HIGH-CHROMIUM OR RUST-PROOF STEEL
High-chromium, or what is called stainless steel containing from 11 to 14 per cent chromium, was originally developed for cutlery purposes, but has in the past few years been used to a considerable extent for exhaust valves in airplane engines because of its resistance to scaling at high temperatures.
| Percentage | |
| Carbon | 0.20 to 0.40 |
| Manganese, not to exceed | 0.50 |
| Phosphorus, not to exceed | 0.035 |
| Sulphur, not to exceed | 0.035 |
| Chromium | 11.50 to 14.00 |
| Silicon, not to exceed | 0.30 |
The steel should be heated slowly and forged at a temperature above 1,750°F. preferably between 1,800 and 2,200°F. If forged at temperatures between 1,650 and 1,750°F. there is considerable danger of rupturing the steel because of its hardness at red heat. Owing to the air-hardening property of the steel, the drop-forgings should be trimmed while hot. Thin forgings should be reheated to redness before trimming, as otherwise they are liable to crack.
The forgings will be hard if they are allowed to cool in air. This hardness varies over a range of from 250 to 500 Brinell, depending on the original forging temperature.
Annealing can be done by heating to temperatures ranging from 1,290 to 1,380°F. and cooling in air or quenching in water or oil. After this treatment the forgings will have a hardness of about 200 Brinell and a tensile strength of 100,000 to 112,000 lb. per square inch. If softer forgings are desired they can be heated to a temperature of from 1,560 to 1,650°F. and cooled very slowly. Although softer the forgings will not machine as smoothly as when annealed at the lower temperature.
Hardening.—The forgings can be hardened by cooling in still air or quenching in oil or water from a temperature between 1,650 and 1,750°F.
The physical properties do not vary greatly when the carbon is within the range of composition given, or when the steel is hardened and tempered in air, oil, or water.
When used for valves the following specification of physical properties have been used:
| Yield point, pounds per square inch | 70,000 |
| Tensile strength, pounds per square inch | 90,000 |
| Elongation in 2 in., per cent | 18 |
| Reduction of area, per cent | 50 |
The usual heat treatment is to quench in oil from 1,650°F. and temper or draw at 1,100 to 1,200°F. One valve manufacturer stated that valves of this steel are hardened by heating the previously annealed valves to 1,650°F. and cooling in still air. This treatment gives a scleroscope hardness of about 50.
In addition to use in valves this steel should prove very satisfactory for shafting for water-pumps and other automobile parts subject to objectionable corrosion.
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quenched in oil from degrees Fahrenheit | 1,600 | 1,600 | 1,650 | ||||||||||||||||
| Tempered at degrees Fahrenheit | 1,160 | 1,080 | 1,100 | ||||||||||||||||
| Yield point, pounds per square inch | 78,300 | 75,000 | 91,616 | ||||||||||||||||
| Tensile strength, pounds per square inch | 104,600 | 104,250 | 123,648 | ||||||||||||||||
| Elongation in 2 in., per cent | 25.0 | 23.5 | 14.5 | ||||||||||||||||
| Reduction of area, per cent | 52.5 | 51.4 | 33.5 |
This steel can be drawn into wire, rolled into sheets and strips and drawn into seamless tubes.
Corrosion.—This steel like any other steel when distorted by cold working is more sensitive to corrosion and will rust. Rough cut surfaces will rust. Surfaces finished with a fine cut are less liable to rust. Ground and polished surfaces are practically immune to rust.
When chromium content is increased to 16 to 18 per cent and silicon is added, from 2 to 4 per cent, this steel becomes rust proof in its raw state, as soon as the outside surface is removed. It does not need to be heat-treated in any way. These compositions are both patented.
S. A. E. STANDARD STEELS
The following steel specifications are considered standard by the Society of Automotive Engineers and represents automobile practice in this country. These tables give the S. A. E. number, the composition of the steel and the heat treatment. These are referred to by letter—the heat treatments being given in detail on pages 134 to 137 in Chap. 8. It should be noted that the percentage of the different ingredients desired is the mean, or halfway between the minimum and maximum.
