JPS63104789A - Production of stainless clad steel - Google Patents

Abstract

PURPOSE:To improve productivity, yield and product quality by performing the rolling at the rolling speed more than the rolling reduction calculated from a specific formula as a function of the heating temperature and further, more than the rolling speed as shown with a prescribed formula. CONSTITUTION:The heating temperature at the time of hot-rolling is denoted by T deg.C and the rolling is performed at the rolling speed more than the rolling reduction (r) shown with the formula I in diagram and the rolling speed V at that time is set to more than the rolling speed calculated from the formula II as the function of the roll radius R, the whole thickness H of material to be rolled, the thickness (h) of clad materials and the rolling reduction (r). Under these set conditions, the stainless steel clad materials 1a and 1b are drawn out from uncoilers 9, 8a and 8b respectively with respect to base metal 2 and heated by an inert gas atmosphere direct electrification heating furnace 10 and subjected to the rolling with hot rolling rolls 7. Since the clad materials 1a and 1b can be thoroughly thinned, the productivity, the yield and the product quality are improved by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for continuously manufacturing thin plate stainless clad steel with good yield and productivity.

[Prior Art] Conventionally, most thin stainless clad steel sheets have been manufactured by assembly rolling, explosion rolling, or cast rolling. However, these methods have problems such as complicated material pretreatment and poor yield.
Compared to solid stainless steel materials, it has not been possible to manufacture them sufficiently cheaply.

Below, the outline and problems of each of these conventional methods will be explained in more detail.

(,) Assembling and rolling method The stainless steel plate of the laminated material and the base steel plate are overlapped,
This method involves removing the air between the two, welding the entire circumference, then heating and rolling it to create a product.

According to this method, a good product with a stable cladding ratio can be obtained, but it takes a considerable amount of time to weld, the periphery needs to be cut off after rolling, and the first half is rolled in sheet form. , there are problems such as poor productivity.

(b) Explosion rolling method First, a thick cladding material of stainless steel and base steel is obtained by the usual explosion cladding method, and then,
In the same way as (-), this is heated and rolled into a product. Although products of relatively good quality can be obtained in this case, problems such as the high cost of explosive bonding itself and poor productivity as the first half of the process is rolled in sheet form have been pointed out. sell.

(c) Cast rolling method For example, in the case of a three-layer clad material, a clad steel ingot is first manufactured by setting the base material in the center of the mold and under-pouring molten stainless steel.

Alternatively, stainless steel may be set in a mold and the base material molten steel may be cast. Then, the product is subjected to blooming rolling, hot rolling, and, if necessary, cold rolling.

In this case, there are problems such as it is difficult to maintain a constant cladding ratio during casting, and the yield is poor because a large amount of the head, bottom, and side surfaces of the steel ingot are cut off.

[Problems to be solved by the invention] In order to improve productivity and yield, the rolling cladding method using coils together is optimal, and furthermore, in order to increase the bonding strength between the base material and the composite material, hot rolling cladding is the most suitable method. A pressure welding method is more preferred.

By the way, in order to handle the material in a coil, there is a limit to the thickness of both the base material and the laminated material, and the thicker the material, the more difficult it becomes to feed it to the rolls in the coil. Furthermore, when attempting to manufacture inexpensive stainless clad steel, the cladding ratio needs to be as small as possible in order to save material costs.

In consideration of the above conditions, if an inexpensive stainless clad steel is to be manufactured by hot rolling of coils together, the thickness of the laminated material must be considerably thinner. For example, when laminating stainless steel as a laminated material with a cladding ratio of 10% to a base material of 4,5111+, which has a thickness that is easy to handle in a coil, the thickness of the laminated material will be about 0.5 mm thinner. Even if an attempt was made to process such a combination into a cladding material using a hot rolling method, there were problems such as it being impossible to press-bond them, or even if they were press-bonded, sufficient bonding strength could not be obtained.

The present inventors conducted research to solve the problems of the hot rolled cladding method for thin sheet materials, and found that: The results of hot-rolled cladding tests revealed that in order to obtain sufficient joint strength through pressure welding, it is necessary to apply a certain rolling reduction rate, and that rolling reduction rate decreases as the temperature increases.

■ The reason why pressure welding is not possible or sufficient joint strength cannot be obtained even if pressure welding is done is that if the laminated material is thin, the temperature at the bonding interface will drop significantly due to heat conduction from the laminated material to the roll. Yes.

■ In order to prevent a drop in temperature at the bonding interface, the rolling speed is adjusted according to the thickness of the laminated material so that the contact time between the rolled material and the roll is shortened until the reduction rate required for the above-mentioned pressure welding is achieved. The inventors have discovered that sufficient bonding strength can be obtained by strictly controlling rolling conditions such as the following, leading to the present invention.

