or more, 0.5% or more -1- is μ・back, and more than 2z When added, austenite is stabilized and the remaining 6r
Long 11j to lower the amount of H austenite to 5z or less
It requires heat treatment for a period of 30 minutes.For this reason, considering economic efficiency, we decided to limit the northern limit to 2z.

Si: 0.3-1.2°'/A, Mn: 0
．． 5-1.5% S1 is 0.3z or more for deoxidizing the molten metal.
] The northern limit is set at 1.2%, since the mechanical properties deteriorate if it becomes too high. In addition to deoxidizing the molten metal, Mn also combines with S to prevent deterioration of mechanical properties during hot temperatures, but this effect is not sufficient when it is less than 0.5%, and when it exceeds 1.5%. and decrease toughness. Therefore, the Mn content is set to 0.5 to 1.51.

Next, the reasons for limiting the chemical components of the inner layer of the present invention will be described.

C: 3.0 to 3.8% Graphitization of the inner layer is inhibited by the diffusion of the components of the outer layer, especially Cr, and in the high chromium T4J iron roll of the present invention, graphitization of less than 3% will result in insufficient graphitization of the shaft. toughness decreases. When C exceeds 3.6%, graphite becomes excessive and the strength of the shaft portion decreases. Therefore, the C content is set to 3.0 to 3.6%.

Si + 3.0 to 3.5% Si requires 3z or more -4- to prevent deterioration of the inner layer material due to the spread of Cr in the outer layer, but if it exceeds 3.5%, graphite becomes excessive. The material deteriorates.

Therefore, the Si content is set to 3.0 to 3.5z.

Cr: 0.5X or less (1.8% or less when solidified) When the Cr content in the inner layer increases due to diffusion from the outer layer, the toughness deteriorates due to whitening of the inner layer, resulting in an increase in residual stress generated inside the roll. This results in a loss. In the present invention, the inner layer C during solidification
There are some planets where the allowable amount of r is 1.8% or less, and for this reason, the C' in the inner layer molten metal is set to 0.5%, although it depends on the injection conditions of the inner layer.
% or less.

rVig+0.02~0.1% Is Mg an important element for spheroidization, o, o2x
If it is less than that, the spheroidization will be poor and the shaft portion will not be strong enough. 'However, when Mg is included in excess of 0.1%, Mg
This causes harmful effects in terms of the chilling effect of g and the formation of dross.

Therefore, the content of Mg is set in the range of 0.02 to 0.1%.

Other alloying elements constituting the inner layer cast iron material include Mn, N
One or more types of i and Mo are added in a total amount of 2.5z for the purpose of imparting strength to the inner layer.

If the total content exceeds 2.5χ, the inner layer will harden and the toughness will decrease, which is unsuitable.

Next, the reasons for limiting the outer layer material to 5% or less retained austenite and 50 pLm or less primary cell size will be explained with regard to their effects. Figure 2 shows the relationship between the amount of retained austenite and the skin evaluation after rolling. As is clear from this [Δ, by suppressing the amount of retained austenite to 5% or less, the roll skin is stabilized and 1■j use is possible. Figure 3 shows the relationship between primary cell size and thermal shock crack depth. As the primary cell size decreases, the maximum crack depth decreases, and the thermal shock properties are significantly improved. Therefore, it is preferable that the primary cell size is 50 gm or less, which is suitable for actual roll production, and by applying this to an actual mill, it is fully expected that even more excellent roughness resistance will be achieved.

(Effects of the Invention) The high chromium cast iron roll of the present invention has wear resistance, toughness, heat resistance, crankability, and surface resistance by limiting the range of ingredients in the outer layer and inner layer as follows. It has excellent roughness and can withstand particularly high load rolling.

The roll of the present invention is manufactured by forming a two-layer ingot using a combined casting method including centrifugal casting, followed by repeated tempering at 400 to bioo°C or quenching from point A or above and tempering at 400 to 600°C. Manufactured by.

(Example) Product body diameter? 75mm, product trunk length 1.750mm, total length 5
, 175 mm work rolls for hot strip mills were manufactured, and sound high chromium cast iron rolls having the components and material properties shown in Table 1 were obtained. When this roll was subjected to rolling on an actual machine, there were no accidents such as wear, roughness, or breakage, and good rolling results were obtained.