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Heat treatment |
|---|---|---|---|---|---|
| 1,010 | 0.05 to 0.15 | 0.30 to 0.60 | 0.045 | 0.05 | Quench at 1,500 |
| 1,020 | 0.15 to 0.25 | 0.30 to 0.60 | 0.045 | 0.05 | A or B |
| 1,025 | 0.20 to 0.30 | 0.50 to 0.80 | 0.045 | 0.05 | H |
| 1,035 | 0.30 to 0.40 | 0.50 to 0.80 | 0.045 | 0.05 | H, D or E |
| 1,045 | 0.40 to 0.50 | 0.50 to 0.80 | 0.045 | 0.05 | H, D or E |
| 1,095 | 0.90 to 1.05 | 0.25 to 0.50 | 0.040 | 0.05 | F |
| S. A. E. Specification no. | Carbon | Manganese | Phosphorus (maximum) | Sulphur |
|---|---|---|---|---|
| 1,114 | 0.08 to 0.20 | 0.30 to 0.80 | 0.12 | 0.06 to 0.12 |
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Nickel (minimum and maximum) | Heat treatment |
|---|---|---|---|---|---|---|
| 2,315 | 0.10 to 0.20 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | G, H or K |
| 2,320 | 0.15 to 0.25 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | G, H or K |
| 2,330 | 0.25 to 0.35 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | H or K |
| 2,335 | 0.30 to 0.40 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | H or K |
| 2,340 | 0.35 to 0.45 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | H or K |
| 2,345 | 0.40 to 0.50 | 0.50 to 0.80 | 0.04 | 0.045 | 3.25 to 3.75 | H or K |
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Nickel (minimum and maximum) | Chromium (minimum and maximum) | Heat treatment |
|---|---|---|---|---|---|---|---|
| 3,120 | 0.15 to 0.25 | 0.50 to 0.80 | 0.04 | 0.045 | 1.00 to 1.50 | 0.45 to 0.75* | G, H or D |
| 3,125 | 0.20 to 0.30 | 0.50 to 0.80 | 0.04 | 0.045 | 1.00 to 1.50 | 0.45 to 0.75* | H, D or E |
| 3,130 | 0.25 to 0.35 | 0.50 to 0.80 | 0.04 | 0.045 | 1.00 to 1.50 | 0.45 to 0.75* | H, D or E |
| 3,135 | 0.30 to 0.40 | 0.50 to 0 80 | 0.04 | 0.045 | 1.00 to 1.50 | 0.45 to 0 75* | H, D or E |
| 3,140 | 0.35 to 0.45 | 0.50 to 0.80 | 0.04 | 0.045 | 1.00 to 1.50 | 0.45 to 0.75* | H, D or E |
| 3,220 | 0.15 to 0.25 | 0.30 to 0.60 | 0.04 | 0.040 | 1.50 to 2.00 | 0.90 to 1.25 | G, H or D |
| 3,230 | 0.25 to 0.35 | 0.30 to 0.60 | 0.04 | 0.040 | 1.50 to 2.00 | 0.90 to 1.25 | H or D |
| 3,240 | 0.35 to 0.45 | 0.30 to 0.60 | 0.04 | 0.040 | 1.50 to 2.00 | 0.90 to 1.25 | H or D |
| 3,250 | 0.45 to 0.55 | 0.30 to 0.60 | 0.04 | 0.040 | 1.50 to 2.00 | 0.90 to 1.25 | M or Q |
| X3,315 | 0.10 to 0.20 | 0.45 to 0.75 | 0.04 | 0.040 | 2.75 to 3.25 | 0.60 to 0.95 | G |
| X3,335 | 0.30 to 0.40 | 0.45 to 0.75 | 0.04 | 0.040 | 2.75 to 3.25 | 0.60 to 0.95 | P or R |
| X3,350 | 0.45 to 0.55 | 0.45 to 0.75 | 0.04 | 0.040 | 2.75 to 3.25 | 0.60 to 0.95 | P or R |
| 3,320 | 0.15 to 0.25 | 0.30 to 0.60 | 0.04 | 0.040 | 3.25 to 3.75 | 1.25 to 1.75 | L |
| 3,330 | 0.25 to 0.35 | 0.30 to 0.60 | 0.04 | 0.040 | 3.25 to 3.75 | 1.25 to 1.75 | P or R |
| 3,340 | 0.35 to 0.45 | 0.30 to 0.60 | 0.04 | 0.040 | 3.25 to 3.75 | 1.25 to 1.75 | P or R |
* Another grade of this type of steel is available with chromium content of 0.15 per cent to 45 per cent. It has somewhat lower physical properties.
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Chromium (minimum and maximum) | Heat treatment |
|---|---|---|---|---|---|---|
| 5,120 | 0.15 to 0.25 | * | 0.04 | 0.045 | 0.65 to 0.85 | B |
| 5,140 | 0.35 to 0.45 | * | 0.04 | 0.045 | 0.65 to 0.85 | H or D |
| 5,165 | 0.60 to 0.70 | * | 0.04 | 0.045 | 0.65 to 0.85 | H or D |
| 5,195 | 0.90 to 1.05 | 0.20 to 0.45 | 0.03 | 0.03 | 0.90 to 1.10 | M, P or R |
| 51,120 | 1.10 to 1.30 | 0.20 to 0.45 | 0.03 | 0.03 | 0.90 to 1.10 | M, P or R |
| 5,295 | 0.90 to 1.05 | 0.20 to 0.45 | 0.03 | 0.03 | 1.10 to 1.30 | M, P or R |
| 52,120 | 1.10 to 1.30 | 0.20 to 0.45 | 0.03 | 0.03 | 1.10 to 1.30 | M, P or R |
—Two types of steel are available in this class, one with manganese 0.25 to 0.50 per cent (0.35 per cent desired), and silicon not over 0.20 per cent; the other with manganese 0.60 to 0.80 per cent (0.70 per cent desired), and silicon 0.15 to 0.50 per cent.
