JP2527606B2 - Alloy steel with excellent wear resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alloy steel having particularly excellent wear resistance, which is used for piston rings, rocker arms, pinion shafts and the like of internal combustion engines of automobiles and the like.

[Prior Art] A piston ring for an internal combustion engine is composed of a pressure ring for maintaining the airtightness of the combustion chamber and an oil ring for preparing a lubricating oil film between the piston ring and the cylinder liner. Of this piston ring,
The pressure ring is loosely fitted directly below the piston head and greatly affected by the combustion gas, and is required to have wear resistance, scuffing resistance, heat resistance and the like.

2. Description of the Related Art In recent years, as the internal combustion engine has become lighter in weight, higher in output and higher in speed, the width of the pressure ring has been actively reduced.
The reduction in width of the piston ring reduces the weight of the piston ring, stabilizes the behavior of the piston ring in the piston ring groove, and improves the consumption of lubricating oil by reducing the oil film thickness.

However, when the piston ring is made thinner in this way, the oil film thickness becomes thinner, wear increases, and the service life shortens.Therefore, cast iron rings, carbon steel, and sirichrome steel, which have been commonly used in the past, have been shortened. Or, a ring made of oil-tempered wire has become unusable. That is, it is difficult to manufacture a cast iron ring that is thin in the axial direction, and it is insufficient in terms of breakage strength.Silicone steel rings have a relatively large cross-sectional area because of their low strength at high temperatures. , Inertia is large and fluttering phenomenon is likely to occur. Therefore, recently, tool steels, spring steels and stainless steels have been used as materials for piston rings, and especially 13Cr martensitic stainless steels (0.65C-13.5Cr-0.3Mo-0.1V) as stainless steels. Has been used as a pressure ring with good results.

However, these piston rings made of martensitic stainless steel are still insufficient in terms of wear resistance and scuffing resistance when used in an engine with severe friction and wear. Also, the pressure ring gas-nitrided using martensitic stainless steel does not have sufficient strength to assemble to the piston, and if the abutment is expanded more than necessary (10T or more, actual force 11 to 13T “T: ring width ( mm) ”) There is a problem of breakage. Further, this pressure ring has a problem of insufficient performance and scuffing for an internal combustion engine having a severe requirement for scuffing resistance, and has a thin Ni-P or Ni-Co-P plating only on the sliding surface or these Pace plating is performed with hard particles (Si ₃ N ₄ ) dispersed. For this reason, in the piston ring of martensitic stainless steel, it is desired to further increase wear resistance and scuffing resistance and to extend the life of the piston ring.

Further, there is a rocker arm as a component for an internal combustion engine of an automobile or the like, which requires wear resistance similarly to a piston ring. Since the rocker arm of the engine is in contact with the cam shaft, it must have excellent wear resistance and scuffing resistance. Also,
As a matter of course, it is necessary to consider the aggression of the cam of the other component.

Further, there is a pinion shaft as a component used in a differential device of an FF vehicle or the like and required to have wear resistance. Since this pinion shaft uses a low-viscosity lubricating oil, excellent seizure resistance and wear resistance are required for parts that slide under high surface pressure conditions such as pinion gears and pinion shafts. Conventional material used (SCr415
・ Carburizing and quenching) sometimes caused problems such as seizure and large wear.

The pinion gear is made by carburizing and quenching SCr415,
Finish the inner diameter surface, which is the sliding surface with the pinion shaft,
Rz is around 6 μm. Therefore, the pinion gear and the pinion shaft are in a sliding condition of high surface pressure, an oil film is not formed on the surface convex portion, and the sliding surfaces of the pinion shaft and the pinion gear are worn by the abrading action.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-described problems of piston rings, rocker arms, and pinion shafts made of stainless steel or the like, and wear resistance of conventional martensitic stainless steels. By providing improved pressure resistance and oil ring (side rail) materials that can achieve higher output and higher speed of the internal combustion engine, the aggressiveness to the mating material is reduced and wear resistance is improved. An object is to provide a material for a rocker arm and a material for a pinion shaft having excellent seizure resistance and wear resistance.

