JPS5813620B2 - Stainless steel - Google Patents

Description

Detailed Description of the Invention The present invention provides (1) adding calcium as a machinability-improving alloying component to austenitic, ferritic, and martensitic stainless steels whose main alloy components are chromium, chromium and nickel, or manganese, chromium, and nickel; 0.006~0,
0.06% and further sulfur 0.05-0.35%, lead 0.0
3-0.30%, selenium 0.03-0.25%, tellurium 0.01-0.20%, bismuth 0.03-0.30%
In a stainless steel in which the remainder is substantially iron, composite inclusions of C-based or C+B-based inclusions and A2-based inclusions are uniformly dispersed in the steel. A free-cutting stainless steel containing composite nonmetallic inclusions.

and (2) chromium, chromium and nickel, manganese, chromium and nickel as main alloy components, and molybdenum,
Calcium 0.0 is added to austenitic, martensitic, austenitic/ferritic, and precipitation hardening stainless steels containing one or more of aluminum, steel, titanium, niobium + tantalum, and nitrogen as a machinability-improving component.
0.06-0.06% and further sulfur 0.05-0.35%
, lead 0.03~0.30%, selenium 0.03~0.25
%, tellurium 0.01~0.20%, bismuth 0.03~
In stainless steel containing one or more of 0.0 and 30% and the remainder substantially consisting of iron, composite inclusions of C-based or C+B-based inclusions and A2-based inclusions are evenly distributed in the steel. The present invention relates to a free-cutting stainless steel containing composite inclusions, which are characterized by being dispersed in.

In one example of a method for manufacturing non-inventive steel, during the casting process of the target stainless steel, the amount of oxygen in the molten steel is adjusted in advance, and then some calcium silicide is poured into the steel. C-based or B+C-based inclusions obtained by adding the remaining calcium silicide to the casting molten metal and further containing specified amounts of other free-machining components and A2
It is obtained by uniformly dispersing system inclusions.

When cutting stainless steel, the heat generated by cutting is large because the steel has high ductility and low thermal conductivity, and the frictional heat between the tool and the chip is difficult to escape, resulting in cracking, galling, seizure, etc. is likely to occur.

For this reason, free-cutting stainless steel containing small amounts of machinability-improving alloying elements such as sulfur, lead, selenium, and steel has become popular.

However, the inclusion of these machinability-improving alloying elements considerably impairs corrosion resistance and strength.

Therefore, calcium-containing free-cutting stainless steel was proposed, and the above-mentioned drawbacks were largely eliminated.

However, since a fairly large amount of calcium is added, the form of the oxide inclusions in the steel changes depending on the type of calcium alloy added, the amount added, and the melting method, but most of the oxide inclusions are C-based inclusions (JISGO555-1956, Ca- Particulate oxides mainly composed of aluminate (AI-Ca-0) (may contain some sulfides) are irregularly dispersed;
Alternatively, the B-based inclusions (discontinuously arranged granular oxides mainly composed of alumina) remain.

These inclusions have a higher softening and melting temperature than A2-based inclusions (elongated inclusions mainly composed of manganese-silicate), and are difficult to use when cutting at high cutting speeds and high cutting temperatures, such as when cutting with cemented carbide tools. Although an increase in wear is suppressed, when the cutting speed is low, such as when cutting a high-speed steel tool, it is difficult to suppress an increase in tool wear.

In addition, C-based inclusions are difficult to plastically deform even when steel is hot-worked, so they do not blend well with the base iron, and microcracks and cavities are likely to occur.

Due to the presence of such cavities, the corrosion resistance in strongly corrosive atmospheres may be inferior to that of the basic component steel.

The present invention allows C-type or C+Er-type inclusions and A2-type inclusions to coexist in a composite manner in stainless steel, and the A2-type inclusions prevent the occurrence of micro-crack cavities during hot working of steel due to the presence of C-type inclusions. This is a free-cutting stainless steel that was developed with the aim of completely eliminating corrosion resistance and preventing deterioration of corrosion resistance, and further improving machinability in a wide range of cutting areas with A2 and C inclusions.

For this reason, as a basic experiment, as shown in Table 1, SUS30
In conventional 4-series Ca stainless steel, aluminum was deoxidized in a furnace, and while the molten steel was being poured into a ladle, the entire amount of CaSi was added and solidified by a conventional method.