[Means for solving the problem] <Hot-rolled cladding conditions under conditions where the temperature drop at the joining interface can be ignored> The present inventor used 5US304, which is an austenitic stainless steel, and a ferritic stainless steel as the bonding materials. 5US444, mild steel was selected as the base material, and hot clad rolling experiments were conducted under various conditions using the test piece (a) and experimental apparatus (b) shown in FIG.

The roll diameter of the rolling mill was 210111 mm, and Ar gas was used as a shield gas during heating.

Laminated material thickness: 2 silk, base material thickness: 4 m, rolling speed: 0
．． A hot rolled cladding test was conducted at 2 m/sec, and the feasibility and degree of bonding were determined based on the relationship between heating temperature and rolling reduction.
Shown in the figure. When the laminated material is 5US304, the heating temperature is T (℃) and the rolling reduction is r = -8X10
It was found that pressure welding was possible at a higher temperature and higher rolling reduction than the straight line AB shown by XT+0.99 (3), and that sufficient bonding strength could be obtained.

For 5US444, 5US30 as shown in Figure 2.
Straight line CD located slightly below straight line AB in case 4
It was found that pressure welding is possible at high temperatures and high rolling reductions, and that sufficient bonding strength can be obtained.

Therefore, in any case, it is possible to join at a higher temperature and a higher reduction rate than the straight line AB shown by equation (3),
Sufficient bonding strength can be obtained.

Furthermore, the rolling speed was changed from 0.2 m/sec to 0.1 m/s.
If the rolling speed is reduced to ec or without changing the rolling speed,
Similar experiments were conducted when the thickness of the laminated material was reduced from 2 silk to 1 mm, that is, under conditions where the bonding interface was more likely to deteriorate due to heat conduction from the rolled material to the roll during rolling, and 5US304 It was confirmed that for each steel type, the relationship between the heating temperature of the welding pool and the rolling reduction ratio was almost the same as the straight line AB and the straight line CD in FIG. 2 for 5US444 and 5US444. Therefore, under the rolling conditions for obtaining the above-mentioned figure 2, that is, the thickness of the laminated material is 2 mm, and the rolling speed is 0.2 m/sec, the temperature decrease due to heat conduction during the contact time between the rolled material and the rolls is It can be seen that the bonding interface has not been reached, and FIG. 2 shows the bonding conditions under conditions where such a temperature drop does not occur.

Manufacturing conditions for rolled cladding to prevent temperature drop at the joint interface〉 Temperature changes at the joint interface during hot rolling include (a) In addition to the temperature drop due to contact heat conduction between the workpiece and the roll, (b) plastic working Strictly speaking, it is quite complex, involving phenomena such as heat generation and heat generation due to the rising phenomenon of the interface. However, the inventors believe that factor (a) is the most important especially in rolling when the thickness of the laminated material is thin, and furthermore,
As a first approximation, we considered the problem as a phenomenon of unsteady heat conduction while ignoring all shape changes during rolling, and then confirmed the validity of such an assumption through experiments.

Based on the above assumptions, and further assuming that the surface of the rolled material is maintained at a certain temperature between the heating temperature of the rolled material and the roll surface temperature when the rolled material and the roll are in contact,
By considering unsteady heat conduction in the direction perpendicular to the bonding interface, in order to suppress the temperature drop at the interface, h≧c', f'ifi'F as c' total constant.
It is expected that condition (4) will be met.

However, in equation (4), h: sheath thickness m α: thermal diffusion coefficient of the laminated material m2/sec, density of the laminated material as ρ, specific heat t'' C as thermal conductivity tk, α;
It is given by ρC.

t: Contact time between the rolled material and the roll sec The contact time t is approximately given by the following equation from geometric analysis.

t≠J and r plane /V (5) However, in equation (5), R: Roll radius 9m r: Reduction ratio H: Total thickness of rolled material 1m V: Rolling speed, m/sec. In addition, when the rolling reduction ratio r is larger than the rolling reduction ratio shown by the straight line AB shown in FIG. 2, the rolling reduction ratio for each heating temperature shown by the straight line AB is adopted instead of the actual rolling reduction ratio. This is because what we are currently concerned about is the temperature drop until the rolling reduction required for bonding is given, and the temperature drop after bonding is not a problem. The following equation is obtained from equations (4) and (5).

