JP2009299095A - Steel sheet to be subjected to dehydrogenation treatment, electroplated steel sheet member, and method for manufacturing electroplated steel sheet member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet to be subjected to dehydrogenation treatment, which can be tempered even in a temperature range in which the dehydrogenation treatment is conducted while maintaining its desired toughness, has a superior workability before being quenched and is superior in balance between strength and toughness after having been tempered and quenched. <P>SOLUTION: The steel sheet to be subjected to the dehydrogenation treatment has a chemical composition including 0.30 to 0.47% C, 0.20% or less Si, 0.30 to 1.0% Mn, 0.015% or less P, 0.02% or less S, 0.002 to 0.030% Ti, 0.05 to 0.50% Cr, 0.050% or less Al, 0.0070% or less N, further including such B as to satisfy the expressions (1): (11/14)×N<SP>*</SP>+0.0005≤B≤(11/14)×N<SP>*</SP>+0.0050, and the expression (2): N<SP>*</SP>=max[N-(14/48)×Ti, 0], wherein B, N and Ti in each expression represent contents (unit: mass%) of the respective elements; and max[ ] represents a function of returning the maximum value of an argument in [ ], and the balance Fe with impurities. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a steel sheet for dehydrogenation used in applications where dehydrogenation treatment is performed for the purpose of suppressing hydrogen embrittlement caused by plating treatment, pickling treatment, and the like, and the steel sheet for dehydrogenation treatment as a raw material. The present invention relates to an electroplated steel plate member and a method for producing the electroplated steel plate member.

  High carbon steel sheets such as S50C to S60C, which are carbon steel materials for machine structures, are formed into the desired shape and then subjected to quenching treatment for increasing strength, and subsequently tempering treatment to ensure toughness. Is tempered to a predetermined hardness to obtain a steel plate member. Conventionally, steel sheet members made of these steel types have been used for applications in which the hardness after tempering has an HRC of about 40, and thus it has been possible to ensure a level of toughness that has no practical problem.

  On the other hand, a steel sheet member having higher strength than before has been demanded due to the recent increasing needs for weight reduction. Therefore, it is conceivable to improve the strength by using these existing steel types, for example, to increase the strength by a method of lowering the tempering temperature or shortening the tempering time. However, such a method is not practical because it significantly deteriorates the toughness of the steel plate member. In addition, it is conceivable to increase the strength of the steel sheet member by adding a large amount of alloy elements, but this increases the strength of the steel sheet before quenching and deteriorates the workability. I can't say that.

  On the other hand, some inventions relating to steel sheets used for the purpose of quenching and tempering in place of such existing steel types have been proposed. For example, Patent Documents 1 to 3 disclose inventions related to high carbon steel sheets having excellent characteristics.

  By the way, the high-strength steel plate member obtained by forming these high carbon steel plates into a predetermined shape is an electroplated steel plate member whose surface is subjected to electroplating such as Cr plating for the purpose of improving corrosion resistance. May be used. In this case, pickling is performed as a pretreatment for electroplating, and in some cases, another electroplating is performed as a base treatment for electroplating. For example, Ni plating is performed as a ground treatment for Cr plating.

Such an electroplated steel sheet member is obtained by, for example, punching a steel sheet → barrel polishing → quenching process → tempering process (usually over 400 ° C.) → pickling → electroplating process → dehydrogenation process (usually baking at 180 to 250 ° C. Manufacturing), the manufacturing cost increases. However, until now, it has been considered difficult to reduce the manufacturing cost of the electroplated steel sheet member by simplifying the manufacturing process of the electroplated steel sheet member, and thus it has not been particularly studied.
Japanese Patent Laid-Open No. 10-251757 JP 2001-81528 A Japanese Patent Laid-Open No. 2001-220642

  The present invention has been made in view of such a current situation, and is excellent in workability before quenching and strength-toughness balance after quenching and tempering, and is provided with a tempering function in the dehydrogenation treatment step so as to be independently tempered. A steel plate for dehydrogenation that can be omitted, and electroplating manufactured using this steel plate for dehydrogenation as a raw material, and omitting the tempering step that was performed separately from the dehydrogenation step It is providing the steel plate member and the manufacturing method of this electroplated steel plate member.

