JP4207137B2 - High hardness and high corrosion resistance stainless steel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a high hardness and high corrosion resistance suitable for use in members and parts that require both high hardness and corrosion resistance, such as blades, coil springs, flapper valves, metal gaskets, blades such as razor blades, etc. It relates to stainless steel.
[0002]
[Prior art]
Conventionally, 13Cr-based martensitic stainless steel mainly containing about 0.5% of C has been used for the above-mentioned applications requiring high hardness and corrosion resistance. These stainless steels are manufactured by performing a heat treatment called quenching and tempering after applying cold working to a predetermined size after annealing and softening. Since a hard martensite phase containing C is obtained by this heat treatment, a very high hardness can be obtained. However, since heat treatment called quenching and tempering is required to obtain high hardness, there are many manufacturing processes of the material, and there is a problem that the manufacturing process is complicated.
For applications where the required hardness is not so high, austenitic stainless steels such as SUS304 and SUS201 are cold-worked. These are strengthened by cold-working the austenitic structure material to introduce and disperse many dislocations and to cause some austenitic phases to undergo work-induced martensitic transformation. However, they have a problem that austenite is stable in order to obtain the same high hardness as the martensitic stainless steel described above, and therefore, a sufficiently high hardness cannot be obtained even if considerably hardened.
[0003]
[Problems to be solved by the invention]
Therefore, recently, there is a demand for stainless steel that does not require complicated heat treatment such as quenching and tempering, and that can obtain high hardness similar to martensitic stainless steel by strengthening mainly by cold working.
An object of the present invention is to provide a stainless steel having a high level of corrosion resistance, which has high hardness obtained mainly by cold working without requiring a complicated heat treatment and has no practical problem.
[0004]
[Means for Solving the Problems]
The inventor has intensively studied austenitic stainless steel in order to obtain high hardness by cold working. As a result, the hardness after cold working is related to the amount of martensite transformed by processing induction, and the higher the amount of martensite, the higher the hardness, but to obtain the desired amount of processing-induced martensite. The present inventors have found that it is necessary to optimize the Ni equivalent related to the ease of processing-induced martensite transformation after limiting individual components. In addition, in order to improve the corrosion resistance, it is necessary to optimize Cr, Mo, Cu, and N, which are elements that improve the corrosion resistance, and further based on the manufacturability, hardness, and corrosion resistance depending on each alloy element. The alloy addition amount needs to be optimized, and an alloy satisfying these requirements has been studied and the present invention has been achieved.
[0005]
That is, according to the first invention of the present invention, in terms of% by weight, C 0.01 to 0.10%, Si 3.0% or less, Mn over 5.0% and 10.0% or less, Ni 1.0 -7.0%, Cr 12.0-18.0%, 1 or 2 types of Mo or W is 3.0% or less (including 0%) at Mo + 1 / 2W, Cu 2.0% or less ( N is 0.02 to 0.15%, the balance is substantially made of Fe, and the A value represented by the formula (1) is 23.58 to 27 , and B is represented by the formula (2). A high-hardness, high-corrosion-resistant stainless steel having a value of 25.15 or more and containing a work-induced martensite phase in an austenite phase of 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among selected elements)
[0006]
Further, the second invention is, in terms of% by weight, C 0.01 to 0.10%, Si less than 1.0%, Mn exceeding 5.0% and 7.0% or less, Ni 2.0 to 7.0. %, Cr 12.0 to 18.0%, one or two of Mo or W is Mo + 1 / 2W, 1.0 to 3.0%, Cu 2.0% or less (including 0%), N 0.02 to 0.15%, the balance is substantially made of Fe, and the A value represented by the formula (1) is 23.58 to 27 , and the B value represented by the formula (2) is 25.15 or more. A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase in a volume of 30% or more in the austenite phase.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among selected elements)
[0007]
A third invention of the present invention is characterized in that the steel composition according to any one of the first and second inventions includes one or more of V, Ti and Nb in a total amount of 0.2% or less. In addition, the steel composition according to any one of the first to third aspects of the present invention includes one or more of B, Mg, Ca, and Al in a total of 0.001. It can contain 10% or less .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is to optimize the balance of alloy elements in order to optimize the ease of processing-induced martensite transformation and the amount of addition of Cr, Mo, Cu, and N, which are elements that improve corrosion resistance. This is one of the features of the invention.
