JP2013104066A - Drawn jis sus303 steel bar excellent in workability and method for production the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce a drawn SUS303 steel bar endowed with excellence in surface properties, workability, and cuttability by using conditions in which the SUS303 being an austenitic sulfurized free-machining steel can be prevented from brittle split occurring when it is drawn and it can remain nonmagnetic after it has been drawn.SOLUTION: There is provided a SUS 303 drawn steel bar containing, by mass%, 0.25-0.50% S, which JIS SUS 303 drawn steel bar is characterized in that the tensile strength is 80-95% when compared with that attained in the case of cold drawing, the relative magnetic permeability is 1.05 or less, and the hydrogen content is 10 ppm or less. Also provided is a method for production thereof comprising the steps of: preceding to drawing, heating a starting stock steel containing 0.25-0.50%, by mass%, S at a temperature of from ≥35°C to below 80°C and subsequent to the heating, drawing the heated stock steel at a temperature of from ≥35°C to below 80°C at an area reduction rate of 10-50%.

Description

  The present invention relates to a SUS303 drawn steel bar of JIS steel type that is nonmagnetic and excellent in workability, and a method for producing the same.

The SUS303 wire containing a large amount of S forms coarse sulfides in the steel material. Therefore, when cold-drawn, the SUS303 wire starts from the interface between the sulfide and the parent phase, regardless of the austenite phase. Brittle vertical cracks occur. Further, when cold drawing is performed on the SUS303 wire, work-induced martensite is generated and exhibits magnetism, so that its use is limited. Furthermore, cold drawn steel bars have poor workability and may be cracked by bending.
At this time, in order to remove distortion and cold-induced martensite due to cold wire drawing, hydrogen is mixed in when bright annealing is performed, and bending workability is deteriorated. That is, the conventional cold drawn steel bar of SUS303 has vertical cracks, and is inferior in non-magnetic and bending workability.

Therefore, in the wire material in which about 3% of Cu is added to SUS303 and S is reduced to less than 0.35%, the toughness of the base material is increased to prevent vertical cracks during wire drawing, and the stability of the austenite phase is improved. In addition, the formation of work-induced martensite at the time of wire drawing is suppressed to maintain non-magnetism (relative magnetic permeability; μ ≦ 1.05).
However, the wire material in which about 3% of Cu is added to SUS303 to reduce S to less than 0.35% not only increases the alloy cost due to the high Cu content, but also completely eliminates vertical cracks during cold drawing. Cannot be suppressed, and the machinability cannot be improved because the S content is small. Moreover, since Cu is included, there is a problem that the use is deviated from the standard of JIS SUS303.

On the other hand, although it is a technique related to the processing of difficult-to-process materials, a technique has been proposed in which a wire former or a steel wire is continuously supplied and heated by in-line induction heating immediately before forging processing to form a part (for example, a patent) Reference 1). According to this technique, since it heats by induction heating, it does not depend on the kind of lubricant. Therefore, generation | occurrence | production of a spark can be prevented and a wire or a steel wire can be heated stably.
However, induction heating is expensive, and it is difficult not only to reduce the total cost required for processing, but also to uniformly heat the cross section. In addition, when the induction heating temperature is in a temperature range where strain aging is generated, stable toughening of the material (suppression of vertical cracks) cannot be expected.

As a technique for solving the problem of equipment cost and uniform heating in the cross section, a technique of directly energizing and heating to 80 to 300 ° C. through a rotating electrode has been proposed (for example, see Patent Document 2). According to this technique, by heating to 80 to 300 ° C., deformation resistance during processing is reduced, workability is improved, and the lubricant does not burn, so the appearance of the product surface is not impaired.
However, the lubricant for processing a stainless steel wire has poor conductivity, as represented by an oxalate film, and cannot be stably energized and heated, for example, sparks are generated during energization heating. In addition, since the energization heating temperature is a temperature range where strain aging is generated, stable toughening of the material (suppression of vertical cracks) cannot be expected.

