JPH0114970B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a completely new manufacturing method for high carbon stainless steel strips. More specifically, the present invention relates to a completely new manufacturing method for high carbon stainless steel strips. By performing secondary diffusion treatment and annealing treatment, a uniform carbon concentration distribution and a uniform carbide with a maximum particle size (hereinafter referred to as maximum particle size) converted to a circular equivalent diameter of 1.5μ or less are achieved. The present invention relates to a method for manufacturing a high carbon styrene steel strip having a distributed structure. The material conventionally used to manufacture safety razor blades (hereinafter simply referred to as razor blade material) is 0.65% C-13.
%Cr martensitic stainless steel is common. In this steel type, coarse eutectic carbides tend to crystallize because C is concentrated in the final solidification region due to component segregation during solidification. The presence of eutectic carbides causes cracking inside the slab or removal of unevenly distributed parts in the steel ingot, resulting in a decrease in the blooming yield. The biggest problem is that it is not completely broken and dispersed by hot rolling, cold rolling and heat treatment, and even when it is made into razor blade material with a thickness of about 0.1 mm, it remains as coarse carbide with a grain size of 3 to 10 μm. be. In a razor blade machined from a material in which coarse carbides are present, the coarse carbides fall off when force is applied to the blade, causing the blade to chip. If this development occurs during sharpening, it will impede sharpness, and if it occurs during use of a razor blade, it will significantly impair the sharpness of the razor blade, resulting in a decrease in product value. In this way, in order to maintain good sharpness in a razor blade, it is necessary to uniformly precipitate fine carbides. Razor blades are used in a quenched and tempered state, and in order to provide good temper softening resistance, it is necessary to uniformly disperse fine carbides. As mentioned above, the quality characteristics required for razor blade materials are strict, and carbide particles with a grain size of 2±1μ must be uniformly distributed in a ferrite pass of 10±5μ. As a manufacturing method to meet this requirement, the solidification rate is accelerated by disposing of the unevenly distributed portions of amorphous carbide as scrap, or by making the steel ingot into a size of about 1 ton, which increases the growth and uneven distribution of eutectic carbides. Various measures have been taken to prevent this, or to improve solidification conditions by continuous casting.
None of these methods completely eliminates coarse carbides. For this reason, it is necessary to easily and stably manufacture stainless steel strips for razor blades that have a stable cutting quality, in other words, steel strips that have sufficient hardness and a structure in which carbides with a maximum grain size of 1.5μ or less are evenly distributed. It was hot. One method that makes this possible is carburization. In JP-A No. 57-126921, a cold steel strip containing 11.0 to 18.0% chromium and up to 0.25% carbon was carburized, diffused and annealed, and then the steel strip was carburized to obtain a predetermined thickness. In order to further refine the carbides, it is disclosed that the fine carbides can be dispersed and precipitated by cold rolling. However, the method of the invention has several drawbacks, and when the average carbon concentration of the entire cross section after carburizing (hereinafter referred to as average carbon concentration) exceeds 0.7%, carbides tend to become coarse. Alternatively, if the diffusion annealing temperature and time are improperly selected, carbides disappear into solid solution or become coarse. Furthermore, once the carbides are precipitated, the rolling rate is
Although finer grains can be refined up to 50%, there was a problem in that fine carbides did not increase even if the rolling rate was increased further. As we investigated and considered these problems and drawbacks, we discovered that the reason for the formation of coarse carbides is that exposure to carburizing temperatures creates coarse regions of crystal grains, and carbon atoms diffuse into these regions. We have clarified that coarse carbides are likely to be formed when the diffusion treatment temperature is high, and that fine carbides disappear into solid solution when the diffusion treatment temperature is high, and that carbides tend to aggregate and become coarse, and we have developed methods to prevent these phenomena from occurring. The present invention was completed by discovering the following. According to the present invention, C: 0.3% or less, Cr: 11.0 to 18.0
A 0.3-2.0 mm thick cold-rolled steel strip or cold-rolled steel sheet material of Fe-Cr stainless steel containing ~ is carburized, subjected to primary diffusion treatment and annealing treatment, and then cold rolled to form carbides. Provided is a method for producing a high carbon stainless steel strip, which comprises dispersing carbides, refining the internal structure, and then uniformly distributing fine carbides by performing a secondary diffusion treatment and an annealing treatment. . When we say cold rolling here. Usually, pickling is carried out before that, and then annealing is carried out, but these may be omitted depending on the case. In the present invention, preferably carburization is carried out to give an average carbon concentration of 0.4 to 1.4%,
