JPH0256419B2 - - Google Patents

Description

[Detailed description of the invention]

This invention has excellent high temperature wear resistance.
The present invention relates to hot working tools made of sintered alloy steel, such as hot rolling rolls of steel wire rods and guide rollers thereof. Conventionally, as described in Japanese Patent Publication No. 57-55782, for example, in weight % (hereinafter % indicates weight %), C: 0.2 to 1.7%, Cr: 3.75 to 4.5%, V: 0.8 to 5.5%, Contains W: 1.5 to 22%, Mo: 0.5 to 8%, one or two of the following, and further contains Co: 4.2 to 17% as necessary, and the remainder is Ti carbides and nitrides with an average grain size of 1.5 μm or less are added to the base material of high-speed steel, which has a composition consisting of Fe and unavoidable impurities.
and carbonitrides (hereinafter referred to as TiC, TiN, and TiCN, respectively): 1 to 10% of one or more of the following are dispersed in a hot working tool made of a sintered alloy steel. It has been known. This conventional hot working tool is repeatedly heated and cooled, for example, the inner surface of the roll is heated to a high temperature under pressure by a running steel wire rod at approximately 1000 to 1100 degrees Celsius, while the outer surface is water-cooled. When used as a hot rolling roll for steel wire rods used under certain conditions, it exhibits excellent thermal shock resistance and no thermal cracks occur, but on the other hand, welding phenomena often occur between the wire rods and the steel wire rods. Not only does it not have sufficient abrasion resistance, but it also causes roughness on the roll surface.
The finished surface of the steel wire was also poor. Therefore, from the above-mentioned viewpoint, the inventors of the present invention have developed a method that improves the high hardness and toughness of the conventional sintered alloy steel hot working tool, as well as its excellent thermal shock resistance. As a result of research aimed at improving high-temperature wear resistance by imparting weldability, we found that TiC, TiN, and
As mentioned above, TiCN is a fine particle with an average particle size of 1.5 μm or less, but by replacing it with vanadium carbide (hereinafter referred to as VC) and TiN, and making the particle size coarser, both have an average particle size of VC: 3~15μm,
TiN: 1.5 to 5 μm, and the content ratio to the whole is VC: 1.5 to 21%, TiN: 1.1 to 19.51%, high hardness and toughness, and excellent thermal shock resistance are maintained. In this state, the weldability with hot-processed materials is significantly reduced, and as a result, excellent high-temperature wear resistance is obtained, and excellent performance is maintained over a long period of time without the occurrence of skin roughness. They obtained research results that showed that This invention was made based on the above research results, and includes: C: 0.2-1.7%, Cr: 3.75-4.5%, Mo: 0.5-8%, W: 1.5-22%, Co: 4.2-17 %, V: 0.8 to 5.5%, and the remainder is Fe and unavoidable impurities. ~21%, also TiN with average particle size: 1.5-5 μm: 1.1
This is a hot working tool made of sintered alloy steel that has excellent high-temperature wear resistance and is made of sintered alloy steel that contains ~19.51% of the following dispersedly. Next, the reason why the composition of the sintered alloy steel constituting the hot working tool of the present invention is limited as described above will be explained. A High-speed steel base (a) C The C component not only dissolves in the matrix of the high-speed steel base to strengthen it, but also combines with Cr, Mo, W, and V to form fine particles in the matrix. It has the effect of forming dispersed carbide and improving wear resistance, but if its content is less than 0.2%, the desired effect cannot be obtained, while if its content exceeds 1.7%, it has the effect of improving wear resistance. Since the toughness of the speed steel matrix decreases, its content is reduced to 0.2 to 1.7%.
It was determined that (b) Cr, Mo, W, and V These components all combine with the C component to form carbides as described above, increasing the hardness of the high-speed steel matrix and improving its wear resistance. , has the effect of solid solution in the matrix of high-speed steel base material and improves oxidation resistance, but the content of each
When Cr: less than 3.75%, Mo: less than 0.5%, W: less than 1.5%, and V: less than 0.8%, the desired effect cannot be obtained, while Cr: 4.5%, Mo: 8%,
If the content exceeds W: 22% and V: 5.5%, the toughness decreases, so the content is reduced to Cr: 3.75 to 4.5%,
Mo: 0.5-8%, W: 1.5-22%, and V: 0.8
It was set at ~5.5%. (c) Co The Co component has the effect of forming a solid solution in the matrix of high-speed steel and improving its heat resistance, but if its content is less than 4.2%, the desired effect of improving heat resistance cannot be obtained. On the other hand, even if the content exceeds 17%, no further improvement in heat resistance can be obtained, so in consideration of economic efficiency, the content was set at 4.2 to 17%. B VC and TiN (a) Content These components coexist in a uniformly dispersed form in the high-speed steel matrix and have the effect of improving the wear resistance of hot working tools, but their content but
If VC: less than 1.5% and TiN: less than 1.1%, the desired wear resistance improvement effect cannot be obtained; on the other hand, if the content exceeds VC: 21% and TiN: 19.51%,
Since the toughness decreases, the content was determined to be 1.5 to 21% for VC and 1.1 to 19.51% for TiN. (b) Average grain size As mentioned above, the average grain size of TiC, TiN, and TiCN in the sintered alloy steel that makes up conventional hot working tools is as fine as 1.5 μm or less, and in this state, hot working The occurrence of welding between the workpiece and the workpiece is unavoidable.On the other hand, in the sintered alloy steel of the hot working tool of this invention, VC and TiN are dispersed in the high-speed steel base, and the VC and TiN are By making the particles relatively coarse, there is no occurrence of welding phenomena, and the high-temperature wear resistance is significantly improved.
Therefore, the average particle size is VC: 3 μ
If the average particle size exceeds 15 μm for VC and 5 μm for TiN, the toughness will decrease and the thermal shock resistance will decrease. The average grain size is set to 3 to 15 μm for VC and 1.5 to 5 μm for TiN.
It was determined that Next, the hot working tool of the present invention will be specifically explained using examples. Example Raw material powders include Cr oxide powder with an average particle size of 1.3 μm, Mo oxide powder with an average particle size of 1.5 μm, and W with an average particle size of 1.2 μm.
Oxide powder, 1.2μm Co oxide powder, 1.5μm
V oxide powder, iron oxide powder of 1.3 μm, and carbon powder of 0.5 μm are prepared, and these raw powders are blended into a predetermined composition, mixed under normal conditions, and then lightly molded into pellets. By subjecting this molded body to co-reduction treatment under conditions of holding the temperature at 1120°C for 4 hours in a hydrogen stream, various high-speed steel powders having the compositions shown in Table 1 were obtained. However, in this high-speed steel powder, the alloy components have not sufficiently diffused into each other to form a complete alloy, and the individual powder particles are weakly bonded to each other.
When this was pulverized, it was easily pulverized to an average particle size of 6.3 μm, and then various high-speed steel powders obtained as a result were mixed with the average granules prepared separately. Diameter: 3.2μm, 6.5μm
3 types of VC powder, 14.8 μm, and
4 types: 1.0μm, 1.5μm, 2.7μm, and 4.9μm
TiN powder, the carbon powder for reducing trace amounts of oxygen contained in the high-speed steel powder and creating a micro-reducing atmosphere between the powders, and the same 1.5 μm for conventional hot rolling roll manufacturing. Using TiCN powder of the same 1.5 μm as TiC powder, these raw powders were blended into the composition shown in Table 1,
Wet mixed for 4 hours under normal conditions and dried.