[Means for Solving Problems] As a result of intensive studies on the wear resistance of conventional martensitic stainless steels, the present invention shows that the addition of Al is a hot work in the stage from the production of fine wires from steel ingots. Based on the idea that the wear resistance can be greatly improved without substantially reducing the workability and cold workability, the optimum content range of C, Si, Mn, Cr, etc. in relation to the Al content was examined. The present invention was completed by launching it.

That is, the alloy steel excellent in wear resistance of the present invention as the first invention is C: 0.55 to 1.10%, Si; 0.9% or less, Mn;
Contains less than 2.0%, Cr; 12 to 25%, Al; 0.05 to 1.10%,
The gist is that the balance consists of Fe and impurity elements.
Then, the second invention is further Ni; 0.2-2.0 in addition to the first invention.
%, Mo; 0.2 to 3.0%, V; 0.1 to 1.5%, Nb; 0.05 to 0.7%, C
u; 0.2 to 2.0% of one or two or more of them are contained, and the balance is Fe and impurity elements. Third
The gist of the invention is that at least the sliding surface of the first and second invention steels is subjected to a surface hardening treatment before use.

[Function] The steel of the present invention exhibits superior properties due to the inclusion of Al, because the microstructure of the steel of the first invention B in FIG. 1 is 400 times the micrograph, and the metal structure of the comparative steel in FIG. 2 is represented. 400 times micrograph, FIG. 3 is a diagram showing the relationship between the grain size and area ratio of carbides having a grain size of 2 μm or more of the present invention steel and comparative steel, and as shown in Table 1, (i) carbide-shaped spheres (Ii) Uniformization of carbide grain size (reduction of coarse carbides), (iii) A when nitriding
This is due to reasons such as an increase in nitride layer hardness due to fine precipitation of lN.

Addition of Al causes addition of other carbide forming elements (C, Cr, Mo, V, N
Unlike the addition of (b, W), a small amount of addition can significantly improve the target wear resistance and scuffing resistance, prevent increase in cylinder bore wear, and hardly deteriorate hot workability. It has excellent characteristics.

The following can be said when the above effect is applied to a piston ring in detail.

(I) Top ring (first pressure ring) FIG. 4 shows a perspective view of the top ring 10. The ring that requires the most scuff resistance as a piston ring is the Rop ring, and the required value varies greatly depending on the individual engine, but in the case of conventional 13Cr martensitic stainless steel, no gas nitriding treatment is performed. Therefore, the gas nitriding treatment is performed, or only the surface sliding on the cylinder bore is subjected to surface treatment such as hard chrome plating, thermal spraying, and Ni-P base composite plating.

The steel of the present invention, even in a quenched and tempered product, can obtain scuff resistance of 13Cr martensitic stainless steel / gas nitriding treatment, and can be used as it is. Even for an engine with a more demanding scuffing resistance, surface treatment gives a value higher than that of conventional hard chrome plating, and good results can be obtained without scuffing.

The wear resistance of conventional 13Cr martensitic stainless steel is not always sufficient, and nitriding depths of 90 μm and 120 μm have been dealt with greatly for demanding engines. However, the larger the nitriding depth, the more the ring 10
Since the assembling strength and the fatigue strength of 12 deteriorated, there was a problem that breakage occurred.

Since the steel of the present invention has improved strength, it does not cause the problem of breakage as described above even at the same nitrogen depth as the conventional one. Moreover, due to the significant improvement in wear resistance, the nitriding depth can be made shallower, the strength is further improved, the gas nitriding treatment time can be shortened, and mass production is further enabled. Further, the reduction of the wear amount can minimize the deterioration of the oil consumption performance and the blow-by gas performance due to the wear, so that the deterioration of the overall engine performance can be prevented.

(Ii) Oil cylinder The contact surface pressure of the oil ring is high due to tension, and depending on the engine, the wear is greater than that of the top ring. However, the reduction of the contact surface pressure due to wear increases the oil consumption amount, and therefore the demand for wear resistance is extremely severe. The steel of the present invention has extremely excellent wear resistance and can solve the above problems.

