JP2781325B2 - Method for producing medium and high carbon martensitic stainless steel strip having fine carbides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high carbon martensitic stainless steel strip, which is used as a material for sharp blades, particularly razors and medical blades.

[0002]

2. Description of the Related Art Among the above applications, high carbon martensitic stainless steels are mainly composed of 13 wt% Cr-0.3
0.7 wt% C steel is used. Among these, the characteristics of the cutting tool manufactured from high carbon martensitic stainless steel are as follows:
It depends on the size of the carbides in the steel. That is,
It is necessary to have a uniform and fine spherical carbide structure. However, medium and high carbon martensitic stainless steels
When solidification is completed, a huge carbide is crystallized and remains as a large carbide having a particle size of 10 μm in the product blade, which causes a loss of sharpness as the blade.

In order to avoid the above disadvantage, Japanese Patent Application Laid-Open No. 58-18 / 1983
No. 9322 proposes to obtain a uniform and fine spherical carbide structure by producing a steel ingot by electroslag melting and then performing hot rolling and annealing while controlling the heating temperature in hot rolling. ing. However, it is difficult to easily manufacture an inexpensive material by this method.

In Japanese Patent Publication No. 3-13292, Cr:
A high carbon martensitic stainless steel containing 10 to 20 wt% and C: 0.5 to 1.2 wt% is heated to a temperature in the range of 1100 ° C. to the solidus temperature and then cooled, and the parent phase at room temperature is made to have a metastable austenitic structure. Thus, there is disclosed a method for producing a high carbon martensitic stainless steel which is excellent in cold rollability and furthermore has a uniform and fine spherical carbide structure by quenching after cold rolling.

[0005]

However, the treatment disclosed in Japanese Patent Publication No. 3-13292 is insufficient as a material for cutting tools because it is difficult to avoid precipitation of giant carbide having a particle size of less than 20 μm. there were.

Accordingly, an object of the present invention is to solve the above problems and propose a method for producing a high carbon martensitic stainless steel strip having uniform and extremely fine spherical carbides.

[0007]

Means for Solving the Problems The present inventors have found that (Fe, Cr) which is a huge carbide produced at the time of solidification completion in the production process from smelting, continuous casting, hot rolling and cold rolling.
_After various studies on the method of miniaturizing ₂₃ C ₆ ,
(Fe, Cr) ₂₃ C ₆ is strong, but by the following method,
It has been found that carbides in steel can be made fine and uniform without causing martensitic transformation cracks in slabs produced by continuous casting.

Namely, by holding slab stage (Fe, Cr) ₂₃ of C ₆ to γ region, (Fe, Cr) with partially forms a solid solution of _{23 C 6, (Fe, Cr} ) 23 C 6 (Fe, Cr) ₂₃ C ₆ itself is spheroidized due to its high interfacial energy, and large carbides are reduced. Further, by subjecting the slab to hot working to impart working strain, (Fe, Cr) ₂₃ C _The present inventors have found that solid solution of No. ₆ and fine spheroidization upon cooling are promoted, and the present invention has been completed.

According to the present invention, the cast slab is cast (solidification temperature −20).
° C.) ~ (after 10-30 hours of heating maintained at a temperature range of solidification temperature -50 ° C.), then cooled to a temperature range from just above M _f point to the M _s point +100 ° C., reheated to 0.5 until then pearlite region After holding for 20 hours, apply surface care, then 1100-1250 ° C
And then hot-rolled for 0.5 to 5 hours,
A method for producing a fine carbide steel strip of high carbon martensitic stainless steel, characterized by successively performing annealing and cold rolling.

[0010] Further, the present invention, prior to the above steps,
A method for producing a fine carbide steel strip of high carbon martensitic stainless steel, characterized in that a slab after casting is subjected to hot working of 5 to 40%.