  As described above, the dehydrogenation treatment performed as a measure against hydrogen embrittlement when electroplating or pickling is performed after quenching is usually performed in a low temperature range of 180 to 250 ° C. On the other hand, the tempering process in the prior art is performed in a high temperature range slightly exceeding 400 ° C. in order to avoid a temperature range in which temper embrittlement occurs. For this reason, in the prior art, providing a tempering function in the dehydrogenation process has not been studied at all.

However, if it becomes possible to provide a tempering function in the dehydrogenation process, equipment and manufacturing costs related to the tempering process can be reduced, and the effect is great.
Therefore, as a result of intensive investigations on chemical compositions that can ensure sufficient toughness even when tempering is performed in a temperature range where dehydrogenation is performed, the inventors have found knowledge (1) to (5) listed below. To complete the present invention.

(1) Tempering brittleness is caused by the grain boundary segregation of P. However, inclusion of B causes B to segregate at the grain boundary in preference to P, thereby suppressing P grain boundary segregation. Therefore, by containing B, sufficient toughness can be ensured even by a tempering process in a low temperature region equivalent to the dehydrogenation process.

(2) By containing B, if the tempering treatment temperature can be set to a low temperature range equivalent to that of the dehydrogenation treatment, it is possible to suppress a decrease in strength due to tempering. Therefore, it becomes possible to reduce the content of C that has been contained so far in order to ensure a predetermined strength after the tempering treatment.

(3) Moreover, since B also has the effect | action which improves hardenability, it becomes possible to compensate for the hardenability fall accompanying reduction of C content by containing B.

(4) Furthermore, since B has the above-described effects due to its extremely small content, there is no increase in strength of the steel sheet before quenching. Therefore, by reducing the C content, the strength of the steel plate before quenching can be reduced, and the workability of the steel plate before quenching can be improved.

(5) B grain boundary segregation suppression and hardenability improvement by B are brought about by B in a solid solution state. For this reason, in order to enable a tempering process in a low temperature region equivalent to the dehydrogenation process and to secure a predetermined hardenability, the lower limit of the B content is contained according to the Ti and N contents in addition to containing Ti. It is necessary to determine On the other hand, if B is contained excessively, manufacturability is hindered, so it is necessary to define the upper limit of the B content. From the above viewpoint, the B content (%) satisfies the following formulas (1) and (2). In the present specification, “%” relating to the composition means “mass%” unless otherwise specified.

^{(11/14) × N * + 0.0005} ≦ B ≦ (11/14) × N * +0.0050 ··· (1)
N ^* = max [N− (14/48) × Ti, 0] (2)

  Here, B, N, and Ti in each formula represent the content (unit: mass%) of each element, and max [] is a function that returns the maximum value of arguments in [].

  In the present invention, C: 0.30% to 0.47%, Si: 0.20% or less, Mn: 0.30% to 1.0%, P: 0.015% or less, S: 0.00. 02% or less, Ti: 0.002% to 0.030%, Cr: 0.05% to 0.50%, sol. Al: 0.050% or less and N: 0.0070% or less, further containing B satisfying the following formulas (1) and (2), the balance having a chemical composition consisting of Fe and impurities Is a steel sheet for dehydrogenation treatment.

^{(11/14) × N * + 0.0005} ≦ B ≦ (11/14) × N * +0.0050 ··· (1)
N ^* = max [N− (14/48) × Ti, 0] (2)

  Here, B, N, and Ti in each formula represent the content (unit: mass%) of each element, and max [] represents a function that returns the maximum value of the arguments in [].

  In the steel sheet for dehydrogenation treatment according to the present invention, the tempering treatment that has been conventionally performed in a high temperature range of, for example, over 400 ° C. is performed in a low temperature range of, for example, 180 ° C. or more and 250 ° C. or less in which the dehydrogenation treatment is performed. Can do.

  In the steel sheet for dehydrogenation treatment according to the present invention, the chemical composition contains (a) Cu: 0.15% or less in place of part of Fe, and / or (b) Ni: 0.15. % Or less, Mo: 0.30% or less, and Nb: 0.030% or less, preferably 1 type or 2 types or more selected from the group consisting of.

  From another viewpoint, the present invention is an electroplated steel plate member provided with an electroplating layer on the surface of the steel plate member, wherein the steel plate member has the chemical composition of the steel sheet for dehydrogenation treatment according to the present invention described above. The electroplated steel plate member.