Fig. 5 shows a three-piece combination type oil ring 30
It is a longitudinal cross-sectional view showing the sliding state of. Reference numeral 14 is a piston, 16 is a groove of an oil ring of the piston, 18 is a cylinder bore, 20 is a side rail, and 22 is a spacer expander. In the case of the side rail 20 of the oil ring 30 of the three-piece combination type, the nitriding depth is limited to 30 to 60 μm even when the gas rail is used after the gas nitriding treatment due to the restriction of strength improvement. Therefore, in an engine that will be used for a long period of time, it is important to have scuff resistance and wear resistance in the exposed state of the base material (quenched and tempered material) due to abrasion of the nitride layer. obtain.

In the case of the oil ring, not only the sliding surface with the cylinder bore 18, but also the three-piece combination oil ring 30 is required to have wear resistance at the contact portion between the side rail 20 and the ear of the spacer expander 22, The steel of the present invention can sufficiently meet this requirement.

The steel of the present invention shows sufficient wear resistance even if used as it is, but its effect can be remarkably improved if it is further subjected to surface treatment such as nitriding, plating, and thermal spraying. The steel of the present invention is preferably subjected to heat treatment before being subjected to nitriding treatment. Examples of the heat treatment include quenching and tempering, and quenching (which also serves as tempering in the nitriding treatment). Nitriding is applied to the surface including the sliding surface, and gas nitriding, gas soft nitriding,
Any of salt bath nitriding, tuftride and ion nitriding can be applied.

Next, the reasons for limiting the chemical composition of the steel for piston rings of the present invention will be described.

C: 0.55 to 1.10% C is an element that obtains the necessary hardness during quenching and, at the same time, forms carbide to provide high strength and wear resistance.
If it is less than 0.55%, the amount of carbide produced is small and the wear resistance obtained due to the presence of carbide is poor. However, if it exceeds 1.10%, the grain size of carbides becomes large, the cylinder liner, which is the counterpart material, wears out, and cold workability into the piston ring shape becomes impossible, so the upper limit was made 1.10%.

Si; 0.9% or less Si is an element that is added as a deoxidizing element during refining and imparts heat resistance, but if added in a large amount, it impairs cold workability such as drawing, so the upper limit was made 0.9%.

Mn: 2.0% or less Like Si, Mn is an element added as a deoxidizing element during refining to increase toughness, but if added in a large amount, cold workability is impaired, so the upper limit was made 2.0%.

Cr: 12-25% Cr combines with C to form a carbide, which improves wear resistance, corrosion resistance and fabric strength, and further has the effect of increasing the hardness of the nitrided hardened layer. If the content is 12% or less, these effects, especially the improvement of wear resistance, are insufficient. Therefore, 12% or more is included. However, if a large amount of Cr is contained, the above-mentioned effect is not remarkable, and conversely, the toughness is lowered and the cold formability is impaired. Therefore, the upper limit of Cr is set to 25%.

Al: 0.05-1.10% Al dissolves in the matrix during quenching and tempering, and increases the strength of the matrix by refining the crystal grains, improving wear resistance and scuffing resistance. As described above, Al improves wear resistance and scuff resistance by spheroidizing carbides and making the grain size uniform during quenching and tempering. In addition, during the gas nitriding treatment, the solid solution of Al in the matrix was changed to Al.
Fine precipitation of N results in a significant increase in the hardness of the nitrided layer, which significantly improves wear resistance and scuff resistance, and prevents an increase in cylinder bore wear. Furthermore, it greatly improves the strength during the joint expansion test. To obtain these effects, addition of 0.05% or more is necessary, and the larger the addition amount, the larger the effect. However, even if the content is 1.10% or more, the effect becomes less remarkable, and the surface property deteriorates during hot and cold rolling due to the formation of inclusions Al ₂ O ₃ (significant decrease in strength when surface scratches remain) and hardenability.・ The upper limit was set to 1.10% because it lowers heat resistance and weakens the nitrided layer.