[0011]

[Function] Giant carbide (Fe, Cr) ₂₃ C ₆ generated during solidification is
First, the slab is (solidification temperature -20 ℃) ~ (solidification temperature -50 ℃)
By heating and holding at a temperature of 10 to 30 hours, a part of the carbide is dissolved, and then from above the M _f point to the M _s point + 100 ° C.
By cooling to the temperature range up to, the carbides are spheroidized to promote the refinement and prevent martensitic transformation cracks, and then subjected to hot rolling, annealing and cold rolling to obtain uniform and extremely fine particles. Spheroidized carbide structure.

Next, the reasons for limiting the above manufacturing conditions will be described. The upper limit of the slab heating temperature (solidification temperature -20 ℃)
The reason for this is that when heated to a temperature higher than (solidification temperature −20 ° C.), the microsegregated portion of the steel melts and becomes brittle. On the other hand, the lower limit was obtained by experiments on a temperature range for efficiently promoting solid solution of carbide (Fe, Cr) ₂₃ C ₆ .
(Coagulation temperature −50 ° C.) Since it was found necessary to be more than (coagulation temperature −50 ° C.), it was set to (coagulation temperature −50 ° C.) In addition, the solid solution of carbide requires holding for 10 hours or more in the above temperature range.On the other hand, even if the heating time exceeds 30 hours, there is no difference in the effect of refining carbide, so the heating time is 10 to 30 hours. Limited to the range.

Next, the cooling to the temperature range from just above the M _f point to the M _s point + 100 ° C. is intended to efficiently change the slab to a pearlite structure without causing martensitic transformation cracks in the slab.

Further, the holding time in the pearlite area is set to 0.
The time of 5 to 20 hours is 0 to change to perlite.
More than 5 hours is required, while if it exceeds 20 hours, the effect is saturated, so it was limited to 0.5 to 20 hours.

The slab heating temperature during the subsequent hot rolling is set to 11
The reason for setting the temperature at 00 to 1250 ° C. and the holding time at 0.5 to 5 hours is that
If the heating temperature is less than 1100 ° C or the holding time is less than 0.5 hours, rolling cannot be performed.On the other hand, if the heating temperature exceeds 1250 ° C or the holding time exceeds 5 hours, loss such as scale loss becomes large. 0.5 to 5 in the range of ~ 1250 ° C
It was decided to hold for a time.

Further, by performing hot working prior to the above-described steps, it is possible to further finely uniform the carbide. That is, in order to promote uniform miniaturization, it is necessary to give a processing strain of 5% or more. On the other hand, even if the processing exceeds 40%, the effect is saturated.
%.

[0017]

【Example】

Example 1 By continuous casting, C: 0.67 wt%, Cr: 13 wt%, Si:
Becomes 0.4 composition of wt% hints balance iron and unavoidable impurities, the solidification temperature:: 0.3 wt% and Mn 1300 ° C., pearlite area: 620 ~730 ℃, M _s point: 210 ° C. and M _f point: 80
A martensitic stainless steel slab having a temperature of ℃ was produced. The dimensions of the slab were 195 mm in thickness, 970 mm in width, and 7000 mm in length, and the weight was about 10 t.

The slab was placed in a soaking furnace without cooling, kept at 700 ° C. for 1 hour, and then heated to 1250 ° C. at a heating rate of 50 ° C./h and kept for 15 hours. Thereafter, the slab was extracted from the soaking furnace and allowed to cool to a surface temperature of 200 ° C. Next, the slab was charged again into the furnace maintained at 500 ° C., heated to 700 ° C. at a rate of 50 ° C./h, and maintained for 10 hours. Next, the slab is extracted from the furnace, allowed to cool to room temperature, and the surface of the slab is cleaned, and held in a heating furnace at 1200 ° C. for 3 hours prior to hot rolling, and then thickened by hot rolling. A hot-rolled steel strip having a length of 4 mm and a width of 960 mm was used.

For comparison, a hot-rolled steel strip according to a conventional method was manufactured. That is, the same surface treatment as described above for the slab is completed at a temperature equal to or higher than the M _s point.
It was placed in a heating furnace at 1200 ° C. and maintained for 3 hours, and then hot-rolled into a hot-rolled steel strip having a thickness of 4 mm and a width of 960 mm.