  As described above, a highly machinable SUS303 drawn steel bar having good bending workability and surface properties while preventing vertical cracking during wire drawing and maintaining non-magnetic properties after wire drawing, and a method for manufacturing the same inexpensively have been proposed. Absent.

JP-A-6-134543 JP-A-6-79389

  The problem to be solved by the present invention satisfies the standard of JIS SUS303, which is an austenitic S free-cutting steel, prevents brittle longitudinal cracks during wire drawing, and maintains non-magnetism after wire drawing. It is another object of the present invention to provide a highly machinable drawn steel bar having good surface properties and a method for producing the same.

The present inventors have made various studies in order to solve the above problems. As a result, strain aging of C and N occurs in JIS SUS303 wire containing 0.25% to 0.50% (preferably 0.35% to 0.45%) of S and having a hydrogen content of 10 ppm or less. Without heating, it is heated to a temperature of 35 ° C. or more and less than 80 ° C., which is a relatively low temperature region from which hydrogen is released, and subsequently subjected to wire drawing with a surface area reduction of 10 to 50% at a temperature of 35 ° C. or more and less than 80 ° C., If the tensile strength of the drawn steel bar obtained in the wire drawing process is 80 to 95% when the wire drawing process is performed at 20 ° C. without heating before and during the wire drawing. I found a good thing. As a result, it was possible to prevent hydrogen pick-up, stably prevent longitudinal cracks during wire drawing, and obtain non-magnetic and good surface properties, workability, and machinability after wire drawing.
This invention is made | formed based on the said knowledge, The place made into the summary is as follows.

(1) JIS SUS303 drawn steel bar containing 0.25% to 0.50% S by mass%, and has a tensile strength of 80 to 95% compared to that during cold drawing, and has a specific permeability. It is a drawn steel bar of JIS SUS303 having excellent workability, characterized by having a magnetic permeability of 1.05 or less and a hydrogen content of 10 ppm or less.
(2) The JIS SUS303 drawn bar steel having excellent workability as described in (1) above, wherein the S content is 0.35 to 0.45%.
(3) A method for producing a drawn steel bar of JIS SUS303 having excellent workability as described in (1) or (2) above, wherein JIS SUS303 contains 0.25% to 0.50% S in mass%. A pre-drawing heating step for heating the drawn material to 35 ° C. or more and less than 80 ° C., and a drawing with a surface area reduction of 10 to 50% at a temperature of 35 ° C. or more and less than 80 ° C. following the pre-drawing heating step. And a wire drawing step of forming the drawn bar steel by processing, and a method of manufacturing a drawn bar steel of JIS SUS303 having excellent workability.
(4) The method for producing a JIS SUS303 drawn bar steel excellent in workability as described in (3) above, wherein the drawn wire material is heated by electric heating.

  According to the method for producing a non-magnetic SUS303 drawn bar steel excellent in workability according to the present invention, the fracture toughness is uniformly improved in the cross section by increasing the interfacial strength of the sulfide and the parent phase in the SUS303 steel, and the wire is drawn. SUS303 having a stable surface property and a good bending workability after drawing can be ensured by stabilizing the austenite phase at the time of wire drawing and ensuring non-magnetism after wire drawing. A drawn steel bar is obtained.

First, the reasons for limitation described in the above (1) and (2) will be described first.
The composition of the JIS SUS303 drawn bar steel of the present invention is, by mass%, C: 0.15% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.20% or less, S: It contains 0.25 to 0.50% or less, Ni: 8.00 to 10.00%, Cr: 17.00 to 19.00%, and the balance is made of iron and inevitable impurities.

  As the content of S contained in the drawn steel bar is increased, the machinability is improved, but the vertical drawing cracks frequently occur during cold drawing. In the present invention, the wire to be drawn is heated to 35 ° C. or more and less than 80 ° C., and subsequently subjected to wire-drawing with a reduction in area described later at a temperature of 35 ° C. or more and less than 80 ° C. Even if it is 25% or more, vertical cracks during wire drawing can be prevented. Usually, in JIS SUS303 wire drawing material containing 0.25% or more of S among stainless steels, wire drawing vertical cracks frequently occur during cold wire drawing. The effect of preventing vertical cracks at the time of wire drawing in the present invention becomes significant when the content of S contained in the drawn steel bar is 0.25% or more.

