JPH04318153A - High cold forgeability electric stainless steel - Google Patents

Abstract

PURPOSE:To restrict formation of coarse grain and to improve cold forgeability of ferritic electric stainless steel by compositely adding specified quantity of Ti, B Mo and Cu to the above steel. CONSTITUTION:This steel consists of <=0.02wt.% C, 0.01-0.05% Si, 0.01-0.50% Mn, 7.00-20.00% Cr, 0.30-2.00% Mo, 0.01-2.00% Cu, 0.05-0.50% Ti, 0.05-3.00% Al, 0.0005-0.05% B, <=0.05% Ni and residue substantially consisting of Fe. Moreover, if necessary, at least a kind of <=1.00% Nb, 1.00% V, moreover at least one kind of <=0.30% Pb, <=0.03% Ca, <=0.20% Se and <=0.20% S is allowed to contain. As crystal grains become fine and have uniform structure in this component, high cold forgeability electric stainless steel having all of excellent cold forge-ability, favorable magnetic characteristics and corrosion resistance can be obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to high-cold forged electromagnetic stainless steel that has excellent cold forging properties and corrosion resistance as well as good soft magnetic properties, and is particularly used as a housing material for electronically controlled fuel injection devices for automobiles. This alloy is suitable for use in sleeves, core materials, various sensors, water solenoid valves, etc.

0002

[Prior Art] With the rapid development of car electronics, the number of vehicles equipped with electronically controlled fuel injection systems for automobiles has increased significantly, but the material used for them is 13Cr-1Si due to the requirements for corrosion resistance and soft magnetic properties. -Al-based ferritic electromagnetic stainless steel is widely used as a practical material.

[0003] In order to reduce processing costs, these parts are
There is a shift from cutting to cold forging, and in particular, parts machining by completely cold forging is becoming more popular. Under such a request,
Attempts have been made to reduce (C+N) in 13Cr-1Si-Al alloys and improve cold forgeability. However, since the shape of the parts of electronically controlled fuel injection devices for automobiles is very complicated, the current 13Cr-1Si-Al alloy is not sufficient even if it has a low (C+N).

On the other hand, with the diversification of automobile fuels, the use of alcohol fuel is being seriously considered, and there is a concern that corrosion may occur due to the generation of organic acids such as acetic acid and formic acid due to oxidation of alcohol. In addition, road dust pollution in winter is becoming more serious, and measures such as banning the use of spiked tires are being considered.As a result, the demand for corrosion resistance against chloride corrosion caused by snow-melting agents is becoming stronger not only in Europe and America but also in Japan. The 13Cr-1Si-Al alloy does not exhibit sufficient durability for these as well.

Furthermore, materials for electronically controlled fuel injection devices for automobiles are particularly required to have soft magnetic properties, and improvements in such magnetic properties are directly linked to improvements in the characteristics of electronically controlled fuel injection devices for automobiles.

[0006]

[Problems to be Solved by the Invention] As mentioned above, the characteristics required of materials for electronically controlled fuel injection devices for automobiles are wide-ranging, and these characteristics are interrelated and often contradictory. It is described as. An object of the present invention is to propose a high-cold forged electromagnetic stainless steel that satisfies all of the characteristics required for materials for electronically controlled fuel injection devices for automobiles as described above.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the inventors conducted extensive studies and obtained the following knowledge. 1) By adding Ti and B in combination to ferritic electromagnetic stainless steel, the effect of reducing C and N in this alloy is improved, and the crystal grains produced by annealing the base material before cold forging are made fine and regular, and each Coarsening of crystal grains is effectively suppressed, and as a result, cracking sensitivity during cold forging is significantly improved, and cold forgeability is dramatically improved. 2) At the same time, the combined addition of Ti and B expands the temperature range in which the product exhibits good magnetic properties, and since each crystal grain exhibits a relatively fine and uniform structure, the soft magnetic properties are also improved. 3) Furthermore, regarding Ti, Nb, and V, C in the base
, N exhibits good magnetic properties and cold forgeability. 4) Furthermore, by adding Ti, B, Mo, and Cu in combination, the corrosion resistance after magnetic annealing is greatly improved. The reason for this is that Ti, B not only fixes C and N and reduces the substantial content, but also Ti, B, Mo, C
This is thought to be due to the coexistence of u, which makes the Cr oxide film extremely dense and strengthens it, and in particular, the corrosion resistance against chloride corrosion and organic acids is dramatically improved.