  From another point of view, the present invention forms the steel sheet for dehydrogenation according to the present invention described above into a steel plate member, and performs electroplating without performing a tempering treatment after performing a quenching treatment on the steel plate member, Next, a method for producing an electroplated steel sheet member, wherein dehydrogenation is performed.

  According to the steel sheet for dehydrogenation treatment according to the present invention, a tempering effect that ensures a desired toughness can be obtained even in a dehydrogenation process performed in a low temperature range of, for example, 180 ° C. or more and 250 ° C. or less. Therefore, according to the present invention, the balance between workability before quenching treatment and strength and toughness after quenching and tempering treatment is excellent, and the tempering treatment step that has been performed separately from the conventional dehydrogenation treatment step can be omitted. A steel sheet for dehydrogenation treatment can be provided. Moreover, while using this steel plate for dehydrogenation as a raw material, the electroplating steel plate member manufactured by omitting the tempering process step performed in a separate process from the dehydrogenation processing step, and the production of this electroplating steel plate member A method can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail. First, the reason for limiting the chemical composition of the steel sheet for dehydrogenation treatment according to the present invention will be described.

C: 0.30% or more and 0.47% or less C significantly affects the strength (hardness) of the steel sheet member after quenching and tempering and the strength of the steel sheet before quenching. The C content is set to 0.30% or more in order to secure a cross-sectional hardness of 45 or more in the plate thickness center portion of the steel plate member as the final product by HRC. On the other hand, if the C content exceeds 0.47%, the strength of the steel plate before the quenching treatment becomes high, and it becomes difficult to form into a steel plate member to be subjected to the quenching treatment, and the steel plate member that is the final product is sufficient It becomes difficult to ensure toughness. Therefore, the C content is set to 0.30% or more and 0.47% or less.

Si: 0.20% or less Si is an element contained in steel as an impurity, but is also an element effective as a deoxidizer, and may be added as necessary. On the other hand, Si is a solid solution strengthening element, and if it is contained in excess, the strength of the steel sheet before quenching increases, and it becomes difficult to form a steel sheet member to be subjected to quenching. Therefore, the Si content is 0.20% or less.

Mn: 0.30% or more and 1.0% or less Mn is an element that is effective as a deoxidizer and is also an element that is effective in increasing the quenching depth during the quenching process and increasing the curing depth. In order to obtain this effect, the Mn content is set to 0.30% or more. On the other hand, when the Mn content exceeds 1.0%, the Ar ₃ point is remarkably lowered, leading to a coarsening of the austenite grain size during quenching, degrading the toughness of the steel plate member after quenching, and the steel plate before quenching This increases the strength of the steel sheet and makes it difficult to form a steel sheet member for quenching. Therefore, the Mn content is set to 0.30% or more and 1.0% or less.

P: 0.015% or less P is an important element in the present invention. P tends to segregate at the austenite grain boundaries, thereby increasing the strength fluctuation in the steel sheet or reducing the grain boundary strength to greatly deteriorate the toughness. For this reason, the smaller the P content, the better. However, in the present invention, B is contained as will be described later. Among these B, B in a solid solution state which does not form BN by combining with N is austenite grains in preference to P during the quenching treatment. Segregates in the boundary and suppresses P grain boundary segregation. Therefore, the upper limit of the P content is relaxed by containing B. In the present invention, good toughness can be secured by setting the P content to 0.015% or less.

S: 0.02% or less S combines with Mn to form MnS to deteriorate the workability of the steel sheet and significantly deteriorate the toughness. Therefore, the smaller the S content, the better. Preferably it is 0.01% or less.

Ti: 0.002% or more and 0.030% or less Ti binds to N in a higher temperature range than B and has a function of fixing N as TiN. Therefore, the amount of B consumed by combining with N It is an element effective in reducing the amount and ensuring effective B. Therefore, the Ti content is set to 0.002% or more. Preferably it is 0.005% or more. However, when it contains excessively, Ti excessively couple | bonds with C and forms TiC, the intensity | strength of the steel plate before a quenching process rises, and it will become difficult to shape | mold into the steel plate member used for quenching. Further, Ti may cause deterioration of toughness and hardenability by forming carbonitride. Therefore, the Ti content is 0.030% or less. Preferably it is 0.025% or less, More preferably, it is 0.020% or less.