Next, by performing a primary diffusion treatment to reduce the carbon concentration in the surface layer and improve rolling properties, the internal structure is refined by cold rolling, and by performing a secondary diffusion treatment, The advantage is that fine carbides can be uniformly precipitated from the surface layer to the center of the plate thickness. The reasons for limiting the conditions of the method of the present invention will be described below. The material steel contains 11.0-18.0% chromium. To give steel corrosion resistance, it must contain at least 11.0% chromium;
If it exceeds 18.0%, the quality is too high for a disposable razor blade material. This is an extremely common range for the chromium content of razor blade materials. Material steel contains less than 0.30% carbon. One key point in carrying out the method of the present invention is how to cheaply produce steel material. Therefore, it can be manufactured without any difficulty using a mass production method, and there is no formation of coarse carbides that cannot be eliminated in subsequent processes when manufacturing large continuous cast slabs, and its high strength allows it to withstand loads such as hot rolling and cold rolling. The limit of carbon content that does not increase is
It was determined to be 0.30%. As for the lower limit, although it is not particularly limited as a component of the invention, the numerical value of ordinary weave in a normal steel manufacturing method is 0.01%. Other so-called inevitable impurities include:
Tolerable amounts of this type of steel that are mixed in with the normal steel manufacturing method are: Si: 1.0% or less, Mn: 1.0% or less, P: 0.04
% or less, S: 0.03% or less, Ni: 0.60% or less, there is no problem. Also, trace amounts of Mo, Nb, V,
W may be contained alone or in combination. These components enhance corrosion resistance, improve hardenability, and reduce decrease in hardness due to tempering after hardening. The thickness of the material is limited to 0.3 mm or more and 2.0 mm or less. The reason for this is that if the plate thickness exceeds 2 mm, the carburizing process time to obtain the desired average carbon concentration will become longer, leading to a decrease in carburizing efficiency, and the load in the subsequent process after carburizing process will increase. It's for a reason. On the other hand, if the sheet thickness is less than 0.3 mm, the amount of reduction in cold rolling is small, and the internal structure cannot be made sufficiently fine, making it difficult to finely precipitate carbides. Carburizing treatment and primary diffusion treatment temperature is 850℃ or higher
The temperature shall be 1050℃ or less. In carburizing, if the temperature is lower than 850°C, the carburizing efficiency will be poor, and if it exceeds 1050°C, the crystallinity will become coarser and the plate will become more deformed, resulting in damage to the plate. For primary diffusion processing,
If the temperature is lower than 850°C, the diffusion rate of carbon atoms is slow and it takes a long time, and if it exceeds 1050°C, the carbides will aggregate and become coarse, and the fine carbides will disappear as a solid solution, which is not preferable. The purpose of limiting the primary diffusion treatment time is to improve rollability by reducing the carbon concentration in the surface layer while preventing carbide precipitation in regions where crystal grains have become coarse. The upper limit of the secondary diffusion treatment temperature was set at 950℃ because
This is to prevent the carbide from coagulating and coarsening or re-dissolving since the treatment time is long. 800 again
Temperatures lower than °C are not preferable because it takes too long for carbon atoms to diffuse. Total rolling ratio R in cold rolling after primary diffusion treatment
(%) was limited to obtain the effect of making the carbides in the coarse grain region fine and breaking and dispersing the carbides precipitated in the carburized layer, and R is at least 50
% was required. If the annealing treatment is carried out at a temperature of 650 to 800°C for 30 minutes or more, sufficient softening can be achieved after cooling. FIG. 1 is a process diagram of the method of the present invention, and the method of the present invention will be specifically explained with reference to this drawing. First, a steel strip or steel plate with a thickness of 0.3 to 2.0 mm is used as a material, and the average carbon concentration is 0.4 to 1.4% at a temperature range of 850 to 1050°C, preferably 0.6 as a razor blade material.
Carburizing is carried out so that the content is within the range of ~1.0%. The carburizing method may be any method as long as it is carried out using a carburizing gas. For example, gas carburizing using shift furnace gas, drip carburizing using gas generated by dripping organic solvent, gas carburizing using hydrocarbon gas diluted with _N2 gas, vacuum carburizing under reduced pressure, and Selected from ion carburizing, etc. The selection can be determined by a carburizing expert as appropriate, taking into account the equipment available to him/her, so there is no need to detail the selection conditions here. The carburizing time is a value specific to the carburizing method and can be determined based on the target carbon content, temperature, material composition, and plate thickness. After carburizing treatment is completed, primary diffusion treatment is performed at 850 to 1050℃.
