JP3566162B2 - Hot tool steel with excellent weldability - Google Patents

Description

【００２１】
【表２】

【００２２】
【表３】

【００２３】
【発明の効果】
以上述べたように、本発明により溶接性に優れ、肉盛溶接工数を削減することによる低コストで高寿命な肉盛補強金型の製造を可能にせしめた金型用鋼を提供することが出来る極めて優れた効果を奏するものである。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hot work tool steel having excellent weldability used for a hot working mold.
[0002]
[Prior art]
Conventionally, SKD61, SKT4 and their improved steels have been used for hot forging dies, extrusion dies and the like. When these are used, they are often subjected to surface treatment by nitriding, PVD, CVD or the like for the purpose of imparting wear resistance. However, although the surface modified layer is hard but very brittle, cracking and chipping are likely to occur, causing large cracks in the mold, and conversely, shortening the mold life.
[0003]
On the other hand, Fe-based alloys, Co-based alloys, Ni-based alloys and the like, which are excellent in heat resistance and wear resistance, are provided only on the entire surface of the mold of SKD61, SKT4 or their improved steels or only in the parts where the mold is severely worn. A method has been used to improve the life of the mold by overlay welding of overlay welding material and overlay welding powder material. However, since these conventional steels have a large C content, the conventional steel has a large C content. Due to rapid heating and quenching after welding, the shape near the weld becomes partially quenched, so that it becomes hardened and brittle, causing weld cracking. In addition, a high residual stress is generated in the heat-affected zone (HAZ) by welding, which may cause cracks during use as a forging die. Furthermore, in order to form a metallurgical layer which connects the mold base material and the overlay material to be used originally, it is necessary to perform underlay welding as a cushioning material.
[0004]
[Problems to be solved by the invention]
In the conventional mold steel as described above, there is a high risk of welding cracks. Further, the need for underlay welding results in poor adhesion strength, and high welding man-hours and welding costs. In addition, in the case where overlay welding is performed on a part of the mold, it is necessary to grind the mold base material extra for performing the underlay welding, and there is a problem that processing time and cost are increased.
[0005]
[Means for Solving the Problems]
In order to solve the conventional problems as described above, the present inventors have intensively developed and as a result, by performing appropriate component design, the crack of the mold base material during welding is suppressed, and A tool steel excellent in weldability that enables direct welding of a target welding material to a mold base material without requiring welding. In addition, since it is assumed that a material excellent in heat resistance, wear resistance, or toughness is welded in advance before use as a mold, the mold base material must have excessive hardness and wear resistance. It is unnecessary, and the component design is made with emphasis on toughness to suppress mold cracking and heat check.
[0006]
The gist of the invention is that
(1) By weight%, C: 0.10 to 0.30%, Si: less than 0.5% , Mn: 1.0% or less, Cr: 1.0 to 3.0%, V: 0.2 0.6%, Nb: 0.01 to 0.10% , one or two of Mo and W containing 0.2 to 2.0% by Mo equivalent (Mo + 1 / 2W), and the balance of Fe and A hot work tool steel excellent in weldability, characterized in that steel consisting of unavoidable impurities is tempered at 500 ° C. or higher to have a hardness of 36 to 42 HRC and to be used as a pre-hardened steel.
[0007]
(2) One or two types of Ni: 0.3 to 1.1% and Co: 0.2 to 1.0% are further added to the component composition described in the above (1). Hot tool steel with excellent weldability.
(3) S: 0.10% or less, P: 0.030% or less, Pb: 0.030 to 0.20%, Te: 0 in addition to the component composition described in the above (1) to ( 2 ). One or two or more of 0.010 to 0.050%, Ca: 0.0003 to 0.020%, Bi: 0.005 to 0.10%, Se: 0.010 to 0.10% were added. A hot work tool steel with excellent weldability, characterized in that:
[0008]
(4) Welding wherein the component composition described in (1) to ( 3 ) above is further reduced to Al: 0.05% or less, O: 0.0050% or less, and N: 0.050% or less. In hot work tool steel with excellent heat resistance .
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail. First, the reasons for limiting the component composition according to the present invention will be described.
C: 0.10 to 0.30%
C is an element for imparting sufficient matrix hardness by quenching and tempering and imparting necessary strength to a mold. However, if it is less than 0.1%, the strength required for the mold is not obtained, and the mold is deformed, and the hardness of 36 to 42 HRC when used in pre-hardened cannot be obtained, and exceeds 0.3%. In addition, lower weldability is required during welding, and a lower slab is required at the time of welding. When pre-hardened, it is combined with a carbide-forming element, resulting in a hardness exceeding 42 HRC, which makes molding difficult. However, in order to maintain the weldability at a higher level, it is desirable that the content be 0.10% or more and less than 0.25%.
[0010]
Si: 1.0% or less Si is added as a deoxidizing agent and is effective in oxidation resistance and hardenability, and suppresses agglomeration of carbides during tempering to promote secondary hardening. However, if added excessively, the weldability is reduced, and the toughness and heat check resistance are also reduced. Therefore, the content is set to 1.0% or less, preferably less than 0.5%.