Cr: 0.05% or more and 0.50% or less Cr is an important element in the present invention, and, like Mn, has the effect of increasing the quenching factor at the time of quenching and increasing the curing depth. As described above, when the content of Mn is excessive, the Ar ₃ point is remarkably lowered, the austenite grain size is increased during quenching, and the toughness of the steel plate member after quenching is deteriorated. Therefore, in this invention, content of Mn is suppressed and Cr is contained actively. For this reason, the Cr content is set to 0.05% or more. On the other hand, if the Cr content exceeds 0.50%, the strength of the steel plate before quenching becomes high, making it difficult to form a steel plate member for quenching and increasing the cost. For this reason, Cr content shall be 0.05% or more and 0.50% or less.

sol. Al: 0.050% or less Al is an element contained in steel as an impurity, but it is also an effective element as a deoxidizer, and may be added as necessary. In order to obtain the deoxidation effect by Al more reliably, sol. The Al content is preferably 0.005% or more, and more preferably 0.010% or more. However, sol. When it contains Al excessively, it becomes easy to produce a surface defect, the intensity | strength of the steel plate before a quenching process rises, and it will become difficult to shape | mold into the steel plate member used for a quenching process. Therefore, sol. Al content shall be 0.050% or less. In addition, when deoxidation is performed only by Si, it is not necessary to add Al.

N: 0.0070% or less N is combined with B to form BN as described above, and reduces the effective B in a solid solution state. Therefore, the smaller the N content, the better. Preferably it is 0.0050% or less.

B: (11/14) × N ^* + 0.0005 ≦ B ≦ (11/14) × N ^* + 0.0050
B is the most important element in the present invention, and has the effect of increasing the quenching factor during quenching and increasing the depth of curing. The effect of improving hardenability by B is brought about by effective B in a solid solution state (hereinafter also referred to as “B ^* ”), and B which forms BN by combining with N contributes to the improvement of hardenability. do not do. Therefore, in order to obtain a predetermined hardness in the steel plate member, B is contained so as to satisfy the following formulas (3) and (4). On the other hand, when the B content is excessive, cracks at the slab stage and narrowing during hot rolling are likely to occur, and problems such as difficulty in production appear. For this reason, B content is made to satisfy following formula (3) and formula (5).

N ^* = max [N− (14/48) × Ti, 0] (3)
B ≧ (11/14) × N ^* + 0.0005 (4)
B ≦ (11/14) × N ^* + 0.0050 (5)

  Here, N and B in each formula represent the content (unit: mass%) of each element, and max [] is a function that returns the maximum value of arguments in [].

  Furthermore, since the steel sheet for dehydrogenation treatment according to the present invention may contain Cu, Ni, Mo, and Nb as optional additive elements, these will also be described.

Cu: 0.15% or less Cu has an action of suppressing peracid washing during pickling and stabilizing the surface state after pickling, and may be contained as necessary. On the other hand, if it is contained excessively, the strength of the steel plate before the quenching treatment is increased, making it difficult to process the steel plate member to be subjected to the quenching treatment and increasing the cost. For this reason, when it contains Cu, it is preferable to make the content into 0.15% or less, and it is still more preferable to set it as 0.12% or less. On the other hand, in order to exhibit such an action more reliably, the Cu content is preferably 0.05% or more, and more preferably 0.08% or more.
One or more selected from the group consisting of Ni: 0.15% or less, Mo: 0.30% or less, and Nb: 0.030% or less. Ni is an element effective for improving toughness, and therefore necessary. You may make it contain according to it. On the other hand, if the Ni content is excessive, Ni is an expensive element, which causes a significant increase in cost, and the strength of the steel sheet before quenching increases, so that it is difficult to process the steel sheet member subjected to the quenching process. It becomes. Therefore, when Ni is contained, the content is preferably 0.15% or less, and more preferably 0.12% or less. On the other hand, in order to exhibit this toughness improving action more reliably, the Ni content is preferably 0.04% or more, and more preferably 0.06%.