Each hot-rolled steel strip thus obtained was heated at 720 ° C.
The process of annealing for 15 hours, and performing cold rolling after pickling was repeated to obtain a cold-rolled steel strip having a thickness of 1.2 mm and a width of 960 mm. A sample was taken from the cold-rolled steel strip, and the structure of the surface layer and the center of the thickness of the sample was observed by a scanning electron microscope with a magnification of 5000 times. After tracing the observed structure, the area of each carbide was measured by image processing, and from this measurement result, the particle size distribution was calculated by processing the equivalent circle diameter of each carbide. The calculation results are shown in FIG. 1 for the surface layer portion of the sample and in FIG. 2 for the center portion of the thickness, respectively, comparing the sample obtained by the method of the present invention with the sample obtained by the conventional method.

From the figure, it can be seen that in the conventional method, the particle size distribution of the carbide is maximum at 0.4 to 0.6 μm, the maximum diameter of the carbide is 1.4 to 1.6 μm, and the particle size of the surface layer and the center of the sample is large. It can be seen that the distribution is significantly different. In contrast, according to the method of the present invention, the particle size distribution is 0.2 to 0.4.
The maximum was at μm, the maximum diameter of the carbide was 1.0 μm or less, and the particle size distribution was uniform between the surface layer and the center of the sample.

Example 2 The same martensitic stainless steel slab as in Example 1 was produced. The dimensions of the slab are as follows: thickness: 195 mm, width:
It was 970 mm and length: 6000 mm and weighed about 8.7 t. This slab is charged to a soaking furnace without cooling,
After holding in a heating furnace of 00 ° C. for 3 hours, by hot rolling,
The slab was 145 mm thick, 970 mm wide and 8000 mm long. That is, hot working of 25.6% was performed.

Thereafter, the slab was allowed to cool to 600 ° C., and then placed in a soaking furnace and maintained at 700 ° C. for 1 hour.
/ H and heated at 1250 ° C for 15 hours. After that, the slab was extracted from the soaking furnace, and the surface temperature was 200
The mixture was allowed to cool to ℃. Next, the slab was charged again into the furnace maintained at 500 ° C., heated to 700 ° C. at a rate of 50 ° C./h, and maintained for 10 hours. Next, after extracting the slab from the furnace and allowing it to cool to room temperature, perform surface care of the slab,
Prior to hot rolling, hold in a heating furnace at 1200 ° C for 3 hours,
Next, a hot-rolled steel strip having a thickness of 4 mm and a width of 960 mm was formed by hot rolling. As a comparison, a hot-rolled steel strip according to the conventional method similar to that of Example 1 was manufactured.

The steps of annealing each steel strip thus obtained at 720 ° C. for 15 hours, pickling and cold rolling are repeated to obtain a cold-rolled steel having a thickness of 1.2 mm and a width of 960 mm. It was a band. A sample was taken from the cold-rolled steel strip, and the structure of the surface layer and the center of the thickness of the sample was observed by a scanning electron microscope with a magnification of 5000 times. After tracing this observed tissue, the area of each carbide was measured by image processing,
From this measurement result, the particle size distribution was calculated by treating each carbide with a circle-equivalent diameter. The calculation results are shown in FIG. 3 for the surface layer portion of the sample and in FIG. 4 for the center portion of the thickness, in comparison with the sample obtained by the method of the present invention and the sample obtained by the conventional method.

From the figure, it can be seen that according to the method of the present invention, 0.2-0.4
The composition ratio of carbide having a particle size of μm increases, and the particle size of the carbide decreases in the range of 0.4 to 1.0 μm, so that the refinement of the carbide is further promoted, and the particle size distribution between the surface layer and the center of the sample is increased. Uniformity has also improved.

Example 3 In order to further clarify the effects of the present invention, the following production was carried out. According to the continuous casting method according to Example 1, C:
0.67wt%, Cr: 13wt%, Si: 0.3wt% and Mn: 0.4wt
%, With the balance being iron and inevitable impurities, solidification temperature: 1300 ° C, pearlite region: 620-730 ° C, M _s
A martensitic stainless steel slab having a point: 210 ° C. and an M _f point: 80 ° C. was produced. Slab dimensions are thickness:
195 mm, width: 970 mm and length: 7000 mm, weight about 10
Four slabs were produced for the material t.