Ni: 0.2 to 2.0% Ni is an element that imparts corrosion resistance, toughness and hardenability, and particularly when Al with a strong ferrite forming tendency is added,
Prevents ferrite formation at high temperatures and improves hardenability and hot workability. If it is less than 0.2%, the above effect is small, so the lower limit was made 0.2%. However, if the content exceeds 2.0%, the cold workability is impaired, so the upper limit was made 2.0%.

Mo; 0.2-3.0% Mo is an element that forms carbides similarly to Cr, increases the hardness of the nitrided layer during nitriding treatment, improves wear resistance, and enhances high temperature strength. To obtain these effects, 0.2%
The above contents are required. However, if it is contained in an amount of 3.0% or more, the above-mentioned effect becomes insignificant and at the same time, the hot workability is deteriorated, so the upper limit was made 3.0%.

V; 0.10 to 1.50%, Nb; 0.05 to 0.70% V and Nb increase tempering softening resistance and high temperature strength, and at the same time refine carbide, and form nitride by nitriding treatment to form a surface layer. It is an element that increases hardness. To obtain the above effect, V; 0.10% or more, Nb; 0.0
It is necessary to contain at least 5%. However, V; 1.5% or more, N
b; If 0.70% or more is contained, the hot workability is deteriorated due to the formation of coarse eutectic carbides.
And 0.70%.

Cu; 0.2-2.0% Cu is an element that enhances the corrosion resistance and oxidation resistance of steel and strengthens the dough. To obtain this effect, it is necessary to add 0.20% or more. However, if added in excess of 2.0%, hot workability is impaired and resistance to nitriding increases, which is not preferable, so the upper limit was made 2.0 or more.

[Example] Next, the effect of the present invention will be made clear by an example comparing with the conventional steel.

(Example 1) 13Cr martensitic stainless steel as the present invention steel and conventional steel having the chemical composition shown in Table 2 was melted in an electric furnace. In Table 2, A to C steels are the first invention steel or the third invention steel, and D to O steels are the second invention steel or the fourth invention steel. Further, P steel is a conventional steel, 13Cr martensitic stainless steel, and Q steel is a conventional hard chrome plating.

The molten sample steel is cast, hot-rolled, and quenched and tempered (hardness target value Hv350-450) to obtain a wear test piece of 10 x 15.7 x 6.3 mm and a seizure test piece. It was processed into a 30 x 30 x 5 mm baking test piece for use. A wear test was conducted on the obtained wear test pieces under the following conditions.

(Abrasion test with LWF-1 abrasion tester) FC material 60 kg time 120 minutes Speed 0.3 m / sec Lubrication oil Low viscosity engine oil 1.5 cc / min supply After the test, the abrasion amount of the sliding surface was measured on the abrasion test piece. The results are shown in Table 3.

Then, another wear test piece was run in an ammonia gas stream at 530
It was heated to ~ 590 ° C and subjected to gaseous nitrogen for 5 hours or more. When the surface hardness was measured after gas nitrogen, it was Hv1000 or more. The wear test piece after the nitriding test was subjected to the wear test under the same conditions as above. The amount of wear of the sliding surface measured after the test is
It is also shown in Table 3.

Next, a seizure test piece manufactured in the same manner as the abrasion test piece was subjected to a seizure test under the following conditions, and the seizure load is also shown in Table 3.

(Seizure test using a mechanical testing laboratory type friction and wear tester) Mating material; FC load; increase by 25kg every 2 minutes until seizure occurs Speed: 1.2m / sec Lubricating oil; Low-viscosity engine oil dripping Seizure load: The load that causes the coefficient of friction to rise sharply to 0.2 or more is regarded as the seizure load. As is clear from Table 3, in the wear test, the wear depth in the case of the quenched and tempered material is 5.8 μm in comparison with the conventional material,
The steel of the present invention, A to O steel, has a thickness of 1.20 to 4.00 μm. The wear depth of the gas nitriding material is 0.2 μm to 2.00 μm for the steels A to O of the present invention, compared to 3.5 μm of the conventional material. In any case, it was confirmed that the steel of the present invention exhibits excellent wear resistance.

Further, in the seizure test, in the case of the quenching and tempering material, the seizure load is 100.0 kg of the conventional material and the steels of the present invention A to O are
Steel weighs 137.5 to 150.0 kg. The seizure load for gas nitriding material is 167.5-187.5kg, compared to 137.5kg for conventional material.
Is. In any case, it was confirmed that the steel of the present invention exhibits excellent scuff resistance.

Next, when assembling the piston ring into the groove of the piston ring, it is necessary to widen the mating opening by 10T or more, so that the assembling strength is required. Quenched and tempered materials have sufficient assembly strength, but gas nitriding materials are brittle. In the case of the conventional material, there is almost no margin at 11 to 13T, and it sometimes breaks due to variations in materials and variations in the amount of expansion, but as shown in Table 2, the steel of the present invention does not break unless it is 20T or more. Have strength.
This is a piston ring for bore diameter φ86mm (B dimension 2.0m
It is the result of the expansion test conducted for m, T size of 3.15 mm, and nitriding depth of 90 μm.

The hardness of the gas nitriding material is shown in Table 3. Compared with the conventional material of 1180, the steels of the present invention, A to G steels, are 1335 to 1450.
It was confirmed that the nitrided layer of the present invention steel has high hardness.

Also, in the case of piston rings where fatigue strength is a problem like keystone rings, there is a problem that breakage occurs especially when brittle materials such as gas nitriding materials and brittle composite plating are plated on the sliding surface with the cylinder wall. There is. Table 4 shows the results of a fatigue test conducted on the piston ring in a dilute sulfuric acid aqueous solution at a constant amplitude stress of 50 kg / mm ² .

Compared with the fatigue strength of the conventional material of 2 × 10 ⁵ , the steel of the present invention [D,
It was confirmed that the fatigue strength of [E, F, G] was significantly improved to 1 to 3 × 10 ⁶ .

Furthermore, using a displacement 2000cc inline 4-cylinder engine, 150
Table 5 shows the wear ratios of the cylinder bores when the time durability test was performed on the steel B of the present invention and the comparative steel (steel of steel B not containing Al).

Cylinder bore wear increases by 1.80 times when the area ratio of angular coarse chrome carbide is as large as 0.98 as in the comparative steel. In the present invention B steel, the chromium carbide is rounded and the area ratio of coarse carbide is as small as 0.54%, so that the cylinder bore wear does not increase to the same extent as the conventional material.

(Example 2) B, E, and J steels shown in Table 2 and SKD11 equivalent as comparative steels were used as test materials to prepare rocker arm pads for vertical engines, and then quenching was performed on the rocker arm pads. After the tempering treatment, the salt bath nitriding treatment is performed at 530 to 590 ° C for 3 hours or more, and the test is performed under the following test conditions, and the rocker arm pad wear amount and the cam wear amount are measured. Shown in the table.

Test conditions for motoring test Engine speed: 2000 rpm Test time: 200 hours Valve spring load: 150% or more (against assembly load of mass-produced engine) Lubricating oil: endurance deterioration oil Camshaft: alloy cast iron As shown in Table 7 below, the steel of the present invention shows better results than the comparative steels because the wear resistance is improved by increasing the amount of carbides and the carbide diameter is made finer (coarse It is thought that this is due to the decrease in aggressiveness to the mating material due to the decrease in carbide.

(Example 3) As test materials, C and G steels shown in Table 2 and SCr415 and SCM440 as conventional steels were used to fabricate a pinion shaft for a differential gear of an FF vehicle, and an actual vehicle test was performed on the pinion shaft. Sliding of the pinion shaft after running 50,000km under the motion condition that the pinion gears make relative motion (8-shaped turning, running with emergency tire on one wheel, running on bad road (including slippery road surface such as mud) The stepped wear depth of the moving surface is shown in FIG. With conventional materials, SCr415 and carburizing and quenching are 40 μm, SCM4
40 ・ Soft nitriding is 25 μm, and the step wear depth is large, whereas the steel of the present invention has a wear amount of 2.2 to 5 μm and a wear amount of 1/8 to 1/5
It was confirmed that it was small and had excellent wear resistance.