The present invention is based on the above knowledge. That is, the present invention provides C: 0.02 wt% or less (hereinafter simply expressed as %), Si: 0.01 to 0.50%, Mn
:0.01~0.50%, Cr:7.00~20.00
%, Mo: 0.30~2.00%, Cu: 0.10~
2.00%, Ti: 0.05-0.50%, Al: 0.
05 to 3.00%, B: 0.0005 to 0.05%, and N: 0.05% or less, with the remainder being substantially Fe (first invention). .

[0009] Furthermore, the present invention further includes Nb:
This is a high-cold forged electromagnetic stainless steel (second invention) having a composition containing at least one selected from V: 1.00% or less and V: 1.00% or less.

[0010] Furthermore, the present invention further provides Pb: 0.30% or less, Ca: 0.03% or less, in addition to the first or second invention.
This is a high-cold forged electromagnetic stainless steel (third invention) having a composition containing at least one selected from Se: 0.20% or less and S: 0.20% or less.

[0011] Furthermore, the present invention is a high-cold forged electromagnetic stainless steel (fourth invention) having a composition that further includes Rem: 0.01% or less in the first, second, or third invention.

[0012] The experimental results that formed the basis of this invention will be explained below. As the test steel, the following a) C: 0.
008%, Si: 0.15%, Mn: 0.20%
, Cr:13.35%, Mo:0.50%, C
u: 0.45%, Ti: 0.11%, Al: 0.7
8%, B: 0.011% and N: 0.015%
steel (Ti, B
Additive steel), b) C: 0.010%, Si: 0.14
%, Mn: 0.20%, Cr: 13.26%,
Mo: 0.49%, Cu: 0.51%, Ti: 0.
10%, Al: 0.73%, B: 0.0003% and N: 0.017%, the remainder being substantially Fe (Ti-added steel), c) C: 0.006% ，
Si: 0.14%, Mn: 0.19%, Cr: 1
3.21%, Mo: 0.49%, Cu: 0.43
%, Ti: 0.003%, Al: 0.73%,
Contains B: 0.0002% and N: 0.015%,
The remainder of the steel (steel without addition of Ti or B) having a composition of substantially Fe was used, and 5 kg of each steel was induction melted in an Ar gas flow to produce ingots of 65 mm in diameter. Each ingot was then hot-forged at 1050°C to produce a round bar with a diameter of 15 mm, which was then cold-rolled to a diameter of 13 mm to obtain a test material. The results of investigating the cracking limit working rate and magnetic properties of each test steel thus obtained are shown in FIGS. 1 and 2.

[0013] Figure 1 shows the relationship between annealing temperature and cold working cracking limit. By adding Ti and B in combination, the annealing temperature range that can be processed without cracking is extended to high temperatures. Furthermore, it can be seen that the critical machining rate for crack occurrence can be increased to a high degree of machining.

FIG. 2 shows the relationship between the annealing temperature and magnetic properties of Steel A and Steel C. Steel A exhibited good magnetic properties over a wide temperature range. On the other hand, for steel c, the temperature is 950 ℃
Although an improvement in magnetic properties was observed in the above temperature range, there was a tendency for the structure to become coarse grained. As mentioned above, by containing Ti and B in a composite manner, a fine grained structure was created, and significant improvements in cold forgeability and magnetic properties were achieved.

[0015]

[Operation] In this invention, the reason why the alloy components are limited to the above composition range is as follows. C: 0.02% or less C is an element that significantly deteriorates corrosion resistance, magnetic properties, and cold forgeability in stainless steel, and is preferably 0.01% or less, but it is unavoidably mixed during the manufacture of stainless steel. In consideration of actual operation, the content was set to 0.02% or less.

Si: 0.01 to 0.50% Si is present in steel and is not only useful as a deoxidizing agent, but also effectively contributes to improving the magnetic properties of ferritic steel. It is also useful for increasing electrical resistance and improving response characteristics in the high frequency range, but on the other hand, it significantly increases hardness and inhibits cold forgeability. However, if it is less than 0.01%, the above effects will be poor, and if it exceeds 0.50%, cold forgeability will be impaired, so the content was limited to 0.01 to 0.50%.

Mn: 0.01-0.50% Mn is an element that is present in stainless steel and is effective as a deoxidizing agent, but excessive addition inhibits magnetic properties, so 0.01% Mn is an element that is effective as a deoxidizing agent.
It was limited to a range of 0.50%.