On the other hand, non-inventive steel does not add aluminum in the furnace and is made by adding a small amount of low AI-C a Si to the bottom of the ladle beforehand.
After placing 2 to 5 kg/t of molten steel, the amount of oxygen in the molten steel was reduced to 100 kg/t.
The molten steel adjusted to ~600 ppm is transferred to the ladle and stirred and mixed (inert gas is blown in if necessary). After the molten steel has calmed down, it is poured into a mold, and the above CaSi is added to the molten steel flow by 5 to 30 ppm.
Kg/t was added, and the mixture was slowly cooled and solidified in a mold while sufficiently stirring and mixing.

As a result, in the above-mentioned hot-produced steel materials, non-metallic inclusions (oxides) in the conventional steel are mostly composed of C-based compounds, whereas those in the steel of the present invention produced by the method described above are mostly composed of composite C.
C+A2 system where the outer periphery of the system is surrounded by A2 system (see Figure 1)
occupied by

Considering this point, in conventional steel, by deoxidizing aluminum by adding it in the furnace,
Oxygen in molten steel is AI.

It is estimated that almost all of the remaining oxygen is fixed as CaO1S102 by Cadi added in the ladle, so that Ca-aluminate is generated and becomes C-based inclusions in shape.

However, in the steel of the present invention, aluminum is not added in the furnace and the ladle is deoxidized first with a small amount of calcium silicide.
Since the total amount of Al intervening from the small amount of CaSi at this point is very small, Ca-Mn-silicate is generated in the steel to form A2-based inclusions.

However, in this case, if the entire amount of CaSi is added at once without adding a small amount of CaSi, the entire amount of Al that intervenes from CaSi will be added to the steel with a nearly 100% yield, and therefore Ca-Mn silicate It has been confirmed in conventional tests that Ca-aluminate is hardly produced, and mainly Ca-aluminate is produced in large quantities.

Next, since a large amount of inclusions made of Ca-Mn-silicate have already been formed in the steel, even if most of the calcium silicide and aluminum are added to the molten steel flow, Ca
- Aluminate is not produced in large quantities.

Therefore, in the steel of the present invention, Ca-Mn-silicate and Ca-aluminate coexist, and when the molten steel slowly cools and solidifies in the mold, Ca-aluminate with a high melting point precipitates first, and later. It is presumed that a large amount of low-melting-point Ca-Mn-silicate precipitates, promotes adsorption and compounding using Ca aluminate as a core, and covers C-based inclusions with A2-based inclusions.

As mentioned above, the alloy composition of the steel of the present invention contains 0.006 to 0.06% calcium as an element that improves machinability, but if calcium is 0.006% or less, it has no effect on extending the life of cemented carbide tools. is weak.

On the other hand, if it exceeds 0.06%, it is not preferable because it actually accelerates tool wear.

The machinability-improving components that coexist with the calcium are 0.05% to 0.35% sulfur, 0.03% to 0.30% lead, 0.03% to 0.25% selenium, and 0.01% to 0.20% tellurium.
%, bismuth from 0.03% to 0.30%, which exist in stainless steel as metal compounds or sulfides that are effective in extending the life of high-speed steel tools. It is suitable for

Therefore, in the alloy composition of the steel of the present invention, a composite of calcium, sulfur, lead, selenium, tellurium, and bismuth is included as components for improving machinability.

As mentioned above, the basic embodiment of the present invention is directed to austenitic, ferritic, and martensitic stainless steels whose main alloy components are chromium, chromium and nickel, chromium and nickel, and manganese.

Examples of steel types standardized by JIS are SUS201, 202, 301, 302, and austenitic steels.
303, 303Se1 304, 304L1305, 3
0 5Jl, 308, 3098, 3108, 316,
316L, 316J1, 316JIL, 317, 317
L, 321, 3 2 9J1, 347, 384, 385
, XM7 and XM15J1, and ferrite type SUS405, 429, 430, 430F and 43
4, and martensitic type SUS 40 3,
410, 410S, 410J1, 416, 420J1,
420J2, 420F, 431, 440A1440B,
440C and 440F.

A modified embodiment of the present invention uses chromium, chromium and nickel, or manganese, chromium and nickel as main alloy components, and further includes molybdenum of 4.0% or less and aluminum 1.0%.
Austenitic, containing one or more of the following: 5% or less, 5.0% or less, titanium 1.2% or less, niobium + tantalum 1.2% or less, and nitrogen 0.25% or less; Targets ferritic, martensitic, austenitic/ferritic, or precipitation hardening stainless steels.

Molybdenum is added for the purpose of improving corrosion resistance, aluminum is added for oxidation resistance, copper has the effect of improving corrosion resistance, and titanium and niobium + tantalum prevent intergranular corrosion. Added with the aim of improving
Nitrogen also has the effect of increasing high-temperature strength.