Regarding the seizure resistance, a seizure test using a mechanical test laboratory type abrasion tester, which is correlated with seizure in the actual vehicle running test of the differential gear, was conducted on the same test steel. Test condition is 10
At 00 rpm (1.2 m / s) under oil bath lubrication (low-viscosity lubricating oil), the load is increased by 25 kg every 2 minutes and the load at which seizure occurs (seizure load) is measured. As shown in the figure. In this test, if a seizure load of 250 kg or more, seizure does not occur even under the condition that a differential frequently occurs.
Therefore, it was confirmed that the steel of the present invention has excellent seizure resistance.

The steel of the present invention exhibits excellent wear resistance and seizure resistance because, unlike the conventional materials, the wavy precipitation formed by the carbon precipitated from the fine granular chromium carbonitride of 2 to 12 μm and the carbide on the surface by soft nitriding treatment. It is obtained by a thing (think of as grain boundary cementite).

[Advantages of the Invention] As described above, the alloy steel excellent in wear resistance of the present invention is made of the conventional martensitic stainless steel piston ring, rocker arm, pinion shaft wear resistance, scuff resistance, etc. In order to further improve the characteristics and prolong the life, 0.05 to 1.10% of Al was added, and the optimum content range of C, Si, Mn, Cr, etc. was found in relation to the Al content. In addition to improving wear resistance and scuff resistance by spheroidizing the carbide and making the particle size uniform,
By surface treatment such as gas nitriding treatment, Al dissolved in the matrix is finely precipitated as AlN to further improve wear resistance and scuff resistance. Further, the steel of the present invention has a number of excellent effects such as a great improvement in assembling strength, a high hardness, and a fatigue strength superior to that of the conventional steel.

[Brief description of drawings]

Figure 1 is a 400x micrograph showing the metallographic structure of the invention steel,
Figure 2 is a 400x photomicrograph showing the metallographic structure of comparative steels.
FIG. 3 is a diagram showing the relationship between the carbide grain size and the area ratio of the invention steel and the comparative steel, FIG. 4 is a perspective view of the pressure ring, and FIG. 5 is a longitudinal section showing the sliding state of a three-piece combination type oil ring. FIG. 6 is a view showing a stepped wear depth of a pinion shaft made of a conventional material and a steel of the present invention, and FIG. 7 is a diagram showing a seizure load of the conventional material and a steel of the present invention. 10 …… Pressure ring, 12 …… Abutment, 14 …… Piston, 18
…… Cylinder bore, 20 …… Side rail, 22 …… Spacer expander, 30 …… Oil ring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Kato 1 Toyota-cho, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Yoshio Fuwa 1, Toyota-cho, Aichi Prefecture, Toyota Motor Co., Ltd. ( 72) Inventor Hikaru Aoyagi 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Shinji Shibata, 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Company, Ltd. (72) Inventor, Yoritari Maeda Aichi 1 Toyota Town, Toyota City, Japan (56) References Japanese Patent Laid-Open No. 59-28562 (JP, A)

Claims (3)

(57) [Claims] 1. A weight ratio of C: 0.55 to 1.10%, Si: 0.9% or less,
An alloy steel with excellent wear resistance, characterized by containing Mn; 2.0% or less, Cr; 12 to 25%, Al; 0.05 to 1.10%, and the balance being Fe and impurity elements. 2. A weight ratio of C: 0.55 to 1.10%, Si: 0.9% or less,
Mn: 2.0% or less, Cr: 12-25%, Al: 0.05-1.10%, Ni: 0.2-2.0%, Mo: 0.2-3.0%, V: 0.1-1.5
%, Nb; 0.05 to 0.7%, Cu; 0.2 to 2.0%, and an alloy steel having excellent wear resistance, characterized in that the balance comprises Fe and impurity elements. 3. An alloy steel having excellent wear resistance according to claim 1 or 2, wherein at least the sliding surface is subjected to a surface hardening treatment before use.