[Table] After that, using a hydrostatic press, pressure molding is performed at a pressure of 3000 kg/cm ² to form a compact with dimensions of diameter: 430 mm x length: 123 mm, and this compact is vacuum-molded. The sintered body was sintered at a temperature of 1230°C for 1 hour to obtain a sintered body with a theoretical density ratio of 99.5%, and then the sintered body was sintered at a temperature of 1200°C, a pressure of 1000 atm, and a holding time of 1000 atm. :
Hot isostatic pressing (HIP) treatment was performed for 30 minutes, and finally immersed in a salt bath at a temperature of 1200℃ for 2 minutes, cooled in two stages, and further heated to a temperature of 560℃ once.
The present invention is a hot working tool which has substantially the same composition as the compounded composition and has dimensions of diameter: 330 mm × length: 95 mm by performing time-hold tempering treatment three times. Sintered alloy steel hot rolling roll (hereinafter referred to as the hot rolling roll of the present invention) 1 to 13
And conventional sintered alloy hot rolling rolls (hereinafter referred to as conventional hot rolling rolls) 1 to 3 were manufactured, respectively. Next, the Rockwell hardness (C scale) and transverse rupture strength of the various hot rolling rolls obtained as a result were measured, and the rolls were installed in a steel wire hot rolling mill, with C: 0.25% and Si: 0.25%,
Mn:

【table】

[Table] Steel material with a composition consisting of 0.4%, P: 0.04% or less, S: 0.04% or less: Rolled 3000 tons,
For the purpose of evaluating high-temperature wear resistance, the average wear depth of the roll caliber surface after rolling was measured, and for the purpose of further evaluating thermal shock resistance, the presence or absence of thermal cracks on the surface was observed. These results are shown in Table 2. From the results shown in Tables 1 and 2, hot rolling rolls 1 to 13 of the present invention are all made of sintered alloys with fine grain sizes of TiC, TiCN, and TiN dispersed in the high-speed steel base. High hardness and toughness almost equivalent to conventional hot rolling rolls 1 to 3 made of steel,
It is clear that this material has even better high-temperature impact resistance while maintaining excellent thermal shock resistance. As mentioned above, the sintered alloy steel hot working tool of the present invention has high hardness, high toughness, and excellent thermal shock resistance, and further has even better high temperature wear resistance. For example, when used as a hot rolling roll for steel wire or a hot rolling guide roll, it exhibits excellent performance over a long period of time.

Claims (1)

[Claims] 1 C: 0.2 to 1.7%, Cr: 3.75 to 4.5%, Mo: 0.5 to 8%, W: 1.5 to 22%, Co: 4.2 to 1.7%, V: 0.8 to 5.5%, Vanadium carbide having an average particle size of 3 to 15 μm: 1.5 to 15 μm in proportion to the total (weight %) of the high-speed steel substrate, with the remainder consisting of Fe and unavoidable impurities (weight %) A sintered alloy with excellent hot wear resistance characterized by being composed of a sintered alloy steel containing dispersed titanium nitride: 1.1% to 19.51%, which also has an average particle size of 1.5 to 5 μm. Steel hot working tools.