The process is carried out in an inert gas, non-oxidizing gas or vacuum to prevent decarburization. The purpose of the primary diffusion treatment is to reduce the carbon concentration of the carburized layer produced in the surface layer due to carburization, and to improve the rollability in the subsequent cold rolling step. However, the crystal grains in the central part of the plate thickness have become coarse due to the heat received during carburizing, and when carbon diffuses into this region, coarse carbides precipitate. Therefore, the upper limit of the primary diffusion treatment time must be set to a time during which carbon does not diffuse to the center of the plate thickness, and this time is defined as t ₁ (minutes) and is given by the following equation. t ₁ = 4.4×10 ^-12 x ² ₁ exp (37200/T ₁ ) −t _c exp {37200 (T _c −T ₁ )/T _c T ₁ } ………(1) However, x ₁ : Carburizing and Plate thickness during primary diffusion treatment (mm), t _c : carburizing treatment time (minutes), T _c : carburizing temperature (〓), T ₁ : primary diffusion treatment temperature (〓) This equation is similar to the diffusion theory equation. It was derived from experimental data. After the primary diffusion treatment, the temperature range of 650 to 800℃ is
Anneal for at least 1 minute. Since the carburized material is sufficiently softened by these heat treatments, cold rolling can be performed. Here we will discuss the background of equation (1). FIG. 2 is a diagram illustrating the thickness of the carburized layer when the method of the present invention is carried out in relation to the square root of the carburizing time. From this, carburized layer thickness D (mm), carburizing temperature T _c
The relationship between (〓) and carburizing time t _c (min) is as follows. D ² = 5.7×10 ¹⁰・t _c・exp (−37200/T _c ) ………(2) Equation (2) depends on the diffusion rate of carbon, so it is generally applicable not only to carburizing treatment but also to diffusion treatment. It can be applied as Eq. Here, if the plate thickness is x ₁ (mm), the depth to which carbon can be diffused by the primary diffusion treatment is x ₁ /2-D. Therefore, to find the primary diffusion processing time, the above equation (1) t ₁ = 4.4×10 ^-12 x ₁ ² exp (37200/T ₁ ) −t _c exp{37200 (T _c −T ₁ )/T _c T ₁ }. As a result of these heat treatments, the carbon concentration in the surface layer of the carburized material is lower than that during carburization, and no coarse carbides are precipitated in the coarse grain region at the center of the plate thickness. It has been softened to a point where cold rolling can be carried out immediately after cooling. Cold rolling is performed once or twice so that the total rolling ratio R (%) or more is achieved as expressed by the following formula. When 0.5≦t≦2.0 R=0.9t−0.2/t×100(%) ………(3) When 0.3≦t<0.5 R=50% However, t: plate thickness at cold rolling (mm ) This is an experimentally derived formula. The material subjected to the carburizing treatment and the primary diffusion has a three-layer structure in which the regions where crystal grains have become coarse due to exposure to the carburizing temperature are narrowed between the carburized layers. By subjecting this to cold rolling, crystal grains are deformed and fractured in coarse grain regions, and carbides are fractured and dispersed within the carburized layer. When secondary diffusion annealing is subsequently performed, as the plate thickness is reduced, the diffusion distance of carbon atoms is shortened, allowing them to diffuse to the center of the plate thickness in a short time, and the crystal grains are refined. Therefore, carbides are finely and uniformly dispersed and precipitated. As mentioned above, in secondary diffusion annealing, it is necessary to make the carbon concentration distribution uniform and to precipitate carbides finely and uniformly, and it is also necessary to prevent the solid solution disappearance of fine carbides and the agglomeration and coarsening of carbides. Therefore, the temperature is set to 800 to 950°C, and the treatment is performed for a time t ₂ (hours) shown by the following formula. t ₂ = 3.33x ₂ (−0.02T ₂ +27.5) (time)
………(4) However, x ₂ : Plate thickness during secondary diffusion treatment (mm), T ₂ : Secondary diffusion treatment temperature (〓) In order to prevent decarburization, the atmosphere in the furnace is non-oxidizing gas, Use inert gas or vacuum. After the secondary diffusion treatment, annealing treatment is performed at 650 to 800°C for 30 minutes or more. By the above treatment, it is possible to produce a stainless steel strip for razor blades in which there are no coarse carbides and in which fine carbides with a maximum grain size of 1.5 μm or less are uniformly precipitated. A detailed explanation will be given below based on examples.