First, the elements Ni, Cr, Mo, W, Mn, Si, Cu, C and N not only satisfy the individual component ranges, but also in the steel of the present invention in order to obtain high hardness and good corrosion resistance. It is necessary to satisfy the specified formula.
The A value shown in the formula (1) indicates the Ni equivalent of the steel of the present invention, and the magnitude of the A value in this formula is an important index that affects the ease of forming the work-induced martensite phase. The A value is obtained by adding a value obtained by adding a coefficient according to the effect of each element to the weight% of each element that affects the ease of transformation to work-induced martensite. As a result of the experiment, in the steel of the present invention, when this A value exceeds 27, it becomes difficult to form work-induced martensite and it becomes difficult to obtain a sufficiently high hardness, so the upper limit of the A value shown in the formula (1) is limited. 27, and the A value was specified in the range of 23.58 to 27 .
[0009]
The B value shown in the formula (2) is an important index that influences the corrosion resistance of the steel of the present invention, and the weight value of Cr, Mo, W, Cu, and N, which are elements that directly improve the pitting corrosion resistance. It is shown as a sum of values with coefficients indicating the degree of contribution of elemental effects. In the steel of the present invention, when this B value is smaller than 15, good pitting corrosion resistance cannot be obtained, so the B value shown in the formula (2) is set to 25.15 or more .
[0010]
The action of each element of the steel of the present invention will be described below.
C is an austenite-forming element in austenitic stainless steel, and is effective for obtaining an austenite structure after solution treatment. It is effective for strengthening the martensite structure that has been induced by cold working and increasing the hardness, but if added over 0.10%, the austenite phase becomes too stable due to solid solution in the matrix. Induced transformation is less likely to occur, or Cr carbide is formed at the austenite grain boundaries, reducing the amount of Cr in the matrix and deteriorating corrosion resistance. On the other hand, if the content is less than 0.01%, not only the sufficient hardness cannot be obtained after cold working, but also a large amount of delta ferrite is generated, which decreases the corrosion resistance, hardness, and hot workability. The content of was made 0.01% to 0.10%.
[0011]
Si is added in a small amount for deoxidation, but even if added over 3.0%, a further improvement effect is not seen, and a large amount of Cr carbide is generated at the austenite grain boundaries, resulting in deterioration of corrosion resistance. Therefore, it was set to 3.0% or less. Desirably, it is less than 1.0%.
Mn is an austenite generating element and is effective for obtaining an austenite structure after the solution treatment. In addition, in the control of the Ni equivalent defined by the A value, Mn can be increased by substituting part of Ni with Mn. Therefore, the cost can be reduced by adding more Mn, which is cheaper than Ni. There are also advantages.
In addition, the solid solubility of N in the austenite phase is increased, and the addition of N is facilitated. In other words, it is very effective for stably adding N (that is, not producing casting defects due to N). Therefore, it is necessary to increase Mn in the N-containing steel, but if it is added over 10.0%, the corrosion resistance is deteriorated. On the other hand, if it is 5.0% or less, a sufficient effect cannot be obtained. % And 10.0% or less. Desirably, it is more than 5.0% and 7.0% or less.
[0012]
Ni is an austenite-forming element like Mn, and is effective for obtaining an austenite structure after solution treatment. If the amount is less than 1.0%, a sufficient effect cannot be obtained. On the other hand, if the amount exceeds 7.0%, the austenite phase becomes too stable, and the processing-induced martensite transformation hardly occurs. Since it becomes difficult to obtain, it was set to 1.0 to 7.0%. Desirably, 2.0 to 7.0% is good.
Cr is an important element having an effect of improving corrosion resistance, particularly pitting corrosion resistance, by forming a passive film. If it is less than 12.0%, sufficient corrosion resistance cannot be obtained. On the other hand, if it is added in excess of 18.0%, delta ferrite is likely to be formed, and the corrosion resistance and hot workability are deteriorated. 0.0%.
[0013]
Mo is an element that is very effective for enhancing the corrosion resistance by strengthening the passive film, and it is desirable to add it when importance is attached to the corrosion resistance. W is also effective for enhancing the corrosion resistance like Mo, but the effect of W alone is small, and when W is added, a part of Mo is equivalent to W (1/2 W corresponds to equivalent Mo) It is desirable to add in the form of replacing with. If added over 3.0%, delta ferrite is generated, and not only the corrosion resistance is deteriorated, but also hot workability and cold forgeability are deteriorated.