The JIS standard steel types of stainless steel to which these elements are added are austenitic, ferrite, and martensitic, as mentioned above.

SUS3 is the type of austenitic/ferrite steel.
29J1 is a typical example, and precipitation hardened stainless steel paddles include SUS630, 631, and 631J.

The various stainless steels mentioned above contain 11 to 28% chromium, 30% or less nickel, and 10% or less manganese.

Hereinafter, the present invention will be specifically explained in detail using examples.

Example 1 Stainless steels with the various chemical components shown in Table 2 were produced in an experimental melting furnace, and then hot forged into round bar shapes (
The specimen was formed into a test piece (diameter: 60 mm), and then subjected to homogenization annealing by heating and holding at 1100°C.

A hot torsion test piece was taken from the test piece, and the normal heating temperature (1000-1200°C) and strain rate (
As a result of investigating the hot workability at temperatures of 1 to 100 SeC-1), all of the steels of the present invention were almost equivalent to comparative steels A2 and A3.

Next, cutting tests were conducted using cemented carbide tools and high-speed steel tools for the steel materials shown in Table 2, and the cutting speed corresponding to a predetermined tool life when cutting each steel material was used as an index of machinability.

It is shown in Table 3.

■) Cutting test conditions using cemented carbide tools Tool: P20 (0,7,7,7,1 0,0,
0.5R) Feed: 0.18mm/rev. Depth of cut: 0.6 mm Cutting oil: None (dry cutting) Cutting speed: The cutting speed at which the tool life reaches 70 minutes is taken as a characteristic value, and is expressed as a ratio when the straight hole of A1 steel is set as 100.

■) Cutting test conditions using high-speed steel tools Tool: SKH5 7 (0, 1 5, 7.7.
1 0,0,0.5 R) Feed: 0. 18m
m/rev. Depth of cut 2: 0.6 mm Cutting oil: None (dry cutting) Cutting speed: The cutting speed at which the tool life reaches 40 minutes is taken as a characteristic value, and is expressed as a ratio when that of A1 steel is set as 100.

As shown in the same table, the machinability of the steel of the present invention, in which composite inclusions in which C-based inclusions are adhered and covered by A2-based inclusions, is evenly dispersed is approximately 50 to 50% higher than that of comparative steels A1 and A2. 110
% (when cutting carbide tools) and about 10 to 30% (when cutting high-speed steel tools).

This is thought to be due to the fact that in cutting cemented carbide tools, C+A2-based inclusions mainly composed of calcium in the workpiece material soften or melt during cutting to form belag, which adheres to the cutting edge surface of the tool and suppresses tool wear.

In addition, it is thought that in workpiece materials in which calcium and sulfur, selenium, tellurium, lead, bismuth, etc. coexist, machinability is further improved by notching and lubrication in the area where all tool chips come into contact.

Next, as a corrosion resistance test, the corrosion loss (
g/m''/h) was determined and is also listed in Table 3 as a ratio, with that of A1 steel set as 100.

As shown in the same table, it was found that the steel of the present invention had almost the same corrosion resistance as the comparative steel AO.

Furthermore, even A11 steel, which has poor corrosion resistance among the steels of the present invention, is significantly superior to A1 steel.

Therefore, it was confirmed that the steel of the present invention contains the above-mentioned machinability-improving elements within a specific range, and even in the presence of C+A2 inclusions, the corrosion resistance was not adversely affected.

Example 2 A ferritic stainless steel having the chemical composition shown in Table 4 was produced in an experimental melting furnace, then hot forged into a round bar-shaped test piece (diameter 60 mm), and homogenized by heating and holding at 820°C. Annealed.

Hot torsion test pieces were taken from the test pieces and hot workability was investigated in the same manner as in Example 1. As a result, all of the steels of the present invention were almost equivalent to comparative steel F1.

Next, the steel materials shown in Table 4 were subjected to the same cutting test as in Example 1, and the machinability is shown in Table 5.

As seen in the same table, the machinability of the steel of the present invention is that of the comparative steel F1.
Approximately 50 to 110% compared to that of (when cutting carbide tools),
An improvement of about 20-40% (when cutting high-speed steel tools) was obtained.

The reason why such effects were obtained is considered to be the same as in Example 1.

Next, regarding the corrosion resistance, the corrosion weight loss was determined in the same manner as in Example 1, and is also listed in Table 5 as a ratio, setting that of F1 steel as 100.