  On the other hand, when the content of S contained in the drawn steel bar exceeds 0.50%, vertical cracks during wire drawing cannot be suppressed even if the present invention is applied. Therefore, it is limited to JIS SUS303 containing 0.25 to 0.50% of S as an applicable steel type of the present invention. Preferably, it is SUS303 of JIS whose S content is 0.35-0.45%. When the S content is 0.35% or more, the machinability is particularly good, and when the S content is 0.45% or less, vertical cracks can be more effectively prevented and stable processing is performed. Sex is obtained.

  As described above, in steel types other than SUS303 such as SUS303Cu containing Cu and SUS304 not containing S, the effect of the present invention is unclear because no drawn vertical cracks occur during cold drawing. Therefore, the target steel type of the present invention is limited to SUS303.

  The composition of the JIS SUS303 drawn bar steel according to the present invention may further include Mo: 2.0% or less, Al: 0.06% or less, Cu: 0.001 to less than 1.0%, and B: 0.0. 01% or less, Ca: 0.01% or less, REM: 0.01% or less, O: 0.02% or less, Sn: 0.3% or less, Bi: 0.15% or less, Nb: 0.6% Hereinafter, Ti: 0.6% or less, Ta: 0.6% or less, W: 0.6% or less, Co: 1.0% or less may be contained. Furthermore, elements other than these can be added to the composition of the JIS SUS303 drawn bar steel of the present invention as long as the effects of the present invention are not impaired.

  Mo is contained for the purpose of improving corrosion resistance, Al is contained as a deoxidizing element, and Cu is contained for the purpose of improving workability. B, Ca, and REM are included for the purpose of improving hot workability, O, Sn, and Bi are included for the purpose of improving machinability, and Nb, Ti, Ta, and W are included for the purpose of improving corrosion resistance. Co is contained for the purpose of improving toughness.

  The drawn steel bar of the present invention is obtained by performing warm wire drawing, and the tensile strength is cold wire drawing at 20 ° C. at the same area reduction rate as the warm wire drawing. The wire was drawn so that it would be 80 to 95% of the above. The tensile strength of the drawn steel bar is preferably 90% or less when cold drawing is performed.

  The drawn steel bar of the present invention limits the relative permeability to 1.05 or less. In the drawn steel bar of the present invention, since the relative permeability is 1.05 or less, the use is limited as in the case where the drawn steel bar exhibits magnetism due to the formation of work-induced martensite. There is no.

Hydrogen in the drawn steel bar deteriorates the toughness and the vertical cracking property at the time of wire drawing and also deteriorates the workability of the drawn steel bar. In the drawn steel bar of the present invention, the hydrogen content is limited to 10 ppm or less. The hydrogen content of a normal SUS303 wire manufactured by hot rolling, annealing, and pickling is 10 ppm or less. However, after the SUS303 wire is drawn, the amount of hydrogen exceeds 10 ppm when bright annealing is performed to remove the strain introduced by the drawing.
In the drawn steel bar of the present invention, the amount of hydrogen is surely reduced to 10 ppm or less by hydrogen release in the pre-drawing heating process described later, so that vertical cracking during drawing is prevented and excellent workability is achieved. It will have.

Next, the reason for limitation described in the above (3) will be described.
In the method for producing a drawn steel bar according to the present invention, warm drawing is performed on a drawn material of JIS SUS303 containing S in an amount of% by mass of 0.25% to 0.50%. In the warm wire drawing, a pre-drawing heating process for heating the drawn material to 35 ° C. or more and less than 80 ° C., and a surface reduction rate of 10 at a temperature of 35 ° C. or more and less than 80 ° C. following the pre-drawing heating step. A wire drawing step of forming a drawn steel bar by performing a wire drawing process of ˜50%.