[0014]
Cu is an element effective for enhancing corrosion resistance when added in a small amount, and has the effect of improving the cold workability by reducing the work hardening index of the austenite phase. It is desirable to add to. If hot addition exceeds 2.0%, the hot workability tends to deteriorate, so Cu was made 2.0% or less.
N is an element that is very effective for increasing the hardness and increasing the corrosion resistance while dissolving in the austenite phase and the martensite phase. 0.0 less than 5% and no sufficient effect is obtained, whereas, when added in excess of 0.15%, from degrading the productivity and impair the integrity of the steel ingot, 0.0 5% 0.15%. A desirable range of N is 0.05 to 0.12%.
[0015]
V, Ti and Nb do not necessarily need to be added, but are effective elements to refine the crystal grains and improve the hardness and ductility by forming primary carbides, and one or more are required Add as appropriate. Among these, one or more types are added in total, and if added in excess of 0.2%, coarse primary carbides are formed, and cold workability is impaired. It should be 2% or less.
[0016]
B, Mg, Ca, and Al are not necessarily added, but by forming oxides and sulfides, S and O segregated at the grain boundaries are reduced, and hot workability is improved. It is effective, and 1 type, or 2 or more types is added as needed. Even if one or more of B, Mg, Ca, and Al are added in total exceeding 0.10%, a further improvement effect cannot be obtained. Since the hot workability and the cold workability are impaired, it is preferable that one or more of B, Mg, Ca, and Al be 0.10% or less in total.
Further, P, which is an impurity element, is not particularly specified as long as it is a level mixed in a normal melting process, and is not particularly specified, but is preferably lower in terms of corrosion resistance.
The steel of the present invention does not achieve the desired high hardness only by satisfying the above component ranges, and generates work-induced martensite by applying cold working such as cold rolling, cold drawing, cold forging, etc. It is necessary to let If the work-induced martensite phase is less than 30% in volume ratio, sufficient high hardness cannot be obtained. Therefore, the volume ratio of the work-induced martensite phase is set to 30% or more.
[0017]
The steel of the present invention can obtain high hardness by applying cold working. By generating a desired amount of processing-induced martensite by appropriate cold processing, the Vickers hardness can be set to 500 or more.
In addition, the steel of the present invention can be subjected to aging treatment at 400 to 600 ° C. after cold working, if necessary, in order to improve ductility, spring characteristics, etc. without reducing the hardness.
[0018]
【Example】
Hereinafter, the present invention will be described based on examples. Steel having chemical components shown in Table 1 was melted by vacuum melting to obtain a 10 kg steel ingot. Here, Steel No. Nos. 1 , 4, 6 , 9, and 14 are steels of the present invention in which the composition, A value, B value, and work induced martensite phase amount after cold working are all within the limited range of the present invention. Nos. 31 to 35 are comparative steels having a composition, A value, B value, work-induced martensite phase amount after cold working, or some of them being out of the limited range of the present invention, No. 31-35. 36 Ri kind SUS420J2 der conventional quenched and tempered steel, otherwise Ru Reference Example der. No. 1 to 35 steel was made into a plate having a thickness of 2 mm by hot forging and hot rolling, heated to 1050 ° C., and then subjected to air cooling solid solution treatment. Then, cold rolling was performed at a reduction rate of 50 to 70%. No. The 36 steel was quenched from 950 ° C. and then tempered at 300 ° C.
[0019]
The amount of work-induced martensite phase was measured by an X-ray diffraction method. About hardness, it calculated | required by measuring Vickers hardness in the longitudinal cross-section of the cold-rolled board. About corrosion resistance, the salt spray test by 5% salt water of 35 degreeC prescribed | regulated to JISZ2371 was done for 100 hours, and it evaluated by the presence or absence of rusting. These results are shown in Table 2. Here, with respect to the presence or absence of rusting by the corrosion resistance test, those that did not rust were marked with ○, and those that rusted were marked with ×.