[0018] Cr: 7.00-20.00% Cr is
It is the main component in this alloy and is one of the most effective elements for corrosion resistance, magnetic properties and electrical resistance, especially Mo,
By coexisting with Cu and Ti, the oxide film after magnetic annealing becomes extremely dense and strong, maintaining excellent corrosion resistance and providing good magnetic properties. However, if the content is less than 7.00%, the addition effect will be poor, while if it exceeds 20.00%, it will not only cause deterioration of magnetic properties (specifically, magnetic flux density) but also inhibit cold forgeability. Therefore, it was limited to a range of 7.00 to 20.00%.

Mo: 0.30-2.00%Mo is Cr
, Ti, and Cu significantly improve corrosion resistance. However, if it is less than 0.30%, the effect is not significant, while if it exceeds 2.00%, it not only impedes cold forgeability but also becomes expensive.
limited to the range of

Cu: 0.10-2.00% Cu is Cr
, Mo, and Ti not only significantly improve corrosion resistance, but also improve deformability with a small amount of addition, effectively contributing to improving cold forgeability, and further improving electrical resistance. However, if it is less than 0.10%, the effect is not significant, while if it exceeds 2.00%, not only will the magnetic properties deteriorate significantly, but the hardness will also increase significantly, impeding cold forgeability. Therefore, 0.10 to 2.0
It was limited to a range of 0%.

[0021] Ti: 0.05 to 0.50% Ti is B
It is the most important element in this alloy, and when it coexists with B, it effectively acts on C and N in the steel, making the crystal grains fine and regularized before cold forging to improve cold forgeability. Improve dramatically. Furthermore, by uniformly and finely dispersing C and N, it also contributes to improving magnetic properties. Furthermore, Ti is M
Coexistence with Cu has the effect of dramatically improving corrosion resistance, particularly against chlorides and organic acids. However, if the content is less than 0.05%, the effect will not be sufficient, while if it exceeds 0.50%, the effect will reach saturation, and this will cause problems in manufacturing, so the content should be reduced to 0.
．． It was limited to a range of 0.05 to 0.50%.

Al: 0.05-3.00% Al is present in this alloy and is useful for improving the magnetic properties together with Si, and also for effectively increasing the electrical resistance and improving the response characteristics in the high frequency range. It is an element, and its contribution to hardness increase is lower than that of Si. However, the content is 0.05%
If it is less than 3.00%, the effect of improving magnetic properties will not be sufficient, while if it exceeds 3.00%, not only will a special refining method be required, but it will also impede cold forgeability.
The content was limited to a range of 0.05 to 3.00%.

B: 0.0005 to 0.05% B is Ti
It is a particularly useful element in this alloy, and C
, N, not only improves the magnetic properties but also refines the grain size and effectively contributes to improving the cold forgeability of the alloy. However, if the content is less than 0.0005%, the effect is not sufficient, while if it exceeds 0.05%, hot and cold workability is inhibited, so 0.0005%
The content was set to be in the range of 0.05% to 0.05%.

N: 0.05% or less N, like C, is an element that significantly deteriorates corrosion resistance, magnetic properties, and cold forgeability in stainless steel, and it is desirable to reduce it as much as possible, but 0.05% Permissible within the following ranges.

The basic components have been explained above, but in this invention, at least one of Nb and/or V is added in order to further improve toughness and improve cold forgeability and magnetic properties. P to take into account
At least one selected from B, Ca, Se, and S can be added, and Rem can also be added to further improve cold forgeability.

[0026] These selected components will be explained below. Nb: 1.00% or less, V: 1.00% or less Both Nb and V are not only useful for improving the toughness of this alloy, but also contribute effectively to improving cold forgeability and magnetic properties. However, if it exceeds 1.00%, cold forgeability will be hindered, so it should be added at 1.00% or less.

[0027] Pb: 0.30% or less, Ca: 0.03%
Below, Se: 0.20% or less, S: 0.20% or less Pb
, Ca, Se, and S are all useful elements that improve the machinability of this alloy, but if they are contained in large amounts exceeding the upper limit, they will instead cause deterioration of corrosion resistance, magnetic properties, and cold forgeability. Each was added below the upper limit.

Rem (lanthanide element): 0.01
The addition of Rem can further improve the cold forgeability, but if it exceeds 0.01%, it not only requires a special melting and refining method but also becomes expensive. It was supposed to be added.

[0029]

[Example] Test steel (N
o. 1~No. 14) was melted by induction in an Ar flow to produce an ingot of 65 mmφ. Each ingot was then hot-forged at 1050°C to produce a round bar with a diameter of 15 mm, which was then cold-rolled to a diameter of 13 mm to obtain a test material. The test materials thus obtained were examined for cold forgeability, magnetic properties, corrosion resistance, and specific resistance as described below. The obtained results are summarized in Table 2.