  Regarding the heating temperature and drawing temperature of the wire to be drawn in the pre-drawing heating process, the interfacial strength between the sulfide and the parent phase in SUS303 steel is increased, the fracture toughness is improved, and vertical cracking during drawing is prevented. Therefore, the temperature is set to 35 ° C. or higher. Further, when the heating temperature and the wire drawing temperature are 35 ° C. or higher, magnetism is hardly generated, so that the relative permeability of the obtained drawn steel bar can be stably secured to 1.05 or lower. Moreover, when the heating temperature and the wire drawing temperature are 35 ° C. or higher, the amount of strain introduced by the wire drawing is reduced, so that the tensile strength does not become too high. For this reason, it is not necessary to perform bright annealing after wire drawing in order to suppress the tensile strength. Therefore, an increase in the amount of hydrogen due to bright annealing does not occur, and a drawn bar steel having a hydrogen amount of 10 ppm or less can be easily obtained.

  However, when heating to 80 ° C. or higher in the temperature range where C and N are easy to move, strain aging occurs and the toughness deteriorates conversely, and seizure occurs at the time of wire drawing, resulting in deterioration of the surface properties and tensile strength. descend. Therefore, the heating temperature and the drawing temperature are limited to 35 ° C. or more and less than 80 ° C. The heating temperature and the drawing temperature of the drawing material in the pre-drawing heating step are preferably 40 ° C. or higher, and more preferably 45 ° C. or higher in order to prevent vertical cracks during drawing. In order to completely suppress strain aging, the heating temperature and the drawing temperature of the drawn material are preferably 70 ° C. or lower.

  Following the heating process before wire drawing, wire drawing with a reduction in area of 10 to 50% is performed at a temperature of 35 ° C. or more and less than 80 ° C., thereby preventing longitudinal cracks in wire drawing and excellent workability and machinability. A non-magnetic SUS303 drawn steel bar having a strength of 80 to 95% when cold drawn and having a hydrogen content of 10 ppm or less and a relative permeability of 1.05 or less can be produced.

  In the SUS303 drawn bar steel manufactured by cold drawing, the relative permeability of the drawn bar steel is usually 10% to 50%, for example, when the area reduction rate (drawing rate) is as large as 10% to 50%. The relative permeability exceeds 1.05. On the other hand, in the drawn bar steel of the present invention, since the pre-drawing heating process is performed at the heating temperature described above, the obtained drawn bar steel is obtained even when a drawing process with a reduction in area of 10% to 50% is performed in the drawing process. The relative permeability can be stably secured to 1.05 or less.

In addition, when the area reduction rate of wire drawing is less than 10%, vertical cracks do not occur even in cold drawing without performing the pre-drawing heating step, but the surface texture of the hot-rolled wire remains and remains. Deteriorates.
In the production method of the present invention in which the pre-drawing heating step is performed, when the surface area reduction rate (working rate) of the drawing process is 10% or more, the surface properties are improved and vertical cracks during drawing can be suppressed. On the other hand, if the area reduction ratio of the wire drawing process exceeds 50%, vertical cracks during wire drawing cannot be sufficiently suppressed even if the heating process before wire drawing is performed. Further, if the area reduction rate exceeds 50%, it may be impossible to secure a relative magnetic permeability of 1.05 or less. Therefore, the area reduction rate of the wire drawing according to the present invention is limited to 10 to 50%, preferably 20 to 40%.

Regarding the tensile strength of the drawn steel bar, the SUS303 drawn steel bar, which is usually manufactured by cold drawing (for example, 20 ° C.), has poor cold workability and cracks when subjected to processing such as bending.
In the wire drawing step in the method for producing a drawn steel bar according to the present invention, a drawn steel bar is formed by performing a drawing process with a surface area reduction of 10 to 50% at a temperature of 35 ° C. or higher and lower than 80 ° C. following the pre-drawing heating step. .
In the present embodiment, since the temperature in the wire drawing step is 35 ° C. or higher, the tensile strength is 95% or less of the case of performing cold wire drawing, and excellent bending workability is obtained.