Mn: 1.0% or less Mn, like Si, is an element that increases the cleanliness of steel and enhances hardenability as a deoxidizing agent. In addition, it combines with S to improve machinability. If it exceeds 1.0%, the weldability and toughness are reduced. Therefore, the upper limit is set to 1.0% or less.
[0011]
Cr: 1.0 to 3.0%
Cr forms a solid solution in the matrix to enhance hardenability, and forms fine carbides during tempering to secure hardness. However, if the content is less than 1.0%, no effect can be obtained, and if it exceeds 2.5%, carbides are aggregated and the toughness is reduced. Therefore, the range was set to 1.0 to 3.0%. In addition, 1.0% or more and less than 2.6% are more preferable.
[0012]
V: 0.2-0.6%
V forms stable carbides, contributes to hardness, increases tempering softening resistance, has a large effect of refining crystal grains, and improves toughness. In particular, it is effective in suppressing the coarsening of the crystal grains in the heat-affected zone (HAZ) in overlay welding, maintaining the toughness of the HAZ at a high level, and suppressing welding cracks. Further, it is effective in suppressing cracks from HAZ during use as a mold. If it is less than 0.2%, the above-mentioned hardening is small, and if it exceeds 0.6%, toughness is reduced due to aggregation of carbides. In addition, it is preferably set to 0.3 to 0.6%.
[0013]
One or two of Mo and W are Mo equivalent (Mo + 1 / 2W) at 0.2 to 2.0% Mo and W form fine carbides, contribute to secondary hardening, and improve softening resistance. Mo is an element that improves heat check resistance, and the effect of Mo is twice that of W. If the Mo equivalent (Mo + 1 / 2W) is less than 0.2%, the effect is insufficient, and if the Mo equivalent is 2.0% or more, the toughness is reduced. Therefore, the range is set to 0.2 to 2.0%.
[0014]
Nb: 0.01 to 0.10%
Nb forms stable carbides, contributes to hardness, increases tempering softening resistance, and has a large crystal grain refining effect to improve toughness. In particular, it is effective in suppressing the coarsening of the crystal grains in the heat-affected zone (HAZ) in overlay welding, maintaining the toughness of the HAZ at a high level, and suppressing welding cracks. Further, it is effective in suppressing cracks from HAZ during use as a mold. The effect is larger than that of V, and the addition of 0.01% or more is effective, and when it exceeds 0.10%, the toughness is reduced.
[0015]
Ni: 0.3 to 1.1%
Ni is an element that increases the toughness of the matrix itself. However, if it is less than 0.3%, there is no effect, and if it exceeds 1.1%, the effect is saturated. Therefore, the range was set to 0.3 to 1.1%.
Co: 0.2-1.0%
Co suppresses agglomeration and coarsening of carbides due to tempering and enhances softening resistance. To obtain these effects, 0.2% is required, and if added over 1.0%, toughness is reduced. Therefore, the range is set to 0.2 to 1.0%.
[0016]
S: 0.10% or less S is an element that combines with Mn to impart machinability. It is added as needed, but if added in excess of 0.10%, toughness, hot workability and heat check resistance are reduced. Therefore, the upper limit is set to 0.10%.
P: 0.030% or less P is an element that improves machinability. However, if the content is small, the effect cannot be obtained, and if added in too large a quantity, the toughness is reduced, and the weldability important for the present invention is reduced. Therefore, the upper limit is set to 0.030%.
[0017]
Pb: 0.030 to 0.20%, Te: 0.010 to 0.050%, Ca: 0.0003 to 0.020%, Bi: 0.005 to 0.10%, Se: 0.010 to 10% One or more of 0.10% of Pb, Te, Ca, Bi, and Se are elements that improve machinability. However, if the content is small, the above effects cannot be obtained. Conversely, if the content is large, the toughness and heat check resistance are reduced, and ground flaws are caused.
[0018]
Al: 0.05% or less Al is added as a deoxidizing agent. If added in excess, the toughness decreases, so the upper limit is made 0.05%.
O: 0.0050% or less When O is excessively present in steel, it forms a coarse oxide and lowers toughness and machinability, so the upper limit is made 0.0050%.
N: 0.050% or less If N is excessively present in steel, the weldability is reduced, so the upper limit is made 0.0050%.
[0019]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples.
The steel of the present invention shown in Table 1 was tapped in a 100 kg vacuum induction melting furnace, cast into an ingot having an average diameter of 200 mm, and forged to obtain a test material. For the weldability test as each characteristic test, the welding material was overlay-welded to the groove of a test piece having a square of 50 mm x 100 mm under the welding conditions shown in Table 2, and then the cross section of the test piece weld was Observed.
As for the mechanical properties, a mechanical property evaluation method was used. For toughness, a Charpy impact test using a 2 mm-U notch test piece (with a test piece hardness of 42 HRC), and for softening resistance, at 600 ° C. Hardness after holding for 30 hours and air cooling (initial hardness: 42 HRC) Further, as for machinability, the flank wear width of the end mill when the 40 HRC material was cut by 3 m with an end mill was determined. Table 3 shows the results. As shown in Table 3, neither the present invention steel test materials A to G had no cracks in the welding test, toughness, relative to have excellent softening resistance, either is H, the I and comparative steels It is also found that cracks occur and the toughness and the softening resistance are inferior. Further, it is understood that the steel of the present invention has machinability equal to or higher than that of the comparative steel.
[0020]
[Table 1]