Regarding cold forgeability, 6mmφ×1
A 1 mmH 2 test piece was prepared, subjected to a compression test using a hydraulic press, and evaluated by the cracking limit processing rate and deformation resistance when compressed to 80%. In addition, the magnetic properties are 10mmφ×5
．． A ring sample of 5 mmφ x 5 mmt was prepared, and 75
After magnetic annealing at 0°C to 1050°C, DC magnetic properties were measured using a B-H loop tracer. Furthermore, the corrosion resistance is 16m
A stepped test piece of mφ x 20mmφ x 35mmH was prepared, and after finishing the surface roughness to 12s or less, it was heated in a vacuum.
Magnetic annealing was performed at 950°C for 2 hours, and then 5% NaC
A salt water spray test was carried out using an aqueous solution of 35° C. for 96 hours, and the presence or absence of rusting was evaluated. In addition, a test piece of 13 mmφ x 2 mm was prepared, polished with sandpaper to a grit of 800, magnetically annealed in vacuum at 950°C for 2 hours, and then subjected to pitting potential in a 3.5% NaCl aqueous solution at 30°C. It was measured. Further, the specific resistance was measured by cold drawing each sample to a diameter of 1 mm, vacuum annealing at 850° C., and using Digivol.

[0031]

[Table 1]

[0032]

[Table 2]

As is clear from Table 2, comparative steel No. 1 containing neither Ti nor B. 9 is cold forgeability, magnetic properties (
In particular, good results were not obtained in either B1) or corrosion resistance. Comparative steel No. containing only Ti.
Although No. 10 has improved magnetic properties and corrosion resistance, it is inferior in cold forgeability, particularly in deformation resistance. Comparative steel No. 1 whose Cr content does not meet the lower limit and does not contain Mo or Cu.
．． No. 11 has good cold workability and magnetic properties, but is poor in corrosion resistance. Steel No. 12 is C, N, Si
, B is contained in excess, so cold workability, magnetic properties, and corrosion resistance are all poor. Steel No. 13 is C
Due to the excessive content of u and Mo, although the corrosion resistance is good, the cold workability and magnetic properties are poor. Steel No. No. 14 has good corrosion resistance because it contains excess Cr and Al, but has poor cold workability. Furthermore, the magnetic flux density (B25) is as low as 1.0T or less, which causes insufficient suction power when used in electronically controlled fuel injection systems for automobiles.

On the other hand, steel No. according to the present invention. 1
~8 all have a cracking limit processing rate of 80% or more and 850
It exhibits low deformation resistance of N/mm2 or less, and has magnetic properties of Hc≦0.80 A/cm and B1≧0.35T.
, B25≧1.20T, and in terms of corrosion resistance, it exhibited a pitting potential of 200 mV or more, and no rust was observed in the salt spray test. Furthermore, it was confirmed that it was not attacked by organic acids at all and had excellent corrosion resistance against alcohol fuel and inferior gasoline.

[0035]

[Effects of the Invention] Thus, according to the present invention, a high-cold forged electromagnetic stainless steel with fine and uniform crystal grains and excellent cold forgeability as well as good magnetic properties and corrosion resistance can be produced. Materials for housings, sleeves, and cores for automotive electronically controlled fuel injectors,
It greatly contributes to industry as various sensors, water solenoid valves, etc.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between annealing temperature and cold work cracking limit.

FIG. 2 is a graph showing the relationship between annealing temperature and magnetic properties.

Claims (4)

[Claims] Claim 1: C: 0.02wt% or less, Si: 0.01
~0.50wt%, Mn:0.01~0.50wt%,
Cr: 7.00-20.00 wt%, Mo: 0.30
~2.00wt%, Cu:0.10~2.00wt%,
Ti: 0.05-0.50wt%, Al: 0.05-3
．． 00 wt%, B: 0.0005 to 0.05 wt%, and N: 0.05 wt% or less, with the remainder being substantially Fe. 2. In claim 1, further Nb: 1.
1.00 wt% or less and V: 1.00 wt% or less. [Claim 3] In Claim 1 or 2, further P
b: 0.30 wt% or less, Ca: 0.03 wt% or less,
A high-cold forged electromagnetic stainless steel having a composition containing at least one selected from Se: 0.20 wt% or less and S: 0.20 wt% or less. 4. The high-cold forged electromagnetic stainless steel according to claim 1, further comprising 0.01 wt% or less of Rem.