V ≧C' ” (! ・J ■■ / h2 (6) Strictly speaking, the thermal diffusion coefficient changes depending on the temperature, but it is considered to be almost constant unless the temperature range is wide, so we set C12α = b (constant). By changing, V ≧ b V plane 7/ h2 (7).

The inventors used 0.3M1 as a laminating material! Using 5US304 and SUS444 with N~1.0 rhyme, and 4.0mm mild steel as the base material, we conducted an experiment by changing the heating temperature and rolling speed. /h”, and by organizing the data by taking ■ on the vertical axis, it was possible to divide the bonded area and non-bonded area into two by a straight line passing through the origin of each laminated material. .

Therefore, as the slope of this straight line, the constant in equation (7) could be determined as follows.

b = 2.2 X 10 m/see Therefore,
Equation (7) is as follows.

V ≧ 2.2 x 10-6
(8) As mentioned above, Ar is used as the heating atmosphere.
, f-sulfur or reducing gas such as hydrogen gas or ammonia decomposition gas is used to heat the mating material and base material to be joined while preventing oxidation of the surfaces, and the rolling reduction rate at that time is (3
), and by selecting a rolling speed that satisfies equation (8) even when the laminated material is thin, e.g. 0.5M1ll or less, sufficient joint strength can be achieved. It becomes possible to manufacture a rolled cladding material having

As described above, the austenitic stainless steel 5US304 and the ferritic stainless steel 5US444 can be joined to the base material under almost the same rolling conditions as the bonding materials. The reason for this is that, although data on the physical properties at high temperatures are not sufficiently detailed for SUS 444 in particular, the thermal conductivity and specific heat, which are the basis of the thermal diffusion coefficient α that influences the thermal conductivity characteristics in equation (4), are Both steel types are 900
℃~1000℃, the values are almost the same (Nikkan Kogyo Shimbun Publishing, 1971, Stainless Steel Handbook P, 106~
(see P, 108), therefore, it is thought that α also becomes a value that hardly changes.

The above laminating materials are representative examples of austenitic stainless steel and ferritic stainless steel, each with 5U
I have explained S304 and SUS 444, but
Other austenitic stainless steels and ferritic stainless steels also have poor mechanical and physical properties at high temperatures.
Since they are not essentially different from 5US304 or SUS444, the present invention can also include the use of these stainless steels as laminated materials.

Further, for the same reason, it can also be applied to a so-called duplex stainless steel in which both austenite and ferrite phases are mixed.

In addition, the base material is not limited to mild steel, but also carbon steel, high-strength steel,
Alternatively, a material other than the laminating material, such as stainless steel, can be selected.

Furthermore, it is possible to adopt the manufacturing method not only for two-layer clad steel with laminating material placed on only one side of the base metal, but also for three-layer clad steel with laminated material placed on both sides, and in that case, if If the plate thicknesses of the laminated materials are different, the lower limit value of the rolling speed may be determined using equation (2) using the thinner plate thickness.

[Examples of the Invention] The method according to the invention was carried out using the apparatus shown in FIG. Heating was done by resistance heating by directly applying electricity to the rolled material, and ammonia decomposition gas was introduced into the furnace to prevent oxidation of the joint surfaces. Note that the roll diameter is 210 m+1. Using such a device, thickness 4. An attempt was made to manufacture three-layer clad steel using Qurn's mild steel 5PCH as a base material and two sheets of 5US304 stainless steel with a thickness of 0.5 as a laminated material. The heating temperature was 1000° C., and the rolling reduction rate and rolling speed were 0, 30, and 0.2 m/aec, respectively, which satisfied equations (1) and (2).

The three-layer hot-rolled clad material produced under the above conditions has sufficient joint strength and can be easily cold-rolled to 1.0 MII at a total reduction of 70% without intermediate annealing. Ta.

1000 for a part of the cladding material thus obtained
A heat treatment of quenching at ℃×10 minutes was performed, and a joint strength test, a tensile test, a bending test, and a cross-sectional microstructural observation were performed as shown below.

To measure the bonding strength between the laminated material and the base material, first
A square cladding test piece was cut out, and each end face of two pieces with a diameter of I Q tart and a length of about 80 mm, which were used as holders for attaching to a tensile testing machine, were joined with silver solder to the laminated material on both sides. It was used as a sample material. Using such a test piece, a tensile test was conducted using an intro/testing machine to examine the strength in the direction perpendicular to the joint surface. As a result, in all of the test pieces, the brazing part broke at a stress of 29 Kq/mrtr2 or more, and the strength of the joint between the laminated material and the base material was sufficient to exceed that. It was known that

Next, as shown in Table 1, the results of the tensile test conducted using the JIS Z220113B test piece showed that it had properties that were comparable to the JIS specified values for 5US304, which are shown as reference values in Table 2. It turns out.