[0021]
[Table 2]

[0022]
[Table 3]

[0023]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a mold steel excellent in weldability and capable of manufacturing a low-cost, long-life overlay reinforcing mold by reducing the number of overlay welding steps. This is an extremely excellent effect that can be achieved.

Claims (4)

In weight percent,
C: 0.10 to 0.30%,
Si: less than 0.5%,
Mn: 1.0% or less,
Cr: 1.0 to 3.0%,
V: 0.2-0.6%,
Nb: 0.01 to 0.10%
By tempering a steel containing one or two of Mo and W in a Mo equivalent (Mo + 1 / 2W) of 0.2 to 2.0% and a balance of Fe and unavoidable impurities at 500 ° C. or more, A hot work tool steel excellent in weldability, characterized in that its hardness is 36 to 42 HRC and used in pre-hardened . Excellent weldability characterized by further adding one or two types of Ni: 0.3 to 1.1% and Co: 0.2 to 1.0% to the component composition according to claim 1. Hot tool steel. The component composition according to claim 1 or 2, further comprising:
S: 0.10% or less,
P: 0.030% or less,
Pb: 0.030 to 0.20%,
Te: 0.010 to 0.050%,
Ca: 0.0003-0.020%,
Bi: 0.005 to 0.10%,
Se: 0.010 to 0.10%
A hot work tool steel excellent in weldability, characterized by adding one or more of the following. 4. A hot weld excellent in weldability, characterized by further comprising Al: 0.05% or less, O: 0.0050% or less, and N: 0.050% or less in the component composition according to claim 1. Tool steel.