[Brief explanation of the drawing]

i, Figure 61 is an explanatory diagram of Puntrai (・) showing the size of the primary crystal cell size, No. 21Δ is a diagram of the amount of retained austenite and the skin score of the actual roll, and Figure 3 is the illustration of the primary crystal cell size and thermal shock strength. It is a diagram showing the rack depth. Patent applicant Agent B. Ritoya Fuki Tomoyuki (and 1 other person) 1st^ 2nd design Ibara/Tome A'-su T night (%) Mitsuyuki Teito j Author (spontaneous) December 2, 1980 Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office ■, Indication of the case 1982 Patent Application No. 205985 2, Name of the invention High chromium cast iron rolling roll 3, Matters of the person making the amendment Relationship with Applicant Address: 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (6
65) Nippon Steel Corporation 4, Agent Address: 704, 6-4-21 Akasaka, Minato-ku, Tokyo (5)
84) 7022 5. Claims and Detailed Description of the Invention column 6 of the specification to be amended, Contents of the amendment (1) The statement of the claims on pages 1 to 2 of the specification is corrected as shown in the attached sheet. do. (2) "rFe C" on page 3, line 16 of the specification is rFe, C
” he corrected. 2. Claims (1) Weight ratio: C: 3.0 to 3.5X, Si: 0.3 to 1.2
%Mn: 0.5-1.5X, Cr: 15-27% Ni
: 0.5-2.0%, l'vlo: 0.5-3.5
An outer layer of high chromium cast iron having a residual austenite content of 5z or less by volume and a Hs hardness of 70 or more; C: 3.0-3.6% by weight, Si : 0.3~1.2X
Cr: 0.5% or less, Mg + 0.02 to 0.1% Mn,
A high chromium cast iron rolling roll comprising: an inner layer containing one or more of Ni and Mo with a balance of 2.5'10 or less and a qualitatively Fe content. (2) Weight ratio: C: 3.0-3.5%, Si: Ll, 3-1
．． 2XMn: 0.5~1.5%, Cr: 15~
27! Ni: 0.5-2.0%, Mo: 0
．． 5 to 3.5 C: 3.0-3.6%, Si: 0.3-1.2%
Cr: 0.5% or less, Mg + 0.02 to 0.1% Mn,
A high chromium cast iron rolling roll comprising one or more of Ni and Mo, and an inner layer consisting essentially of Fe at 2.5z or less. (3) The rolling roll according to claim 1 or 2, wherein the rolling roll has a fine and dense solidified structure with a primary cell size of 50 pm or less in the outer layer.

Claims (3)

[Claims] (1) Weight, Ii ratio: C: 3.0-3.5Z, Si: 0.3-1.2%
Mn-0.5~1.5%, Cr: 15~2
7% Ni 0.5-2.0%, Mo: 0.5
~3.52 The balance is substantially Fe, 1niJ61, the amount of retained austenite is 5% or less, and the Hs hardness is 70
An outer layer of high chromium cast iron having the following: gr, quantitative ratio of C30 to 3.6%, Sl: (1.3 to 1.2% Cr:
0.5% or less, Mg: 0.02-0.1%Mn, Ni
, an inner layer consisting of 2.5% or more of one kind of Mo, or one of C, zero or more, and the balance substantially consisting of Fe. (2) Weight 4i ratio: C: 3.0-3.5%, Si: 0.3-1.2
XMn: 0-5~1.5% + Cr: 15~2
7XN i: 0.5-2.0%, Mo: 0.
5 to 3.5% V: 0.1 to 1.0% The remainder may be substantially Fe. High chromium cast iron with retained austenite content of 5% or more per area ratio and Hs hardness of 70 or more at 713. Outer layer: C by weight ratio: 3. Q~3.8%, Si:0.3~1.2%C
r: 0.5% or less, Mg: 0.02-0. lXMn,N
1. A high chromium iron rolling roll comprising one or more of Mo, 2.5z or less, and an inner layer consisting essentially of Fe. (3) A rolling roll according to claim 1 or 2, which is formed by forming a fine and dense solidified structure in which the outer layer has a primary cell size of 50 pm or less.