Further, as a result of a bending test carried out at a bending radius of 4III, no peeling or cracking was observed at the bonding interface, indicating that it had sufficient bending ductility.

In addition, the cross-sectional structure of the cladding material is as shown in Figure 5.
No precipitates such as carbides were observed near the joint interface, indicating a healthy structure.

Example 28 Ferritic stainless steel 5US444 with a thickness of Q and 5 mm was used as a laminating material. Using mild steel 5PCH with a thickness of 4 mm as the base material, a three-layer clad material with a thickness of l and Q mm was obtained under the same hot rolling cladding conditions and cold rolling conditions as in Example 1. However, in this case, the final heat treatment conditions before the test were rapid cooling at 900°C for XIO minutes.

The cladding material thus produced was also subjected to a bonding strength test, a bending tensile test, a bending test, and a cross-sectional structure observation using the same machine as in Example 1.

The results of the joint strength test were 27 for all test pieces.
The brazing part broke at a stress of more than Ky/mm2,
It is known that the strength of the joint between the laminated material and the base material is sufficiently high.

As shown in Table 3, the results of the tensile test and test revealed that the material had properties comparable to those of the JIS specified values of 5US444 shown in Table 4 as a reference.

In addition, as a result of the bending test, no peeling or cracking was observed at the bonding interface, and it had sufficient bending ductility.

Furthermore, as a result of microscopic microstructural observation of the cross section of the cladding material, no precipitates such as carbides harmful to workability and mechanical properties were observed near the joint interface.

[Effects of the Invention] As described above, according to the present invention, even if a base steel plate with a thickness of 6 mm or less, which is easy to handle in a coiled state, is used, a sufficiently thin stainless steel laminated material can be made according to the thickness. Stainless clad steel with a small cladding ratio can be produced with high yield and high efficiency.
It is extremely effective in reducing costs.

Furthermore, according to the present invention, compared to the assembly rolling method, explosion rolling method, and cast rolling method, the time during which the laminate material and the base material are kept at high temperature after joining is extremely short, so that the laminate material is Since the diffusion force of C into stainless steel rarely occurs, the precipitation of Cr-based carbides that are harmful to the mechanical properties and workability of the cladding material near the bonding interface is suppressed, so it has excellent properties. It is possible to produce stainless steel clad steel.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the shape of the test piece and the outline of the testing apparatus used to determine the bonding conditions in the hot rolled cladding test. Figure 2 shows 5US304 and 5US4 with a thickness of 2mm.
FIG. 4 is a diagram showing the relationship between the weldable heating temperature and the rolling reduction rate in case No. 44; Figure 3 shows rolling speeds V, ! for the cases where the laminated materials are 5US304 and 5US444°. : A diagram showing joinable areas organized according to the relationship of J■r7h2. FIG. 4 is a schematic diagram of a hot rolled clad manufacturing apparatus used in an example of the present invention. FIG. 5 is a diagram showing the metal structure of a cross section near the joint interface of 5US304 stainless clad steel manufactured by the method of the present invention. 1, la, lb... laminated material, 2... base material, 3...
・Dummy plate, 4... Ar gas introduction hole, 5... Heating furnace, 6... Oxidation prevention heating jig, 7... Hot rolling roll, 8a, 8b... Laminated material uncoiler-19 ...Base material uncoiler-110...Atmosphere direct current heating furnace, 1
1... Ammonia decomposition gas introduction hole, 12... Clad material coiler.

Claims (4)

[Claims] (1) When producing clad steel using a hot rolling method using stainless steel as a laminated material, the laminated material and base material are heated in an inert gas atmosphere or a reducing gas atmosphere.
When the heating temperature is T (℃), rolling is performed at a rolling reduction rate r or more determined from r = -8 × 10^-^4 × T + 0.99 (1), and the roll radius is R (m), When the total thickness of the rolled material is H (m), the thickness of the stainless steel of the mating material is h (m), and r is used for each heating temperature determined by equation (1), V = 2. .2×10^-^6×√(RHr)/h^2(2
) The rolling speed V (m/sec) obtained from the relational expression
A method for producing stainless clad steel, which comprises rolling at a rolling speed of at least 100 mL. (2) The method for manufacturing stainless clad steel according to claim 1, wherein the laminated material is austenitic stainless steel. (3) The method for manufacturing stainless clad steel according to claim 1, wherein the bonding material is ferritic stainless steel. (4) The method for manufacturing stainless clad steel according to claim 1, wherein the laminated material is an austenitic-ferritic duplex stainless steel.