JP2000063995A - Free cutting steel with rust resistance and atmosphere corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel as a material for OA equipment parts, etc., having rust resistance and atmosphere corrosion resistance satisfactorily suited for use in an indoor environment even if plating treatment is omitted and also having excellent machinability while not necessarily requiring annealing treatment before machining. SOLUTION: The steel has a composition consisting of, by weight, 0.001-0.050% C, 0.1-3.0% Si, 0.1-2.0% Mn, >0.03-0.2% P, 5.0-11.0% Cr, <=1.0% Ni, <=1.0% Cu, <=1.0% Mo, <0.01% Al, 0.1-0.5% S, 50-200 ppm O, and the balance essentially Fe with inevitable impuirities or further containing, if necessary, either or both of 0.05-0.30% Se and 0.05-0.25% Pb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to free-cutting steel having rust and weather resistance, which is used as a component material for various office automation equipment, office equipment, electronic equipment, FA equipment and the like.

[0002]

2. Description of the Related Art Conventionally, materials used for office automation equipment such as shaft materials for copying machines have no rust in an indoor environment,
In addition, there were the following two cases in order to obtain sufficient machinability when cutting into a predetermined shape. 1. Expensive stainless steel such as SUS303, 416, 430F is used. 2. Free-cutting steel such as low-priced SUM23, 24 is used after being plated and plated.

When stainless free cutting steel such as SUS303, 416, 430F is used, it has more excellent rust and weather resistance than is necessary under operating conditions such as indoor environment, so the cost of the material is high. When using free-cutting steels such as SUM23, 24, in the plating process after cutting, the cost and the number of processes increase and the delivery problem occurs, and the weather resistance due to the variation of the plating layer thickness increases. There were problems such as the treatment of the plating waste liquid that causes deterioration and environmental problems.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a rusting and weathering resistance which is sufficiently suitable for use in an indoor environment without applying a plating treatment, and does not necessarily require an annealing treatment before cutting. It is to provide a steel with good machinability without need.

[0005]

As a result of various experiments conducted in order to solve the above problems, Cr is 5 to 11% by weight.
%, The addition of P is effective for improving the rust and weather resistance because it strengthens the passivation film on the surface, and also improves the machinability by making the matrix brittle. I found out that. Further, it was found that good machinability can be obtained by controlling the amount of oxygen and adjusting the dispersion of MnS to a suitable state.

In order to achieve the above-mentioned object, the means of the present invention is, in the invention of claim 1, the component composition of C: 0.001 to
0.050%, Si: 0.1 to 3.0%, Mn: 0.1
~ 2.0% or less, P: more than 0.03 to 0.2% or less, C
r: 5.0 to 11.0%, Ni: 1.0% or less, Cu:
1.0% or less, Mo: 1.0% or less, Al: 0.01%
It is a free-cutting steel excellent in rust and weather resistance, characterized by containing less than S, 0.1 to 0.5%, O: 50 ppm or more, and the balance being substantially Fe.

According to the invention of claim 2, particularly when machinability is required, the chemical composition of the means of claim 1 is further S
e: 0.05 to 0.30%, Pb: 0.05 to 0.25
% Is a steel to which one kind or two or more kinds are added.

The reason for limiting the range of components according to the present invention will be described for each component. C: 0.001 to 0.050% When the amount of C is increased, solid solution strengthening is promoted, the austenite phase increases, and a martensite phase is easily generated during cooling, resulting in high hardness. Moreover, excessive addition also leads to deterioration of rust resistance and weather resistance. Therefore, the upper limit of the amount of C is set to 0.050%. However, if the amount of C is extremely reduced, the cost at the time of production is increased and the molten steel becomes in a peroxidized state to make the steel material brittle, so the lower limit is set to 0.
It was 001%.

Si: 0.1 to 3.0% Addition of Si has the effects of preventing the peroxidation of molten steel, increasing the ferrite phase, and decreasing the hardness. Therefore, the lower limit is set to 0.1%. Further, in order to reduce the hardness after hot rolling, the addition of Si, which is a ferrite-forming element, is effective, but excessive addition increases the hardness of the ferrite phase and, conversely, reduces machinability. . Therefore, the maximum is 3.0%.

Mn: 0.1-2.0% Mn improves the machinability by forming a compound with S, but excessive addition increases the hardness after hot rolling, so 2.0%. Below. Moreover, since Mn is an element effective in preventing the peroxidation of molten steel, the lower limit was made 0.1%.

P: more than 0.03% to 0.2% or less When the amount of P added increases, the machinability and rust / weather resistance are improved, so that it is desirable to be high, and 0.03 to obtain the effect. % Addition is required. However, if added in excess, it causes deterioration of toughness, so a maximum of 0.2
%.

S: 0.1 to 0.5% By addition of S, a compound can be formed with Mn to improve the machinability, but addition of a large amount causes a reduction in hot workability, so 0 .5% or less. Further, if the addition of S is suppressed, the machinability is reduced, so the content was made 0.1% or more.

Ni: 1.0% or less If the amount of Ni added is increased, the rust and weather resistance are improved,
Since the quench-hardenability is high, the content was made 1.0% or less.

Cr: 5.0 to 11.0% Since Cr is an important element for increasing rust and weather resistance, it is preferable that a large amount of Cr be contained, but if a large amount of Cr causes an increase in cost, it is 11.0%. Below. Further, if the Cr content is less than 5.0%, it becomes difficult to secure the rust and weather resistance necessary for use in an indoor environment, so the content was made 5.0% or more.