  Mo is also an element effective for improving toughness, and may be contained as necessary. On the other hand, when it contains excessively, the intensity | strength of the steel plate before a quenching process will become high, and the process to the steel plate member used for a quenching process will become difficult, and the increase in cost will also be caused. Therefore, when Mo is contained, its content is preferably 0.30% or less, and more preferably 0.28% or less. On the other hand, the Mo content is preferably 0.02% or more, and more preferably 0.05% or more, in order to exhibit this toughness improving effect more reliably.

  Furthermore, Nb has the effect of refining austenite crystal grains and improving toughness during the quenching treatment, and may therefore be included as necessary. On the other hand, if excessively contained, carbide is formed, the strength of the steel plate before quenching treatment is increased, and it becomes difficult to form into a steel plate member to be subjected to the quenching treatment, or the hardenability during the quenching treatment is reduced. To do. Therefore, when Nb is contained, the content is preferably 0.030% or less, and more preferably 0.025%. On the other hand, the Nb content is preferably 0.005% or more, and more preferably 0.010% or more, in order to exhibit this toughness improving effect more reliably.

Ni, Mo and Nb may be contained alone or in combination of two or more.
The balance other than those described above is Fe and impurities.

Use The steel sheet for dehydrogenation treatment according to the present invention contains B, thereby suppressing grain boundary segregation of P causing temper embrittlement, and is sufficient even by tempering treatment in a low temperature region equivalent to dehydrogenation treatment. It is possible to ensure toughness. For this reason, if a steel plate member is manufactured using the steel sheet for dehydrogenation processing according to the present invention as a raw material, a tempering process can be performed together with the dehydrogenation process.

  Further, the steel sheet for dehydrogenation treatment according to the present invention can improve the hardenability of the steel sheet by containing B, and can improve the strength (hardness) of the steel sheet member by low-temperature tempering called dehydrogenation treatment. As a result, the C content can be reduced, thereby reducing the strength of the steel sheet before quenching and improving workability.

  Therefore, the steel sheet for dehydrogenation treatment according to the present invention has excellent workability before quenching treatment and has an excellent strength-toughness balance after quenching treatment. In addition, a steel sheet member having good toughness can be obtained by performing a dehydrogenation treatment that also serves as a tempering treatment without performing the high-temperature tempering that has been essential in the prior art. It is possible to omit the high temperature tempering process.

  As described above, the steel sheet for dehydrogenation treatment according to the present invention is used for dehydrogenation treatment, more specifically, dehydrogenation treatment (for example, heating to 180 ° C. or more and 250 ° C. or less after quenching treatment). This is used for applications in which dehydrogenation treatment is performed. And if it is such a use, it can be applied to any use and is not limited to the use to which electroplating is performed. For example, an application in which only pickling is performed after quenching and dehydrogenation is performed thereafter is exemplified.

Example of production method of steel sheet for dehydrogenation treatment The steel sheet for dehydrogenation treatment according to the present invention has the above-described chemical composition. Therefore, if produced by a conventional method, it has excellent workability before quenching treatment and quenching. After the treatment, it is possible to obtain a steel plate member having both high strength and excellent toughness by performing a dehydrogenation treatment that also serves as tempering without performing conventional high temperature tempering. Therefore, the manufacturing method of the steel sheet for dehydrogenation processing according to the present invention is not particularly limited. Below, the suitable manufacturing method of the steel plate for dehydrogenation which concerns on this invention is illustrated.

(A) Hot rolling completion temperature: 850 ° C. or more and 910 ° C. or less When the hot rolling completion temperature exceeds 910 ° C., the scale thickness becomes too thick, and the pickling efficiency and yield decrease, and the surface quality deteriorates. Sometimes. On the other hand, when the hot rolling completion temperature is less than 850 ° C., the deformation resistance of the steel ingot or the steel slab may increase and the hot rolling itself may not be performed. Therefore, the hot rolling completion temperature is preferably 850 ° C. or more and 910 ° C. or less.

(B) Winding temperature: 550 ° C. or more and 660 ° C. or less If the coiling temperature is too low, the steel plate becomes strong, and when the hot-rolled steel plate is subjected to quenching, the workability of the steel plate before quenching deteriorates. To do. For this reason, it is preferable that winding temperature shall be 550 degreeC or more. On the other hand, if the coiling temperature is too high, the scale thickness becomes too thick, so that the pickling efficiency and the yield are lowered, and the surface quality is deteriorated. For this reason, it is preferable that winding temperature shall be 660 degrees C or less.