[Table] Examples Table 1 shows the chemical composition of the steel material used to carry out the present invention. Of the steel materials A, B, C, and D, A and B are martensitic stainless steel.
SUS410, C is ferrite stainless steel
SUS430, D is medium carbon martensitic stainless steel. E is a high carbon martensitic stainless steel used as a comparative steel. These A, B, C, D, and E steels are manufactured by the normal steelmaking hot-rolling and cold-rolling process, and are 0.5 and 0.5, respectively.
Cold rolled to plate thickness of 1.0, 1.0, 1.4, 0.25~0.30mm,
The one that had been annealed and pickled was used. Example 1 A 0.5 mm thick material of A steel was treated with N ₂ : 45%, H ₂ : 25%,
950 in a mixed gas atmosphere of CO: 20%, _CH4 : 10%
After carburizing at ℃ for 17 minutes, primary diffusion treatment at 950℃ for 20 minutes in _N2 gas atmosphere, and annealing at 700℃ for 30 minutes, the plate thickness was reduced to 0.25mm by cold rolling. After _that , the average carbon concentration was 0.693%, and the maximum particle size relative to the total carbide amount was The proportion of carbides with a diameter of 1.5μ or less was 100%. Comparative Example FIG. 3 shows the hardness of comparative steel E plates rolled to the same thickness as the material produced in Example 1, which were quenched and tempered at various temperatures for 1 hour. The material of Example 1, shown by curve 1, exhibits better resistance to temper softening than the comparative material e, shown by curve e, exhibiting a H _v 680 in the 350° C. tempering carried out in the case of razor blades. Example 2 A 1.0 mm thick material of B steel was carburized at 980°C for 25 minutes in a mixed gas atmosphere of N ₂ : 50% and CH ₄ : 50%, and carburized for 60 minutes at 950°C in an N ₂ gas atmosphere. After performing a secondary diffusion treatment and a softening treatment at 700℃ for 30 minutes, the plate thickness was reduced to 0.3 mm by cold rolling, and then a secondary diffusion treatment at 850℃ for 5 hours in a _N2 gas atmosphere and a softening treatment at 700℃ for 5 hours.
A softening treatment was performed for 120 minutes. At this time, the average carbon analysis value was 0.702%, and the proportion of carbides with a maximum particle size of 1.5 μm or less in the total amount of carbides was 100%. Figures 4a and b show the carbide distribution state in the plane parallel to the thickness direction of this example material and comparative steel E rolled to the same thickness.
Shown below. A is a micrograph of this example material magnified 1000 times, and carbides with a maximum particle size of 1.5μ or less are uniformly dispersed. (b) is a similar micrograph of comparative material e, but coarse carbides are observed. Example 3 Only the time for the primary diffusion process in Example 2
It was set as 120 minutes. The average carbon concentration is the same as 0.700%, but the proportion of carbides with a maximum particle size of 1.5μ or less in the total amount of carbides is 65%, and the particle size of the remaining carbides is 1.5%.
It was within the range of ~2.0μ. Many carbides with a diameter exceeding 1.5μ were present around the center of the plate thickness, but this indicates that coarse carbides were precipitated in areas with coarse grains because the primary diffusion treatment time was long. Example 4 The same treatment as in Example 2 was performed except that the cold rolling rate was changed from 70% to 0%. At this time, the proportion of carbides with a maximum particle size of 1.5μ or less in the total amount of carbides was 45%. This indicates that the crystal grains and carbides in the carburized layer were not sufficiently refined due to the low cold rolling rate. Example 5 In Example 2, the temperature of the secondary diffusion treatment was set to 1050℃.
It was carried out for 5 hours at ℃. At this time, the proportion of carbides with a maximum particle size of 1.5 μm or less in the total amount of carbides was 12%. This indicates that because the temperature of the secondary diffusion treatment was high, the fine carbides disappeared as a solid solution and became agglomerated and coarsened. Examples 2 to 5 are summarized in Table 2.