As shown in the same table, it was found that the steel of the present invention had almost the same corrosion resistance as the comparative steel FO.

From this point of view, even if calcium and one or more of sulfur, lead, selenium, tellurium, and bismuth are contained in combination within the range described below, and C+A2 inclusions are dispersed, the corrosion resistance of the basic component steel will not be improved. It turned out that there was no damage.

Example 3 A martensitic stainless steel having the chemical composition shown in Table 6 was produced in an experimental melting furnace, then hot forged into a round bar (60 mm in diameter) test piece, and further heated at 850°C.
Homogenization annealing was performed by heating and holding.

A hot torsion test piece was taken from the test piece and the hot workability was investigated in the same manner as in Example 1. As a result, the present invention steel was compared to comparative steel M.
It was found that it had almost the same hot workability as M7.

Next, the steel materials shown in Table 5 were subjected to the same cutting test as in Example 1, and the machinability is shown in Table 7.

As shown in the same table, the machinability of the 416 series inventive steel M5 is improved by about 30% (when cutting carbide tools) and about 20% (when cutting high-speed steel tools) compared to the comparative steel M1. The machinability of the 410 series uninvented steels M3 and M4 is approximately 80,100% (when cutting carbide tools) and approximately 120,1% compared to that of the comparative steel MO.
50 (when cutting high-speed steel tools).

In addition, the machinability of the 440F series inventive steel M12 is improved by about 30% (when cutting carbide tools) and about 15% (when cutting high speed steel tools) compared to that of the comparison steel M7, and the 440C series inventive steel M9,
It was found that the machinability of MIO and Mll was improved by about 130% (when cutting carbide tools) and about 140 to 165% (when cutting high-speed steel tools) compared to that of comparative steel M6.

Next, regarding corrosion resistance, the corrosion weight loss was determined in the same manner as in Example 1, and the ratio is also shown in Table 7, with the values of M1 steel and MI steel set as 100.

As shown in the same table, the corrosion resistance of the 416 series inventive steel M5 is slightly superior to that of the comparative steel M1.

In addition, the corrosion resistance of the 410 series inventive steel M3 and M4 is that of the comparative steel MO.
It turns out that there is not much difference from that of .

Moreover, almost the same tendency was observed for the 440F and 440C steels of the present invention and comparative steels.

As mentioned above, conventional ferrite, austenitic, martensitic, austenitic and Adding an appropriate amount of calcium to hardened stainless steel, as well as an appropriate amount of machinability-improving alloy components such as sulfur, lead, selenium, tellurium, and bismuth, creates C-based or C+B-based inclusions and A2-based inclusions in the steel. The machinability of non-inventive steel, which has composite inclusions evenly distributed with objects, is significantly improved compared to conventional stainless steel as well as calcium-containing free-cutting stainless steel made of C-based inclusions. It was confirmed that not only the hot workability and corrosion resistance but also the material strength were comparable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged photograph (600 times) of C+A2 inclusions present in the steel A6 of the present invention.

Claims (1)

[Claims] 1. An austenitic, ferritic, or martensitic stainless steel whose main alloy components are chromium, chromium and nickel, or manganese, chromium, and nickel, with zero calcium added as a machinability-improving alloy component. .006～
0.06%, sulfur 0.05-0.35%, lead 0.0
3-0.30%, selenium 0.03-0.25%, tellurium 0.01-0.20% and bismuth 0.03-0.3
In stainless steel containing 0% of one or more of the above, the remainder being substantially iron, a composite of C-based or (C+B)-based inclusions and A2-based inclusions in the steel. A free-cutting stainless steel containing composite nonmetallic inclusions, characterized in that the inclusions are evenly distributed. 2. The main alloy components are chromium, chromium and nickel, or manganese, chromium and nickel, and molybdenum4.
0% or less, aluminum 1.5% or less, copper 5.0% or less, titanium 1.2% or less, niobium + tantalum 1.2% or less, and nitrogen 1.2% or less. Contains austenitic: ferrite, martensitic, austenite-ferrite, or precipitation hardening stainless steel, with 0.006 to 0.06% calcium and 0.05 to 0.05% sulfur as machinability-improving alloy components.
0.35%, lead 0.03-0.30%, selenium 0.03
-0.25%, tellurium 0.01-0.20% and bismuth 0.03-0.30%, and one or more of them are added, and the remainder is essentially iron. , C-based or (C+B)-based inclusions in steel and A
A free-cutting stainless steel containing composite nonmetallic inclusions, characterized in that composite inclusions with two-type inclusions are evenly dispersed.