  When the temperature in the wire drawing process is 80 ° C. or higher, the tensile strength is less than 80% when cold drawing is performed, the effect of preventing work cracking is saturated, and the tensile strength is insufficient. It becomes. Also, in order to reduce the tensile strength of the drawn steel bar to less than 80% when cold drawing, if the temperature of the drawing process is raised to 80 ° C or higher, seizure occurs during drawing, The surface properties of the steel bar deteriorate.

  In order to make the tensile strength of the drawn steel bar obtained by the method for producing the drawn steel bar of the present invention 80 to 95% when cold drawing is performed, the drawn material is drawn before drawing. What is necessary is just to perform the warm wire drawing which heats to 35 degreeC or more and less than 80 degreeC, and performs a wire drawing process with a surface-reduction rate of 10 to 50% at the temperature below 35 degreeC or more and less than 80 degreeC. It should be noted that, when the strength is compared, when manufacturing is newly performed from the raw material melting stage as a comparative material, it is extremely difficult to manufacture a steel having exactly the same component content. Therefore, as a strength comparison material, the content of each element specified in JIS SUS303 may be within ± 10% which is a range that does not substantially affect the strength.

  Moreover, in the manufacturing method of the drawn steel bar of this invention, it is preferable to apply | coat a lubricant to a to-be-drawn material after performing a wire drawing process after a heating process before wire drawing. Any lubricant can be used without limitation as long as it is generally used as a wire drawing lubricant such as mineral oil.

Next, the reason for limitation described in the above (4) will be described.
About the heating method of a to-be-drawn material, it is preferable to carry out an electrical heating as a method of heating the cross section of steel materials uniformly and efficiently cheaply. The cross-section can be uniformly and efficiently heated by setting the heating temperature of the drawn material in the pre-drawing heating step to a low temperature of 35 ° C. or higher and lower than 80 ° C. and heating by current heating.

  If a lubricant is applied to the surface of the drawn material before the pre-drawing heating step, spark marks may be generated and the surface properties may deteriorate. For this reason, in the pre-drawing heating process, the drawn material is heated by energization heating in a state where the surface of the drawn material is unlubricated, and after the pre-drawing heating process, the lubrication is performed before the drawing process. It is preferable to prevent the occurrence of spark marks by applying an agent.

  Examples of the present invention will be described below. Table 1 shows the chemical composition of the drawn wire material of the example.

  Steel materials having the chemical composition shown in Table 1 were melted in a 150 kg vacuum melting furnace and cast into a slab of φ180 mm. The slab is hot-rolled to φ9.5 to φ15.0 mm, the hot-rolling is finished at 1050 ° C., held at 1050 ° C. for 5 minutes, and then subjected to water-cooling continuous heat treatment and pickling. A drawn material was obtained. Then, bright annealing was performed on a part of the wire drawing material, and the wire drawing material was heated to the temperature shown in Table 2 by oven furnace heating or current heating in the atmosphere (heating process before wire drawing). Thereafter, die drawing was performed to a diameter of 9.4 mm with the area reduction shown in Table 2 while maintaining the temperature of the pre-drawing heating process within 3 minutes. 1-No. 21 drawn steel bars (drawing process). In addition, after the heating process before wire drawing, the lubricant was applied before the die drawing wire drawing process. No. 1-No. Table 2 shows the production conditions of the 21 drawn steel bars.

Then, no. 1-No. 21 drawn steel bars were evaluated for the presence or absence of drawn vertical cracks, surface properties, relative magnetic permeability, hydrogen content, bending workability, and tensile strength.
No. 1-No. For each of the 21 wire drawing materials, the temperature of the wire drawing step is set to 20 ° C. at the same area reduction rate as that of the warm wire drawing instead of the warm wire drawing processing in which the heating process and the wire drawing process are performed. The tensile strength of the drawn steel bar when wire drawing was performed (cold wire drawing) was measured. 1-No. Strength ratio ((tensile strength after warm wire drawing / tensile strength after cold wire drawing) × 100 (%) (strength ratio% against cold wire)) It was.
The evaluation results are shown in Table 3.