These slabs were placed in a soaking furnace without cooling, kept at 700 ° C. for 1 hour, and then heated at a heating rate of 50 ° C./h to the heating temperature of A in Table 1, respectively. 1 B
After that, the slab was extracted from the soaking furnace and allowed to cool until the surface temperature reached the temperature of C in Table 1. Then, the slab was charged again into the furnace maintained at 500 ° C., heated at a heating rate of 50 ° C./h to each of the heating temperatures of D in Table 1, and maintained at the same holding time of E. Next, the slab was extracted from the furnace and allowed to cool to room temperature, and then the surface of the slab was cleaned. Here, none of the slabs caused martensitic transformation cracking, but only slab No. b was cracked by grain boundary oxidation of the slab surface because the slab heating temperature was close to the solidification temperature,
As the scratches could not be removed by normal slab surface care,
Subsequent processing was stopped only for slab No. b. Therefore, for slab Nos. A, c and d, 1200 ° C prior to hot rolling
For 3 hours, and then hot-rolled to form a hot-rolled steel strip having a thickness of 4 mm and a width of 960 mm.

The steps of annealing each steel strip thus obtained at 720 ° C. for 15 hours, pickling and cold rolling are repeated to obtain a cold-rolled steel having a thickness of 1.2 mm and a width of 960 mm. It was a band. A sample was taken from the cold-rolled steel strip, and the structure of the surface layer and the center of the thickness of the sample was observed by a scanning electron microscope with a magnification of 5000 times. After tracing this observed tissue, the area of each carbide was measured by image processing,
From this measurement result, the particle size distribution was calculated by treating each carbide with a circle-equivalent diameter. Table 2 shows the results. The grain size distribution of carbide in the steel strip obtained from slab Nos. A and c was the same as that in Example 1, but the grain size distribution of carbide in the steel strip obtained from slab No. d was Heating temperature is 1150
Since the temperature was as low as ° C., sufficient promotion of solid solution of carbides could not be achieved, which was equivalent to the conventional method.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As described above, according to the method of the present invention, the carbide of the medium- and high-carbon martensitic stainless steel strip can be made uniform and extremely fine, and the maximum particle size of the carbide is 1.0 μm. It can be:
Therefore, for example, when used for a blade, the blade material with extremely small blade spill and excellent sharpness can be manufactured in large quantities and at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a carbide particle size distribution.

FIG. 2 is a diagram showing a carbide particle size distribution.

FIG. 3 is a diagram showing a carbide particle size distribution.

FIG. 4 is a diagram showing a carbide particle size distribution.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) C21D 9/46 C21D 8/00-8/02 C21D 7/13 C21D 6/00 102

Claims (2)

(57) [Claims] The slab after casting is heated and maintained in a temperature range of (solidification temperature -20 ° C) to (solidification temperature -50 ° C) for 10 to 30 hours, and then the M _f
Cooled to a temperature range of from just above a point to M _s point +100 ° C., subjected to subsequent reheating to surface care After for 0.5 to 20 hours to pearlite region, then heated to 1100 to 1250 ° C.
A method for producing a fine carbide steel strip of high carbon martensitic stainless steel, characterized in that hot rolling is performed after holding for 0.5 to 5 hours, followed by annealing and cold rolling. 2. The cast slab is subjected to hot working of 5 to 40%, and then is heated and maintained in a temperature range of (solidification temperature -20 ° C) to (solidification temperature -50 ° C) for 10 to 30 hours. , M _s point +10 from just above the M _f point
After cooling to a temperature range of up to 0 ° C., reheating to the pearlite area and holding for 0.5 to 20 hours, the surface was treated, then heating to 1100 to 1250 ° C. and holding for 0.5 to 5 hours, followed by hot rolling. , Followed by annealing and cold rolling. A method for producing a fine carbon steel strip of high carbon martensitic stainless steel, comprising the steps of: