HK1020360A1 - Use of a steel for cutting tool holders - Google Patents

Abstract

The invention relates to a steel containing in weight-%: 0.3-0.5 C, from traces to max. 1.5 Si, 0.2-1.5 Mn, max. 0.03 P, preferably max. 0.025 P, 0.01-0.2 S, 4-7 Cr, from traces to max. 1 Ni, 0.5-2.0 Mo, which can completely or partly be replaced by the double amount W, from traces to max. 1 Co, 0.2-1.5 V, from traces to max. 0.5 Nb, from traces to a total of max. 0.2 % of rare earth metals, balance essentially iron, impurities and accessory elements in normal amounts, as a material for cutting tool holders.

Description

Application of steel on tool fixture

The invention relates to the use of a steel having a specific composition for use as a material for a tool holder.

A tool holder is a component to which or in which a tool tip is attached, wherein the tool tip is the actual working part during machining. The tool body and the drill rod are typical tool holders with cemented carbide components for efficient machining. The material used for such tool holders is typically a steel known in the art as holder steel. The fixture steel should meet a variety of requirements:

tool holders, such as tool bodies and drill rods, often have complex profiles and the most significant machining of the tool holders is performed while the steel is in a soft annealed condition. However, the steel used must be capable of air-hardening and not undergo significant dimensional changes during the quenching process.

Some tool holders are hardened and tempered, while the surface thereof to which the cemented carbide inserts are attached is induction hardened. Therefore, the material used must be induction hardenable.

The machining rate of machining by cutting is increasing, which makes the tool holder very hot. Therefore, the material must have good high temperature hardness.

Some types of tool holders, such as certain drill rods with cemented carbide drill bits joined by brazing, are subjected to PVD (physical vapor deposition) plating after quenching so as not to wear the drill bit helix on the drill rod during the drilling and cutting process. Thus, the material must be capable of PVD plating without a significant reduction in hardness.

Some types of tool holders, such as tool bodies, are subjected to high pulsating loads during use. Therefore, the material must have good mechanical properties, including good toughness and fatigue strength.

Many types of tool holders have complex profiles. There are often fine threaded holes and long, fine drilled holes. Therefore, the material should have excellent machinability, especially when high speed steel tools are used.

Low alloy tool steels or medium alloy tool steels are used as tool holder materials. The following table lists the compositions of several typical steels for fixtures. The steel contains only iron, impurities and incidental elements other than the elements in weight% shown in the table. None of the known clamp steels is entirely satisfactory for meeting the above specified requirements.

Reference steel	C	Si	Mn	S	Cr	Ni	Mo	V
									1	0.52	0.3	0.8	Up to 0.035	1.0	-	-	1.15
2	0.42	0.3	0.8	Up to 0.035	1.0	-	-	-
									3	1.0	1.5	0.8	At most 0.020	1.0	-	-	-
4	0.45	0.28	0.64	0.012	0.8	1.8	0.25	-
									5	0.55	0.28	0.75	0.023	0.93	0.10	-	0.015
6	0.51	0.30	0.39	0.002	0.94	2.95	0.25	-
									7	0.40	0.27	0.81	-	0.90	0.16	-	-
8	0.50	1.12	1.0	0.001	3.10	-	0.88	0.49
									9	0.36	0.22	0.77	0.013	1.1	0.10	0.17	-

The present invention provides an alloy steel which can be used as a material for tool holders, which more satisfactorily meets the requirements than prior art steels. The composition of the steel is given in the appended claims. The invention also relates to a tool holder made of said steel.

The roles of the individual elements and their interactions will be explained below. All percentages, when referring to the chemical composition of the steel, refer to% by weight.

Carbon should be present in an amount of at least 0.3%, preferably at least 0.35%, suitably at least 0.37% in order to obtain a satisfactory hardness and strength of the steel. The carbon content should not exceed 0.5%, preferably not exceed 0.45%, and a suitable amount is not exceed 0.41%. When the carbon content is higher, the steel becomes too hard and brittle. Typically the steel contains 0.39% C.

Silicon, which may be present in amounts from traces up to 1.5%, but preferably the steel should contain at least 0.40% silicon. The silicon in the steel is in solid solution but may also be present as silicon-calcium oxide, which is in turn preferably modified with sulphur to form sulphides covering said oxides to render them substantially plastic, wherein said inclusions act as a lubricating film during machining of said steel. Preferably, the steel should not contain more than 1.2% Si. The preferred range of Si content is 0.7% to 0.9% or 0.6% to 0.8%. A typical (nominal) Si content is 0.7%.

Manganese, the content of which should be at least 0.2%, in order to improve the temper resistance of the steel and, when the steel contains more sulphur, to prevent hot shortness of the steel by the formation of manganese sulphides. However, the steel should not contain more than 1.5% manganese, preferably at most 1.0% manganese. The particularly preferable manganese content is 0.3 to 0.5%, and the most preferable manganese content is 0.4%.

Sulphur, which should be present in an amount of at least 0.01%, in order to impart sufficient machinability to the steel. The maximum S content in the steel should not exceed 0.2%. If the sulphur content is higher, there is a risk of hot shortness occurring, which cannot be completely compensated by a corresponding increase in the manganese content. Preferably, the maximum S content in the steel should not exceed 0.05%. The preferable sulfur content is 0.01-0.03%. A typical (nominal) sulphur content is 0.02%.

The content of chromium in the steel is between 4 and 7 percent so as to endow the steel with good hardenability. Preferably 4.5-5.5% of chromium; typically 5.0% chromium.

Nickel, which is not an important element in the steel, but is allowed to be present at most 1%, preferably at most 0.5%.

Molybdenum, which improves the hardenability as well as the temper resistance of the steel and thereby its hot hardness, whereby the molybdenum content should be at least 0.5%; at most 2.0%. The preferable content of molybdenum is 1.2%, and the preferable range is 1.2-1.6%. Typically, the steel contains 1.4% molybdenum. In principle, molybdenum can be replaced completely or partially with twice the content of tungsten. However, tungsten is an expensive alloying element, and it also complicates the processing of scrap steel recovery. Therefore, tungsten contents exceeding the contents identified as impurities should be avoided.

Cobalt should not be present in the steel for the same reasons as tungsten, but may be tolerated up to 1.0% cobalt, preferably up to 0.05%.

Vanadium, which contributes to the temper resistance and wear strength of the steel, should be present in the steel in an amount of at least 0.2% but not more than 1.5%. Preferably, the content of vanadium is between 0.6 and 1.3 percent, and the proper range is between 0.8 and 1.1 percent; typical vanadium content is 0.95%.

The steel may also contain effective amounts of oxygen and calcium, more particularly 50 to 100ppm oxygen and 5 to 75ppm calcium, to interact to form calcium oxide, which may be modified by sulfur, as previously described.

Niobium, which forms insoluble primary carbonitrides, should not exceed a content of 0.5%. Preferably, the niobium content should not exceed the level of impurities. Titanium, zirconium, aluminum and other strong carbide and/or nitride forming elements are also undesirable impurities and therefore their content should not exceed impurity levels.

Rare earth elements such as cerium, lanthanum and other rare earth elements may also be added to the steel to give the steel isotropic properties, desirable machinability, excellent mechanical properties and good hot workability. The total content of rare earth metals may be at most 0.4%, preferably at most 0.2%.

The nominal (typical) composition is as follows: 0.37-0.41C, 0.40-1.20 Si,0.30-0.50 Mn, up to 0.025P, 0.010-0.030S, 5.00-5.30 Cr, up to 0.25 Ni,1.25-1.50 Mo, up to 0.20W, up to 0.20 Co, 0.90-1.00V, up to 0.005 Ti, up to 0.030 Nb, up to 0.25 Cu, up to 0.020 Al,5-50ppm Ca,60-90ppm O, and the balance iron.

The steel is quench hardened from an austenitizing temperature between 860 ℃ and 1100 ℃, preferably between 960 ℃ and 1050 ℃, wherein the quenching temperature is selected within the temperature range according to the required hardness. When the steel is quenched at a temperature in the low temperature section between 960-1050 ℃, particularly at 960 ℃ or slightly higher, a hardness of 48HRC may be obtained before tempering; if the steel is quenched at a temperature in the high temperature range between 960-1050 c, i.e. at 1050 c or close to 1050 c, a hardness of 54HRC may be obtained before tempering. The tempering treatment can be performed at a low temperature of 180-250 ℃ or at a high temperature of 550-600 ℃ to obtain high hardness and excellent toughness. The figure shows a typical tempering curve for a steel according to the invention after quenching at different temperatures between 960-1025 ℃.

The invention is explained in more detail below with reference to the experiments carried out.

Steels with multiple heats of the composition of table 1 were refined. The content of each element in the given composition refers to the average of the measurements at different points in the ingot produced. In table 1, the composition of comparative material SS2242 is also included. The content of the comparative material is a nominal content. The contents of phosphorus, sulfur, aluminum, nitrogen, calcium and oxygen are not mentioned. For all materials, the remaining amounts are iron and normal amounts of impurities, except for the impurities or incidental elements mentioned in the table.

The results of the machinability tests performed on the material in the soft annealed condition are also shown in table 1. The values shown refer to the peripheral speed (average) of the drill bit at which the drill bit is rotated so that the drill bit can reach a total drilling length of 1000mm before wearing out. The table also shows the number of holes that can be drilled by rotating the drill bit at a rate of 30 meters/minute before the bit wears out.

TABLE 1

	Composition in weight%
															Heat of furnace	C	Si	Mn	P	S	Cr	Mo	V	Al	N	Ca	0ppm	Drilling V using high speed steel drill bit1000Per minute of rice	At VcNumber of drilled holes of =30 m/min
Comparative steel	.39	1.0	.40		.0007	5.3	1.3	.9			.0000	4	27	24
															DV42700	.39	1.03	.40	.017	.022	5.2	1.3	.9	.007	.021	.002	35	31	224
DV42858	.41	.90	.43	.016	.023	5.1	1.3	.9	.001	.025	.0005	22	34	＞800
															DV42954	.44	.98	.40	.016	.027	5.2	1.3	.9	.001	.033	.0006	15	30	80
DV43521	.44	.45	.41	.014	.026	5.2	1.3	1.0	.016	.029	.002	31	47	＞800
															DV43734	.36	.48	.39	.015	.026	5.4	1.3	.94	.011	.023	.009	109	42	＞800
DV44136	.41	.62	.42	.017	.029	5.2	1.3	1.0	.018	.019	.003	75	39	＞800
															DV44569	.40	.43	.41	.015	.031	5.5	1.3	1.0	.005	.022	.007	57	39	＞800
DV44610	.40	.70	.39	.014	.024	5.2	1.3	1.0	.005	.020	.009	74	39	＞800

Claims (19)

1. Use of a steel as a material for a tool holder, wherein the steel contains (in weight%):

0.3-0.5C, from traces up to 1.5 Si,0.2-1.5 Mn, up to 0.03P, 0.01-0.2S, 4-7 Cr, from traces up to 1 Ni,0.5-2.0 Mo, which may be completely or partially substituted by twice the W content, from traces up to 1 Co, 0.2-1.5V, from traces up to 0.5 Nb, with a total content from traces up to 0.2% rare earth metals, the balance essentially normal amounts of iron, impurities and incidental elements.

2. Use according to claim 1, wherein the steel contains at most 0.025 phosphorus.

3. Use according to claim 1, wherein the steel contains 0.35-0.45 carbon.

4. Use according to claim 3, wherein the steel contains 0.37-0.41 carbon.

5. Use according to claim 1, wherein the steel contains 0.4-1.2 silicon.

6. Use according to claim 5, wherein the steel contains 0.7-0.9 silicon.

7. Use according to claim 5, wherein the steel contains 0.6-0.8 Si.

8. Use according to claim 1, wherein the steel contains 0.2-1.0 manganese.

9. Use according to claim 8, wherein the steel contains 0.3-0.5 manganese.

10. Use according to claim 1, wherein the steel contains 0.01-0.05 sulphur.

11. Use according to claim 1, wherein the steel contains 0.01-0.03 sulphur.

12. Use according to claim 1, wherein the steel contains 4.5 to 5.5 chromium.

13. Use according to claim 1, wherein the steel contains 1-2 molybdenum.

14. Use according to claim 13, wherein the steel contains 1.2-1.6 molybdenum.

15. Use according to claim 1, wherein the steel contains 0.6 to 1.3 vanadium.

16. Use according to claim 1, wherein the steel contains 0.8-1.1 vanadium.

17. Use according to claim 1, wherein the steel contains 50-100ppm oxygen and 5-75ppm calcium.

18. Use according to claim 1, wherein the steel contains a total content of rare earth metals of at most 0.4%.

19. Tool holder made of steel having a composition according to any one of the preceding claims.