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Chromium (minimum and maximum) | Vanadium (minimum and maximum) | Heat treatment |
|---|---|---|---|---|---|---|---|
| 6,120 | 0.15 to 0.25 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | S |
| 6,125 | 0.20 to 0.30 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | S or T |
| 6,130 | 0.25 to 0.35 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | T or U |
| 6,135 | 0.30 to 0.40 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | T or U |
| 6,140 | 0.35 to 0.45 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | T or U |
| 6,145 | 0.40 to 0.50 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | U |
| 6,150 | 0.45 to 0.55 | 0.50 to 0.80 | 0.04 | 0.04 | 0.80 to 1.10 | 0.15 | U |
| 6,195 | 0.90 to 1.05 | 0.20 to 0.45 | 0.03 | 0.03 | 0.80 to 1.10 | 0.15 | U |
| S. A. E. Specification no. | Carbon (minimum and maximum) | Manganese (minimum and maximum) | Phosphorus (maximum) | Sulphur (maximum) | Silicon (minimum and maximum) | Heat treatment |
|---|---|---|---|---|---|---|
| 9,250 | 0.45 to 0.55 | 0.60 to 0.80 | 0.045* | 0.045 | 1.80 to 2.10 | V |
| 9,260 | 0.55 to 0.65 | 0.50 to 0.70 | 0.045* | 0.045 | 1.50 to 1.80 | V |
* Steel made by the acid process may contain maximum 0.05 phosphorus.
LIBERTY MOTOR CONNECTING RODS
The requirements for materials for the Liberty motor connecting rods are so severe that the methods of securing the desired qualities will be of value in other lines. The original specifications called for chrome-nickel but the losses due to the difficulty of handling caused the Lincoln Motor Company to suggest the substitution of chrome-vanadium steel, and this was accepted by the Signal Corps. The rods were accordingly made from chromium-vanadium steel, containing carbon, 0.30 to 0.40 per cent; manganese, 0.50 to 0.80 per cent; phosphorus, not over 0.04 per cent; sulphur, not over 0.04 per cent; chromium, 0.80 to 1.10 per cent; vanadium, not less than 0.15 per cent. This steel is ordinarily known in the trade as 0.35 carbon steel, S. A. E., specification 6,135, which provides a first-rate quality steel for structural parts that are to be heat-treated. The fatigue resisting or endurance qualities of this material are excellent. It has a tensile strength of 150,000 lb. minimum per square inch; elastic limit, 115,000 lb. minimum per square inch; elongation, 5 per cent minimum in 2 in.; and minimum reduction in area, 25 per cent.
The original production system as outlined for the manufacturers had called for a heat treatment in the rough-forged state for the connecting rods, and then semi-machining the rod forgings before giving them the final treatment. The Lincoln Motor Company insisted from the first that the proper method would be a complete heat treatment of the forging in the rough state, and machining the rod after the heat treatment. After a number of trial lots, the Signal Corps acceded to the request and production was immediately increased and quality benefited by the change. This method was later included in a revised specification issued to all producers.
The original system was one that required a great deal of labor per unit output. The Lincoln organization developed a method of handling connecting rods whereby five workmen accomplished the same result that would have required about 30 or 32 by the original method. Even after revising the specification so as to allow complete heat treatments in the rough-forged state, the ordinary methods employed in heat-treating would have required 12 to 15 men. With the fixtures employed, five men could handle 1,300 connecting rods, half of which are plain and half, forked, in a working period of little over 7 hr.
Fig. 14.—Rack for holding rods.
Fig. 15.—Sliding rods into tank.
The increase in production was gained by devising fixtures which enabled fewer men to handle a greater quantity of parts with less effort and in less time.
In heat-treating the forgings were laid on a rack or loop A, Fig. 14, made of 1¼-in. double extra-heavy pipe, bent up with parallel sides about 9 in. apart, one end being bent straight across and the other end being bent upward so as to afford an easy grasp for the hook. Fifteen rods were laid on each loop, there being four loops of rods charged into a furnace with a hearth area of 36 by 66 in. The rods were charged at a temperature of approximately 900°F. They were heated for refining over a period of 3 hr. to 1,625°F., soaked 15 min, at this degree of heat and quenched in soluble quenching oil.
In pulling the heat to quench the rods, the furnace door was raised and the operator pulls one of the loops A, Fig. 15 forward to the shelf of the furnace, supporting the straight end of the loop by means of the porter bar B. They swung the loop of rods around from the furnace shelf and set the straight end of the loop on the edge of the quenching tank, then raise the curved end C, by means of their hook D so that all the rods on the loop slide into the oil bath.
Before the rods cooled entirely, the baskets in the quenching tank were raised and the oil allowed to partly drain off the forgings, and they were stacked on curved-end loops or racks and charged into the furnace for the second or hardening heat. The temperature of the furnace was raised in 1½ hr. to 1,550°F., the rods soaked for 15 min. at this degree of heat and quenched in the same manner as above.
They were again drained while yet warm, placed on loops and charged into the furnace for the third or tempering heat. The temperature of the furnace was brought to 1,100°F. in 1 hr., and the rods soaked at this degree of heat for 1 hr. They were then removed from the furnace the same as for quenching, but were dumped onto steel platforms instead of into the quenching oil, and allowed to cool on these steel platforms down to the room temperature.