JPH03180447A - Drill steel - Google Patents

Abstract

PURPOSE:To obtain the drill steel excellent in wear resistance and toughness by specifying the compsn. of C, Si, Mn, Cr, Mo, W, V, Nb, Co and Fe and their compositional relationship. CONSTITUTION:The steel is a one for drills constituted of, by weight, 0.70 to 1.20% C, 0.30 to 1.50% Si, <=1.0% Mn, 3.0 to 6.0% Cr, 5.0 to 10.0% Mo, 1.0 to 9.0% W, 0.5 to 1.25% V, 0.5 to 1.0% Nb, 5.0 to 12.0% Co and the balance Fe with impurities inevitable in steel making as well as satisfying 0.8 to 1.5 Nb/V ratio, in which the kinds and amounts of carbides in the steel are suitably regulated to improve the wear resistance and toughness of a high speed steel. By using the steel, the machining service life of a material hard to work such as a stainless steel for drills or the like can remarkably be improved.

Description

[Detailed description of the invention]

[Industrial Field of Application J] The present invention relates to a drill steel suitable for drilling in materials that are difficult to machine, such as mainly stainless steel. [Prior art] 5KH51 is commonly used as steel for drills, but when machining sticky and highly work-hardened work materials such as stainless steel, it has poor chip crushability and low cutting temperatures. This causes an increase in L height and cutting resistance, which significantly deteriorates machining life. Conventionally, Co-based high-speed steel such as JIS 5KH56 or 5KH59 has been selected as the drill steel used for cutting such difficult-to-process materials.