[Table] Example 6 A 1.4 mm thick material of C steel was carburized at 950 °C for 100 minutes in CH ₄ gas at a pressure of 300 mmHg, and primary diffusion treatment was performed at 930 °C for 40 minutes in N ₂ gas atmosphere. ℃
The plate was softened for 40 minutes, cold rolled to a thickness of 0.7 mm, intermediately annealed at 760°C for 5 minutes, cold rolled to a thickness of 0.34 mm, and then rolled to a thickness of 0.34 mm in a _N2 gas atmosphere. Secondary diffusion treatment for 5.0 hours at 680°C
Figure 5 shows the carbide distribution in a cross section perpendicular to the rolling direction when the specimen was annealed for 60 minutes. (a) is
1000x, (b) a 400x micrograph. Despite the average carbon analysis value being 0.918%, there are no coarse carbides at all, and carbides with a particle size of 2μ or less are uniformly distributed. Example 7 A 1.0 mm thick material of D steel was carburized at 1000°C for 15 minutes in a CH ₄ gas atmosphere at a pressure of 300 mmHg.
First diffusion treatment at 900°C for 60 minutes in _N2 gas atmosphere and softening treatment at 720°C for 30 minutes, and after cold rolling to a plate thickness of 0.3mm, at 920°C in _N2 gas atmosphere. After 3.6 hours of secondary diffusion treatment and 60 minutes of softening treatment at 720℃, the average carbon analysis value was
It was 0.627%. Furthermore, the proportion of carbides with a maximum particle size of 1.5μ or less in the total amount of carbides was 100%. Example 8 Figure 6 shows a case manufactured by the method of the present invention using a 1.0 thick material of A steel and an average carbon concentration of 0.65%, and a case manufactured by the method disclosed in JP-A-126921-1983. The maximum carbide grain size (μ) converted to yen in b is shown for each cold rolling ratio. In the method of the present invention, the maximum grain size is 1.5 μ or less at a cold rolling rate of 50% or more. On the other hand, in the conventional method, even if the cold rolling rate is 50% or more, the maximum grain size cannot be made finer than 1.7μ.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the method of the present invention. FIG. 2 is a diagram in which the carburized layer thickness at each carburizing temperature is plotted against the square root of time. Figure 3 shows Example 1
It is a figure which shows the quenching-tempering hardness curve of the material manufactured in and comparative material e. FIG. 4 is a micrograph showing the carbide distribution in the annealed state of the material produced in Example 2 (a) and Comparative material (b). FIG. 5 is a micrograph showing the carbide distribution in the annealed state of Example 6. Figure 6 shows the method of the present invention and JP-A-57-
126921 is a diagram showing changes in the maximum grain size of carbide in razor blade materials manufactured by the method of No. 126921. FIG.

Claims (1)

[Claims] 1 Fe containing C: 0.3% or less, Cr: 11.0 to 18.0%
- After carburizing 0.3 to 2.0 mm thick cold-rolled steel strip or cold-rolled steel plate material of Cr-based stainless steel, performing primary diffusion treatment and annealing treatment, cold rolling is performed to disperse carbides. , refine the internal structure,
A method for producing a high carbon stainless steel strip, which comprises uniformly distributing fine carbides by subsequently performing a secondary diffusion treatment and an annealing treatment. 2. The method according to claim 1, wherein the average carbon concentration of the entire cross section after carburizing treatment is 0.4 to 1.4.
%. 3. The method according to claim 1, characterized in that the cold rolling after the primary diffusion treatment is carried out so that the total rolling ratio R (%) becomes the value shown in the following formula: how to. When 0.5≦t≦2.0, R=0.9t−0.2/t ×100 (%) When 0.3≦t<0.5, R=50 (%) where t: plate thickness during cold rolling (mm) 4. The method according to the range 1, 2 or 3, wherein the carburizing treatment is carried out at 850 to 1050°C.
The temperature of the primary diffusion treatment is 850 to 1050.
℃, the treatment time is 0 to t ₁ minute, and the 2-hour diffusion treatment is performed at the treatment temperature 800 to 1000℃, and the treatment time t is ₂ hours. However, t ₁ and t ₂ are based on the following formula. t ₁ = 4.4×10 ^-12 x ₁ ² exp (37200/T ₁ ) −t _c exp {37200 (T _c −T ₁ )/T _c T ₁ } (min) t ₂ = 3.33x ₂ (−0.02T ₂ +27.5) (hours) However, x ₁ : Plate thickness at primary diffusion treatment (mm) x ₂ : Plate thickness at secondary diffusion treatment (mm) T _c : Carburizing temperature (〓) T ₁ : Primary diffusion treatment temperature (〓) T ₂ : Secondary diffusion treatment temperature (〓) t _c : Carburizing treatment time (minutes)