CS274196B1 - Valve seat for internal combustion engines and method of its thermal treatment - Google Patents

Abstract

The goal of the solution is to create the valve seat that is characterized by good thermal stability and resistance against corrosion, optimal resistance against wear and high frame stability while at the same time minimizing the production costs. The goal is achieved by the fact that the seat is made of the material, with the maximal content of sulphur up to 0.10 percent by weight that is formed by the combination of the following elements:3.20 up to 3.80 percent by weight of carbon2.20 up to 3.80 percent by weight of silicon0.60 up to 1.00 percent by weight of manganese0.30 up to 0.60 percent by weight of phosphor1.10 up to 1.60 percent by weight of chrome0.30 up to 0.60 percent by weight of nickel1.10 up to 1.60 percent by weight of molybdenum0.60 up to 1.00 percent by weight of copper0.10 up to 0.30 percent by weight of vanadiumthe rest is iron.The cast pieces of the valve seats are heated up to the temperature between 550 and 580 degrees C; they are exposed to this temperature for the duration of 90 minutes, whereupon they are freely air-cooled.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the material composition of the intake and exhaust valve seats of internal combustion engines operating preferably on unleaded petrol and to a method for their thermal treatment.

The prior art valve seats of internal combustion engines intended for unleaded fuel combustion are made of steel powders which forge at high temperatures in precision dies in an inert gas environment. The disadvantage of this technology is its complexity, which consists in the production of powders of various components, the high cost and labor of precision dies, the consumption of inert gases and electric energy needed for remelting steel and the mechanical or thermal process of producing forging powders. Further, valve seats of internal combustion engines for the combustion of unleaded petrol are known, made of special gray cast iron, in which tungsten is used as an alloy to increase the wear resistance. A disadvantage of this type of chemical composition of the valve seat material is that tungsten, which affects the formation of supercooled graphite, forms tungsten carbide, which negatively affects the machinability of the seat surfaces and, at the same time, due to the graphite shape does not fully provide the desired lubricating properties. In addition, increased surface hardness above 40 HRc due to draining or lower tempering adversely affects the machinability of the valve seat surface and at the same time imposes higher quality requirements on the cutting tools. Among the other materials used to produce valve seats for unleaded gasoline internal combustion engines, special cast iron 3 is known to have a carbon content of greater than 3.8% by weight, which is used as an alloying element of tin as compared to the prior art. The disadvantage of these materials is higher production costs and, moreover, with an increased carbon content above 3.8% by weight. eliminates an increased amount of free graphite during the casting process, which, while partially beneficially affects wear resistance, on the other hand, reduces the strength of the base metal mass and hence the impact resistance, which is extremely undesirable in terms of valve seat function.

Said disadvantages of the prior art materials are eliminated by a combustion engine seat, preferably for unleaded petrol and made of special gray cast iron, with a maximum sulfur content of up to 0.1% by weight, in that the chemical composition of its material is a combination of the following elements :

3.20 to 3.80 wt. carbon

2.20 to 3.80 wt. silicon

0.60 to 100% wt. of manganese

0.30 to 0.60 wt. phosphorus

1.10 to 1.60 wt. of chromium

0.30 to 0.60 wt. nickel

1.10 to 1.60% weight. molybdenum

0.60 to 1.00 wt. copper

0.10 to 0.30 wt. Vanadium remainder iron.

The valve seat casting is then heated to a temperature of 550 to 580 ° C, which is left at this temperature for a period of 90 minutes, followed by free cooling in air.

By using valve seats in internal combustion engines operating preferably on unleaded petrol, which are made of special gray cast iron with the above chemical composition and subsequently tempered at 550-580 ° C to a surface hardness of 31-39 HRc, their very good thermal stability is achieved and corrosion resistance, as well as optimum wear resistance at the same time high impact strength values, and thus a significant increase in their overall service life. Due to a suitable chemical composition, lamellar graphite is formed in the seat casting, which positively affects the lubrication properties of the seating surfaces of the valve seats. Simultaneously, production is simplified and production costs are minimized due to improved machinability of the castings, and also because some of the alloys such as chromium are the accompanying element of most feedstock materials at the desired low concentration and therefore can be used to produce valve seats and metal waste.

The intake and exhaust valve seats of the present invention, which are particularly intended for use in unleaded gasoline internal combustion engines, are made of a special gray cast iron having the following chemical composition:

CS 274 196 B1

3.20 to 3.80% wt. carbon 2.20 to 3.30% wt. silicon 0.60 to 1.00% wt. of manganese 0.40 to 0.60% wt. phosphorus max 0.10 wt. open 1.10 to 1.60% wt. of chromium 0.30 to 0.60% wt. nickel 1.10 to 1.60% wt. molybdenum 0.60 to 1.00% wt. copper 0.10 to 0.30% wt. vanadium residue iron.