Mo: 1.0% or less Mo is desirable because it improves rust and weather resistance, and promotes the formation of ferrite to lower the hardness, but it is preferable that a large amount of Mo is added to the manufacturing cost. Since it will lead to an increase, it was set at 1.0% or less.

Cu: 1.0% or less Addition of Cu improves rust and weather resistance, but excessive addition causes deterioration of hot workability, so the content was made 1.0% or less.

Al: less than 0.01% By controlling the addition of Al as a deoxidizer, the oxygen concentration can be increased and the dispersion of sulfides can be made in a good state with respect to machinability. Therefore, it is set to less than 0.01%.

O: 50 to 200 ppm By controlling the addition of Si, Mn, and Al as deoxidizing agents so that the oxygen concentration in the steel is 50 ppm or more, the dispersion of sulfides is in good condition for machinability. Can be Therefore, the oxygen concentration is set to 50 ppm or more. Further, when the oxygen concentration is too high, the toughness is deteriorated, so the content is set to 200 ppm or less.

Se: 0.05 to 0.30%, Pb: 0.03
One or two or more of the above 05 to 0.25% is an effective element for improving the machinability. Therefore, when further machinability is required, it may be appropriately used according to the use of the material, but excessive addition causes deterioration of weather resistance, so the limit range is set to Se: 0.05 to
One or two or more of 0.30% and Pb: 0.05 to 0.25% were used.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A steel ingot is melted in a 100 kg vacuum melting furnace, and the steel type shown in invention steel 1 of Table 1 as a steel corresponding to the chemical composition of claim 1 corresponds to the chemical composition of claim 2. As the steel to be used, the steel grades shown in the invention steel 6 in Table 1 were obtained. Further, a material having a diameter of 20 mm was manufactured by hot rolling.

[0021]

EXAMPLES Next, examples of the steel of the present invention will be described. With respect to the steel types having the component compositions shown in Table 1, a 100 kg steel ingot was melted and hot rolled to manufacture a raw material having a diameter of 20 mm. A test piece was prepared from the material that was cooled after hot rolling and the material that was annealed, and the hardness, machinability, and rust / weather resistance were evaluated.

[0022]

[Table 1]

[0023]

[Table 2]

The machinability was evaluated under the conditions shown in the machinability evaluation method of Table 2 so that the tip of the drill was 10 mm from the surface of the test piece.
The time (s) required for perforation was set, and 7 s or less, which is almost equal to or higher than that of free-cutting stainless steel, was passed. The results are shown in Table 4.

The rust and weather resistance were evaluated by using a test piece having a diameter of 12 mm and a height of 21 mm in a cooled state after hot rolling and using a cycle wetting test and a wetting test shown in the rust and weather resistance test method of Table 3. I went there. However, the conditions of the cycle wetting test were such that holding at 10 ° C. for 1.5 hours and holding at 30 ° C. for 3.5 hours were repeated 20 times. The comparative steel 6 has a thickness of 6 μm.
It has been plated. The results are shown in Table 4.
The evaluation method was a five-stage evaluation from no rusting: A to remarkable rusting: E, and if C or more, it was passed in the use of the indoor environment.

[0026]

[Table 3]

[0027]

[Table 4]

As is clear from the result list shown in Table 4 above, regarding the machinability, the steel types of the invention steels 1 to 6 have excellent drill piercing properties of 7 s or less in any state.
However, Comparative Steel 1 with low Si content and low ferrite content and high hardness, Comparative Steel 2 with low P content, Comparative Steel 3 with low oxygen content and inappropriate sulfide distribution
Further, Comparative Steel 5 in which the amount of ferrite is small and the hardness is high because the amount of Cr is low, results in poor machinability.

Regarding the rust and weather resistance, the steel grades of the invention steels 1 to 6 have rust and weather resistance equal to or higher than that of the comparative steel 6 which has been plated at a high manufacturing cost, but the comparative steel 5 has a Cr content. Results in poor rust and weather resistance.

Therefore, the invention steel of the present application is a steel having excellent machinability by adding P and controlling the oxygen concentration, and having rust and weather resistance equivalent to or higher than that of the plated case.

[0031]

EFFECT OF THE INVENTION The invention steel of the present invention has the machinability equivalent to that of the conventional free-cutting stainless steel annealed by the above composition, even if it is not necessarily annealed. Furthermore, it is a free-cutting steel with excellent rust and weather resistance that is excellent in cost performance because it has rust and weather resistance equivalent to or better than that of a case subjected to plating treatment, which has a high manufacturing cost.

Claims (2)

[Claims] 1. C: 0.001 to 0.050 in% by weight.
%, Si: 0.1 to 3.0%, Mn: 0.1 to 2.0
%, P: more than 0.03 to 0.2% or less, Cr: 5.0 to 1
1.0%, Ni: 1.0% or less, Cu: 1.0% or less,
Mo: 1.0% or less, Al: less than 0.01%, S: 0.0.
1 to 0.5%, O: 50 to 200 ppm, the balance being essentially Fe and unavoidable impurities, which is a free-cutting steel excellent in rust and weather resistance. 2. C: 0.001-0.050 in% by weight.
%, Si: 0.1 to 3.0%, Mn: 0.1 to 2.0
%, P: more than 0.03 to 0.2% or less, Cr: 5.0 to 1
1.0%, Ni: 1.0% or less, Cu: 1.0% or less,
Mo: 1.0% or less, Al: less than 0.01%, S: 0.0.
1 to 0.5%, O: 50 to 200 ppm and S
e: 0.05 to 0.30%, Pb: 0.05 to 0.25
%, Containing 1 or 2 or more, and the balance being substantially Fe.
And free-cutting steel with excellent rust and weather resistance, which is characterized by containing unavoidable impurities.