The dehydrogenation steel plate according to the present invention may be a hot rolled steel plate or a cold rolled steel plate.
In the case of a hot-rolled steel sheet, it may be a hot-rolled steel sheet, or a steel sheet that has been softened by hot-rolled sheet annealing. When hot-rolled sheet annealing is performed, it is preferable that the annealing temperature is 650 ° C. or more and 760 ° C. or less, and the annealing time is 0.1 hours or more and 30 hours or less. Usually, after pickling treatment and processing into a steel plate member, quenching is performed.

  In the case of a cold-rolled steel sheet, the steel sheet may be a cold-rolled steel sheet or may be a steel sheet that has been softened by annealing. Here, the hot-rolled steel sheet used for cold rolling may be a steel sheet as hot-rolled as described above, or may be a steel sheet softened by hot-rolled sheet annealing. Examples of the cold rolling rate of cold rolling include 20% or more and 70% or less. When annealing is performed, it is preferable that the annealing temperature is 650 ° C. or more and 760 ° C. or less, and the annealing time is 0.1 hours or more and 30 hours or less. Cold rolling and annealing may be repeated a plurality of times.

Steel plate member and manufacturing method thereof The steel plate member according to the present invention has the above-described chemical composition and an electroplating layer on the surface. Since the present invention is characterized in that the tempering process is also performed by the dehydrogenation process performed to remove the hydrogen that has entered the steel sheet member due to the electroplating process or the like, and thus benefits are obtained by this effect. It shows a typical use that can be done. The type of electroplating is not particularly limited, and a typical example is Cr plating.

  The electroplated steel sheet member according to the present invention is obtained by forming the above-described dehydrogenation-treated steel sheet into a steel sheet member, subjecting the steel sheet member to a quenching process, and then performing an electroplating without performing a tempering process, and then performing a dehydrogenation process. It is manufactured by applying. By using the above-mentioned steel sheet for dehydrogenation treatment, it becomes possible to provide a tempering function in the dehydrogenation treatment, so that it is possible to ensure good toughness without performing a tempering treatment separately from this dehydrogenation treatment. Because you can.

  Thus, according to the present invention, the balance between workability before quenching and strength and toughness after quenching and tempering is excellent, and tempering is performed in a dehydrogenation process performed in a low temperature range of, for example, 180 ° C. or higher and 250 ° C. or lower. A steel plate for dehydrogenation that has a function and enables the omission of a separate and independent tempering process, and the tempering process that is performed in a separate process from the dehydrogenation process while using the steel sheet for dehydrogenation as a raw material. An electroplated steel plate member manufactured by omitting the steps and a method for manufacturing the electroplated steel plate member are provided.

Furthermore, the present invention will be described more specifically with reference to examples.
Slab No. having the chemical composition shown in Table 1. 1 to 29 were heated to 1250 ° C. and hot rolled under conditions of a finishing temperature of 870 ° C. and a winding temperature of 620 ° C. to obtain a 2.6 mm thick hot rolled steel sheet. The obtained hot-rolled steel sheet was pickled and subjected to each test.

As an evaluation method, first, regarding hot-rolled steel sheets, YS, TS, and El were measured by a tensile test to evaluate mechanical properties. The tensile test was performed based on JIS Z 2241.
Next, after holding the hot-rolled steel sheet at 870 ° C. for 20 minutes, it was subjected to a quenching process in which oil quenching was performed, and further subjected to a pickling process and a Cr plating process, followed by a dehydrogenation process that was held at 200 ° C. for 4 hours. .

However, no. Since 15 to 17 are existing steel types, and remarkable deterioration of toughness was expected, tempering treatment was performed by holding at 300 ° C. for 2 hours after quenching treatment and before Cr plating treatment.
The steel sheet thus dehydrogenated was measured for the cross-sectional hardness at the central part (1 / 2t) of the plate thickness, and toughness was also evaluated by a Charpy test. The Charpy test was performed based on JIS Z 2242 by collecting test pieces in the rolling direction and the direction perpendicular to the rolling direction. The results are shown in Table 2.

  No. in Tables 1 and 2. Nos. 1 to 14 are examples of the present invention that satisfy all the conditions defined in the present invention. Nos. 15 to 17 are existing steel types (S35C, S50C, S60C in this order). 18 to 29 are comparative examples that do not satisfy the conditions defined in the present invention.