  The drawn bar steel was evaluated for the presence or absence of longitudinal cracks by visually observing the surface of the drawn bar steel. The case where there was no vertical crack was evaluated as “none”, and the case where it occurred was evaluated as “present”. The drawn steel bars of the examples of the present invention were all excellent in that there were no drawn vertical cracks.

  The surface properties of the drawn bar steel were evaluated by visually observing the surface of the drawn bar steel and checking for surface seizure and poor gloss. The case where surface burn-in occurred was evaluated as “burn-in”, the case where poor gloss occurred was evaluated as “bad”, and the case where surface properties were good was evaluated as “good”. The drawn steel bars of the examples of the present invention were all excellent in surface properties.

The relative permeability of the drawn steel bar was measured by bringing a meter of a permeability meter into contact with the surface of the drawn steel bar. The relative permeability of the drawn steel bar of the present invention example was 1.05 or less, which was excellent.
The amount of hydrogen in the drawn steel bar was measured by taking a sample from the drawn steel bar after the wire drawing process and measuring it with an inert gas melting-heat conduction measurement method. The hydrogen content of the drawn steel bars of the inventive examples was all 10 ppm or less.

The bending workability of the drawn bar steel was evaluated by performing a 90 ° bending test with the radius of the drawn bar steel as the bending radius, and whether or not cracking occurred. The case where cracking occurred was evaluated as “×”, and the case where cracking did not occur was evaluated as “◯”. The bending workability of the drawn steel bars of the examples of the present invention was all good.
The tensile strength was evaluated by a tensile test according to JIS Z 2241. The strength ratio of the drawn steel bar of the inventive example was in the range of 80 to 95%.

On the other hand, Comparative Example No. In Nos. 11 to 16, the heating temperature in the pre-drawing heating process or the area reduction rate in the drawing process is outside the scope of the present invention, and the surface properties, longitudinal cracks, relative magnetic permeability, hydrogen content, bending workability, tensile strength Any one or more of the strength ratios were inferior.
Comparative Example No. No. 17 was high in the amount of hydrogen because of bright annealing, and was inferior in bending workability. Comparative Example No. 18-21 has a chemical composition outside the scope of the present invention, and the effects of the present invention are not recognized.

  As is apparent from the above examples, according to the present invention, the SUS303 wire can be stably drawn without the occurrence of drawn vertical cracks, and the nonmagnetic SUS303 is excellent in surface properties, workability, and machinability. The drawn steel bar can be provided at low cost and is extremely useful in the industry.

Claims (4)

A JIS SUS303 drawn steel bar containing 0.25% to 0.50% S in mass%,
JIS SUS303 with excellent workability, characterized by having a tensile strength of 80 to 95% compared to that during cold drawing, a relative permeability of 1.05 or less, and a hydrogen content of 10 ppm or less. Drawn steel bar.   The drawn steel bar of JIS SUS303 having excellent workability according to claim 1, wherein the content of S is 0.35 to 0.45%. A method for producing a drawn steel bar of JIS SUS303 excellent in workability according to claim 1 or 2,
The wire drawing material of JIS SUS303 containing 0.25% to 0.50% S in mass% is heated to 35 ° C. or more and less than 80 ° C. JIS SUS303 drawn bar steel excellent in workability, characterized by comprising a wire drawing step of forming the drawn bar steel by drawing at a temperature reduction of 10 to 50% at a temperature of not lower than 80 ° C and lower than 80 ° C Manufacturing method.   The method of manufacturing a drawn steel bar of JIS SUS303 with excellent workability according to claim 3, wherein the drawn wire material is heated by electric heating.