Reference Example No. 2. Invention steel No. 2 4 and conventional steel no. For 36, a corrosion resistance test was conducted in 5% sulfuric acid, 20% nitric acid, 20% hydrochloric acid, and 20% sodium hydroxide solution at 50 ° C., and the weight loss after the test was measured to evaluate the corrosion resistance in an aqueous solution. .
[0020]
[Table 1]
[0021]
[Table 2]
[0022]
[Table 3]
[0023]
As can be seen from Table 2, steel No. 1 of the present invention. 1 , 4, 6 , 9, and 14 all show a high hardness of 500 or more after the Vickers hardness after cold working. In addition, it can be seen that the steel of the present invention does not show rusting by the salt spray test and has high hardness and good corrosion resistance.
On the other hand, comparative steel No. 1 in which any one or more of the composition, the A value, the B value, and the work-induced martensite phase amount after cold working deviate from the range defined in the present invention. 31-35 and conventional steel No. No. 36 shows that one or more characteristics of hardness and corrosion resistance by salt spray are worse than the steel of the present invention.
In particular, the comparative steel no. Nos. 32-34 have low hardness, and high hardness cannot be obtained. In addition, comparative steel no. No. 31 is rusted and has insufficient corrosion resistance.
[0024]
FIG. 1 shows a comparison of the corrosion resistance of the steel of the present invention and conventional steel in sulfuric acid, nitric acid, hydrochloric acid, and sodium hydroxide solutions. FIG. 1 shows that the steel of the present invention has smaller corrosion weight loss after immersion in various acid and alkaline aqueous solutions than that of conventional steel, and is superior in corrosion resistance to various acid and alkaline aqueous solutions.
In Table 3, Reference Example No. 2. Invention steel No. 2 4 shows the room temperature tensile properties of the solution treatment state before cold working, but the steel of the present invention has a low Vickers hardness of 300 or less in the solution treatment state, and shows a large value of elongation and drawing. This shows that the steel of the present invention has good cold workability and is easy to cold form.
[0025]
【The invention's effect】
As described above, the high hardness and high corrosion resistance stainless steel of the present invention has high hardness and excellent corrosion resistance. Therefore, members and parts that require both high hardness and corrosion resistance, such as leaf springs, coil springs, and flappers. When used for blades such as valves, metal gaskets, razor blades, etc., the service life is improved, and there is a remarkable industrial effect.
[Brief description of the drawings]
FIG. 1 is a diagram showing corrosion resistance.

Claims (4)

By weight%, C 0.01 to 0.10%, Si 3.0% or less, Mn 5.0% to 10.0% or less, Ni 1.0 to 7.0%, Cr 12.0 to 18.0%, one or two of Mo or W are Mo + 1 / 2W of 3.0% or less (including 0%), Cu 2.0% or less (including 0%), N 0.05 to 0.15%, the balance consists of Fe and inevitable impurities, and the A value represented by the formula (1) is 23.58 to 27 , the B value represented by the formula (2) is 25.15 or more, A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase in an austenite phase of 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among the selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among the selected elements) By weight%, C 0.01 to 0.10%, Si less than 1.0%, Mn over 5.0% and 7.0% or less, Ni 2.0 to 7.0%, Cr 12.0 ˜18.0%, one or two of Mo or W are Mo + 1 / 2W, 1.0 to 3.0%, Cu 2.0% or less (including 0%), N 0.05 to 0.00. 15%, the balance is Fe and inevitable impurities, and the A value represented by the formula (1) is 23.58 to 27 , the B value represented by the formula (2) is 25.15 or more, and the austenite phase A high-hardness, high-corrosion-resistant stainless steel characterized by containing a work-induced martensite phase at 30% or more by volume.
A = Ni + 0.65Cr + 0.98Mo + 0.49W + 1.05Mn + 0.35Si + Cu + 12.6 (C + N) ………… (1)
(However, calculation is made assuming that no additive element is selected among the selected elements)
B = Cr + 3.3Mo + 1.65W + Cu + 30N (2)
(However, calculation is made assuming that no additive element is selected among the selected elements) A high-hardness, high-corrosion-resistant stainless steel characterized by containing one or more of V, Ti, and Nb in a total of 0.2% or less in the steel composition according to claim 1 or 2 . A high-hardness, high-corrosion-resistant stainless steel characterized in that the steel composition according to any one of claims 1 to 3 contains one or more of B, Mg, Ca, and Al in total of 0.10% or less. steel.