As shown in Table 2, no. In Examples 1 to 14 of the present invention, before the quenching treatment, TS is 600 MPa or less and excellent in workability, and the dehydrogenation treatment is performed even though the tempering treatment is held at 300 ° C. for 2 hours. Although the cross-sectional hardness at the center of the subsequent plate thickness is high strength of 45 or more in HRC, the Charpy impact value in the rolling direction (L direction) is 45 J / cm ² or more and excellent toughness.

In contrast, no. No. 15 has a Charpy impact value in the rolling direction (L direction) after the dehydrogenation treatment of 33.5 J / cm ² despite the tempering treatment held at 300 ° C. for 2 hours, and the toughness is poor. It is.

No. 16 and 17, TS before quenching treatment is over 600 MPa, the workability is unsatisfactory, and the rolling direction after dehydrogenation treatment is performed despite the tempering treatment being held at 300 ° C. for 2 hours ( L direction) Charpy impact values are 5.0 and 3.0 J / cm ² , and the toughness is poor.

No. In No. 18, since the Si content exceeds the upper limit of the range defined in the present invention, TS before quenching is 637 MPa, and workability is poor.
No. In No. 19, since the Mn content is below the lower limit of the range defined in the present invention, the cross-sectional hardness at the sheet thickness center after the dehydrogenation treatment was as low as 31.5.

No. In No. 20, since the Mn content exceeds the upper limit of the range defined in the present invention, TS before quenching is over 600 MPa, and workability is poor.
No. In both Nos. 21 and 22, since the P content exceeded the upper limit of the range defined in the present invention, the toughness after the dehydrogenation treatment was poor.

No. In No. 23, the S content exceeded the upper limit of the range defined in the present invention, and thus the toughness after the dehydrogenation treatment was unsatisfactory.
No. In No. 24, the Cr content exceeds the upper limit of the range defined in the present invention, so that the workability before quenching is unsatisfactory and the toughness after dehydrogenation is unsatisfactory.

No. No. 25 has poor workability before quenching because the Cu content exceeds the upper limit of the range defined in the present invention.
No. No. 26 has poor toughness because the Ti content falls below the lower limit of the range defined by the present invention and the B content falls below the lower limit of the range defined by the present invention.

  Furthermore, no. No. 27 exceeds the upper limit of the range specified by the present invention for Ti content. No. 28 exceeds the upper limit of the range specified by the present invention for the Mo content. In No. 29, the Nb content exceeds the upper limit of the range defined in the present invention, so that all have poor workability before quenching.

Claims (5)

In mass%, C: 0.30 to 0.47%, Si: 0.20% or less, Mn: 0.30 to 1.0%, P: 0.015% or less, S: 0.02% or less, Ti: 0.002-0.030%, Cr: 0.05-0.50%, sol. Al: 0.050% or less and N: 0.0070% or less, further containing B satisfying the following formulas (1) and (2), the balance having a chemical composition consisting of Fe and impurities A steel sheet for dehydrogenation treatment.
^{(11/14) × N * + 0.0005} ≦ B ≦ (11/14) × N * +0.0050 ··· (1)
N ^* = max [N− (14/48) × Ti, 0] (2)
Here, B, N, and Ti in each formula represent the content (unit: mass%) of each element, and max [] represents a function that returns the maximum value of the arguments in [].   2. The steel sheet for dehydrogenation treatment according to claim 1, wherein the chemical composition contains Cu: 0.15% or less in mass% instead of part of Fe.   The chemical composition is one or two selected from the group consisting of Ni: 0.15% or less, Mo: 0.30% or less, and Nb: 0.030% or less in mass% instead of part of Fe. The steel sheet for dehydrogenation treatment according to claim 1 or 2, comprising a seed or more.   An electroplated steel plate member having an electroplated layer on the surface of the steel plate member, wherein the steel plate member has the chemical composition according to any one of claims 1 to 3. Element.   The steel sheet for dehydrogenation according to any one of claims 1 to 3 is formed into a steel sheet member, and after the steel sheet member is subjected to quenching treatment, electroplating is performed without performing tempering treatment, A method for producing an electroplated steel sheet member, characterized by performing a dehydrogenation treatment.