Valve seats are manufactured by casting the above-mentioned special gray cast iron, not melted in an electric induction furnace and cast into sand molds produced by higher specific pressures. The casting arrangement may be a Christmas tree and an inlet shaft guided through the center of the mold. The hardness of the castings after casting is 40 to 48 HSc.

In order to achieve optimum material properties, ie microstructure and machinability of castings, valve seats are tempered in chamber or other furnaces with precise temperature control. The tempering takes place in such a way that after the castings have been heated to a temperature of 550 to 580 ° C, the valve seats are left at this temperature for a period of 90 minutes, followed by free cooling of the castings in air. The hardness of the castings after tempering should be 31-39 HRc. The obtained structure is mixed, acicular, martensitic-beinitic-sorbitic. Steadite and carbides are evenly distributed in a sieve shape. The shape of the graphite is fine, lamellar, slightly supercooled and increases the lubricating ability of the seating surfaces of the valve seats.

EXAMPLE 1.

For the spark-ignition engine intake and exhaust valves for unleaded petrol operation, a batch of 6 500 valve seats and the following chemical composition of the material was produced:

carbon ... 3.80 % wt. silicon ... 2.74 % wt. manganese ... 0.61 % wt. phosphorus 0.43 % wt. sulfur • · · 0.03 % wt. chrome * · · 1, 28 % wt. nickel • · · 0.37 % wt. molybdenum ... 1, 16 % wt. currency «· · 0.76 % wt. vanadium • · ♦ 0.16 % wt. iron • .. residue.

The measured surface hardness after casting ranged from 42 to 47 HRc. After tempering at about 570 ° C for 90 minutes, the surface hardness decreased to 34-38 HRc. These valve seats were fitted with combustion engines of test cars, which showed almost no wear when dismantled after 120,000 km.

EXAMPLE II.

For the intake and exhaust valves of spark-ignition internal combustion engines a batch of 6,500 seats with the following chemical composition of the material was produced:

carbon ... 3.51 wt.

Silicon ... 2.30 wt.

CS 274 196 Bl

manganese phosphorus ... 0.70 wt. ... 0.40 wt. sulfur ... 0.05 wt. chrome ... 1.12 wt. nickel ... 0.58 wt. molybdenum ... 1.58 wt. currency ... 0.62 wt. vanadium ... 0.20 wt. iron ... the rest.

The measured surface hardness after casting was between 41 and 47 HRc. The tempering was carried out at a temperature of about 575 ° C for 90 minutes and the surface hardness decreased to 32-37 HRc.

EXAMPLE III.

For the intake of 6,500 carbon silicon manganese phosphorus sulfur chromium nickel molybdenum copper vanadium iron and gasoline engine exhaust valves a batch of saddles of the following chemical composition was produced:

3.80% wt.

2.80% wt. 0.90% wt. 0.55 wt. 0.09 wt.% 1.59 wt. 0.35% wt. 1.20% wt. 0.95 wt. 0.25 wt. residue.

The measured surface hardness after casting was between 42 and 48 HRc. Tempering was performed at a temperature of about 555 ° C for 90 minutes and the surface hardness dropped to 34-39 HRc.

The valve seats produced according to the invention can be used in all types of internal combustion engines and preferably in particular in internal combustion engines intended for operation on unleaded petrol. These valve seats have very good thermal stability, corrosion resistance, high impact strength and low degree of wear and show a very long service life.

Claims (2)

SUBJECT OF THE INVENTION 1.10 to 1.60% 0.60 to 1.00% 0.10 to 0.30% wt. carbon mass silicon mass. Manganese mass phosphorus mass. chromium nickel wt. molybdenum mass copper mass. vanadium iron. CS 274 196, 4 1.10 to 1.60% 0.30 to 0.60% Valve seat of internal combustion engines, preferably for the combustion of unleaded petrol, made of special gray cast iron with a maximum sulfur content of up to 0,10% by weight, characterized in that the chemical composition of its material consists of a combination of the following elements: 3.20 to 3.8% 2.20 to 3.30% 0.60 to 1.00% 0.30 to 0.60% 2. A method of heat treating a valve seat according to claim 1, wherein the valve seat cast is heated to a temperature of 550 to 560 [deg.] C. and maintained at that temperature for a period of 90 minutes, followed by free cooling in air.