[Problem to be Solved by the Invention J] The lifespan of a drill is caused by wear, chipping, breakage, etc. of the cutting edge, but the lifespan also changes depending on the machining process. Drilling machines with relatively low rigidity have large drill runout, and even drills using conventional Co-based high-speed steel,
There is a limit to its lifespan. The chipping and wear of the drill cutting edge are affected by the wear resistance and toughness of the drill steel, and it is essential to improve these IIM properties. The present invention relates to a drill steel that has improved wear resistance and toughness over conventional Co-based high-speed steels such as 5KH56 and 5KH59. EMeans and actions for solving the problemJ Generally, the wear resistance of high-speed steel depends on the hardness of the matrix and the type and amount of carbides present in the steel. In particular, the influence of hard carbide remaining after quenching is large, and it is particularly determined by the main component VW. However, some of the MC carbides are dissolved in the solid solution during quenching and distributed to the matrix, so in order to actually form a large amount of &IC carbides, it was necessary to increase the amount of ■ and at the same time increase the CI. Such a method causes the agglomeration and coarsening of MC carbides, leaving a large amount of MC carbides during quenching, but on the other hand, it reduces the C and VNk of the matrix, making it impossible to obtain sufficient secondary hardening through tempering. As a result of reducing the hardness, there is a limit to the improvement of wear resistance and toughness. The present inventors added Nb to form stable undissolved NbC carbide as a means of controlling the base hardness and residual carbide after heat treatment, and at the same time, the Nb/V It was discovered that by keeping the ratio within an appropriate range, it was possible to improve the wear resistance and toughness by facilitating the solid solution of C1 into the matrix. That is, the steel of the present invention has C: 0.70 to 0.70 in ILKt%.
1.20%, Si: 0.30-1.50%, 14
n: 1.0% or less, Cr: 3.0-6.0%, Mo
: 5.0~10.0%, W+1.0~9.0%,
■20, 5~! , 25%, Nb: 0.5-1.0%, (
:o:5.0-12. [1%, the balance is steel containing iron and impurities inevitable in steelmaking, and the Nb/V ratio is 0.
It is steel for drills that satisfies 8 to 1.5. Next, the reasons for limiting the alloy elements constituting the steel of the present invention will be described below. C: Cr, Mo, W, V, Nb7. , Contains at least 0.7% or more of C-C, which is necessary for base reinforcement of drill steel and NbC formation. Excess C of 1.2% or more
Since this impairs workability and toughness, the upper limit is set at 1.2%. Si: It is effective as a deoxidizing agent in steel manufacturing, and at the same time improves strength and softening resistance, but addition of a large amount impairs hot and cold workability, so the range is limited to 0.3 to 1.5%. do. Like Mn:Si, Mn is added as a deoxidizer on 5J14, but since it has little effect on improving wear resistance and toughness, its range is set to 1.0% or less. C": Mainly forms L3Cs carbide, and during quenching, most of it dissolves in the base, strengthening the base and increasing high temperature strength. Cr also has the effect of increasing hardenability. At least 433% Above 6% is necessary, and above 6% has no merits in terms of characteristics or economy, so the range should be reduced to 3%.
~6%. Mo: Increases the resistance to tempering and softening, and also increases the secondary effect, thereby imparting wear resistance. 6 Mo: 5.0% or more to obtain the hardness required for drill steel. However, if 10% or more, rod-shaped coarse M and C carbides are formed and the hardenability is deteriorated, so the optimum component range is set to 5.
．． 0 to 10.0%. W: Like Mo, increases temper hardening ability and softening resistance, and imparts heat resistance. At the same time, it mainly forms &+6C type carbides and provides wear resistance. If it is less than 1%, the effect will be small, and if it is more than 9%, hot workability will be impaired and M
, which causes coarsening of C-type carbides and impairs hardenability and toughness, so the range is set to 1.0 to 9.0%. V: A strong jl carbide-forming element in high-speed steel. If there are many additives, a large amount remains as undissolved residual carbide during quenching, which contributes to wear resistance. Also, V is
6 The Vl of the steel of the present invention, which contributes to secondary tempering hardening, is kept within a range that leaves almost no undissolved residual carbide after quenching, that is, within a range necessary for secondary tempering. VO15%
Below, the amount of carbide precipitated by tempering is small, so it is not possible to obtain a hardness of IIR (: 65 or higher) required for steel for drilling. At 1.25% or more, the undissolved residual coarse carbides are formed, and the grinding This range is set to 0.5, as it becomes a factor that inhibits sex.
~1.25%. Nb: Most of Nb forms stable and hard NbC carbide and does not dissolve into the matrix during quenching heating, improving wear resistance, which is one of the objectives of the present invention. On the other hand, the fine distribution has the effect of inhibiting the coarsening of crystal grains, thereby improving toughness. Below 0.3%, the effect is only 7f.
If it is less than 1.0%, the hardenability and ultimate hardness will be lowered, and at the same time, NbC carbides will become coarser, so the range is set to 0.3 to 1.0%. It has been found that the best relationship between wear resistance and toughness is given when the Nb/V ratio is 0.8 to 1.5%. Below .8,
As shown in the examples in Table 2 and the effects in Table 3, the toughness and cutting durability are reduced, and if the Nb/V ratio exceeds 1.5 and is added to the machine, the heat treatment hardness is insufficient and the jizz resistance is reduced. The Nb/V ratio should be 0.8 to 1.0 because wear resistance and cutting durability decrease.
It was limited to a range of 5. Co: Fully solid solution in the base, has the effect of strengthening the base and increasing the softening resistance, and has resistance to the upper temperature limit of the tool.In order to make the above effect effective, the Co content must be at least 65.0%. need to be added. The more Co there is, the more remarkable the effect is, but 1
Addition of 2.0% or more reduces hot and cold elongation, impairs workability, and is expensive, impairing economic efficiency, so it is set at 12.0% or less. [Example] Table 1 shows a 50 kg steel ingot produced in a vacuum melting furnace and forged. The chemical composition of the present invention steel and Hisame steel, which were made into φ20 round steel after rolling, are shown. Table 2 shows the quenching and tempering depth, austenite grain size, and bending fracture due to three-point bending load when φ20 test steel was heat-treated at a quenching temperature of 1200°C and annealing temperature of 560'Cx lH three times. The mating material S (1g
415, a friction speed of 0.24 m/sec, a friction distance of F' of 400 m, and a final load of 12.6 g. As shown in Table 2, the steel of the present invention has a hardness of HRC 65 or higher, which is required for drill steel, and has superior toughness and wear resistance to the comparative steel. Table 3 shows a φ6 straight drill made from the sample steel.
The cutting conditions that show the cutting durability when drilling with a drilling machine are: rotation speed 745r, p, m,
Cutting speed 14m/win, feed 0.15m*/"f!
V, the hole depth was 20 m5 + a through hole, and water-soluble cutting oil was used. The work material is 5tlS304. HB185
It's for you. Table 3 [Effect 1] According to the steel of the present invention, it is possible to obtain improvements in wear resistance and toughness that are necessary for steel for drills, so it can significantly improve the cutting life of difficult-to-process materials such as stainless steel. be able to.

Claims (1)

[Claims] (1) In weight%, C: 0.70-1.20%, Si: 0
．． 30-1.50%, Mn: 1.0% or less, Cr: 3.
0-6.0%, Mo: 5.0-10.0%, W: 1.0
~9.0%, V: 0.5~1.25%, Nb: 0.5~
1.0%, Co: 5.0 to 12.0%, and the remainder contains iron and impurities inevitable in steelmaking, and the steel for drilling has a Nb/V ratio of 0.8 to 1.5.